A Novel Fatigue Evaluation Approach with Direct Steady Cycle Analysis (DSCA) Based on the Linear Matching Method (LMM)

2019 ◽  
Vol 795 ◽  
pp. 383-388 ◽  
Author(s):  
Xiao Tao Zheng ◽  
Zhi Yuan Ma ◽  
Hao Feng Chen ◽  
Jun Shen
Keyword(s):  
Fatigue Life ◽  
Evaluation Method ◽  
Low Cycle Fatigue ◽  
Effective Strain ◽  
Strain Range ◽  
Matching Method ◽  
Evaluation Approach ◽  
Perfectly Plastic ◽  
Fatigue Evaluation ◽  
Linear Matching Method

The traditional Low Cycle Fatigue (LCF) evaluation method is based on elastic analysis with Neuber’s rule which is usually considered to be over conservative. However, the effective strain range at the steady cycle should be calculated by detailed cycle-by-cycle analysis for the alternative elastic-plastic method in ASME VIII-2, which is obviously time-consuming. A Direct Steady Cycle Analysis (DSCA) method within the Linear Matching Method (LMM) framework is proposed to assess the fatigue life accurately and efficiently for components with arbitrary geometries and cyclic loads. Temperature-dependent stress-strain relationships considering the strain hardening described by the Ramberg-Osgood (RO) formula are discussed and compared with those results obtained by the Elastic-Perfectly Plastic (EPP) model. Additionally, a Reversed Plasticity Domain Method (RPDM) based on the shakedown and ratchet limit analysis method and the DSCA approach within the LMM framework (LMM DSCA) is recommended to design cyclic load levels of LCF experiments with predefined fatigue life ranges.

Plastic and Creep Analyses of the Superheater Header Tubeplate Using Linear Matching Method

2004 ◽  
Author(s):  
Haofeng Chen ◽  
Alan R. S. Ponter
Keyword(s):  
Complex Geometry ◽  
Strain Range ◽  
Inelastic Strain ◽  
Cyclic Hardening ◽  
Matching Method ◽  
Plastic Strain Range ◽  
Integrity Assessment ◽  
Perfectly Plastic ◽  
Shakedown Limit ◽  
Linear Matching Method

In 2003 ASME PVP conference, a series of numerical procedures for integrity assessment based upon recently developed Linear Matching Method were presented [1]. A typical example of holed plate was used to verify these procedures for the evaluation of plastic and creep behaviours of complex geometry components based on linear solutions, which can be easily implemented into the commercial FE code ABAQUS through user subroutines. In this paper, a more complex 3D tubeplate in a typical AGR superheater header is analysed for the shakedown limit, reverse plasticity, ratchet limit and creep relaxation based on application of the Linear Matching Method. Both the perfectly plastic model and the cyclic hardening model are adopted for the evaluation of the plastic strain range. For the evaluation of accumulated creep strains, flow stresses and elastic follow-up factors with differing dwell times at the steady cyclic state, a creep-reverse plasticity model is adopted. The total inelastic strain range over the cycle at the steady cyclic state is calculated. By comparing these results with ABAQUS step-by-step inelastic analyses, the applicability of the methods is verified.

scholarly journals Limit, Shakedown and Ratchet Analyses of Defective Pipeline Under Internal Pressure and Cyclic Thermal Loading

2011 ◽  
Author(s):  
Weihang Chen ◽  
Haofeng Chen ◽  
Tianbai Li ◽  
James Ure
Keyword(s):  
Plastic Strain ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Collapse Mechanism ◽  
Cycle Fatigue ◽  
Matching Method ◽  
Plastic Strain Range ◽  
Fatigue Assessment ◽  
Linear Matching Method

In this study, the limit load, shakedown and ratchet limit of a defective pipeline subjected to constant internal pressure and a cyclic thermal gradient are analyzed. Ratchet limit and maximum plastic strain range are solved by employing the new Linear Matching Method (LMM) for the direct evaluation of the ratchet limit. Shakedown and ratchet limit interaction diagrams of the defective pipeline identifying the regions of shakedown, reverse plasticity, ratcheting and plastic collapse mechanism are presented and parametric studies involving different types and dimensions of part-through slot in the defective pipeline are investigated. The maximum plastic strain range over the steady cycle with different cyclic loading combinations is evaluated for a low cycle fatigue assessment. The location of the initiation of a fatigue crack for the defective pipeline with different slot type is determined. The proposed linear matching method provides a general-purpose technique for the evaluation of these key design limits and the plastic strain range for the low cycle fatigue assessment. The results for the defective pipeline shown in the paper confirm the applicability of this procedure to complex 3-D structures.

