January 07, 2004
Book "Physical bases of the metal magnetic memory method"
UDC 620.179.14
ISBN 5-8122-0265-6
Publisher – ZAO "TISSO", Moscow, 2004, 389 p.
The book "Physical bases of the metal magnetic memory method" is developed by candidate of technical science Vlasov V.T. and by doctor, professor of the "Power equipment repairs and modernization" Chair of the Institute of State Employees’ Qualification Improvement Dubov A.A.
The history and logic of magnetism science development is considered. Based on design and experimental researches, development of the domain structure theory is given on the example of pure polycrystalline iron from positions of modern knowledge in quantum physics, dislocations theory and fracture mechanics.
A unique effect – magnetoplastics, being the basis of the metal magnetic memory method (MMM) is presented and scientifically substantiated for the first time.
The diagram of magneto-mechanical states of a ferromagnetic at force and magnetic fields interaction is developed. Definition of weak and strong magnetic fields from positions of their energy interactions with force fields is first given.
Boundary conditions and MMM application scope are established.
Metal fatigue damaging physics if considered and the model of the fatigue damaging accumulation process is suggested, revealing the possibility of quantitative assessment of the material's state at MMM and other methods application.
Intended for non-destructive testing and engineering diagnostics specialists, research engineers, students of higher educational establishments, technical and engineering employees of machine-building enterprises and occupied in various branches of industry, dealing with the problem of reliability assuring at operation of equipment and structures.
Foreword
Modern diagnostics of structural materials' state, possessing a large range of various physical methods and means, is not already limited by the tasks of non-destructive testing, but is more and more used at solution of the tasks of determination of mechanical characteristics of materials, and methods and means of residual and operation internal stresses measurement occupy the principal place. Magnetic methods of non-destructive inspection became wide spread among these methods.
All the known magnetic methods of structural materials diagnostics, being mainly ferromagnetic, can be divided in two groups: active, with creation of "forced" magnetic field of specified orientation in the material of the investigated part, and passive, using the product residual magnetization caused by external magnetic fields of natural or artificial origin.
Active magnetic methods use the dependence of the material's magnetic characteristics on its structure or phase state determined by the material's technological or operational pre-history, and start changing significantly only at sufficient mechanical stresses, being close to limiting ones. At the same time, practically complete absence of sensitivity to material anomalies, located deep inside the part, limits the potential of active magnetic methods.
The known passive magnetic methods of diagnostics of ferromagnetic materials' stress-strained state represent a more sophisticated tool, however, they are also characterized by low sensitivity to anomalies, located deep inside the material, and ambiguity of the material's state assessment results.
The Metal Magnetic Memory method (MMM) occupies a special place among passive NDT methods. This is the second method after the acoustic emission, using the internal energy of materials.
For many years, in the course of a complicated struggle, the MMM method has been gaining its right for recognition, proving with numerous practical results its indisputable effectiveness at assessment of a stress-strained state and early diagnostics of fatigue damages of equipment and structures at objects of power, petrochemical, machine-building industry as well as of various types of transport.
Based on the analysis of experimental investigation results and on practical diagnostics of engineering objects' state in various branches of industry, the conclusion on presence of at least three kinds of physical effects underlying the MMM method was made.
Indeed, it can be immediately said that one of the effects is the magnetoelastic one, which is known for a long time and seems to be thoroughly investigated.
The second effect can be referred to the phenomenon of dispersion of external magnetic fields by discontinuity flaws or structural inhomogeneities of the investigated material, which is well investigated at the influence on ferromagnetic materials with strong magnetic fields, but which, certainly, exists at weak magnetic fields as well.
The third effect was presumably referred to processes of magnetic fields interaction with dislocations and their clusters. The direct experimental proof confirming significant increase of dislocations density in stress concentration zones was obtained at tensile testing of steel samples using special-purpose magnetometers and at investigation of foils dislocation structure using electronic microscope.
However, despite the large number of works on magnetism and, in particular, on investigation of magnetoelasticity and features of ferromagnetic materials behavior in external magnetic fields on the one hand, and on solid-state physics and physical metallurgy on the other hand, there was no more or less convincing explanation of physics of effects used by the MMM method till date. The correct idea of the method physics is necessary for creation of theoretical model and development of quantitative criteria for materials' state assessment.
It was established experimentally that the MMM method uses dependence of the internal magnetic field parameters, registered on the surface of a product under diagnostics, on macrocharacteristics structural ferromagnetic materials' stress-strained state (SSS). In other words it can be said that the MMM method is based on little-studied macroeffects, being the consequence of correlation and indirect interaction of force fields with electromagnetic fields of microparticles, sequentially forming an atom, a primitive lattice cell, then its unit cell, the lattice itself, a domain, and, finally, a domain group on condition of the lattice imperfection due to its defects (interstitial atoms, lattice vacancies, dislocations and twins). The aim of this work was explaining of these macroeffects reflecting the domain structure changing and creation of theoretical model of the MMM method.
The task put in such a way arose neither in the theory of magnetism nor in the materials science or strength theories (including elasticity, plasticity and fracture mechanics). However, a large number of experimental data and theoretical conclusions, required for solution of the set task, is accumulated in these branched of science. Besides, as it will be demonstrated below, it was impossible to solve the task without application of initial knowledge in the field of quantum physics.
The book was written at the creative cooperation of authors, at which the design investigations were continuously compared to and corrected according to results of experimental investigations, obtained during more that a 20-year experience of development and introduction of the MMM method to practice.
Certain results of theoretical investigations, presented in the book, may cause arguments among the readers, being not less than the MMM method itself. The book is intended for constructively working specialists, scientists and experts able to perceive critically any well-established theories and ideas in the field of the magnetic phenomena physics, the materials science, fracture mechanics and engineering diagnostics.