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.

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.

scholarly journals Constitutive Modeling of Time-Dependent Response of Human Plantar Aponeurosis

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
P. G. Pavan ◽  
P. Pachera ◽  
C. Stecco ◽  
A. N. Natali
Keyword(s):  
Experimental Data ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Transverse Isotropy ◽  
Model Fitting ◽  
Viscoelastic Behavior ◽  
Time Dependent ◽  
Plantar Aponeurosis ◽  
Structural Conformation ◽  
Dependent Behavior

The attention is focused on the viscoelastic behavior of human plantar aponeurosis tissue. At this purpose, stress relaxation tests were developed on samples taken from the plantar aponeurosis of frozen adult donors with age ranging from 67 to 78 years, imposing three levels of strain in the physiological range (4%, 6%, and 8%) and observing stress decay for 240 s. A viscohyperelastic fiber-reinforced constitutive model with transverse isotropy was assumed to describe the time-dependent behavior of the aponeurotic tissue. This model is consistent with the structural conformation of the tissue where collagen fibers are mainly aligned with the proximal-distal direction. Constitutive model fitting to experimental data was made by implementing a stochastic-deterministic procedure. The stress relaxation was found close to 40%, independently of the level of strain applied. The agreement between experimental data and numerical results confirms the suitability of the constitutive model to describe the viscoelastic behaviour of the plantar aponeurosis.

Constitutive Description of Temperature-Dependent Nonproportional Cyclic Viscoplasticity

1997 ◽  
Vol 119 (1) ◽  
pp. 12-19 ◽  
Author(s):  
Xian Jie Yang
Keyword(s):  
Evolution Equations ◽  
Kinematic Hardening ◽  
Complex Loading ◽  
Deformation Resistance ◽  
Material Behavior ◽  
Temperature History ◽  
Loading History ◽  
Dependent Behavior ◽  
Proposed Model ◽  
Hardening Rules

This paper is concerned with the constitutive modeling of the temperature history dependent behavior of metallic materials under uniaxial and nonproportional cyclic loadings. In the study, a class of kinematic hardening rules characterized by a decomposition of the total kinematic hardening variable is discussed. A new nonproportionality is defined. In order to consider the influence of complex cyclic loading and temperature histories on materials behavior, an apparent isotropic deformation resistance parameter Qasm is proposed and the evolution equations of the isotropic deformation resistance Q are offered to correlate the memory effect of previous loading history on material behavior. The proposed model is applied to the description of complex cyclic deformation behavior of 1Cr18Ni9Ti stainless steel, and this model gives good results for the prediction of complex tests under complex loading history and at stepwise temperature changes.

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.

Dynamic Material Behavior Modeling Using Internal State Variable Plasticity and Its Application in Hard Machining Simulations

2005 ◽  
Vol 128 (3) ◽  
pp. 749-759 ◽  
Author(s):  
Y. B. Guo ◽  
Q. Wen ◽  
K. A. Woodbury
Keyword(s):  
Internal State ◽  
Kinematic Hardening ◽  
Material Behavior ◽  
Machining Process ◽  
Hard Machining ◽  
Internal State Variable ◽  
Strain Rates ◽  
Material Constants ◽  
State Variable ◽  
Jc Model

Work materials experience large strains, high strain rates, high temperatures, and complex loading histories in machining. The problem of how to accurately model dynamic material behavior, including the adiabatic effect is essential to understand a hard machining process. Several conventional constitutive models have often been used to approximate flow stress in machining analysis and simulations. The empirical or semiempirical conventional models lack mechanisms for incorporating isotropic/kinematic hardening, recovery, and loading history effects. In this study, the material constants of AISI 52100 steel (62 HRc) were determined for both the Internal State Variable (ISV) plasticity model and the conventional Johnson-Cook (JC) model. The material constants were obtained by fitting the ISV and JC models using nonlinear least square methods to same baseline test data at different strains, strain rates, and temperatures. Both models are capable of modeling strain hardening and thermal softening phenomena. However, the ISV model can also accommodate the adiabatic and recovery effects, while the JC model is isothermal. Based on the method of design of experiment, FEA simulations and corresponding cutting tests were performed using the cutting tool with a 20 deg chamfer angle. The predicted chip morphology using the ISV model is consistent with the measured chips, while the JC model is not. The predicted temperatures can be qualitatively verified by the subsurface microstructure. In addition, the ISV model gave larger subsurface von Mises stress, plastic strain, and temperature compared with those by the JC model.

