Stresses in Pin-Loaded Glass-Epoxy Plates Using Transmission Photoelasticity
Materials which exhibit orthotropic elastic behavior, are birefringent, and which can be used for transmission photoelasticity studies are not commonplace. With the increasing usage of fiber-reinforced materials for advanced structural applications, there has been an interest in having such a material available. With a material available, the stress state around holes, notches, and other geometric discontinuities can be evaluated in much the same way they have been evaluated in isotropic materials, namely, by fabricating photoelastic analogues. Horridge (1955) and Hayashi (1958) were the first to suggest the concept of birefringent fiber-reinforced materials. However, Phi and Knight (1969), Sampson (1970), and Dally and Prabhakaran (1971) made significant contributions to the concept by advancing both the fabrication techniques and the characterization of materials which exhibited orthotropic elastic properties and which were transparent. The basis for these materials was the embedding of transparent glass fibers in an transparent epoxy matrix. The indicies of refraction of the glass and epoxy were matched so the composite was indeed transparent. There was considerable difficulty in fabricating the materials. The presence of voids, fiber sizing, index matching, and obtaining sufficient fiber volume fraction were just a few of the problems encountered. However, after considerable effort, sufficient quantities of the material could be fabricated so that specimens representing a fiber-reinforced structural component could be made and photoelastic data obtained. Since then Cernosek (1976), Prabhakaran (1976), Chandrashekhara and Jacob (1977), Agarwal and Chaturvedi (1978), Doyle (1980), and Chaturvedi (1982) have made contributions to the subject with both experiments and with the theory of characterization. Efforts have been made to use the material to study the stress state in problems of interest in the mechanics of composite materials (Yoloshin 1980, Prabhakaran 1982). This paper summarizes other work with the material to study the stress state in a problem of interest in the mechanics of composite materials. Specifically this paper examines the stresses around a hole in a plate that is loaded by a pin through the hole. The problem has a direct application to the connecting of composite structures. This paper describes the problem and the experimental set-up used to study it. Typical isochromatic and isoclinic fringe patterns are presented. A scheme to separate the stresses is discussed and then numerical results for the stresses around the hole are presented and interperted. Some of the work has been reported elsewhere (see Hyer and Liu 1984,1985).
KeywordsRadial Stress Fringe Pattern Circumferential Stress Experimental Mechanics Isochromatic Fringe
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