METHOD OF MEASURING INTRINSIC STRESSES IN STRUCTURAL COMPONENTS OF MACHINES AND APPARATUS AND DEVICES FOR PERFORMING SUCH METHOD

Intrinsic stresses are stresses within structural bodies which occur without the action of external forces or torques. Such stresses may impair the mechanical strength, dimensional accuracy and ability to properly function, and for that reason must be known in order to satisfy exacting demands, for example, those to be met by the rotors of turbines or generators. For determining intrinsic stress, a measuring area on the surface of the body is provided with strain gages such as bonded wire strips, which furnish an electric magnitude in response to deformation. Thereafter, a ring-shaped groove or slot is cut around the measuring area. The cutting, such as by means of a milling tool, has the effect of reducing the intrinsic stresses in the retaining core within the ring. The electrically measured changes in elongation are a measure of the intrinsic stresses in the undisturbed region of the material prior to the cutting operation. By a stepwise cutting operation of the groove, non-uniform distributions of intrinsic stress can also be ascertained along the depth of the body.