Solving Internal Stress Measurement Problems by a New Magnetoelastic Method

Abstract

Nondestructive measurement of internal stresses has conventionally been restricted to the utilization of x-ray diffraction method that yields absolute stress values under certain physical conditions. This method is, however, accompanied by a number of drawbacks, such as shallow depth of penetration and high cost. It is also very difficult to use it to the continuous monitoring of internal stresses in industrial processes.

In this paper, magnetoelastic interaction was used to evaluate the internal stresses through analyzing the statistics of magnetization transitions (Barkhausen noise). These transitions were excited by a controlled magnetic field and detected electro­magnetically. The average amplitude of the signal generated by the transitions was used to characterize the transition statistics. It has been shown that this amplitude is very sensitive to the stresses in the material and can be applied to nondestructive stress measurement in ferromagnetic materials.

This paper will present the results of stress measurements using the above principle in several practical applications. The results show the potential of this method both in the laboratory for static measurements and in process control for dynamic, continuous monitoring of the stress level. The advantages, as well as the disadvantages, of this method over the conventional ones are discussed.