Papers by Keyword: Woven Composites

Abstract: A mixed numerical-experimental technique based on vibration tests is modified and applied to determine the elastic material properties of woven composites. This non-destructive technique consists of physical experiments, numerical modelling and material identification procedure. For the purpose of characterization, two carbon fiber panels were prepared by manual layout technology. An evaluation of the accuracy of woven composite elastic properties is executed comparing the numerical and experimentally obtained resonant frequencies.

Abstract: Reliable experimental data on compressive strength of composite material are important, especially for designing structures having dominant compressive stresses, such as bolted joints. Composite materials usually have lower compressive strengths compared to tensile strengths. Woven composites added more complications. Initial waviness in woven composites makes the compressive strengths even much lower. Therefore, in this paper, experimental study on the compressive strengths of woven composites will be presented. The experiments used standard ASTM D3410M-03. Woven glass-epoxy will be tested extensively. The specimens were produced using standard hand layup techniques. Several layup configurations were tested, namely (0/90)_s, (0/90/±45)_s and (±45)_s. The results showed that woven glass-epoxy generated failure modes specifically found in compressive tests of composites, such as: fiber micro-buckling, fiber crushing and shear band-formation. It was also found that unlike in the case of tensile tests, the layup configurations did not affect the compressive strength values. It seems that the fiber orientation will not affect significantly the compressive strengths. The epoxy matrix played more dominant role on the compressive behavior of woven glass-epoxy composites.

Abstract: Based on the micro-structure, a mosaic model was established to obtain the stresses distribution of the C/C composite beam subjected to bending load. Then a subroutine for failure analysis was introduced to calculate the failure index of the composite beam. A corresponding laminate model was used to validate the calculation of the mosaic model. The results indicated that the method combining micro stresses and macro failure criterion was suitable for strength analysis of composite structure, which could be used in guiding the design of composite.

Abstract: The present paper is concerned with modelling damage and fracture in notched woven fabric composites. Previous experimental work has shown that damage at a notch in a variety of GFRP and CFRP composites based on woven fabric reinforcement comprises matrix damage and fibre tow fracture along the plane of maximum stress. It is these experimental observations that inform the failure modelling developed here, in which a cohesive zone approach is used within a 2-D finite element framework. The cohesive zone parameters are based on previously reported experimental measurements for the strength and toughness of the woven fabric materials under investigation. The approach is shown to provide predictions of notched strength that are in very good agreement (less than 11% discrepancy) with experimental results from the literature for a range of GFRP and CFRP woven fabric systems.

Abstract: This research work was concerned with the evaluation of mechanical properties; flexural strength and impact strength of coconut coir textile composites. The coir fabric reinforcement was in a form of woven and cross ply structure. The two types of laminates orientations for cross-ply structures were 0/90 degrees and 45/-45 degrees. Composites with fibre weight fraction of 30% were prepared by hand lay-up and vacuum bagging technique. Mechanisms of composites failure were examined using scanning electron microscopy (SEM). Results have shown that the woven coir reinforced composites exhibited higher impact resistance and flexural strength (warp woven) compare to cross-ply composites. Moreover, 0/90 degrees orientations demonstrated better strength performance compare to 45/-45 degrees. However, damage propagation on woven composites was found to be larger than cross-ply composites. Normality test of data distribution were evaluated using Minitab software and it was proven that all samples were in a very stable behaviour (p > 0.05). Experimental results were also validated using one way analysis of variance technique (one way-ANOVA) and it revealed there was statistically significant difference (p < 0.05) between all different fabric structures of coir fabric as reinforcement in composite.

Abstract: 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.

Abstract: Experimental static and fatigue tension-tension tests were carried out on 5HS/RTM6 composite intact coupons and coupons incorporating adhesively-bonded (FM300-2) stepped flush joints. The results show that the adhesive joint, which is widely used in repairs, significantly reduces the static strength as well as the fatigue life of the composite. Both, the static and the fatigue failure of the ‘repaired’ coupons occur at the adhesive joint and involve crack initiation and propagation. The latter is modelled using interface finite elements based on the decohezive zone approach. The material degradation in the interface constitutive law is described by a damage variable, which can evolve due to the applied loads as well as the number of fatigue cycles. The fatigue formulation, based on a published model, is adapted to fit the framework of the pseudotransient formulation that is used as a numerical tool to overcome convergence difficulties. The fatigue model requires three material parameters. Numerical tests show that a single set of these parameters can be used to recover, very accurately, the experimental S-N relationship. Sensitivity studies show that the results are not mesh dependent.