International Journal of Impact Engineering 35 (2008) 1293–1302 On the application of genetic algorithms for optimising composites against impact loading M. Yong , B.G. Falzon, L. Iannucci Department of Aeronautics, Imperial College, London SW7 2AZ, UK Received 27 December 2006; received in revised form 8 October 2007; accepted 9 October 2007 Available online 17 October 2007 Abstract A genetic algorithm (GA) was adopted to optimise the response of a composite laminate subject to impact. Two different impact scenarios are presented: low-velocity impact of a slender laminated strip and high-velocity impact of a rectangular plate by a spherical impactor. In these cases, the GA’s objective was to, respectively, minimise the peak deflection and minimise penetration by varying the ply angles. The GA was coupled to a commercial finite-element (FE) package LS DYNA to perform the impact analyses. A comparison with a commercial optimisation package, LS OPT, was also made. The results showed that the GA was a robust, capable optimisation tool that produced near optimal designs, and performed well with respect to LS OPT for the more complex high-velocity impact scenario tested. r 2007 Dr Matthew Yong. Published by Elsevier Ltd. All rights reserved. Keywords: Genetic algorithms; Impact; Composites; Optimisation; Finite elements 1. Introduction The increasing use of composites in high-performance and weight-critical applications has seen a corresponding increase in the number of impact events involving these materials. Unfortunately, even minor impact events can cause a significant reduction particularly in the residual compressive strength [1], and this is a cause for concern where structural integrity is critical. Alternatively, the configurable, lightweight properties of composite materials make them attractive choices in designs subject to impact threats. The main goals of optimising a structure against impact are to improve damage resistance, damage tolerance, or energy absorption. Damage resistance is a property that enables a structure to resist the onset of damage. This may be of interest in structures where impact events do not feature in their primary role, such as skin panels on aircraft. Damage tolerance enables a structure to resist the effects of damage. This is of interest in structures where being hit is likely and the subsequent post-impact performance is important. A possible use of damage- tolerant designs would be in dual-purpose armour panels for light vehicles that also serve some structural role. Examples of energy-absorbing designs would be helicopter subfloors and automotive crash barriers, where the goal is to dissipate as much of the kinetic energy as possible. 2. Optimisation studies Despite the potential weight, cost and performance advantages of optimisation against impact, limited work has been done on optimising fibre-reinforced, polymer matrix composite structures against impact threats. In the wider context of impact optimisation, most of the improvements tend to be experimentally found, which involves testing a limited sample of the vast design space [2,3]. The conclusions are thus locally optimal and specific to the test circumstances. Other approaches use analytical techniques to determine the optimal design [4,5], with the associated limitations of theory on model complexity and accuracy. The limited numerical optimisation work on composite armour may be partly due to the numerical cost associated ARTICLE IN PRESS www.elsevier.com/locate/ijimpeng 0734-743X/$ - see front matter r 2007 Dr Matthew Yong. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijimpeng.2007.10.004 Corresponding author. Tel.: +44 20 7594 5100; fax: +44 20 7584 8120. E-mail address: matthew@globaloptimiser.com (M. Yong).