Influence of fiber orientation on the inherent acoustic nonlinearity in carbon fiber reinforced composites

Abstract

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.

Influence of laminate sequence and fabric type on the inherent acoustic nonlinearity in carbon fiber reinforced composites

“…Chakrapani et al reported the inherent NCNL response of composites using the NRUS technique. 22 The influence of fiber orientation on the NCNL response was studied in intact UD CFRP laminates by varying the fiber orientation along the length of the sample. The current article builds on the previous work by the authors 22 in terms of characterizing the effect of laminate sequence and fabric type on the NCNL response.…”

“…22 The influence of fiber orientation on the NCNL response was studied in intact UD CFRP laminates by varying the fiber orientation along the length of the sample. The current article builds on the previous work by the authors 22 in terms of characterizing the effect of laminate sequence and fabric type on the NCNL response. The NCNL characteristics of four different laminate sequences were investigated and they were compared to the results obtained from the previous orientation study.…”

“…Although the source of hysteresis has been identified in geomaterials, it is more challenging in the case of multi-material structures such as concrete and composites. 22,23 These materials exhibit a high baseline non-classical nonlinearity which can increase due to damage. Hence, characterization of the damage state becomes difficult.…”

“…They identified three strain ranges: (i) low strain linear zone, where the material behaves linear elastic and no frequency shift exists, (ii) mid-range strain classical nonlinear zone where a quadratic softening in frequency can be observed, and (iii) high strain non-classical non-equilibrium zone where the response is controlled by slow and fast-dynamics and linear softening can be observed. Chakrapani et al 22 used the three parameters [(a), (b), and (c)] to show that UD composites exhibit NCNL behavior, and explored the effect of fiber orientation on the NCNL response. Additionally, the classical and non-classical strain zones were identified by fitting quadratic and linear functions.…”

Studies on nonlinear mechanical wave behavior to characterize cement based materials and its durability

“…Linear (resonant frequencies and quality factor), and nonlinear hysteretic parameters corresponding to first bending and longitudinal modes of vibration were investigated. (Chakrapani, Barnard, & Dayal, 2015). Under dynamic loading, the nonlinear behavior arises from the interfacial friction, debonding, and subsequent interfacial slip between fibers and matrix (Nelson & Hancock, 1978).…”