Instytut Podstawowych Problemów Techniki

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A three-dimensional photoelastic model investigation of a body with voids loaded by uniform pressure on the external surface is presented. The model represents a certain rock region weakened by the crossing of a shaft with a horizontal excavation. The ″stress freezing″ technique was applied by loading the model hydraulically in a special container. The results are presented in the form of stress diagrams in the characteristic cross sections. In the introduction a short review of the most important prublications dealing with photoelastic rock investigations in mining is given.

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The authors present a certain method of investigation of twodimensional photoelastic models with rigid constraints. It consists in the fact that cementing of constraints with the model is performed under
load, and photoelastic investigation — without external loads.
In the paper are presented advantages of the method , particularly when being used together with a conventional investigation.
The method is presented on an example of a halfplane under uniaxial load, the boundary of which is attached to a rigid constraint of finite length.

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The paper contains an example of application of the photoelastic method to designing of a dam buttress. Testing procedures are described, special attention being paid to the method of realization of a uniform loading along the boundary of the model. Program of investigations is suggested rendering it possible to determine an optimum crosssection of the dam buttress.
In the paper is described the optimization procedure of the shape of the dam buttress based on the results of photoelastic investigations. As the optimization criterion is assumed the condition of minimum volume of the buttress at a determined stress value on the upstream side. Optimum section parameters calculated on the ODRA 1204 computer are presented in the form of tables and diagrams.

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The problem of determination of shapes of plane structures satisfying the condition of constant boundary stresses is formulated in the paper. Survey of relevant literature on this subject is given. Moreover, an experimental method consisting in improving the initial model by adding or substracting some material is presented in a more detailed manner. The displacement of the boundary calculated on the basis of photoelastic investigations and an approximate value of the stress gradient give the new improved shape of the model. This procedure may be repeated as long as the uniform boundary stress is obtained. The method described is illustrated on the example of determination of the transition line between a column and a beam.

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The paper concerns the method of determination of the stress distribution in a turbogenerator rotor by means of photoelastic methods. General formulation of the problem reduced to the plane
case is presented.
A short survey of the photoelastic methods is given as applied to the investigation of rotating elements, and the technique used by the authors is described. I t consists in making photoelastic
photographs of a rapidly rotating model by using flash sources of light. In describing the experimental stand, attention is drawn to certain improvements, e.g. free suspension of the rotating
model on an elastic shaft with oil damper and the coupling of the shutter of the camera with the photoelastic cell and flash lamp.
On the basis of the performed experiments it was proved that the method is applicable to this kind of investigations, although (this follows from the available literature) the method has not been widely used.

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First the application of the two basic types of models is described and the range of applicability of the photoelastic methods in investigations of water dams is presented.
An example is given of the application of photoelasticity to experimental verification of the cross-sections of a buttress dam as determined by the designers. A "semi-spatial" model made of hard resin was investigated in two cases: loading only a) by its own weight, b) by its own Weight and hydrostatic pressure. The state of stress due to its own weight was modelled by the method of rotation making use of the "frozen-stress" method. The photoelastic picture of stresses due to case b) was obtained by loading the model with the "frozen" state of stress due to the weight of the sample by a hydrostatic pressure; to obtain the latter a hydraulic device was employed, which was designed for this experiment.
To ilustrate the results the isochromes, boundary stresses and the employed apparatus are presented. Finally the results of the investigations are given as well as conclusions and suggestions concernning
the design. The investigations constitute a part of the work of the Stress Analysis Division, on photoelastic investigations on two dams: a buttress and a gravity dam.

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The problem of stresses in a triangle loaded by own weight is discussed. Six models have been tested with the following ratios of the Young moduli of the triangle and the foundation; 0.011; 0.36; 0.82; 1; 2.76; 90. The introductory experiments were based on the centrifugal method combined with freezing; then the flash light method has been employed. In the latter tests the models were made of high-sensitive rubberlike epoxy resins polimerized in the laboratory of the Institute.
Special equipment designed and built in the Laboratory of Stress Analysis of the IBTP-PAN has been described.
A brief discussion of the obtained results follows, and the idea of a new method is outlined enabling us to obtain a more correct stress distribution in the case when a field of gravitational, forces is acting upon a body composed of parts having different elastic properties.

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