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This work examines the flexural and impact behavior of self-reinforced poly(ethylene terephthalate) (srPET) composites, which were produced by film stacking from fabrics composed of braiding commingled yarns with high-tenacity PET (serving as the reinforcements) and copolymerized PET (mPET) (serving as the matrix). The influence of the hybrid yarns, fabric architectures, and processing conditions on the mechanical properties of srPETs were studied. [ABSTRACT FROM AUTHOR]

Studies of numerical simulation and experimental validation are carried out on the planar orthogonal braided composites cantilever beam. On the basis of single-cell model, the model of 1 × 1 orthogonal braided fibre structure is established with the SolidWorks engineering drawing software. Six different loading models are analysed using the finite element software ANSYS. The effective elastic constants are obtained with the homogenisation theory. The finite element model of a cantilever beam is then established, which is made of orthogonal braided composites, where the angle between fibre orientation and periphery varies from 0° to 90°. The experiment is carried out and the natural frequencies are obtained using the free vibration measuring method. The effects caused by the additional mass of sensor are eliminated according to vibration theory, and the results are consistent with those obtained by numerical simulation. [ABSTRACT FROM AUTHOR]

The aim of this study is to provide an adequate understanding of the damage mechanism of three-dimensional braided composites based on offline measurements using the superconducting quantum interference device (SQUID) technique. This paper presents research into SQUID flux imaging for 3D braided composites under impact energy. Experimental results show that SQUID flux imaging can be considered as a suitable technique to detect defects of three-dimensional (3D) braided composites subjected to different energy impacts. When the deformation degenerates into internal cracking, the magnetic field signals decrease. The method provides an accurate calculation of the location of defects. The method will not only locate a defect, but can also be used for determining the internal characteristics of 3D braided composites, such as the braiding fibre orientation. Compared with the ultrasonic testing technique, the SQUID method is a more suitable non-destructive testing technique for 3D composite materials. This study shows that the SQUID testing technique is an effective tool for inspecting the state-of-failure of 3D braided composites. [ABSTRACT FROM AUTHOR]

Three-dimensional braided composites have a skin-core structure and can be divided into three kinds of regions: interior, surface, and corner, which have different mechanical properties. Based on the structure characteristics and stiffness average volume formula, a new approach for testing and predicting longitudinal tensile modulus of three-dimensional braided composites is proposed in this paper. This approach can not only provide a basis to establish test standard for three-dimensional braided composites but also predict the longitudinal tensile modulus of three-dimensional braided composites. It is verified by an application example. Additionally, the effects of the number of rows and columns of yarns in preforms on longitudinal tensile modulus of three-dimensional braided composites are discussed here. [ABSTRACT FROM PUBLISHER]

Three-dimensional viscoelastic properties of four-step three-dimensionally (3D) braided composites are studied in this paper. Based on the three-cell division scheme, a multi-scale model for 3D braided composites is proposed. A periodic boundary condition is applied to characterize the periodic structure of 3D braided composites and yarns. Given the viscoelastic parameters of resin matrix and the elastic constants of fibers, the viscoelastic properties of yarns are obtained by the finite element method and Prony Series fitting. The three-dimensional viscoelastic constitutive relationship of interior cells is derived based upon the viscoelastic properties of yarns and resin matrix. Moreover, the viscoelasticity of 3D braided composites is studied by creep experiment. The viscoelastic deformation obtained from the multi-scale method agrees well with the experimental results. The influence of the two independent micro-structural parameters, braiding angles, and fiber volume fractions, on the viscoelastic properties of 3D braided composites is investigated in detail. [ABSTRACT FROM AUTHOR]

Three dimensional braided composite materials exhibit better performance in terms of structural integrity, through-thickness strength and impact resistance, than laminated composites. Other advantages regarding production are the ability to produce composite structures with intricate geometries close to the near-net-shape, and also with continuous changes in its cross-section. These properties are a consequence of the internal geometry of the 3D braided composites, in which yarns are interlaced following specific patterns programmed on a braiding machine. In this article, the operation of a typical rotary braiding machine is emulated in order to automatically obtain the geometry of a braiding unit cell. Once the geometrical description is obtained, a finite element model has been developed in order to carry out virtual testing of 3D composite materials. An AS4/epoxy braided material system has been virtually tested and a theory-experimental correlation has been performed for the longitudinal modulus and yield strength compression, using a failure criterion based on constituents and interface failures. [ABSTRACT FROM AUTHOR]

This article reports the bending fatigue behavior of a four-step 3-D rectangular braided composite at different stress levels. The S–N curve and the stress vs. deflection history were recorded to investigate the bending fatigue behaviors of the braided composite. Specifically, the area of the stress hysteresis loop in each loading cycle and the accumulated area of the whole loading cycles were calculated from the stress vs. deflection history curves. All the integral areas were compared at different stress levels for analyzing the energy absorption. Then, the energy absorptions during the bending fatigue were compared to analyze the energy dissipation mechanisms taking place during the fatigue process. The stiffness degradation was also calculated to show the fatigue damage. The damage morphologies of the 3-D braided composite specimens were photographed to compare the failure modes under different stress levels. [ABSTRACT FROM PUBLISHER]

