多条滚动接触疲劳裂纹共存时的瞬态扩展行为分析

利用有限元法建立考虑轮轨瞬态滚动接触载荷的三维滚动接触疲劳斜裂纹扩展分析模型,分析现场中成群出现的钢轨滚动接触疲劳裂纹之间的相互影响。该模型可以准确反映高频轮轨瞬态滚滑行为对裂纹载荷边界和裂纹面接触的影响,突破了以往研究中基于赫兹接触的稳态接触载荷边界假设带来的种种局限。基于实测,模型中裂纹扩展角度取典型值30°,长度和深度分别取10~20 mm和2~4 mm (长深比固定为5),考虑间距在5~20 mm范围内变化,分析多至5条裂纹共存情况下的裂尖应力场强度因子。300 km/h运行速度下的计算结果表明:相同尺寸的多裂纹共存时某一裂纹尖端的节点力相较于单裂纹时低,但多裂纹时的接触刚度更低,使得裂纹尖端附近两裂纹面间的相对位移较单裂纹更大,最终使得多裂纹工况的裂尖应力场强度因子随裂纹数量的增多而增大;对于特征尺寸(长度)为15 mm的等间距多裂纹,当裂纹间距大于5 mm时,3条裂纹共存模型即足以将裂纹间相互影响精确考虑在内,较5条裂纹共存模型的误差仅为1.7%。对于文中所研究的多裂纹,当裂纹间距大于裂纹特征尺寸时,裂纹间的相互影响可以忽略,即可采用单裂纹模型进行计算。

Transient Propagation Behaviors of Multiple Rolling Contact Fatigue Cracks

A finite element model was developed to study the transient propagation behavior of multi rail cracks under the transient wheel rail rolling contact loads.The influences of the transient rolling sliding behavior on the load boundary of the cracks and the contact between crack faces are considered in the developed model,which breaks through the limitations of the assumption of the steady state rolling contact boundary based on Hertz theory widely employed in the previous studies.In light of the actual measurements,the angle of cracks was set to be a typical value of 30°,the length and depth were taken as 10 to 20 mm and 2 to 4 mm,respectively (a fix ratio of 5 between the length and the depth),the crack space was taken as 5 to 20 mm in the model,the stress intensity factors at the crack tip under the condition of coexistence of up to 5 cracks were analyzed at running speed of 300 km/h.Results show that with respect to the single crack case,the interaction between multi cracks reduces the the nodal forces at the crack tip,while increases the relative displacement between the crack faces near the tip,and consequently,leads to higher stress intensity factors.For parallel cracks of 15 mm long (the same sizes assumed for each crack),their interactions can be captured accurately by a 3 crack model when the crack spacing is greater than 5 mm,whose error is only 1.7% with respect to that of a 5 crack model.For the multiple cracks studied in this paper,the interaction between cracks can be ignored when the crack spacing is greater than the crack length,so a single crack model can provide sufficient accuracy.