NEW METHOD NDE RESIDUAL STRESS
Introduction
Internal stresses are to be considered as the following: 1) Operational strains referring to loads that the material is subject and calculated 2) Residual stresses in the material caused by heat treatments or stresses caused by welding, forging, casting, etc. The new technique is able to measure the applied load and residual stress that are balanced on the surface of the material, and in a relatively large volume, at times even the same size as the entire structures. This stress is part of the metal’s elasticity field and has a three axis spatial orientation.
Description
Elastic oscillations (also called vibrations) of an elastic material consisting of elementary masses alternately moving around their respective balance positions; these movements cause a transformation of the potential energy into kinetic energy. This phenomenon takes place due to reactions (elastic forces) that the aforementioned masses produce in opposition to elastic movements; these reactions are proportional according to Hooke’s Law to the same movements. The elastic waves that are produced propagate according to a fixed speed that depends on how rapidly the elemental masses begin to oscillate.
Elastic waves of this type are called “permanently progressive”, and they propagate at a constant speed which is absolutely independent of the speed with which the elemental masses move during the oscillating motion, and therefore also their respective oscillations. It is easy to verify that the elastic oscillations, from a material point P (in which the elemental mass m is supposedly concentrated) are harmonic. In reality, due to the fact that in any moment the elastic force that is applied to P is proportional to the distance x of the point from its position of balance 0, P acceleration (caused by the proportionality between the forces and the corresponding accelerations) is also proportional to x; this is demonstrated in the harmonic movement. The impulse creates in the metallic mass a harmonic oscillation (vibration) which is characterized by a specific frequency
