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.

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.

Characterization and Modeling of Time-Dependent Behaviour of Braided Packing Rings

2016 ◽  
Author(s):  
Mehdi Kazeminia ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Viscoelastic Behavior ◽  
Material Behavior ◽  
Time Dependent ◽  
Nonlinear Material ◽  
Dependent Behavior ◽  
Sealing Performance ◽  
Proposed Model ◽  
Packing Rings ◽  
Linear Viscoelastic Behavior ◽  
Linear Viscoelastic

The sealing performance of packed stuffing boxes used in valves and compressors depends on the ability of the structure to maintain a minimum threshold contact pressure through a sufficient period of time. Packing rings exhibit combined creep and relaxation behavior due to internal disordered porous structure and nonlinear material behavior in addition to the interaction with other structural components. A comprehensive understanding of the time-dependent behavior of packing rings is essential for increasing the sealing performance. In this paper, the time-dependent linear viscoelastic behavior of packing material is constitutively simulated. The experimental investigation is carried out in a special test bench which was designed and developed to study the characteristics of the time-dependent behavior of packing rings. The results show that the proposed model can successfully be exploited to determine the time-dependent behavior of packing rings for application in the design of packed stuffing boxes.

Crack Propagation in a Nonlinearly Viscoelastic Solid With Relevance to Adhesive Bond Failure

1993 ◽  
Vol 60 (4) ◽  
pp. 793-801 ◽  
Author(s):  
W. G. Knauss ◽  
G. U. Losi
Keyword(s):  
Crack Propagation ◽  
Superposition Principle ◽  
Adhesive Layer ◽  
Adhesive Bond ◽  
Material Behavior ◽  
Nonlinear Material ◽  
Material Response ◽  
Propagation Axis ◽  
Bonded Joint ◽  
Time Temperature Superposition Principle

The problem of crack propagation through a material possessing nonlinearly viscoelastic material response is considered, including the influence of stress-induced free-volume changes on the rheology, as well as the formation of voids as material failure is approached. This particular material response is confined to a thin layer along the crack propagation axis, while the bulk of the material behaves in a linearly viscoelastic manner, thus simulating the situation arising in the growth of a crazeled crack, or the failure of a bonded joint with a thin adhesive layer strained uniformly across its thickness. The nonlinear material behavior thus governs simultaneously the stress and strain distribution at the crack tip as well as the crack speed solely in dependence on the applied load (stress intensity factor). Only quasi-static motion is considered, the velocities being understood to be “reduced” by temperature according to a time-temperature superposition principle. Comparisons with a model based on linearly viscoelastic considerations and rate-insensitive properties of the damaged material are presented.

Necessity of Kinematic Strain Hardening in Simulating Impact Events

2017 ◽  
Author(s):  
Sharang Kirloskar ◽  
Gurmeet Singh ◽  
Avinash Kumar
Keyword(s):  
Strain Hardening ◽  
Impact Loading ◽  
High Speed ◽  
Kinematic Hardening ◽  
Material Behavior ◽  
Isotropic Hardening ◽  
Measurement Systems ◽  
Tension And Compression ◽  
Hardening Rules ◽  
Impact Events

Impact events are very high speed and short duration events. Experimental analysis of such events tends to be extremely expensive and challenging to study because of the apparatus and measurement systems required to capture the event. Due to this, impact events are studied extensively through simulations. The ability to simulate these events is a dictating factor for developing better and more efficient designs. Traditionally, loads occurring due to impact events are assumed to monotonically increase and hence pure isotropic strain hardening is sufficient to model the material behavior. However, this assumption doesn’t hold true for all impact events. When the loads caused by an impact do not monotonically increase but instead oscillate causing tension and compression cycles, pure isotropic hardening could lead to unrealistic results. In this work, different strain hardening rules are studied and analyzed for a plate under impact loading. The process to obtain a parameter which sets a realistic combination of isotropic and kinematic strain hardening rules is demonstrated and discussed. Limitations of the existing practice of using isotropic hardening in impact loading cases are studied. An alternative approach to accommodate the kinematic hardening rule into material models using LS-DYNA, a finite element solver, is discussed.

Application of a Unified Constitutive Theory to the Nonproportional Multiaxial Strain Deformation of 1045 Steel

1992 ◽  
Vol 114 (2) ◽  
pp. 147-155 ◽  
Author(s):  
J. A. Sherwood ◽  
E. M. Fay
Keyword(s):  
Inelastic Strain ◽  
Material Model ◽  
Flow Equation ◽  
Material Behavior ◽  
Nonlinear Material ◽  
Unified Theory ◽  
Strain Plasticity ◽  
Dependent Strain ◽  
1045 Steel

An automated procedure for the determination of the material constants in a constitutive equation which is used to model the multiaxial nonlinear material behavior of isotropic materials is discussed. The material model used in this research is a unified theory where the time-dependent strain (creep) and time-independent strain (plasticity) are treated as one (unified) inelastic strain. The flow equation considers the inelastic rate of strain and it is assumed that inelastic strain is present at all levels of stress. Application of the model to proportional and nonproportional biaxial loadings is presented.

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.

Constitutive Relationships for the Time-Dependent Deformation of Metals

1976 ◽  
Vol 98 (1) ◽  
pp. 47-51 ◽  
Author(s):  
A. R. S. Ponter ◽  
F. A. Leckie
Keyword(s):  
High Temperature ◽  
Strain Hardening ◽  
Potential Function ◽  
Inelastic Deformation ◽  
Kinematic Hardening ◽  
Constitutive Relations ◽  
Thermal Softening ◽  
Time Dependent ◽  
Polycrystalline Metal ◽  
State Potential

The paper discusses the constitutive relations for the inelastic deformation of a polycrystalline metal at high temperature. Commencing from a description of a dislocation structure in terms of strain hardening and thermal softening, the general form of the constitutive relation is developed in terms of a potential function. The existence of a stationary state potential is established and generalizations of isotropic and kinematic hardening are described.

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.

Sign in / Sign up

Export Citation Format

Share Document