Strength assessment of composite beams under combined loads for application in mechanical suspension systems

Abstract

Composite materials are currently an essential resource for the development of lightweight components in the automotive industry. High strength-to-weight ratio and corrosion resistance make composites a good alternative to traditional materials, such as in mechanical suspension systems, where the design of composite leaf springs has been the focus of recent studies. This paper aims to propose a structural concept for a composite leaf spring for heavy vehicles, which should resist the severe stresses caused by poor road conditions, maintaining the stiffness characteristics required for the design, allowing reduction in composite mass, and offering means to dissipate the energy absorbed by the suspension system. Considering rough road applications, suspension springs are commonly subjected to flexural–torsional forces, which justifies the search for a spring concept with increased resistance to these two types of forces. The concept of a sandwich beam with external layers of composite material and a core of more flexible material is explored in the paper. When the fibers of the composite are oriented longitudinally, the sandwich beam can benefit from the high strength of the composite in this direction when subjected to the non-uniform torsion phenomenon. Finite element models are used to obtain failure loads of different concepts of composite beams, and interaction diagrams are plotted considering different combinations of flexural and torsional loads. A representative model of a suspension spring is considered, where simplified geometric constraints are assigned to analyze the structural performance of the sandwich spring concept. Finally, the potential application of a sandwich spring is discussed.