Estimation of Fatigue Limit of a A356-T6 Automotive Wheel in Presence of Defects

Abstract

The automotive wheel is a critical safety component in the vehicle and, for such a reason, it has also to meet strict requirements about technological properties. This component is produced by low pressure die casting technique and the casting defects related to the process have to be properly considered having a high effect in decreasing both static and dynamic resistance of the component. Effectively, casting defects like porosities influence the fatigue crack initiation and strongly affect the fatigue life too. One of the most common problem in the real component is the mismatch between the experimental data and literature. In fact, many scientific researches were carried out on small samples produced in a controlled condition and therefore it is difficult to direct transfer the laboratory results to a real cast component with a well-defined shape and different thicknesses.\ud In the present study, an aluminum alloy A356-T6 wheel was analyzed in order to correlate the fatigue performance taking in to account the casting defects.\ud The fatigue limit of the component was studied by rotating bending fatigue tests executed on the whole wheels. Microfractographic analyses on the broken wheels were carried out on the fracture surfaces using a Scanning Electron Microscope in order to identify the crack initiation zone: it was recognized that the crack always started from shrinkage porosities. The statistical population of these defects was therefore investigated on samples taken from the wheel in crack nucleation positions of the spoke and the maximum expected defect size on the component was estimated by the statistics of extreme values. The experimental fatigue limit was finally compared with the theoretical value predicted with the Murakami’s method

Evaluation of Fatigue Characteristics of Aluminum Alloys and Mechanical Components Using Extreme Value Statistics and C-Specimens

“…In particular, for casting aluminum, porosity and other casting defects are detrimental to the fatigue [7][8][9]. The equation was modified for aluminum alloys [10][11][12].…”

Effect of Material Type and Minimum Diameter of Specimens on the Fatigue Life

“…The difference between fatigue testing using Ultrasonic at 20 kHz reaches a fatigue life of 10 7 cycles for 9 minutes, but with the conventional method at 100 Hz it is achieved for 1 day which results in a drastic reduction in fatigue testing time and costs [3]. The results of the A356 automotive wheel specimen cut at the bottom inner corner of the wheel p-ISSN : 1412-114X e-ISSN : 2580-5649 http://ojs2.pnb.ac.id/index.php/LOGIC spokes which were tested for fatigue at S 120 MPa broken at a fatigue life of 380000 cycles showed a decrease in the value of the specimen cut exactly on the inner rim bar, the fatigue test at S 120 MPa broke at fatigue life 360000 cycles [4]. Different treatments on fatigue test specimens resulted in different fatigue life of specimens treated with annealing, giving grooves and corroding can reduce fatigue life than the untreated condition.…”

Effect of microstructure on the high cycle fatigue behaviour of DP 600 and SPFH 590 steels with and without a hole

“…Traditionally, the fatigue properties of the base material are taken into consideration while designing a wheel. However, an actual wheel would contain many weaker zones such as bolt hole, vent hole and notches depending on the design [2][3][4][5]. Therefore, during operation under cyclic loading conditions, the fatigue cracks are initiated from either the above-mentioned weaker zones.…”