Fracture mechanisms and size effects of brittle metallic foams: In situ compression tests inside SEM

Abstract

a b s t r a c tIn situ compressive tests on specially designed small samples made from brittle metallic foams were accomplished in a loading device equipped in the scanning electron microscopy (SEM). Each of the small samples comprises only several cells in the effective test zone (ETZ), with one major cell in the middle. In such a system one can not only obtain sequential collapse-process images of a single cell and its cell walls with high resolution, but also correlate the detailed failure behaviour of the cell walls with the stressstrain response, therefore reveal the mechanisms of energy absorption in the mesoscopic scale. Meanwhile, the stress-strain behaviour is quite different from that of bulk foams in dimensions of enough large, indicating a strong size effect. According to the in situ observations, four failure modes in the cell-wall level were summarized, and these modes account for the mesoscopic mechanisms of energy absorption. Paralleled compression tests on bulk samples were also carried out, and it is found that both fracturing of a single cell and developing of fracture bands are defect-directed or weakness-directed processes. The mechanical properties of the brittle aluminum foams obtained from the present tests agree well with the size effect model for ductile cellular solids proposed by Onck et al.

Experimental Validation of RVE Based Failure Simulations of Macro‐Porous Materials

“…The aim is to design specimens, which well reproduce the stress state of the periodic simulations. This approach is similar to the work by Song et al (2008) [6]. In the current paper we treat planar macro-porous ceramics characterized by distributions of closed spherical pores under uniaxial compression, but the idea is in principle also applicable to three-dimensional RVEs.…”

Correlation between ceramic additions and compressive properties of Zn–22Al matrix composite foams

“…Size effect is an important issue in the mechanical testing of metallic foams [19][20][21]. That means the value of the specimen size relative to the mean cell size has great influence on the mechanical properties of the metallic foams.…”

“…A small specimen is required for the observations on the microstructure failure. Song et al [21] found that the failure process of a specimen with insufficient cell is homologous to that of a specimen with many cells. Both of them are defect-directed or weakness-directed processes.…”

An advanced approach for the generation of complex cellular material representative volume elements using distance fields and level sets

“…mechanical, acoustical, thermal, transport-related, … ) of this type of materials strongly depends on their microstructure and this particular link is the subject of an increasing number of studies, for various fields of application, mechanics and acoustics being the most represented. Next to purely experimental studies [5][6][7][8][9][10][11], computational models at the microstructural scale, or homogenization-based and multi-scale models may bring a more in-depth understanding of the relationship between the local morphological features of the material and its global behavior. Closely related to experimental characterizations are the numerical simulations that use the real geometry of materials, thanks to the use of computer-aided tomography data, to build finite element models [12][13][14][15].…”