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.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.