Prestrain Values Research Articles

The Effect of Plastic Deformation on the Magnetic Aftereffect in Iron

The interstitial diffusion-controlled magnetic aftereffect in polycrystalline iron was measured at 23°C and at a constant applied field in the Rayleigh region as a function of the amount of plastic prestrain in the sample (from 0.04% to 3.8% tensile strain). The magnitude of the aftereffect was found to vary with the strain ε according to the following relationship 1/Ba0 = k0+k1ε1/2, where Ba0 is the magnitude of the aftereffect (total aftereffect induction) and k0 and k1 are constants. The aftereffect magnitude Ba0 was found to be proportional to dB/dH for all the prestrain values of this investigation and therefore the decrease of Ba0 with strain was attributed entirely to increased, stabilization-independent, resistance to domain wall motion while the stabilization force remained constant with strain. The proportionality constant may be considered as a fictitious magnetic field Hf(Ba0 = HfdB/dH) with a value of 0.02 Oe for an iron sample which contains 23 ppm carbon and 20 ppm nitrogen. The aftereffect kinetics were found to be independent of prestrain, as reflected by the constancy of the ratio of the aftereffect induction of the nondeformed sample to the aftereffect induction of the prestrained samples over the time interval of the aftereffect.

Effect of Temperature on Stress-Corrosion Fracture

Abstract Prestrained samples of copper-beryllium alloy (1.8 Be, 0.3 Co) were exposed to an ammonia atmosphere at −20, 30 and 90 C (−4, 86, 194 F). It was found that the effect of temperature is related to the amount of plastic deformation. Above a critical value of plastic prestrain, temperature effect reverses; a longer exposure is needed to fracture a sample at 90 than at 30 C. This temperature dependence is explained by considering the number and distribution of dislocations.