Study On Creep Properties Of Open Cell Nickel Foams

By combining experimental study with theoretical analysis,the creep properties of open cell nickel foams are studied.First of all,the development ,manufacturing techniques,spec and capability are introduced briefly.The microstructure of nickel foams is analysed,the influence of its structural parameters is discussed:The rate of creep strain shows strongly depence of relative density; The rate of creep strain of nickel foams with non-hollow struts is nearly unaffected by the varied cross-sections,while the ratio of the void-size to strut-size affects the strain rate much more. At room temperature, the open cell nickel foam was used to conduct a tension creep experiments, The result shows that when the relative density of open cell nickel foam is kept constant,both the creep and the rate of creep increase as stress increases,while the first stage creep reduces as stress increases.The result of tension creep experiment at room temperature is well described by Gibson and Ashby's cellular structural model.It is also studied by combining four sorts of FEM models: the B model, where bending of struts perpendicular to the applied stress is dominant; The C model, where compression of struts parallel to the applied stress is dominant; The BC model, combining perpendicular struts deforming by bending(as for the B model) and parallel struts deforming by compression (as for the C model); The S model, with a tetrakaidecahedral geometry where struts forming a 45°angle with the applied stress deform into a S shape owing to complex bending moments.After analyzing the result of FEM ,analytic equations and experiments data, the specialty of four FEM model whicn describe the phenomenon of creep of foams is compared.According to the curve of experiments data, it is composed of first stage creep and secondary creep , as shows that B model is well fitted to the qualitative analysis of the creep of nickel foams.So both analytic equation and FEM of B model is well to describe the creep of nickel foams.It means that Gibson and Ashby's cellular structural analytic equation is rational math to describe the creep of nickel foams.