Plastic Strain Concentration in a Cylindrical Shell Subjected to an Axial or a Radial Temperature Gradient

1987 ◽  
Vol 109 (2) ◽  
pp. 184-187 ◽  
Author(s):  
H. Hu¨bel
Keyword(s):  
Cylindrical Shell ◽  
Temperature Gradient ◽  
Plastic Strain ◽  
Thermal Loading ◽  
Kinematic Hardening ◽  
Hardening Material ◽  
Radial Temperature ◽  
Strain Concentration ◽  
Asme Code ◽  
Concentration Factors

Plastic strain concentration factors for use in elastic fatigue analyses (like Ke in ASME Code) are usually overly conservative, but may be unsafe in certain cases. Especially for unnotched structures under thermal loading, many elastic-plastic analyses demonstrated that these plastic strain concentration factors are too restrictive. Thus, the present work derives appropriate factors for the idealized case of a cylindrical shell made of a linear kinematic hardening material and subjected to a radial or an axial temperature gradient. The results obtained are considered to be applicable to many practical problems.

scholarly journals On the Plastic Strain Accumulation in Notched Bars During High-Temperature Creep Dwell

2020 ◽  
Vol 36 (2) ◽  
pp. 167-176 ◽  
Author(s):  
Daniele Barbera ◽  
Haofeng Chen
Keyword(s):  
High Temperature ◽  
Cyclic Loading ◽  
Plastic Strain ◽  
Kinematic Hardening ◽  
High Temperature Creep ◽  
Strain Accumulation ◽  
Material Models ◽  
Cyclic Loading Condition ◽  
Hardening Material ◽  
Temperature Creep

ABSTRACTStructural integrity plays an important role in any industrial activity, due to its capability of assessing complex systems against sudden and unpredicted failures. The work here presented investigates an unexpected new mechanism occurring in structures subjected to monotonic and cyclic loading at high temperature creep condition. An unexpected accumulation of plastic strain is observed to occur, within the high-temperature creep dwell. This phenomenon has been observed during several full inelastic finite element analyses. In order to understand which parameters make possible such behaviour, an extensive numerical study has been undertaken on two different notched bars. The notched bar has been selected due to its capability of representing a multiaxial stress state, which is a practical situation in real components. Two numerical examples consisting of an axisymmetric v-notch bar and a semi-circular notched bar are considered, in order to investigate different notches severity. Two material models have been considered for the plastic response, which is modelled by both Elastic-Perfectly Plastic and Armstrong-Frederick kinematic hardening material models. The high-temperature creep behaviour is introduced using the time hardening law. To study the problem several results are presented, as the effect of the material model on the plastic strain accumulation, the effect of the notch severity and the mesh element type and sensitivity. All the findings further confirm that the phenomenon observed is not an artefact but a real mechanism, which needs to be considered when assessing off-design condition. Moreover, it might be extremely dangerous if the cyclic loading condition occurs at such a high loading level.

Plastic Strain Concentrations in Perforated Structures Subjected to Alternating Loads

1982 ◽  
Vol 104 (3) ◽  
pp. 161-167 ◽  
Author(s):  
R. D. Kichko ◽  
M. Badlani ◽  
F. Spaniel ◽  
W. J. O’Donnell ◽  
J. S. Porowski
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Plastic Strain ◽  
Shear Loading ◽  
Monotonic Loading ◽  
The Finite Element Method ◽  
Perforated Plates ◽  
Strain Concentration ◽  
Elastic Plastic ◽  
Concentration Factors

Perforated plates with a uniform triangular penetration pattern subjected to alternating loads are analyzed. The cases of equibiaxial and shear loading are considered and the finite element method is used to obtain elastic-plastic solutions for various ligament efficiencies. The plastic strain concentrations for alternating loads are compared to those for monotonic loading. Useful methods of obtaining plastic strain concentration factors for alternating loads using the results for monotonic loading are given.

An Assessment of Kinematic Hardening Thermal Ratcheting

1974 ◽  
Vol 96 (3) ◽  
pp. 214-221 ◽  
Author(s):  
T. M. Mulcahy
Keyword(s):  
Thermal Loading ◽  
Kinematic Hardening ◽  
Isotropic Hardening ◽  
Strain Accumulation ◽  
Hardening Material ◽  
Perfectly Plastic ◽  
Thermal Ratcheting

Analytical comparisons are made between the thermal ratcheting response of a kinematic hardening material, a perfectly plastic, and an isotropic hardening material for a two-element assembly. Significant differences were found in the range of mechanical and thermal loading for which ratcheting occurred and the magnitude of the strain accumulation when ratcheting did occur. The kinematic hardening strain accumulation predicted was always smallest.

Comparison of Fatigue Damage Estimates Using the ASME Code and Other Methods

2006 ◽  
Author(s):  
Som Chattopadhyay
Keyword(s):  
Finite Element ◽  
Fatigue Damage ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Local Strain ◽  
Fatigue Curve ◽  
Cycle Fatigue ◽  
Strain Concentration ◽  
Asme Code ◽  
Concentration Factors

Fatigue damage calculations have been performed in a specific design application using the method outlined in the ASME Code Section III as well as the local strain approach. For both methods, the finite element stress analysis results for a structural component subject to a specified set of transient loadings have been considered. The local strain approach is based on computing strain ranges from the elastic stresses using the material stress strain curve and Neuber’s rule. The allowable number of cycles is determined from the strain ranges and the continuous cycling fatigue curve for the material. A comparison of the fatigue damages predicted by the two methods demonstrates some of the conservatisms of the ASME Code procedure over the local strain approach. The sources of conservatism lie in the low cycle fatigue strain concentration factors and inherent safety factors in the design fatigue curves of the ASME Code. Some of the non-conservatisms in the ASME Code fatigue evaluation could primarily arise from the low cycle fatigue strain concentration factors for stress ranges in the vicinity of 3Sm for the material, a result based on experimental and finite element studies. We have also included an assessment approach based on a material distance parameter for the same problem.

The Effect of Infrequent Thermal Overloads on the Behavior of Plates Subjected to Cyclic Thermal Loading

1984 ◽  
Vol 106 (1) ◽  
pp. 86-92
Author(s):  
J. Phillips
Keyword(s):  
High Temperature ◽  
Thermal Cycle ◽  
Thermal Loading ◽  
Kinematic Hardening ◽  
Material Behavior ◽  
Thermal Loads ◽  
Plate Material ◽  
Hardening Material ◽  
Perfectly Plastic ◽  
Deformation Properties

Many components in high-temperature plant experience steady mechanical loads combined with cyclic thermal loads due to routine shutdowns. Less frequent but more severe thermal loads due to unplanned shutdowns may interrupt this routine loading pattern. This paper presents the results of computer calculations on the effect of such thermal overloads on the behavior of a “Bree plate.” Particular attention is given to the creep and plastic ratchetting deformation properties of the system. It is shown that the plate material properties are an important factor in the problem. With an elastic-perfectly plastic plate material, behavior can be predicted from an appropriate linear combination of the results for each type of thermal cycle, multiplied by an enhancement factor in certain cases. With a bilinear kinematic hardening, material behavior is generally determined by the properties of the overload thermal cycle. These results are relevant to many high-temperature design problems.

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