Calculation of Stress Relaxation Properties for Type 422 Stainless Steel

1999 ◽  
Vol 122 (1) ◽  
pp. 66-71 ◽  
Author(s):  
F. V. Ellis ◽  
Sebastian Tordonato
Keyword(s):  
Stainless Steel ◽  
Stress Relaxation ◽  
Uniaxial Stress ◽  
Rupture Time ◽  
Flow Rule ◽  
Time Data ◽  
Creep Equation ◽  
Relaxation Properties ◽  
Two Parameter ◽  
Rupture Strain

Analytical life prediction methods are being developed for high-temperature turbine and valve studs/bolts. In order to validate the approach, the calculated results are compared to the results of uniaxial stress relaxation testing, bolt model testing, and service experience. Long time creep, creep-rupture, and stress relaxation tests were performed by the National Research Institute for Metals of Japan (NRIM) for 12 Cr-1 Mo-1 W-1/4V, Type 422 stainless steel bolting material, at 500, 550, and 600°C. Based on these results and limited tests for a service-exposed bolt, the creep behavior can be described using a two-parameter material model: ε/εr=1−1−t/trm+1δ where εr is the rupture strain, tr is the rupture time, and m and δ are material constants. For comparison with the measured uniaxial stress relaxation properties, the stress relaxation was calculated using the two-parameter creep equation and a strain-hardening flow rule. The rupture time data was correlated using time-temperature parameter methods. A power law was used for the rupture strain versus rupture time relationship at each temperature. The calculated stress versus time curves were in good agreement with the measured at all temperatures and for initial strain levels of 0.10, 0.15, 0.20, and 0.25 percent. [S0094-9930(00)01701-7]

Calculation of Stress Relaxation Properties for 1CrMoV Bolt Material

2003 ◽  
Author(s):  
Fred V. Ellis ◽  
Sebastian Tordonato
Keyword(s):  
Stress Relaxation ◽  
Power Law ◽  
Uniaxial Stress ◽  
Flow Rule ◽  
Creep Equation ◽  
Relaxation Properties ◽  
Stress Levels ◽  
Long Time ◽  
Power Law Creep ◽  
Good Agreement

Analytical life prediction methods have been developed for high temperature turbine and valve bolts. For 1CrMoV steel bolt material, long time creep-rupture and stress relaxation tests were performed at 450°C, 500°C, and 550°C by the National Research Institute for Metals of Japan. Based on analysis of their data, the isothermal creep behavior can be described using a power law: ε=Kσn(t)m+1 where ε is the creep strain, t is the time, σ is the stress, K, n, and m are material constants. The time power is a primarily a function of temperature, but also depends slightly on stress. To obtain the value for the time power typical of low stress, the creep equation constants were found in two steps. The time power was found using the lower stress data and a heat-centered type regression approach with the stress levels taking the place of the heats in the analysis. The heat constants were then calculated at all stress levels and regression performed to obtain the stress dependence. For comparison with the measured uniaxial stress relaxation properties, the relaxed stress as a function of time was calculated using the power law creep equation and a strain hardening flow rule. The calculated stress versus time curves were in good agreement with the measured at initial strain levels of 0.10%, 0.15%, and 0.20% for all temperatures except 500°C. At 500°C, good agreement was found using the creep properties typical of a stronger (within heat variation) material.

An Improved Analytical Method for Life Prediction of Bolting

2000 ◽  
Vol 123 (1) ◽  
pp. 70-74 ◽  
Author(s):  
F. V. Ellis ◽  
D. R. Sielski ◽  
R. Viswanathan
Keyword(s):  
Stress Relaxation ◽  
Creep Strain ◽  
Life Prediction ◽  
Prediction Method ◽  
Uniaxial Stress ◽  
Life Assessment ◽  
Flow Rule ◽  
Creep Equation ◽  
Strain Limit ◽  
History Of

A research project was conducted to develop and validate an improved, analytical life prediction method for high-temperature turbine and valve studs/bolts. The life prediction method used the two-parameter creep equation, an incremental calculation procedure and a strain hardening flow rule. The failure criterion was an accumulated inelastic or creep strain limit of 1 percent. The life prediction procedure recommends the use of the service history of operating temperature, number/stress level of tightenings, cycle time, etc., to calculate the stress relaxation behavior. Life assessment uses the measured bolt length to calculate the accumulated creep strain. The link between the current condition, i.e., accumulated creep strain, and the remaining creep life, i.e., time to accumulate 1 percent strain, is obtained by a prediction of the future creep strain accumulation under the intended loading cycle(s) imposed during future operation. In order to validate the approach, the calculated results were compared to the results of uniaxial stress relaxation testing, bolt model testing, and service experience. The analytical procedure coupled with other industry wide NDE and measurement procedures is expected to provide broad guidelines to utilities for bolting life assessment.

