Development of Evaluation Methods for Microscopic Damage Initiation and Growth in Composite Material Systems for Simultaneous Material/Structure Optimization

细观损伤的萌生和扩展过程是损伤容限复合材料体系和复合材料结构构件优化设计的重要信息。在本研究中，发展了原位微观评价方法，以实验表征碳纤维增强高温聚合物基复合材料层合板在载荷作用下的微观损伤演化。采用了三种原位测量技术：原位光学显微镜(OM)、原位扫描电子显微镜(SEM)和原位扫描声学显微镜(SAM)。选用正交层合板定量测量了(1)90度层合板中横向裂纹的萌生，(2)多个横向裂纹的演化，以及(3)横向裂纹尖端的分层。在此基础上，提出了几种理论模型来解释CFRP层合板的微观损伤演化。[1]采用高温环氧树脂(TGDDM/DDS)、增韧或改性TGDDM/DDS和交错预浸料作为实验材料，研究了增韧交错对层合板分层抑制的影响。每种方法都提供了互补的信息。[3]成功地发展了微线或微网格方法，用于原位观察层间变形和损伤演化。[4]对疲劳加载下的损伤演化进行了量化，并与单调加载下的损伤演化进行了比较。在定性微观测量的基础上，建立了理论模型。

Microscopic damage initiation and growth procedure is the most important information for optimum design of damage-tolerant composite material systems as well as composite srucural members. In the present study, in-situ microscopic evaluation methods were developed in order to experimentally characterize the microscopic damege evolution in carbon fiber reinforced high-temperature polymer matrix composite laminates under loading. Three types of in-situ measurement techniques were used : in-situ optical microscope (OM), in-situ scanning electron microscoped (SEM) and in-situ scanning acoustic microscopes (SAM). Cross-ply laminates were selected for quantitative measurements of (1) initiation of transverse cracks in 90-degree laminas, (2) multiple transverse crack evolution, and (3) delamination from the tips of transverse cracks. Based upon the above observation, several theoretical models were proposed to explain the microscopic damage evolution in CFRP laminates.[1] High-temperature epoxy (TGDDM/DDS), toughened or modified TGDDM/DDS,and interleaved prepregs were used for experiments to study the effects of toughened interleaves on delamination suppression.[2] In-situ OM,SEM,and SAM were sucessfully used for damage evolution measurements in CFRP laminates. Each method provided complementary information.[3] Micro-line or micro-grid methods were sucessfully developed for in-situ SEM observation of interlaminar deformation and damage evolution.[4] Damage evolution under fatigue loading was quantified and compared with that under monotonic loading. Theoretical models were established based upon the qualitative imcroscopic measurements.