Prediction of Creep Life on Notched Bar Specimens of Grade 92 Steel

2016 ◽  
Author(s):  
Haruhisa Shigeyama ◽  
Yukio Takahashi ◽  
Jonathan Parker
Keyword(s):  
Finite Element ◽  
Creep Damage ◽  
Creep Data ◽  
Creep Failure ◽  
Creep Tests ◽  
Energy Fraction ◽  
Damage Models ◽  
Finite Element Software ◽  
Notched Specimens ◽  
Life Fraction

Creep tests on two kinds of circumferentially notched round bar specimens as well as plain bar specimen were performed to obtain the multiaxial and uniaxial creep data. Creep damage models of strain fraction and energy fraction rule were developed using these creep data. Then creep damage analyses using a finite element software, MSC Marc, were carried out on notched specimens of both types and creep failure lives were predicted using the creep damage models of classical life fraction rule and developed strain or energy fraction rule. Experimental failure lives of all the conditions of notched specimens were compared with analytical results. As a result, creep failure lives obtained by life fraction rule were underestimated in the short term region and overestimated in the long term region. On the other hands, it is apparent that the majority of creep failure lives obtained by strain and energy fraction rule were predicted with an accuracy within a factor of two. Furthermore, some interrupted creep tests and creep void observations were conducted on the notched specimens of both types. The distributions of creep void number density were in good agreement with the distributions of creep damage calculated by finite element analyses.

Creep Fatigue Interactions in a 1 CrMo V Steel

1976 ◽  
Vol 190 (1) ◽  
pp. 319-330 ◽  
Author(s):  
E.G. Ellison ◽  
A.J.F. Paterson
Keyword(s):  
Plastic Strain ◽  
High Strain ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Cyclic Creep ◽  
Creep Data ◽  
Creep Tests ◽  
Brittle Transition ◽  
Creep Fatigue ◽  
Cyclic Plastic Strain

Static and cyclic creep tests have been carried out on a 1 Cr Mo V steel at 565 °C. In addition, the effects of prior high strain fatigue on subsequent creep behaviour has been studied. A well defined ductile/brittle transition was noted which was unaffected by the type of load controlled cycle. The material softened under cyclic plastic strain and no experimental evidence was obtained which indicated that fatigue and creep damage interacted in a load controlled test to give rise to unexpectedly short lives. The conclusion derived is that “softened creep” data should be used in predictions of deformation and rupture behaviour, and that the use of virgin creep data can give rise to substantial errors.

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.

The Review of Computational FE Software for Creep Damage Mechanics

2012 ◽  
Vol 510 ◽  
pp. 495-499 ◽  
Author(s):  
De Zheng Liu ◽  
Qiang Xu ◽  
Zhong Yu Lu ◽  
Dong Lai Xu
Keyword(s):  
Finite Element ◽  
Damage Mechanics ◽  
Creep Damage ◽  
Damage Analysis ◽  
Finite Element Software ◽  
Current State ◽  
Computational Capability

This paper reports a review on the computational (finite element) software for creep damage analysis. Firstly, it summarizes the current state of how to obtain such computational capability then it concludes with a preference of in-house software. It further reviews the validation practice. Finally, it completes with an outlines of the approach to be used in the developing in-house FE software.

scholarly journals A Study of Coupled Creep Damaged Constitutive Model of Artificial Frozen Soil

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Dongwei Li ◽  
Junhao Chen ◽  
Yan Zhou
Keyword(s):  
Finite Element ◽  
Constitutive Model ◽  
Damage Mechanics ◽  
Yield Criterion ◽  
Creep Damage ◽  
Confining Pressure ◽  
Frozen Soil ◽  
Finite Element Program ◽  
Finite Element Software ◽  
Frozen Clay

Artificial frozen soil is a kind of typical creep material, and the frozen clay under the unloading stress paths of high-confining pressure conforms to the improved the Zienkiewicz–Pande parabola-type yield criterion, and the Mohr–Coulomb yield function can describe the shear yield surface of artificial frozen clay under low-confining pressure. Based on the results of triaxial creep and shear tests for artificial frozen soil, the viscoplastic damage variable and evolution rule of artificial frozen clay were obtained by using the theory of viscoelastic-plastic mechanics and damage mechanics. An improved Zienkiewicz–Pande parabola-type yield criterion was used instead of a linear Newton body to obtain a coupled constitutive model of viscoelastic-plastic damage in the frozen soil under the unloading stress paths and to derive the coupling flexibility matrix for viscoelastic and viscoplastic damage. A finite element program of artificial frozen soil considering creep damage was written in the Visual Fortran 6.6A environment and embedded into the nonlinear finite element software ADINA as a user subroutine. The results of numerical simulation and laboratory testing were identical, with a maximum error of no more than 4.8%. This work shows that it is reasonable to describe the creep constitutive model of frozen soil with the viscoelastic-plastic-coupled constitutive model.

