Abstract Here we present the first real-time three dimensional (3D) observations of damage evolution in a carbon fibre reinforced polymer (CFRP) composite tube under torsion. An in-situ torsion test of 1/1 45° (diamond) braided carbon fibre-epoxy circular composite tube was performed and the damage process was characterised by synchrotron X-ray computed tomography (CT). A number of damage modes and their damage sequence has been identified and monitored globally and in more detail within a representative region of interest. In particular, intra-tow cracks and inter-tow debonding have been found to occur almost simultaneously at low shear strains (1.5%). It is noteworthy that inter-tow debonding was initially constrained within repeated braid units before propagating and connecting with other damage modes in 3D. The area fraction of inter-tow debonds was quantified at different stages and it was found to dramatically increase with increasing shear strain beyond 1.5%. The total volume fraction of the observed intra-tow cracks of various forms was seen to grow rapidly beyond shear strain of 2.0%. Beyond the peak shear stress (at a shear strain of 2.5%), fibre micro-buckling and kink bands occur in the tows subjected to torsion induced axial compression at crimped regions close to tow crossovers. Tow crossovers control many aspects of damage propagation under torsion, positively by localising inter-tow debonds and negatively by initiating fibre micro-buckling.

中文翻译：

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用原位 X 射线计算机断层扫描研究扭转作用下编织复合管的损伤演变

摘要 在这里，我们首次对碳纤维增强聚合物 (CFRP) 复合材料管在扭转情况下的损伤演变进行了实时三维 (3D) 观察。进行了1/1 45°（金刚石）编织碳纤维-环氧树脂圆形复合管的原位扭转试验，并通过同步加速器X射线计算机断层扫描（CT）表征了损坏过程。许多损坏模式及其损坏顺序已在全球范围内被识别和监控，并且在感兴趣的代表性区域内更详细。特别是，已发现在低剪切应变 (1.5%) 下，丝束内裂纹和丝束间脱粘几乎同时发生。值得注意的是，在传播和连接 3D 中的其他损坏模式之前，丝束间脱粘最初被限制在重复的编织单元内。在不同阶段量化丝束间脱粘的面积分数，发现它随着剪切应变增加超过 1.5% 而显着增加。观察到的各种形式的丝束内裂纹的总体积分数在超过 2.0% 的剪切应变时迅速增长。超过峰值剪切应力（剪切应变为 2.5%），纤维微屈曲和扭结带出现在丝束中，在靠近丝束交叉处的卷曲区域受到扭转引起的轴向压缩。丝束交叉控制扭转下损伤传播的许多方面，积极地通过定位丝束间脱粘和消极地通过启动纤维微屈曲。观察到的各种形式的丝束内裂纹的总体积分数在超过 2.0% 的剪切应变时迅速增长。超过峰值剪切应力（剪切应变为 2.5%），纤维微屈曲和扭结带出现在丝束中，在靠近丝束交叉处的卷曲区域受到扭转引起的轴向压缩。丝束交叉控制扭转下损伤传播的许多方面，积极地通过定位丝束间脱粘和消极地通过启动纤维微屈曲。观察到的各种形式的丝束内裂纹的总体积分数在超过 2.0% 的剪切应变时迅速增长。超过峰值剪切应力（剪切应变为 2.5%），纤维微屈曲和扭结带出现在丝束中，在靠近丝束交叉处的卷曲区域受到扭转引起的轴向压缩。丝束交叉控制扭转下损伤传播的许多方面，积极地通过定位丝束间脱粘和消极地通过启动纤维微屈曲。