ANALYSIS OF THE STRUCTURAL INTEGRITY OF AN AUTOMOBILE ALUMINIUM ALLOY WHEELWITH SELECTED COOLING HOLE GEOMETRIES

Abstract

Aluminium alloy wheels are increasingly popular for their light weight and good thermal conductivity. However, there are efforts to introduce Cooling Holes (CH) to reduce their weight without compromising structural integrity. Varieties of CH in use are mostly of parabolic or circular geometry. Literature is sparse on the use of triangular, square and oval shaped CH in wheel design. This study was, therefore, designed to investigate the structural integrity of an aluminium alloy wheel with triangular, quadrilateral and oval shaped CH.

Five-armed-wheel (6JX14H2ET42) with parabolic CH each of 3466 mm2 area were sourced from the James Watt market, Benin city. Young's Modulus, yield stress, and Poison's ratio were determined. Inner surface of the wheel-tyre assembly was prepared and strain rosette attached at points between 0° and 180° at interval of 30° at wheel's well, Inboard Bead Seat (IBS) and Outboard Bead Seat (OBS). The assembly was mounted on an hydraulically operated static radial test rig and loaded statically with Radial Load (RL) of 4750 N and Inflation Pressures (IP) of 0.3 and 0.15 MPa, respectively. Mean contact patch and strains were measured and converted to contact angle and stresses using trigonometric and stress-strain equations, respectively. A 3-D numerical model for a wheel with parabolic-CH was developed and solved using Finite Element Method (FEM) to determine stress distribution at well, IBS and OBS. The FEM and experimental stress values were analysed using ANOVA at α0.05. Further numerical study was conducted for quadrilateral-CH and oval-CH at Aspect Ratios (AR) 0.78 and 0.71, respectively at 4750 N RL and IP of 0.3 MPa, with equal CH area of 3466 mm2. Numerical study was also conducted at IBS with CH area of 2229 mm2 for triangular-CH at AR 1 and 0.5; quadrilateral-CH and oval-CH each at AR 1, 0.5, 0.33 and 0.25.

Young's Modulus, yield stress, Poison's ratio and contact angle for parabolic¬-CH were 22.29±0.02 GPa, 222.50±0.25 MPa, 0.42±0.02 and 30.25±3.50º, respectively. At IP of 0.3 and 0.15 MPa, experimentally obtained stresses at well, IBS and OBS were 6.29±1.52 and 4.47±1.05; 5.45±0.91 and 4.14±0.93; 4.86±0.21 and 3.56±1.63 MPa, respectively. Corresponding FEM results at well, IBS and OBS at 4750 N loading at IP of 0.30 and 0.15 MPa were 6.75±2.82 and 4.68±0.05, 5.33±1.15 and 2.78±1.36, and 2.50±0.33 and 1.50±0.45 MPa, respectively. The FEM and experimental results had no significant difference. Numerically obtained stresses at well, IBS and OBS at 4750 N loading and IP of 0.3 MPa were 4.96±1.24, 4.83±1.24 and 2.00±0.82 MPa and 4.76±0.74, 4.69±1.26 and 1.91±0.90 MPa, respectively for quadrilateral-CH and oval-CH. Numerical inboard stresses at AR of 1 and 0.5 for triangular-CH were, respectively, 5.59±1.50 and 5.84±1.86 MPa. Inboard stresses at AR 1, 0.5, 0.33 and 0.25 for quadrilateral-CH were 5.56±1.18, 5.08±1.30, 5.01±0.45 and 4.49±1.26 MPa, respectively; for oval-CH, 4.46±1.40, 4.37±1.14, 4.63±1.04 and 4.37±1.44 MPa, respectively.

The study established that oval-shaped cooling-hole aluminium alloy wheel possessed highest structural integrity than all others investigated.