On the Measurement of Material Creep Parameters by Nanoindentation

2004 ◽  
Vol 841 ◽  
Author(s):  
J. A. LaManna ◽  
W. C. Oliver ◽  
G. M. Pharr
Keyword(s):  
Material Constant ◽  
Uniaxial Stress ◽  
Complete Characterization ◽  
Indentation Load ◽  
Amorphous Selenium ◽  
Load History ◽  
Time Data ◽  
Creep Equation ◽  
Uniaxial Creep ◽  
Material Creep

ABSTRACTPrevious studies of how material creep parameters can be measured by nanoindentation testing have focused mostly on measurement of the stress exponent for creep, n, and the activation energy, Qc. However, a more complete characterization requires that the material constant A in the uniaxial creep equation εu =Aσn (where εu is the uniaxial strain rate and σ is the uniaxial stress) also be evaluated. Here, we begin to address this issue by performing simple nanoindentation creep experiments in amorphous selenium at temperatures above and below the glass transition. At 35°C and above, the material exhibits a simple linear viscous creep behavior that is load history independent. This allows the parameter A to be determined from the indentation load-displacement-time data by means of an analytical solution. To examine the validity of the approach, values of the parameter A measured in nanoindentation tests are compared to independent measurements obtained in uniaxial tension creep experiments.

scholarly journals Long-term stress relaxation properties of SUS 316 stainless steel.

1987 ◽  
Vol 36 (401) ◽  
pp. 117-122 ◽  
Author(s):  
Toshio OHBA ◽  
Koichi YAGI ◽  
Chiaki TANAKA ◽  
Kiyoshi KUBO
Keyword(s):  
Stainless Steel ◽  
Stress Relaxation ◽  
Relaxation Properties ◽  
316 Stainless Steel

First and Second Order Elastoplastic Analyses of Thin-Walled Metal Members using Generalized Beam Theory

2018 ◽  
Author(s):  
Miguel Abambres
Keyword(s):  
Finite Element ◽  
Stainless Steel ◽  
Cross Section ◽  
Beam Theory ◽  
Second Order ◽  
Flow Rule ◽  
Non Linear ◽  
Thin Walled ◽  
Shell Finite Element ◽  
Generalized Beam Theory

Original Generalized Beam Theory (GBT) formulations for elastoplastic first and second order (postbuckling) analyses of thin-walled members are proposed, based on the J2 theory with associated flow rule, and valid for (i) arbitrary residual stress and geometric imperfection distributions, (ii) non-linear isotropic materials (e.g., carbon/stainless steel), and (iii) arbitrary deformation patterns (e.g., global, local, distortional, shear). The cross-section analysis is based on the formulation by Silva (2013), but adopts five types of nodal degrees of freedom (d.o.f.) – one of them (warping rotation) is an innovation of present work and allows the use of cubic polynomials (instead of linear functions) to approximate the warping profiles in each sub-plate. The formulations are validated by presenting various illustrative examples involving beams and columns characterized by several cross-section types (open, closed, (un) branched), materials (bi-linear or non-linear – e.g., stainless steel) and boundary conditions. The GBT results (equilibrium paths, stress/displacement distributions and collapse mechanisms) are validated by comparison with those obtained from shell finite element analyses. It is observed that the results are globally very similar with only 9% and 21% (1st and 2nd order) of the d.o.f. numbers required by the shell finite element models. Moreover, the GBT unique modal nature is highlighted by means of modal participation diagrams and amplitude functions, as well as analyses based on different deformation mode sets, providing an in-depth insight on the member behavioural mechanics in both elastic and inelastic regimes.

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