Determination of Initial Stresses by Measuring the Deformations Around Drilled Holes

Methods have been proposed for determining the inherent stresses in structural components by disturbing their stress equilibrium through some mechanical device and measuring the resulting deformations. This principle is the basis of the stress methods of E. Heyn and O. Bauer, the casting of stress grids for determining the tendency of various cast irons to develop stresses, and the drilling methods of G. Sachs. These methods have the disadvantages, however, that they can be successfully used only with specially shaped pieces (e.g., those with round or rectangular cross-sections), that every form of test piece requires another kind of injury and hence of calculation, and that the tested parts are rendered useless. In part, moreover, only mean stresses can be determined, which may differ greatly from the maximum stresses. The new test method, which seeks to eliminate these disadvantages, is likewise based on a disturbance of the equilibrium of forces, and is done by drilling a hole, which, however, is so small that the part can be used again. This method serves, among other things, for determining the inherent stresses in castings, welded parts, rolled structural shapes, and finished structures.