Creep and Plastic Strains of 304 Stainless Steel at 593°C Under Step Stress Changes, Considering Aging

1982 ◽  
Vol 49 (2) ◽  
pp. 297-304 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Constitutive Equations ◽  
Time Dependent ◽  
304 Stainless Steel ◽  
Flow Rule ◽  
Strain Component ◽  
Plastic Strains ◽  
Aging Effects ◽  
Stress Changes ◽  
Step Down

Nonlinear constitutive equations for varying stress histories are developed and used to predict the creep behavior of 304 stainless steel at 593°C (1100°F) under variable tension or torsion stresses including reloading, complete unloading, step-up, and step-down stress changes. The strain in the constitutive equations (a viscous-viscoelastic model) consists of: linear elastic, time-independent plastic, time-dependent-recoverable viscoelastic, and time-dependent-nonrecoverable viscous components. For variable stressing, the modified superposition principle, derived from the multiple integral representation, and the strain hardening theory were used to represent the recoverable and nonrecoverable components, respectively, of the time-dependent strain. Time-independent plastic strains were described by a flow rule of similar form to that for nonrecoverable, time-dependent strains. The material constants of the theory were determined from constant stress creep and creep recovery data. Considerable aging effects were found and the effects on the strain components were incorporated in each strain predicted by the theory. Some modifications of the theory for the viscoelastic strain component under step-down stress changes were made to improve the predictions. The final predictions combining the foregoing features made satisfactory agreements with the experimental creep data under step stress changes.

Creep and Plastic Strains Under Side Steps of Tension and Torsion for 304 Stainless Steel at 593°C

1983 ◽  
Vol 50 (3) ◽  
pp. 580-586 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Viscoelastic Model ◽  
Single Step ◽  
304 Stainless Steel ◽  
Plastic Strains ◽  
Test Results ◽  
Aging Effects ◽  
Creep And Recovery ◽  
Stress Changes ◽  
Abrupt Changes ◽  
Step Down

Results of nonproportional stress changes on creep and plastic strains resulting from abrupt changes in proportion of tension and torsion are reported. Both step-up and step-down changes are included. Constitutive equations based on data for single step creep and recovery tests previously reported are used to describe the test results. A viscous-viscoelastic model with aging effects and modifications for step-down tests predicted the creep behavior reasonably well. The prediction of time-independent plastic strains is also described.

Creep and Creep Recovery of 304 Stainless Steel Under Combined Stress With a Representation by a Viscous-Viscoelastic Model

1980 ◽  
Vol 47 (4) ◽  
pp. 755-761 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Viscoelastic Model ◽  
Multiple Integral ◽  
Time Dependent ◽  
304 Stainless Steel ◽  
Creep Recovery ◽  
Strain Component ◽  
Stress Dependence ◽  
Nonlinear Stress ◽  
Stress States

Creep and creep-recovery data of 304 stainless steel are reported for experiments under constant combined tension and torsion at 593°C (1100°F). The data were represented by a viscous-viscoelastic model in which the strain was resolved into five components—elastic, plastic (time-independent), viscoelastic (time-dependent recoverable), and viscous (time-dependent nonrecoverable) which has separate positive and negative components. The data are well represented by a power function of time for each time-dependent strain. By applying superposition to the creep-recovery data, the recoverable creep strain was separated from the nonrecoverable. The form of stress-dependence associated with a third-order multiple integral representation was employed for each strain component. The time-dependent recoverable and nonrecoverable strains had different nonlinear stress dependence; but, the time-independent plastic strain and time-dependent nonrecoverable strain had similar stress-dependence. A limiting stress below which creep was very small or negligible was found for both recoverable and nonrecoverable components as well as a yield limit. The limit for recoverable creep was substantially less than the limits for nonrecoverable creep and yielding. The results showed that the model and equations used in the analysis described quite well the creep and creep-recovery under the stress states tested.

Creep and Plastic Strains Under Stress Reversal in Torsion With and Without Simultaneous Tension for 304 Stainless Steel at 593°C

1983 ◽  
Vol 50 (3) ◽  
pp. 587-592 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Viscoelastic Model ◽  
Single Step ◽  
304 Stainless Steel ◽  
Creep Recovery ◽  
Plastic Strains ◽  
Test Results ◽  
Aging Effects ◽  
Stress Changes ◽  
Constant Tension ◽  
Stress Reversals

Results of creep experiments under stress reversals in torsion with and without constant tension are reported. Constitutive equations based on data for single step creep and creep recovery tests previously reported are used to describe the test results. A viscous-viscoelastic model with aging effects and modifications for step-down stress changes and stress reversals predicted the creep behavior reasonably well. The prediction of time-independent plastic strains is also described.

