Simulation of the creep expansion of porous sandwich structures

Recently developed sandwich structures consist of a porous metal core sandw iched between two fully dense face sheets. These structures are produced by pressurizing a metal powder compact with an inert gas prior to consolidati on by hot isostatic pressing ("hipping"). After consolidating and hot rolli ng the compact to a sheet form, a high-temperature annealing step is used t o expand the internally pressurized gas-filled micropores. This expansion r esults in a porous core sandwich structure with integrally bonded face shee ts. Recent experimental studies([1]) with a Ti-6Al-4V porous core sandwich have indicated that the expansion rate exhibits a maximum during thermal ra mping to 920 degreesC but then continued to expand over many hours at a con stant temperature. Significant grain growth also accompanied the expansion. A microstructure-dependent creep model has been developed for a body conta ining a distribution of spheroidal pores. The body's constitutive behavior is described by microstructure-dependent creep potentials for dislocation ( power law) and diffusion-accommodated grain-boundary sliding (DAGS). It has been used to simulate the expansion of Ti-6Al-4V sandwich structures subje cted to thermal cycles similar to those studied experimentally. The simulat ed response compared well with experimental results. The model was then use d to identify an attainable core porosity as a function of the initial gas pressure and initial core relative density at the completion of the expansi on process step.