非线性超声技术表征金属和有机材料塑性损伤的对比试验研究

摘要

非线性超声信号对材料微观组织演化非常敏感，可用于材料早期服役损伤的检测与表征。基于非线性超声纵波信号测量，研究纯铜和有机高分子材料 PMMA 的超声非线性参量随着材料塑性损伤程度的变化关系。试验结果表明，随着塑性应变的增加，纯铜的超声非线性参量随着变形量的增加而显著增大，而 PMMA 材料的超声非线性参量几乎不变。利用扫描电子显微镜与透射电子显微镜分别对两种材料进行微观组织观察，发现纯铜在塑性变形过程中位错密度逐渐增加，这可能是导致超声非线性参数增大的主要因素。无位错结构的 PMMA 材料在塑性变形过程中仅发生了高分子链段的变化，而非线性超声信号对此却不太敏感。从试验结果可以看出，材料损伤过程中位错结构的演化能引起非线性超声信号的显著变化。%Nonlinear ultrasonic testing technology is expected to be an important means of testing and characterization of early-damage for in-service engineering materials due to its high sensitivity to micro-structure evolution.The paper studied the nonlinear parameters of copper and organic polymer materials PMMA which undergo various degrees of plastic damage,based on the measurements of ultrasonic nonlin-ear parameters using longitudinal wave.The results show that,with the increase of plastic strain,the non-linear parameters of copper significantly increase as the plastic deformation increases,while the nonlinear parameters of PMMA nearly keep unchanged.Micro-structures of the two materials were observed by the scanning electron microscopy and transmission electron microscopy,indicating that dislocation densities of copper gradually increase during the process of plastic deformation;whereas changes in polymer chain segments are observed at dislocation-free PMMA materials.It is concluded that the changing of dislocation densities may be the predominant factor leading to the change of ultrasonic non-linearity during the process of plastic damage.