Staff

Abstract:
In this work, a new, simple method is presented, which enables identifcation of material properties of solids basing on the digital image correlation (DIC) measurements. It may be considered as a simplifed alternative of low computational complexity for the well-known fnite element model updating (FEMU) method and virtual felds method (VFM). The idea of the introduced sub-global equilibrium (SGE) method is to utilize the fundamental concept and defnition of internal forces and its equilibrium with appropriate set of external forces. This makes the method universal for the use in the description of a great variety of continua. The objective function is the measure of imbalance, namely the sum of squares of residua of equilibrium equations of external forces and internal forces determined for fnite-sized part of the sample. It is then minimized with the use of the Nelder–Mead downhill simplex algorithm. The efciency of the proposed SGE method is shown for two types of materials: 310 S austenitic steel and carbon-fber-reinforced polymer (CFRP). The proposed method was also verifed based on FE analysis showing error estimation.

Keywords:
Identifcation of material constant,Digital image correlation,Nelder–Mead downhill simplex algorithm,Finite element analysis,Optimization,Linear elasticity

Abstract:
The paper concerns the experimental analysis of the energy conversion process during uniaxial tension of 310S austenitic steel. The plastic work distributions were obtained taking into account the influence of strain rate and plastic anisotropy based on the displacement gradient determined experimentally using Digital Image Correlation (DIC) method. On the other hand, the energy dissipated as heat was obtained by the calculation of heat sources from the transient heat conduction equation basing on both the evolution of the temperature field determined by Infrared Thermography and mechanical field provided by DIC. It was shown that the proportions between the terms of the heat conduction equation and between the particular components of the energy dissipated as heat are significantly different for various process durations. As a measure of energy conversion the energy storage rate was used. At the beginning of the plastic deformation, the values are in the range from 0.4 to 0.6 depending on the strain rate and then decrease monotonically up to the level of around 0.15 with the increasing strain. Moreover, just before the end of the process the values decrease significantly and become close to 0 or even negative, which means that the material loses its ability to store the energy.

Keywords:
digital image correlation, infrared thermography, energy conversion, transient heatconduction equation, heat sources, energy storage rate

Abstract:
This paper focuses on the experimental determination of the distribution of material, lattice and plastic rotation during deformation of crystalline aggregate. The proposed methodology uses standard electron backscattering diffraction technique combined with 3D digital image correlation data. The presented approach is used for analysis of rotations during deformation of aluminium multicrystal.

Keywords:
image analysis, electron backscattering diffraction, plastic deformation, misorientation, plastic rotation

Abstract:
The aim of this work was to determine the stress distribution during plastic deformation, based on the displacement field obtained using the digital image correlation (DIC) method. To achieve stress distribution, the experimentally measured displacement gradient and the elastoplastic material model with isotropic hardening were used. The proposed approach was implemented in the ThermoCorr program. The developed procedure was used to determine stress fields for uniaxial tension and simple shear processes, carried out on samples made of austenitic steel 304L. Both material parameters, such as the Young's modulus, Poisson's ratio, yield stress, and parameters of the hardening curve, were acquired experimentally. The macroscopic force obtained from the DIC-based stresses and its finite element analysis (FEA) equivalent were compared with that measured during the experiment. It was shown that the DIC-based approach gives more accurate results with respect to FEA, especially for a simple shear test, where FEA significantly overestimates the value of experimentally obtained macroscopic force.

Keywords:
stress field determination, digital image correlation (DIC), finite element analysis (FEA), elastoplastic constitutive model, plastic work

Keywords:
Digital image correlation, Infrared thermography, Energy conversion, Heat sources, Transient heat conduction equation

Keywords:
image analysis, plastic deformation, misorientation, plastic rotation