Accession Number : ADA119912

Title :   Further Trials of a Strain Hardening Index of Fatigue Damage.

Descriptive Note : Final rept.,

Corporate Author : NAVAL RESEARCH LAB WASHINGTON DC

Personal Author(s) : Krafft,J M

PDF Url : ADA119912

Report Date : 28 Sep 1982

Pagination or Media Count : 22

Abstract : Previous cyclic-strain;, smooth-specimen fatigue tests of alpha-beta titanium alloys displayed an anomalous endurance enhancement for some of the alloy conditions. This could be explained by associating resistance to fatigue damage directly with the stress-normalized plastic strain hardening rate at the point of maximum cyclic tensile stress. Since this rate also controls the extent of stress-relaxation-induced tensile creep strain in each cycle, it was thought that fatigue damage might be associated with it. To test this hypothesis, data with varied load hold time, and over a full range of cyclic life, is reported here for some of the previously reported alloys of Ti-6A1-4V, as well as for an A36 steel plate. Notch fatigue tests of the A36, combined with those of Yoder et al for the titanium alloys, are compared to the smooth specimen data. Results tend to support the damage-inhibiting role of the plastic strain hardening rate, but not of the creep strain portion of each cycle. Notch fatigue data agrees with smooth specimen trends if Neuber's rule is used to characterize the stress concentration factor, particularly with the A36 steel. As with Yoder's notch fatigue results smooth specimen LCF life, though quite different in the range less than a thousand cycles, tends to converge near the endurance limit, thus mitigating adverse effects of alloy conditions which favor resistance to fatigue crack propagation in alpha-beta titanium alloys. (Author)

Descriptors :   *Steel, *Titanium alloys, *Strain hardening, *Fatigue(Mechanics), *Crack propagation, Fatigue life, Heat treatment, Microcracking, Stress concentration, Modulus of elasticity, Plastic properties, Failure(Mechanics), Tensile stress, Stress relaxation, Notch toughness, Factor analysis, Stress strain relations, Displacement, Creep, Fatigue tests(Mechanics)

Subject Categories : Metallurgy and Metallography
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE