An Improved Mechanism-Based Creep Constitutive Model Using Stress-Dependent Creep Ductility

2016 ◽  
Author(s):  
Yu Zhou ◽  
Chen Xuedong ◽  
Zhichao Fan ◽  
Han Yichun
Keyword(s):  
Damage Mechanics ◽  
Constitutive Models ◽  
Continuum Damage Mechanics ◽  
Creep Process ◽  
Ferritic Steels ◽  
Creep Tests ◽  
Creep Ductility ◽  
Wide Range ◽  
Stress Levels ◽  
Stress Dependent

Creep ductility which is assumed to be constant at a given temperature in many creep constitutive models, actually varies with temperature, stress level and creep strain rate, etc. In this paper, the relationship between creep ductility and stress levels of ferritic steels has been briefly discussed from the perspective of failure mechanisms. It can be generally divided into three regimes, including the upper shelf, lower shelf and the transition regime. The four-parameter logistic model has been adopted to quantitatively describe the stress-dependent creep ductility. Furthermore, a modified mechanism-based continuum damage mechanics (CDM) model for ferrtic steels has been proposed using the stress-dependent creep ductility model. Uniaxial creep tests of 2.25Cr1Mo0.25V steel at three stress levels have been carried out and the experimental data points realistically reflecting the creep behavior have been carefully selected to fit the improved CDM model using genetic algorithm (GA). It is shown that the improved model has the capability to characterize the whole creep process of ferritic steels and the stress-dependent creep ductility over a wide range of applied stress.

Creep Behaviors Calculated by Varying Material Constants Obtained from Different Stress Regions for a Closed-End P91 Pipe

2016 ◽  
Vol 35 (5) ◽  
pp. 441-447
Author(s):  
Zhao Yanping ◽  
Gong Jianming ◽  
Wang Xiaowei ◽  
Li Qingnan
Keyword(s):  
Damage Mechanics ◽  
Creep Damage ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Creep Tests ◽  
Material Constants ◽  
Mechanics Model ◽  
Stress Region ◽  
Wide Range ◽  
Tertiary Stage

AbstractIn order to predict the creep life of a component at high temperature both accurately and economically, continuum damage mechanics approach is used based on experimental creep data. However, material constants used in the models have a great relationship with the performed stress range of creep tests. In this paper, several sets of material constants were obtained from a wide range of stresses on P91 steel. The creep damage tolerance parameter was used to classify these sets, and the modified continuum damage mechanics model was used to investigate a pipe under closed-end condition. Results have illustrated the main difference lies on the tertiary stage while slight difference on the primary and secondary stages, and the contribution of the tertiary stage to the total damage decreased when using material constants from higher stress region.

Stress Relaxation Continuum Damage Constitutive Equations for Relaxation Performance Prediction

2012 ◽  
Vol 455-456 ◽  
pp. 1434-1437
Author(s):  
Jin Quan Guo ◽  
Wei Zhang ◽  
Xiao Hong Sun
Keyword(s):  
Stress Relaxation ◽  
Constitutive Equations ◽  
Damage Mechanics ◽  
Constitutive Models ◽  
Continuum Damage Mechanics ◽  
Creep Model ◽  
Continuum Damage ◽  
Relaxation Equation ◽  
Creep Tests ◽  
Analysis Technique

Stress relaxation constitutive equations based on Continuum Damage Mechanics, Kachanov-Robatnov creep model, and stress relaxation equation has been developed by analyzing stress relaxation damage mechanisms and considering the relationship that stress relaxation is creep at various stresses. And, the constitutive differential equations were integrated to predict stress relaxation performance by using numerical analysis technique. In order to validate the approach, the predicted results are compared to the experimental results of uni-axial isothermal stress relaxation tests conducted on 1Cr10NiMoW2VNbN steel with the same temperature of creep tests. Good agreement between results of relaxation tests and the predicted results indicates that the developed constitutive models can be used in the relaxation behavior evaluation of high temperature materials.

scholarly journals Constitutive Model for Concrete: An Overview

2015 ◽  
Vol 10 (Special-Issue1) ◽  
pp. 782-788 ◽  
Author(s):  
Mehdi Shekarbeigi ◽  
Hasan Sharafi
Keyword(s):  
Constitutive Model ◽  
Damage Mechanics ◽  
Constitutive Models ◽  
Continuum Damage Mechanics ◽  
Constitutive Modelling ◽  
Continuum Damage ◽  
Endochronic Theory ◽  
Small Deformations

