Of Fiber Reinforced Composite Residual Stress Measurement

For the existence of the residual stress of materials, structure of fatigue intensity and life etc have great influence on the performance.The size of the residual stress, direction and distribution with the manufacture processing or treatment methods varing ,the randomness of the residual stress mainly adopts experiment method in country and abroad. In recent years,the development of materials science, made of composite materials used in modern engineering more and more widely, of which the most widely used is fiber reinforced materials with the maximum amount. It is the proportion of small, high strength and modulus, in aerospace, automotive or medical applications has irreplaceable advantages.Composite materials is a matter of two or more different combination in different ways, although with the advantages out of a single material , but after processing, the shrinkage in all directions is inconsistent.After curing, the internal of composite will exist residual stress, resulting in lower component of the strength, fatigue and even damage, and resulting in greater losses.?The residual stress of composite should not be ignored.Therefore, the accurate measuring the residual stress of composite material component has important meaning.In measuring residual stresses ways, drilling method, cutting method and the transfer layer method belong to mechanical measurement methods, thiese testing methods are harmful, causing some damage to the components, but the ways is mature, high accurate; X ray diffraction, neutron diffraction, and other physical measurement, is non-destructive components, but these only limitations on the crystallization of isotropic homogeneous materials, and equipment was expensive, difficult to spread.Drilling hole method develop to be a mature way and is widely used testing methods of residual stress that it is simple, high precision, small ?damage on the component. In this paper, combination of photoelastic coating technique is proposed based on blind hole method to measure the residual stress of composite materials, using computer image processing technology to extract the strain fringes of the hole, according to anisotropic elasticity theory and the residual stress release standard, the residual stress in measured point can be calculated. This method is simple convenient, accurate, strongly intuitionistic, and full, for measurement of the composite structure of strain, The paper detail the measurement principle and measurement methods. As reinforced polypropylene and carbon / epoxy composite material example, actual measurement of the isotropic material and orthotropic materials the residual stress are done, and achieved to a satisfactory results.At the same time,simulation is done using finite element compared with experiment.