考虑塑性的钢轨表面疲劳微裂纹分析
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摘要
目的研究塑性条件下受重复轮轨荷载的钢轨表面的初始疲劳裂纹行为。方法建立含表面微裂纹的钢轨二维有限元模型,通过耦合裂纹面对应节点达到无裂纹的效果。经过几次循环加载后取消节点耦合设置,达到出现裂纹的效果。分析随着轮轨循环加载钢轨的响应,计算残余应力强度因子,并利用渐进状态(随着循环次数的增加,裂纹尖端区新产生的塑性越来越小,裂尖小范围内塑性不再增加)下的应力强度因子计算初始疲劳裂纹扩展速率。结果有限元模拟中,轮轨荷载循环加载在钢轨上表面,使其产生拉伸残余应力,且随着深度增加,拉伸残余应力越来越小。裂纹萌生后,不同角度的裂纹残余(KI)都随循环次数的增加而减小,但残余(KII)都随循环次数的增加而增大。受残余应力的影响,渐进状态下的钢轨表面初始微裂纹应力强度因子随裂纹角度(θ)的增加而增加。结论钢轨表面的残余应力加快了初始微裂纹的扩展速率,降低了钢轨的使用寿命。
The work aims to study initial fatigue micro-crack behavior on rail surface which is subjected to cyclic wheel/rail loading under plastic stresses. A 2 D finite model of rail with a surface crack was established. The corresponding nodes of the crack surface were coupled to achieve the effect without crack. After several cyclic loading, the joint coupling was released to show the crack. The residual stress intensity factor was calculated by analyzing the response of rail by cyclic wheel/rail loading. The initial fatigue crack growth rate was also calculated by stable stress intensity factors in the asymptotic state(As the number of cycles increased, the new plasticity in the crack tip became smaller and smaller, and the plasticity did not increase within the small range of crack tip). In the finite element simulation, the rail was subjected to cyclic wheel/rail loading to produce tensile residual stress on the upper surface, and the tensile residual stress became smaller and smaller with the increase of depth. After crack initiation, the residue(KI) of crack at different angles decreased with the increase of cyclic number, but residue(KII) increased with the increase of cyclic number. Under the influence of residual stress, the stable stress intensity factor of initial micro-crack on rail surface in the asymptotic state increased with the increase of crack angle(θ). The residual stress on the rail surface accelerates the propagation rate of the initial micro-crack and reduces the service life of rail.
The work aims to study initial fatigue micro-crack behavior on rail surface which is subjected to cyclic wheel/rail loading under plastic stresses. A 2 D finite model of rail with a surface crack was established. The corresponding nodes of the crack surface were coupled to achieve the effect without crack. After several cyclic loading, the joint coupling was released to show the crack. The residual stress intensity factor was calculated by analyzing the response of rail by cyclic wheel/rail loading. The initial fatigue crack growth rate was also calculated by stable stress intensity factors in the asymptotic state(As the number of cycles increased, the new plasticity in the crack tip became smaller and smaller, and the plasticity did not increase within the small range of crack tip). In the finite element simulation, the rail was subjected to cyclic wheel/rail loading to produce tensile residual stress on the upper surface, and the tensile residual stress became smaller and smaller with the increase of depth. After crack initiation, the residue(KI) of crack at different angles decreased with the increase of cyclic number, but residue(KII) increased with the increase of cyclic number. Under the influence of residual stress, the stable stress intensity factor of initial micro-crack on rail surface in the asymptotic state increased with the increase of crack angle(θ). The residual stress on the rail surface accelerates the propagation rate of the initial micro-crack and reduces the service life of rail.
引文
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[17]江晓禹,李孝滔,李煦,等.轮轨高速滚动接触及钢轨疲劳裂纹扩展研究[J].西南交通大学学报,2016,51(2):274-281.JIANG Xiao-yu,LI Xiao-tao,LI Xu,et al.Research on wheel/rail rolling contact at high speed and fatigue crack propagation in rail[J].Journal of Southwest Jiaotong University,2016,51(2):274-281.
