Highly non-linear solitary wave imaging method for detecting cylindrical defects in the metal plate of an adhesive composite metal structure

In this paper, a non-destructive testing (NDT) method based on highly non-linear solitary waves (HNSWs) was employed to detect defects in the metal plate of an adhesive composite metal structure. Firstly, HNSWs were generated by applying impulses to a one-dimensional granular chain of steel spheres. Proof-of-concept finite element (FE) simulations were then performed using Abaqus software to investigate the reflection behaviour of HNSWs at the interface of the chain and the two-layer material with defects. The time-of-flight (TOF) of primary reflected solitary waves (PSWs) was confirmed as a good indicator for defect localisation and sizing. A HNSW generator and detector device was used in the experiment and HNSW B-scan and C-scan inspections of adhesive composite steel specimens were achieved. The TOF imaging results accurately indicated the locations of cylindrical defects in the bottom steel block. The linear correlation between the peak value of the pulsed TOF profile and the defect diameter was determined. The contours of TOF with different values were introduced to reconstruct the shape of the circular defective region. Through selecting the correct threshold of TOF, the relative error of the area surrounded by the contour compared to the actual area of the five investigated defects could be less than 6.5%.