CFRP Barely Visible Impact Damage Inspection Based on Nonlinear Ultrasound Signal Sparse Reconstruction

In the whole life time of carbon fiber reinforced plastic (CFRP) component, it will inevitably suffer from low-energy impact (LEI) loads, which may lead to barely visible impact damage (BVID). Thus, non-destructive testing of impact damage has attracted more and more attention. In this paper, the detection of BVID in CFRP plates induced by LEI is investigated by means of nonlinear ultrasound with the help of signal sparse reconstruction with overcomplete dictionary obtained from the training of the acquired responses of the undamaged component. A damage inspection and structural health monitoring (SHM) framework for the CFRP component is proposed. The intact CFRP plate specimen and specimens with 12- and 16-J BVID were tested using the proposed method. Experimental results have shown that all the BVIDs could be detected effectively using a short segment of response signal. The proposed method has potential application in instrumentation design for unsupervised damage inspection and SHM during daily maintain in the service of the CFRP material.

I. Introduction

Carbon fiber reinforced plastic/polymer (CFRP) is an advanced composite material made of carbon fiber and various resins. The most significant advantage of CFRP is high strength and stiffness combined with low density. Therefore, CFRP materials are widely used in the aviation, aerospace, defense and automotive industries. The growing demand for CFRP results in extensive interesting in nondestructive testing (NDT) methods of this material [1]–[3], especially in the phase of manufacturing and maintenance of key components related to safety. Impact, especially when the loads are applied normal to the fiber direction, would reduce strength of CFRP material significantly and also affect the fatigue failure. Low-energy impact (LEI) is inevitable throughout the service life of CFRP components. LEI may produce external or internal deformation/breakage corresponding to visible impact damage (VID) and barely visible impact damage (BVID) [4]–[6] separately. Usually, BVID, which is difficult or even impossible to be detected from the surface using visual inspection, is more difficult to be detected than VID. Hence a reliable, sensitive and unsupervised inspection method for BVID is very important to both production and maintenance of CFRP component to avoid catastrophic failure.