Plateau stress estimation of impact compression test on aluminum foam using X-ray computed tomography observation

Abstract

The plateau stress of aluminum (Al) foam is an important mechanical parameter that is closely related to its energy absorptivity. An estimation method for plateau stress was proposed by simply assuming that when the mean true compressive stress on a maximum-porosity cross section perpendicular to the direction of compressive loading reaches the critical value, the nominal compressive stress becomes equal to the plateau stress. In this study, using commercial-purity A1050 Al, A6061 Al alloy and ADC12 Al alloy die castings containing a large amount of gases, uniform Al foam and two types of functionally graded (FG) Al foam were fabricated by the friction stir welding (FSW) route precursor process. The local porosity distributions for the fabricated Al foams were obtained from the observation of X-ray computed tomography (CT) images, then drop weight impact tests were carried out to evaluate the plateau stresses. Through the comparison of the test results with the results obtained by the estimation method, the applicability of the estimation method for plateau stress to impact compression tests on uniform aluminum Al foam and each foam layer of FG Al foam was examined. It was shown that the plateau stresses can be evaluated approximately within ±20% error when the proof stress is employed as the critical value.