Living things evolve in order to adapt to its external environments. If it is possible to simulate evolution in a living world on a computer, we realize an adaptive system like living things in nature. Evolutionary algorithm is a stochastic optimization method simulated the process of evolution in nature. The three main categories of evolutionary algo rithms are Genetic Algorithm(GA) by Holland [1], Evolutionary Programming(EP) by Fogel [2], and Evolution Strategy (ES) by Rechenberg [3]. These algorithms are fundamentally iterative generation and alter nation process to operate on a population of candidate solutions. These algorithms can be classified into two types from the viewpoint of a rep resentation method. In the EP and ES, individuals represent candidate solutions by means of integer or real variables, neither string nor bit, 235 Evolutionary Computation: Theory and Applications Downloaded from www.worldscientific.com by UNIVERSITY OF BIRMINGHAM LIBRARY -INFORMATION SERVICES on 03/22/15. For personal use only.
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.
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