| Summary: | The volume of components manufactured from cast aluminum alloys in both the aerospace and automotive industries has seen a tremendous rise in the past 10 years. In the automotive industry, cast wheels also provide aesthetically appealing designs for the consumers, which is an important factor for their increased demand. The cyclic nature of in-service loading in some applications makes fatigue performance a key design consideration. Manufacturers use standardized testing procedures (SAE J328) to assess the fatigue life of wheels for regular driving or cornering conditions. Recently, a leading North American wheel manufacturing company has begun testing the radial fatigue life of wheels following rim indentation. The development of this test has highlighted the need for a tool to support the wheel design process that is capable of predicting the fatigue life of cast components following permanent deformation.
A considerable amount of research work has already been conducted on establishing the effects of microstructure and casting defects on the fatigue life of cast aluminum alloy A356. However, there has been limited work published on the effects of initial plastic deformation on the fatigue life of cast alloy A356. Thus, the current research project aims to quantify the effects of initial plastic strain on the fatigue life of automotive wheels manufactured from A356. Specifically, the research aims to enhance the understanding of the impact of rim indentation on the fatigue life of a wheel.
A finite element model was developed to predict the deformation occurring during application of a static load during the rim indentation test. The residual stress distribution occur¬ring after the T6 heat treatment process was used as an input to the rim indentation model. The model was then extended to calculate the stress state of the wheel under radial fatigue test conditions. Lab-scale experiments were performed to characterize the fatigue behavior of alloy A356 following different amounts of pre-strain (plastic strain). This data was used to develop an empirical relationship to relate the fatigue life to initial plastic strain and the cyclic stress state. Industrial-scale rim indentation and radial fatigue tests were used to validate the overall model predictions.
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