scholarly journals Temperature-Dependent Fatigue Characteristics of P91 Steel

2020 ◽  
Vol 14 (2) ◽  
pp. 69-78
Author(s):  
Władysław Egner ◽  
Piotr Sulich ◽  
Stanisław Mroziński ◽  
Halina Egner
Keyword(s):  
Constitutive Model ◽  
Internal State ◽  
Low Cycle Fatigue ◽  
Constitutive Modelling ◽  
Thermomechanical Coupling ◽  
Irreversible Processes ◽  
Experimental Investigations ◽  
Model Parameters ◽  
State Variables ◽  
P91 Steel

AbstractIn this paper, the experimental investigations, constitutive description and numerical modelling of low-cycle fatigue behaviour of P91 steel in non-isothermal conditions are presented. First, experimental tests are performed to recognise different aspects of material behaviour. Then, an appropriate constitutive model is developed within the framework of thermodynamics of irreversible processes with internal state variables. The model describes two phases of cyclic softening, related to plastic mechanisms. An important goal of the presented research is to include thermomechanical coupling in the constitutive modelling. Next, the model parameters are identified based on the available experimental data. Some parametric studies are presented. Finally, numerical simulations are performed, which indicate the significant influence of thermomechanical coupling on the response of the constitutive model in thermomechanical fatigue conditions.

scholarly journals A Unified Constitutive Model for Creep and Cyclic Viscoplasticity Behavior Simulation of Steels Based on the Absolute Reaction Rate Theory

2017 ◽  
Vol 2017 ◽  
pp. 1-13
Author(s):  
Huayan Chen ◽  
Xiangguo Zeng ◽  
Yang Guo ◽  
Fang Wang
Keyword(s):  
Constitutive Model ◽  
Reaction Rate ◽  
Internal State ◽  
Rate Theory ◽  
State Variables ◽  
Absolute Reaction Rate Theory ◽  
Reaction Rate Theory ◽  
Absolute Reaction Rate ◽  
The Absolute ◽  
Absolute Reaction

In this work, the viscoplasticity and creep behavior for modified 9Cr-1Mo and 316 stainless steels were investigated. Based on the absolute reaction rate theory, a unified constitutive model incorporating internal state variables was proposed to characterize the evolution of the back stress. Also, the model was implemented by the ABAQUS system with the semi-implicit stress integration. Compared to the experimental data, the results demonstrated that the proposed approach could effectively simulate the cyclic softening and hardening behavior for such structural steels.

Latest Development in Physics-Based Modeling of Coiled Tubing Plasticity and Fatigue

SPE Journal ◽  
2021 ◽  
pp. 1-12
Author(s):  
Zhanke Liu ◽  
Steven Tipton ◽  
Dinesh Sukumar
Keyword(s):  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Experimental Investigations ◽  
Cycle Fatigue ◽  
State Variables ◽  
Coiled Tubing ◽  
Wall Thinning ◽  
Fatigue Damage Accumulation ◽  
Wide Range ◽  
Novel Algorithms

Summary Coiled tubing (CT) integrity is critical for well intervention operations in the field. To monitor and manage tubing integrity, the industry has developed a number of computer models over the past decades. Among them, low-cycle fatigue (LCF) modeling plays a paramount role in safeguarding tubing integrity. LCF modeling of CT strings dates back to the 1980s. Recently, novel algorithms have contributed to developments in physics-based modeling of tubing fatigue and plasticity. When CT trips into and out of the well, it goes through bending/straightening cycles under high differential pressure. Such tough conditions lead to low- or ultralow-cycle fatigue, limiting CT useful life. The model proposed in this study is derived from a previous one and is based on rigorously derived material parameters to compute the evolution of state variables from a wide range of loading conditions. Through newly formulated plasticity and strain parameters, a physics-based damage model predicts CT fatigue life, along with diametral growth and wall thinning. The revised modeling approach gives results for CT damage accumulation, diametral growth, and wall thinning under realistic field conditions, with experimental validation. For 20 different CT alloys, it was observed that the model improved in accuracy overall by approximately 18.8% and consistency by 14.0%, for constant pressure data sets of more than 4,500 data points. The modeling results provide insights into the nonlinear nature of fatigue damage accumulation. This study allowed developing recommendations to guide future analytical modeling and experimental investigations, summarize theoretical findings in physics-based LCF modeling, and provide practical guidelines for CT string management in the field. The study provides a fundamental understanding of CT LCF and introduces novel algorithms in plasticity and damage.

