Modeling Coupled Flow-Stress-Damage during Creep Deformation

2012 ◽  
Vol 204-208 ◽  
pp. 3294-3298
Author(s):  
Ru Bin Wang ◽  
Wei Ya Xu ◽  
Jiu Chang Zhang
Keyword(s):  
Creep Deformation ◽  
Failure Process ◽  
Damage Model ◽  
High Stress ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Coupled Flow ◽  
Creep Failure ◽  
Plastic Model ◽  
Elastic Plastic

In order to reflect the tertiary rheological characteristics of hard rocks at the high stress states, a new nonlinear visco-elastic-plastic model is proposed on the basis of linear visco-elastic-plastic model and nonlinear visco-elastic-plasticity. And then the corresponding constitutive model are deduced, which can be used for describing rocks’ long-term strength characteristics and their creep deformational behavior and time-dependent damage under interaction of coupled seepage-stress field in rock engineering. At last, considering the time effect of rock damage in the process of tertiary creep, a coupled seepage -stress creep damage model for investigating the whole creep deformation behavior, including tertiary creep failure process is established, and the related equations governing the evolution of stress, creep damage and rock permeability along with the creep deformation of rock is introduced.

Modeling the Temperature Dependence of Tertiary Creep Damage of a Ni-Based Alloy

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon
Keyword(s):  
Temperature Dependence ◽  
Creep Deformation ◽  
Mechanical Response ◽  
Axial Stress ◽  
Nauk Sssr ◽  
Damage Model ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Continuum Damage ◽  
Over Time

To capture the mechanical response of Ni-based materials, creep deformation and rupture experiments are typically performed. Long term tests, mimicking service conditions at 10,000 h or more, are generally avoided due to expense. Phenomenological models such as the classical Kachanov–Rabotnov (Rabotnov, 1969, Creep Problems in Structural Members, North-Holland, Amsterdam; Kachanov, 1958, “Time to Rupture Process Under Creep Conditions,” Izv. Akad. Nauk SSSR, Otd. Tekh. Nauk, Mekh. Mashin., 8, pp. 26–31) model can accurately estimate tertiary creep damage over extended histories. Creep deformation and rupture experiments are conducted on IN617 a polycrystalline Ni-based alloy over a range of temperatures and applied stresses. The continuum damage model is extended to account for temperature dependence. This allows the modeling of creep deformation at temperatures between available creep rupture data and the design of full-scale parts containing temperature distributions. Implementation of the Hayhurst (1983, “On the Role of Continuum Damage on Structural Mechanics,” in Engineering Approaches to High Temperature Design, Pineridge, Swansea, pp. 85–176) (tri-axial) stress formulation introduces tensile/compressive asymmetry to the model. This allows compressive loading to be considered for compression loaded gas turbine components such as transition pieces. A new dominant deformation approach is provided to predict the dominant creep mode over time. This leads to development of a new methodology for determining the creep stage and strain of parametric stress and temperature simulations over time.

An improved nonlinear damage model of rocks considering initial damage and damage evolution

2020 ◽  
Vol 29 (7) ◽  
pp. 1117-1137 ◽  
Author(s):  
Wenlin Feng ◽  
Chunsheng Qiao ◽  
Shuangjian Niu ◽  
Zhao Yang ◽  
Tan Wang
Keyword(s):  
Damage Evolution ◽  
Least Squares Method ◽  
Damage Model ◽  
Creep Damage ◽  
Secondary Creep ◽  
Nonlinear Creep ◽  
Creep Failure ◽  
Initial Damage ◽  
Nonlinear Damage Model ◽  
Creep Damage Model

The experimental results show that the creep properties of the rocks are affected by the initial damage, and the damage evolution also has a significant impact on the time-dependent properties of the rocks during the creep. However, the effects of the initial damage and the damage evolution are seldom considered in the current study of the rocks' creep models. In this paper, a new nonlinear creep damage model is proposed based on the multistage creep test results of the sandstones with different damage degrees. The new nonlinear creep damage model is improved based on the Nishihara model. The influences of the initial damage and the damage evolution on the components in the Nishihara model are considered. The creep damage model can not only describe the changes in three creep stages, namely, the primary creep, the secondary creep, and the tertiary creep, but also reflect the influence of the initial damage and the damage evolution on creep failure. The nonlinear least squares method is used to determine the parameters in the nonlinear creep damage model. The consistency between the experimental data and the predicted results indicates the applicability of the nonlinear damage model to accurately predict the creep deformation of the rocks with initial damage.

