The mechanical properties of sheets or tubes metals in different directions are usually different due to the micro and macro tex-ture produced in rolling process,which shows obvious anisotropy.At present,the normal anisotropy coefficient r value is commonly used to quantitatively characterize the anisotropy.By assuming the existence of-r value,the yielding locus in two-dimensional stress state was given based on the Hi1148 yield criterion,and the possible abnormal deformation behavior was discussed.If the material with r＜-0.5 can be fabricated,an abnormal phenomenon of increasing cross-section size by stretching,and decreasing by compression will occur,which can be called"negative deformation material".If this abnormal phenomenon exists objectively,the existing plastic constitutive relation on the base of the associated flow rule is not suitable for this kind of material.Therefore,"hypothesis on negative deformation theory"is put forward.It is hoped that more researchers can prove that this hypothesis is a correct theory or a fallacious idea through in-depth researches in the future for activating academic ideas,so that breakthroughs in plasticity theory and original innovations will be promoted.
yielding locusanisotropyabnormal deformation behaviorhypothesis on negative deformation theory
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