Staff

Abstract:
This study investigates thermal strains in fibre reinforced polymeric samples manufactured using a modified Fused Deposition Modelling (FDM) method. The investigated material was a composition of polylactic acid (PLA) resin and continuous carbon fibres. Each test sample was equipped with two Bragg grating (FBG) sensors, one embedded inside and the other bonded to the surface. Both sensors monitored temperature-induced deformations
during the conditioning of the specimens in a thermal chamber. Multiscale, analytical and finite element method based models were implemented to quantify the temperature deformations. Research has revealed that in investigated samples, bending occurs due to thermal loading. This can result in an inaccurate estimation of the coefficient of thermal expansion when relying on surface deformation measurements. A proposed solution involves the use of one FBG sensor embedded inside the specimen or two FBG sensors placed symmetrically, capable of measuring axial thermal deformation and averaging the effects associated
with bending.

Keywords:
Continuous Carbon Fibre Reinforced Polymer Composites, Fibre Bragg gratings, Thermal expansion , Additive manufacturing, Multiscale modelling

Abstract:
This paper describes some insights on applicability of a Selective Laser Melting and Direct Metal Laser Sintering technology-manufactured turbine blade models for aerodynamic tests in a wind tunnel. The principal idea behind this research was to assess the possibilities of using ‘raw’ DLMS printed turbine blade models for gas-flow experiments. The actual blade, manufactured using the DLMS technology, is assessed in terms of surface quality (roughness), geometrical shape and size (outline), quality of counterbores and quality of small diameter holes. The results are evaluated for the experimental aerodynamics standpoint. This field of application imposes requirements that have not yet been described in the literature. The experimental outcomes prove the surface quality does not suffice to conduct quantitative experiments. The holes that are necessary for pressure measurements in wind tunnel experiments cannot be reduced below 1 mm in diameter. The dimensional discrepancies are on the level beyond acceptable. Additionally, the problem of ‘reversed tolerance’, with the material building up and distorting the design, is visible in elements printed with the DLMS technology. The results indicate the necessity of post-machining of the printed elements prior their experimental usage, as their features in the ‘as fabricated’ state significantly disturb the flow conditions.

Keywords:
additive manufacturing,compressor blade,Direct Metal Laser Sintering (DLMS) technology,experimental aerodynamics,rapid prototyping,Selective Laser Melting SLM

Abstract:
In this work, significant strength and ductility variations are reported for AlSi10Mg parts fabricated at different orientations using laser powder bed fusion (LPBF). Hardness and surface roughness of the specimens at different orientations were measured. Tensile testing together with digital image correlation technique were conducted on the specimens. XY specimens showed the highest yield stress and ultimate tensile strength while XZ specimens showed the highest ductility. Hardness measurements for different specimens were in accordance with the tensile test results, following the same order as the UTS values, XY specimens being the highest and XY-45° (out-of-plane) specimens being the lowest. Fractography of the broken surfaces of the specimens under tensile testing revealed the microstructural features and various defects in the tensile fracture. The anisotropy in mechanical properties is attributed to the microstructural anisotropy as well as presence of various types of defects induced by the AM process, which affects the deformation and failure mechanism of the parts. Linear relationships between experimental Vickers hardness versus yield stress and UTS measurements were developed. In case of material selection for different applications, these relationships can be used as a simple tool for converting hardness and yield stress (or UTS) values to each other. An equivalent strain-hardness relationship was also proposed which can be used for health monitoring of parts subject to tensile loading.

Keywords:
Laser powder bed fusion, Hardness, Mechanical properties, Defects, Microstructure

Abstract:
The paper is related to the material behaviour of additively manufactured samples obtained by the direct metal laser sintering (DMLS) method from the AlSi10Mg powder. The specimens are subjected to a quasi-static and dynamic compressive loading in a wide range of strain rates and temperatures to investigate the influence of the manufacturing process conditions on the material mechanical properties. For completeness, an analysis of their deformed microstructure is also performed. The obtained results prove the complexity of the material behaviour; therefore, a phenomenological model based on the modified Johnson–Cook approach is proposed. The developed model describes the material behaviour with much better accuracy than the classical constitutive function. The resulted experimental testing and its modelling present the potential of the discussed material and the manufacturing technology.

Keywords:
AlSi10Mg aluminium alloy, additive manufacturing, DMLS method, compression, SHPB experiment, constitutive model

Abstract:
The deformation and failure of a Li-ion pouch battery under a high-velocity impact are studied experimentally and numerically. Ballistic tests were performed with 9 × 19 mm small-caliber projectiles travelling at 360 m/s, using state-of-the-art recording equipment and post-mortem examination under CT scan. The experimental observations are followed by a numerical simulation of the detailed multi-layer battery model. The study provides an insight into mechanisms of the progressive delamination and fracture of subsequent layers. The predicted residual velocity is very close to the measured values, but the impact energy absorption of the battery was found to be relatively low. The presented experimental and numerical analysis may contribute to a design of protection systems, in which rechargeable Li-ion batteries are included.

Keywords:
2D and 3D multilayered FE models, CT scan, delamination, high-velocity projectile impact, large format pouch battery, residual velocity

Abstract:
The purpose of this work is to check if additive manufacturing technologies are suitable for reproducing porous samples designed for sound absorption. The work is an inter-laboratory test, in which the production of samples and their acoustic measurements are carried out independently by different laboratories, sharing only the same geometry codes describing agreed periodic cellular designs. Different additive manufacturing technologies and equipment are used to make samples. Although most of the results obtained from measurements performed on samples with the same cellular design are very close, it is shown that some discrepancies are due to shape and surface imperfections, or microporosity, induced by the manufacturing process. The proposed periodic cellular designs can be easily reproduced and are suitable for further benchmarking of additive manufacturing techniques for rapid prototyping of acoustic materials and metamaterials.

Keywords:
porous materials, designed periodicity, additive manufacturing, sound absorption

Abstract:
This paper presents equilibrium mechanics and a finite element model for analysing a scissor structure that contains pivots with zero bending stiffness representing structural instability. The pivot at the centre of each structural unit, which is a feature of scissor structures, can be used to transfer the displacement between the units. It cannot, however, transfer the rotation between these units, and the angular stiffness must be considered independently for each unit. To construct a general model of the scissor structure, a scissor unit was developed using the left and right boundary connections of adjacent units to simulate a periodically symmetric structure. The proposed method allows us to obtain an accurate distribution of the internal forces and deflections without the use of special elements to account for central pivots.

Keywords:
scissor structure, deployable structure, smart bridge, scissors finite element, equilibrium mechanics

Abstract:
Scissors mechanisms are commonly used in safety engineering during the construction of temporary structures, owing to their inherent advantages of foldability, transformability, and reusability. We effectively utilized these scissors mechanism features to develop a lightweight, deployable emergency Mobile Bridge (MB) based on optimization, and control of the folding structure. Here, we discuss the problems of optimal reinforcement layout for the MB by formulating and solving three optimization problems, namely: (a) the load capacity maximization problem, (b) the weight minimization problem, and (c) coupling the load capacity maximization problem and the weight minimization problem. The potential benefits resulting from the application of reinforcement were evaluated using a combination of finite element analysis and an optimization algorithm based on the differential evolution method. The results demonstrate the significant positive influence of the additional reinforcing members. In particular, the limit load was increased by over 10 times, while the weight was decreased to approximately half. The proposed methodology enabled the development of a substantially improved version of the MB characterized by a higher load capacity and lower weight in comparison to the initial bridge design.

