Analysis of torsion bar failure occurring during the pre-strained manufacturing for heavy off-road tracked vehicles

Abstract

The torsion bar used in the suspension system of the heavy off-road tracked vehicle was broken during the pre-strained manufacturing. A series of investigations were conducted including chemical composition analysis, metallographic examination, residual stress detection, hardness evaluation, and fractographic analysis. The anomalous phenomena were analyzed comprehensively under the condition that the fracture features could not conclude directly. The results showed that the low tempering temperature of the torsion bar was the root cause of fracture, which resulted in excessive residual stress. The hardness is higher than the standard 14 HBW. The maximum difference of residual stress was 278 MPa. They reduced the torsional resistance. Consequently, the fracture occurred during pre-strained. The excessive residual stress triggered the advent of cracks and intergranular fracture. The possibility of failure caused by chemical composition and inclusions was excluded. Due to the results and the related research, changing the tempering temperature to 290-310℃ (holding for 2 h) may avoid failure. The analysis procedure in this work provides a means to determine failure cause under the difficulty of fracture analysis, and it offers possible routes to improve the performance of the torsion bar.