Abstract Carbon fiber reinforced polymer (CFRP) composites with remarkable mechanical properties are widely used in aerospace crafts as load-bearing components. However, harsh environmental conditions challenge the security design of lightweight composite structures. In this work, the effects of cryogenic temperature from 77 K to 298 K and cryogenic stability after 50, 100 and 150 cycles on the mechanical properties and failure modes of CFRP laminates with various stacking sequences were experimentally investigated. In-situ static tensile and three-point bending tests were conducted. A progressive damage model was developed based on three-dimensional (3D) Hashin criterion. Unique insights into the internal microdefect and damage evolution of laminates after 150 thermocycling were obtained by X-ray computed tomography (X-ray CT) technique. The results revealed significant degradation in tensile strength and modulus of laminates with the decrease in temperature due to changes in failure mode. The flexural properties improved by over 50% thanks to shrinkage in chemical bonding between matrix molecules. The influence of thermocycling on the mechanical properties was shown insignificant (0.2%–13%) under slow cooling rates. The degradation in properties of quasi-isotropy laminates looked more significant than that of unidirectional due to the coupling effect of thermal expanding mismatch between material (fiber and matrix) and layer. Quasi-isotropy laminated exhibited significantly greater microcrack volume fractions (more than 6-fold after 150 cycles). As thermocycling rose, the microcracks gradually expanded and nucleation occurred within the interfacial layer. The results here provide a way for the structure design of cryogenic composite tanks under complex working environments by studying the temperature effect.

中文翻译：

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碳纤维增强聚合物复合材料的力学性能和内部微缺陷演变：低温和热循环效应

摘要 碳纤维增强聚合物（CFRP）复合材料具有卓越的力学性能，作为承重部件被广泛应用于航空航天领域。然而，恶劣的环境条件对轻质复合结构的安全设计提出了挑战。在这项工作中，通过实验研究了 77 K 至 298 K 的低温温度和 50、100 和 150 次循环后的低温稳定性对具有不同堆叠顺序的 CFRP 层压板的力学性能和失效模式的影响。进行了原位静态拉伸和三点弯曲试验。基于三维 (3D) Hashin 准则开发了渐进式损坏模型。通过 X 射线计算机断层扫描 (X 射线 CT) 技术获得了对 150 次热循环后层压板内部微缺陷和损伤演变的独特见解。结果表明，由于失效模式的变化，随着温度的降低，层压板的拉伸强度和模量显着降低。由于基体分子之间化学键的收缩，弯曲性能提高了 50% 以上。在缓慢冷却速率下，热循环对机械性能的影响不显着（0.2%–13%）。由于材料（纤维和基体）与层之间的热膨胀失配的耦合效应，准各向同性层压板的性能退化看起来比单向层压板更显着。准各向同性层压板显示出显着更大的微裂纹体积分数（150 次循环后超过 6 倍）。随着热循环的增加，微裂纹逐渐扩大，界面层内发生成核。