scholarly journals Time-Dependent Behavior of Rock Materials

2021 ◽  
Author(s):  
Chrysothemis Paraskevopoulou
Keyword(s):  
Rock Mass ◽  
Stress Relaxation ◽  
Time Dependent ◽  
Cost Overruns ◽  
Rock Materials ◽  
Dependent Behavior ◽  
Rock Mass Deformation ◽  
Waste Repositories ◽  
Long Term Behavior

Understanding the geomechanical behavior of a geological model is still an on-going challenge for engineers and scientists. More challenges arise when considering the long-term behavior of rock materials, especially when exposed to environments that enable time-dependent processes to occur and govern overall behavior. The latter is essential in underground projects such as nuclear waste repositories. The lifespan can exceed one million years or other openings where the project’s lifetime and sustainability are the critical design parameter. In such cases, progressive rock mass deformation that can lead to instabilities, time-dependent overloading of support and delayed failure are considered the product of time-dependent phenomena. Understanding and predicting the overall impact of such phenomena aims to achieve design optimization, avoiding dlivery delays and thus cost overruns. This chapter provides more insight into the time-dependent behavior of rocks. Simultaneously, the emphasis is given to investigating and analyzing creep deformation and time-dependent stress relaxation phenomenon at the laboratory scale, and in-depth analyses are presented. This work further develops the understanding of these phenomena, and practical yet scientific tools for estimating and predicting the long-term strength and the maximum stress relaxation of rock materials is presented. The work presented in this chapter advances the scientific understanding of time-dependent rock, and rock mass behavior increases the awareness of how such phenomena are captured numerically and lays out a framework for dealing with such deformations when predicting tunnel deformations.

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.

Influence of grain direction on the time-dependent behavior of wood analyzed by a 3D rheological model. A mathematical consideration

Holzforschung ◽  
2018 ◽  
Vol 72 (10) ◽  
pp. 889-897 ◽  
Author(s):  
Sabina Huč ◽  
Staffan Svensson
Keyword(s):  
Rheological Model ◽  
Tensile Load ◽  
Longitudinal Direction ◽  
Material Behavior ◽  
Time Dependent ◽  
Sustained Load ◽  
Uniaxial Tensile ◽  
Material Parameters ◽  
Dependent Behavior ◽  
Natural Time

AbstractA three-dimensional (3D) rheological model for an orthotropic material subjected to sustained load or deformation under constant climate has been mathematically formulated. The elastic and viscoelastic compliance matrices are symmetric, where the mathematical derivation of the latter is shown. The model is linear and requires constant numerical values for the elastic and viscoelastic material parameters. The model’s ability to predict the natural time-dependent response in three material directions simultaneously is demonstrated on a Douglas fir (Pseudotsuga menziesii) specimen subjected to a constant uniaxial tensile load. The material extends in a longitudinal direction and contracts in the transverse directions with time. The required material parameters are taken from the literature when possible, otherwise they are assumed. Furthermore, the influence of misalignment between the directions of observation and wood material directions on induced time-dependent strains is analyzed. The analyses show that the misalignment has a large effect on the material behavior. In some cases, the specimen under constant uniaxial tension even extends in the perpendicular transverse direction with time. The obtained results clearly demonstrate the high importance of considering the alignment of material directions precisely in order to be able to interpret the time-dependent behavior of wood correctly.

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