中文摘要：

超声背散射法可通过多晶体金属内部的空间方差信号,实现微观结构参数的无损评价,但表面粗糙度对评价模型的精度及实用性存在显著影响.基于高斯声束理论推导垂直入射粗糙界面的纵波声场,以此研究声能的Wigner分布规律;在超声的波长远大于粗糙度的前提下,构造表面粗糙度修正系数,并建立粗糙界面的单次散射响应模型,揭示粗糙度对超声波背向散射的影响规律.用304不锈钢制备轮廓均方根值为0.159μm的光滑试块和25.722μm的粗糙试块开展超声背散射实验,结果表明模型在粗糙度修正前后均可实现光滑试块的晶粒尺寸有效评价,但未经修正的传统模型对粗糙试块的晶粒尺寸评价结果与金相法结果的相对误差高达-21.35%,而本模型的评价结果与金相法结果符合得很好,相对误差仅为1.35%.可见,本模型能有效补偿粗糙度引起的超声背散射信号衰减,从而提高晶粒尺寸无损评价的精度.

英文摘要：

In the diffuse ultrasonic backscatter describing the scattering of elastic waves from polycrystalline metal material,the spatial variance of the signal is used as a primary measure of microstructure. Previously, theoretical singly-scattered response models have been developed for the diffuse backscatters of elastic waves within polycrystalline materials, which take into consideration both transducer beams and microstructural scattering information. However, the surface roughness of the liquid-solid interface induces a noticeable change of spatial variance amplitude, and its effect on the diffuse ultrasonic backscatter that can severely degrade the accuracy and practicability of the microstructure parameter evaluation was neglected in previous models.Therefore, a new singly-scattered response model for the rough surface polycrystalline samples is developed by following the forms similar to previous models for longitudinal-to-longitudinal scattering at normal incidence. In particular,we assume that the surface is slightly rough, specifically, the surface roughness value should not be larger than the magnitude of the wavelength. Hence, the modified expressions of ultrasonic reflection and transmission coefficients for the randomly rough interface can be applied to the singly-scattered response model. Then, with the modified transmission coefficient, a Gaussian beam is adopted to model the transducer beam pattern at normal incidence for longitudinal wave propagation through a rough liquid-solid interface to the polycrystal. Next, the Wigner transform of the displacement field is derived with a parameter of the surface roughness root mean square value. After that, a new expression of the calibration parameter including the modified reflection coefficient is given to provide a conversion between the displacement field and the experimental transducer voltage. Finally, the rough surface singly-scattered response model is built and the surface roughness correction coefficient is presented here to quantify the effect of th