Foams of Gray Cast Iron as Efficient Energy Absorption Structures: A Feasibility Study

Abstract

Gray cast iron foams are produced using a reticulated polyurethane by using a modified investment casting process. To evaluate the attributes of the produced micro-geometries, foam segments and single struts are investigated by light and electron microscopy in 2D, and synchrotron micro-computed tomography in 3D. Mechanical properties are determined by macro/micromechanical testing and nanoindentation. In the microstructure of the gray cast iron struts, both flake-like coarse type A and locally fine undercooled type D graphite particles are observed. The distribution of the two graphite types is heterogeneous and is the likely cause for the large scatter of the mechanical properties of the single struts. The high graphite content and the resulting brittle behavior of the struts lead to strong serrations in the stressstrain curve of the foams with a negative effect on energy absorption. We found a relatively low energy absorption efficiency of below 50% as compared to 75% in 316L austenitic steel struts. The small specimen size results in scale effects which strongly influence the mechanical properties of the foams. Further improvement in the fabrication of gray cast iron foams is needed to tailor graphite distributions and optimize performance of cast iron-based foams.

Modeling of Complex Gray Cast Iron Open‐Cell Foams Revealing Insights on Failure and Deformation on Different Hierarchical Length‐Scales

“…For the results shown here, fracture strain at the onset of damage corresponded to the maximum stress, as determined from the stress–strain curves of the struts that we measured previously (point “c” in Figure 4). [ 38 ] Regarding stress triaxiality under tensile loading, we assumed isotropic material properties and, accordingly assumed a value of 0.33 based on micromechanical models provided by Collini and Pirondi. [ 32 ] For quasistatic analysis, we kept the strain rate constant.…”

“…Elastic–plastic material behavior was assigned based on our previous microtensile test results on single struts. [ 38 ] Due to the large variations in the mechanical properties between single foam struts, average values of the mechanical properties were used. Accordingly, the constitutive material parameters were: elastic modulus E = 143 GPa, Poisson's ratio ν = 0.3, density ρ = 7.3 g cm −3 , and yield strength σ y = 200 MPa.…”

“…Accordingly, the constitutive material parameters were: elastic modulus E = 143 GPa, Poisson's ratio ν = 0.3, density ρ = 7.3 g cm −3 , and yield strength σ y = 200 MPa. [ 38 ] A dynamic explicit solver was used to assess the quasistatic failure and damage evolution in the foams and reliably compute the large nonlinear deformations. A quasistatic deformation behavior of the foam was accomplished with a loading rate of 1 m s −1 .…”

“…Typical values for the Poisson's ratio ν ¼ 0.3 [44] and density ρ ¼ 7.86 g cm À3 [45] were taken from data available in the literature. Hardening (region b-c in Figure 4) was also defined based on the study by Kaya et al [38] A ductile damage model was implemented where damage began with nucleation of microvoids at interfaces between (brittle) particles and the surrounding ductile matrix phases. Certain voids grow and interactions between neighboring voids lead to plastic strain concentration between voids, resulting in local necking.…”

Effects of the cell number and anisotropy in the open cell metal foams on the energy absorption efficiency

“…[20] martensitik faz dönüşümünün sertleşmeye katkısının sanılan kadar fazla olmadığını ve mikroyapının daha fazla önem taşıdığını belirtmiştir. Bunun yanında açık hücreli dökme demir köpüklerde açık bir plato bölgesi oluşmamıştır [21].…”