Novel forms of inverse analysis to characterise properties of fibre-matrix composites
Novel approaches to the determination of material properties and damage parameters of fibre-matrix composites using inverse analysis are presented. In inverse analysis system identification techniques are used to update some form of mathematical model (normally a FE model) using data from an over-determined number of tests. Initially, pultruded GFRP box-section beams are subjected to a quasi-static impact or bending crush. The results of the impact tests are presented to corroborate those in the literature that have been obtained using simpler geometries such as flat plates. In the first form of inverse analysis, a model-updating approach is applied to progressive tearing damage in pultruded composite box-section beams. The difference between empirical data (from a programme of three-point bend tests) and a FE model is minimised by a genetic algorithm to produce an optimal solution. The solution is in the form of a FE model that can be subsequently analysed to determine the structural integrity of the damaged specimen. Secondly, a unidirectional composite disc from the same GFRP pultruded section is analysed in diametral compression to both verify and improve the validity of the diametral compression test in determining the material properties. Coupons are cut from damaged specimens and test results are presented. The strain distribution within the disc is compared to known laminate theory in order to process data obtained by speckle-shearing interferometry. Finally, speckle-shearing interferometry is used to characterise the response of the pultruded box-section exhibiting progressive tearing damage. Out-of-plane displacement-gradient data is used to determine and characterise damaged regions or flaws. The differences between the need to perform it programme of unequivocal static tests and the collection of full-field optical data are highlighted. It is shown that the shearing interferometry approach is the superior method.