Keywords: polymer matrix composites, delamination, damage mechanics, computational simulation, finite element analysis, crashworthiness.

Composite materials have seen an increase in their use over the past three decades, in a wide range of fields such as aerospace, automotive, rail, and construction. The benefits of using composites are high strength, low weight, design flexibility, and the ability to tailor their response to specific loading conditions. However, common to all applications is the need to develop methods to predict the mechanical behaviour of composite structures, which is of particular importance for industries where the design assessment stage is based on computer simulation. The automotive industry is perhaps the best example of a field where the lack of predictive modelling of composites' behaviour has hindered their use in high production volume vehicles, even if the benefits of composites for automotive safety are evident when compared to metallic structures.

Finite Element models of composite materials generally make use of multilayered shell elements to model the laminate. Fibre direction, orthotropy, elasticity and failure mode are characteristics of each ply of that laminate, resulting in a computationally efficient approach. However, this modelling approach presents the major drawback that it cannot model the important delamination failure mode.

In this work, a fracture energy approach for modelling mixed-mode delamination of composite materials and other bonded structures is introduced. The modelling approach consists of treating intralaminar and interlaminar behaviour of the composite separately. An existing ply damage model is used for intralaminar behaviour, where each individual layer is modelled with shell or solid elements. Interlaminar behaviour is modelled via a new delamination contact interface based on fracture toughness concepts. The development and application of the delamination algorithm in the commercial FE code PAM-CRASH is described. Examples of applications of this modelling approach are given and include a glass/polyester composite tube crush and a carbon NCF hat sectioned member under axial loading. The proposed approach can be considered predictive as only coupon test data is used for the input parameters of the ply model and the delamination contact interface.

1

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