scholarly journals On Shakedown, Ratchet and Limit Analyses of Defective Pipeline

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Haofeng Chen ◽  
Weihang Chen ◽  
Tianbai Li ◽  
James Ure
Keyword(s):  
Plastic Strain ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Collapse Mechanism ◽  
Cycle Fatigue ◽  
Matching Method ◽  
Direct Evaluation ◽  
Plastic Strain Range ◽  
Fatigue Assessment ◽  
Linear Matching Method

In this study, the limit load, shakedown, and ratchet limit of a defective pipeline subjected to constant internal pressure and a cyclic thermal gradient are analyzed. Ratchet limit and maximum plastic strain range are solved by employing the new linear matching method (LMM) for the direct evaluation of the ratchet limit. Shakedown and ratchet limit interaction diagrams of the defective pipeline identifying the regions of shakedown, reverse plasticity, ratcheting, and plastic collapse mechanism are presented, and parametric studies involving different types and dimensions of part-through slot in the defective pipeline are investigated. The maximum plastic strain range over the steady cycle with different cyclic loading combinations is evaluated for a low cycle fatigue assessment. The location of the initiation of a fatigue crack for the defective pipeline with different slot type is determined. The proposed linear matching method provides a general-purpose technique for the evaluation of these key design limits and the plastic strain range for the low cycle fatigue assessment. The results for the defective pipeline shown in the paper confirm the applicability of this procedure to complex 3-D structures.

scholarly journals Creep Fatigue Life Assessment of a Pipe Intersection with Dissimilar Material Joint by Linear Matching Method

2016 ◽  
Vol 853 ◽  
pp. 366-371
Author(s):  
Daniele Barbera ◽  
Hao Feng Chen ◽  
Ying Hua Liu
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Direct Method ◽  
Life Assessment ◽  
Dissimilar Material ◽  
Matching Method ◽  
Fatigue Life Assessment ◽  
Creep Fatigue ◽  
The Impact ◽  
Linear Matching Method

As the energy demand increases the power industry has to enhance both efficiency and environmental sustainability of power plants by increasing the operating temperature. The accurate creep fatigue life assessment is important for the safe operation and design of current and future power plant stations. This paper proposes a practical creep fatigue life assessment case of study by the Linear Matching Method (LMM) framework. The LMM for extended Direct Steady Cycle Analysis (eDSCA) has been adopted to calculate the creep fatigue responses due to the cyclic loading under high temperature conditions. A pipe intersection with dissimilar material joint, subjected to high cycling temperature and constant pressure steam, is used as an example. The closed end condition is considered at both ends of main and branch pipes. The impact of the material mismatch, transitional thermal load, and creep dwell on the failure mechanism and location within the intersection is investigated. All the results demonstrate the capability of the method, and how a direct method is able to support engineers in the assessment and design of high temperature component in a complex loading scenario.

Novel and Applicable Method to Determine Equivalent Strain Range and Equivalent Strain Direction Under Multiaxial Non-Proportional Loading

2019 ◽  
Author(s):  
Charles R. Krouse ◽  
Grant O. Musgrove ◽  
Taewoan Kim ◽  
Seungmin Lee ◽  
Muhyoung Lee
Keyword(s):  
Fatigue Life ◽  
Turbine Blade ◽  
Low Cycle Fatigue ◽  
Dimensional Space ◽  
Strain Range ◽  
Element Model ◽  
Equivalent Strain ◽  
Loading Conditions ◽  
Proportional Loading ◽  
Strain Direction

Abstract When considering mechanical components that are subjected to complex loading conditions, it is difficult to achieve accurate predictions of low-cycle fatigue life. For multiaxial and non-proportional loads, the principal strain directions vary in three-dimensional space with time. The commonly accepted methods to determine fatigue life under such loading conditions are based on a critical plane approach, and they rely heavily on accurate strain range estimates. However, there is no singly accepted method to determine the critical plane, equivalent strain magnitude, or equivalent strain direction. Furthermore, current suggestions are computationally intensive and challenging to implement. This paper offers a novel and concise method to accurately determine equivalent strain range and equivalent strain direction under multiaxial, non-proportional loading in three-dimensional space. A practical approach is provided for implementing the method, and an example of an application using a finite element model of a first stage turbine blade is discussed. To demonstrate the approach, ANSYS Mechanical was used to simulate a turbine blade under transient loading conditions and to determine the resulting strains. Equivalent strain range results were applied to a Coffin-Manson relation to determine the low-cycle fatigue life of every node within the finite element model of the first stage turbine blade. The post-processing of the strain predictions, which yielded the equivalent strain range and equivalent strain direction, is discussed in detail.

