SHAPE FORMING
There are many composites present in this 2018 A350
block approach is commonly used in the aerospace industry for the design and analysis of composite structures. In this approach, a lot of small-sized experiments must be conducted to characterise the material property; this data and knowledge will then be used for the testing and analysis of structures with increased size and complexity. Analysing tools were also developed and validated step by step, until the analysis of primary full structures. Such procedures have largely reduced the risk in composite structure development, and gradually builds up experience and confi dence for applying CFRP composites in aerospace. A series of experimental methods has been proposed for characterising the critical stress for diff erent failure modes. Some of them have been nicely established, such as the uniaxial compression test for measuring the transverse compression strength and the double cantilever beam test for measuring the mode I delamination fracture toughness. Some of them have proved challenging, for example the transverse tension test has not been properly recognised because of massive scatter from traditional dog-bone specimens. Fibre failure strength has always been diffi cult to measure, since
premature failure is highly likely to happen in the matrix fi rst. Improving the material characterisation skills has been a shared interest of industry and
the academic community. One recent piece of progress is the standardisation of the testing method for mode II delamination fracture toughness. The mechanical response of CFRP composites can change depending on the rate of load applied. The failure strength may increase with the increase in loading rate, while the fracture toughness may have negative strain rate dependence. Comprehensive study of CFRP material at diff erent loading rates then becomes necessary for a safe design of structures that are potentially threatened with impact load. Similarly, fatigue damage resistance needs to be investigated for structures under cyclic load. Experiments are expensive and time consuming, while numerical methods are deemed to be a cost-eff ective alternative. Several commercial fi nite element analysis packages have been widely used in aerospace industry, in which many of these mainstream failure theories for various damage modes have been successfully integrated. Some software also enables user- defi ned features, allowing highly sophisticated damage models for certain applications. The failure of CFRP composites is so highly complicated that it remains challenging for any existing damage model to successfully predict the failure behaviour of composites in all cases. Numerical simulation cannot completely replace experiments at the moment, however, it has proved useful for guiding the design of structures and analysing their
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