Simplified Analysis Methods for Primary Load Designs at Elevated Temperatures

2011 ◽  
Author(s):  
Peter Carter ◽  
T.-L. Sam Sham ◽  
R. I. Jetter
Keyword(s):  
Elevated Temperatures ◽  
Design Procedure ◽  
Inelastic Strain ◽  
Temperature Dependent ◽  
Perfectly Plastic ◽  
Reference Stress ◽  
Analysis Methods ◽  
Elastic Perfectly Plastic ◽  
Further Development ◽  
Primary Load

The use of “simplified” (reference stress) analysis methods is discussed and illustrated for primary load high temperature design. Elastic methods are the basis of the ASME Section III, Subsection NH primary load design procedure. There are practical drawbacks with this current NH approach, particularly for complex geometries and temperature gradients. The paper describes an approach which addresses these difficulties through the use of temperature-dependent elastic, perfectly-plastic analysis. Traditionally difficulties associated with discontinuity stresses, inelastic strain concentrations and multiaxiality are addressed. A procedure is identified to provide insight into how this approach could be implemented. Though preliminary in nature, it is intended to provide a basis for further development and eventual Code adaptation.

Creep Analysis for Pressurized Components Under Creep Conditions Based on Isochronous Stress-Strain Curve and Elastic-Perfectly Plastic Material Model

2018 ◽  
Author(s):  
Qi-Wei Xia ◽  
Jian-Guo Gong ◽  
Fu-Zhen Xuan
Keyword(s):  
Elevated Temperatures ◽  
Plastic Material ◽  
Strain Curve ◽  
Inelastic Strain ◽  
Material Model ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Perfectly Plastic ◽  
Creep Analysis ◽  
Elastic Perfectly Plastic

This work is to address the creep analysis for components at elevated temperatures based on isochronous stress-strain curve and the elastic-perfectly plastic material model through numerical analyses. Numerical results presented that the creep deformation is very sensitive to the target inelastic strain chosen for analysis. A small inelastic strain, corresponding to a small yield stress, can cause very conservative result for the case studied. Moreover, the target inelastic strain, corresponding to the minimum inelastic strain along with the given path, is different from each other for various internal pressures.

scholarly journals Thermo-Mechanical Modeling of Distortions Promoted during Cooling of Ti-6Al-4V Part Produced by Superplastic Forming

2016 ◽  
Vol 838-839 ◽  
pp. 196-201
Author(s):  
Maxime Rollin ◽  
Vincent Velay ◽  
Luc Penazzi ◽  
Thomas Pottier ◽  
Thierry Sentenac ◽  
...  
Keyword(s):  
Finite Element ◽  
Thermal Stresses ◽  
Superplastic Forming ◽  
Model Material ◽  
Material Behavior ◽  
Mechanical Modeling ◽  
Temperature Dependent ◽  
Finite Element Software ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic

In AIRBUS, most of the complex shaped titanium fairing parts of pylon and air inlets are produced by superplastic forming (SPF). These parts are cooled down after forming to ease their extraction and increase the production rate, but AIRBUS wastes a lot of time to go back over the geometric defects generated by the cooling step. This paper investigates the simulations of the SPF, cooling and clipping operations of a part on Abaqus® Finite element software. The different steps of the global process impact the final distortions. SPF impacts the thickness and the microstructure/behavior of material, cooling impacts also the microstructure/behavior of material and promotes distortions through thermal stresses and finally, clipping relaxes the residual stresses of the cut part. An elastic-viscoplastic power law is used to model material behavior during SPF and a temperature dependent elastic perfectly plastic model for the cooling and clipping operations.

Net-Section Limit Pressure and Engineering J Estimates for Axial Part-Through Surface Cracked Pipes

2007 ◽  
Author(s):  
Yun-Jae Kim ◽  
Chang-Sik Oh ◽  
Tae-Kwang Song
Keyword(s):  
Estimation Method ◽  
Small Strain ◽  
Perfectly Plastic ◽  
Reference Stress ◽  
Plastic Materials ◽  
Axial Part ◽  
Elastic Perfectly Plastic ◽  
Axial Surface ◽  
Good Agreement ◽  
J Estimation

This paper provides net-section limit pressures and a reference stress based J estimation method for pipes with internal axial surface cracks under internal pressure. Based on systematic small strain FE limit analyses using elastic-perfectly plastic materials, closed-form approximations of net-section limit pressures are presented. Then, based on proposed net-section limit moments, a method to estimate elastic-plastic J is proposed based on the reference stress approach. Comparison with extensive FE results shows overall good agreement.