Creep Failure Simulations for 316H at 550°C

2012 ◽  
Author(s):  
Nak Hyun Kim ◽  
Yun Jae Kim ◽  
Catrin M. Davies ◽  
Kamran M. Nikbin ◽  
David W. Dean
Keyword(s):  
Experimental Data ◽  
Damage Model ◽  
Creep Damage ◽  
Inelastic Strain ◽  
Compact Tension ◽  
Creep Failure ◽  
Creep Ductility ◽  
Summation Rule ◽  
Creep Damage Model ◽  
Damage Summation

In this work a method to simulate failure due to creep is proposed using finite element damage analysis. The creep damage model is based on the creep ductility exhaustion concept. Incremental damage is defined by the ratio of incremental inelastic (plastic & creep) strain and multi-axial ductility. A simple linear damage summation rule is applied. When accumulated damage becomes unity, element stresses are reduced to almost zero to simulate progressive crack growth. The model is validated through comparison with experimental data on various sized compact tension, C(T), specimens of 316H stainless steel at 550 °C. The influence of the inelastic strain rate on the uniaxial ductility is considered. Good agreement is found between the simulated results and the experimental data.

Multi-Axial Concrete Models for Nonlinear Analysis

2014 ◽  
Vol 1065-1069 ◽  
pp. 2099-2103
Author(s):  
Hu Qi ◽  
Yun Gui Li
Keyword(s):  
Constitutive Model ◽  
Nonlinear Analysis ◽  
Damage Model ◽  
Nonlinear Characteristic ◽  
Plastic Model ◽  
Elastic Plastic ◽  
Plastic Damage ◽  
Damage Constitutive Model

The most widely used multi-axial concrete models including elastic-plastic model and elastic plastic damage model are expounded and it is recognized that the elastic plastic damage model is more reasonable to reflect nonlinear characteristic of concrete. The development and application of elastic plastic damage model is comprehensively appraised and a practical elastic plastic damage constitutive model is established. Finally the dynamic trend of constitutive model of concrete development is introduced.

Probabilistic Creep Modeling of 304 Stainless Steel Using a Modified Wilshire Creep-Damage Model

2020 ◽  
Author(s):  
Md. Abir Hossain ◽  
Jaime A. Cano ◽  
Calvin M. Stewart
Keyword(s):  
Stainless Steel ◽  
Monte Carlo ◽  
Temperature Stress ◽  
Creep Deformation ◽  
Material Properties ◽  
Probabilistic Model ◽  
Damage Model ◽  
Creep Damage ◽  
304 Stainless Steel ◽  
Creep Damage Model