Abstract:
The presented discussion concerns the behavior of a thin-walled hexagonal aluminum honeycomb structure subjected to blast loading. The shock wave affecting the structure is generated by detonation of the C4 charge in an explosive-driven shock tube (EDST). The EDST set-up is an instrumented device that makes it possible to study blast effects in more stable and repeatable conditions than those obtained in a free-air detonation. The formation of folds characteristic of a honeycomb deformation in the axial compression distributes the initial loading over a time period, which is considered as an efficient method of energy dissipation. The test configuration is modeled in the Ls-Dyna explicit code, which enables analysis of the mechanisms of energy absorption that accompanies structural deformation under a blast loading. The conclusions reached in the performed experimental and numerical investigation can be applied to the modeling and optimization of cellular structures used to mitigate blast loadings.

Keywords:
thin-walled hexagonal aluminum honeycomb, dynamic compression, blast energy absorption, EDST, numerical simulation of blast effects

Abstract:
Thin steel plates with an array of holes, i.e. perforated plates, are used as a passive add-on improving protective properties of armours against small-calibre projectiles. A number of holes in such plates increases the probability of asymmetrical contact between the plate and the projectile, due to which small-calibre projectiles may be destabilized or fragmented before they reach the main-armour. The aim of the study is to analyse the defeat mechanisms provided by 4-mm-thick slotted super-bainitic plates (Pavise™ SBS 600P) against hard-core 7.62mm P80 0.30 AP×51 (0.308 Win) projectiles. To show the dependence between the hit-point and projectile failure, moments when projectiles hit the pre-armour plate were recorded by an ultra-high speed camera and their behaviour after the impact was captured by the flash X-ray radiography. The obtained results complemented by the Lagrangian FEM analysis confirm that slotted steel plates have high protection effectiveness against small-calibre projectiles.

Keywords:
Light-weight ballistic protectionPerforated add-on armourSuper-bainitic steelArmour-piercing (AP) projectile

Abstract:
This paper attempts to fill the gap in the literature by introducing and discussing an enhanced physical model of the MR damper. The essence of the presented model is to combine the effect of compressibility of the MR fluid enclosed in each chamber with the effect of blocking the flow between the chambers in the case of a low pressure difference. As it will be shown, the concurrence of both considered phenomena significantly affects mechanical behaviour of the damper, influences its dissipative characteristics, and in particular, it is the reason behind the distinctive 'z-shaped' force–velocity hysteresis loops observed in experiments. The paper presents explanation of the observed phenomena, detailed derivation of the thermodynamic equations governing response of the damper, their implementation for various constitutive models of the magnetorheological fluid and, finally, formulation of the corresponding reduced and parametric models. Experimental validation shows that proper identification of physical parameters of the proposed mathematical model yields the correct shapes of force–velocity hysteresis loops.

Keywords:
Magnetorheological fluid dampers, Smart fluids, Hysteresis modelling

Abstract:
Aircraft touchdown is one of the most difficult and dangerous phases of a flight. The paper presents an aerial light aircraft, prepared and produced by vibroacoustic tests, using an aircraft landing and landing monitoring system (AVI). The concept is based on the use of an ultrasonic transceiver head and vibration transducer, together with an appropriate signal processing and analysis system. The system measures the touchdown speed and altitude of the aircraft in the final phase of the flight and determines the level of load transmitted to the aircraft during the landing. Thanks to data archiving, it allows for better estimation of the wear rate of the structure, which is important in determining the causes of possible malfunction. It can be used with light and ultralight aircraft and, after adaptation, in unmanned aircraft. It can also be used to evaluate the art of piloting during landing.

Keywords:
aircraft landing, landing monitoring system

Abstract:
Mobile Bridge™ is a deployable bridge that uses a scissors mechanism to achieve its useful structural form. The bridge has a compact size in its undeployed state and can be transported easily to where it is needed. Its rapid deployment makes this type of bridge very useful in areas struck by natural disasters by enabling vehicles to cross terrain that has been made impassable. In previous research, experiments and analyses were conducted on a small-scale bridge designed for pedestrians. In order to consider a bridge of increased size, it is necessary to assess whether design and analysis techniques of the small scale bridge are applicable to the full-scale one. In this paper, we consider a full-scale deployable bridge with a lower deck and two scissor units, that allows for a light vehicle to pass across. We have carried out a light vehicle loading test in order to investigate its basic structural characteristics. Furthermore, the paper presents the theoretical design method and numerical models based on the experimental work followed by validation and comparison with the obtained experimental values.

Keywords:
Full-scale Mobile Bridge, Scissor type of emergency bridge, Scissors mechanism, Vehicle loading test

Abstract:
Paper discusses a concept and conservation methodology of the XVII. century curvilinear canvas painting „Adoration of the Magi” from the Saint-Aubain Cathedral church in Namur (Belgium). Atypical form of the painting bowed in the horizontal plane, adapted to a, wall and its enormous size (3.70 x 4.50 m) required using some innovative technologies and materials. Restoration work required access to both the face and the back of the picture. But how to overturn the painting? How to strengthen its support? How to tight. it? Such problems can be solved only by the interdisciplinary collaboration of a team of professionals. In this way decisions about the conservation were discussed in the group of experts from various disciplines. The article focuses o! n the problem of curvilinear canvas stretching, which is presented fro m different points of view. In the council participated restorers, scientist and engineers. Finally, we agreed that the basic premise of the conservation process was a detailed analysis of the canvas shape and its preservation on each step of the conservation works. The concept required construction of two curved platforms: concave and convex. The new system of the canvas overturning was also designed. An innovating method of strengthening of the canvas vertical direction during lining process by using Kevlar fibres was applied. The XVII. century stretcher frame was preserved as an example of historical construction. The new stretching system was built out of the original stretcher frame. The conservation works were finished in 2014, the painting was put in the frame and fixed on the wall. The optical analysis of its shape achieved one year after showed that its state is stable.

Abstract:
The paper describes the ballistic impact test, in which fragment simulating projectiles (FSPs) of a 20-mm-diameter have been used against 40-mmthick plates made of an aluminum alloy AA7020-T651. To perforate plates, the projectiles must have reached a velocity higher than 890 m/s. Based on the performed ballistic test, the plugging failure mode is numerically modeled using the LS-DYNA software package. Results obtained due to the calculations in the Finite Element Method (FEM) are compared with the results from the Smoothed Particle Hydrodynamics (SPH). A condition of geometrical similarity between the target deformed experimentally and its numerical representation is introduced to evaluate the performed simulations.

Keywords:
Ballistic impact test, Fragment simulating projectile (FSP), Plugging failure mode, Smooth Particle Hydrodynamics (SPH), Optical scanning

Abstract:
Adaptive Impact Absorption focuses on adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and embedded semi-active dissipaters with controllable mechanical properties. Application of such devices allows to modify dynamic characteristics of the structure during the period of impact and to precisely control the process of energy dissipation. The paper presents an overview of research conducted at the Department of Intelligent Technologies of the Institute of Fundamental Technological Research dedicated to design and applications of various systems of Adaptive Impact Absorption. Wide range of presented examples covers adaptive hydraulic and pneumatic landing gears, skeletal systems equipped with controllable elements and detachable joints as well as adaptive inflatable structures.

