Multiaxial Creep of 2618 Aluminum Under Proportional Loading Steps

1984 ◽  
Vol 51 (1) ◽  
pp. 133-140 ◽  
Author(s):  
J.-L. Ding ◽  
W. N. Findley
Keyword(s):  
Strain Hardening ◽  
Kinematic Hardening ◽  
Superposition Principle ◽  
Viscoelastic Model ◽  
Creep Recovery ◽  
Strain Component ◽  
Proportional Loading ◽  
Dependent Strain ◽  
Stress States ◽  
Multiaxial Creep

Creep data of 2618-T61 aluminum alloy under multistep multiaxial proportional loadings at 200°C (392°F) are reported. Two viscoplastic flow rules were developed using constant stress creep and creep recovery data. One was based on the accumulated strain (isotropic strain hardening), and the other on a tensorial state varible (kinematic hardening). Data were represented by two models: a nonrecoverable viscoplastic model, and a viscous-viscoelastic model in which the time-dependent strain was resolved into recoverable (viscoelastic) and nonrecoverable components. The modified superposition principle was used to predict the viscoelastic strain component under variable stress states. The experiments showed that the viscous-viscoelastic model with either isotropic strain hardening or kinematic hardening gave very good predictions of the material responses. Isotropic strain hardening was best in some step-down stress states. The viscoelastic component accounted for not only the recovery strain but also the transient creep strain upon reloadings and step-up loadings.

Nonproportional Loading Steps in Multiaxial Creep of 2618 Aluminum

1985 ◽  
Vol 52 (3) ◽  
pp. 621-628 ◽  
Author(s):  
J. L. Ding ◽  
W. N. Findley
Keyword(s):  
Experimental Data ◽  
Strain Hardening ◽  
Kinematic Hardening ◽  
Superposition Principle ◽  
High Stress ◽  
Material Behavior ◽  
Time Dependent ◽  
Nonlinear Material ◽  
Strain Component ◽  
Dependent Strain

Experimental data on the creep behavior of 2618-T61 aluminum alloy under nonproportional loadings are presented. Among the important findings are the anisotropy induced by creep strain, synergistic effects during creep recovery, and strongly nonlinear material behavior at high stress levels. Data were compared with two theoretical models, a viscous-viscoelastic (VV) model and a viscoplastic (VP) model. In the VV model the time-dependent strain was decomposed into recoverable (viscoelastic) and nonrecoverable components. The VP model differs from the VV model in that all the time-dependent strain is assumed nonrecoverable. In each model, three viscoplastic flow rules based on different hardening natures, namely, isotropic strain hardening, kinematic hardening, and independent strain hardening were derived to describe the time-dependent nonrecoverable strain component, and compared with experiments. The viscoelastic component in the VV model was represented by the third-order multiple integral representation combined with the modified superposition principle. Predictions for all theories used material constants obtained from creep and recovery data only. Possible causes for the discrepancies between theories and experimental data were discussed. Further experimental and theoretical work necessary for the study of the time-dependent material behavior at high temperature were also suggested.

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.

Viscoelastic–Viscoplastic Cyclic Deformation of Polycarbonate Polymer: Experiment and Constitutive Model

2016 ◽  
Vol 83 (4) ◽  
Author(s):  
Chao Yu ◽  
Guozheng Kang ◽  
Fucong Lu ◽  
Yilin Zhu ◽  
Kaijuan Chen
Keyword(s):  
Constitutive Model ◽  
Kinematic Hardening ◽  
Viscoelastic Model ◽  
Creep Recovery ◽  
Strong Nonlinearity ◽  
Viscoplastic Strain ◽  
Cyclic Tension ◽  
Nonlinear Viscoelastic ◽  
Tension Tests ◽  
Proposed Model

A series of uniaxial tests (including multilevel loading–unloading recovery, creep-recovery, and cyclic tension–compression/tension ones) were performed to investigate the monotonic and cyclic viscoelastic–viscoplastic deformations of polycarbonate (PC) polymer at room temperature. The results show that the PC exhibits strong nonlinearity and rate-dependence, and obvious ratchetting occurs during the stress-controlled cyclic tension–compression/tension tests with nonzero mean stress, which comes from both the viscoelasticity and viscoplasticity of the PC. Based on the experimental observation, a nonlinear viscoelastic–viscoplastic cyclic constitutive model is then constructed. The viscoelastic part of the proposed model is constructed by extending the Schapery's nonlinear viscoelastic model, and the viscoplastic one is established by adopting the Ohno–Abdel-Karim's nonlinear kinematic hardening rule to describe the accumulation of irrecoverable viscoplastic strain produced during cyclic loading. Furthermore, the dependence of elastic compliance of the PC on the accumulated viscoplastic strain is considered. Finally, the capability of the proposed model is verified by comparing the predicted results with the corresponding experimental ones of the PC. It is shown that the proposed model provides reasonable predictions to the various deformation characteristics of the PC presented in the multilevel loading–unloading recovery, creep-recovery, and cyclic tension–compression/tension tests.