Abstract: A new parameterized finite element model (FEM) is established for 3-Dimensional (3D) five-directional rectangular braided composites. The model precisely simulates the spatial configuration of the braiding yarns and the axial yarns with consideration of the cross-section deformation as well as the surface contact in the braiding process. Moreover, this model orients in the same reference frame as the composites and the relationships among the structural parameters, particularly the braiding angle and the interior braiding angle, are investigated. A prediction of the effective elastic properties and the meso-scale mechanical response of 3D five-directional braided composites have been presented to verify the validation of the FEM. The effects of the braiding parameters on the mechanical properties are investigated in detail in this study. The results indicate that it is convenient to predict all the elastic constants of 3D five-directional braided composites with different parameters simultaneously using the FEM. Moreover, the FEM can successfully predict the meso-scale mechanical response of 3D five-directional braided composites containing periodical structures. In the mean while, the geometric characteristics and the mechanical properties of 3D five-directional and 3D four-directional braided composites have been compared. [Copyright &y& Elsevier]

Braided and filament wound CFRP were fabricated with varied fiber orientations. These composites exhibited not only similar trends in their experimental strength and stiffness properties but also good correlations with predictions made by CLT. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper the mechanical behaviour in bending of textile reinforced mineral matrix composite beams is analyzed. Two types of textile reinforcement made in E-glass fibers are considered: unidirectional rovings and chopped strand mat (CSM). The mineral matrix is an inorganic phosphate cement (IPC) and presents the advantage to be non-alkaline. The beams are hollow with square cross section, they are realized by bonding together composite plates having the dimensions . The plates are manufactured by pultrusion process, using the roving and the mineral matrix. In the first part of the paper we present the manufacturing process, and in the successive sections the mechanical characteristics of the composite itself in tension and shear are assessed. During the characterization tests, it has been emphasized that the shear behaviour is the weak point of the composite. Therefore, in order to enhance the mechanical behaviour of the beams, specimens have been strengthened using three types of reinforcement: internal reinforcement with struts, 3D external braiding and continuous wrapping by CSM reinforced mineral matrix. In the second part of the paper, the test in four point bending of four beams is presented. The analysis of the experimental results is governed by the search for a correlation between the phenomena observed at material level and those occurred during the tests of the structural elements. [Copyright &y& Elsevier]

In this paper, a two-dimensional triaxial braided composite model has been studied using the nonlinear explicit finite-element code LSDYNA. The unit cell consists of six subcells and material properties associated with shell element integration point simulate braiding architecture. The local material properties were selected by correlation of the global behavior of a coupon model with static specimen tests. By changing subcell size and orientation angle at integration points, different braids architectures were obtained. Panel ballistic models were performed with benefits of computation efficiency of shell elements. Mechanical properties, panel impact threshold velocities, and failure initiations for braids with bias angles of 75, 60, 45, and 30° were studied. Boundary effects were also investigated. [ABSTRACT FROM AUTHOR]

The behavior of dry fibers is a key component in modeling composite materials. However, it can become very expensive in computation time to model each individual filament. We propose here a new multi-scale method featuring beam elements embedded in truss elements. Truss elements are used to model contact responses and traction while beams elements are used to characterize flexion. This approach is compared to three different models using truss elements only, beam elements only, and a reference case. The reference case is also validated by experimental results of a glass braid being extended to drape over a square mandrel. The embedded element cumulative error on estimation of the deformed braid angle, thickness and length compared to the reference case is lower than their pure truss and pure beam models, while being 8 times faster than the reference case. • Textile are modelled at the fiber level using chains of finite elements. • Fiber behavior is modelled using beam elements embedded in truss elements. • A biaxial braid conforming to a square mandrel is modelled. • Accuracy of textile modelling is improved while being 8 times faster. [ABSTRACT FROM AUTHOR]

Microstructure of four-step 3D braiding preform with 1 x 1 pattern and complex rectangular cross-sections is studied by means of the control volume method. The complex rectangular configuration refers to the geometrical shape jointed by two or more rectangles together. Following the formation rule of the braiding process, the paths of the carriers are traced, particularly in the joint region where two rectangles join together. According to the formation procedures, three unit cell models, both topological and geometrical, are developed corresponding to the microstructure of the interior, surface, and corner in the joint region. The study shows that, in the joint region, the control volume of the unit cell is a cube in the interior, a hepta-prism in the corner, and a penta-prism in the surface, respectively. In addition, the study is able to demonstrate the difference in the braiding pattern and the spatial orientation of braiding yarns in the unit cells between those in the joint region of a complex rectangle and the corresponding region of a simple rectangle by four-step braiding process. [ABSTRACT FROM AUTHOR]

This paper proposes a method of deriving the engineering and strength properties of unidirectional lamina from laminate properties. Simple straight-sided untabbed tension and compression specimens are used to obtain the laminate properties. The derivation approach is an extension of existing methods that use cross-ply or angle-ply test specimens and back-out factors (also known as cross-ply factors) to derive unidirectional lamina strengths in the fiber direction. This method may reduce the cost of testing and improve the accuracy of strength predictions. It may be used to characterize some newer material forms such as two-dimensional braids. [ABSTRACT FROM AUTHOR]

The application of braided composite materials in the automotive industry requires an in-depth understanding of the mechanical properties. To date, the intralaminar fracture toughness of braided composite materials, typically used for describing post-failure behavior, has not been well-characterized experimentally. In this paper, a modified compact tension test, utilizing a relatively large specimen and a metallic loading frame, is used to measure the transverse intralaminar fracture toughness of a tri-axial braided composite. During testing, a relatively long fracture process zone ahead of the crack tip was observed. Crack propagation could be correlated to the failure of individual unit cells, which required failure of bias-yarns. The transverse interlaminar fracture toughness was found to be two orders of magnitude higher than the reference interlaminar fracture toughness of the same material. This is due to the fact, that intralaminar crack propagation requires breaking of fibers, which is not the case for interlaminar testing. [ABSTRACT FROM AUTHOR]