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材料力学性能早期退化在微观结构上表现为位错和晶带滑移等缺陷的变化,在超声波检测中表现为高次谐波的产生。发展了一套在材料疲劳实验机上直接任线测量超声非线性系数的实验系统,在相同条件下测量了同一试件作不同输入电压下的二次谐波和基波幅度,二次谐波幅度和基波幅度平方的线性相关系数r=0 9996,表明实验系统是可靠的。同时利用该系统进行了三组不同加载应力的镁合金试件疲劳在线非线性超声检测实验。实验结果表明,在疲劳寿命的55%之前,超声非线性系数对疲劳加载周数具有很高的灵敏度。因此,利用超声非线性系数可以很好地表征镁合金的疲劳早期退化。另外在中低周疲劳范围内,加载应力的大小以及拉-拉和拉压疲劳模式的变化对实验结果没有明显的影响。
Early degradation of mechanical properties of materials in the microstructure showed dislocation and band slip and other defects change in the ultrasonic test showed the generation of higher harmonics. A set of experimental system for measuring the non-linear coefficient of ultrasound directly on the material fatigue testing machine was developed. Under the same conditions, the second harmonic and fundamental wave amplitude, the second harmonic amplitude And the linear correlation coefficient r = 0 9996 of the square of the amplitude of the fundamental wave, which indicates that the experimental system is reliable. At the same time, the system was used to perform fatigue online nonlinear ultrasonic testing of three groups of magnesium alloy specimens with different loading stresses. Experimental results show that the non-linear coefficient of ultrasound has a high sensitivity to fatigue loading cycles before the fatigue life of 55%. Therefore, the use of ultrasonic non-linear coefficient can be a good characterization of magnesium alloy fatigue early degradation. In addition, in the range of medium-low cycle fatigue, the magnitude of loading stress and the change of fatigue mode of pull-pull and pull-compression have no obvious effect on the experimental results.