The Analysis Of The Critical Size Of The Crack Which Cause Tyre Fracture

Tyre fracture is one of the most seriously threaten to the train safety.It’s important to analyze the critical size of the crack for solving and preventing tyre fracture.This paper takes the tyre of combined wheel as the research object.The stresses under the various loading conditions and the stress intensity factors of different crack in the tyre are analysed with the finite element method,based on which the critical size of the tyre under the various conditions are estimated.Based on the analysis of stress distribution of the tyre under the various loading conditions(heat treatment residual stress,fitting stress,mechanical load,baking thermal load),according to the load of the wheel from manufacturing process to service,superposing of different loading conditions(heat treatment residual stress+fitting stress,heat treatment residual stress+fitting stress+mechanical load,heat treatment residual stress+fitting stress+mechanical load+thermal baking load)is performed,and then the stress distributions of various loading conditions combinations of tyre are analysed.In this research,stress conditions of three thicknesses of the tyre(90 mm new tyre,40 mm wear tyre,30 mm wear tyre)are considered,and the effects of the tyre weariness on the stress distribution are examined.On the basis of tyre stress analysis,the stress intensity factors of crack tip under different conditions were calculated by empirical formula and FRANC3 D software respectively.The effect of loading conditions,tyre thickness and crack sizes on the stress intensity factors of cracks are studied.The critical sizes which cause the tyre fracture are estimated by comparing the stress intensity factors of the crack tips with the fracture toughness of the tyre steel.The results show that circumferential stress of tyre press fitting is most significant under all possible loading conditions.The Fitting stress is the main threaten to the tyre safety.For the A-type crack,when the tyre is worn to 40 mm,the critical crack size is 20×33.3 mm under pressing stress and the combination load with heat treatment residual stress and fitting stress.For the B-type crack,when the tyre is worn to 40 mm,the critical crack size is 20×33.3 mm under the combination loadwith heat treatment residual stress and fitting stress.Furthermore,the results shows that when the limit of wear thickness increases from 30 mm to 40 mm,the critical crack size rises from 10×16.6 mm to 10×25mm under the combination load with heat treatment residual stress and fitting stress,and the safety of tyre is obviously improved.