Ohrndorf A, Krupp U, Christ H-J
Institut für Werkstofftechnik, Universität Siegen, Paul-Bonatz-Str. 9-11, 57076 Siegen, Germany.
Technol Health Care. 2006;14(4-5):201-8.
The aim of this paper is to report on the characterization of the influences of foam homogeneity and the cell strut material on the mechanical behaviour and the fracture mode of metallic foams that are promising candidates for new perfectly tailored medical implants. For two open-cell foams with identical cell geometries produced in the same precision-casting process but using different cell strut materials, the stress-strain behaviour and the evolution of damage until fracture is compared. To account for effects arising from a change in the geometry of the cell structure and the resulting homogeneity of the foam, the main characteristics of fracture for the group of closed-cell foams were included in this study. Monotonic tests carried out in compression revealed that foam homogeneity is the major factor with respect to the formation of deformation bands prior to cell collapse in metallic foams. The influence of the cell strut ductility is particularly pronounced in monotonic tension where the fracture mode changes from extremely brittle fracture to strongly plastically deformed cells, with substantial fracture elongation. In tension-tension fatigue as well as under symmetric push-pull loading conditions, damage is governed by a combination of cyclic creep and fatigue crack propagation through the specimen. From a mechanistic point of view no fundamental differences between the three foams tested were detected for these loading conditions. However, in compression-compression fatigue the same dependencies in terms of homogeneity and ductility influence the mechanisms of strain evolution that are active in monotonic compression.
本文旨在报告泡沫均匀性和胞壁材料对金属泡沫力学行为和断裂模式的影响特性，这些金属泡沫是新型定制医疗植入物的理想候选材料。对于在相同精密铸造工艺中生产但使用不同胞壁材料的两种具有相同胞体几何形状的开孔泡沫，比较了其应力-应变行为以及直至断裂的损伤演变。为了考虑胞体结构几何形状变化和由此产生的泡沫均匀性所带来的影响，本研究纳入了闭孔泡沫组的主要断裂特征。压缩单调试验表明，对于金属泡沫，在胞体坍塌前变形带的形成方面，泡沫均匀性是主要因素。胞壁延展性的影响在单调拉伸中尤为明显，此时断裂模式从极脆性断裂转变为胞体强烈塑性变形且具有显著断裂伸长率的情况。在拉-拉疲劳以及对称推-拉加载条件下，损伤由循环蠕变和疲劳裂纹贯穿试样的扩展共同控制。从机理角度来看，在这些加载条件下，未检测到所测试的三种泡沫之间存在根本差异。然而，在压-压疲劳中，在均匀性和延展性方面相同的相关性会影响单调压缩中活跃的应变演变机制。
