Optimum Design of a Composite Helical Spring by Multi-criteria Optimization

ABSTRACT: A new methodology for the optimum design of composite helical springs with braided fibrous reinforcement is presented in this article. A multi-objective evolutionary algorithm is implemented to optimize two conflicting goals: minimize mass and maximize stiffness. Several design variables that have an influence on the mechanical properties of the spring must be considered: the braiding angle, number of plies and the standard design parameters of a helical spring. Design goals are set such as for standard metallic springs: equivalent mechanical performance, mass reduction, and comparable cost. Three different braided reinforcements in carbon, kevlar, and glass were analyzed with the same epoxy matrix. In helical springs, shear plays the most important role on spring performance. Taking into account the shear properties of braided composites and a series of technological constraints, a range of composite springs was devised, among which an optimal spring was selected for an automotive application, namely to replace the metallic spring of the suspension of a sport utility vehicle. KEY WORDS: composite materials, helical spring, design, multi-objective optimization