Section D Neuber's Relationship Between Stress and Strain Concentration Factors and Application to Low-Cycle Fatigue

2009 ◽  
pp. 11-11-3
Keyword(s):  
Low Cycle Fatigue ◽  
Stress And Strain ◽  
Cycle Fatigue ◽  
Strain Concentration ◽  
Concentration Factors

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.

Application of the Deformation Theory of Plasticity for Determining Elastoplastic Stress and Strain Concentration Factors

1976 ◽  
Vol 98 (4) ◽  
pp. 1152-1156 ◽  
Author(s):  
J. P. Eimermacher ◽  
I.-Chih Wang ◽  
M. L. Brown
Keyword(s):  
Deformation Theory ◽  
Analytical Data ◽  
Local Stress ◽  
Failure Criteria ◽  
Constitutive Law ◽  
Stress And Strain ◽  
Strain Concentration ◽  
Theory Of Plasticity ◽  
Concentration Factors ◽  
Von Mises

The deformation theory of plasticity is considered as a means for obtaining a solution to the problem of calculating stress and strain concentration factors at geometric discontinuities where the local stress state exceeds the yield strength of the material. Through the use of the Hencky-Nadai constitutive law and the Von Mises failure criteria, the elastoplastic element stiffness matrix is derived for a plane stress triangular plate element. An elastoplastic solution is arrived at by considering direct-iterative and finite element techniques. Verification of the analytical results is obtained by considering a numerical example and comparing the calculated results with published experimental and analytical data.

Subsea Pipeline Lateral Buckling Design—Strain Concentration or Strain Capacity Reduction Factors

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Safety Margin ◽  
Local Buckling ◽  
Cycle Fatigue ◽  
Lateral Buckling ◽  
Strain Concentration ◽  
Strain Capacity ◽  
Global Strain ◽  
Capacity Reduction

A strain concentration factor is typically incorporated in the higher-pressure and high-temperature (HPHT) pipeline lateral buckling assessment to account for nonuniform stiffness or plastic bending moment. Increased strain concentration can compromise pipeline low cycle fatigue and lateral buckling capacity, leading to an early onset of local buckling failure. In this paper, the philosophy of local buckling mitigation using the strain concentration factor is examined. The local buckling behavior is evaluated. Global strain reduction and evolution against buckling are analyzed with respect to varying joint mismatch level. The concept of a strain reduction factor (SNRF) due to joint mismatch is developed based on the global strain capacity reduction with reference to the uniform configuration. It is demonstrated that the SNRF in terms of strain capacity reduction is a unique characteristic parameter. As opposed to strain concentration, it is an invariant insensitive to evaluation methods and design strain demand level, hence more representative as a limiting design metric to maintain the safety margin. The rationale for its introduction as an alternative to the strain concentration factor is outlined and its benefits are established. The method for obtaining the SNRF and its application is developed. The discernible difference and scenarios for application of either factor are discussed, including low and high cycle fatigue, linearity and stress concentration, engineering criticality assessment (ECA), and lateral buckling. Additional causal factors giving rise to mismatch such as pipe schedule transition and buckler arrestor are also discussed. Iterations of finite element (FE) analyses are performed for a pipe-in-pipe (PIP) configuration in a case study.

Comparisons of low cycle fatigue behavior of CP-Ti under stress and strain-controlled modes in transverse direction

2019 ◽  
Vol 746 ◽  
pp. 27-40 ◽  
Author(s):  
Le Chang ◽  
Bin-Bin Zhou ◽  
Tian-Hao Ma ◽  
Jian Li ◽  
Xiao-Hua He ◽  
...  
Keyword(s):  
Transverse Direction ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Stress And Strain ◽  
Cycle Fatigue ◽  
Cp Ti

NEW METHODS IN FATIGUE OF STRUCTURES

2014 ◽  
Vol 11 (03) ◽  
pp. 1343005
Author(s):  
DANG VAN KY
Keyword(s):  
Fatigue Strength ◽  
Low Cycle Fatigue ◽  
Inelastic Strain ◽  
Stress And Strain ◽  
Multiscale Approach ◽  
Cycle Fatigue ◽  
Efficient Manner ◽  
Hydrostatic Tension ◽  
Shakedown Theory ◽  
Elastic Shakedown

Combining the application of the shakedown theory and a multiscale approach to analysis of fatigue allows interpreting all types of fatigue problems in an efficient manner. The description of the stabilized mechanical state after shakedown at the engineering macroscopic scale and at the mesoscopic scale of grains gives access to the engineering values which will drive the fatigue damage of the structure. The evolution of stress and strain tensors thus obtained for a cycle of fatigue allows predicting the fatigue strength of structures. At high cycle fatigue (HCF), when elastic shakedown takes place, the fatigue strength can be described by a simple combination of mesoscopic shear amplitude and hydrostatic tension at any point of the calculated structure, irrespective of the complexity of the structure and the loading. Two new developments incorporating spectral or modal approaches allow analyzing the fatigue resistance of structures undergoing vibrations in a very efficient manner. At low cycle fatigue (LCF), from the stabilized state of stress and strain, the fatigue strength is derived from a combination of the inelastic strain energy and the hydrostatic pressure. Numerous examples of fatigue analysis are presented.

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