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High fidelity geometry models of the preforms are essential in mechanical property analysis for composite materials. The paper presents a virtual braiding method to generate digital material twins of 3D braided preforms. The four-step 3D braiding process is simulated based on the concept of virtual fiber and according to the rule of yarn movement. Fiber-level models of the preform are constructed which display the micro-scale architectures explicitly, including compressive deformations of yarn cross-sections and variations of yarn paths. The Micro-CT test is employed to investigate the internal fiber structures of 3D braided preform and quantitatively verify the accuracy of the proposed modeling method. Influence of the braiding parameters, such as yarn tension and arrangement angle in the initial state on geometric parameters of the preform is then investigated. [ABSTRACT FROM AUTHOR]

The inter-ply shear deformation of 3D woven preform is inevitable in the forming process. Numerical simulation of the inter-ply shear process is therefore necessary to establish the high-precision fiber structure model and understand the deformation mechanisms. Here, a research strategy for inter-ply shear behavior of 3D woven preform is proposed. A new fixture is developed for inter-ply shear experiments. The unit cell model of the preform is generated using virtual fibers. Then the inter-ply shear test is replicated through numerical simulation. Micro-CT tests are carried out on the sample before and after inter-ply shear deformation, which confirmed that the virtual fiber model can accurately reproduce the fiber structure and micro-deformation. The virtual experiment results show that the macro-scale inter-ply shear deformation of the preform is composed of several yarn level deformations including the local tension, extrusion and buckling of warp/binder yarns, and slippage between warp and weft yarns. [ABSTRACT FROM AUTHOR]

The inter-ply shear deformation of 3D woven preform is inevitable in the forming process. Numerical simulation of the inter-ply shear process is therefore necessary to establish the high-precision fiber structure model and understand the deformation mechanisms. Here, a research strategy for inter-ply shear behavior of 3D woven preform is proposed. A new fixture is developed for inter-ply shear experiments. The unit cell model of the preform is generated using virtual fibers. Then the inter-ply shear test is replicated through numerical simulation. Micro-CT tests are carried out on the sample before and after inter-ply shear deformation, which confirmed that the virtual fiber model can accurately reproduce the fiber structure and micro-deformation. The virtual experiment results show that the macro-scale inter-ply shear deformation of the preform is composed of several yarn level deformations including the local tension, extrusion and buckling of warp/binder yarns, and slippage between warp and weft yarns. [ABSTRACT FROM AUTHOR]

Image 1 [ABSTRACT FROM AUTHOR]

Numerical simulation is a key means to evaluate the forming performance of 3D woven preforms (3DWPs). However, the macroscopic continuous model of 3DWPs cannot predict the orientation and deformation of yarns, while the microscopic discrete model is unsuitable for large-size samples forming simulation due to computational constraints. A novel mesoscopic hybrid element yarn model is thus proposed to establish a large-size 3D woven virtual yarn preform (VYP) model and the L-shaped virtual forming simulation model. The L-shaped forming experiment of the 3DWP is designed and executed, and the accuracy of the numerical simulation models is verified from three aspects: the mechanical curve, the sample's macroscopic morphology, and the local meso -structure features. Subsequently, the deformation behavior of the yarn structure inside the 3DWP during the L-shaped forming process is analyzed by combining experimental and simulation results. Furthermore, the effects of the L-shaped angle and chamfer radius on the deformation behavior of the 3DWP are studied, which helps guide the structural design of 3DWPs. [ABSTRACT FROM AUTHOR]