Abstract
A constitutive model for tufts bridging a mode I delamination is presented. The tuft is modelled as a rod, laterally supported by an elastic medium and clamped at both ends. A fracture mechanics approach is introduced to describe the progressive debonding of the tuft from the embedding laminate. The debonding model requires the identification of stiffness, strength and toughness properties, which depend both on the laminate/tuft architecture and the constituent materials. Such identification is carried out via experimental data obtained from tensile tests on single tufts inserted in a pre-delaminated non-crimp fabric composite. The experimental results are complemented by micro-scale finite element analysis. The mode I bridging law obtained from the constitutive model is implemented into a meso-scale cohesive zone formulation. This formulation is applied to predict the response to delamination of tufted Double Cantilever Beam (DCB) coupons. The cohesive zone approach is validated by means of experimental data from DCB tests. It is shown that the proposed micro- to meso-scale modelling approach yields results in good agreement with the experiments.
Highlights
Through-the-thickness reinforcement (TTR) is applied to 2dimensional composites in order to control and suppress delamination
It is clear that the delamination initially propagates through the untufted region, up to the first tuft row
The proposed multi-scale approach is based on a micro-mechanical model describing the mode I response of bridged interfaces, coupled with a meso-scale cohesive zone formulation for tufted structures
Summary
Through-the-thickness reinforcement (TTR) is applied to 2dimensional composites in order to control and suppress delamination. Most common TTR methods include Z-pinning [1], stitching [2] and tufting [3]. Tufting is the most recent among them and is performed by inserting carbon, glass or aramid threads through the thickness of a dry preform by means of a single needle. Neighbouring tufts are interconnected to each other by a seam on one side of the preform and form thread loops on the other. Tufts become integral parts of the preform architecture, making it locally 3-dimensional. Despite the proved potential of tufts to counteract the propagation of delamination in composite parts [4], a complete study of their crack bridging behaviour is not available in the open literature
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