Variation Of Internal Stress Research Articles

Stress relaxation, internal stress, and work hardening in some Bcc metals and alloys

The stress-time relation during stress relaxation is interpreted in terms of a power relation between dislocation velocity and the effective stress. Such interpretation gives not only the velocity-stress exponent, but also the internal stress in the work-hardened state. The velocitystress exponents thus obtained agree with those obtained from etch pit dislocation velocity measurements. The variation of internal stress with strain shows that work hardening is largely due to the development of internal stresses. The temperature dependence of flow stress arises from the increase of effective stress with decreasing temperature, consistent with a thermally activated process for dislocation motion.

Interpretation of High Coercivity in Ferromagnetic Materials

In the generally accepted theory of the ordinary magnetization curves of ferromagnetics, due to Becker, Kersten and many others, and fully described by Becker and Doring1., coercivity is related to the amplitude of internal stress variations through their effect on domain boundary movement. Although there can be little doubt as to the correctness of the basic ideas, or to their wide applicability, the treatment cannot account for coercivities of 500 oersted, and more, which are obtained in modern permanent magnet materials, without arbitrary and improbable assumptions about the magnitude and character of the internal stress variations. It occurred to one of us some years ago that for those alloys of the dispersion-hardening type for which the higher coercivities are found, an entirely different type of explanation might be possible, and some preliminary calculations gave promising results. This line of inquiry was interrupted by the War, and no more than vague references to it have been published2, though it has been discussed verbally and in correspondence with others interested. A systematic attack on the problem was resumed at the beginning of 1946, and a full account of the work has now been prepared. In view of the inevitable delays in publication a brief account may be appropriate here. It may be stated quite frankly that the immediate stimulus to this communication has been two short and admirable papers by Neel3, which have just appeared, and which show that he has been thinking along similar lines with particular reference to powder magnets.