Image-guided failure assessment of porous materials

摘要

Lightweight metallic cellular materials have the potential for use in composite structures such as plates, shells, and tubes. In order to evaluate the usefulness of these porous materials, an understanding of their failure mechanisms is essential. We have developed a technique called image-guided failure assessment that allows for the 3-dimensional analysis of fracture initiation and progression on the microscopic level. The technique has already been used to study trabecular bone failure, and theobjective of this study was to use the technique to study porous aluminum alloys. Image-guided assessment involves the use of a novel micro-compression device to apply and maintain loads, and the use of micro-computed tomography, providing 68μm isotropic resolution in this application, to image the specimens. Specimens were compressed and imaged at intervals of increasing strain (0%, 0.8%, 4%, 8%, 16%, and 32% strain). The advantage of using a nondestructive approach to assess failure is that subsequentimages of increasing strain can be animated to give visual information regarding fracture initiation and progression. In our tests, damage was seen to accumulate and propagate in local bands rather than being evenly distributed throughout the structure.This implies that local strains may be much larger than the apparent strain. These preliminary results demonstrate the usefulness of image-guided failure assessment in obtaining both visual and mechanical data regarding fracture initiation andprogression. The technique is applicable to a multitude of porous materials and might, in the future, become a new standard in the mechanical assessment of these structures.