[2]FARJOO M,PAL S,DANIEL W,et al.Stress intensity factors around a 3D squat form crack and prediction of crack growth direction considering water entrapment and elastic foundation[J].Engineering fracture mechanics,2012,94:37-55.
[3]FARJOO M,DANIEL W,MEEHAN P A.Modelling a squat form crack on a rail laid on an elastic foundation[J].Engineering fracture mechanics,2012,85(85):47-58.
[4]FLETCHER D I,SMITH L,KAPOOR A.Rail rolling contact fatigue dependence on friction,predicted using fracture mechanics with a three-dimensional boundary element model[J].Engineering fracture mechanics,2009,76(17):2612-2625.
[5]DUBOURG M C,LAMACQ V.A predictive rolling contact fatigue crack growth model:onset of branching,direction,and growth-role of dry and lubricated conditions on crack patterns[J].Journal of tribology,2002,124(4):680-688.
[6]BROUZOULIS J,EKH M.Crack propagation in rails under rolling contact fatigue loading conditions based on material forces[J].International journal of fatigue,2012,45(3):98-105.
[7]RINGSBERG J W,LINDB?CK T.Rolling contact fatigue analysis of rails inculding numerical simulations of the rail manufacturing process and repeated wheel-rail contact loads[J].International journal of fatigue,2003,25(6):547-558.
[8]SEO J W,GOO B C,CHOI J B,et al.Effects of metal removal and residual stress on the contact fatigue life of railway wheels[J].International journal of fatigue,2008,30(10):2021-2029.
[9]BOGDANSKI S,BROWN M W.Modelling the threedimensional behaviour of shallow rolling contact fatigue cracks in rails[J].Wear,2002,253(1):17-25.
[10]MELLINGS S,BAYNHAM J,ADEY R A.Automatic crack growth prediction in rails with BEM[J].Engineering fracture mechanics,2005,72(2):309-318.
[11]PARIS P C.A critical analysis crack propagation laws[J].Trans ASME ser D,1963,85(4):528-533.
[12]TANAKA K.Fatigue crack propagation from a crack inclined to the cyclic tensile axis[J].Engineering fracture mechanics,1974,6(3):493-498.
[13]CHAN K S,DAVIDSON D L,OWEN T E,et al.A fracture mechanics approach to high cycle fretting fatigue based on the worst case fret concept-II.Experimental evaluation[J].International journal of fracture,2001,112(4):331-353.
[14]曹世豪,李煦,文良华,等.钢轨表面裂纹扩展方向研究[J].表面技术,2014,43(3):37-42.CAO Shi-hao,LI Xu,WEN Liang-hua,et al.Analysis of propagation direction of rail surface crack[J].Surface technology,2014,43(3):37-42.
[15]曹世豪,江晓禹,文良华.轴重和摩擦力对轮轨接触疲劳的影响[J].表面技术,2013,42(6):10-14.CAO Shi-hao,JIANG Xiao-yu,WEN Liang-hua.Influence of axle load and friction on the fatigue of wheel/rail contact[J].Surface technology,2013,42(6):10-14.
[16]王文健,刘启跃.PD3和U71Mn钢轨钢疲劳裂纹扩展速率研究[J].机械强度,2007,29(6):1026-1029.WANG Wen-jian,LIU Qi-yue.Study on fatigue crack growth rate of PD3 and U71Mn rail steel[J].Journal of mechanical strength,2007,29(6):1026-1029.
[17]江晓禹,李孝滔,李煦,等.轮轨高速滚动接触及钢轨疲劳裂纹扩展研究[J].西南交通大学学报,2016,51(2):274-281.JIANG Xiao-yu,LI Xiao-tao,LI Xu,et al.Research on wheel/rail rolling contact at high speed and fatigue crack propagation in rail[J].Journal of Southwest Jiaotong University,2016,51(2):274-281.