Relationship between anelastic and nonlinear viscoplastic behavior of 316 stainless steel at low homologous temperature
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T H E experiment reported here was designed t o test whether a complete deformation model proposed recently by Hart 1 was fully consistent over its entire predictive r a n g e . The consistency test t o be described is especially stringent since, according t o the model, stress-strain rate measurements in the fully plastic s t r e s s r a n g e already determine the most important parameters of the model. The m o d e l then predicts a low s t r e s s anelastic behavior that depends on the same parameters. Consistency r e q u i r e s that the same parameter values yield a reliable description for both fully plastic and anelastic behavior. The measurements were made on Type 316 Stainless Steel at 25°C. The anelasticity measurements were made by recording strain-time histories a f t e r each of a sequence of abrupt load changes, all at s t r e s s levels low enough so that no unrecoverable (plastic) straining occurred. These measurements were performed in the same way as those reported e a r l i e r by Nir et al2 for high p u r i t y A1. The plastic stress-strain rate behavior was measured by load relaxation testing. Such measurements had already been reported for this material by Yamada and Li.3 However, because of the metallurgical variability of this material, it s e e m e d desirable to repeat the plastic r a n g e tests on the same specimen for which the anelasticity measurements had been made. The relationship of the load relaxation test data to the stress-strain rate characteristics has been described in detail elsewhere. 4 In the following w e s h a l l first describe the theoretical model that is under t e s t . The characterization of the experimental specimen will then be described. The experimental results and data analysis will then be presented for the two types of t e s t . Finally w e
N. NIR and F. H. HUANG are Postdoctoral Associate and Research Associate, respectively, and E. W. HART and CHE-YU LI are Professors, all with Cornel[ University. E. W. Hart is o n leave from General Electric Research and Development Center, Schenectady, NY 12301. Manuscript submitted June l , 1976. METALLURGICAL
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s h a l l discuss the agreement between the two types of test. THE DEFORMATION MODEL The deformation model is described in considerable detail and in three-dimensional context in Ref. 1. We s h a l l l i m i t our description here t o uniaxial deformation for simplicity. The theoryS that underlies the model is phenomenological and thus l e a d s directly to deformation constitutive relations. The theory is a state variable theory, and the constitutive equations represent a plastic equation of state. The model represents a synthesis of t h r e e deformation mechanisms whose mutual relationship is most easily described by the rheological d i a g r a m of Fig. 1. The t h r e e mechanisms are represented by t h r e e elements labeled 1, 2, and 3. We s h a l l r e f e r t o them in our discussion by the n a m e s a-element (or s t o r e d
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F i g . 1--A s c h e m a t i c rheologica
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