Amine Bouterf

Toward 4D mechanical correlation

Background :The goal of the present study is to illustrate the full integration of sensor and imaging data into numerical procedures for the purpose of identification of constitutive laws and their validation. The feasibility of such approaches is proven in the context of in situ tests monitored by tomography. The bridging tool consists of spatiotemporal (i.e., 4D) analyses with dedicated (integrated) correlation algorithms.Methods :A tensile test on nodular graphite cast iron sample is performed within a lab tomograph. The reconstructed volumes are registered via integrated digital volume correlation (DVC) that incorporates a finite element modeling of the test, thereby performing a mechanical integration in 4D registration of a series of 3D images. In the present case a non-intrusive procedure is developed in which the 4D sensitivity fields are obtained with a commercial finite element code, allowing for a large versatility in meshing and incorporation of complex constitutive laws. Convergence studies can thus be performed in which the quality of the discretization is controlled both for the simulation and the registration.Results :Incremental DVC analyses are carried out with the scans acquired during the in situ mechanical test. For DVC, the mesh size results from a compromise between measurement uncertainties and its spatial resolution. Conversely, a numerically good mesh may reveal too fine for the considered material microstructure. With the integrated framework proposed herein, 4D registrations can be performed and missing boundary conditions of the reference state as well as mechanical parameters of an elastoplastic constitutive law are determined in fair condition both for DVC and simulation.

Damage measurements via DIC

The present paper is devoted to the measurement of damage by resorting to image correlation techniques. This full-field measurement procedure gives access to 2D and 3D displacements that can be utilized to analyze damage mechanisms, to estimate damage fields, and to determine material parameters of damage growth laws. Different features associated with image correlation are addressed in the context of continuum damage mechanics. Applications concerning damage detection, damage quantification and damage model validation are presented.

On the Use of Digital Image Correlation for the Analysis of the Dynamic Behavior of Materials

The present chapter is devoted to the analysis of the mechanical behavior of materials subjected to dynamic loadings via digital image correlation (DIC). This measurement technique provides 2D or 3D displacement fields that can be evaluated thanks to the use of high-speed cameras. Various declinations of DIC are first presented. Uncertainty quantifications are also discussed. Last, different examples illustrate how DIC can be used to analyze and quantify deformation, damage and fracture mechanisms of brittle and ductile materials.

Fast four-dimensional tensile test monitored via X-ray computed tomography: Single projection–based digital volume correlation dedicated to slender samples

The measurement of four-dimensional (i.e. three-dimensional space and time) displacement fields of in situ tests within X-ray computed tomography scanners (i.e. lab-scale X-ray computed tomography) is considered herein using projection-based digital volume correlation. With a single projection per loading (i.e. time) step, the developed method allows the loading not to be interrupted and to vary continuously during the scan rotation. As a result, huge gains in acquisition time (i.e. more than two orders of magnitude) need to be reached. The kinematic analysis is carried out using predefined space and time bases combined with model reduction techniques (i.e. proper generalized decomposition with space–time decomposition). The accuracy of the measured kinematic basis is assessed via gray-level residual fields. An application to an in situ tensile test composed of 127 time steps is performed. Because of the slender geometry of the sample, a specific beam space regularization is used, which is composed of a stack of rigid sections. Large improvements on the residual, the signal-to-noise ratio of which evolves from 9.9 to 26.7 dB, validate the procedure.