中文摘要：

有机玻璃是比较典型的粘弹性材料，基力学性能依赖于时间和应力水平。本文对有机玻璃的本构关系进行试验研究。首先，对有机玻璃进行不同应力水平下的蠕变试验。得出了与初始应力水平相关的蠕变关系式。在此蠕变过程中，有机玻璃会出现银纹化现象。本文利用光学显微镜观测了银纹的生长过程，得到不同应力水平下的银纹损伤值。通过定义损伤区的有效应力。导出了银纹区的应力一应变关系式。本文采用宏观和细观相结合的方法。研究材料在破坏之前的缺陷演化对材料力学性能的影响。所定义的损伤区应力以及由此导出的本构关系避免了文献中对相关问题不确切的假设，具有一定的适用性。

英文摘要：

PMMA（polymethylmethacrylate） is a typical viscoelastic material, and its mechanical properties strongly depend on time and stress. Its constitutive relationship is studied by experiment. First, creep tests are carried out under different stresses, and creep relationship that is relevant to initial stress is established. In the process of creep, craze damage in PMMA may take place. The craze process of PMMA is then observed with an optical microscope, and the craze images are transformed into damage data quantitatively by using MIAS（ micro-image analysis software）. Through defining the effective stress in damaged PMMA, the stress-strain relationship of damaged area is derived. The effect of damage evolution on mechanical properties of PMMA is studied by using a macro-description method combined with a meso-scale investigation. Compared with the traditional craze-stress hypothesis, the stress defined in this paper and the proposed stress-strain relationship in the damaged area are more rational and applicable.