裂纹面摩擦接触引起的断裂韧性增长的研究

采用弹黏塑性的材料本构关系, 建立了压、剪混合型裂纹常速准静 态扩展的力学模型, 求得了裂纹面摩擦接触条件下裂纹尖端场的数值解, 并基于数 值结果讨论了扩展裂纹的摩擦效应. 计算和分析表明, 裂纹面的摩擦效应主要表现 在两个方面. 第一方面是摩擦会导致裂纹尖端区材料的断裂韧性增高, 并且裂纹面间的摩擦作用越强, 增韧效果越显著. 摩擦增韧的机制可以解释为裂纹 面间的摩擦作用导致裂纹尖端塑性区尺寸变大, 使裂纹尖端场的塑性变形能增加, 从而使得裂纹尖端区材料增韧. 摩擦生热并不是导致材料断裂韧性增长的根本机制. 第二方面是摩擦会导致``断裂延缓'. 利用裂纹面的摩擦来提高构件的承载能力和延长构件的服役寿命具有较大的工程实用价值.

Researches on the enhancement of fracture toughness induced by friction between crack faces

Mechanical model is established for the mixed-mode crack in elastic-viscoplastic material with friction present between the crack faces. Asymptotic and numeric solutions to the crack-tip fields are got and the frictional effects are discussed with the crack loaded under compression and shear. Calculations and analyses are made to determine the boundary of the crack-tip plastic region and to obtain the plastic deformation energy in it. It is indicated that the crack-tip plastic region will be enlarged and the plastic deformation energy in the crack-tip region will be enhanced when the crack faces are frictionally contacted. From the viewpoint of energy, the plastic deformation energy can be viewed as the fracture toughness of the material in the crack-tip region. Therefore, the fracture toughness of the material in the crack-tip region can be enhanced by the friction between the crack faces. Further analysis indicates that the enhancement of the fracture toughness is mainly due to the increment of the plastic deformation energy in the crack-tip region other than the frictional heat produced on the crack faces. It is indicated by the calculation and analysis of the phase-angle of the crack-tip load that probable hysteresis of the crack growth can occur due to the friction between the crack faces. In engineering, friction between the crack faces can be produced artificially through design and manufacture to improve the carrying capacity and prolong the service life of the cracked components loaded under compression and shear.