Keywords:
adaptive impact absorption, safety engineering, smart structures, optimal control

Abstract:
Paper discusses a concept and conservation methodology of the XVIIIth century curvilinear canvas painting ‘Adoration of the Magi’ from the Saint–Aubain Cathedral church in Namur (Belgium). Atypical form of the painting bowed in the horizontal plane, adapted to the apse wall and its very large size (3.70 x 4.50 m) required using some innovative technologies and materials. The basic premise of the conservation process was a detailed analysis of the canvas shape and its preservation on each step of the conservation works. The concept required construction of two curved platforms: concave and convex. The new system of the canvas overturning was also designed. An innovative method of strengthening of the canvas during lining process in vertical direction by using Kevlar fibres was applied. Required strengthening and modification of the stretching frame is also discussed.

Keywords:
curvilinear, large-size, lining, stretching, Kevlar fibres

Abstract:
A railway bridge has been the object of investigation in the context of structural health monitoring (SHM). The current work is focused on utilization of experimental data for refining a numerical model of the structure as well as on tests of dynamic excitations using a controlled hydraulic shaker and passing trains. The numerical model has been matched to experimental measurements using experimental modal analysis - classical and operational. The tailored SHM system for monitoring of the bridge consists of 15 piezoelectric strain sensors taking advantage of wireless communication for data transfer. Experimental responses of the bridge collected by the SHM system are confronted with the ones produced by the FE numerical model of the bridge. The long-term objective of the investigation is to elaborate a method for assessment of structural condition and prediction of remaining lifetime of the bridge.

Keywords:
Bridge Monitoring, Experimental Measurements, Modal Analysis, Wireless SHM

Abstract:
Paper discusses large size canvas paintings stretching methods and deformations and damages specific for large canvas resulting from an incorrect stretching. Analysis of the preservation state of a wooden stretcher construction and its functionality was an important step in development of the program of conservation work. The case study of M. H Loders painting „Adoration of the Magi” (XVIII c.) from the cathedral Saint - Aubain in Namur (Belgium) is presented. The painting is exhibited 5,5 m above the floor and has a unique shape, as the wooden stretcher frame is adjusted to the round apse walls. Thus usual direct inspection was difficult due to poor access to the reverse side of the painting. Preliminary conclusions on the construction and preservation state of the stretcher frame were drawn on the basis of a thorough inspection of the painting surface. Actual shape of the painting and precise stretchers dimensions were measured with a laser scanner. More information concerning the stretcher frame construction was obtained from a simple micro-camera system combined with LED lighting introduced from the canvas reverse side.

Keywords:
3D Laser Scanner, Deformation, Large - Size Painting, Wooden Stretcher Frame

Abstract:
A railway bridge has been the object of investigation since mid 2007 as a response to increasing interest in structural health monitoring (SHM) from Polish Railways. It is a typical 40 m long, steel truss structure spanning a channel in Nieporet near Warsaw. There is over 1500 similar bridges in the railway network in Poland. The integrated system consists of two components – weigh in motion (WIM) part for identification of train load and SHM part for assessing the state of the bridge. Two aspects of wireless transmission are considered – short range (in the vicinity of the bridge, 2.4GHz) and far range (from the bridge to the data analysis center, GSM). The system is designed to be energetically self-sufficient, batteries are recharged by solar panels. Both the subsystems use piezoelectric strain sensors. Numerical model of the bridge corresponds well to the experimental data and provides a good starting point for considering different scenarios of simulated damage in the structure.

Keywords:
SHM, Piezo sensors, Wireless transmission, Bridge dynamics, Railway infrastructure

Abstract:
The article presents a review of recent research carried out in the Department of Intelligent Technologies of Institute of Fundamental Technological Research, dedicated to application of systems for adaptive impact absorption to adaptive aircraft landing gears, novel concept of protective MFM structures, flow-control based airbags, maritime applications of inflatable structures, and development of adaptive wind turbine blade – hub connections.

Keywords:
Adaptive Impact Absorption, Adaptive Structure, Optimal Control

Abstract:
Podwozia lotnicze są traktowane przez konstruktorów samolotów jako elementy konieczne, ale z wielu względów mające negatywny wpływ na projekt. Z punktu widzenia aerodynamiki podwozia w trakcie lotu, stawiają dodatkowy opór aerodynamiczny (mniejszy w przypadku podwozi chowanych), a z punktu widzenia możliwości przewożenia ładunków, pochłaniają część masy startowej samolotu, która mogłaby być wykorzystana na transport towarów lub pasażerów. Biorąc pod uwagę takie uwarunkowania, idealne podwozie lotnicze powinno ważyć jak najmniej i zajmować minimalną ilość miejsca.
Obecnie najpopularniejszym rodzajem podwozia stosowanego w lotnictwie jest typ olejowo-gazowy, który charakteryzuje się najkorzystniejszym stosunkiem sprawności do wagi. Sprawność obecnie stosowanych podwozi lotniczych dochodzi do 80%. Aczkolwiek jest to wartość, która jest uzyskiwana dla jednego predefiniowanego przypadku lądowania z określoną energią uderzenia samolotu o pas startowy. Praktyka pokazuje, że w rzeczywistości zmienność warunków lądowania jest dużo większa niż zakres, na jaki można zaprojektować klasyczne podwozie pasywne. Najczęściej energia uderzenia przy lądowaniu jest znacząco mniejsza od tej, jaką konstruktorzy zakładają do obliczeń w procesie projektowania.
Dwa przedstawione problemy w projektowaniu podwozi lotniczych mogą zostać rozwiązane dzięki koncepcji nowego podwozia gazowego przedstawionego w tym artykule. Po pierwsze, dzięki zastosowaniu technologii inteligentnych i wykorzystaniu materiału funkcjonalnego stało się możliwe zaprojektowanie amortyzatorów czysto gazowych w podwoziach do aparatów latających, dzięki czemu możliwe jest wyeliminowanie oleju hydraulicznego o znacznie większej gęstości od gazu i efektywne obniżenie ciężaru podwozia samolotu. Po drugie dzięki wprowadzeniu inteligentnego sterowania przepływem gazu w amortyzatorze, stała się możliwa adaptacja rzeczywistych charakterystyk pracy amortyzatora do aktualnej wartości energii uderzenia samolotu o pas startowy.
Artykuł przedstawia wstępną fazę badań koncepcyjnych nad gazowym absorberem uderzeń przeznaczonym od zastosowania w podwoziu aparatu latającego, sterowanym przy pomocy zaworu piezoelektrycznego. W trakcie badań wykonano serię prób na modelu numerycznym, która została zweryfikowana przy pomocy badań eksperymentalnych, do których zaprojektowano i zrealizowano sterowanie w pętli zamkniętej dla szybkiego zaworu piezo elektrycznego zintegrowanego z absorberem gazowym.

Keywords:
podwozia lotnicze, podwozie adaptacyjne, adaptacyjna dyssypacja energii

Abstract:
This paper demonstrates progress in Adaptive Impact Absorption (AIA) research field obtained recently in our research group and is based on previously published conference communicates. The monograph (Ref.[1]), under preparation, will present soon more detailed discussion of the considered problems. In contrast to the standard passive systems the proposed AIA approach focuses on active adaptation of energy absorbing structures (equipped with sensor system detecting and identifying impact in real time and controllable semi-active dissipaters, so called structural fuses) with high ability of adaptation to extreme overloading. A semi-active or fully-active solutions can be applied, which depend on constant or time-dependent modifications realized via controllable dissipative devices. Feasible, adaptive dissipative devices under considerations can be based on MR fluids or (hydraulic or pneumatic) piezo-valves. The presentation will be devoted to the following applications of AIA concept: Adaptive Landing Gears (ALG) for mitigation of exploitative aircraft loads and adaptive flow control based airbags for emergency landing of the helicopter.

