Early Damage Detection in Composites during Fabrication and Mechanical Testing

Abstract

Fully integrated monitoring systems have shown promise in improving confidence in composite materials while reducing lifecycle costs. A distributed optical fibre sensor is embedded in a fibre reinforced composite laminate, to give three sensing regions at different levels through-the-thickness of the plate. This study follows the resin infusion process during fabrication of the composite, monitoring the development of strain in-situ and in real time, and to gain better understanding of the resin rheology during curing. Piezoelectric wafer active sensors and electrical strain gauges are bonded to the plate after fabrication. This is followed by progressive loading/unloading cycles of mechanical four point bending. The strain values obtained from the optical fibre are in good agreement with strain data collected by surface mounted strain gauges, while the sensing regions clearly indicate the development of compressive, neutral, and tensile strain. Acoustic emission event detection suggests the formation of matrix (resin) cracks, with measured damage event amplitudes in agreement with values reported in published literature on the subject. The Felicity ratio for each subsequent loading cycle is calculated to track the progression of damage in the material. The methodology developed here can be used to follow the full life cycle of a composite structure, from manufacture to end-of-life.

In Situ Damage Detection for Fiber‐Reinforced Composites Using Integrated Zinc Oxide Nanowires

“…An analysis of both histograms, and most notably the ZnO voltage measurement, shows a higher number of hits at lower magnitude. This result follows a similar trend to that of data obtained using traditional AET sensors as well as established alternative sensors in prior works which have correlated the emission amplitude with damage severity . Using the method established in this work, it can be inferred that the hit amplitude from the ZnO nanowires corresponds to the severity of the detected damage, i.e., more frequently occurring low‐level damage such as matrix cracking corresponds to low‐amplitude voltage emission, while fiber failure can be expected to correspond to higher‐amplitude voltage emission.…”

“…The detected emissions from both the microphone and the voltage reading show excellent coherence in both time of damage occurrence as well as the relative amplitude of the detected emissions, thus validating the ability of the voltage resulting from the ZnO to detect damage in situ during the test. Several works have conclusively established the use of AET sensors similar to the high‐frequency microphone used in this work for detecting matrix cracking, interfacial debonding, and in some cases fiber breakage occurring during flexural loading; however, the classification of such damage using AET signal features such as amplitude distribution is complicated . There is, however, a general agreement in the correlation between increasing amplitude and damage severity indicating the early damage detected by both the microphone and voltage measurements likely corresponds to matrix cracking, while higher amplitude signals occurring later during testing are expected to correspond to interfacial debonding or fiber breakage.…”

Damage Propagation Analysis in the Single Lap Shear and Single Lap Shear-Riveted CFRP Joints by Acoustic Emission and Pattern Recognition Approach

“…The sensors have an operating frequency range of 150 kHz to 400 kHz, with a resonant frequency of 300 kHz. It has been indicated in several reports that the AE signals will not be above 400 kHz in Fiber Reinforced Plastics (FRP) [20,21]. The narrowband sensor is selected based on that observation and to reduce the recording of noise signals.…”

“…The peak amplitude has been used by many researchers for categorizing the failure modes in fiber reinforced composites [21]. It is one of the most debated parameters for characterizing failure modes.…”

Multiaxial Damage Characterization of Carbon/Epoxy Angle-Ply Laminates under Static Tension by Combining In Situ Microscopy with Acoustic Emission

“…At the same time, the acoustic emission (AE) technique was applied to monitor the acoustic response of the laminates throughout the tests. AE is a NDT method that has been used in several applications for the damage characterization of composites and other engineering materials [22][23][24][25][26], either as a self-standing technique, or in combination with other NDT methodologies [27][28][29]. However, no direct correlation of the AE activity to multiaxial stresses developed in composite materials is found in the literature.…”