Micromechanical Characterization of Metal Foams

Abstract

Cellular materials such as foams, honeycombs, or auxetic structures are an interesting type of structural materials for lightweight constructions or dynamic energy absorbers. These microheterogeneous materials consist of a hierarchical structure. Foams can be separated into a macro scale, meso scale, and micro scale dealing with the entire specimen or component, individual pores, and individual struts, respectively. As a result, the macroscopic foam properties are strongly related to the mesoscopic and microscopic properties as a superposition of geometrical structural response and material properties. Whereas the geometry can be easily determined, e.g., by computer tomography measurements, the evaluation of real micro material properties of individual struts or cell walls is still a very challenging task. The material properties of these constituents of open‐cell or closed‐cell foams significantly differ from bulk material properties due to changes in boundary condition during production and different scaling effects, such as different surface‐to‐volume ratios of oxide layers or different cooling conditions due to less material in struts than in the bulk. However, the need for reliable micro material properties for the realistic forecast of macroscopic properties of components made of foam by numerical simulations makes the micromechanical characterization and testing of metal foams to an emerging field of research. The present contribution deals with the most relevant achievements in the field from the beginnings to the present day.

Microstructural damage behaviour of Al foams

“…The present work investigates the correlation between the mechanical properties and the microstructure of Al foam struts. As in literature [1,15] the bulk material from the same alloy has different mechanical properties than the strut material from the present Al foam due to different cooling velocity during manufacturing, micro stresses and large surface-to-volume ratio resulting in different microstructure. Due to the large surface-to-volume ratio defects (oxides, pores and intermetallics) have a stronger impact on the mechanical properties than in bulk material.…”

“…Due to the manufacturing conditions the cooling velocity is significantly faster than for the production of bulk material. The properties of the strut material cannot be assumed to be equal to the material properties from bulk material [1,15,16]. Additionally, the surface-to-volume ratio is different and surface inhomogeneities play an important role for foams.…”

Micromechanical Characterisation of Ni/PU Hybrid Foams

“…The stiffness under bending of the individual struts differs between 144 GPa and 482 GPa, which equals a difference of 70.1%. Reasons for these variations can be found in the manufacturing process and geometry of the struts [ 8 , 9 ]. The coating produces a nanocrystalline Ni layer on top of a graphite lacquer which is applied on the PU template during the coating process of the hybrid foam.…”

“…The size of the struts and the force to be expected during deformation preclude the use of standard macroscopic testing machines. For these reasons, there is almost no literature available on the mechanical testing of individual struts [ 9 ]. Kaya et al [ 10 , 11 ] have conducted tensile tests on individual struts of an open-cell steel foam.…”

Fabrication of 17‐4PH Stainless Steel Foam by a Pressureless Powder Space Holder Technique

“…[ 1,2 ] For example, porous copper foam, which has a large surface area and excellent thermal conductivity, offers outstanding performance as a low‐profile heat sink in passive cooling applications. [ 3 ] In addition, porous titanium foam is an ideal material for artificial joints and bones due to its good biocompatibility. [ 4 ] The well‐known 17‐4PH stainless steel is the most commonly used type for porous stainless steel systems, because the strength and hardness of the matrix can be increased by an aging treatment.…”