Creep Experiments Under Nonproportional Loadings With Stress Reversals for 2618 Aluminum

1984 ◽  
Vol 106 (4) ◽  
pp. 397-404 ◽  
Author(s):  
J. L. Ding ◽  
W. N. Findley
Keyword(s):  
Shear Stress ◽  
Strain Hardening ◽  
Synergistic Effects ◽  
Kinematic Hardening ◽  
High Stress ◽  
Creep Recovery ◽  
Flow Rule ◽  
Nonproportional Loading ◽  
Stress Levels ◽  
Stress Reversals

Experiments on creep of 2618-T61 aluminum under nonproportional loading steps combined with shear stress reversals, are reported. Compared to previous work, the stress levels, under which nonproportional loading steps were performed, were relatively low in the current work. In addition to the features of the material responses under nonproportional loadings such as anisotropy induced by creep strain, synergistic effects on creep and creep recovery, more findings related to stress reversals were a cyclic softening effect. The effect of shear stress reversal on tension creep was not significant because of the low stress levels. Isotropic strain hardening, kinematic hardening and independent strain hardening theories were evaluated. An auxiliary rule was developed for the isotropic and independent strain hardening approaches to extend the capabilities of the theories. Creep under stress reversals predicted by the kinematic flow rule was well described at low stresses but was too exagerated at high stress levels.

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.

scholarly journals A nonlinear viscoelastic–viscoplastic constitutive model for adhesives under creep

2021 ◽  
Author(s):  
Yi Chen ◽  
Lloyd V. Smith
Keyword(s):  
Yield Criterion ◽  
Kinematic Hardening ◽  
Viscoelastic Model ◽  
Three Dimensional ◽  
Creep Recovery ◽  
Element Analysis ◽  
Viscoplastic Model ◽  
Nonlinear Viscoelastic ◽  
Residual Strains ◽  
Scarf Joints

AbstractIn this study, we consider the nonlinear viscoelastic–viscoplastic behavior of adhesive films in scarf joints. We develop a three-dimensional nonlinear model, which combines a nonlinear viscoelastic model with a viscoplastic model using the von Mises yield criterion and nonlinear kinematic hardening. We implement an iterative scheme for the viscoplastic solution and a numerical algorithm with stress correction for the combined viscoelastic–viscoplastic model into finite element analysis. The viscoelastic component of the model is calibrated using creep-recovery data from adhesive films in scarf joints. The viscoplastic parameters are calibrated from the residual strains of recovered creep tests with varying load durations. A two-dimensional form of the model shows good agreement with the three-dimensional model for the scarf joint considered in this work and is compared with experiment. The numerical results show favorable agreement with the experimental creep and recovery responses of two epoxy adhesive systems. We also discuss the contribution of nonlinear viscoelasticity and viscoplasticity to the stress/strain distribution along the adhesive center lines. Viscoplasticity tends to lower the stress concentration.

Simultaneous and Mixed Stress Relaxation in Tension and Creep in Torsion of 2618 Aluminum

1986 ◽  
Vol 53 (3) ◽  
pp. 529-535 ◽  
Author(s):  
J. L. Ding ◽  
W. N. Findley
Keyword(s):  
Stress Relaxation ◽  
Kinematic Hardening ◽  
Theoretical Models ◽  
Material Behavior ◽  
Time Dependent ◽  
Creep Recovery ◽  
State Variable ◽  
Dependent Behavior ◽  
Stress States ◽  
Tensile Relaxation

The time dependent behavior of 2618-T61 aluminum under mixed loads and constraints (tension relaxation and torsion creep) is investigated. Experiments include tensile relaxation; simultaneous tension relaxation with step changes in torsion creep and reversed torsion; and alternate creep and relaxation. Results were compared with theoretical models developed previously using as input creep and creep recovery data under constant stress states only. Experimental observations were generally well described by strain hardening flow rules. Some failures in describing the material behavior by the state variable approaches (kinematic hardening) are also discussed.

scholarly journals Crystallographic orientation-dependent strain hardening in a precipitation-strengthened Al-Cu alloy

2021 ◽  
Vol 205 ◽  
pp. 116577
Author(s):  
Brian Milligan ◽  
Dong Ma ◽  
Lawrence Allard ◽  
Amy Clarke ◽  
Amit Shyam
Keyword(s):  
Strain Hardening ◽  
Crystallographic Orientation ◽  
Cu Alloy ◽  
Dependent Strain
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