轴箱内置型铁路车轴疲劳性能与寿命评估

Fatigue performance and life assessment of railway axle with inside axle box

开展了EA4T合金钢材料的低周疲劳试验、旋转弯曲高周疲劳试验与裂纹扩展速率试验,考虑载荷类型、表面质量与尺寸系数等因素,修正了标准小试样疲劳极限以预测全尺寸车轴的疲劳性能;建立了轴箱内置铁路车轴(内箱车轴)的有限元模型,分析了内箱车轴与传统轴箱外置铁路车轴(外箱车轴)临界安全部位的差异;基于安全寿命设计理论,结合修正的线性Miner疲劳累积损伤准则和载荷谱,研究了内箱车轴的疲劳强度与服役性能;分别采用Paris公式、NASGRO方程和LAPS模型拟合了裂纹扩展速率曲线,基于损伤容限设计方法估算了内箱车轴和外箱车轴的裂纹扩展寿命。研究结果表明:标准小试样的疲劳极限明显高于全尺寸车轴,其疲劳极限均值分别为369、286 MPa;与传统外箱车轴相比,由于加载位置的改变,内箱车轴的临界安全部位从卸荷槽处转移至轴身中部;内箱车轴疲劳总寿命为2.5×1012 km,满足30年服役寿命的设计要求;但是在运输或服役过程中车轴表面不可避免会存在缺陷,缺陷处存在严重的应力集中,为裂纹的萌生和扩展提供了便利条件,使车轴疲劳寿命大幅降低;当车轴临界安全部位的裂纹深度扩展到5 mm时,内箱车轴和外箱车轴的剩余寿命分别仅为3.2×105、2.0×105 km,应根据无损探伤精度合理制定无损检测周期,确保车轴安全服役。

Low cycle fatigue test,high cycle fatigue test under rotating bending and crack growth rate test of EA4 T alloy steel were carried out.Considering load type,surface quality,dimension coefficient and other factors,the fatigue limit of standard small specimen was modified to predict the fatigue performance of full-scale axle.The finite element model of railway axle with inside axle box(RAIB)was established.The difference of critical safety position between RAIB and traditional railway axle with outside axle box(RAOB)was analyzed.Based on the safe life design theory,combined with the modified linear Miner fatigue cumulative damage criterion and load spectrum,the fatigue strength and service performance of RAIB were studied.The crack growth rate curves were fitted by using the Paris formula,NASGRO equation and LAPS model,respectively.Based on the damage tolerance design method,the crack propagation lifes of RAIB and RAOB were estimated.Analysis result shows that the fatigue limits of standard small specimens is obviously higher than that of full-scale axles,and the mean values of fatigue limit are 369 and 286 MPa,respectively.Compared with the traditional RAOB,the critical safety position of RAIB has been transferred from unload groove to axle center due to the change of loading position.The total fatigue life of RAIB is 2.5×1012 km,which meets the design requirements of 30-year service life.However,there are inevitably defects on the surface of the axle during transportation or service,and serious stress concentration exists at the defect,which provides convenient conditions for the initiation and propagation of cracks and greatly reduces the fatigue life of axle.When the crack depth in critical safety position of axle extends to 5 mm,the residual lives of RAIB and RAOB are only 3.2×105 and 2.0×105 km,respectively,and the non-destructive inspection interval should be reasonably formulated according to the accuracy of non-destructive test to ensure the safe service of axle.1 tab,9 figs,30 refs.