Keywords:
Adaptive Impact Absorption, Controlled Shock-absorbers, Adaptive Landing Gear, Inflatable Structures

Abstract:
Podczas każdego lądowania samoloty są narażone na duże przeciążenia dynamiczne mające zdecydowany wpływ na trwałość i niezawodność konstrukcji nośnej. Wielkość przeciążeń, jakim poddawany jest kadłub samolotu, zależy w dużej mierze od poprawnej pracy podwozia lotniczego. Głównym elementem podwozia, który pochłania największą ilość energii kinetycznej związanej z momentem przyziemienia jest amortyzator. Optymalne działanie amortyzatora lotniczego ma decydujący wpływ na zużycie zmęczeniowe materiałów konstrukcyjnych oraz na bezpieczeństwo lądowania.
Wprowadzenie systemu adaptacyjnego, który będzie w stanie modelować charakterystykę dyssypacji po przeprowadzeniu diagnozowania energii kinetycznej związanej z prędkością przyziemienia i ciężarem samolotu, znacznie poprawi efektywność działania amortyzatora lotniczego, zwiększając niezawodność eksploatacyjną konstrukcji i bezpieczeństwo lotu.

Keywords:
podwozia lotnicze, podwozie adaptacyjne, adaptacyjna dyssypacja energii

Abstract:
The concept of the design of adaptive materials composed of elements with controllable yield stresses is presented and the corresponding, gradient-based numerical design tools are described. Numerical simulation of the adaptation effect to various impact scenarios is demonstrated. The crucial point to get an additional value of energy dissipation (due to synergy of repetitive use of dissipaters in honeycomb-like cellular microstructure) is
to pre-design an optimal distribution of yield stress level in all controllable elements, triggering the desired sequence of local collapses. High effectiveness of active impact energy absorption by the yield stress adjustment demonstrates the potential application of the concept e.g. in shock-absorbing systems.

Abstract:
The growing use of 3D-printed (additively manufactured) structural components implies the need to develop effective methods of damage assessment. This study focuses on guided wave propagation and its interaction with structural damage. The waves were excited using a laser scanning system which allows for easy excitation of the waves at various points at the surface. Also, the excitation is broadband, giving the ability to excite more guided wave modes at once. The combined laser scanning with a single piezoelectric measurement transducer takes advantage of reciprocity to reconstruct the full propagating wavefield. The investigated sample was printed from an aluminum alloy. The first set of measurements was realized for an intact (healthy) sample. Next, an artificial damage was introduced in order to study the wave interaction with it. Machine learning-based signal process algorithms were developed to analyze the wave interaction with the damaged plate. The obtained results show a good potential of guided wave-based techniques for the structural health monitoring of 3D-printed structures. © 2024, The Society for Experimental Mechanics, Inc.

Keywords:
3D printing; Guided waves; k-means clustering; Laser ultrasonics; Nondestructive evaluation; Principal component analysis

Abstract:
The contribution describes three innovative external airbag systems developed by the
authors for the protection of flying objects during emergency landings. The first one is the
AdBag system dedicated for small drones, which is designed to protect the carried equipment
and prevent damages to objects or injuries to people at the crash location. The second system
is external airbag designed for ultralight aircraft Skyleader 600, which provides significant
reduction of touchdown velocity and deceleration levels during emergency landings, thereby
improving protection of the pilot and the passengers. Finally, the last presented solution is the
Spring-Drop system with specialized airbag deployment technique, which is dedicated for
specialised airdrop operations where the touchdown conditions can be extremely harsh and
unexpected, while protection of transported cargo is of crucial importance. Both conceptual
studies, numerical simulations and experimental tests of the three proposed systems are
presented and discussed.

Keywords:
External airbags, adaptive system, emergency landing, human safety

Abstract:
The paper is related to the energy absorptive properties of additively manufactured metallic cellular structures. The samples of Honeycomb, Auxetic, rhomboidal Lattice and a regular Foam are subjected to dynamic compression due to the blast tests. The cuboidal samples are manufactured by the Direct Metal Laser Sintering (DMLS) method using AlSi10Mg aluminium powder. The experimental tests are performed by means of an Explosive Driven Shock Tube (EDST). The measured results of the transmitted forces in relation to the shortening of the samples allow to analyse of the deformation processes of each selected geometry. In addition, the evaluation of the structural responses leads to the identification of the structure properties, such as the equivalent stress over equivalent strain or the energy absorption per a unit of mass. Moreover, the process of compression is modelled numerically using the explicit code LS-DYNA R9.0.1. The obtained simulations provide the complete analysis of the experimentally observed mechanisms.

Abstract:
The main objective of this study is related to the modeling of an aluminum thin-walled honeycomb structure under blast loading. The blast test is performed by means of an explosively driven shock tube (EDST). A planar shock wave is generated by a small amount of an explosive charge detonated in front of the tube. The honeycomb core is compressed by a movement of the steel plate located at the end of the tube. In the experiment, the honeycomb deformation is recorded by a high-speed camera and the absorbed loading by the structure is measured by a force sensor fixed on the rear sample face. The simulation of the material behavior is carried out using the Lagrangian approach implemented in LS-DYNA, ver. R9.0.1. The shock pressure generated by the explosion is recalculated to define the force applied to the plate being in contact (*AUTOMATIC_SURFACE_TO_SURFACE with friction) with the honeycomb and causing its deformation. The honeycomb is meshed by shell elements with a default formulation ELFORM: BELYTSCHKO-TSAY. The front plate is assumed as a rigid body to induce a uniform deformation of the honeycomb structure modeled using *MAT_SIMPLIFIED_JOHNSON_COOK 098 with parameters published in, [1-2]. The simulations are performed for different number of unit cells to define the honeycomb, from a single cell to fifty-three cells, aiming to indicate a minimal cell number required to model properly the entire structure. A dependence of numerical results on the mesh size, unit cell dimensions, friction conditions and the strain rate has been verified. The comparison between values of the load absorbed by the sample crushed numerically and experimentally shows a good agreement providing an insight into mechanisms of blast wave absorption by honeycomb structures. Such an analysis may be further applicable in development of advanced cellular structures applied to dissipate blast energy.

Abstract:
With a rapid development of modern Additive Manufacturing Technologies it seems inevitable that they will sooner or later serve for production of specific porous and meta-porous acoustic treatments. Moreover, these new technologies are already being used to manufacture original micro-geometric designs of sound absorbing media in order to test microstructure-based effects, models and hypothesis. In the view of these statements, this work reports differences in acoustic absorption measured for porous specimens which were produced from the same CAD-geometry model using several additive manufacturing technologies and 3D-printers. A specific periodic unit cell of open porosity was designed for the purpose. The samples were measured acoustically in the impedance tube and also subjected to a thorough microscopic survey in order to check their quality and look for the discrepancy reasons.

Keywords:
Sound absorption, Additive Manufacturing Technologies

Abstract:
Small drones with total mass of a few kilograms are becoming more and more popular in many applications increasing the probability of occurrence of emergency situations caused by an equipment failure or a human error. In case of a fall from a high altitude very often it is possible to use parachute rescue systems, which however require relatively long time for deployment and development of braking forces. The touchdown velocity may be large enough to exceed limit accelerations for UAV equipment. The paper presents the concept of deployable airbag systems, in particular with adaptive flow control, which provides a possible solution to the above-mentioned problems. The paper discusses the overall control and adaptation strategy. Simplified methods for mathematical modeling are proposed and formulated for an example on a cylindrical airbag. The conceptual part is concluded with the presentation of the methodology of experimental verification and results of initial tests of the integrated airbag system.