Abstract Pressure vessel components subject to high temperature and pressure are susceptible to life-limiting creep and/or creep-induced failure. Traditional continuum damage mechanics (CDM) based creep-damage model are used extensively for the prediction and design against creep in these components. Conventional creep experiments show considerable uncertainty in the creep response of materials where scatter can span decades of creep life. The objective of this paper is to introduce the probabilistic methods into a deterministic creep-damage model in order to predict experimental uncertainty. In this study, a modified Wilshire model capable of creep deformation, damage, and rupture prediction is selected. Creep deformation data for 304 stainless steel is collected from the literature consisting of quintuplicate (five) tests at 600°C with varying stress levels. It is hypothesized that the scatter in creep data is due to: test condition (temperature fluctuations and eccentric loading), initial damage (pre-existing surface and sub-surface defects), and metallurgical (local variation in microstructure) uncertainties. Probability distribution functions (pdfs) and Monte Carlo simulations are applied to introduce the uncertainties into the modified Wilshire equations. The domain of each source of uncertainty must be defined. A systematic calibration approach is followed where the material constant for each creep curve (in the quintuple) are obtained and statistical analysis is performed on the material properties to assess the random distribution associated with each uncertain material parameter. The probabilistic calibration begins with the introduction of test condition randomness (±2°C and ±3.2% MPa of nominal temperature/stress) in accordance with the ASTM standards. Cross calibration of temperature-stress variability proceeds the approximation of initial damage uncertainty which captures the remaining scatter in the data. Deterministic calibration unveils the range of variabilities associated with the material properties. The best-fitted pdfs are assigned to each uncertain parameter and subsequently, the deterministic model is converted into a probabilistic model where reliability is a tunable factor. A large number of Monte Carlo simulation are conducted to generate probabilistic creep deformation, minimum-creep-strain-rate (MCSR), and stress-rupture (SR) predictions. It is demonstrated that the probabilistic model produces quantitatively and qualitatively good fits when compared with experimental data. Future work will be directed towards the inclusion of service condition related uncertainty (power plant, turbine blade, Gen IV nuclear reactor application) into the probabilistic framework where the uncertainties are more robust.

Application of the Monkman-Grant Relationship for Ultrafine-Grained Metallic Materials

2013 ◽  
Vol 577-578 ◽  
pp. 137-140
Author(s):  
Marie Kvapilová ◽  
Jiří Dvořák ◽  
Petr Král ◽  
Milan Svoboda ◽  
Vàclav Sklenička
Keyword(s):  
Creep Deformation ◽  
Damage Tolerance ◽  
Creep Damage ◽  
Tolerance Factor ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Metallic Materials ◽  
Ultrafine Grained ◽  
Ultrafine Grained Materials ◽  
The Relationship

The applicability of the Monkman-Grant relationship was analyzed and validated for ultrafine-grained metallic materials under investigation. A special attention has been given to the creep damage tolerance factor which is defined as the ratio of the strain to fracture to the Monkman-Grant ductility and which describes the coupling between creep deformation and damage based on continuum creep damage approach. It was found, that ultrafine-grained materials generally obey the Monkman-Grant relationship, however, the relationship is especially suitable for materials exhibiting short secondary creep and long tertiary creep stages when dislocation-controlled creep is dominant.

Temperature and Orientation Dependence of Creep Damage of Two Ni-Base Superalloys

2007 ◽  
Author(s):  
Ali P. Gordon ◽  
Sameer Khan ◽  
David W. Nicholson
Keyword(s):  
Gas Turbines ◽  
Damage Model ◽  
Creep Damage ◽  
General Purpose ◽  
Orientation Dependence ◽  
Tertiary Creep ◽  
Directionally Solidified ◽  
Element Analysis ◽  
Stress And Deformation ◽  
Marine Air

Both polycrystalline (PC) and directionally-solidified (DS) Ni-base superalloys are commonly applied as turbine materials to primarily withstand creep conditions manifested in either marine-, air- or land-based gas turbines components. The thrust for increased efficiency of these systems, however, translates into the need for these materials to exhibit considerable strength and temperature resistance. This is critical for engine parts that are subjected to high temperature and stress conditions sustained for long periods of time, such as blades, vanes, and combustion pieces. Accurate estimates of stress and deformation histories at notches, curves, and other critical locations of such components are crucial for life prediction and calculation of service intervals. In the current study, the classical Kachanov-Rabotnov model for tertiary creep damage is implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture experiments on samples from two representative Ni-base superalloys (PC and DS) tested at temperatures between 649 and 982°C and two orientations (longitudinally- and transversely-oriented for the DS case only) are applied to extend this damage formulation. The damage model coefficients corresponding to secondary and tertiary creep constants are characterized for temperature and orientation dependence. This updated formulation can be implemented for modeling full-scale parts containing temperature distributions.

