有机玻璃残余应力与双折射条纹的关系

 本文通过实验,讨论了有机玻璃残余应力与双折射条纹（冻结应力条纹和热应力条纹）的定量关系,得出可以根据热应力条纹由应力光学定律直接获取有机玻璃残余应力的结论。作者基于这一论点,考察了不同冷却条件下平板有机玻璃残余应力沿断面的分布规律;研究了热处理工艺参数对消除有机玻璃残余应力的影响;测定了三种不同型号飞机舱玻璃的残余应力。

RELATIONSHIP BETWEEN RESIDUAL STRESS AND BIREFRINGENCE FRINGES IN POLYMETHYLMETHACRYLATE

It is one of the key technical problems for determining residual stress by means of photoelastic method to clarify the relationship between residual stress and birefringence fringes, i. e. isochromatic fringes caused by frozen stress and thermal stress, in polymethylmethacrylate （PMMA）.The relationship is investigated by means of annealing and making a cut in frozen stress specimen only containing the fringe caused by frozen stress and in the first slice of thermal stress specimen prepared by cooling only. It is concluded that the residual stress in PMMA depends only upon the thermal stress caused by cooling, and is irrelevant to the loads added at high elastic state and to the amount of the fringe caused by frozen stress, and furthermore the relationship between the residual stress and the amount of thermal stress fringe conforms to the stress-optical law. Equa-tion（ 3 ）is the expression for such relationship and can be used to determine the residual stress quantitatively in engineering. In illustration of application, the distributions of the residual stresses in PMMA specimens cooled at different speeds are examined （Fig. 9 ）, the residual stresses in two different types of canopies are determined （Fig. 10）, quantitative relationship between annealing temperature and residual stress is established （Fig.11）, and distributions of the residual stresses in DYB-4 PMMA in different parts of a canopy are considered. It is shown that the conclusions drawn in fhis paper may be useful for quantitative determination of residual stress in PMMA, and benefit the quality control, life prediction and failure analysis of PMMA airplane canopies.