STP467

    The Role of Residual Stresses in Increasing Long-life Fatigue Strength of Notched Machine Members

    Published: Jan 1970


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    Abstract

    High compressive residual stress and high hardness were utilized to obtain high fatigue strength in nonrotating bending. A compressive residual stress of 250 ksi, obtained in a 0.25-in. notch in SAE 1045 specimens of 1.50-in. diameter, resulted in a one million-cycle fatigue strength of ±230 ksi. An investigation showed that, over the range studied, maximum residual stress from heat treatment was produced with maximum hardness, medium carbon content, maximum section size (to 4-in. diameter), and minimum hardenability. At high hardness, cold working by shot peening was found to decrease the high residual stress from heat treatment. Fatigue tests were run on peened and unpeened specimens of various hardnesses with a machine that had provisions for applying a mechanical mean stress. Various net mean stress conditions, residual plus mechanical, could then be obtained. The fatigue strength of hard specimens with a tensile, applied mean stress was reduced by the presence of crack-like defects created by peening. Data were interpreted in terms of a theory in the literature involving crack initiation, crack propagation, and yielding.

    Keywords:

    fatigue strength at N cycles, residual stress, notch sensitivity, steels, heat treatment, shot peening, crack initiation, crack propagation, yield strength, fatigue (materials), hardness, tests, evaluation, residual stress relaxation


    Author Information:

    Nelson, DV
    Research engineer, research physicist, and staff physicist, Caterpillar Tractor Co., Peoria, Ill.

    Ricklefs, RE
    Research engineer, research physicist, and staff physicist, Caterpillar Tractor Co., Peoria, Ill.

    Evans, WP
    Research engineer, research physicist, and staff physicist, Caterpillar Tractor Co., Peoria, Ill.


    Paper ID: STP26849S

    Committee/Subcommittee: E08.01

    DOI: 10.1520/STP26849S


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