In the last three decades, the constitutive modelling of concrete evolved considerably. This paper describes various developments in this field based on different approaches such anelasticity, plasticity, continuum damage mechanics, plastic fracturing, endochronic theory, microplane models, etc. In this article the material is assumed to undergo small deformations. Only time independent constitutive models and the issues related to their implementation are discussed

Development and Finite Element Implementation of Stress-Dependent Elastoviscoplastic Constitutive Model with Damage for Asphalt

2003 ◽  
Vol 1832 (1) ◽  
pp. 96-104 ◽  
Author(s):  
Andrew C. Collop ◽  
A. (Tom) Scarpas ◽  
Cor Kasbergen ◽  
Arian de Bondt
Keyword(s):  
Finite Element ◽  
Constitutive Model ◽  
Damage Mechanics ◽  
Compressive Strain ◽  
Local Strain ◽  
Continuum Damage Mechanics ◽  
Dependent Case ◽  
Strain Compatibility ◽  
Incremental Formulation ◽  
Stress Dependent

The development and finite element (FE) implementation of a stress-dependent elastoviscoplastic constitutive model with damage for asphalt is described. The model includes elastic, delayed elastic, and viscoplastic components. The strains (and strain rates) for each component are additive, whereas they share the same stress (i.e., a series model). This formulation was used so that a stress-based nonlinearity and sensitivity to confinement could be introduced into the viscoplastic component without affecting the behavior of the elastic and delayed elastic components. A simple continuum damage mechanics formulation is introduced into the viscoplastic component to account for the effects of cumulative damage on the viscoplastic response of the material. The model is implemented in an incremental formulation into the CAPA-3D FE program developed at Delft University of Technology in the Netherlands. A local strain compatibility condition is utilized such that the incremental stresses are determined explicitly from the incremental strains at each integration point. The model is demonstrated by investigating the response of a semirigid industrial pavement structure subjected to container loading. Results show that the permanent vertical strains in the non-stress-dependent case are significantly lower than the permanent vertical strains in the stress-dependent case. Results also show that in the stress-dependent case, there is a more localized area of high permanent vertical compressive strain directly under the load at approximately halfdepth in the asphalt compared with the non-stress-dependent case, in which the distribution is more even.

THE FOUNDATIONS OF CONTINUUM DAMAGE MECHANICS

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Siamak Yazdani ◽  
Sevenn Borgersen ◽  
Asli Pelin Gurgun ◽  
Hossein Nazari
Keyword(s):  
Damage Mechanics ◽  
Nonlinear Behavior ◽  
Continuum Damage Mechanics ◽  
Uniaxial Stress ◽  
Internal Variable ◽  
Continuum Damage ◽  
Damage Potential ◽  
Variable Theory ◽  
Wide Range ◽  
The Many

Damage Mechanics has become a useful theory in describing the nonlinear behavior of solids driven by the nucleation and growth of cracks and microcracks. This approach, based on the first principles of mechanics and thermodynamics, has also been combined with classical theories of plasticity to address a wide range of loading applications. In spite of the many different damage mechanics models and representations that are proposed, the foundation of damage mechanics is not well understood or at least not thoroughly published giving rise to the many inaccurate definitions and formulations. The intent of this paper is to provide the background of the continuum damage mechanics outlining the fundamentals on which this field theory is set up. The internal variable theory of continuum thermodynamics is reviewed and is shown that with Legendre transformation technique, various potential functions can be developed for damage mechanics formulation in either stress or strain space. The concept of constrained or neighboring equilibrium state is also introduced and is explained. The paper will conclude with the derivation of the general damage potential and a suggestion is given for the isotropic damage formulation with the resulting uniaxial stress-strain relation.

scholarly journals Viscoelastic Damage Characteristics of Asphalt Mixtures Using Fractional Rheology

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5892
Author(s):  
Qipeng Zhang ◽  
Xingyu Gu ◽  
Zilu Yu ◽  
Jia Liang ◽  
Qiao Dong
Keyword(s):  
Damage Evolution ◽  
High Stress ◽  
Creep Damage ◽  
Asphalt Mixtures ◽  
Creep Process ◽  
Model Parameters ◽  
Creep Tests ◽  
Steady Stage ◽  
Stress Levels ◽  
Different Temperatures

The mechanical behavior of asphalt mixtures at high stress levels are characterized by non-linear viscoelasticity and damage evolution. A nonlinear damage constitutive model considering the existence of creep hardening and creep damage mechanisms in the entire creep process is proposed in this study by adopting the fractional rheology theory to characterize the three-stage creep process of mixtures. A series of uniaxial compressive creep tests under various stresses were conducted at different temperatures to verify the model. The results indicated that the model predictions were in good agreement with the creep tests. The relationship between the model parameters and applied stresses was established, and the stress range in which the mixture exhibited only creep consolidation was obtained. The damage to the asphalt mixture was initiated in the steady stage; however, it developed in the tertiary stage. A two-parameter Weibull distribution function was used to describe the evolution between the damage values and damage strains at different stress levels and temperatures. The correlation coefficients were greater than 0.99 at different temperatures, indicating that a unified damage evolution model could be established. Thus, the parameters of the unified model were related to material properties and temperature, independent of the stress levels applied to the mixtures.