Identification of Stress Multiaxiallity Effect on Creep Damage by a Combination of Experiments and Numerical Analyses

2009 ◽  
Author(s):  
Yukio Takahashi
Keyword(s):  
Finite Element ◽  
Synergetic Effect ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Compact Tension ◽  
Simple Expression ◽  
Creep Rupture ◽  
Creep Tests ◽  
Element Analysis ◽  
Rupture Behavior

Structural materials experience various stress states and their integrity under a wide variety of stress multiaxility needs to be evaluated in design and life management for various components. Especially creep rupture behavior is known to be quite sensitive to the stress multiaxiality. To systematically evaluate the multiaxial effect on creep rupture behavior of modified 9Cr-1Mo steel, a number of creep tests were conducted on round-bar specimens with circumferential notches. Strong effects of temperature and deformation rate on the reduction of area were observed and their synergetic effect was modeled by a simple expression. Then crack growth in compact tension specimens was simulated by finite element analysis to derive ductility under higher stress triaxiality. Finally, true rupture strain was expressed as a function of temperature, inelastic strain rate and triaxiality factor and its validity was demonstrated through finite element analyses on notched bar and compact tension specimens employing it as a local fracture criterion.

Influence of Multiaxial Stresses on Creep Properties of Phosphorus Alloyed Oxygen Free Copper

2009 ◽  
Author(s):  
Rui Wu ◽  
Lai-Zhe Jin ◽  
Rolf Sandstro¨m
Keyword(s):  
Finite Element ◽  
Spent Nuclear Fuel ◽  
Primary Creep ◽  
Limited Extent ◽  
Creep Tests ◽  
Creep Properties ◽  
Notched Specimens ◽  
Basic Model ◽  
Stress States ◽  
Fitting Parameters

Phosphorus alloyed oxygen free copper (Cu-OFP) canisters are planned to be used for spent nuclear fuel in Sweden. The copper canisters will be subjected to creep under multiaxial stress states in the repository. Creep tests have therefore been carried out using double notch specimens having a notch acuity of 0.5 in Cu-OFP at 75°C. The creep results from the notched specimens are compared with those from the smooth ones. It shows that the creep lifetime for notched specimens can be estimated to be two orders of magnitude or more longer than that for the smooth ones, indicating notch strengthening for the investigated Cu-OFP material. Metallographic examinations after failure show that pores and creep cavities to a limited extent are observed only adjacent to fracture. To interpret the tests for the notched creep specimens, finite element computations have been performed with a new basic model for primary creep without fitting parameters. The creep strain versus time could be simulated successfully. Initially the stresses at the notches are almost twice as high as in the centre of the specimens. The highest stresses are relaxed rapidly. At the studied temperature 75°C, the creep exponent of Cu-OFP is about 85, thus, deep down in the power-law breakdown regime. This contributes strongly to the homogenous stress distribution across the centre section. Since the redistribution of stresses has taken place before large creep deformation has occurred, the specimens are not notch sensitive in agreement with observations.

Evaluation of Stress-Increase Caused by Geometric Imperfections in Longitudinally-Welded Hot Reheat Steam Piping of Mod. 9Cr-1Mo Steel

2017 ◽  
Author(s):  
Haruhisa Shigeyama ◽  
Yukio Takahashi ◽  
Masatsugu Yaguchi
Keyword(s):  
Finite Element ◽  
Creep Damage ◽  
Peak Stress ◽  
Finite Element Analyses ◽  
Geometric Imperfections ◽  
Stress Increase ◽  
Damage Models ◽  
Dimensional Finite Element ◽  
Reheat Steam ◽  
Welded Pipe

In this paper, effect of geometric imperfections on peak stress in softened heat affected zone (HAZ) of longitudinally-welded hot reheat steam piping of mod. 9Cr-1Mo steel was investigated by parametric two-dimensional finite element analyses. Four parameters representing amount of ovalization, amount of flattening, range of flattening and amount of linear misalignment were used in order to express the geometric imperfections of the pipe. The peak stress of a longitudinally-welded pipe with a flattening ratio of about 1% reached about 1.5 times of mean diameter stress. Then, estimation formulas of the stress-increase factor were developed based on the results of finite element analyses. In addition, creep damage distributions were also calculated using three kinds of creep damage models and changes of the creep damage due to the geometric imperfections were compared. The ratios of creep damage increase due to the geometric imperfections were found to be equivalent in the three creep damage models applied.

