Abstract The present study investigated nonlinear elastic-plastic stress-strain relationships of discontinuous carbon fiber-reinforced thermoplastics (CFRTPs) using experiments and numerical simulations. In the experiments, we conducted uniaxial tensile tests and three-point bending tests for two types of CF/PA6 (carbon fiber/polyamide 6) specimen: injection-molded specimens with short fiber length and aligned fiber orientation, and compression-molded specimens with long fiber length and random fiber orientation. Comparison of the experiment results indicated that the injection-molded specimens exhibited a nonlinear stress-strain response, while the compression-molded specimens exhibited an almost linear response. These results implied that long discontinuous fibers effectively increased the yielding point of composites, even if the composites had random fiber orientation, which eliminated orientation dependence on mechanical properties of the composites. Furthermore, we attempted to simulate elastic-plastic stress-strain relationships of discontinuous CFRTPs in an effort to understand the effect of the microstructure, including fiber length. For this purpose, we employed fiber-based simulations to deal with the microstructure of fibers and matrix and the constitutive law of the matrix. The simulated results indicated that fiber length influences the nonlinearity of the stress-strain relationships of discontinuous CFRTP composites.

中文翻译：

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不连续碳纤维增强热塑性塑料的弹塑性响应评估：基于载荷传递的微机械模拟的实验和考虑

摘要 本研究使用实验和数值模拟研究了不连续碳纤维增强热塑性塑料 (CFRTP) 的非线性弹塑性应力应变关系。在实验中，我们对两种 CF/PA6（碳纤维/聚酰胺 6）试样进行了单轴拉伸试验和三点弯曲试验：纤维长度短且纤维取向一致的注塑试样，以及具有长纤维长度和随机纤维取向。实验结果的比较表明，注塑试样表现出非线性应力应变响应，而压缩成型试样表现出几乎线性的响应。这些结果表明，长的不连续纤维有效地提高了复合材料的屈服点，即使复合材料具有随机纤维取向，这消除了对复合材料机械性能的取向依赖性。此外，我们试图模拟不连续 CFRTP 的弹塑性应力应变关系，以了解微观结构的影响，包括纤维长度。为此，我们采用基于纤维的模拟来处理纤维和基体的微观结构以及基体的本构规律。模拟结果表明，纤维长度会影响不连续 CFRTP 复合材料的应力-应变关系的非线性。我们试图模拟不连续 CFRTP 的弹塑性应力应变关系，以了解微观结构的影响，包括纤维长度。为此，我们采用基于纤维的模拟来处理纤维和基体的微观结构以及基体的本构规律。模拟结果表明，纤维长度会影响不连续 CFRTP 复合材料的应力-应变关系的非线性。我们试图模拟不连续 CFRTP 的弹塑性应力应变关系，以了解微观结构的影响，包括纤维长度。为此，我们采用基于纤维的模拟来处理纤维和基体的微观结构以及基体的本构规律。模拟结果表明，纤维长度会影响不连续 CFRTP 复合材料的应力-应变关系的非线性。