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| COMPARATIVE STUDY ON SUBSEQUENT YIELD SURFACES TESTED BY USING SINGLE AND MULTIPLE SPECIMEN |
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Abstract Through tension-torsion test with thin-walled tubular specimens of 45 annealing steel, the subsequent yield surfaces under different pre-tension deformation are investigated after the prescribed pre-strain. The yielding is defined by the several levels of offset strain, the effects of the chosen plastic strain offsets and the prescribed pre-strain levels on subsequent yield surface are explored. The initial and the subsequent yield surfaces are determined by the probe methods of multiple identical specimens method and single-specimen method, the rationality and limitations are discussed by the two probe method. The experimental results of yield surface for 45 steel are as follows: (1) The shape of initial yield surface tested by using multiple specimens and single-specimen method were found to be close to the von-Mises surface; (2) The shape of yield surface is significantly affected by test sequence with single-specimen method, the first yield point tested in opposite directions of preloading, the yield surface appears "inner concave"，if the test sequence is changed, the " inner concave" will no longer appear ; (3) The shape of yield surface is affected by test amounts of yield points through the single-specimen method, when the yield surface is tested by many yield points, the subsequent yield point will deviate from the yield surface because the strain hardening is caused by the cumulative plastic strain,; (4) Subsequent yield surface shape and size have the obvious difference between using the single-specimen method and the multiple-specimen method respectively，the shape of yield surface tested with single-specimen method is affected by cumulative plastic strain, the results by the probe method of multiple identical specimens are proved to be more accurate; (5) Subsequent yield surface is defined by a smaller offset strain with multiple-specimen method, the " inner concave" will also appear, but the phenomenon is not obvious.
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Received: 28 August 2013
Published: 28 June 2014
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2014, Vol. 35 
