Uncertainties on the mechanical behaviour of bronze sheets: influence on the failure in bending

Abstract

Copper alloys are extensively used in the manufacture of electrical and electronic components, which strength depends on the material mechanical properties, which in turn depend on the metallurgical state. Even though the mechanical properties remain within the specifications, the subsequent formability limits may depend strongly on the material batch. Considering the forming stage to manufacture plug-in type connectors made of CuSn6P thin sheets, a crack may appear in the components, in the bent area subject to high strains, when changing the material batch. The aim of this study is to take account of these variations of the mechanical behavior through a probabilistic approach, to predict the formability limit. The mechanical properties of the materials from the two batches were characterized in tension, to highlight the differences. The initial yield stress and the tensile strength are higher for one material, while the maximum equivalent plastic strain at rupture, determined through a hybrid experimental-numerical approach, is lower. And a significant difference in the transverse anisotropy coefficient is evidenced. A 3D parametric finite element model of the forming stage is developed to investigate the role of some mechanical properties and process parameters on the formability limit in bending. The range of the parameter values comes from the experimental data. Their influence is evaluated through a design of experiments, with the aim of highlighting the influence of the variations of the mechanical properties and process parameters on the fracture criterion, using a probabilistic approach with Gauss’s law.