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Strength Prediction of Mechanical Joints in Composite Laminates Based on Subcritical Damage Modelling

Atas, Akin (2012) Strength Prediction of Mechanical Joints in Composite Laminates Based on Subcritical Damage Modelling. PhD thesis, University of Sheffield.

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This thesis presents the experimental and numerical results of an investigation into the strength prediction of mechanical joints in HTS40/977-2 carbon fibre reinforced plastic (CFRP) composite laminates. A range of double-lap single fastener tensile tests were performed in order to establish a database of strength and subcritical damage patterns (transverse matrix cracks in the 90˚ layers, axial splits within the 0˚ and ±45˚ layers and delamination between the adjacent layers). Penetrant enhanced X-ray radiography was used to identify the subcritical damage patterns of the specimens after testing. One of the aims of the investigation was to evaluate the performance of a widely used strength prediction method, progressive failure analysis (PFA). Three-dimensional PFA subroutines that consider the linear and nonlinear shear stress-strain behaviour were developed and linked to the finite element software ANSYS. The Hashin failure criteria were used to detect the onset of in-plane matrix and fibre damage modes and damage propagation was simulated by the elastic material property degradation rules (empirical correlation factors). In other words, PFA uses empirical correlation factors in order to account for the subcritical damage modes which provide stress concentration relief around the fastener hole boundary. The strength prediction and damage evolution capability of the PFA was assessed using the experimental data established in the present study. The success of the PFA was shown to be dependent on several parameters including the shear stress-shear strain nonlinearity, material system, laminate lay-up, stacking sequence and the joint geometry. Another aim of the investigation was to develop a strength prediction method based on modelling the subcritical damage mechanisms, which is universally applicable without resorting to analytically/experimentally determined correlation factors. Discrete modelling of the initiation and growth of these subcritical damage modes, using cohesive zone elements (CZEs), directly simulated the local stress redistributions and superseded the role of the correlation factors. CZEs use a strength-based failure criterion to predict the onset of damage and a fracture mechanics based approach to predict its growth. The only material properties required to simulate the subcritical damage modes were the interfacial strength and fracture energies of the particular material system used. It has been shown that the effect of various joint geometries, laminate lay-ups and stacking sequences on the joint strength was accounted for by the method developed. Numerical predictions correlate well to measured strength data and damage pattern observations.

Item Type: Thesis (PhD)
Additional Information: Other e-mails: akin_atas@hotmail.com akin@balikesir.edu.tr
Keywords: Composite laminates, mechanical joints, strength prediction, finite element modelling, cohesive zone elements, progressive failure analysis, subcritical damage modelling, Ansys.
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Mechanical Engineering (Sheffield)
Depositing User: Mr Akin Atas
Date Deposited: 08 Oct 2012 14:48
Last Modified: 08 Aug 2013 08:49
URI: http://etheses.whiterose.ac.uk/id/eprint/2712

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