Daniel Stephen Price

Analysis of Nonlinear Shear Deformations in CFRP and GFRP Textile Laminates

Carbon fibre-reinforced polymer (CFRP) and glass fibre-reinforced polymer (GFRP) woven composites are widely used in aerospace, automotive and construction components and structures thanks to their lower production costs, higher delamination and impact strengths. They can also be used in various products in sports industry. These products are exposed to different in-service conditions such as large tensile and bending deformations. Composite materials, especially ±45° symmetric laminates subjected to tensile loads, exhibit significant material as well as geometric non-linearity before damage initiation, particularly with respect to shear deformations. Such a nonlinear response needs adequate means of analysis and investigation, the major tools being experimental tests and numerical simulations. This research deals with modelling the nonlinear deformation behaviour of CFRP and GFRP woven laminates subjected to in-plane tensile loads. The mechanical behaviour of woven laminates is modelled using nonlinear elasto-plastic as well as material models for fabrics in commercial finite-element code Abaqus. A series of tensile tests is carried out to obtain an in-plane full-field strain response of [+45/-45]2s CFRP and GFRP laminates using digital image correlation technique according to ASTM D3518/D3518M-94. The obtained results of simulations are in good agreement with experimental data.

Analysis of nonlinear deformations and damage in CFRP textile laminates

Carbon fibre-reinforced polymer (CFRP) textile composites are widely used in aerospace, automotive and construction components and structures thanks to their relatively low production costs, higher delamination and impact strength. They can also be used in various products in sports industry. These products are usually exposed to different in-service conditions such as large bending deformation and multiple impacts. Composite materials usually demonstrate multiple modes of damage and fracture due to their heterogeneity and microstructure, in contrast to more traditional homogeneous structural materials like metals and alloys. Damage evolution affects both their in-service properties and performance that can deteriorate with time. These damage modes need adequate means of analysis and investigation, the major approaches being experimental characterisation, numerical simulations and microtomography analysis. This research deals with a deformation behaviour and damage in composite laminates linked to their quasi-static bending. Experimental tests are carried out to characterise the behaviour of woven CFRP material under large-deflection bending. Two-dimensional finite element (FE) models are implemented in the commercial code Abaqus/Explicit to study the deformation behaviour and damage in woven CFRP laminates. Multiple layers of bilinear cohesive-zone elements are employed to model the onset and progression of inter-ply delamination process. X-ray Micro-Computed Tomography (MicroCT) analysis is carried out to investigate internal damage mechanisms such as cracking and delaminations. The obtained results of simulations are in agreement with experimental data and MicroCT scans.

Evaluation of a Kinematically-Driven Finite Element Footstrike Model

A dynamic finite element model of a shod running footstrike was developed and driven with 6 degree of freedom foot segment kinematics determined from a motion capture running trial. Quadratic tetrahedral elements were used to mesh the footwear components with material models determined from appropriate mechanical tests. Model outputs were compared with experimental high-speed video (HSV) footage, vertical ground reaction force (GRF), and center of pressure (COP) excursion to determine whether such an approach is appropriate for the development of athletic footwear. Although unquantified, good visual agreement to the HSV footage was observed but significant discrepancies were found between the model and experimental GRF and COP readings (9% and 61% of model readings outside of the mean experimental reading ± 2 standard deviations, respectively). Model output was also found to be highly sensitive to input kinematics with a 120% increase in maximum GRF observed when translating the force platform 2 mm vertically. While representing an alternative approach to existing dynamic finite element footstrike models, loading highly representative of an experimental trial was not found to be achievable when employing exclusively kinematic boundary conditions. This significantly limits the usefulness of employing such an approach in the footwear development process.