The Experimental Studies Of The Mechanical Properties Of The Composite Materials And An Implementation Technique Of Moire Interferometry At Worksite

The composite materials have been becoming more and more important new materials for engineering structures in recent twenty years, but it is difficult to study the mechanical properties of the composite materials due to their varieties and complexity. Because of the distinguishing qualities of the moire interferometry method such as whole field measurement, real time observation, and high sensitivity, this method is becoming an important technique in studying composite materials.By considering the fact that many factors may lead to errors in the actual problem of measuring the in-plane displacement and strain, a grating compensation device and an lighting system are designed based on the theory of interferometry. The measured in-plane displacement and strain can be compensated accurately and quantitatively by using this device and system. A strict demonstration is also given by using the theory of light interference.At present, moire interferometry method is still limited in the laboratory and is incapable of solving many engineering problems. In this thesis, the technique of replicating deformed grating from the surface of the test body at worksite is investigated, and methods for solving all kinds of problems e-merged in the technical processes are analysed. On the basis of light-vector analysis method and the theory of light interference, several methods for extracting strain and displacement information are studied. The potential virtues of the moire interferometry method can be available by the technique of replicating at worksite and measuring in laboratory.As an important application of the technique of replicating deformed grating at worksite, the problems of the mode I crack growth in hybrid materials ARALL and GLALL under fatigue loading are studied. The crack tip strain field, crack opening displacement — COD and J-intergral are obtained. It isproved that COD and J-integral methods could be used as the criterion of the crack growth. The relationship between COD and J-integral is also obtained. The mechanism of the steadily growing crack of hybrid materials is analysed according to the principles of energy balance.As another successful application of replicating deformed grating, the joint effects of the interlamina shearing stresses caused by the solidification of materials and loads are studied. A comparison is also given between this method and the real time moire interferometry method.By using moire interferometry method, the whole processes of compres-sive damage of Kevlar 49/Epoxy composite materials are studied. Several types of damage are investigated. The mechanism of compressive damage is discovered.By using the hybrid method that combines moire interferometry method with the finite element method, two types of problems are studied. One is the hybrid displacement boundary value problem , the other is local full-displacement boundary value problem. By comparing with the experimental method and the finite element method respectively, the amount of the errors and the reason of the errors are analysed. In some cases, the problems , which can t be solved by using experimental method only, can be resolved by this hybrid method. Therefore, the hybrid method is useful in experiment stress analysis.On the basis of the validity of the hybrid method , the inverse problems of the finite element method are discussed. The structure stiff coefficients and stress situations could be solved by using this method. The analyses of several typical problems are presented.