Abstract:
The paper presents the application of various 3D imagining methods to study the state of the mural painting in the dome of Blessed Ladislaus' Chapel of St. Anne's Church in Warsaw. The temple was built on the embankment of the Vistula river in the XV-th century. The chapel was added to the nave in the XVII-th century. From the beginning this location of the church caused a lot of structural problems. The church stability was disturbed due to digging an underground tunnel nearby in the years 1947-49. The Ladislaus' Chapel, situated close to the tunnel on the side of the escarpment was the most endangered. The current rescue work of the mural painting of the chapel dome required an accurate measurement and inventory of the architectural structure. The dome was measured using various methods: laser scanning and photogrammetry. As a result, we obtained 4 models of the chapel dome, which could be combined and compared.

Abstract:
The paper describes mathematical modelling of adaptive skeletal structures, which are equipped with semi-active dissipaters based on smart fluids or fast-operating valves and utilize the paradigm of real-time adaptation to external loading. The proposed approach is based on three subsequent stages: i) exact thermodynamic modelling of a single semi-active dissipater with the use of mass, momentum and energy conservation laws, ii) global description of the entire skeletal structure considered as an assembly of semi-active dissipaters in certain geometrical configuration, iii) real-time control of the fluid flow inside semi-active dissipaters providing instantaneous adaptability to actual dynamic loading. This methodology enables accurate representation of mechanical characteristics of the skeletal structure and reliable analysis of its adaptation capabilities.

Keywords:
adaptive structures, skeletal structures, impact absorption, vibration damping

Abstract:
We have experienced many times a phenomenon in which a bridge is washed away due to a typhoon, heavy rain in the rainy season, localized torrential rain, tsunami, and other flood disasters, or in which a bridge is damaged by an earthquake or a tremor. There is accordingly increasing demand for new technology and science to restore bridges that have been washed away or damaged. The paper presents a new type of emergency bridge, called Mobile Bridge™(MB), which can be quickly constructed in case of damages after a natural disaster. The concept of the bridge is based on the application of scissor-type mechanism, which provides its rapid deployment. Up to now several experimental MBs of different size were constructed and tested. The presented research reviews fundamental numerical and experimental results for the MB version 4.0 (MB4.0). Experimental testing included strain and acceleration measurements in free and forced loading conditions. From these results, it was possible to estimate basic dynamic characteristics of the bridge. Besides, in order to provide a basis for development of new construction methods for structural reinforcement and suppression of vibrations, various numerical analyses were conducted. The conducted research allows for a better and safer design of the movable and foldable full-scale bridge, the MB.

Keywords:
deployable bridge, scissors-type bridge, emergency bridge, light-weight structure, temporary bridge

Abstract:
The paper presents a new type of emergency bridge, which can be quickly constructed in case of damages after a natural disaster. The concept of the bridge is based on the application of scissor-type mechanism, which provides its rapid deployment. In case of deployable structures apart from static analysis of different configurations of expansion, it is very important to investigate the dynamic behavior of the system. High compliance and flexibility of the scissors-type bridge may influence user's comfort and safety in case of heavy dynamic loads such as human induced impacts, wind gusts or earthquakes. Up to now, the authors constructed several types of the experimental MBs. The presented research reviews fundamental numerical and experimental results for the Mobile Bridge 4.0. Experimental testing included strain and acceleration measurements in free and forced loading conditions. From these results, it was possible to estimate basic mechanics characteristics, that is statics and dynamic property, of the bridge. The conducted research allows for a better and safer design of the structure of the Mobile Bridge.

Keywords:
Deployable Bridge, Scissors-type bridge, Emergency Bridge, Dynamic property, Natural frequency, Acceleration measurement

Abstract:
Protection of combat-vehicles against impacts of small-calibre projectiles may be improved by the application of relatively thin and hard steel plates perforated by a plurality of holes. It is observed that due to the contact with a plate,the core of armour-piercing (AP) projectiles may be shattered, partially eroded or rotated, depending on the hit-position. The contact asymmetry is the strongest when a projectile hits a hole edge, its core undergoes bending and tends to fracture. The presented study discusses two methods of modelling of the contact and interactions between a bullet and a steel target. One of them is the explicit Lagrangian simulation of impacts of a fully represented AP projectile, another one is the semi-analytical model based on the integration of the motion equations of a 6 DOF rigid projectile. The results of numerical and semi-analytical approaches are compared with the ballistic impact experiment, in which the defeat mechanisms provided by 4-mm-thick slotted bainitic plates (Pavise™ SBS 600P) against hard-core 7.62 mm P80 0.30 AP x 51 (.308 Win) projectiles were verified, [1].

Abstract:
This contribution reviews the challenges in adaptive self-protection of structures. A proper semi-active control strategy can significantly increase structural ability to absorb impact-type loads and damp the resulting vibrations. Discussed systems constitute a new class of smart structures capable of a real-time identification of loads and vibration patterns, followed by a low-cost optimum absorption of the energy by structural adaptation. Given the always surging quest for safety, such systems have a great potential for practical applications (in landing gears, road barriers, space structures, etc.). Compared to passive systems, their better performance can be attributed to the paradigm of self-adaptivity, which is ubiquitous in nature, but still sparsely applied in structural engineering. Being in the early stages of development, their ultimate success depends on a concerted effort in facing a number of challenges. This contribution discusses some of the important problems, including these of a conceptual, technological, methodological and software engineering nature.

Keywords:
adaptive impact absorption, smart structures, semi-active control, safety engineering

Abstract:
Environmental and mechanical quantities need to be measured and registered in order to provide engineers and researchers with data required for diagnostics of heritage structures' condition. Analysis of the needs of diagnostic measurements and monitoring of historic structures shows that a large number of structures should be supervised. However hardware costs and resources needed to implement existing technologies constitute a barrier for a wide usage of modern sensors. The presented research shows that everyday usage of smartphones can be extended into a technology suitable for technical diagnostic purposes. Smartphone has many intrinsic sensors factory installed so it is already a sensing device. By calibrating the sensors the smartphone can be upgraded from being a sensing device to become the real measuring equipment. This emerging technology called Smartphone Aided Structural Monitoring and Measurements (SASMM) is not limited to the examples presented in this paper.

Abstract:
The stress–strain behavior of the rolled AA7020 aluminum tempered in T651 conditions is studied at various strain rates and temperatures. Basing on tensile, shear and compression tests, the effects of strain and strain-rate hardening, thermal softening and plastic anisotropy are discussed. The parameters of the thermo-viscoplastic flow and fracture models proposed by Johnson and Cook are identified and validated basing on the numerical modeling.
The obtained constitutive relations may be applied to model more complex states of stresses resulted from different loading conditions.

Keywords:
AA7020-T651, flow and fracture models, metals under dynamic loadings, numerical simulation of metal deformation

Abstract:
The paper describes enhanced physical model of MR damper which takes into account the effects of blocking the flow between the chambers in case of low pressure difference and the compressibility of the fluid enclosed in each chamber. Combination of both effects is considered as the reason of gene ration of the characteristic shapes of force-velocity hysteresis loops. The subsequent sections of the paper contain derivation of the thermodynamic equations governing response of the damper and their implementation for two constitutive models of the magnetorheological fluid. Successful qualitative comparison against the experiment proves the correctness of applied assumptions and the relevance of the proposed model.

