Abstract
The effect of external stress on the ferro-magnetism has been studied by many investigators, and recently Bozorth studied the strain sensitivity of permalloy to magnetism. According to the results of our experiment about changes of magnetic induction caused by tension and compression below the elastic limit, induction of mild steel increased rapidly as the increase of stress at first, and reaches to a maximum. Then induction decreases slowly as stress increases. When stress was small, the relation between induction B and stress σ would be represented by the following expression, and we obtained fairly good agreement between observed values and calculated ones. [numerical formula] where Bs is the saturation induction, B0 is the value of induction when σ=0, and c is a fundamental constant which depends upon materials, - for given material c=0.04. Generally, strain sensitivity ∧is a function of induction B, and it has a maximum value when the induction has a value corresponding to maximum permeability, and we found that the expression of strain sensitivity of permalloy, introduced by Bozorth, holds well for mild steel. In this case, it is assumed that the anisotropy constant of mild steel is about half of that of pure iron and perhaps it will be the effect of carbon.
