Castable Plastics in Photoelastics Stress Analysis

Citation

Matzdorff, Roger Edward (1950) Castable Plastics in Photoelastics Stress Analysis. Engineer's thesis, California Institute of Technology. doi:10.7907/1CAZ-4A36. https://resolver.caltech.edu/CaltechETD:etd-02182009-112040

Abstract

An investigation was begun on the feasibility of utilizing castable, thermosetting plastics in experimental stress analysis by means of either photoelasticity or electrical strain gages imbedded in the plastic. The first phase of the study was the development of a casting technique that would give a stress free casting suitable for photoelastic work. This was considerably complicated by the inherent shrinkage which occurs during the polymerization of the plastic. A good method was found for casting solid models, and a workable method was devised for casting hollow section models. The second phase constituted the development and evaluation of the optimum physical properties of a resin known as Castolite. The results were encouraging with the exception that the strain creep was excessive. The rate of creep, however, is slow and it is possible to use the material for two dimensional photoelasticity with results comparable to those obtained from other photo-elastic materials. The desirable features are a very low optical creep, stress-strain and stress-fringe number curves that are linear for constant loading time, no time-edge stress effects, chemical stability under high temperatures, modulus of elasticity of 600,000 psi, and a fringe value of 175 psi per in-fringe in tension. An additional feature is the ability to bond two or more cured plastic pieces together with the liquid plastic itself. The strength of the bonded area is equal to the rest of the structure. Three dimensional frozen stress properties were not determined, but there is evidence that the resin would be suitable.

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