Ammrc Cr 71-2/4 the Effects of Surface Layer on Plastic Deformation

In Chapter I, mptallographic evidence of the existence of the surface layer is given. Using etch-pit techniques on an ironsilicon alloy, it is shown that the dislocition concentration of strained specimens decreases away from the surface. In Chapter II, a relationship is given between the surface-layer stress and fatigue failure. When surface-layer stress attains a critical value, the specimens fractured. An excellent correlation is reported between the life predicted from surface-layer stress data and fatigue life found experimentally. In Chapter III, surfacelayer stress at the root of notches is reported. The surfacelayer stress was found to increase rapidly as the stress concentration increased. In Chapter IV, the crack propagation rate for an iron-silicon alloy is reported. The crack propagation rate under plane stress conditions decreased in specimens given the SLE treatment. An exam.nation of the surfaces showed that the dislocation concentration was much lower in the SLE-treated sample than in the untreated specimens. Chapter V reports an unsuccessful attempt to detect slip-line formation and strain under sustained loads up to 500 hr. It is believed that greater measurement sensitivity is required for successful detection.