Use of life and strain fraction rules for creep life prediction of pressurized pipe components undergoing geometry change

2005 ◽  
Vol 40 (4) ◽  
pp. 385-394 ◽  
Author(s):  
T H Hyde ◽  
W Sun ◽  
A. A Becker
Keyword(s):  
Life Prediction ◽  
Small Deformation ◽  
Creep Damage ◽  
Deformation Analysis ◽  
Stress And Strain ◽  
Creep Failure ◽  
Creep Life Prediction ◽  
Failure Life ◽  
Life Predictions ◽  
Life Fraction

The results of creep failure life predictions of pressurized plain pipes, pipe bends, and a thick-walled pipe with a circumferential weld are used to demonstrate the applicability of a stress-based life fraction rule (LFR) and a strain-based strain fraction rule (SFR), under conditions of geometric non-linearity (GNL). The material properties used are related to a CrMoV pipe, at 640°C. Both the LFR and the SFR predictions are based on the stress and strain solutions obtained from the finite element calculations using a Norton creep law. The results obtained were compared with those obtained from corresponding creep damage analyses. For the cases investigated, it has been shown that, compared with damage results, conservative failure lives with consistent failure positions were obtained for the pipe weld, using both the LFR and the SFR methods. For plain pipes and pipe bends, the SFR prediction produces conservative results. However, the LFR prediction overestimates the failure life for the range of pipe diameter ratios investigated. The results obtained indicate that the LFR and SFR methods have potential for predicting creep failure lives in cases when the effect of geometry change is significant and hence the method based on the steady state peak stresses obtained from small deformation analysis is not applicable.

Creep Failure Behavior of Notched Structure in the Simulated Steam Turbine Rotor: Experimental and Damage Analysis

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Tian-Ye Niu ◽  
Cheng Gong ◽  
Jian-Guo Gong ◽  
Fu-Zhen Xuan
Keyword(s):  
Constitutive Equation ◽  
Steam Turbine ◽  
Contact Region ◽  
Creep Damage ◽  
Turbine Rotor ◽  
Failure Behavior ◽  
Creep Failure ◽  
Creep Tests ◽  
Blade Root ◽  
Evolution Behavior

Abstract Notched structures widely exist in steam turbine components in fossil power plant, e.g., the groove of the rotor, etc. Previous studies indicate that creep failures occur at the groove of the rotor or the adjacent regions. Thus, it is essential to study the creep failure behavior of the notched structures for the safe operation of the system. In this work, creep tests of the simulated steam turbine component have been conducted at the temperature of 605 °C, and the creep-damage constitutive equation is used to track the evolution behavior of creep strain and damage of this component. The influence of structural and loading configurations on creep failure behavior of the component is discussed. Results demonstrate that the shearing failure at the contact area between the blade root and the rotor is observed for the tested component, while the cracking at the groove of the rotor is not found. Creep-damage constitutive equation employed in this work could provide an adequate solution of the simulated component. Parametric studies indicate that creep crack initiation and creep failure of the simulated components may occur at the contact region (i.e., between the blade root and the rotor) and the groove of the rotor, which is closely related to structural and loading configurations of the components.

Modeling the Creep Damage of P91 Steel Using Peridynamics

2019 ◽  
Author(s):  
Shank S. Kulkarni ◽  
Alireza Tabarraei ◽  
Xiaonan Wang
Keyword(s):  
Experimental Data ◽  
High Temperature ◽  
Structural Integrity ◽  
Creep Damage ◽  
Creep Model ◽  
Creep Tests ◽  
P91 Steel ◽  
Damage Models ◽  
Modeling Creep ◽  
Non Local

Abstract Creep is an important failure mechanism of metal components working at a high temperature. To ensure the structural integrity and safety of systems working at high temperature it is essential to predict failure due to creep. Classical continuum based damage models are used widely for modeling creep damage. A more recently developed non-local mechanics formulation called peridynamics has displayed better performance in modeling damage with respect to classical local mechanics methods. In this paper, the peridynamic formulation is extended to model creep in metals. We have chosen Liu-Murakami creep model for developing a peridynamic formulation for modeling creep. The proposed formulation is validated by simulating creep tests for P91 steel and comparing the results with experimental data from the literature.

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