Development of “Material Specific” Creep Continuum Damage Mechanics-Based Constitutive Equations

2020 ◽  
Author(s):  
Ricardo Vega ◽  
Jaime A. Cano ◽  
Calvin M. Stewart
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Creep Strain ◽  
Creep Deformation ◽  
Damage Evolution ◽  
Damage Mechanics ◽  
Constitutive Models ◽  
Continuum Damage Mechanics ◽  
Creep Strain Rate ◽  
Continuum Damage

Abstract The objective of this study is to introduce a method for creating “material specific” creep continuum damage mechanics-based constitutive models. Herein, material specific is defined as a constitutive model based on the mechanism-informed minimum creep strain rate (MCSR) equations found in deformation mechanism maps and calibrated to available material data. The material specific models are created by finding the best MCSR model for a dataset. Once the best MCSR model is found, the Monkman Grant inverse relationship between the MCSR and rupture time is employed to derive a rupture equation. The equations are substituted into continuum damage mechanics-based creep strain rate and damage evolution equations to furnish predictions of creep deformation and damage. Material specific modeling allows for the derivation of creep constitutive models that can better the material behavior specific to the available data of a material. The material specific framework is also advantageous since it has a systematic framework that moves from finding the best MCSR model, to rupture time, to damage evolution and, creep strain rate. Data for Alloy P91 was evaluated and a material specific constitutive model derived. The material specific model was able to accurately predict the MCSR, creep deformation, damage, and rupture of alloy P91.

scholarly journals Nonlocal Theories in Continuum Mechanics

10.14311/610 ◽  
2004 ◽  
Vol 44 (5-6) ◽  
Author(s):  
M. Jirásek
Keyword(s):  
Damage Mechanics ◽  
Continuum Theory ◽  
Nonlinear Behavior ◽  
Continuum Damage Mechanics ◽  
Internal Variable ◽  
Continuum Damage ◽  
Hardening Modulus ◽  
Wide Range ◽  
Discrete Media ◽  
Dynamic Phenomena

The purpose of this paper is to explain why the standard continuum theory fails to properly describe certain mechanical phenomena and how the description can be improved by enrichments that incorporate the influence of gradients or weighted spatial averages of strain or of an internal variable. Three typical mechanical problems that require such enrichments are presented: (i) dispersion of short elastic waves in heterogeneous or discrete media, (ii) size effects in microscale elastoplasticity, in particular with the size dependence of the apparent hardening modulus, and (iii) localization of strain and damage in quasibrittle structures and with the resulting transitional size effect. Problems covered in the examples encompass static and dynamic phenomena, linear and nonlinear behavior, and three constitutive frameworks, namely elasticity, plasticity and continuum damage mechanics. This shows that enrichments of the standard continuum theory can be useful in a wide range of mechanical problems. 

Finite Element Damage Analyses for Predictions of Creep Crack Growth

2010 ◽  
Author(s):  
Chang-Sik Oh ◽  
Nak-Hyun Kim ◽  
Sung-Hwan Min ◽  
Yun-Jae Kim
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Crack Growth ◽  
Damage Mechanics ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Simulation Method ◽  
Creep Tests ◽  
Creep Ductility ◽  
Creep Crack

This paper provides the virtual simulation method for creep crack growth test, based on finite element (FE) analyses with damage mechanics. Creep tests of smooth bars are used to quantify the constants of creep constitutive equation. The reduction of area resulting from creep tests of smooth and notched bar is adopted as a measure of creep ductility under multiaxial stress conditions. The creep ductility exhaustion concept is adopted for calculating creep damage, which is defined as the ratio of creep strain to the multiaxial creep ductility. To simulate crack propagation, fully damaged elements are forced to have nearly zero stresses using user-defined subroutine UHARD in the general-purpose FE code, ABAQUS. The results from 2D or 3D FE analyses are compared with experimental data of creep crack growth. It is shown that the predictions obtained from this new method are in good agreement with experimental data.

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