Connecting the mechanics of strength with ferromagnetism: theoretical basis of complex stressed state inspection

Zagidulin, Timur; Spector Sci-Tech LLC; Russian Federation

Zagidulin, R.V.; Spector Sci-Tech LLC; Russia
Zagidulin, T.R.; Spector Sci-Tech LLC; Russia

ID: ECNDT-0425-2018

Magnetic techniques of stressed state inspection of steel pieces and elements of structures use semi-empirical dependencies of structure-sensitive magnetic parameters on mechanical strain of metal value. A challenge to obtain their symbolic description in general cases of complex stressed state of metal (two- or three-axial) still have not any strict solution.

In order to simplify structural strength calculations the complex stressed state of metal in theory of strength is usually reducing to equal one-axial strain of metal. Applying this approach to existing symbolic expressions for structure sensitive magnetic parameters of linearly strained metal, we expanded ones in common case of complex stressed state.

Proceeding from the law of energy conservation the equation between increments of magnetized metal energy after and before deformation, and specific potential energy of deformation of metal, depending on the principal stresses obtained.

Solving the composed equation in some approximation allowed within ferromagnetism the symbolic expressions obtained, concluding to dependence of residual magnetization and residual magnetic field of metal on the components of complex stressed state.

The dependence verified experimentally throughout the range of deformation from quiescent state to destruction of metal in scientific researches carried by different authors. Its behavior influenced by large number of external factors are considering in dependence obtained: magnetic properties, relation between mechanical and magnetic states of metal, rate of principal stresses interconnection, their signs and bulk symmetry.

Obtained symbolic expressions, based on common hypothesis of mechanics of strength which suggests that any complex stressed state may be represented by equal one-axial stress, expands on structure-sensitive magnetic parameters: the mechanical strain value determined on empiric dependence of residual magnetic field on one-axial strain – this is total effective mechanical strain of metal in complex stressed state.