EXPERIMENTAL CHARACTERIZATION AND NUMERICAL MODELING OF THE DEFORMATION AND FRACTURE BEHAVIOR OF POROUS TI6AL4V UNDER STATIC AND DYNAMIC COMPRESSION LOADINGS
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For applications that involve impact loading, a good understanding of the material behavior under dynamic loading is critical. Due to their high specific strength, metallurgical stability, and corrosion resistance, porous titanium and its alloys have a wide range of applications including the development of impact resistant structures. The objective of this study is to gain a good understanding of the mechanical behavior of porous Ti6Al4V under both static and dynamic loading through experimental characterization and numerical modeling. To study the dynamic behavior of materials, Split Hopkinson Pressure Bar (SHPB) capable of applying uniaxial compressive loading for a strain rate range of 100-10000 /s, was designed and developed. The compressive mechanical behavior of Ti6Al4V with 0, 10, and 20% porosity, at the strain rate of 0.001 ,1000 ,4000 and 8000 /s was characterized with the standard material test machine and developed SHPB. SEM and EBSD analyses were carried out to study the failure mechanisms and texture development due to solidification and deformation. To gain insights into the experimental observation, numerical simulations on a mesoscale RVE (representative volume element) were conducted using ABAQUS 6.11 and Johnson Cook model. Parametric studies were used to investigate the effects of matrix properties, the density and the morphology of porosity on the material response.It was concluded that both deformation and fracture exhibited appreciable rate sensitivity. The material strength increased, and the failure strains decreased with the increased strain rates. Texture effect is negligible on the deformation process as all the samples had reasonably consistent textures due to solidification. The macroscopic experiments, the microstructure analysis and modeling work suggest that the formation of adiabatic shear band (ASB) is likely the major failure mechanism for Ti6Al4V and the band likely nucleates from the pores. Pore morphology played a significant role in the deformation and fracture process. As porosity increases, strength decreases but failures strain increases. For the same porosity, the denser the pore distribution, the sooner the failure would occur through the interconnection of the shear bands formed between the pores. The pore shape that has higher stress concentration also leads to lower strength and earlier failure.