关键词: 裂纹闭合, 力磁效应, 磁特性参数, 表征模型, 铁磁性材料

Abstract: Determination and characterization of crack closure under low cycle fatigue loads were difficult in engineering practice. The characterization law and models of critical state of crack closure were studied based on magnetic property parameters. Graded loading and unloading experiments were carried out by using Q235B steel as the experimental materials. The TSC-5M-32 metal magnetic memory detector was used to collect magnetic characteristic parameters. The effects of different plastic zones at the crack tip and the crack tail on the magnetic field were investigated. The changing law of the synthetic magnetic characteristic parameter ΔHp at the critical state of crack closure was analyzed by comparing the critical load of crack closure determined by the flexibility differential method. The results show that the cracks close up when the load is less than Pop critical point， and at the same time ΔHp has a minimum inflection point； the crack is in the closure critical state when the load equals to the Pop， and at the same time ΔHp jumps sharply upward with turning points； the cracks open fully when the load is greater than Pop， and at the same time ΔHp fluctuates around at a higher level. Furthermore， the characterization model of crack closure state was established based on magnetic property parameters. The verification results show that， for the loading and unloading phases， the maximum relative errors between the model predicted values and measured values are 9.398% and 11.549% respectively， which provides a new method to judge and characterize the crack closure states for engineering practice. 

Key words: crack closure, magneto-mechanical effect, magnetic property parameter, characterization model, ferromagnetic material