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Staszczak M., Urbański L., Gradys A. D., Cristea M.♦, Pieczyska E. A., Nucleation, Development and Healing of Micro-Cracks in Shape Memory Polyurethane Subjected to Subsequent Tension Cycles,
Polymers, ISSN: 2073-4360, DOI: 10.3390/polym16131930, Vol.16, No.13, pp.1-22, 2024Streszczenie: Thermoresponsive shape memory polymers (SMPs) have garnered increasing interest for their exceptional ability to retain a temporary shape and recover the original configuration through temperature changes, making them promising in various applications. The SMP shape change and recovery that happen due to a combination of mechanical loading and appropriate temperatures are related to its particular microstructure. The deformation process leads to the formation and growth of micro-cracks in the SMP structure, whereas the subsequent heating over its glass transition temperature Tg leads to the recovery of its original shape and properties. These processes also affect the SMP microstructure. In addition to the observed macroscopic shape recovery, the healing of micro-crazes and micro-cracks that have nucleated and developed during the loading occurs. Therefore, our study delves into the microscopic aspect, specifically addressing the healing of micro-cracks in the cyclic loading process. The proposed research concerns a thermoplastic polyurethane shape memory polymer (PU-SMP) MM4520 with a Tg of 45 °C. The objective of the study is to investigate the effect of the number of tensile loading-unloading cycles and thermal shape recovery on the evolution of the PU-SMP microstructure. To this end, comprehensive research starting from structural characterization of the initial state and at various stages of the PU-SMP mechanical loading was conducted. Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and scanning electron microscopy (SEM) were used. Moreover, the shape memory behavior in the thermomechanical loading program was investigated. The obtained average shape fixity value was 99%, while the shape recovery was 92%, which confirmed good shape memory properties of the PU-SMP. Our findings reveal that even during a single loading-unloading tension cycle, crazes and cracks nucleate on the surface of the PU-SMP specimen, whereas the subsequent temperature-induced shape recovery process carried out at the temperature above Tg enables the healing of micro-cracks. Interestingly, the surface of the specimen after three and five loading-unloading cycles did not exhibit crazes and cracks, although some traces of cracks were visible. The traces disappeared after exposing the material to heating at Tg + 20 °C (65 °C) for 30 min. The crack closure phenomenon during deformation, even without heating over Tg, occurred within three and five subsequent cycles of loading-unloading. Notably, in the case of eight loading-unloading cycles, cracks appeared on the surface of the PU-SMP and were healed only after thermal recovery at the particular temperature over Tg. Upon reaching a critical number of cycles, the proper amount of energy required for crack propagation was attained, resulting in wide-open cracks on the material’s surface. It is worth noting that WAXS analysis did not indicate strong signs of typical highly ordered structures in the PU-SMP specimens in their initial state and after the loading history; however, some orientation after the cyclic deformation was observed. Słowa kluczowe: polyurethane shape memory polymer, glass transition temperature, tensile loading cycles, structure analysis, micro-cracks, healing Afiliacje autorów:
Staszczak M. | - | IPPT PAN | Urbański L. | - | IPPT PAN | Gradys A. D. | - | IPPT PAN | Cristea M. | - | Petru Poni Institute of Macromolecular Chemistry (RO) | Pieczyska E. A. | - | IPPT PAN |
| | 100p. |
2. |
Staszczak M., Urbański L., Cristea M.♦, Ionita D.♦, Pieczyska E.A., Investigation of Shape Memory Polyurethane Properties in Cold Programming Process Towards Its Applications,
