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Finite Element Analysis of Composite Matrix Material with Micro-damage Healing Ability

In composite aircraft structures, damage is almost inevitable, and it occurs at several length scales due to the heterogeneous structure of composite materials. Application of materials with self-healing ability can successfully resolve these problems. Therefore, in this work, a constitutive model for modelling of micro-damage initiation and healing phenomena in polymer matrix materials is presented. Materials that are able to heal damage already exist for some time and (Barbero et al., 2005) proposed constitutive model for self-healing composites with extrinsic autonomic healing mechanism. Composite materials with extrinsic self-healing ability contain microcapsules with healing agent, embedded in matrix, which release the healing agent when damaged. The constitutive model proposed in this work utilises a material with intrinsic healing mechanism. Intrinsic self-healing means that the healing phenomenon results from material’s chemical structure. On the other hand, phenomena such as viscoelasticity and viscoplasticity are not considered in this research due to simplified constitutive model, but which are present in the matrix material in this research. Scalar damage and healing evolution laws are taken from (Darabi et al., 2011) and (Abu Al-Rub et al., 2010), respectively. Parameters of these laws are modified to describe the behaviour of the matrix material. Damage evolution law used here is strain rate-dependent and able to capture damage nucleation both during the loading and unloading present in simulations of cyclic loading. The concept of nominal, healing and effective configurations is taken from (Darabi et al., 2012). Stress, strain and tangent stiffness tensors in healing and nominal configuration are related by means of strain equivalence hypothesis, what makes the numerical implementation of the constitutive model relatively straightforward. In this initial phase of the research, an advanced ethylene/methacrylic acid (E/MAA) copolymer, DuPont™ Surlyn® 8940 thermoplastic resin, is used as a self-healing matrix material. The healing ability of ethylene/methacrylic acid (E/MAA) copolymer has already been proven for healing of delamination cracks, (Wang et al., 2012). In this experiment, the pure E/MAA copolymer in the form of thin layers was placed between the carbon fibre/epoxy composite plies, thus increasing the fracture toughness of the composite material. Firstly, the proposed constitutive model is developed and validated in Matlab and then implemented into Abaqus user subroutine UMAT. Simple static test cases as well as loading/unloading tests are applied in the validation of the proposed model.

micro-damage, intrinsic healing, self-healing, matrix materials, continuum damage healing mechanics

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