钻孔法和光栅应变花测试复合材料的残余应力

A Study on Grating Rosette and its Application in Measuring Residual Stresses of Composite Material

残余应力对材料、结构的疲劳强度和使用寿命等性能的影响早已为人们所熟知,由于它的大小、方向和分布随制造加工或处理方法不同而有很大的随机性,国内外对它的研究很重视。对于各向异性的复合材料,随着加上生产制造过程及工艺参数的不同,其中的残余应力的大小、方向等就更加复杂。从国内外对残余应力的研究中,可以看出大多数都着重于实验研究。本文应用钻孔法和云纹干涉技术的成果,针对残余应力测试中的特点,尤其是在利用钻孔法和云纹干涉技术测试残余应力时存在的问题,在目前绝大多数云纹干涉技术所使用的正交光栅的基础上,提出并研制出一种三个方向的光栅,即在原来 0°、90°两个方向光栅上,再加上一个 45°方向的光栅,在进行云纹干涉测试时,一次加载时就可以同时测试出三个独立的位移场:u场、v场和s场,利用这三个位移场就可以得到相应的三个应变:ε0、ε90和ε45,进而可以计算得到相应的应力。

Residual stresses are induced during most manufacturing processes involving material deformation, heat treatment, machining or processing operations that transform the shape or change the properties of a material. Residual stresses may be sufficiently large to cause local yielding and plastic deformation, and can severely affect component performance. For this reason it is vital to deduce the residual stress states either from measurements or modeling predictions. Because of the randomness of residual stresses, it is very difficult to study the problem by theory. The present treatment generally emphasizes on methods of measuring residual stresses. In this paper, a grating rosette was made. A grating with 45° angle was added to the crossed grating (0° and 90° direction), so that the grating rosette could contribute three directional deformation fields to this kind moiré interference technique. It should be stressed that in moiré interferometry simple grating or crossed grating is applied in general. In crossed grating moiré interferometry, two fringe patterns can be obtained to determine the full strain evaluation ( ε\-1, ε\-2 and γ\-(xy)). For measuring residual stress, if the specimen was moved during drilling hole, it is very difficult to reposition it with high precision. There must be errors as we compared the corresponding moiré patterns (before and after drilling) to determine the full strain evaluation. Especially as computing γ\-(xy) by the derivatives of two fringe patterns, a very small rotation of specimen may result in sizable errors.