Creep and Creep Recovery of 304 Stainless Steel at Low Stresses With Effects of Aging on Creep and Plastic Strains

1981 ◽  
Vol 48 (4) ◽  
pp. 785-790 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Plastic Strain ◽  
Viscoelastic Model ◽  
Time Dependent ◽  
304 Stainless Steel ◽  
Dislocation Creep ◽  
Creep Recovery ◽  
Power Functions ◽  
Transition Stress ◽  
Stress Levels

Creep and creep recovery data of 304 stainless steel are reported for experiments at low stress levels under combined tension and torsion at 593°C (1100°F). The data were represented by a viscous-viscoelastic model in which the strain was resolved into five components—elastic, plastic (time-independent), viscoelastic (time-dependent recoverable), and viscous (time-dependent nonrecoverable) which has separate positive and negative components. Only part of the creep strain at low stresses was recovered upon complete unloading following creep (as also found at high stresses), and each time-dependent strain data was well represented by a power function of time. But the stress dependence below a transition stress was approximately a linear relation with no creep limits and no cross effects such as were found in a previous analysis for higher stress levels above a transition stress. The transition stress for nonrecoverable strains agrees with the Frost-Ashby boundary between diffusional flow and dislocation creep. Aging decreased the creep rate and plastic strain. Results for different times of aging at 593°C (1100°F) under pure tension stresses were well represented by power functions of aging time up to 1000 h for each creep component and plastic strain.

Creep of 2618 Aluminum Under Step Stress Changes Predicted by a Viscous-Viscoelastic Model

1980 ◽  
Vol 47 (1) ◽  
pp. 21-26 ◽  
Author(s):  
J. S. Lai ◽  
W. N. Findley
Keyword(s):  
Constitutive Equations ◽  
Superposition Principle ◽  
Viscoelastic Model ◽  
Multiple Integral ◽  
Constant Stress ◽  
Time Dependent ◽  
Stress Tests ◽  
Linear Elastic ◽  
Stress Changes ◽  
Dependent Strain

Nonlinear constitutive equations are developed and used to predict from constant stress data the creep behavior of 2618 Aluminum at 200°C (392°F) for tension or torsion stresses under varying stress history including stepup, stepdown, and reloading stress changes. The strain in the constitutive equation employed includes the following components: linear elastic, time-independent plastic, nonlinear time-dependent recoverable (viscoelastic), nonlinear time-dependent nonrecoverable (viscous) positive, and nonlinear time-dependent nonrecoverable (viscous) negative. The modified superposition principle, derived from the multiple integral representation, and strain-hardening theory were used to represent the recoverable and nonrecoverable components, respectively, of the time-dependent strain in the constitutive equations. Excellent-to-fair agreement was obtained between the experimentally measured data and the predictions based on data from constant-stress tests using the constitutive equations as modified.

On the Plastic and Viscoplastic Constitutive Equations—Part II: Application of Internal Variable Concepts to the 316 Stainless Steel

1983 ◽  
Vol 105 (2) ◽  
pp. 159-164 ◽  
Author(s):  
J. L. Chaboche ◽  
G. Rousselier
Keyword(s):  
Constitutive Equations ◽  
Kinematic Hardening ◽  
Cyclic Hardening ◽  
Internal Variable ◽  
Cyclic Behavior ◽  
Strain Component ◽  
Aging Effects ◽  
Viscoplastic Strain ◽  
Complex Phenomena ◽  
Hardening Rules

The constitutive equations developed in Part I with a combination of isotropic and nonlinear kinematic hardening rules can describe the usual monotonic and cyclic behavior of metals and alloys. Some materials, especially type 316 stainless steels, show interaction of many complex phenomena such as viscoplasticity, cyclic hardening, time softening and aging effects. . . On the basis of experimental results obtained in Electricite de France or taken from the literature the descriptive ability of the developed constitutive equations is discussed and a new methodology is proposed which treats instantaneous plasticity and creep by using a viscoplastic strain component alone.

Constitutive Equations for Large Plastic Deformation of Metals

1983 ◽  
Vol 105 (3) ◽  
pp. 162-167 ◽  
Author(s):  
C. S. Hartley ◽  
R. Srinivasan
Keyword(s):  
Stainless Steel ◽  
Constitutive Equations ◽  
True Strain ◽  
Type Equation ◽  
Power Laws ◽  
Maximum Load ◽  
Least Square ◽  
304 Stainless Steel ◽  
True Strain Rate ◽  
Increasing Temperature

Calculations of deformation behavior in metal forming operations require constitutive equations valid at large plastic strain. This work examines the quality of fit provided by two types of equations, an exponential form which generalizes power laws and a saturation-type relation, to data produced by isothermal, uniaxial testing of annealed 304 stainless steel and Zircaloy-4 at a constant total true strain rate and various temperatures. The use of annealed material reduces the number of independent parameters to three in the exponential equation and to four in the saturation-type equation. Physical reasoning places limits on the values of some parameters and identifies two with the true stress, σm, and true strain, εm, at the maximum load sustained by the specimen. Least-square fits of the data reveal that the Voce form of the saturation-type equation exhibits the lowest standard deviation of all equations studied. Material parameters representing σm, εm, and σs, the saturation stress, generally followed expected trends for the temperature dependence of measures of strength and ductility, except that εm, of 304 stainless steel tended to decrease with increasing temperature.

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