1,721,140 research outputs found
0/90 Unsymmetric Plates as a Tool to measure Damage in Composite Materials
No full textIn the present work we explore the possibility of employing 0/90 unsymmetric plates as a
tool to measure damage in composite materials under thermal stress. The behaviour of
0/90 plates under such loads is investigated in the presence of diffuse damage, whose
description is given by micromechanics-based models. The thermal induced plate
deformations can be quantitatively related to adequate damage indicators and, being
measurable parameters, can explicitly assess its magnitude and its possible evolution
Damage Propagation in composite structures using an embedded global-local Approach
No full textSince most composite materials are characterised by brittle failure, with low margin of safety through ductility, the failure mechanisms in composites must be investigated and suitable prediction analysis tools need to be developed. In many structural applications a three-dimensional progressive damage approach, able to take into account all the physical phenomena characterising the damage on-set and propagation until the final failure, needs to be adopted.
In the present paper a three-dimensional progressive damage approach for laminated composites will be presented. This approach is based on the use of a progressive damage finite element with the geometrically non-linear finite element formulation for stress calculation. The FEM element has been integrated with Hashin’s failure criteria to split fibre and matrix failure modes and with the ply discount method to simulate the stiffness degradation in each ply. The FEM tool was tested together with an embedded global-local approach in order to prove its effectiveness when dealing with complex structures that need to be modelled by using different mesh densities and different element types.
As an application, the structural behaviour of a notched panel under tensile load has been investigated and the obtained numerical results have been compared with numerical and experimental data from literature. Finally, a comparison between a full 3D model and a global-local model has been performed in order to evaluate the effectiveness of the developed progressive damage approach in global-local analyses
Finite element analysis of the stability (buckling and post-buckling) of composite laminated structures: well established procedures and challenges
No full textFinite element procedures for the analysis of composite structures under compressive loads (buckling and post-buckling) generally are not deployed in books because they are still considered object of research whereas they are deemed as assessed by researchers that focus their papers on restricted audience topics. Therefore, regarding these procedures, a gap exists in literature between what researchers consider as well established and what has been already published. The aim of this paper is to contribute to close this gap by providing an insight in linear and non-linear buckling analyses and in their use with composite structures. Both modelling and analysis considerations are presented and discussed, focusing on what can be considered as best practice when dealing with this kind of problems. Applications (to a stiffened panel and to a wing box) are provided for demonstrating the effectiveness of the procedures presented
Influence of Loading Conditions on the Impact Damage Resistance of Composite Panels
No full textIn this paper the onset of impact induced delaminations in stiffened composite panels is analysed by using an approach based on a threshold critical impact force. This approach is adopted in combination with geometrically non-linear finite element analyses in order to investigate the influence of the in-service loading conditions on the impact damage resistance of the composite panels. An application to a stiffened composite panel under compression is presented in order to point out the sensitivity of the impact damage resistance to the level of load. Finally, indications on a novel approach, able to take into account the non-linearity of the composite stiffened panels' response, are given
A Novel FEM Model For biaxial Non-Crimp Fabric Composite Materials under tension
No full textThis paper presents a novel finite element based approach able to represent the complex architecture of the non-crimp fabric (NCF) composite materials. By means of the stiffness averaging method, implemented in the research oriented FEM (finite element method) code B2000, the developed model is able to simulate the NCFs mechanical performances. Applications to simple coupons loaded in tension are presented in order to demonstrate the capability and the effectiveness of the presented approach. Nevertheless, the proposed methodology can be applied and extended to all NCF geometries. First, for validation purposes the numerical results detained for a specific configuration have been compared with experimental results available from literature. Then, a parametric study has been carried out to investigate the influence of the bundle waviness on the tension stiffness. Finally, due to the degradation of the in-plane mechanical properties, the presence of the stitching has been investigated
Influence of Damage Onset and Propagation on The Tensile Structural Behaviour of Protruding Composite Joints
No full textIn the present paper, a detailed numerical investigation of the structural behaviour of single-lap protruding composite joints under tensile loading has been carried out using a three-dimensional progressive damage FEM model. The adopted FEM model is based on a combination of Hashin’s failure Criteria, ply-discount material’s degradation rules and penalty method (for contact-friction phenomena).
Some joints’ configurations with different hole’s diameter and different interfaces (composite/composite and composite/aluminium) have been analysed. The numerical results in terms of strain curves, load-displacement curves and damage propagation have been compared with experimental data in order to point out the effectiveness and the weak points of the proposed progressive damage approach. Comparisons between the numerical damage and no-damage approach for each configuration have been carried out in order to analyse the influence of progressive damage approach on the numerical simulation of the overall structural behaviour. Also the influence of penalty contact stiffness on the damage onset and damage propagation inside the joints has been investigated. Finally, particular emphasis has been given to the damage onset and damage propagation inside the joints critically discussing the differences among the analysed geometrical configuration
Delamination Growth in Composite Panels Under Compressive Load
No full textIn this paper, crack growth analyses on composite panels containing embedded delaminations has been performed using the geometrically non linear FEM code B2000, based on the Total Lagrangian Formulation. The code has been improved with an effective Virtual Crack Closure Technique to evaluate Energy Release Rate and with Penalty Method to evaluate contact forces. Validation of the proposed tool has been performed with experimental and numerical data available in bibliography for Double Cantilever Beam specimens and panels with embedded delaminations
A Global/Local Finite Element Approach for Predicting Interlaminar and Intralaminar Damage Evolution in Composite Stiffened Panels Under Compressive Load
No full textThis paper addresses the prediction of intralaminar and interlaminar damage onset and evolution in composite structures through the use of a finite element based procedure. This procedure joins methodologies whose credibility has been already assessed in literature such as the Virtual Crack Closure Technique (for delamination) and the ply discount approach (for matrix/fiber failures). In order to establish the reliability of the procedure developed, comparisons with literature experimental results on a stiffened panel with an embedded delamination are illustrated. The methodology proposed, implemented in ANSYS as post-processing routines, is combined with a finite element model of the panel, built by adopting both shell and solid elements within the frame of an embedded global/local approach to connect differently modelled substructures
Effects of Geometrical and Material Features on Damage Onset and Propagation in Single-lap Bolted Composite Joints under Tensile Load: Part I – Experimental Studies
No full textAn experimental investigation has been carried out in single-lap bolted composite joints in order to point out the influence of geometrical and material characteristics on the damage onset and propagation under tensile loading conditions. Protruding and countersunk joints have been considered, with different bolt diameters and different interfaces (composite-to-composite and composite-to-aluminum). First, static tensile tests have been performed on single-lap joints. Then, non-destructive ultrasonic evaluations have been conducted at intermediate load levels and at final failure in order to show the real onset and evolution of damage inside the joints in terms of fibers and matrix breakage
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