Chakrapani Sunil Kishore, Barnard Daniel J, Dayal Vinay
Center for Nondestructive Evaluation, 111 Applied Sciences Complex II, 1915 Scholl Road, Ames, Iowa, 50011.
Department of Aerospace Engineering, Iowa State University, 1200 Howe Hall, Ames, Iowa 50011.
J Acoust Soc Am. 2015 Feb;137(2):617-24. doi: 10.1121/1.4906165.
This paper presents the study of non-classical nonlinear response of fiber-reinforced composites. Nonlinear elastic wave methods such as nonlinear resonant ultrasound spectroscopy (NRUS) and nonlinear wave modulation spectroscopy have been used earlier to detect damages in several materials. It was observed that applying these techniques to composites materials becomes difficult due to the significant inherent baseline nonlinearity. Understanding the non-classical nonlinear nature of the composites plays a vital role in implementing nonlinear acoustic techniques for material characterization as well as qualitative nondestructive testing of composites. Since fiber reinforced composites are orthotropic in nature, the baseline response variation with fiber orientation is very important. This work explores the nature of the inherent nonlinearity by performing nonlinear resonant spectroscopy (NRS) in intact unidirectional carbon/epoxy samples with different fiber orientations with respect to major axis of the sample. Factors such as frequency shifts, modal damping ratio, and higher harmonics were analyzed to explore the non-classical nonlinear nature of these materials. Conclusions were drawn based on the experimental observations.
本文介绍了纤维增强复合材料的非经典非线性响应研究。诸如非线性共振超声光谱法（NRUS）和非线性波调制光谱法等非线性弹性波方法，此前已被用于检测多种材料中的损伤。据观察，由于显著的固有基线非线性，将这些技术应用于复合材料变得困难。理解复合材料的非经典非线性特性，对于采用非线性声学技术进行材料表征以及复合材料的定性无损检测至关重要。由于纤维增强复合材料本质上是正交各向异性的，基线响应随纤维取向的变化非常重要。这项工作通过对完整的单向碳/环氧样品进行非线性共振光谱法（NRS），研究了不同纤维取向相对于样品主轴的固有非线性特性。分析了诸如频率偏移、模态阻尼比和高次谐波等因素，以探究这些材料的非经典非线性特性。基于实验观察得出了结论。
