Abstract Carbon fibre reinforced polymer (CFRP) composite structures may experience light surface damage such as shallow surface scratch around 50 μm or less in applications. In this study, critical bending loads of 2D woven CFRP panels with and without shallow surface scratches were assessed under three-point-bending (3-p-b) conditions and then modelled by a simple strength theory for composite fracture. This closed-form tensile strength solution is a non- Linear Elastic Fracture Mechanics (LEFM) model derived specifically for heterogeneous composites. Direct tensile tests of the CFRP panels (without shallow surface scratch) were also performed, and measured tensile strength was compared with that from 3-p-b tests. The relative error between the two different tests was only around 6.7%. The ply thickness around 140 μm was selected as the controlling composite microstructure parameter or characteristic composite unit Cch in this non-LEFM model. This simple model shows that a suitable composite characteristic microstructure measurement such as Cch = ply thickness can significantly simplify composite fracture analysis. A simple statistical analysis using a 2D normal distribution methodology for strength measurements was also introduced so that the experimental scatters can be analysed. The 95% reliability band can be conveniently used in safe design of composite structures.

中文翻译：

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由拉伸强度模型确定的具有浅表面划痕的 CFRP 板的临界弯曲载荷

摘要 碳纤维增强聚合物 (CFRP) 复合结构在应用中可能会遇到轻微的表面损伤，例如约 50 μm 或更小的表面划痕。在这项研究中，在三点弯曲 (3-pb) 条件下评估了具有和不具有浅表面划痕的 2D 编织 CFRP 面板的临界弯曲载荷，然后通过简单的强度理论对复合材料断裂进行建模。这种封闭形式的拉伸强度解决方案是一种非线性弹性断裂力学 (LEFM) 模型，专门用于异质复合材料。还进行了 CFRP 板的直接拉伸测试（无浅表面划痕），并将测得的拉伸强度与 3-pb 测试的拉伸强度进行比较。两种不同测试之间的相对误差仅为 6.7% 左右。在该非 LEFM 模型中，选择 140 μm 左右的层厚度作为控制复合材料微观结构参数或特征复合单元 Cch。这个简单的模型表明，合适的复合材料特征微观结构测量值（例如 Cch = 层厚度）可以显着简化复合材料断裂分析。还引入了使用 2D 正态分布方法进行强度测量的简单统计分析，以便可以分析实验散射。95% 的可靠性带可以方便地用于复合结构的安全设计。这个简单的模型表明，合适的复合材料特征微观结构测量值（例如 Cch = 层厚度）可以显着简化复合材料断裂分析。还引入了使用 2D 正态分布方法进行强度测量的简单统计分析，以便可以分析实验散射。95% 的可靠性带可以方便地用于复合结构的安全设计。这个简单的模型表明，合适的复合材料特征微观结构测量值（例如 Cch = 层厚度）可以显着简化复合材料断裂分析。还引入了使用 2D 正态分布方法进行强度测量的简单统计分析，以便可以分析实验散射。95% 的可靠性带可以方便地用于复合结构的安全设计。