Keywords:
magnetorgeological fluids, MRF dampers, physical-based modeling

Abstract:
This contribution presents the concept of smart, deployable skeletal structures along with existing and prospective applications. The first part introduce s the concept of multi-folding, which is the basis for the design of all smart deployable skeletal structures. In the second part three diverse innovative applications are described: deployable mobile bridge, adaptive impact absorber and controllable valve.

Keywords:
smart skeletal structures, adaptive impact absorption, safety engineering

Abstract:
The paper presents a concept of new adaptive valve s, which can be applied in the Adaptive Inflatable Structures for impact absorption - high-performance membrane and bistable snap-through valve. The main idea behind those concepts is to employ fluid flow in order to assist actuation of the system.

Keywords:
adaptive impact absorption, inflatable structures, high performance valves

Abstract:
Znaczny rozwój inwestycji wielkogabarytowych obiektów sportowych stworzył potrzebę równoległego rozwoju metod monitorowania bezpieczeństwa stadionów mogących pomieścić dziesiątki tysięcy ludzi. Powszechną cechą eksploatacji wielkich stadionów jest ich wykorzystanie zarówno do organizacji imprez sportowych jak i masowych imprez kulturalnych np. koncertów. Specyfika takich dużych imprez sportowych i kulturalnych niesie w sobie zagrożenia dla konstrukcji na skutek nieprzewidywalnych na etapie projektowania zmian obciążeń wywołanych drganiami i montażem na elementach konstrukcji dodatkowego ciężkiego sprzętu.
Mając na uwadze powyższe uwarunkowania jako cel badań przyjęto opracowanie, wdrożenie i przetestowanie w praktyce światłowodowego systemu monitorowania deformacji konstrukcji stadionu mieszczącego się w Warszawie przy ulicy Łazienkowskiej 3, należącego do WOSiR, a obecnie użytkowanego przez Klub Piłkarski

Keywords:
monitorowanie konstrukcji, systemy FBG, monitorowanie deformacji konstrukcji stadionu

Abstract:
In the last years one can observe an increasing interest in structural health monitoring (SHM) from Polish Railways. There are several hundreds of steel truss bridges of various spans and similar topologies in Polish railway infrastructure. One of them, located over a canal in Nieporęt near Warsaw with span of 40m became an object of investigation and implementation of an integrated SHM system. The system consists of two components – weigh in motion (WIM) part for identification of train load and SHM part for assessing the bridge state. The WIM module supplies load data required for SHM inverse analyses, however it can operate as an independent system for monitoring of railway traffic providing information about axle loads and rolling stock identification. Many in-situ installations of SHM systems suffer from a troublesome and time- consuming way of data acquisition via standard cables. In order to facilitate data collection related with this way of acquisition, an alternative solution of wireless transmission of the measured data from the field to analysis centre is proposed. Two aspects of wireless transmission are considered – short range (in the vicinity of the bridge) and far range (from the bridge to the centre of analysis). This paper takes up the practical issue of design and implementation of the integrated SHM system for truss steel railway bridge with a special insight into the monitoring of railway traffic.

Keywords:
Structural Health Monitoring, monitoring of steel railway bridges

Abstract:
Adaptive Impact Absorption focuses on adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and semi -active dissipaters with controllable mechanical properties which enable change of system dynamic characteristics in real time. The article present s a review of research conducted at the Department of Intelligent Technologies of the Institute of Fundamental Technological Research dedicated to applications of systems for Adaptive Impact Absorption. Wide range of presented examples covers pneumatic landing gears, bumpers for offshore towers, wind turbine blade-hub connections and d protective barriers for automotive applications.

Keywords:
adaptive impact absorption, safety engineering, smart structures, optimal control

Abstract:
In the last years one can observe an increasing interest in structural health monitoring (SHM) from Polish Railways. There are several hundreds of steel truss bridges of various spans and similar topologies in Polish railway infrastructure. One of them, located over a canal in Nieporęt near Warsaw with span of 40m became an object of investigation and implementation of an integrated SHM system.
The system consists of two components – weigh in motion (WIM) part for identification of train load and SHM part for assessing the bridge state. The WIM module supplies load data required for SHM inverse analyses, however it can operate as an independent system for monitoring of railway traffic providing information about axle loads and rolling stock identification.
Many in-situ installations of SHM systems suffer from a troublesome and time-consuming way of data acquisition via standard cables. In order to facilitate data collection related with this way of acquisition, an alternative solution of wireless transmission of the measured data from the field to analysis centre is proposed. Two aspects of wireless transmission are considered – short range (in the vicinity of the bridge) and far range (from the bridge to the centre of analysis).
This paper takes up the practical issue of design and implementation of the integrated SHM system for truss steel railway bridge with a special insight into the monitoring of railway traffic.

Keywords:
SHM systems, monitoring of railway bridges

Abstract:
In-situ measurements collected with standard cabling suffer from the serious disadvantage of no automation, which implies frequent visits to the monitored structure in order to gather the requested data. For minimizing the man effort involved, a system of wireless transmission (WT) of in-situ collected data has been proposed. Principal ideas of such system should be pretty universal in a number of applications related to structural health monitoring (SHM). However each WT system should be customized for a specific application to provide the best performance. The proposed WT system is dedicated to rail traffic monitoring and SHM of railway bridges. The idea is to design smart sensors to be mounted on the bridge and equipped with electronic modules for short-range wireless transfer of SHM data. The far-range wireless transfer from the local bridge unit to a remote analysis centre will be performed using the GSM technology.

Keywords:
SHM, monitoring of railway bridges

Abstract:
W zagadnieniach identyfikacji i lokalizacji źródeł aktywności wibroakustycznej maszyn, istotnym problemem jest wizualizacja pól rozkładu wielkości akustycznych na wybranych powierzchniach oraz określenie udziału poszczególnych źródeł w bilansie energetycznym sygnału wibroakustycznego maszyny.
Stosowane w wibroakustyce metody formowania wiązki (beamforming) polegają na przestrzenno-czasowym przetwarzaniu sygnału rejestrowanego przez matrycę mikrofonową. Identyfikacja źródła odbywa się poprzez analizę zależności amplitudowo-fazowych sygnałów akustycznych padających na poszczególne przetworniki matrycy. Ponieważ z metodologicznego punktu widzenia interesujące jest określenie możliwości zastosowania metody kształtowania wiązki w przypadku złożonych urządzeń posiadających źródła o małej aktywności wibroakustycznej, obiektem wstępnych prac był zasilacz hydrauliczny typu Silentflo firmy MTS. Rezultaty otrzymane w wyniku przeprowadzonych badań w pełni potwierdzają zalety metody beamformingu w określeniu lokalizacji i identyfikacji źródeł aktywności wibroakustycznej maszyn.

Keywords:
Wibroakustyka, Lokalizacja źródeł akustycznych, Beamforming

Abstract:
The class of ultra-light aircraft becomes more and more popular among the enthusiasts of aviation due to low formal requirements of getting the pilot license and low costs of the equipment. Therefore, the training of the pilots starts to be a large-scale task. One of the most difficult operation for the inexperienced pilots is touch-down and it often happens to strike the ground with a high sink speed. In consequence the training machines are endangered of fast structural damage. A potential solution would be to mount a system of adaptive landing gear for light aircraft with a capability of recognition of the actual landing impact and tuning the landing struts in order to conduct the smoothest landing operation possible. In the case of the ultra-light aircraft class the weight of the components is the crucial task and therefore the low-weight pneumatic system is proposed for these application.
The paper presents a concept of an adaptive landing system and adequate control strategy for a small aerial vehicle. The objective of the work was to develop a fully functional model of the landing system and experimental verification of it. The system is based on the new pneumatic impact absorbers actuated via piezo-stacks. The concept assumes designing of the system with the capability of adaptation to actual energy of impact scenario identified by a dedicated sensing system for impact energy recognition.
The designed control system was dedicated to process the data from the system of impact energy recognition in order to perform the optimal landing scenario. The objective of the control strategy was minimization of the structure’s deceleration peaks during the touchdown.
The presented results consist of numerical analysis of the adopted strategy of control and experimental verification of the concept on the dedicated experimental device. The results proved that the proposed method allowed minimization of the maximal deceleration level acting on the demonstrator.

