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1、哈尔滨工业大学工学博士学位论文 - II - 不明显。试验结果表明，CFRP 层合板试样的冲击阻抗性能及损伤容限性能均 在冲击能量为 9J处发生突变。采用热揭层方法观测发现当冲击能量超过 9J后， 除基体裂纹和分层两种冲击损伤形式外，试样表面开始出现纤维折断现象，揭 示了当冲击能量超过阈值 9J后层合板冲击损伤发生突变的破坏机理。 本论文在适用于复合材料单向板改进的 Hashin失效准则基础上，建立了针 对本文采用的纤维织物增强复合材料的静态力学强度失效准则。在 Hou等人提 出的适用于复合材料单向板低速冲击失效准则的基础上，改进了纤维及基体破 坏的失效准则，建立了针对本文采用的纤维织物增强复
2、合材料层合板的冲击损 伤失效准则。本文通过引入复合材料基本强度参数预测不同孔隙率 CFRP 层合 板的力学性能， 并结合刚度突然退化模型， 采用 ABAQUS软件建立有限元模型， 较为准确地预测了不同孔隙率 CFRP 层合板的静态力学强度及冲击损伤投影面 积。 关键词：复合材料层合板；孔隙率；力学性能；湿热环境；损伤行为；强度预 测Abstract - III - Abstract Carbon fiber reinforced epoxy composites have been used extensively in various fields including the aerospa
3、ce, aeronautics, and defense industries, largely due to their outstanding specific strength and stiffness to weight ratios compared with conventional engineering materials, such as Aluminum and Titanium alloy. Voids are among the most common manufacturing defects in composites because of the special
4、 manufacturing process of CFRP structures. In general, voids have detrimental effects on the static strength and fatigue life of composite laminates. Furthermore, the main drawback of composite laminates is their susceptibility to internal damage when they are subjected to low-velocity impact, and e
5、ven minor damage can cause considerable reduction in the structural integrity. Voids always cause a greater susceptibility to water penetration and environmental conditions. Because the voids accelerate moisture absorption for the composites in the hygrothermal conditions, which results in the degra
6、dation in the properties of composite laminates. However, there are few researches published on the role of voids on mechanical performance when laminates are exposed to hygrothermal and drying environments. The objective of this research is to investigate the effect of voids on the static mechanica
7、l performance, bending fatigue and impact properties of CFRP laminates that are respectively exposed to room temperature, hygrothermal and drying environments. A finite element analysis model is established to simulate the static mechanical performance and impact damage of laminates with different p
8、orosities. The paper investigates the effect of porosity and hygrothermal conditions on the void microstructure, curing degree, Barcol scale of hardness and the static mechanical performance of CFRP laminates. The experimental results show that porosity has detrimental effects on the static strength
9、 of composite laminates. ILSS and compressive strength decrease significantly with the increasing void contents, while the minimum rate occurs in tensile strength. The effect of hygrothermal conditions on the static strength of composite laminates is discussed in the paper. Compared with the non-age
10、d specimens, ILSS and compressive strength of aged specimens decrease significantly with the similar porosity. For a similar porosity, the tensile, compressive strength and ILSS of the dried specimens are lower than those of the non-aged specimens, yet higher than those of the aged specimens. The be
11、nding strength of aged and dried specimens is higher than that of the non-aged specimens in the case of the similar porosities. Studied with the metallurgical microscope and scanning electron microscope (SEM), matrix cracks emanate from 哈尔滨工业大学工学博士学位论文 -IV- the void and penetrate by voids for the po
12、res can act as stress concentration points. The effect of porosity and hygrothermal treatment on the bending fatigue properties and residual bending strength of CFRP composite laminates are also investigated and discussed. The experiment results reveal that voids may cause a remarkable decrease in f
13、atigue life while exerting only a minor effect on the static flexural strength. With an increase in the number of loading cycles, the accumulation of irreversible structural damage leads to a change in the macroscopic mechanical properties of the composites, and have been studied by the metallurgica
14、l microscope and scanning electron microscope (SEM). Then, we test the residual flexural strength of CFRP laminates to study the changing macroscopic mechanical properties of the cumulative damage on the composite materials. The retentions of residual bending strength decrease with the increasing vo
15、id contents. The influence of porosity, environmental factors and impact energy on impact resistance and damage tolerance properties of CFRP laminates are evaluated. For the same impact energy, the dent depth and damage area increase with increasing void contents. TAI decrease significantly with inc
16、reasing impact energy, while no obvious effects of void contents on the TAI are observed. The curves of impact resistance and damage tolerance mutate at the impact energy of 9J. The thermal deply technique indicates that fiber cracks can be observed in the plies of the specimens, include the types of impact damage of matrix cracks and delamination while the impact energy increases to 9J. The paper reveals the failure mechanism of impac
