Low-Cycle Fatigue of Pressurized Steel Elbows Under In-Plane Bending

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
George E. Varelis ◽  
Spyros A. Karamanos
Keyword(s):  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Local Strain ◽  
Material Model ◽  
Fatigue Curve ◽  
Cyclic Stress ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Analysis And Design

The present study examines the mechanical behavior of steel process piping elbows, subjected to strong cyclic loading conditions. The work is numerical, supported by experimental data on elbow specimens subjected to in-plane cyclic bending, with or without internal pressure, resulting in failure in the low-cycle-fatigue range. The investigation of elbow behavior is conducted using rigorous finite element analysis accounting for measured elbow geometry and the actual material properties. An advanced cyclic plasticity material model is employed for the simulation of the tests. Emphasis is given on the value of local strain and its accumulation at the critical elbow location where cracking occurs. Based on the cyclic stress–strain curve of the material and the strain-based fatigue curve from the test data, the use of Neuber's formula leads to a fatigue analysis and design methodology, offering a simple and efficient tool for predicting elbow fatigue life.

Experimental and Numerical Investigation of Pressurized Pipe Elbows Under Strong Cyclic Loading

2013 ◽  
Author(s):  
George E. Varelis ◽  
Jan Ferino ◽  
Spyros A. Karamanos ◽  
Antonio Lucci ◽  
Giuseppe Demofonti
Keyword(s):  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Local Strain ◽  
Material Model ◽  
Testing Procedure ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Dimensional Measurements

The present work examines the behavior of pipe elbows subjected to strong cyclic in-plane bending loading in the presence of internal pressure. In the first part of this work the experimental procedure is presented in detail. The tests are conducted in a constant amplitude displacement-controlled mode resulting to failures in the low-cycle fatigue range. The overall behavior of each tested specimen, as well as the evolution and concentration of local strains are monitored throughout the testing procedure. Different internal pressure levels are used in order to examine their effect on the fatigue life of the specimens. The above experimental investigation is supported by rigorous finite element analysis. Using detailed dimensional measurements and material testing obtained prior to specimen testing, detailed numerical models are developed to simulate the conducted experiments. An advanced cyclic plasticity material model is employed for the simulation of the tests. Emphasis is given on the local strain development at the critical part of the elbow where cracking occurs. Finally, the results of the present investigation are compared with available design provisions in terms of both ultimate capacity and low-cycle fatigue.

Cyclic Plastic Deformation of a Circular Plate With Work Hardening

1984 ◽  
Vol 106 (4) ◽  
pp. 336-341
Author(s):  
R. Winter
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Nonlinear Behavior ◽  
Strain Curve ◽  
Strain Range ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Element Analysis

An experimental and theoretical study was performed of the nonlinear behavior of a simply supported flat circular aluminum plate under reversed cyclic central load. The application is for the analysis of cyclic stress and strain of structural components in the plastic range for predicting low-cycle fatigue life. The main purpose was to determine the relative accuracy of an elastic-plastic large deformation finite element analysis when the material properties input data are derived from monotonic (noncyclic) stress-strain curves versus that derived from cyclic stress-strain curves. The results showed that large errors could be induced in the theoretical prediction of cyclic strain range when using the monotonic stress-strain curve, which could lead to large errors in predicting low-cycle fatigue life. The use of cyclic stress-strain curves, according to the model developed by Morrow, et al., proved to be accurate and convenient.

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.

Low Cycle Fatigue Tests and Simulations on Steel Elbows

2013 ◽  
Author(s):  
Patricia Pappa ◽  
George E. Varelis ◽  
Spyros A. Karamanos ◽  
Arnold M. Gresnigt
Keyword(s):  
Finite Element ◽  
Low Cycle Fatigue ◽  
Local Strain ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Out Of Plane ◽  
Strain Gauge Measurements ◽  
Number Of Cycles

In this paper the low cycle fatigue behaviour of steel elbows under strong cyclic loading conditions (in-plane and out-of-plane) is examined. The investigation is conducted through advanced finite element analysis tools, supported by real-scale test data for in-plane bending. The numerical results are successfully compared with the experimental measurements. In addition, a parametric study is conducted, which is aimed at investigating the effects of the diameter-to-thickness ratio on the low-cycle fatigue of elbows, focusing on the stress and strain variations. Strain gauge measurements are compared with finite element models. Upon calculation of local strain variation at the critical location, the number of cycles to fracture can be estimated.