Polymers, ISSN: 2073-4360, DOI: 10.3390/polym16020219, Vol.16, No.2, pp.219-1-219-20, 2024Streszczenie: Thermoresponsive shape memory polymers (SMPs) with the remarkable ability to remember a temporary shape and recover their original one using temperature have been gaining more and more attention in a wide range of applications. Traditionally, SMPs are investigated using a method named often “hot-programming”, since they are heated above their glass transition temperature (Tg) and after that, reshaped and cooled below Tg to achieve and fix the desired configuration. Upon reheating, these materials return to their original shape. However, the heating of SMPs above their Tg during a thermomechanical cycle to trigger a change in their shape creates a temperature gradient within the material structure and causes significant thermal expansion of the polymer sample resulting in a reduction in its shape recovery property. These phenomena, in turn, limit the application fields of SMPs, in which fast actuation, dimensional stability and low thermal expansion coefficient are crucial. This paper aims at a comprehensive experimental investigation of thermoplastic polyurethane shape memory polymer (PU-SMP) using the cold programming approach, in which the deformation of the SMP into the programmed shape is conducted at temperatures below Tg. The PU-SMP glass transition temperature equals approximately 65 ◦C. Structural, mechanical and thermomechanical characterization was performed, and the results on the identification of functional properties of PU-SMPs in quite a large strain range beyond yield limit were obtained. The average shape fixity ratio of the PU-SMP at room temperature programming was found to be approximately 90%, while the average shape fixity ratio at 45 ◦C (Tg − 20 ◦C) was approximately 97%. Whereas, the average shape recovery ratio was 93% at room temperature programming and it was equal to approximately 90% at 45 ◦C. However, the results obtained using the traditional method, the so-called hot programming at 65 ◦C, indicate a higher shape fixity value of 98%, but a lower shape recovery of 90%. Thus, the obtained results confirmed good shape memory properties of the PU-SMPs at a large strain range at various temperatures. Furthermore, the experiments conducted at both temperatures below Tg demonstrated that cold programming can be successfully applied to PU-SMPs with a relatively high Tg. Knowledge of the PU-SMP shape memory and shape fixity properties, estimated without risk of material degradation, caused by heating above Tg, makes them attractive for various applications, e.g., in electronic components, aircraft or aerospace structures. Słowa kluczowe: polyurethane shape memory polymer, cold programming, thermal expansion, shape fixity, shape recovery Afiliacje autorów:
Staszczak M. | - | IPPT PAN | Urbański L. | - | IPPT PAN | Cristea M. | - | Petru Poni Institute of Macromolecular Chemistry (RO) | Ionita D. | - | inna afiliacja | Pieczyska E.A. | - | IPPT PAN |
| | 100p. |
3. |
Nabavian Kalat M., Staszczak M., Urbański L., Fernandez C.♦, Vega C.♦, Cristea M.♦, Ionita D.♦, Lantada A.♦, Pieczyska E.A., Investigating a shape memory epoxy resin and its application to engineering shape-morphing devices empowered through kinematic chains and compliant joints,
MATERIALS AND DESIGN, ISSN: 0264-1275, DOI: 10.1016/j.matdes.2023.112263, Vol.233, No.112263, pp.1-15, 2023Streszczenie: 4D printing is the additive manufacturing (3D printing) of objects that can transform their shape in a controlled and predictable way when subjected to external stimuli. A thermo-responsive shape memory polymer (SMP) is a highly suitable material to 4D print smart devices, due to its actuation function and the capability of recovering its original shape from the deformed one upon heating. This study presents the results of employing an epoxy resin in the additive manufacturing of complex-shaped smart devices with shape-morphing properties using laser stereolithography (SLA). To quantify the shape memory behaviour of the shape memory epoxy (SMEp), we first investigate the thermomechanical properties of the 3D-printed specimens in a tensile testing machine coupled with an environmental thermal chamber. This approach allows us to determine the shape fixity and recovery of SMEp. Next, we propose effective designs of complex-shaped