Analysis of the Secondary Creep of a Rotating Flat Disk

1972 ◽  
Vol 1 (4) ◽  
pp. 227-228
Author(s):  
J.G. Lenard
Keyword(s):  
Creep Strain ◽  
Creep Behavior ◽  
Flow Rule ◽  
Strain Rates ◽  
Secondary Creep ◽  
Uniform Thickness ◽  
Hyperbolic Sine ◽  
Flat Disk ◽  
Linear Creep ◽  
Associated Flow Rule

Secondary creep behavior of a rotating hollow disk of uniform thickness is considered. The hyperbolic sine creep law is used to relate stress and creep strain rate; the applicability of Tresca’s criterion and associated flow rule is assumed. The creep strain rates so obtained are compared to results, given by the exponential and linear creep laws. Recommended limits of applicability of the linear and exponential laws are established.

Creep Parameters Determination by Omega Model to Norton Bailey Law by Regression Analysis for Austenitic Steel SS-304

2021 ◽  
Vol 324 ◽  
pp. 188-197
Author(s):  
Mohsin Sattar ◽  
A. Rahim Othman ◽  
Shahrul Kamaruddin ◽  
Mohammad Azad Alam ◽  
Mohammad Azeem
Keyword(s):  
Regression Analysis ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Complete Analysis ◽  
Mechanical Equipment ◽  
Strain Rates ◽  
Secondary Creep ◽  
Creep Data ◽  
Ss 304 ◽  
Omega Model

In the material’s creep failure analysis, the difficulty of assessing the applied thermo-mechanical boundary conditions makes it critically important. Numerous creep laws have been established over the years to predict the creep deformation, damage evolution and rupture of the materials subjected to creep phenomena. The omega model developed by the American Petroleum Institute and Material Properties Council is one of the most commonly used creep material models for numerical analysis over the years. It is good in defining the fitness of mechanical equipment for service engineering evaluation to ensure the reliable service life of the equipment. The Omega model, however, is not readily accessible and specifically incorporated for creep evaluation in FEA software codes and creep data is always scarce for the complete analysis. Therefore, extrapolation of creep behavior was performed by fitting various types of creep models with a limited amount of creep data and then simulating them, beyond the available data points. In conjunction with the Norton Bailey model, based on API-579/ASME FFS-1 standards, a curve fitting technique was employed called regression analysis. From the MPC project omega model, different creep strain rates were obtained based on material, stress and temperature-dependent data. In addition, as the strain rates increased exponentially with the increase in stresses, regression analysis was used for predicting creep parameters, that can curve fit the data into the embedded Norton Bailey model. The uncertainties in extrapolations and material constants has highlighted to necessitate conservative safety factors for design requirement. In this case study, FEA creep assessment was performed on the material SS-304 dog bone specimen, considered as a material coupon to predict time-dependent plastic deformation along with creep behavior at elevated temperatures and under constant stresses. The results indicated that the specimen underwent secondary creep deformation for most of the period.

Limits of Economy of Material in Plates

1955 ◽  
Vol 22 (3) ◽  
pp. 372-374
Author(s):  
H. G. Hopkins ◽  
W. Prager
Keyword(s):  
Yield Condition ◽  
Transverse Load ◽  
Constant Thickness ◽  
Flow Rule ◽  
Plate Material ◽  
Uniform Thickness ◽  
Simply Supported ◽  
Varying Thickness ◽  
Limiting Case ◽  
Associated Flow Rule

Abstract The paper is concerned with the limits of economy of material in a simply supported circular plate under a uniformly distributed transverse load. The plate material is supposed to be plastic-rigid and to obey Tresca’s yield condition and the associated flow rule. The criterion of failure adopted is that used in limit analysis. It is shown that the plate of uniform thickness has a weight efficiency of about 82 per cent. Stepped plates of segmentwise constant thickness are discussed, and the plate of continuously varying thickness is treated as the limiting case obtained by letting the number of steps go to infinity.

scholarly journals THE INITIAL CREEP OF COLUMNAR-GRAINED ICE: PART II. ANALYSIS

1965 ◽  
Vol 43 (8) ◽  
pp. 1423-1434 ◽  
Author(s):  
L. W. Gold
Keyword(s):  
Creep Rate ◽  
Creep Strain ◽  
Power Law ◽  
Creep Behavior ◽  
Minimum Creep Rate ◽  
Transient Creep ◽  
Time Dependent ◽  
Secondary Creep ◽  
Stress Dependence ◽  
Deflection Rate

Observations on the initial creep behavior of columnar-grained ice are analyzed by assuming that the creep strain at a given time has a power-law dependence on the applied constant compressive stress. The exponent for the stress was time-dependent during transient creep. For first load it started at a low value, increased to a maximum of about 2.23 approximately 75 minutes after the application of the load, and decreased thereafter. For reload it started at a high value and decreased continuously to a constant value of 1.46 by 100 minutes after the application of the load. Creep rates at a given time, calculated from the observed power-law dependence of the creep strain on stress, also had a power-law dependence on stress for time greater than about 25 minutes after the application of the load. The observations are shown to be in agreement with observations by Krausz (1963) on the deflection rate of ice beams and by Steine-mann (1954) and Glen (1958) on the stress-dependence of the minimum creep rate during secondary creep. The observations indicate that the creep rate during secondary creep varies approximately as t−0.5.

A Unified Viscoplastic Model for High Temperature Low Cycle Fatigue of Service-Aged P91 Steel

2013 ◽  
Author(s):  
R. A. Barrett ◽  
P. E. O’Donoghue ◽  
S. B. Leen
Keyword(s):  
High Temperature ◽  
Low Cycle Fatigue ◽  
Kinematic Hardening ◽  
Material Model ◽  
Fatigue Behaviour ◽  
Cyclic Softening ◽  
Flow Rule ◽  
Strain Rates ◽  
Cycle Fatigue ◽  
Hyperbolic Sine

The finite element (FE) implementation of a hyperbolic sine unified cyclic viscoplasticity model is presented. The hyperbolic sine flow rule facilitates the identification of strain-rate independent material parameters for high temperature applications. This is important for the thermo-mechanical fatigue of power plant where a significant stress range is experienced during operational cycles and at stress concentration features, such as welds and branch connections. The material model is successfully applied to the characterisation of the high temperature low cycle fatigue behaviour of a service-aged P91 material, including isotropic (cyclic) softening and non-linear kinematic hardening effects, across a range of temperatures and strain-rates.

Gradient of Soil Constitutive Model

2010 ◽  
Vol 168-170 ◽  
pp. 1126-1129
Author(s):  
Wen Xu Ma ◽  
Ying Guang Fang
Keyword(s):  
Plastic Strain ◽  
Strain Gradient ◽  
Soil Analysis ◽  
Natural Material ◽  
Flow Rule ◽  
The Finite Element Method ◽  
Gradient Effect ◽  
Non Local ◽  
Associated Flow Rule ◽  
Plastic Strain Gradient

For the soil is a very complex natural material, significant strain gradient effect exist in soil analysis. Based on the "gradient" phenomenon, we add the plastic strain gradient hardening item into the traditional Cambridge yield surface. By using the consistency conditions and associated flow rule, we get the explicit expression of plastic strain gradient stiffness matrix. And the finite element method of plastic strain gradient is also shown in this article. Plastic strain gradient is actually a phenomenological non-local model containing microstructure information of the material. It may overcome the difficulties in simulating the gradient phenomenon by traditional mechanical model.

Sign in / Sign up

Export Citation Format

Share Document