金属材料疲劳损伤检测的非线性声学方法*

金属材料的疲劳损伤有前期、后期两个阶段,前期疲劳损伤主要来源于位错,而随着疲劳程度的不断加深,位错密度也不断的增加,这将导致疲劳后期微裂纹的产生。这两个阶段产生声学非线性效应的机理不同,分别用位错模型、微裂纹模型对其产生非线性效应的机理进行了阐述,并对不同阶段的疲劳试样进行了相关实验研究。实验结果表明:对于材料早期疲劳损伤,随着疲劳程度的增加,其接收声波信号中的非线性谐波成分越来越显著,并且随着激励电压的增加,非线性效应更加明显,因此可用接收信号中的谐波激发情况来评估材料的早期疲劳损伤程度。而对于材料疲劳后期出现微裂纹后,其产生的非线性与早期疲劳损伤相比,谐波成分更加丰富,并且随激励电压的增加谐波幅度增加明显,可据此来判断材料中的疲劳损伤阶段。

Nonlinear acoustic method for detecting fatigue in metal materials

Fatigue of metal materials has two stages. Early fatigue mainly comes from dislocation. With the deepening of fatigue, dislocation density also increases continuously, which will lead to the occurrence of micro-cracks in the late fatigue period. Mechanism of the acoustic nonlinear effect in these two stages is different, which was described with dislocation and micro-crack model respectively. Relevant experiments on fatigue specimens in different stages were carried out. The experimental results show that the nonlinear harmonic components of the received signals become more and more significant with the increase of the fatigue degree for early fatigue of the material and the non-linear effect becomes more obvious as the excitation voltage increases. Therefore, harmonics excitation situation in the received signals can be used to assess the fatigue. For the post-fatigue, the nonlinearity of the material is more abundant than that of early fatigue because of the micro-cracks and harmonics amplitudes increase obviously with the increase of excitation voltage, which can be used to judge the stage of fatigue.