在实际成形过程中,碳纤维复合材料往往处于复杂的应力状态,开展近于真实载荷环境下的力学试验分析,能够更准确地认识实际应用中材料的成形性能和变形机理.为获得碳纤维织物的基本力学特性,设计了平纹碳纤维织物拉伸试样及成形试样,进行了单轴拉伸、双轴拉伸、镜框剪切试验和方盒冲压成形实验研究,对比了不同双拉比及纱线取向对力学性能及成形性能的影响.研究结果表明:碳纤维织物具有高度的非线性、各向异性和双拉耦合特性,即经纬向纤维的力学性能会相互影响;剪切变形是成形过程中的主要变形模式,当剪切角达到临界锁死角时,织物发生起皱现象;同种织物不同纱线取向试样表现出不同的成形性能,因此可以根据零件几何形状选择合适纤维取向的织物,从而减少缺陷,优化成形零件的力学性能.研究结果为后续建立碳纤维织物本构模型和成形仿真奠定了基础.
Composite material in forming process is usually subject to complex loading conditions that can induce a stress field with two or even three dynamic principal stresses. The experimental analysis of composite material could approximate the real loading condition to produce a multiaxial stress field for validating the material formability. This paper presents an experimental study on the mechanical properties and forming behavior of carbon woven fabric. Uniaxial tensile, biaxial tensile and picture frame tests were carried out to get the basic mechanical properties of a carbon woven fabric. Experimental results indicate that the carbon woven fabric has highly nonlinear, anisotropic and biaxial tensile coupling characteristics. Square-box stamping of the carbon woven fabric was implemented to investigate its forming behavior. It is found that in-plane shear is the main deformation mode during stamping. The fabric will wrinkle when the shear angle reaches a critical lock angle. Samples with different initial fiber yarn orientation render different forming properties. Therefore, one can reduce defects and optimize the mechanical properties of formed parts by choosing suitable yarns direction of the fabric based on its geometry. Results of this study lay an experimental foundation for developing woven fabric constitutive model and conducting numerical simulation on forming in the future work.
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