Simulating the Residual Stress in an A356 Automotive Wheel and Its Impact on Fatigue Life

Abstract

Keeping the weight of unsprung rotating components low is critical for fuel efficiency in automobiles; therefore, cast aluminum alloys are the current material of choice for wheels. However, pores formed during solidification can combine with residual stresses and in-service loads to reduce the fatigue life of this safety critical part. In this study, a model of the residual stresses arising from the quench stage of a T6 heat treatment was developed. The resulting predictions were compared to residual strain measurements made on quenched wheels via a strain gage/sectioning technique. The predictions were shown to be sensitive to the alloy's flow stress behavior, yet no data were available for the temperature-dependent and strain-rate-dependent inelastic behavior of A356 in the as-solutionized condition. Measurements of this behavior were made using a GLEEBLE 3500, and the data were incorporated into the model, significantly improving the correlation between model and experiment. In order to determine the influence of residual stress upon the final fatigue performance of the wheel during service, the change in stress level due to machining was first calculated. The residual stress was then compounded together with a service stress to determine the local stress at all points in the wheel during idealized operation. Finally, the fatigue behavior was predicted using a unified initiation and propagation model based on this local stress and an idealized pore size.

Internal Stress Generation during Quenching of Thick Heat Treatable Aluminium Alloys

“…The skin-core effect clearly appears with about 300 MPa compressive stresses at the surface and 200 MPa tensile stresses in the centre. Stresses are higher in absolute value at the surface than in the centre since the quenching rate is higher at the surface than in the centre [7,15]. As expected, quench induced stresses are slightly lower in compression and in tension for the AA7040 alloy compared to the AA7449 alloy.…”

Fatigue Life Analysis of Aluminum Wheels by Simulation of Rotary Fatigue Test

“…The fatigue life of an A356 wheel was predicted by integrating the residual stress into the in-service loading and wheel casting defects (pores). The residual stress showed a moderate influence on the fatigue life of the wheel, which was more sensitive to casting pore size and service stress due to applied loads [6]. By improved Smith formula, Yang, Cui and Zhao used finite element analysis of stress values as the basic parameters for wheel fatigue life prediction.The wheel bending fatigue test results verified the method [7].…”

The Effect of Strain Rate, Specimen Geometry and Lubrication on Responses of Aluminium AA2024 in Uniaxial Compression Experiments

“…3-9% increase in flow stress from quasi-static to high loading rates for AA6061-T651 alloy [1], although the effect of strain rate on stressstrain response becomes more pronounced at elevated temperatures [2,3]. The microscopic mechanism leading to strain rate sensitivity of aluminium alloys is still a matter of debate, however dislocation movement has been linked to explain strengthening and rate dependency of the material.…”