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This study presents an investigation on the mechanical properties and failure mechanisms of composites made of plain woven fabrics reinforced with carbon fibers, aramid fibers, and their intralayer hybrids. The specimens were fabricated by hand lay-up method. Tension, compression, and shear tests were performed in accordance with the relevant standards to investigate the tensile, compression, and shear properties of carbon fiber, aramid fiber, and carbon/aramid fiber intralayer hybrid plain woven composites. Accurate strain field was obtained by digital image correlation (DIC) technology and compared with the results measured by the strain rosettes. Furthermore, a multi-scale modeling strategy was developed to predict the mechanical properties of the hybrid composites. The fiber monofilament model was used to calculate the effective properties of carbon and aramid yarns at the micro-scale level. Representative volume element (RVE) models of the hybrid composite were constructed considering the real fabric pattern at the meso-scale level. The predicted results agree well with the experimental data which validates the multi-scale modeling strategy. The presented information on the tensile, compressive, and shear properties and finite element simulation method of carbon/aramid intralayer hybrid composites should be useful in subsequent research as well as in designing new high-performance composites and structures. [ABSTRACT FROM AUTHOR]

Due to the excellent mechanical properties and strong design flexibility, the 3D woven composite engine casing shows great potential in high performance fields. This article adopted the method of double-layer weaving and adding yarn to achieve the variable thickness of the 3D woven composite engine casing. The purpose of this article is to study the compression performance and failure mechanism of this variable thickness casing in different thickness zones through experiments and numerical simulations to lay a foundation for future optimization and inclusiveness research on this casing with complex thickness changes. Three types of representative volume cells are established for progressive damage analysis. 3D-Hashin criteria and von-Mises stress criterion are used as damage criteria for yarns and matrix. The progressive damage process and the proportion of damage in the inner and outer layers of three types of 3D woven tubes under axial compression load are analyzed. Results show that the main failure modes of the three types of tubes are yarn-matrix compressive cracking along direction 3 and matrix failure. The damages are mostly concentrated in the warp bending area. The proportions of warp yarn damage in the inner and outer layers of three tubes are different. [ABSTRACT FROM AUTHOR]

Carbon fiber laminated composites are widely used in aerospace and high speed railways industries due to their high specific strength and stiffness, but the poor interlaminar properties affect their further applications. In order to solve the problem of poor interlayer performance of woven laminated composites, this paper proposes a new type of laminated composite, called single-sided-loop two-dimensional (2D) woven laminated composites (SWLC). By introducing loop warp yarns to the thickness of general 2D woven laminated composites (GWLC), the loop between its preform and resin can improve the way of the fibers attached to the substrate and increase the volume content of the fibers between the layers. The mechanical behavior of SWLC is investigated experimentally and numerically. For numerical simulations, a unit cell is established based on the fine periodic structure. A progressive damage model is established using the 3D Hashin and the von-Mises criteria. Numerical results are in good agreement with the experimental data. Results show that the looped fabric can improve interlayer properties at the expense of slight reduction of some in-plane properties. [ABSTRACT FROM AUTHOR]

Carbon fiber laminated composites are widely used in the aerospace industry due to their excellent lightweight and excellent mechanical properties. However, when subjected to external impact, delamination damage occurs between the layers of composite materials, and thus how to suppress delamination and improve the interlaminar strength of composite laminates has become the focus of the research field. Based on the idea of interlayer toughening, a new double-sided-loop two-dimensional (2D) woven laminated composites (DWLC) is designed, woven and laminated using the RTM molding process. DWLC is based on a 2D fabric with the introduction of loop warp yarns in thickness direction, which form Z-directional loops and thus form a synergistic toughening layer with the resin matrix between the layers after lamination during the forming process. In order to study the mechanical properties of DWLC, the tensile, compressive, interlaminar shear mechanical properties and damage behavior of DWLC are experimentally and numerically investigated. In addition, the internal damage and failure fracture are examined using micro computed tomography (Micro-CT). Strength prediction model of DWLC is established based on a representative volume element (RVE) with a mesoscopic geometric model. Three-dimensional (3D) Hashin and Von-Mises criteria are introduced as the failure criteria for the component materials. The results show that due to the existence of loops, the in-plane fiber volume content of DWLC decreases, resulting in a decrease of tensile and compressive strengths but an increase of interlaminar shear strength. [ABSTRACT FROM AUTHOR]

