NDT problem 

Composite materials such as CFRP are playing an important role in aerospace structures, where light weight and high strength material is desired. During their manufacture and operation, composite materials may sustain defects such as wrinkles, delamination, ply cracking, etc. Non-destructive inspection is required for structural integrity and safety considerations, and ultrasound is more often used among other methods. However, traditional ultrasonic arrays have seen drawbacks in some aspects, for example, the need for physical contact with specimen; the need for liquid couplant; difficulties in inspection of curved surfaces. Research into laser induced phased arrays (LIPAs) is motivated because it fills in the gap of traditional ultrasonic arrays[1]. 

Project aims and objectives 

This project aims to detect and characterise wrinkles in CFRP materials using LIPAs while minimising the scanning time. This aim is achieved through 4 objectives: 

  1. Obtain a forward model of thermoelastic ultrasound generation mechanism by laser in CFRP 
  1. Obtain a forward model of ultrasound propagation in defect-free and defective CFRP samples 
  1. Optimise the scanning strategy to minimise the data collection time for the detection problem. 
  1. Optimise the imaging quality for the characterization problem. 

Progress so far 

The directivity, the angle-dependent amplitude, of the laser generated ultrasound has been exhaustively studied. It has been modelled using finite element (FE) and analytical approaches, and compared with experimental measurements. The next step would be to incorporate this ultrasonic generation model to a semi-analytical finite element (SAFE) model for fast simulation of LIPA datasets on CFRP. 

[1] Stratoudaki T, Clark M, Wilcox PD. Laser induced ultrasonic phased array using full matrix capture data acquisition and total focusing method. Optics express. 2016 Sep 19;24(19):21921-38.