Metallic open-cell foams--a promising approach to fabricating good medical implants.

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.

Application of the EBSD technique to describe the initiation and growth behaviour of microstructurally short fatigue cracks in a duplex steel.

Up to 90% of the fatigue life of engineering alloys results from the initiation and propagation of microstructurally short cracks. Owing to their strong interactions with microstructural features, e.g. grain and phase boundaries, they exhibit substantially non-uniform propagation kinetics as compared with the growth rate of long cracks, which can be well described using a power-law function of the range of the stress-intensity factor DeltaK. In the present paper interactions between the crystallographic misorientation of grain and phase boundaries and microcracks in an austenitic/ferritic stainless steel are discussed and quantified by means of fatigue experiments in combination with the electron backscattered diffraction technique. In the second part a numerical model for the simulation of microcracks is introduced, which is capable of taking real microstructural arrangements into consideration.

Reactivity pattern of 15 HLA-Dw1 homozygous typing cells in primary mixed lymphocyte culture.

The Dw1 specificity was highly correlated with the serologically determined HLA-DR1 antigen in the Eighth International Histocompatibility Workshop 1980. By testing a large number of HLA-Dw1, DR1 defined homozygous typing cells (HTC) in a checkerboard primary mixed lymphocyte reaction, on a panel of about 30 HLA-DR1 heterozygous individuals, and in family segregation, three Dw1 "subtypes" could be defined in association with certain HLA-A, -B, and -C-antigens. HTC TA, FRI, and FRA carrying the HLA haplotypes A11, B35, Cw4 or A3, B35, Cw4 in the homozygous state gave positive typing results with most HLA-DR1 positive panel members and stimulated only four other Dw1 HTCs (SRR less than or equal to 35%). In contrast to this operationally "broad" specificity, Dw1-HTC-HEN (HLA-A2, B44, C-, homozygous) was non-stimulatory to all HTCs except one, but gave high responses against these, leading to the definition of a "narrow" specificity included in the "broad" one. Another such "narrow" specificity was represented by HTC FEE (HLA-A2, B27, Cw2 homozygous). Typing patterns with FEE were mostly different from those defined with other HTC. In family studies a specific typing pattern for this HTC could be shown to segregate with HLA. However, within some of these responses a contribution of the HLA haplotype in the trans position must be assumed.