The interaction of guided waves with a material discontinuity is not well understood. This study investigates the propagation behavior of the fundamental Lamb-wave modes, the symmetric mode (S₀) and the anti-symmetric mode (A₀), upon interaction with welded joints of dissimilar materials. A plate with an intact AA6061-T6/AZ31B dissimilar joint was employed, and the interaction of the propagating wave with the material interface was scrutinized numerically and validated experimentally. Plane-wave approximation was also adopted to investigate the behavior of the symmetric modes, and its performance was compared to the numerical and experimental results. The effect of the angle of incidence on the reflection, transmission, and mode conversion of the incident modes was analyzed. The study was conducted as the excited Lamb wave propagated from AA6061-T6 to AZ31B (forward), and when the propagation direction was reversed (backward). Different techniques were developed to identify the in-plane and out-of-plane modes from the three-dimensional measurements and to separate wave reflections and transmissions of the joint. The fundamental shear-horizontal guided-wave mode (SH₀ mode) has evolved upon the interaction of the obliquely-incident Lamb-wave S₀ mode with the interface. While the reflection of the SH₀ mode from the joint was found to be well-pronounced, its transmission to the other material is extremely weak. The analytical solution, using plane-wave approximation, was accurate for predicting the behavior of the in-plane modes (S₀ and S₀–SH₀ modes). Despite the peaks appearing at the critical angle, the absolute values of the reflection coefficients of the studied modes have shown similar trends between the forward and the backward propagation directions. The total reflection of the excited wave, from the material interface, was not observed in any condition. The transmission coefficients of the S₀ and A₀ modes are almost constant until reaching very steep incidence angles $(\hat{i}>78°)$. The results were experimentally validated on an intact AA6061-T6/AZ31B friction-stir-welded joint using an excitation frequency of 200 kHz. Measurements along the transmission and reflection directions were conducted using a three-dimensional scanning laser vibrometer. Experimental results showed very good agreement with both the analytical and the numerical ones.

导波与材料间断的相互作用尚不十分清楚。本研究研究了基本Lambwave模式，对称模式（S ₀）和反对称模式（A ₀），与异种材料的焊接接头相互作用时。使用具有完整AA6061-T6 / AZ31B异种接头的板，并且对传播波与材料界面的相互作用进行了数值检查，并进行了实验验证。还采用平面波近似来研究对称模式的行为，并将其性能与数值和实验结果进行了比较。分析了入射角对入射模式的反射，透射和模式转换的影响。进行研究时，激发的兰姆波从A6061-T6传播到AZ31B（正向），并且传播方向反向（向后）。开发了不同的技术来从三维测量结果中识别平面内和平面外模式，并分离关节的波反射和透射。基本的水平剪切导波模式（SH ₀模式）是在倾斜入射Lamb-wave S ₀模式与界面相互作用的基础上发展而来的。虽然发现SH ₀模式从关节处的反射很明显，但它向其他材料的透射却非常微弱。使用平面波逼近的解析解决方案可以准确地预测平面内模式（S ₀和S ₀ – SH _{0）的行为。}模式）。尽管峰值出现在临界角，但是所研究模式的反射系数的绝对值在向前和向后传播方向之间显示出相似的趋势。在任何情况下都未观察到从材料界面发出的激发波的全反射。S ₀和A ₀模式的透射系数几乎恒定，直到达到非常陡峭的入射角为止$（\widehat{\mathrm{一世}}>78°）$。在完整的A6061-T6 / AZ31B搅拌摩擦焊接接头上，使用200 kHz的激励频率，对实验结果进行了实验验证。使用三维扫描激光振动计进行沿透射和反射方向的测量。实验结果与分析和数值结果都显示出很好的一致性。