Simulation of Delamination Initiation and Growth in Fiber Composite Laminates

Sammanfattning: This thesis concerns the topic of delaminations in unidirectional fiber reinforced plastic composite laminates.A model for the simulation of delamination initiation and growth has been developed. It is based on fracture mechanics and formulated as a combination of a cohesive zone model and a linear elastic adhesive penalty formulation. The model includes a damage formulation and it can be shown to comply with the laws of thermodynamics, but without being defined as a generalized standard material model.The delamination model is adopted for use with shell elements, where the nodal points are located in the middle plane of the shell. By accounting for the thickness offset in the adhesive penalty contact it is possible to tie the noncoincident nodes together. No change is needed in the cohesive zone model.Delaminations growing along the fibers in a (0° , 0°) interface may not behave identically toa delamination growing in a (45° , 45°) interface. The interface toughness may depend on the local fiber orientation. This orientation is evaluated in the delamination model by calculating the growth direction of the delamination front and comparing it with the orientation of the surrounding fibers.The model has been validated on several applications: both simulations of a simple test specimen, for examining delamination growth in a single interface, as well as more complex situations for analysing the initiation and growth of delaminations in laminates subjected to low velocity impacts. The results from simulations compare well to experimental results.

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