Made to measure…Delaminations

Who are you?: Osman Ajmal

What is your role?: PhD Researcher

What is your work about?: Locating and measuring the growth of embedded delaminations in composite materials.

I beg your pardon?: Delaminations are one of the more prevalent forms of defects in composite materials such as Fibre Reinforced Polymers (FRPs). Non-Destructive Evaluation (NDE) is used to determine the position and size of delaminations during testing.

OK. Why?: FRPs are used in a wide variety of industries. They have applications as components of cars, aeroplanes, spacecraft and even sporting goods! By understanding how these defects in structural elements behave under different loading scenarios, these materials can be better tailored for different applications.

And?: My work compares existing and novel methods to detect these defects. Figure 1a is a finite element model of a typical specimen with an embedded defect, whilst Figure 1b shows a typical output from the real specimen, monitored by Digital Image Correlation (DIC).  Analysis of the DIC data gives, in this case, longitudinal surface strains which can be used to detect the presence of delaminations.


Figure 1: Longitudinal strain contours of composite laminate specimen with an embedded square shaped artificial delamination in three point bending. (a) Finite Element Modelling (b) Digital Image Correlation

So what?: By comparing different NDE techniques to each other and to FEA, my work aims to determine the “resolution” of the different techniques. This is done by comparing the results of different techniques for the testing of the same structural elements and the same loading scenarios. By using artificial inserts, model defects can be created during the manufacturing process. During testing, these defects can be monitored: because the size of the delamination is known, the NDE technique can be assessed against what it   should detect, and if possible calibrated accordingly.

Final thought: The wide range of readily applicable NDE techniques are literally ‘made to measure’ defects in structural elements. It is important to determine how well they do this for delaminations in the composites used in modern cars, aeroplanes, ships and all the rest.