Simulation of ultrasonic materials evaluation experiments including scattering phenomena due to polycrystalline microstructure

To evaluate and optimize the performance of ultrasonic inspection and evaluation procedures, we employ the Generalized Point Source Superposition technique (GPSS), which allows to simulate the propagation of ultrasonic waves and their interaction with defects. This contribution reports on the combination of GPSS with the theoretical description of ultrasonic scattering phenomena in microscopically inhomogeneous media. The theory comprises phenomena like local and global directional and position dependent scattering effects in macroscopically isotropic polycrystalline materials. The presented work addresses the main ‘ingredients’ of the simulation procedure and the influence of the grain size on the simulation results

Multi-scale modeling of the viscoelastic behavior of 3D woven composites

International audienceA method is presented to predict numerically the homogenized viscoelastic behavior of 3D woven composites using only its constituents’ behavior. It is based on elastic homogenizations applied to the Laplace-Carson transform of the time-dependent viscoelastic behavior of the constituents. Two scale changes are necessary: from micro- to meso-scale to obtain the homogenized behavior of the consolidated yarns, and from meso- to macro-scale. The temperature and cure dependent viscoelastic behavior of the matrix is identified from experimental data, using the time-temperature superposition principle with the cure dependent glass transition temperature as reference temperature. The meso-scale representative unit cell of the composite is extracted from X-ray microtomography images. The homogenized viscoelastic behavior is used to calculate the evolution of the apparent moduli of the composite with temperature between -50 °C and 200 °C. The results are in good agreement with experimental data over the temperature range where the matrix behavior was properly identified

Modelling of Ultrasonic Scattering in Polycrystals Aiming for Tools to Simulate Experiments in NDT&E

Numerical simulations of ultrasonic propagation and nondestructive testing and materials characterization proceduresmust comprise microstructural scattering phenomena. This objective requires a convenient microstructural scatteringmodel allowing the simulation of ultrasonic time signals, e.g. backscattering signals (A-scans), flexibility in shape and macroscopic material inhomogeneity (local microstructure variations, defects, etc.) of the considered component, and the evaluation of analytical scattering coefficient formulae ensuring fast simulation algorithms.A general theoretical approach delivers the analytical basis. A 3D model for the numerical realization of proper statistical grain distributions for single-phase macroscopically isotropic polycrystals is developed, and ultrasonic backscattering signals are numerically simulated using the analytical scattering coefficient formulae provided by the theory

Coupled stress and energy analysis of crack onset in textile composites at the mesoscopic scale

International audienceA coupled stress and energy criterion is used to analyze crack initiation at the mesoscopic scale in a four-layer plain weave glass-epoxy composite. The choice of possible crack configurations is restricted based upon optical microscope observations of damage mechanisms on a specimen edge during tensile testing. It is found that transverse yarn cracking accompanied by yarn-yarn decohesions around the crack tips is the first damage that occurs in the composite. For the stress condition in the yarns, a criterion developed for modeling failure of unidirectional plies in a laminate is applied. For the energy condition, the difference between the potential energies of an undamaged and a cracked unit cell is calculated, using identical mesh topologies. The energy criterion is found to be dominant in the studied case. It leads to an estimation of the crack initiation strain much closer to experimental observations by acoustic emission than the stress criterion alone and allows to determine crack length and orientation at damage onset. The coupled criterion leads to the conclusion that the yarn-yarn decohesions are a direct consequence of the transverse yarn cracks, and its length can be determined through the energy criterion

Comparison between voxel and consistent meso-scale models of woven composites

International audienc

Mesures de champs de déformations par corrélations d'images pour l'identification de modèles mécaniques microscopiques de composites à matrice polymère

International audienc

Full field strain measurements by digital image correlation for the validation of micro-scale mechanical models of polymer matrix composites

International audienc

Full field strain measurements by digital image correlation for the validation of micro-scale mechanical models of polymer matrix composites

International audienc

Mesures de champs de déformations par corrélations d'images pour l'identification de modèles mécaniques microscopiques de composites à matrice polymère

International audienc

Approches multimodèles pour la conception de structures composites à renfort tissé

National audienc