On the interpretation of shadow-moiré fringes

Shadow moiré is presented as one of the methods used to determine loci of constant height in curved surfaces (isotathmics). A general expression to interpret the fringes is derived taking into consideration possible rotations and translation of the grating. A discussion of the influence of such rotations and translation on the sensitivity of the response is also presented. Furthermore, simplified equations are obtained for particular cases of practical interest. An example of application to the case of an inverted perforated tube is shown.     

Experimental means of analyzing stresses and strains in rocket propellant grains

This paper reviews several methods used by the author in the stress analysis of rocket propellantgrain models with different boundary conditions, subjected to different loading conditions. The objective of the analysis is to help the designer to develop a stress-wise better grain configuration. Some assumptions have to be introduced to attain this goal in a practical way since some propellants behave nonlinearly, nonelastically, and are heterogeneous and anisotropic. Several indices are presented to evaluate designs. The method used by the author to “optimize” designs is also presented.     

Determination of loads between elements in granular media

A procedure is explained in this paper to determine the magnitude of several in-plane loads (normal and shear) applied to the outer boundaries of contacting particles used to model granular media. The approach is general, but in the test the particles have been modeled using disks. Maximum shear stresses at selected points in the field of the disks were determined photoelastically. The original equations of Hertz, as presented by Poritsky, permit the use of coefficients of influence for the computation. Examples of application and estimates of the precision obtained are also given.     

Experimental analysis of slow viscous flow using photoviscosity and bubbles

Photoelasticity in solids is a well-developed technique for stress and strain analysis. Less progress has been made in applying a similar effect, photoviscosity, to flow analysis. This paper has three objects: (1) to simplify photoviscous methods; (2) to compare velocity profiles obtained from photoviscosity with those obtained by the double-exposure bubble technique; (3) to determine the principal strain rates and the maximum shear stress from photoviscotity. The problem of slow viscous flow about a cylindrical obstacle in a rectangular channel was selected for the comparison. The fluid was a suspension of milling yellow dye in water. Strain rates and stresses averaged over the path of ligh can be obtained easily using photoviscosity. The bubble technique is shown to be a very powerful tool that permits the determination of the velocity field in three-dimensional problems.     

Experimental study of large-diameter thin-wall pressure vessels

An experimental stress analysis of three cylindrical pressure vessels with radius/thickness ratios ranging from 100 to 238 and different head closures is described. Brittle coatings and electrical strain gages were employed to determine stress distributions over the entire outer surface of the vessels. Electrical strain gages alone were used to determine stresses on the inside surface of the vessels. Particular emphasis was placed on determining stress concentrations and on nonlinear effects produced by geometric imperfections. An attempt was also made to correlate the failure, which started in the cylindrical portion of the three vessels, with the elastic-stress distribution. It was found that the imperfections in the cylinder were not significant if the vessel was fabricated from a ductile steel. However, if the vessel was constructed from a high-strength but brittle steel, the imperfections significantly lower the bursting strength of the vessel.