变厚板塑性形变超声非线性响应及其实验

Ultrasonic Nonlinear Response of Plate with Varying Thickness in Plastic Deformation and Experiment

超声波在变厚板中的传播特性尚不明确,构建高精度超声非线性响应模型是将超声非线性技术用于变厚板早期损伤检测的关键。基于金属塑性形变的本构关系,推导单轴拉伸下变厚板塑性应变的分布方程,将表征变厚板塑性应变分布的函数与超声波波动方程结合,构建变厚板超声非线性响应模型。由构建模型可知:二次谐波幅值(A_(2))与基波幅值(A_(1))二次方的比值(A_(2)/A_(1)^(2))随传播距离及波数均呈“二次方”增长;相同传播距离,A_(2)/A_(1)^(2)与总体塑性形变呈正相关,A_(2)/A_(1)^(2)携带了变厚板塑性形变信息。在COMSOL中构建铝合金变厚板弹塑性模型,验证了利用线性方程描述变厚板塑性应变分布的合理性;构建电磁超声系统,验证了超声非线性响应模型的有效性。制备不同塑性形变的变厚板试件,研究电磁超声表面波在其中的传播规律。实验结果表明,构建的超声非线性响应模型能够精确描述变厚板中超声波的传播行为。该文为利用超声非线性技术实现变厚板塑性损伤的量化检测提供理论基础,为超声非线性技术在异形结构上的应用提供了研究思路。

Since the propagation characteristics of ultrasound in plate with varying thickness(PWVT)are not clear,it is important to construct high-precision model of ultrasonic nonlinear response(UNR)to detect early damage on PWVT by ultrasonic nonlinearity.Based on the constitutive relationship of metal with plastic deformation,the distribution equation of plastic strain in PWVT under uniaxial tension is deduced.The model of UNR in PWVT is obtained by combining the distribution equation and the wave equation of ultrasound.The model shows that the ratio of A_(2)(the second harmonic amplitude)to A_(1)^(2)(square of the fundamental wave amplitude),A_(2)/A_(1)^(2),increases“quadratically”with the propagation distance and wave number,and A_(2)/A_(1)^(2) is positively correlated with the plastic deformation at constant distance,namely,A_(2)/A_(1)^(2) carries the information of plastic deformation in PWVT.The elastic-plastic model of aluminum alloy PWVT is constructed in COMSOL,which verifies the rationality of the linear equation in describing the distribution of PWVT’s plastic strain.The electromagnetic acoustic system is constructed and the effectiveness of the model of UNR is verified.In experiment,the PWVT specimens with different plastic deformation are prepared,and their propagation behaviors of ultrasound are studied by electromagnetic ultrasonic surface waves.The experimental results show that the model of UNR can describe the propagation behavior of ultrasound in PWVT accurately.This paper provides a theoretical basis for quantitative detection of plastic damage in PWVT by ultrasonic nonlinearity and a research idea for the application of ultrasonic nonlinearity to special-shaped structures.