In an ideal world composite multiscale analysis combined with FEA would predict, with accuracy and confidence, the strength and stiffness of any structure. Unfortunately the failure modes of composites are incredibly complex. Indeed, such is the scale of the task that a number of failure mechanisms are still not consistently replicable in a laboratory, let alone capable of being modelled mathematically (see World Wide Failure Exercise opposite).

As a result, it is not possible to carry out the design and analysis of composite structures without some physical testing. FAC Technology has access to a suite of test rigs which enables us to accurately perform static and dynamic tests. In addition, we use a range of sensors, control systems, and software to capture vastly more information then would be obtained from standard material characterisation tests. In particular we use high resolution (and occasionally ultra-high speed) cameras in conjunction with a digital image correlation platform (developed and programmed in-house) to gain an insight into the root mechanisms of where and why composite materials and structures fail.

The results from these tests are then fed back into the design process to identify any discrepancies between predicted and experimental data.

World Wide Failure Exercise

The World Wide Failure Exercise is a series of global projects that aim to establish the efficacy of most the promising theories in predicting the behaviour of composite materials. The program was initiated in the early 1990s and is now entering its third round of testing and evaluation. Even with a large scale program undertaken by academia, great care must be taken when obtaining reliable test data, as noted by Professor Richard M. Christensen, whose theory was included in WWFE-II:

“In all fibre composites assessments, the quality of the data is the matter of the first importance. It is not difficult to find examples of well-regarded data that differ by as much as 50% or 100% or even more. Great differences in failure data values for composites is the rule, not the exception”

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