devices, with the aim of promoting shape morphing through micro-actuators and compliant joints acting as active regions in combination with multiplying mechanisms or kinematic chains in each of the devices. We manufacture the complex-shaped prototypes by using SLA directly from the computer-aided designs. The shape memory trials of the 3D-printed prototypes reveal quite precise shape recovery of the devices, illustrating their shape-memory. In fact, the inclusion of micro-actuators and compliant joints within the complex-geometry devices allows for local triggering, deformation and recovery, resulting in a prompt response of the devices to heat. Therefore, innovative designs, along with the suitable smart material and high-quality manufacturing process, lead to 4D printed devices with fast actuation and shape-morphing properties. Overall, this research may contribute to the development of smart materials and 4D printing technology for applications in fields such as biomedical engineering, robotics, transport and aerospace engineering. Słowa kluczowe: Shape memory polymers,Shape memory epoxy,Shape morphing structures,Laser stereolithography,3D and 4D printing Afiliacje autorów:
Nabavian Kalat M. | - | IPPT PAN | Staszczak M. | - | IPPT PAN | Urbański L. | - | IPPT PAN | Fernandez C. | - | inna afiliacja | Vega C. | - | inna afiliacja | Cristea M. | - | Petru Poni Institute of Macromolecular Chemistry (RO) | Ionita D. | - | inna afiliacja | Lantada A. | - | inna afiliacja | Pieczyska E.A. | - | IPPT PAN |
| | 140p. |
4. |
Pieczyska E.A., Staszczak M., Maj M., Kowalczyk-Gajewska K., Golasiński K.M., Cristea M.♦, Tobushi H.♦, Hayashi S.♦, Investigation of thermomechanical couplings, strain localization and shape memory properties in a shape memory polymer subjected to loading at various strain rates,
SMART MATERIALS AND STRUCTURES, ISSN: 0964-1726, DOI: 10.1088/0964-1726/25/8/085002, Vol.25, No.8, pp.085002-1-15, 2016Streszczenie: This paper presents experimental and modeling results of the effects of thermomechanical couplings occurring in a polyurethane shape memory polymer (SMP) subjected to tension at various strain rates within large strains. The SMP mechanical curves, recorded using a testing machine, and the related temperature changes, measured in a contactless manner using an IR camera, were used to investigate the polymer deformation process at various loading stages. The effects of thermomechanical couplings allowed the determination of the material yield point in the initial loading stage, the investigation of nucleation and development of the strain localization at larger strains and the estimation of the effects of thermoelastic behavior during the unloading process. The obtained stress–strain and thermal characteristics, the results of the dynamic mechanical analysis and estimated values of the shape fixity and shape recovery parameters confirmed that the shape memory polymer (T g = 45°C) is characterized by good mechanical and shape memory properties, as well as high sensitivity to the strain rate. The mechanical response of the SMP subjected to tension was simulated using the finite element method and applying the large strain, two-phase model. Strain localization observed in the experiment was well reproduced in simulations and the temperature spots were correlated with the accumulated viscoplastic deformation of the SMP glassy phase. Słowa kluczowe: shape memory polymer, thermomechanical coupling, infrared camera, tension test, strain rate, strain localization, constitutive model Afiliacje autorów:
Pieczyska E.A. | - | IPPT PAN | Staszczak M. | - | IPPT PAN | Maj M. | - | IPPT PAN | Kowalczyk-Gajewska K. | - | IPPT PAN | Golasiński K.M. | - | IPPT PAN | Cristea M. | - | Petru Poni Institute of Macromolecular Chemistry (RO) | Tobushi H. | - | Aichi Institute of Technology (JP) | Hayashi S. | - | SMP Technologies Inc. (JP) |
| | 40p. |
5. |
Pieczyska E.A., Maj M., Kowalczyk-Gajewska K., Staszczak M., Gradys A., Majewski M., Cristea M.♦, Tobushi H.♦, Hayashi S.♦, Thermomechanical properties of polyurethane shape memory polymer–experiment and modelling,
