Design of structures for optimal static strength using ESO R. Das a , R. Jones a,b, * , Y.M. Xie c a DSTO Centre of Expertise in Structural Mechanics (DSTO CoE-SM), Department of Mechanical Engineering, Monash University, Wellington Road, Vic. 3168, Australia b Rail CRC, Department of Mechanical Engineering, Monash University, Wellington Road, Vic. 3168, Australia c School of Civil and Chemical Engineering, RMIT, Vic. 3001, Australia Received 13 April 2004; accepted 8 May 2004 Available online 30 July 2004 Abstract This paper presents a modified evolutionary structural optimisation (ESO) algorithm for optimal design of damage tolerant structures. The proposed ESO algorithm uses fracture strength as the design objective. The formulation outlined here can be used for shape optimisation of structures and allows for cracks to be located along the entire structural boundary. In this work we use an approximate method for evaluating the stress intensity factors associated with the cracks. This extended ESO algorithm is illustrated using the problem of the optimal shape design of a ‘cutout’ in a rectangular plate under biaxial loading and the design of a shoulder fillet under uniaxial tension. It is found that this method reduced the maximum stress intensity factor for the optimum shape and produced a near uniform level of fracture criticality around the boundary. It is also shown that the shapes optimised for stress and fracture strength may differ. This highlights the need to explicitly include fracture parameters in the design objective function. The results agreed well with those reported in the literature using a biological method. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Structural optimisation; Finite element analysis; Fracture; Damage tolerance; Stress intensity factors 1. Introduction The damage tolerance design philosophy has now become an integral part of the standard design practice in many industrial sectors. The need that the structures be stronger, lighter, safer and more durable was first experienced by aerospace industries. However, it is now recognised that other capital intensive industries such as railway, ship building, mining etc. have the same requirements in order to be commercially com- petitive in global environment. Australia expects to double its rail tonnage capacity over the next 10 years. * Corresponding author. Present address: Department of Mechanical Engineering, Monash University, P.O. Box 31, Wellington Road, Clayton, Vic. 3800, Australia. Tel.: +61-3-9905-3809; fax: +61-3-9905-1825. E-mail address: rhys.jones@eng.monash.edu.au (R. Jones). 1350-6307/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2004.05.002 Engineering Failure Analysis 12 (2005) 61–80 www.elsevier.com/locate/engfailanal