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Fibre Reinforced Polymer composite materials (FRP’s) are now widely utilised in many
applications including aircraft, yachts, motor vehicles, chemical and process plant, sporting
goods and a wide range of military equipment. They are an extremely broad and versatile class
of material, encompassing a wide range of fibre and matrix combinations that provide a
multiplicity of component design and manufacturing options. Their high strength coupled
with light weight leads to their use wherever structural efficiency is at a premium.
FRP’s are inherently more complex than metals. By their nature, they are heterogeneous in
construction (asymmetric arrays of many thousands of fibres, each with diameter of the order
10 microns, in a polymeric matrix) and they are anisotropic (the strength parallel to the fibres
being typically two orders of magnitude greater than that in the transverse directions). Thus,
it is perhaps not unsurprising to find that the challenge in predicting the strength of an FRP
laminate with accuracy is significantly larger than that in predicting the strength of a
conventional metal.
In moving from the metals world to the FRP world, a structural designer is faced with many
more variables and the need for an additional set of design methods. It is, perhaps, self evident
that such methods must be accurate and valid in order to extract the maximum structural
performance in terms of strength, deformation and stiffness. The consequences of using
methods that have not been benchmarked against satisfactory data are potentially unsafe
designs or over design, resulting in unnecessary cost and weight. In most of the early
applications of FRP’s (typically military, in the 1960s) this challenge was circumvented by a
‘make and test’ approach which was entirely justified at the time, given the relative novelty
of the materials, the absence of proven analytical tools and the relatively poor computation
capabilities. Whilst much development work has been conducted since then (and continues to
this day) the degree of maturity of the current tools for predicting the strength and
deformation of an FRP material, in the general case, has been a somewhat open question.
Over the last 12 years the editors of the book have organized and coordinated an
international activity, known as the World Wide Failure Exercise, to improve the foundation
on which design theories are based, namely the prediction of deformation and failure strength
of laminated composite structures. Within the Exercise the leading failure theories for
composite laminates have been compared with one another and with experimental data. As the
Exercise progressed, the results were published in three special issues, of the international
journal, ‘Composites Science and Technology’. The contributors of theoretical papers included
many internationally renowned scientists, designers and engineers from six countries and
experimental work was gathered from different groups in UK, USA and Germany. |