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首页> 外文期刊>Journal of aerospace engineering >Characterization of Damage in Triaxial Braided Composites under Tensile Loading
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Characterization of Damage in Triaxial Braided Composites under Tensile Loading

机译：拉伸载荷下三轴编织复合材料的损伤特征

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摘要

Carbon fiber composites that utilize flattened, large tow yarns in woven or braided forms are being used in many aerospace applications. The complex fiber architecture and large unit cell size in these materials present challenges for both understanding the deformation process and measuring reliable material properties. In this paper composites made using flattened 12k and 24k (referring to the number of fibers in the fiber tow) standard modulus carbon fiber yarns in a 0° / +60° /-60° triaxial braided architecture are examined. Standard straight-sided tensile coupons were tested with the 0° axial braid fibers either parallel to (axial tensile test) or perpendicular to (transverse tensile test) the applied tensile load. The nonuniform surface strain resulting from the triaxial braided architecture was examined using photogrammetry. Local regions of high strain concentration were examined to identify where failure initiates and to determine the local strain at the time of failure initiation. Splitting within fiber bundles was the first failure mode observed at low to intermediate strains. For axial tensile tests the splitting was primarily in the ±60° bias fibers, which were oriented 60° to the applied load. At higher strains in the axial tensile test, out-of-plane deformation associated with localized delamination between fiber bundles or damage within fiber bundles was observed. For transverse tensile tests, the splitting was primarily in the 0° axial fibers, which were oriented transverse to the applied load. The initiation and accumulation of local damage caused the global transverse stress-strain curves to become nonlinear and caused failure to occur at a reduced ultimate strain for both the axial and transverse tensile tests. Extensive delamination at the specimen edges was also observed. Modifications to the standard straight-sided coupon geometry are needed to minimize these edge effects when testing the large unit cell type of material examined in this work.
机译：碳纤维复合材料利用机织或编织形式的扁平大束丝，已在许多航空航天应用中使用。这些材料中复杂的纤维结构和较大的晶胞尺寸对理解变形过程和测量可靠的材料性能都提出了挑战。在本文中，研究了使用扁平12k和24k（指纤维束中的纤维数量），在0°/ + 60°/ -60°三轴编织结构中的标准模量碳纤维纱制成的复合材料。使用平行于（轴向拉伸试验）或垂直于（横向拉伸试验）所施加拉伸载荷的0°轴向编织纤维对标准的直面拉伸试样进行测试。使用摄影测量法检查了由三轴编织结构产生的不均匀表面应变。检查了高应变浓度的局部区域，以识别故障的起始位置，并确定故障起始时的局部应变。在低到中等应变下，纤维束内的分裂是第一个破坏模式。对于轴向拉伸测试，劈裂主要是在±60°的偏斜纤维中进行的，该纤维相对于所施加的载荷定向为60°。在轴向拉伸试验中，在较高应变下，观察到与纤维束之间局部分层或纤维束内损坏相关的平面外变形。对于横向拉伸测试，劈裂主要是在0°轴向纤维上进行的，该纤维横向于所施加的载荷定向。局部损伤的产生和累积导致整体横向应力-应变曲线变为非线性，并导致轴向和横向拉伸试验的极限应变降低时发生破坏。在样品边缘也观察到广泛的分层。在测试这项工作中检查的大单位晶格类型的材料时，需要对标准的直面试样的几何形状进行修改，以最大程度地减少这些边缘效应。

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