Abstract:
Plasma Electrolytic Oxidation (PEO) is the most advanced of the anodizing methods. In comparison to traditional anodizing PEO provides coatings with higher wear- and corrosion- resistance and hardness. Moreover, PEO is carried out in an alkalic bath, instead of strong acids, which makes this method more environmentally friendly. PEO is an excellent surface treatment for light metals, like magnesium or aluminium. More often light metals are produced by additive technologies (3d printing). The microstructure of additively manufactured alloys strongly differs from casting alloys. Characteristic melting pools are observed. AlSi10Mg alloy presents eutectic structure surrounded by Si-net. The microstructure is strongly connected to laser paths. Fine-grain microstructure results in higher strength than cast alloy. In this study, traditional anodizing, hard anodizing (HA) and PEO were carried out on AlSi10Mg manufactured by Direct Metal Laser Sintering (DMLS). Moreover, PEO was also performed on cast AlSi10Mg alloy. Thin, conversion coatings were obtained (thickness under 10 μm). A microstructure of oxide coatings was observed. Scratch resistance was tested and allowed to describe the films' adhesion. PEO coatings are vastly porous and include more SiO2 oxides than traditional and HA coatings. SiO2 oxides are more difficult to obtain as silicon has higher resistance than aluminium. Moreover, PEO guarantees more phase-mixed surface microstructure, including amorphous, ceramic phases, which cannot be formed in low-voltage processes. In comparison to traditional and HA oxide coatings, PEO coatings exhibit better adhesion and scratch resistance. Traditional anodizing and hard anodizing on additively manufactured AlSi10Mg provide the critical load LC1 at which coating begins to be broken of 8.5N and 10N respectively. A similar LC1 value can be obtained for PEO performed on cast alloy (7.8N), while in the case of additively manufactured AlSi10Mg this LC1 is increased four times to 42.1N.

Keywords:
Additive manufacturing, Plasma Electrolytic Oxidation, Aluminium alloys AlSi10Mg

Abstract:
Additive Manufacturing is one of the most rapidly developing production technologies in the last decade. In case of polymeric materials the Fused Deposition Modelling (FDM) provides low cost and high versatility, however is limited by low accuracy and mechanical properties of applied polymeric materials. One of the ways of overcoming the latter deficiency is the modification of the FDM process allowing for the reinforcement of the printed composites with continuous fibres. The objective of the research is to present the performance of additively manufactured Carbon Fibre Reinforced Polymer (CFRP) sample with embedded Fiber Bragg Grating sensors (FBG) under the influence of mechanical loading and temperature changes. FBG sensors were introduced to the middle of the specimen during manufacturing process. Experimental results show high nonlinearity due to a relatively low glass transition temperature of the PLA material. Additionally, the numerical modelling using the Finite Element Method provides more complex insight into the influence of embedded fibre optic on the AM composite material.

Abstract:
The paper presents a new type of emergency bridge, which can be quickly constructed in case of damages after a natural disaster. The concept of the bridge is based on the application of scissor-type mechanism, which provides its rapid deployment. In case of deployable structures apart from static analysis of different configurations of expansion, it is very important to investigate the dynamic behavior of the system. High compliance and flexibility of the scissors-type bridge may influence user's comfort and safety in case of heavy dynamic loads such as human induced impacts, wind gusts or earthquakes. Up to now, the authors constructed several types of the experimental MBs. The presented research reviews fundamental numerical and experimental results for the Mobile Bridge 4.0. Experimental testing included strain and acceleration measurements in free and forced loading conditions. From these results, it was possible to estimate basic mechanics characteristics, that is statics and dynamic property, of the bridge. The conducted research allows for a better and safer design of the structure of the Mobile Bridge.

Keywords:
Deployable Bridge, Scissors-type bridge, Emergency Bridge, Dynamic property, Natural frequency, Acceleration measurement

Abstract:
The world has seen many kinds of natural disasters, which have critically influenced the residents' lives by causing damage to infrastructure. To realize rapid rescue efforts in an emergency situation, we propose a deployable emergency bridge, called Mobile Bridge TM [1], based on the theory of foldable structures[2]and the concept of Multi-Folding Microstructures (MFM)[3]. The current research presents the fundamental,numerical and experimental results obtained for the pedestrian and vehicle Mobile Bridges. In this paper, it is considered the localized linearization problem with the fixed an angle although this bridge contains a geometrical nonlinearity of scissors structure. Additionally, a seismic response analysis is conducted for the case where the Mobile Bridge is used in the disaster area as an emergency bridge. This allows for a better and safer structural design of the Mobile Bridge, which is patented in [4],[5].

Abstract:
Wśród europejskiego dziedzictwa obrazów wielkoformatowych można wyróżnić szczególną grupę płócien nieplanarnych. W trakcie prowadzonych prac badawczych i konserwatorskich należy odpowiedzieć na pytania o pierwotny kształt aktualnie zdeformowanego obrazu, stopień zniekształcenia płótna, wpływ pełzania na deformację oraz bezpieczny sposób przywrócenia właściwego kształtu i zabezpieczenia przed jego zmianą w przyszłości. Wielkoformatowe obrazy na płótnie podlegają znaczącym deformacjom wynikającym z procesów reologicznych aktywowanych zmianami wilgotności i temperatury. Deformacje te narastają wraz z upływem czasu pod wpływem sił wynikających z ciężaru własnego i napięcia na krośnie. Efekty te mają tym większe znaczenie im większa jest powierzchnia obrazu. Ich konserwacja i prawidłowe napięcie stanowią szczególnie trudne wyzwanie konserwatorskie. Wszystkie te problemy pojawiły się w trakcie konserwacji obrazu „Pokłon Trzech Króli” H.M. Lodera, który znajduje się w katedrze w Namur (Belgia). Obraz o wymiarach 3.70m x 4.50m zawieszony był w prezbiterium kościoła i miał wygiętą formę, zbliżoną do łuku ściany absydy. Strzałka łuku krosna wynosiła 37cm. Do najpoważniejszych problemów należały katastrofalne w skutkach deformacje osłabionego mechanicznie podobrazia. Płótno pod wpływem własnego ciężaru i zachodzących procesów reologicznych wyciągnęło się i zaczęło obwisać, tak że jego nadmiar zebrał się w części centralnej u dołu malowidła. W trakcie prowadzonych prac opracowana została metodyka pomiaru, korekcji kształtu i napinania obrazów wielkoformatowych. Po wykonaniu zdalnych pomiarów optycznych zawieszonego na ścianie obrazu (globalny i lokalny skaning laserowy, fotogrametria) dokonano identyfikacji zdeformowanego i pierwotnego kształtu płótna. Następnie zaproponowano nowatorski sposób wzmocnienia i napinania płótna polegający na wprowadzeniu w warstwie dublażowej układu nici aramidowych poprowadzonych wzdłuż tworzących zidentyfikowanej powierzchni prostokreślnej płótna. Wielokrotnie większy moduł sprężystości nici aramidowych niż płótna dublażowego umożliwia przeniesienie dominującej części naprężeń wynikających z napięcia płótna i ciężaru własnego obrazu. W połączeniu ze znacznie mniejszą wrażliwością aramidu na zmiany wilgotności i temperatury znacząco zmniejsza się także intensywność procesów reologicznych ograniczając pełzanie, obwisanie i utrwalając krzywoliniowy kształt obrazu.

