Impact damage assessment in biocomposites by micro-CT and innovative air-coupled detection of laser-generated ultrasound

Abstract

The increasing use of natural fibre composites in at least semi-structural applications along with a demand for a fast and accurate damage detection for quality purpose and in-service reliability promote a need for non-contact non-destructive testing techniques. To this purpose, ultrasound is probably one of the most widely used testing techniques but the need of a coupling fluid like water limits its use with natural fibre composites. In this work, a novel non-contact set-up based on laser excitation of ultrasound and detection with a broadband, air-coupled optical microphone is presented and tested on flax/PLA laminates. This material system has been characterized in terms of quasi-static mechanical properties and low velocity impact response. The outcomes of this study demonstrate the potential of this non-contact and nondestructive system for quality and damage inspection purposes of natural fibre composites.

Mechanical Properties of Natural Fiber Composites

“…In order to better understand the degradation phenomena occurring in NFCs submitted to moisture environment, it is necessary to characterise the corresponding damage and deformation mechanisms. Different types of techniques can be used to characterise damage and strain in NFCs: optical and electronic microscopy (Pickering et al, 2016;Malinowski et al, 2018), acoustic emission (De Rosa et al, 2009;Assarar et al, 2011), digital image correlation Unlusoy et al, 2019), ultrasonic scanning (Lebaupin et al, 2019;Fischer et al, 2019), infra-red thermography (Boccardi et al, 2018;Zhang et al, 2018) and X-ray micro-tomography (Rasket et al, 2012;Perrier et al, 2017). Figure 4 illustrates the ability of X-ray micro-tomography to analyse damage development in NFCs.…”

Local Ultrasonic Resonance Spectroscopy: A Demonstration on Plate Inspection

“…The optical microphone does not have any moving parts, as is normally the case for conventional US receivers (piezoelectric material or membrane). It measures the US directly in the air by measuring the change of the refractive index as acoustic waves travel through the Fabry-Pérot etalon [18,[25][26][27]. However, the housing of the microphone itself (or the etalon mirrors) can have a certain natural behavior which could affect the signal.…”

“…The CFRP including flat-bottom hole and delamination was studied on C-scans and Lamb wave tomography images. A similar experimental setup as the one used in our experiment has already been applied to the inspection of impact damage in biocomposites [18]. The only parameter being analyzed on the US signal captured by the optical microphone was amplitude in the time domain.…”

Characterization of low-velocity impact and post-impact damage of luffa mat composite using acoustic emission and digital image correlation

“…11,12 The high sensitivity of composite materials to impact, especially during low velocity impacts, is of concern to researchers and designers of cars, ships, and aircraft. In reality, composite materials are likely to be subjected to unintended shocks from a variety of sources, including aeronautics, tool drops during repair, impacts between two panels during assembly, bird strikes during service life, 13,14 and shocks or stone impacts in vehicles over the course of their lifetime. 15,16 Several research studies have been performed in recent years to further understand the impact behavior of synthetic fiber composites such as carbon, 17 glass, 18 and kevlar 19 in order to create structures that are more tolerant to low-velocity impact damage, which is determined by the material characteristics (matrix and fiber types, reinforcement architecture, stacking sequence, fibermatrix interface quality, and component thickness) as well as the impactor shape.…”