Abstract:
This thesis details the development and implementation of a new constitutive model for aluminum alloys, specifically designed to improve existing finite element simulation tools for analyzing materials and structures under dynamic loads and varying temperatures and strain rates. The main objective was to create a model for aerospace-typical aluminum alloys with orthotropic properties. The explicit finite element code DYNA3D was used as a numerical test-bed for implementing the new model, which includes an orthotropic yield criterion, damage growth, and a failure mechanism. To characterize the materials and derive model constants, a series of experimental tests were performed, including uniaxial tensile tests on two aluminum alloys (AA7010 and AA2024) at different strain rates, temperatures, and orientations, as well as Taylor cylinder impact tests and plate impact tests for validation. The constitutive model was initially a simple isotropic temperature and strain rate-dependent model, which was iteratively improved by coupling it with Hill's orthotropic yield criterion, and later with damage evolution and failure criteria. A key part of the work was the development of procedures for deriving parameters for the Johnson-Cook and Mechanical Threshold Stress models from tensile test data. The Taylor cylinder impact test was used as a primary validation experiment, with numerical simulations comparing results to experimental post-test geometries, such as side profiles and impact-interface footprints. The final model was implemented using a developed elastic predictor/plastic corrector/damage mapping integration algorithm, and numerical results for Taylor impact tests showed good agreement with experimental data, demonstrating the model's ability to accurately capture major and minor plastic strain distributions and damage evolution.
