Ciampa Francesco, Scarselli Gennaro, Meo Michele
Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, United Kingdom.
Department of Engineering for Innovation, University of Salento, Lecce 73100, Italy.
J Acoust Soc Am. 2017 Apr;141(4):2364. doi: 10.1121/1.4979256.
Recent nonlinear elastic wave spectroscopy experiments have shown that the nonlinear ultrasonic response of damaged composite materials can be enhanced by higher vibrations at the local damage resonance. In this paper, the mathematical formulation for the generation of nonlinear wave effects associated with continuous periodic excitation and the concept of local defect resonance is provided. Under the assumption of both quadratic and cubic approximation, the existence of higher harmonics of the excitation frequency, superharmonics of the damage resonance frequency and nonlinear wave effects, here named as nonlinear damage resonance intermodulation, which correspond to the nonlinear intermodulation between the driving and the damage resonance frequencies, is proved. All these nonlinear elastic effects are caused by the interaction of propagating ultrasonic waves with the local damage resonance and can be measured at locations different from the material defect one. The proposed analytical model is confirmed and validated through experimental transducer-based measurements of the steady-state nonlinear resonance response on a damaged composite sample. These results will provide opportunities for early detection and imaging of material flaws.
最近的非线性弹性波谱实验表明，在局部损伤共振处的更高振动可以增强受损复合材料的非线性超声响应。本文给出了与连续周期激励相关的非线性波效应产生的数学公式以及局部缺陷共振的概念。在二次和三次近似的假设下，证明了激励频率的高次谐波、损伤共振频率的超谐波以及非线性波效应（这里称为非线性损伤共振互调）的存在，它们对应于驱动频率和损伤共振频率之间的非线性互调。所有这些非线性弹性效应都是由传播的超声波与局部损伤共振的相互作用引起的，并且可以在与材料缺陷位置不同的地方进行测量。通过基于实验换能器对受损复合材料样品稳态非线性共振响应的测量，对所提出的分析模型进行了确认和验证。这些结果将为材料缺陷的早期检测和成像提供机会。
