Predicting consolidation-induced wrinkles and their effects on composites structural performance
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ORIGINAL RESEARCH
Predicting consolidation-induced wrinkles and their effects on composites structural performance Balazs Varkonyi 1 & Jonathan P.-H. Belnoue 1
&
James Kratz 1
&
Stephen R. Hallett 1
Received: 15 July 2019 / Accepted: 30 September 2019 # The Author(s) 2019
Abstract The majority of high-performance composite parts are nowadays designed using advanced numerical simulations that are able to accurately predict a part’s strength and deformation, providing that the internal ply architecture and exact fibre orientation are known with sufficient accuracy. However, most parts have some deviation of the fibre orientation from the ‘as-designed’ geometry, leading to the simulation overestimating the component’s strength. Up until recently, the advancement of the process simulation tools has not been sufficient to allow knowledge of this fibre deviation before any part has been manufactured, thus leading to overly conservative designs and costly experimental optimisation of the manufacturing process to reduce fibre path defects. This results in additional cost, waste of material and increased fuel consumption (due to the unnecessary weight of the components). This paper shows how state-of-the-art composite manufacturing simulations of the autoclave consolidation process can predict and help to mitigate against out-of-plane wrinkle formation in components made from toughened UD prepregs and thus raise confidence in failure analyses predictions. The industry relevant case of a stepped laminate is used as an example. Model predictions for the internal ply geometries are quantitatively compared to micrograph images of real samples. It is then shown how the input of the simulated ply architecture helps improving the accuracy of the failure simulations. Keywords Manufacturing simulation . Failure analysis . Wrinkles . Toughened prepreg
Introduction Carbon fibre composites components made using prepreg technology are generally of better quality than those produced by other techniques and are thus favoured by the aerospace sector. They are nevertheless still prone to the formation of fibre path defects such as wrinkles. These defects can be detrimental for the components’ integrity (e.g. through thickness strength reduction greater than 50% has been observed and, in general, the reduction of the tensile and compressive strength can be as great as 30% [1]) and are therefore of great concern. Wrinkles can either originate from defects already present in the as received reinforcement/prepreg or be inherent to the design and manufacture of the component (e.g. the component geometry, the stacking sequence, the cure and pressure cycle
* Jonathan P.-H. Belnoue [email protected] 1
Bristol Composite Institute (ACCIS), University of Bristol, University Walk, Bristol, UK
etc) [2]. It is the wrinkles arising from this second factor that are the most concerning as they are reproducible and are formed every time the component is manufactured. In the case where such a wrinkle is formed, the entire part has to b
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