Use of passive magnetic method for stress assessment

Many materials that could cause real threat of the catastrophe caused by fatigue wear, exceeding stress limits or emerging of plastic deformation have magnetic properties that could affect the local magnetic field. As far as quite well known and applicable are active magnetic method for condition monitoring, passive techniques which bases only on the existence of natural magnetic field of Earth still need researches and improvement. It is obvious that every physical object which enclose in magnetosphere interacts for Earth magnetic field, follows to special physics laws. Such objects could focus or deflect the magnetic lines around its matter. Own magnetic field of object: H = -nabla(w) where dasiawpsila-magnetic potential, is a function of magnetization gradient: w = w (div M). So, the measure magnetic field of object depends on object magnetization and distribution of this volume in medium (space). Considering magnetoelastic effects (Villary Effect, magnetostriction), the additional stress causes transformation to magnetic state of material which reflect to magnetization of object. Due to simply model analysis, the laboratory experiment was proposed and performed. Controlling plastic and elastic range of specimen deformation, there was proved that exist relation between stress and magnetization degree which is strict connected with the deformation and effort state. Magnetic anomalies which are generated due to magneto-mechanic effect were collected by the three axial fluxgate magnetometer what allows exhibition of the own magnetic field component, which is least sensitive for the disturbances which are present in the real world. In the paper, it was proved that exist dependence between the stress and magnetization degree but it is very complex because additionally it depends on the kind of material and magnetization, history of magnetization and on deformation and temperature. Calculation for model evaluation was performed. This leads to general dependence which allow for reliable stress estimation: M=M(stress, plastic strain, shape and dimension of object, measurement distance). Further directions and comments about development of the techniques which allows exact stress assessment of technical objects made with ferromagnetic materials, were included.