Due to their superior overall properties, 3D integrated woven spacer composites overcome the weakness of traditional sandwich composites under low-velocity impact (LVI). The dynamic response of carbon fiber 3D integrated woven spacer composites under LVI and failure behavior under compression after impact (CAI) were experimentally investigated in this work. The impact damage patterns were analyzed using ultrasonic C-scan and micro-CT techniques at various energy, while digital image correlation (DIC) was used for CAI analysis. The results indicate that the impact damaged areas of X-type specimens is 365.1 mm2 under the impact energy of 7 J, while that of Y-type specimens is 371.4 mm2. The maximal absorbed energy is very close for two types of 3D integrated woven spacer composite specimens, which is about 6.99 J. The residual strength of X-type specimens decreases by 38.9% after the impact energy of 7 J, while that of Y-type specimens is reduced by 24.6%. The damage mechanism of the composites under LVI and CAI was obtained, which can provide some guidance for designing more suitable 3D integrated woven spacer composite structures in engineering practice. • The LVI response of the carbon fiber 3D integrated woven spacer composites is experimentally investigated. • The residual performances under the weft and warp direction compression are obtained and compared. • The 3D integrated woven spacer composite exhibits good interlayer performances and a high degree of damage tolerance. • X-type and Y-type specimens exhibit distinct buckling modes, residual strength and failure modes under compressive load. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) woven composites have been widely used in structural components due to their excellent mechanical and near-net-shape properties. However, for some special applications, it is expected that 3D woven composites can be damaged at designated locations under a specific load. In this research work, a new kind of defect-prefabricated 3D woven composites (DP3DWCs) are designed, where defects are prefabricated by cutting weft or warp yarns in defect-free 3D woven composites (DF3DWCs). The tensile mechanical properties of the DF3DWCs and the DP3DWCs are investigated experimentally and numerically. The mesoscopic geometry models of the DF3DWCs and the DP3DWCs were established by multi-objective searching algorithm. The progressive damage models were established using the 3D Hashin criteria and the von Mises failure criterion. Numerical results agree well with the experimental data. The influence of the number of defect layers on the mechanical properties was also discussed. The obtained results indicate that the defects have little effect on the elastic modulus, while tensile strengths decrease linearly with the increase of the number of defect layers. Failure mechanisms of yarns and matrix in the non-defective and defective materials were studied, and the volume fraction of elements of each failure mode was computed and analysed. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) plain fabric is prone to delamination when subjected to bending, shear, impact loads. To enhance the interlayer properties of 2D plain fabrics, standing up loops is added. In this paper, specimens of the double-sided-loop 2D woven laminated composites (DWLC) and general 2D woven laminated composites (GWLC) are made for double cantilever beam (DCB) tests and end-notch flexure (ENF) tests to study their toughening mechanism. Test results show that the values of model I and mode II interlaminar fracture toughness are increased by 870% and 250% for the DWLC compared with the GWLC. Based on the three-linear cohesive zone model (CZM), finite element (FE) models of composite laminates specimens of DCB and ENF considering the phenomenon of interlaminar bridging are established, and numerical results are in good agreement with the experimental data, that verifies the accuracy of the FE models. Using the verified FE models, model I and mode II fracture properties of the DWLC specimens of DCB and ENF with different initial crack lengths are investigated, and the results show that the stress is redistributed and the load gradually decreases as the length of the prefabricated cracks increases. The obtained fracture toughness of the DWLC provides a reference for the toughening methods and the engineering applications of DWLC. [ABSTRACT FROM AUTHOR]