Measurement and Calibration of the Parameters of Hypoplasticity Model for an Iraqi Soil

2020 ◽  
Vol 857 ◽  
pp. 243-252
Author(s):  
Aysar Hassan Subair ◽  
Ala Nasir Aljorany
Keyword(s):  
Constitutive Model ◽  
Void Ratio ◽  
Initial Stresses ◽  
Model Parameters ◽  
State Variables ◽  
Soil Behavior ◽  
Dense Sand ◽  
Hypoplastic Model ◽  
Material Parameters ◽  
Wide Range

There are many constitutive models that have been used to model the mechanical behavior of soils. Some of these models are either unable to represent important features such as the strain softening of dense sand or required many parameters that can be hard to obtain by standard laboratory tests. Because of that, a more reliable constitutive model, which is capable to capture the main features of the soil behavior with easily obtained parameters, is required. The Hypoplasticity model is considered as a promising constitutive model in this respect. It is considered as a particular class of rate non-linear constitutive model at which the stress increment is expressed in a tensorial equation as a function of strain increment, actual stress, and void ratio. The hypoplastic model required only eight material parameters (critical friction angle critical, maximum and minimum void ratio respectively), granular stiffness hs and the model constants n, α, β). The appealing feature of the hypoplastic model is that the material parameters are separated from the state variables (void ratio and the initial stresses). This feature enables the model to simulate the soil behavior under a wide range of stresses and densities with the same set of material parameters. In this research, a brief description of the Hypoplasticity model is presented. Detailed discussions regarding the measurement and calibration of the model parameters of an Iraqi soil are then exposed. It is concluded that only Consolidated Drained (CD) triaxial test, oedometer test, and the well-known limit density tests are needed to get all the parameters of the hypoplasticity model.

Constitutive modelling of the elastic–plastic behaviour of 7050-T7451 aluminium alloy

1992 ◽  
Vol 27 (2) ◽  
pp. 85-92 ◽  
Author(s):  
M D Kuruppu ◽  
J F Williams ◽  
N Bridgford ◽  
R Jones ◽  
D C Stouffer
Keyword(s):  
Aluminium Alloy ◽  
Yield Stress ◽  
Bauschinger Effect ◽  
Internal State ◽  
Constitutive Modelling ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
State Variables ◽  
Fatigue Cycle ◽  
Internal State Variables

This paper presents an extension of the Ramaswamy, Stouffer, and Laflen unified elastic–viscoplastic theory which uses internal state variables to represent a strain rate insensitive aluminium alloy namely 7050-T7451 alloy. The model constants are evaluated from the results of a uniaxial tensile test, with strain hold at saturation, and a fatigue loop. Strain holds in the saturated region of tensile monotonic curves resulted in significant amounts of stress relaxation. The material response is cyclically stable and reveals a strong Bauschinger effect. There is a significant reduction in the yield stress between the initial yield and the subsequent tensile yield stress observed after a fully reversed fatigue cycle. All of these material characteristics were predicted successfully.

Latest Development in Physics-Based Modeling of Coiled Tubing Plasticity and Fatigue

2021 ◽  
Author(s):  
Zhanke Liu ◽  
Steven M. Tipton ◽  
Dinesh Sukumar
Keyword(s):  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Experimental Investigations ◽  
Cycle Fatigue ◽  
State Variables ◽  
Coiled Tubing ◽  
Wall Thinning ◽  
Fatigue Damage Accumulation ◽  
Wide Range ◽  
Novel Algorithms

Abstract Coiled tubing (CT) integrity is critical for well intervention operations in the field. To monitor and manage tubing integrity, the industry has developed a number of computer models over the past decades. Among them, low-cycle fatigue (LCF) modeling plays a paramount role in safeguarding tubing integrity. LCF modeling of CT strings dates back to the 1980s. Recently, novel algorithms have contributed to developments in physics-based modeling of tubing fatigue and plasticity. As CT trips into and out of the well, it goes through bending-straightening cycles under high differential pressure. Such tough conditions lead to low- or ultralow-cycle fatigue, limiting CT useful life. The model proposed in this study is derived from a previous one and based on rigorously derived material parameters to compute the evolution of state variables from a wide range of loading conditions. Through newly formulated plasticity and strain parameters, a physics-based damage model predicts CT fatigue life, along with diametral growth and wall thinning. The revised modeling approach gives results for CT damage accumulation, diametral growth, and wall thinning under realistic field conditions, with experimental validation. For 20 different coiled tubing alloys, it was observed that the model improved in accuracy overall by about 18.8% and consistency by 14.0%, for constant pressure data sets of more than 4,500 data points. The modeling results provide insights into the nonlinear nature of fatigue damage accumulation. This study allowed developing recommendations to guide future analytical modeling and experimental investigations, to summarize theoretical findings in physics-based LCF modeling, and to provide practical guidelines for CT string management in the field. The study provides a fundamental understanding of CT LCF and introduces novel algorithms in plasticity and damage.