A High Temperature Primary Load Design Method Based on Elastic Perfectly-Plastic and Simplified Inelastic Analysis

2020 ◽  
Author(s):  
M. C. Messner ◽  
R. I. Jetter ◽  
T.-L. Sham
Keyword(s):  
Finite Element ◽  
High Temperature ◽  
Creep Damage ◽  
Elastic Analysis ◽  
Allowable Stress ◽  
Perfectly Plastic ◽  
Inelastic Analysis ◽  
Stress Classification ◽  
Elastic Perfectly Plastic ◽  
Primary Load

Abstract The current primary load design provisions of Section III, Division 5 of the ASME Boiler and Pressure Vessel Code, covering high temperature nuclear components, represent an allowable stress methodology using elastic analysis and stress classification procedures to approximate stress redistribution caused by creep and plasticity. This process is difficult to implement and automate in modern finite element frameworks. This paper describes an alternate primary load design approach that uses elastic perfectly-plastic analysis in conjunction with the reference stress concept to eliminate stress classification while retaining a link to the existing Section III, Division 5 allowable stresses. This global, structural allowable stress check is supplemented with a local check to guard against the initiation of creep damage at local stress discontinuities like headers, nozzles, and other stress concentrations. This check is based on a simple elastic-creep analysis with creep damage calculated with the time-fraction approach, using the current ASME minimum-stress-to-rupture values already provided in the current Code. Both the global and local checks are easily implemented in modern finite element analysis software and greatly simplify Section III, Division 5 primary load design when compared to the current design-by-elastic-analysis method. Several examples demonstrate the utility of the new approach and its potential to reduce over-conservatism.

Reference Stress Solutions for Idealized Branch Junctions

2007 ◽  
Author(s):  
Yun-Jae Kim ◽  
Kuk-Hee Lee
Keyword(s):  
Three Dimensional ◽  
Limit Load ◽  
Perfectly Plastic ◽  
Reference Stress ◽  
Plastic Materials ◽  
Pipe Radius ◽  
Plastic Limit Load ◽  
The Mean ◽  
Elastic Perfectly Plastic ◽  
Good Agreement

The present work presents plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) FE limit analyses using elastic-perfectly plastic materials. The proposed solutions are valid to ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0. Comparison with FE results shows good agreement.

Elastic-Plastic J and COD Estimates for Circumferential Through-Wall Cracks Between Elbows and Straight Pipes Under Bending

2007 ◽  
Author(s):  
Tae-Kwang Song ◽  
Yun-Jae Kim
Keyword(s):  
Crack Opening ◽  
Small Strain ◽  
Opening Displacement ◽  
Limit Loads ◽  
Elastic Plastic ◽  
Perfectly Plastic ◽  
Reference Stress ◽  
Plastic Materials ◽  
Elastic Perfectly Plastic ◽  
Reference Stress Approach

A method for elastic-plastic fracture mechanics analyses is presented for the circumferential through-wall crack in weldment joining elbows and attached straight pipes, subject to in-plane bending, based on the reference stress approach. Based on small strain finite element limit analyses using elastic-perfectly plastic materials, closed-form limit loads for circumferential through-wall cracks in between elbows and straight pipes under bending are given. Then applicability of the reference stress based method to approximately estimate J and crack opening displacement (COD) is proposed.

Application of Elastic-Perfectly Plastic Cyclic Analysis to Assessment of Creep Strain

2012 ◽  
Author(s):  
Peter Carter ◽  
Robert I. Jetter ◽  
T.-L. (Sam) Sham
Keyword(s):  
Creep Strain ◽  
Full Range ◽  
Inelastic Strain ◽  
Cyclic Creep ◽  
Rapid Screening ◽  
Full Time ◽  
Perfectly Plastic ◽  
Stress Classification ◽  
Simplified Method ◽  
Elastic Perfectly Plastic

A cyclic elastic-perfectly plastic analysis method is proposed which provides a conservative estimate to cyclic creep strain accumulation within the ratchet boundary. The method is to check for ratcheting based on an elastic-perfectly material with a temperature-dependent pseudo yield stress defined by temperature, time and stress to give 1% accumulated inelastic strain. It does not require stress classification and is also applicable to a full range of temperature within and below the creep regime. This simplified method could be used as a rapid screening calculation, with full time-dependent creep analysis used if necessary. An ASME Boiler and Pressure Vessel Code, Section III draft Code Case based on this simplified method is introduced.

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