超声双折射法测试铝合金的内部应力

声各向同性的金属材料在应力作用下表现出声各向异性,这是用声弹性法分析材料内部应力的基础。本文用偏振方向平行或垂直于应力方向的超声纯横波对LY11型铝合金进行测试。实验结果表明:材料在拉、压单轴应力作用下,偏振方向平行和垂直于应力方向的超声纯横波的声速都发生了变化。实验在分析材料声各向异性的基础上计算材料声弹性双折射系数,得到测试LY11型铝合金内部应力的理论公式,并对其内部的残余应力进行评估。实验中利用双换能器回振法测量声速,时间测试精确度可达10^-11s,可精确测量声速的微小变化量。

Measurement of stress in aluminum alloy by acoustic birefringence

Acoustic anisotropy effect occurs when a isotropic metal is submitted to stress which is the base of measurement of stress in material by acoustoelastic effect.In this pa- per,orthogonally polarized pure mode shear waves were used to test LY11 Aluminum al- loy.Experimental results show that the presence of stress causes small changes in phase velocities of shear waves,which is called acoustoelastic birefringence effect.The acous- toelastic coefficients are acquired by the analysis of the acoustic anisotropy,and theoretical equations of measuring stress in material are obtained.Furthermore,the residual stress is evaluated.The phase velocities are measured by a sing-around method by which small changes in velocity can be detected.The precision of time interval can reach to 10¹¹s.