Simulation of damage on carbon fibre laminates using the Ladevèze material model

This paper focuses on the development of a numerical model based on the Ladevèze material model for the design of purposely introduced weak points/defects and the prediction and manipulation of its failure response. To identify mechanical properties and damage parameters mechanical testing on carbon prepreg coupons was carried out. The experimental work involved tensile testing at 0°, compression testing at 0°, cyclic in-plane shear testing at ±45°,+45° and ±67.5° fibre orientation. The cyclic tests involved five load-unload cycles with increasing load levels for the identification of the elastic damaging behaviour and furthermore the inelastic behaviour of the system. Mode I and Mode II samples were also manufactured for the characterisation of fracture toughness and the description of delamination. Out of these tests the identified material parameters, damage and coupling factors were introduced on the model. The model which was implemented in the Pam-CrashTM [1] finite element solver was verified for fibre damage under tension and compression. The case of shear loading was also studied and verified taking into account matrix shear and transverse damage evolution, which are coupled through the implementation of a factor.Lloyd’s Register Foundation; UK Department for Business, Innovation and Skills (BIS) Regional Growth Fund (RGF); Higher Education Funding Council for England (HEFCE) ; Structural Integrity Research Foundation (SIRF)

Geometric modeling of 3D woven preforms in composite T-joints

A common method to fabricate net-shaped three-dimensional (3D) woven preforms for composite T-joints is to weave flat 3D preforms via a standard weaving machine with variation in binder yarn path and then separate the preform in the form of a bifurcation. Folding introduces fiber architecture deformation at the 3D woven bifurcation area. In this paper, a geometric modeling approach is proposed to represent the realistic fiber architecture, as a preprocessor for finite element analyses to predict composite structural performance. Supported by X-ray micro-computed tomography (mCT), three important deformation mechanisms are observed including yarn stack shifting, cross-section bending, and cross-section flattening resulting from the folding process. Furthermore, a set of mathematical formulae for simulation of the deformations in the junction region are developed and satisfactory agreement is observed when compared with mCT scan results

Parameter estimation in equivalent circuit analysis of dielectric cure monitoring signals using genetic algorithms.

This communication concerns the treatment of dielectric data obtained from experiments following the chemical hardening process (cure) in thermosetting resins. The aim is to follow, in real time, the evolution of the individual parameters of an equivalent electrical circuit that expresses the electrical behavior of a curing thermoset. The article presents a methodology for the sequential inversion of impedance spectra obtained in cure monitoring experiments. A new parameter estimation technique based on genetic algorithms is developed and tested using different objective functions. The influence of the objective functions on the modelling performance is investigated. The new technique models successfully spectra contaminated with high noise levels. The introduction of regularization in the optimization function rationalizes the effects of outliers usually detected in cure monitoring dielectric spectra. The technique was successfully applied to the analysis of a series of spectra obtained during the cure of an epoxy thermosetting resin

A simplified discrete finite element model for non-crimped fabric composites

This paper introduces a simplified method for the modelling of tow based composite materials that allows the representation of varying material properties and fibre architecture. Traditionally two different approaches are utilised to simulate the mechanical behaviour of composites: (i) continuum models in which homogenised material properties are used [1]; and (ii) discrete models in which resin and fibre tows are represented as separate materials [2]. Continuum models are computationally efficient and thus appropriate for modelling the mechanical response of relatively large structures, whereas discrete models operate at the meso-level and offer greater predictive capabilities at the cost of expensive solutions. The methodology proposed here is based on the concepts developed for modelling the draping of non-crimp fabrics [3] and constitutes an intermediate solution that combines relative computational efficiency with the capability to model fibre tows and resin separately. This type of representation allows easy incorporation of the influence of locally inserted binder tows in a finite element with respect to both variations in material properties and local tow architecture.This paper introduces a simplified method for the modelling of tow based composite materials that allows the representation of varying material properties and fibre architecture. Traditionally two different approaches are utilised to simulate the mechanical behaviour of composites: (i) continuum models in which homogenised material properties are used [1]; and (ii) discrete models in which resin and fibre tows are represented as separate materials [2]. Continuum models are computationally efficient and thus appropriate for modelling the mechanical response of relatively large structures, whereas discrete models operate at the meso-level and offer greater predictive capabilities at the cost of expensive solutions. The methodology proposed here is based on the concepts developed for modelling the draping of non-crimp fabrics [3] and constitutes an intermediate solution that combines relative computational efficiency with the capability to model fibre tows and resin separately. This type of representation allows easy incorporation of the influence of locally inserted binder tows in a finite element with respect to both variations in material properties and local tow architecture