Proposal for a Total Fatigue Life Assessment Methodology That Predicts Fatigue Life From Defect Initiation to Through Wall Leak

2020 ◽  
Author(s):  
Joseph Batten ◽  
Chris Currie ◽  
Jonathan Mann ◽  
Andrew Morley
Keyword(s):  
Fatigue Life ◽  
Effective Strain ◽  
Strain Range ◽  
Assessment Methods ◽  
Life Assessment ◽  
Assessment Methodology ◽  
Traditional Assessment ◽  
Fatigue Life Assessment ◽  
Definition Of

Abstract Even with improvements to remove excessive conservatisms, current fatigue assessment approaches can result in high Cumulative Usage Factors (CUFs) for some analyses. In order to improve plant availability from these assessments and mitigate future changes to design codes, an improvement in understanding in this area is desirable. Hence the proposal for a Life Assessment Methodology (LAM) was created. The LAM is a concept for an approach based on modelling each stage of fatigue life to predict total fatigue life, as a means of minimising conservatism in an assessment, where necessary. It should also be capable of incorporating statistical methods to assign reliability figures to calculated plant lives. This paper describes the proposed definition of the LAM and how a proof of concept version of the LAM was developed to assess the Bettis Bechtel Stepped Pipe (BBSP) test. The results were presented with two seeded cases (fixed inputs) and a range of lives corresponding to associated Target Reliabilities (TRs). The Best Estimate (BE) and TR associated lives produced were based on using the latest methods available for calculating Fatigue Initiation (FI) and Fatigue Crack Growth (FCG), whereas the seeded Effective Strain Range (ESR) comparison case used current deterministic assessment methods. The results for the case study concluded that there is a benefit to pursuing the development of the LAM when compared to traditional assessment methods. It highlighted and quantified the conservatism present in traditional assessment methods for these cases as well as the need to understand the required TR for a specific component as this can have a large effect on the predicted life. With further refinements to the method, a more realistic and robust output of the total fatigue life distribution (for specific cases) would be obtained, which in turn would allow us to better quantify the conservatism associated with a TR.

Multiaxial Low Cycle Fatigue Life Prediction at 300 °C Using Equivalent Strain Appoach

2011 ◽  
Vol 361-363 ◽  
pp. 1669-1672
Author(s):  
Wen Xiao Zhang ◽  
Guo Dong Gao ◽  
Guang Yu Mu
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Strain Range ◽  
Cyclic Fatigue ◽  
Equivalent Strain ◽  
Multiaxial Fatigue ◽  
Fatigue Life Prediction ◽  
Cycle Fatigue

The low cycle fatigue behavior was experimentally studied with the 3-dimension notched LD8 aluminum alloy specimens at 300°C. The 3- dimension stress-strain responses of specimens were calculated by means of the program ADINA. The multiaxial fatigue life prediction was carried out according to von Mises’s equivalent theory. The results from the prediction showed that the equivalent strain range can be served as the valid mechanics for predicting multiaxial high temperature and low cyclic fatigue life.

Thermo-Mechanical Fatigue Life of Coke Drum Skirt Attachment Designs

2016 ◽  
Author(s):  
Gurumurthy Kagita ◽  
Balaji Srinivasan ◽  
Penchala Sai Krishna Pottem ◽  
Gudimella G. S. Achary ◽  
Subramanyam V. R. Sripada
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Effective Strain ◽  
Analysis Model ◽  
Transfer Coefficients ◽  
Elastic Plastic ◽  
Mechanical Fatigue ◽  
Section Viii ◽  
Thermocouple Temperature ◽  
Transient Thermal

