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The subject of structural ratchetting, or cyclic strain accumulation has been developed primarily during the past 20 years. The major contributions to the literature in this area are reviewed, with particular attention to thermal ratchetting.
An attempt is made to classify the various types of strain accumulations that can be experienced by structures when they are subjected to cyclic loading. Under isothermal cyclic loading, ratchetting mechanisms may be classified as: (a) isothermal coaxial cyclic strain accumulation, (b) isothermal conjugate cyclic strain accumulation, and (c) complex isothermal cyclic strain accumulation. Cumulative stress relaxation growth, sometimes considered to be a form of ratchetting, is time dependent and therefore not properly a form of structural ratchetting.
Most investigations in structural ratchetting have been concerned with simple thermal ratchetting produced by cyclic temperature applications, in the presence of a sustained load or in materials exhibiting different yield points in tension and compression. Studies are reviewed which take into account: (a) changes in material properties, (b) strain hardening, and (c) biaxial stresses. Stress relaxation is studied by some investigators, but this cannot be considered to be bonafide thermal ratchetting, as the strain accumulation is time dependent.
Overall progress in thermal ratchetting analysis is reviewed, and areas that require investigation are suggested. A failure criterion is proposed for structures undergoing cyclic strain accumulation.
strains, stresses, cyclic loads, stress cycle, creep properties, plastic deformation, yield strength, compressive properties, elastic properties
Professor, Polytechnic Institute of Brooklyn, Brooklyn, N.Y.