Thermodynamic Formulation of Endochronic Cyclic Viscoplasticity With Damage- Application to Eutectic Sn/Pb Solder Alloy

2007 ◽  
Vol 23 (4) ◽  
pp. 433-444 ◽  
Author(s):  
C. F. Lee ◽  
Y. C. Chen
Keyword(s):  
Internal State ◽  
Low Cycle Fatigue ◽  
Cyclic Stress ◽  
Irreversible Thermodynamics ◽  
Damage Parameter ◽  
Fatigue Tests ◽  
Future Research ◽  
Mathematical Form ◽  
State Variables ◽  
Endochronic Theory

AbstractIn this paper, an endochronic theory of cyclic viscoplasticy with damage is established based on the irreversible thermodynamics of continuous media with internal state variables containing an isotropic damage parameter. The constitutive equations derived have the same mathematical form as those of convectional endochronic theory without damage, except the effective stress with damage is used. This result coincides with the Lemaitre's statements of stain equivalence principle.Using the experimental cyclic stress-strain curves of 63Sn/37Pb solder bars, corrected from the uniaxially constant displacement amplitude cyclic tests under MTS Tytron microtester, the computational results of cyclic stess-strain curves with several degrees of damage can reproduce the experimental data quite well. Based on compressive buckling appeared in the vicinity of the compressive end parts of the hysteresis loop, the critical values of damage are determined between 0.3 and 0.4.The evolution equation of damage proposed in terms of the intrinsic damage time scale and its results in the modified Coffin-Manson LCF law can be extended in the future research for a statistical theory of life distribution under low cycle fatigue tests.

scholarly journals Machine learning based multiscale calibration of mesoscopic constitutive models for composite materials: application to brain white matter

2021 ◽  
Author(s):  
Duncan Field ◽  
Yanis Ammouche ◽  
José-Maria Peña ◽  
Antoine Jérusalem
Keyword(s):  
Machine Learning ◽  
Composite Materials ◽  
White Matter ◽  
Constitutive Model ◽  
Constitutive Models ◽  
Constitutive Modelling ◽  
Model Parameters ◽  
Brain White Matter ◽  
Specific Loading ◽  
Spatially Varying

AbstractA modular pipeline for improving the constitutive modelling of composite materials is proposed.The method is leveraged here for the development of subject-specific spatially-varying brain white matter mechanical properties. For this application, white matter microstructural information is extracted from diffusion magnetic resonance imaging (dMRI) scans, and used to generate hundreds of representative volume elements (RVEs) with randomly distributed fibre properties. By automatically running finite element analyses on these RVEs, stress-strain curves corresponding to multiple RVE-specific loading cases are produced. A mesoscopic constitutive model homogenising the RVEs’ behaviour is then calibrated for each RVE, producing a library of calibrated parameters against each set of RVE microstructural characteristics. Finally, a machine learning layer is implemented to predict the constitutive model parameters directly from any new microstructure. The results show that the methodology can predict calibrated mesoscopic material properties with high accuracy. More generally, the overall framework allows for the efficient simulation of the spatially-varying mechanical behaviour of composite materials when experimentally measured location-specific fibre geometrical characteristics are provided.

Constitutive Model for Sn-Pb Solder Under Fatigue Loading

2002 ◽  
Author(s):  
Y. Wei ◽  
C. L. Chow ◽  
M. K. Nielsen ◽  
H. E. Fang
Keyword(s):  
Constitutive Model ◽  
Mechanical Response ◽  
Internal State ◽  
Hold Time ◽  
Fatigue Loading ◽  
Loading Frequency ◽  
State Variables ◽  
Load Paths ◽  
Internal State Variables ◽  
Failure Predictions

The paper presents a constitutive model for Sn-Pb solder which captures the response of this complex material subject to a variety of load paths including fatigue loading. Internal state variables are established to characterize grain coarsening and material degradation observed experimentally. A damage-coupled viscoplastic constitutive model is formulated to take into account the effects of temperature and loading rates on mechanical response. The influence of fatigue loading frequency or strain rate, hold time and temperature on mechanical behavior and fatigue life for 63Sn-37Pb solder alloy is examined. The fatigue failure predictions are compared with those obtained experimentally and found to be satisfactory.

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