Abstract:
The stress–strain behavior of the rolled AA7020 aluminum tempered in T651 conditions is studied at various strain rates and temperatures. Basing on tensile, shear and compression tests, the effects of strain and strain-rate hardening, thermal softening and plastic anisotropy are discussed. The parameters of the thermo-viscoplastic flow and fracture models proposed by Johnson and Cook are identified and validated basing on the numerical modeling.
The obtained constitutive relations may be applied to model more complex states of stresses resulted from different loading conditions.

Keywords:
AA7020-T651, flow and fracture models, metals under dynamic loadings, numerical simulation of metal deformation

Keywords:
scissor type of bridge, emergency bridge, strut reinforcement, sectional optimization

Abstract:
Control of crash or impact process may be based on change of mechanical characteristics due to modification of inner structural connections. Presented work covers numerical and experimental analysis of sandwich fabric composite cantilever beam subjected to a low velocity impact. A set of metallic electrical conductors was placed between composite layers causing their controlled delamination when subjected to an electrical explosion. In result, separation of initially connected components in the vicinity of the exploded conductor is obtained, leading to the change of global mechanical characteristics, allowing for modification of beam behavior. Exploding bridge wire (EBW) phenomenon is known from the end of the 18th century [1] and being in use today, mainly for ignition of high explosive materials [2] as well as in physics of high energy [3]. This effect is caused by a rapid heating of a conductor subjected to a pulse of high voltage electric current, what changes its state of matter from solid to vapor, expanding in surrounding continuum and forming a strong pressure wave. Afterwards, in result of current discharge through the formed plasma channel, additional heat is applied to the system increasing the effect. Depending on explosion parameters and properties of continuum elastic, elasto-plastic or shock waves can be observed. In case of action on the composite, exploding wire embedded between layers acts on adjacent surfaces causing their progressive separation in the vicinity of the explosion. Delamination decoupling adhesive is being extended by the pressure acting in the direction normal to the surface of the composite. Figure 1 depicts an example of experimental delamination process from a medium voltage EBW system. A cantilever beam made of layered sandwich composite was modelled with shell finite elements. Problem was solved in a commercial FEM LS-DYNA package using explicit time integration with nonlinear material and geometric formulation. The delamination was simulated by a controlled separation of a connection between layers in the area surrounding the predefined location of the EBW wire. The initiation time of layers’ separation was one of controllable parameters allowing for a wide search for solution dependencies. Numerical solution was compared with experimental results, showing good convergence and proving control feasibility. Also an analytical, rigid perfectly plastic model for explanation of first order effects was used for demonstration of governing principles [4].

Keywords:
Exploding bridge wire

Keywords:
adaptive inflathigh performance valves, adaptive inflatable structures

Keywords:
Smart And Adaptive Structures, Adaptive Impact Absorption, Safety Engineering

Keywords:
high performance valve, bistable elements, snap-through, adaptive impact absorption

Abstract:
Many natural disasters such as earthquakes, floods, torrential rains occur around the world, and we to undertake quick rescue actions. However, there are many recovery problems because of the occurrence of secondary disasters at each rescue worksite.So, from the previous study of optimal structures and control regulation of MFM[1]-[2], we propose a new type of foldable bridge with scissors structure called Mobile Bridge[3]. Applying scissors mechanism to bridge form, Mobile Bridge provides not only mobility but also good structural performance, because the whole bridge can be expand or fold quickly. In this paper, we discuss the vehicles passing test on the real scale Mobile Bridge in order to evaluate the design method and application limits.

Keywords:
Mobile Bridge, deployable structures, temporary bridges, scissors-type structures

Abstract:
Paper discusses a concept and conservation methodology of the XVIIIth century curvilinear canvas painting “Adoration of the Magi” from the Saint – Aubain Cathedral church in Namur (Belgium). Atypical form of the painting bowed in the horizontal plane, adapted to the apse wall and its very large size (3.70 x 4.50 m) required using some innovative technologies and materials. The basic premise of the conservation process was a detailed analysis of the canvas shape and its preservation on each step of the conservation works. The concept required construction of two curved platforms: concave and convex. The new system of the canvas overturning was also designed. An innovative method of strengthening of the canvas during lining process in vertical direction by using Kevlar fibres was applied. Required strengthening and modification of the stretching frame is also discussed.

Keywords:
curvilinear, large-size canvas painting, lining, stretching, Kevlar fibres

Abstract:
Religious art objects preserved in the form of curved canvas paintings present a very interesting subject for the research, both from technical and conservation points of view. The work concentrates on theoretical and experimental analysis of mechanically correct stretching of curvilinear canvas to avoid folding and buckling of paintings. It is shown that treating curvilinear canvas as a ruled surface might be a very promising solution. Reverse engineering can help to discover the ruled surface shape adequate to the individual curved painting.

Keywords:
canvas, stretching, ruled surface, religious paintings

Abstract:
Nowadays large stadium structures are designed for assumed static loads and it is difficult to calculate important influence of real stresses resulting from dynamic loads caused by moving crowds. The paper presents Structural Health Monitoring System, based on multiplexed Fiber Bragg Grating sensors. They are used to measure strains and temperature of structural elements and allow us to measure dynamic deformations to observe changes in structural behaviour of the stadium during cheering on a football competition and calculate instantaneous anthropogenic loads.

Keywords:
Structural Health Monitoring, FBG sensors, monitoring of concrete structures

Abstract:
Dissipation of the energy in mechanical systems is a vitally important engineering and scientific problem. Current stringent safety requirements enforce substantial change of methods of structural design and application of new solutions and technologies which ensure structural integrity.
Currently applied passive safety systems are typically not equipped with control devices. Their dynamic characteristics remains unaltered and thus it is well adjusted to a narrow range of actual loadings. In case of impact loading, it is highly advantageous to apply systems of Adaptive Impact Absorption (AIA), which are capable of fast change of the dynamic characteristics. Recent fast development of the material technologies and, in particular, development in the field of functional (smart) materials and electronic measurement and control systems had created new possibilities of practical applications of the AIA systems.
During the adaptation process the choice of optimal control strategy is followed by adjustment of the dynamic characteristics of adaptive elements of the absorber. These elements can entirely made of functional materials (as e.g. shape memory alloys) or, alternatively, they can be equipped with controllable devices, so-called structural fuses, which provide controlled response of the element. Depending on type of applied control, the changes of structural parameters occur only once (usually before impact) or they are controlled in real time during the impact process.
The systems of Adaptive Impact Absorption can be effectively used to increase the level of safety during the action of the impact loading. In particular, very promising results are obtained with the use of adaptive inflatable structures. However, the possibilities of their practical applications are limited due to the lack methods allowing for the efficient and fast control of the gas flow during impact.
The presented work focuses on the pneumatic adaptive impact absorbing system equipped with a novel, high performance valve, which utilizes bistable snap-through effect. Snap-through effects are mainly the subject of theoretical analysis and they do not find many practical engineering applications.

Keywords:
smart structures, high performance valves, adaptive pneumatic systems, adaptive impact absorption