Identification et quantification des mécanismes de dommages mécaniques dans les polymères renforcés de fibres de verre par tomographie à rayons X

Owing to their advantageous properties compared to conventional engineering materials, the use of fiber reinforced polymers (FRP) is in constant increase. Due to their heterogeneous nature, various damage mechanisms initiate on different scales under mechanical loading. Consequently, this calls for the application of advanced non-destructive test methods, which provide insight into the material bulk. Within this thesis, a comprehensive evaluation of 2D and 3D full-field measurement techniques, including Digital Image Correlation (DIC) and Digital Volume Correlation (DVC), will be conducted for the characterization of damage in FRP. A specific focus will be placed on identifying the notch-sensitivity and the strain-damage interplay in the investigated glass fiber mat reinforced polymer composite. In this regard, X-ray computed tomography (XCT) will be coupled with finite element based approach to Digital Volume Correlation. This will enable for the the identification and quantification of damage initiation and growth in glass fiber reinforced polymers under various loading conditions. However, the major limitation of CT imaging is acquisition time, which limits the number of possible acquired scans. In addition, material behavior between two consecutive scans cannot be accessed. Time-dependent phenomena (e.g., relaxation, creep, crack propagation) cannot be captured. This limitations will be addressed by utilizing Projection-based Digital Volume Correlation (P-DVC) method, which relies on spacetime discretizations of sought displacement fields. An alternative approach is adopted within this thesis: spatial modes are constructed via scan-wise DVC, leaving only the temporal modes to be identified through P-DVC. For the first time, the temporal modes are constructed such that they are compatible with the loading history of the experiment. In this regard, temporal shape functions are introduced. The displacement fields are sought in a 4D (i.e., 3D in space and 1D in time) vector space generated by a reduced spacetime kinematic basis. Only one projection per loading level is still needed. The so-called PDVC enhanced DVC method enables for the quantification of damage growth over the entire loading history up to failure.