AN APPRAISAL OF THE PROT METHOD OF FATIGUE TESTING. PART I
Abstract
The validity of the equations of Prot (Rev. met. 45, no. 12:481 , 1948 and ibid 48:822, 1951) for fatigue testing under progressive loading was investigated. Conventional fatigue-test data were also obtained for comparison with the values of E (endurance limit) predicted by the progressive loading tests. Generally, the exponent n of alpha (loading rate) that gave the best approximation to a linear plot of the experimental data was about 0.371 and 0. 1786 for the ingot-Fe and 75S-T Al alloy, respectively. The value of the endurance limit for these materials was affected by completely reversed stresses whose amplitudes were smaller than the endurance limit. For high rates of load increase, the ingot-Fe failed by yielding before a crack appeared. The value of the endurance limit of ingot-Fe was only slightly affected by changes in n; a change of 34.8% in n resulted in changes of 3.67 and 6.35% in the endurance limit for tests started at initial stress levels of 10,000 and 30,000 psi, respectively. Raising the initial stress level from 10,000 to 30,000 psi raised the endurance limit of the ingot-Fe by only 800 to 1800 psi, the amount depending upon which value of n was used to interpret the data. Changing the initial stress level of the 75S-T Al alloy from 10,000 to 20,000 psi increased the indicated fatigue limit from 17,000 to 20,500 psi; as values determined by the Prot method correspond to an infinite number of cycles, these values were below the fatigue strength of 25,000 psi at 10 to the power of 8 as determined from the conventional S-N diagram.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1953
- Accession Number
- AD0001785
Entities
People
- A.p. Boresi
- T.j. Dolan
Organizations
- University of Illinois Urbana–Champaign