Modeling Creep Deformation and Damage Behavior of Tempered Martensitic Steel in the Framework of Additive Creep Rate Formulation

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
J. Christopher ◽  
B. K. Choudhary
Keyword(s):  
Creep Rate ◽  
Internal Stress ◽  
Creep Strain ◽  
Creep Deformation ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Time Behavior ◽  
Secondary Creep ◽  
Modeling Creep ◽  
Applied Stresses

Additive creep rate model has been developed to predict creep strain-time behavior of materials important to engineering creep design of components for high temperature applications. The model has two additive formulations: the first one is related to sine hyperbolic rate equation describing primary and secondary creep deformation based on the evolution of internal stress with strain/time, and the second defines the tertiary creep rate as a function of tertiary creep strain. In order to describe creep data accurately, tertiary creep rate relation based on MPC-Omega methodology has been appropriately modified. The applicability of the model has been demonstrated for tempered martensitic plain 9Cr-1Mo steel for different applied stresses at 873 K. Based on the observations, a power law relationship between internal stress and applied stress has been established for the steel. Further, a higher creep damage accumulation with increasing life fraction has been observed at low stresses than those obtained at high stresses.

Strain and Damage-Based Analytical Methods to Determine the Kachanov–Rabotnov Tertiary Creep-Damage Constants

2011 ◽  
Vol 21 (8) ◽  
pp. 1186-1201 ◽  
Author(s):  
Calvin M. Stewart ◽  
Ali P. Gordon
Keyword(s):  
Creep Behavior ◽  
Creep Deformation ◽  
Analytical Methods ◽  
Numerical Optimization ◽  
Creep Damage ◽  
Tertiary Creep ◽  
Nickel Base Superalloy ◽  
Trial And Error ◽  
Nickel Base ◽  
Base Superalloy

In the power generation industry, the goal of increased gas turbine efficiency has led to increased operating temperatures and pressures necessitating nickel-base superalloy components. Under these conditions, the tertiary creep regime can become the dominant form of creep deformation. In response, the classical Kachanov–Rabotnov coupled creep-damage constitutive model is often used to predict the creep deformation and damage of Ni-base superalloys. In this model, the secondary creep behavior can be determined through analytical methods while the tertiary creep behavior is often found using trial and error or numerical optimization. Trial and error may produce no constants. Numerical optimization can be computationally expensive. In this study, a strain-based and damage-based approach to determine the tertiary creep behavior of nickel-base superalloys has been developed. Analytically determined constants are found for a given nickel-base superalloy. Creep deformation and damage evolution curves are compared. Methods to deal with stress dependence are introduced and studied.

A Microstructural Sensitivity Study of 316H Austenitic Stainless Steel to Inter-Granular Creep Fracture

2011 ◽  
Vol 488-489 ◽  
pp. 658-661
Author(s):  
B. Chen ◽  
Peter E.J. Flewitt ◽  
David John Smith ◽  
C.M. Younes
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Damage Model ◽  
Creep Damage ◽  
Longitudinal Section ◽  
Sensitivity Study ◽  
Assessment Procedure ◽  
Creep Failure ◽  
Creep Ductility ◽  
Damage Prediction

A preliminary sensitivity examination of the ductility exhaustion based creep damage prediction model, currently used in the R5 high temperature assessment procedure, showed that material property inputs had significant effects on damage prediction. In the present work, the link between the microstructural factors and the susceptibility to inter-granular high temperature creep failure is considered. The latter was judged to be associated with the low creep ductility. Here, the longitudinal section of a creep specimen and the fracture surface were examined. Auger electron spectroscopy was used to investigate the grain boundary composition in this specimen, which failed after a creep test of 1038h at 550°C under a triaxial stress state. The present results demonstrate that there is a possibility to correlate the susceptibility to high temperature inter-granular fracture from the low temperature fracture investigations. Finally, the susceptibility of the pre-treated 316H stainless steel to inter-granular high temperature failure and the contribution to the creep damage model are briefly discussed.

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