Skirt to bottom head attachments of coke drums experience severe thermo-mechanical cyclic stresses, causing failures due to low cycle fatigue. Accordingly, many skirt attachment designs have evolved over a period of time starting with simple conventional weld build up design, improved weld build up design, integral forged attachment design and others. The objective of this paper is to compare thermo-mechanical fatigue life of three different skirt attachment designs using elastic-plastic fatigue assessment methods of ASME Section VIII, Division 2. A transient thermal analysis model is first developed incorporating appropriate boundary conditions. The time-dependent variable heat transfer coefficients at the inner surface of the coke drum, which change with the operation stages and the levels of oil filling and water quenching, are determined based on the field measured thermocouple temperature data on the outer surface of the coke drum. Sequentially coupled elastic-plastic transient thermo-mechanical stress analyses of coke drum skirt attachments are carried out using both Twice Yield and cycle-by-cycle methods. The effective strain ranges and the fatigue life of three different skirt attachment designs are calculated and compared.

scholarly journals Linear Matching Method for Parametric Studies of Weldments Creep-Fatigue Endurance

2013 ◽  
Author(s):  
Yevgen Gorash ◽  
Haofeng Chen
Keyword(s):  
Bending Moment ◽  
Evaluation Procedure ◽  
Geometrical Parameters ◽  
Matching Method ◽  
Individual Parameter ◽  
Creep Fatigue ◽  
Parametric Studies ◽  
Fatigue Evaluation ◽  
Fatigue Endurance ◽  
Linear Matching Method

This paper presents parametric studies on creep-fatigue endurance of the steel AISI type 316N(L) weldments defined as types 1, 2 and 3 according to R5 Vol. 2/3 Procedure classification at 550°C. The study is implemented using the Linear Matching Method (LMM) and based upon previously developed creep-fatigue evaluation procedure considering time fraction rule. Several geometrical configurations of weldments with individual parameter sets, representing different fabrication cases, are developed. For each of configurations, the total number of cycles to failure N* in creep-fatigue conditions is assessed numerically for different loading cases. The obtained set of N* is extrapolated by the analytic function dependent on normalised bending moment M̃, dwell period Δt and geometrical parameters. Proposed function for N* shows good agreement with numerical results obtained by the LMM. Therefore, it is used for the identification of Fatigue Strength Reduction Factors (FSRFs) intended for design purposes and dependent on proposed variable parameters.

Effect of Loading on Stress Intensification Factors

2005 ◽  
Vol 128 (1) ◽  
pp. 33-38
Author(s):  
Rudolph J. Scavuzzo
Keyword(s):  
Fatigue Life ◽  
Evaluation Method ◽  
Fatigue Testing ◽  
Plastic Material ◽  
Strain Curve ◽  
Correct Prediction ◽  
Piping System ◽  
Testing Methods ◽  
Strain Cycle ◽  
Perfectly Plastic

The basic objective of this investigation is to determine the effect of loading on the stress intensification factors of Markl’s fatigue evaluation method for metal piping. Markl’s method is based on the fatigue testing of 4 in. schedule 40 carbon steel cantilever piping. Subsequent testing using a four-point loading showed that the S-N data were different from that predicted by the procedure and equation developed by Markl. Markl’s method is based on determining the elastic-plastic forces in a piping system by multiplying the elastic system stiffness by the actual deflection. In this manner a fictitious force is calculated to determine piping stresses assuming the elastic beam bending equation, Mc/I, applies even in partially plastic pipes. Previous analytical work on this topic by Rodabaugh and Scavuzzo (“Fatigue of Butt Welded Pipe and the Effect of Testing Methods–Report 2: Effect of Testing Methods on Stress Intensification Factors,” Welding Research Bulletin 433, July 1998) showed that these measured differences should occur between cantilever and four-point tests using Markl’s method. The basic assumption in this analytical comparison is that strain-cycle correlations lead to the correct prediction of fatigue life. Using the measured alternating strain, both types of test geometries lead to the same prediction of fatigue life using these strain-cycle correlations. In this study, the same analytical assumptions used by Rodabaugh and Scavuzzo (above) are applied to a pipe where the load is varied from a four-point loading through its extremes. Loads were varied from a cantilever to an end moment by changing the dimensions of four-point loading. Also, the shape of a bilinear stress-strain curve was varied from a perfectly plastic material to various degrees of work hardening by increasing the tangent modulus in the plastic regime. The results of the study indicate that Markl’s method is conservative by predicting too short a fatigue life for four-point loading for a given stress. As indicated by this study, the differences can be very large in the low-cycle regime for a perfectly plastic material and for a four-point loading approaching an end moment. Thus, piping could be over designed with unnecessary conservatism using the current ASME Code method based on stress intensification factors.

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