Fatigue behaviour of die-casting aluminum alloy suspension arms for scooters

The aim of the paper is at qualifying a methodology for the fatigue life assessment of structural components obtained by die-casting for vehicle applications. Full-scale fatigue tests were conducted on the back suspension arms of mid-size scooters. Two loading conditions, i.e. bending and combined bending plus torsion, were considered as representative of typical operating conditions. Fatigue tests showed that the locations of failure initiation is different for the two loading configurations. Material was characterized by means of small size standard specimens extracted from the components in order to be representative of the effective material conditions, particularly of the surface. Both static (tensile) and fatigue tests were conducted, making use of three different R-ratios. A finite element (FEM) model of the suspension arm, representative of full-scale test conditions was set-up in order to interpret the tests. The sub-modelling approach was adopted in order to get accurate evaluations of the stressstrain fields with reasonable computing resources and elaboration time. Combined elastic and elasticplastic analyses were necessary to estimate the stress cycles in the regions critical for fatigue damage. Employing the material properties given by small-size specimens and the proposed FE analysis technique, predictions of either the locations of failure initiation and the fatigue strength of the component were obtained, in quite good agreement with full-scale tests.