Papers by Keyword: Braided Composites

Abstract: L shaped braided composites under fatigue load was researched, using piezoelectric sensors and active Lamb wave monitoring technology. HHT transform based signal envelope obtaining method and the damage index method based on signal energy change were used to monitor the damage extending of the braided composites.

Abstract: In this paper, the fracture process of 3D four-directional carbon/epoxy braided composites with different braiding angles under the monotonic tensile loading were investigated by the acoustic emission (AE) technique. The AE cumulative energy, event rate, amplitude, and the peak frequency were analyzed. At the same time, combining with the load-displacement curve varying feature, the fracture processes were divided into different stages to deeply understand the damaged mechanisms of the textile composites. Furthermore, the fracture surfaces of the specimens were observed under optical microscopy. Results reveal that the behavior of AE parameters described well the fracture process in the 3D braided composites with different braiding angles, and the damage mechanisms of the composites can be successfully identified by AE characteristics.

Abstract: Braided composite tubular structures are of interest as viable energy absorbing components to improve vehicle passive safety. Unfortunately, there are many difficulties in predicting the crash response of braided composite tubes. In this study, a progressive failure model for braided composite materials, which had been implemented as a user material model in ABAQUS/Explicit, was used to simulate the axial crash response of braided composite tubes. It was shown that the model adequately captured the failure characteristics (such as matrix cracking, fiber fracturing and delamination) and energy absorption of braided composite tubes under axial compression. In addition, the simulation results show that braided composites have higher energy absorption performance compared to traditional metals.

Abstract: The polymer constitutive equations are implemented within strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. Based on the constitutive polymer model developed by Goldberg, nonlinear strain rate dependent triaxial braided composite has been analyzed. To verify the formulation, the tensile deformations of a representative polymer are computed across a wide range of strain rates. Results computed using the developed constitutive equations correlate well with experimental data.

Abstract: Enhancing the performance and lightness of different structures has already been achieved by the employment of fibre reinforced composite materials. Nowadays, a new challenging perspective is being given to these materials by the inclusion of non-metallic conductive components. This emerging technology will lead to multifunctional composites with possible applications in structural health monitoring and traffic monitoring. The aim is to avoid corrosion problems from metallic components, as well as to eliminate the need of expensive equipments used for the health monitoring of large infrastructures. In the present research, the strain-sensing capability of a core-reinforced hybrid carbon fibre/glass fibre braided composite has been investigated in order to develop continuous monitoring system. The characterization of sensing behaviour was performed with the help of an instrumental set-up capable of measuring the change in electrical resistance with mechanical stresses applied to the samples. The effect of core composition (carbon fibre/glass fibre weight ratio) on the strain sensitivity of the braided composites has been studied in order to find out the optimum composition for best sensing capability. Among the three compositions studied (23/77, 47/53 and 100/0), composites with lowest amount of carbon fibre showed the best strain sensitivity with gauge factors up to 23.4 at very low flexural strain (0.55%). Attempts have also been made in this research to develop a piezoresistive matrix for the braided composites in order to further enhance their strain sensitivity. For this purpose, the strain sensing capability of an unsaturated polyester matrix dispersed with chopped carbon fibres (1mm and 3 mm lengths) at various weight % (0.5, 0.75 and 1.25%) was evaluated in order to find out their optimum length and concentration. It was observed that chopped fibres with different lengths showed similar strain sensitivity, which however, improves with the decrease in their concentrations.

Abstract: As for 2.5-D layer-to-layer angle interlock braided composites, the cross section of the warp tow was represented in double-convex lens form, and the center line of the warp tow was along the sinusoid. The arranging characteristic of weft tow fibers along the cross section outline of the longitude fibers was studied in detail. A novel finite element model for 2.5-D braided composites was established to predict elastic modulus. The finite element software ANSYS was adopted to study the mechanical properties of the model and presented its stress nephogram, and the influence of the braided structure parameters on the elastic modulus of this material was analyzed in detail. To validate this model, qualified experimental samples were made by VARTM technique, and then tensile tests were performed to determine the mechanical properties. The results show that the conclusions of finite element method (FEM) fit well with the experimental values, and this model can be used to predict effectively the macro modulus of 2.5-D braided composites.

Abstract: An extensive test campaign has been conducted to characterise the different failure modes observed in heavy tow (24k) carbon and glass braided composites. The Digital Image Correlation (DIC) technique was used to obtain complete strain field measurement of large strains to failure. Failure in the fibre direction, under tension and compression loading were investigated; in the tension direction relatively large strains to failure were measured due to tow straightening damage mechanisms. Another important test is tensile shear loading which can undergo very large strains to failure due to fibre re-orientations in the loading direction. This latter, so-called ‘scissoring’ mechanism, has been quantified through changes of fibre angle during the complete loading history. Data gathered from coupon testing was used to characterise a material damage, with failure, model for the heavy tow braids, using a general composite damage model available in the explicit Finite Element (FE) code PAM-CRASHTM. Finally, four-point bending tests on braided carbon and glass composite beams with full field strain measurements to failure was carried out and used to validate the numerical model. A good agreement between simulation and experimental results was obtained.

Abstract: A CAD/CAM idea with its relation model including the analyses of braid process, yarns internal geometry and mechanical properties is proposed. An infrastructure of CAD/CAM system with platform and criterions which endure expandability is introduced. Based on the platform, some subsystems are built to accomplish various tasks such as 3D modeling, finite element analysis and braided process simulation. In order to implement the platform, parameter transferring is analyzed and an example is given. Based on the braiding process of composite, the axis direction stiffness/flexibility matrix, cell stiffness and engineering constants is acquired by the analysis of yarns and cell. At last, a proper and feasible collaborative environment and the tasks assignment is proposed. Based on the platform, an analysis instance is finished and the results are exhibited.