Modelling of Delamination Growth in Composite Structures

Doktorsavhandling, 2002

Delaminations constitute an important damage and failure mode in polymeric composite laminates. In order to explicitly incorporate and model the delamination progression within a finite element analysis, the meso-modelling concept is applied in the present work. The laminate is thereby represented by separate layers connected with interfaces. By assigning damage and fracture properties to the interfaces, the layers can debond and introduce a delamination in the structure. For the control of the traction and damage evolution in the interface, an ideal plastic constitutive formulation incorporating isotropic damage is adopted. The model allows for general mixed mode delamination initiation and progression. Experimental data on mixed mode fracture toughness is used to calibrate the interfacial energy dissipation whereas the interlaminar normal and shear fracture stresses are used to determine delamination initiation. To allow for large deformation analyses, a novel interface formulation based on the concept of regularized strong discontinuity is developed. By a multiplicative division of the regularized deformation gradient, a transformation of the spatial tractions and displacement discontinuities into the corresponding quantities on a material configuration is achieved. With a specialisation to brittle failure within a geometrically non-linear setting, the general transformation is reduced into a rotation transformation. As a result, the interface formulation can be implemented as an interface element and the above mentioned interface model, with the corresponding calibration procedure, can be applied. In order to obtain a computationally efficient structural formulation with high accuracy, a 3-D shell formulation with thickness stress and strain is used for the layer discretization. A accompanying interface element with the kinematics derived from the shell theory is utilized together with the rotational interface formulation to connect the shell elements. Numerical results are presented that display the capability of the proposed interfacial modelling strategy to efficiently describe general delamination growth.