Development studies on in-situ observation apparatus of microscopic damage for durability evaluation of high-temperature composites under HSCT simulated environment

为了评估和保证先进的CFRP层合板结构的耐久性，有必要制定的破坏过程，包括横向裂纹的萌生和扩展，分层，纤维失效，直到最终断裂。针对高温复合材料在HSCT模拟环境下的耐久性评价问题，研制了一套高温复合材料细观损伤原位观测装置，并在此基础上开发了有限元分析程序，对材料的破坏过程进行了模拟。在实验中确定了以下故障阶段，并从理论上进行了阐述：（1）在90度层中横向裂纹的产生，（2）多个横向裂纹的演变，（3）在横向裂纹尖端处产生的分层的产生和增长，以及（4）纤维失效。我们成功地提出了一个新的有限元程序，以更严格的方式来表征90度铺层中横向裂纹的萌生。该程序具有以下特点：（1）实现了聚合物基体的弹塑性行为;（2）引入了内聚单元，对横向裂纹的萌生和扩展进行了物理理解;（3）引入了Weibull-of-Weibull模型，对沿着纤维长度的多纤维失效进行了描述。

In order to evaluate and assure the durability of advanced CFRP laminate structures, it is necessary to formulate the failure process including initiation and growth of transverse cracks, delamination, and fiber failure up to the final fracture. The allowable design strain is still limited due to lack of accurate formulation of the failure process.In the present study, the authors developed an in-situ observation apparatus of microscopic damage for durability evaluation of high-temperature composites under HSCT simulated environment Based on the experimental results, finite element analysis(FEA) code was developed to simulate the failure process up to the final fracture. The following failure stages were identified in the experiments and theoretically formulated : (1)initiation of transverse cracks in 90-degree plies, (2)evolution of multiple transverse cracks, (3)initiation and growth of delamination generated at the transverse crack tips, and (4)fiber failure.In particular, we successfully presented a new FEM code to characterize the initiation of transverse cracks in 90-degree plies in more rigorous way. This code includes the following features : (1)Elasto-plastic behavior of the polymer matrix was realized, (2)Cohesive elements were introduced for physical understanding of transverse crack initiation and growth, and (3)The Weibull-of-Weibull model was introduced to formulate the multiple fiber failures along a fiber length.