SMART MATERIALS AND STRUCTURES, ISSN: 0964-1726, DOI: 10.1088/0964-1726/24/4/045043, Vol.24, pp.045043-1-16, 2015Streszczenie: In this paper extensive research on the polyurethane shape memory polymer (PU-SMP) is reported, including its structure analysis, our experimental investigation of its thermomechanical properties and its modelling. The influence of the effects of thermomechanical couplings on the SMP behaviour during tension at room temperature is studied using a fast and sensitive infrared camera. It is shown that the thermomechanical behaviour of the SMP significantly depends on the strain rate: at a higher strain rate higher stress and temperature values are obtained. This indicates that an increase of the strain rate leads to activation of different deformation mechanisms at the micro-scale, along with reorientation and alignment of the molecular chains. Furthermore, influence of temperature on the SMP's mechanical behaviour is studied. It is observed during the loading in a thermal chamber that at the temperature 20°C below the glass transition temperature (Tg) the PU-SMP strengthens about six times compared to the material above Tg but does not exhibit the shape recovery. A finite-strain constitutive model is formulated, where the SMP is described as a two-phase material composed of a hyperelastic rubbery phase and elastic-viscoplastic glassy phase. The volume content of phases is governed by the current temperature. Finally, model predictions are compared with the experimental results. Słowa kluczowe: shape memory polyurethane, thermomechanical couplings, infrared camera, temperature change, dynamic mechanical analysis, strain rate, constitutive model Afiliacje autorów:
Pieczyska E.A. | - | IPPT PAN | Maj M. | - | IPPT PAN | Kowalczyk-Gajewska K. | - | IPPT PAN | Staszczak M. | - | IPPT PAN | Gradys A. | - | IPPT PAN | Majewski M. | - | IPPT PAN | Cristea M. | - | Petru Poni Institute of Macromolecular Chemistry (RO) | Tobushi H. | - | Aichi Institute of Technology (JP) | Hayashi S. | - | SMP Technologies Inc. (JP) |
| | 40p. |
6. |
Pieczyska E.A., Maj M., Kowalczyk-Gajewska K., Staszczak M., Urbański L., Tobushi H.♦, Hayashi S.♦, Cristea M.♦, Mechanical and Infrared Thermography Analysis of Shape Memory Polyurethane,
Journal of Materials Engineering and Performance, ISSN: 1059-9495, DOI: 10.1007/s11665-014-0963-2, Vol.23, No.7, pp.2553-2560, 2014Streszczenie: Multifunctional new material—polyurethane shape memory polymer (PU-SMP)—was subjected to tension carried out at room temperature at various strain rates. The influence of effects of thermomechanical couplings on the SMP mechanical properties was studied, based on the sample temperature changes, measured by a fast and sensitive infrared camera. It was found that the polymer deformation process strongly depends on the strain rate applied. The initial reversible strain is accompanied by a small drop in temperature, called thermoelastic effect. Its maximal value is related to the SMP yield point and increases upon increase of the strain rate. At higher strains, the stress and temperature significantly increase, caused by reorientation of the polymer molecular chains, followed by the stress drop and its subsequent increase accompanying the sample rupture. The higher strain rate, the higher stress, and temperature changes were obtained, since the deformation process was more dynamic and has occurred in almost adiabatic conditions. The constitutive model of SMP valid in finite strain regime was developed. In the proposed approach, SMP is described as a two-phase material composed of hyperelastic rubbery phase and elastic-viscoplastic glassy phase, while the volume content of phases is specified by the current temperature. Słowa kluczowe: constitutive model, dynamic mechanical analysis, shape memory polyurethane, strain rate, temperature change, thermomechanical couplings Afiliacje autorów:
Pieczyska E.A. | - | IPPT PAN | Maj M. | - | IPPT PAN | Kowalczyk-Gajewska K. | - | IPPT PAN | Staszczak M. | - | IPPT PAN | Urbański L. | - | IPPT PAN | Tobushi H. | - | Aichi Institute of Technology (JP) | Hayashi S. | - | SMP Technologies Inc. (JP) | Cristea M. | - | Petru Poni Institute of Macromolecular Chemistry (RO) |
| | 20p. |