Optimisation of Through-Thickness Embedding Location of Fibre Bragg Grating Sensor in CFRP for Impact Damage Detection.

Helena Rocha,Ugo Lafont,João P Nunes

doi:10.3390/polym13183078

Helena Rocha, Ugo Lafont + Show 1 more

Open Access

https://doi.org/10.3390/polym13183078

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Abstract

Aerospace composites are susceptible to barely visible impact damage (BVID) produced by low-velocity-impact (LVI) events. Fibre Bragg grating (FBG) sensors can detect BVID, but often FBG sensors are embedded in the mid-plan, where residual strains produced by impact damage are lower, leading to an undervaluation of the damage severity. This study compares the residual strains produced by LVI events measured by FBG embedded at the mid-plan and other through-thickness locations of carbon fibre reinforced polymer (CFRP) composites. The instrumented laminates were subjected to multiple low-velocity impacts while the FBG signals were acquired. The FBG sensor measurements allowed not only for the residual strain after damage to be measured, but also for a strain peak at the time of impact to be detected, which is an important feature to identify the nature and presence of BVID in real-life applications. The results allowed an adequate optical fibre (OF) embedding location to be selected for BVID detection. The effect of small- and large-diameter OF on the impact resistance of the CFRP was compared.

Highlights

The aircraft and aerospace industries have shown an increased demand for fibre reinforced polymer (FRP) composites in the past few decades, aiming to replace metallic structures
This paper studies the residual strain measured by Fibre Bragg grating (FBG) sensors at different through-thickness locations of carbon fibre reinforced polymer (CFRP) composites subjected to LVI tests
Different through-thickness embedding locations of FBG sensors in CFRP laminates were studied for barely visible impact damage (BVID) detection

Summary

Introduction

The aircraft and aerospace industries have shown an increased demand for fibre reinforced polymer (FRP) composites in the past few decades, aiming to replace metallic structures. FRP composites allow the mechanical performance to be increased and the weight ratios of structural parts to be decreased, which, allows the initial purpose of reducing fuel consumption, carbon dioxide emissions, and costs to be attained [1]. Aeronautic composites are prone to BVID, produced by LVI, which can produce front-face damage, and internal transverse cracks, delaminations, and fibre breakage that can go undetected during inspection operations [3]. FBG sensors are deemed a matured technology for SHM [5], able to monitor LVI damage both under static and dynamic conditions [6]. For a given impact energy, damage detectability depends on the distance between FBG and impact location, whereas damage extent is dependent on the material properties and structure of the composite

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