The following is an excerpt.
PhD Candidates Jens Kristian Holmen and Lars Edvard Dæhli both put aluminium alloys to the test in their contributions to the 21st European Conference on Fracture in Catania, Italy next week. Here are the abstracts:
Jens Kristian Holmen:
Predicting ductile failure from micromechanical simulations
Unit-cell models were in this study utilized to numerically determine the failure locus of a cast and homogenized AA6060 aluminum alloy. Simulations were conducted for moderate and high stress triaxiality ratios, and for various Lode parameters between generalized tension and generalized compression. We estimated the orientation of the localization band that minimizes the failure strain in the unit-cell models for all the imposed stress states. The energy based Cockcroft-Latham (CL) failure criterion was calibrated based on the numerically determined failure locus and used in finite element simulations that we evaluated against experimental tests. Test-specimen geometries included smooth tension tests, notched tension tests and plane strain tension tests. These were designed to cover a wide range of stress states. The points of failure in the experimental tests were predicted with reasonable accuracy by the numerical simulations. We see that the method used for numerically determining the failure locus can be improved by refining the micromechanical simulations. Better agreement between the simulations and the experiments can also be obtained, for instance by employing a different macroscopic failure criterion than the CL criterion.
Lars Edvard Dæhli:
Unit cell simulations and porous plasticity modelling for recrystallization textures in aluminium alloys
The well-known Gurson model has been heuristically extended to incorporate effects of matrix anisotropy on the macroscopic yielding of porous ductile solids. Typical components of recrystallization textures for aluminium alloys were used to calibrate the Barlat Yld2004-18p yield criterion using a full-constraint Taylor homogenization method. The resulting yield surfaces were further employed in unit cell simulations using the finite element method. Unit cell calculations are invoked to investigate the evolution of the approximated microstructure under pre-defined loading conditions and to calibrate the proposed porous plasticity model. Numerical results obtained from the unit cell analyses demonstrate that anisotropic plastic yielding has great impact on the mechanical response of the approximated microstructure. Despite the simplifying assumptions that underlie the proposed constitutive model, it seems to capture the overall macroscopic response of the unit cell. However, to further enhance the numerical predictions, the model should be supplemented with a void evolution expression that accounts for directional dependency, and a void coalescence criterion in order to capture the last stages of deformation.