Comparative Study of Microstructure and High Temperature Low Cycle Fatigue Behaviour of Nickel Base Superalloys Inconel 713LC and MAR-M247

2016 ◽  
Vol 713 ◽  
pp. 86-89 ◽  
Author(s):  
Ivo Šulák ◽  
Karel Obrtlík ◽  
Ladislav Čelko
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Cyclic Stress ◽  
Fatigue Tests ◽  
Casting Defects ◽  
Cycle Fatigue ◽  
Stress Strain Curve ◽  
Nickel Base

The present work is focused on the study of microstructure and low cycle fatigue behavior of the first generation nickel-base superalloy IN 713LC (low carbon) and its promising second generation successor MAR-M247 HIP (hot isostatic pressing) at 900 °C. Microstructure of both alloys was studied by means of scanning electron microscopy (SEM). The microstructure of both materials is characterized by dendritic grains, carbides and casting defects. Size and morphology of precipitates and casting defects were evaluated. Fractographic observations have been made with the aim to reveal the fatigue crack initiation place and relation to the casting defects and material microstructure. Low cycle fatigue tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 900 °C in air. Hardening/softening curves, cyclic stress-strain curve and fatigue life data of both materials were obtained. Cyclic stress-strain curve of MAR M247 is shifted approximately to 120 MPa higher stress amplitudes in comparison with IN 713LC. Significantly higher fatigue life of MAR-M247 has been observed in Basquin representation. On the other hand IN 713LC shows prolonged lifetime compared with MAR-M247 in the Coffin-Manson representation. Results obtained from high temperature low cycle fatigue tests are discussed.

Low Cycle Fatigue Behavior of Q345b Steel under Uniaxial Cycle Loading

2014 ◽  
Vol 904 ◽  
pp. 95-98
Author(s):  
Xiang You ◽  
Rui Dong Wang ◽  
Shi Ming Cui ◽  
Yong Jie Liu ◽  
Qing Yuan Wang
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Constant Strain Rate ◽  
Strain Curve ◽  
Strain Range ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Cycle Loading ◽  
Reversed Cyclic ◽  
Q345b Steel

In this paper, the low cycle fatigue (LCF) behavior of Q345b steel was experimentally investigated in fully reversed cyclic axial configurations at room temperature. The strain range of 0.3%, 0.4%, 0.5%, 0.6% and 0.7% at constant strain rate of 0.005 s-1 was adopted. Cyclic stress-strain curve and strain life relationship were analyzed according to the Ramberg-Osgood relationship and Coffin-Manson relationship respectively. Suitable parameters were obtained showing good agreements with the experimental fatigue data.

scholarly journals A Mechanism-Based Approach From Low Cycle Fatigue to Thermomechanical Fatigue Life Prediction

2015 ◽  
Vol 138 (7) ◽  
Author(s):  
Xijia Wu ◽  
Zhong Zhang
Keyword(s):  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Thermomechanical Fatigue ◽  
Cyclic Stress ◽  
Ductile Cast Iron ◽  
Cycle Fatigue ◽  
Physical Strain ◽  
Creep Fatigue ◽  
Damage Process

Deformation and damage accumulation occur by fundamental dislocation and diffusion mechanisms. An integrated creep–fatigue theory (ICFT) has been developed, based on the physical strain decomposition rule that recognizes the role of each deformation mechanism, and thus relate damage accumulation to its underlying physical mechanism(s). The ICFT formulates the overall damage accumulation as a holistic damage process consisting of nucleation and propagation of surface/subsurface cracks in coalescence with internally distributed damage/discontinuities. These guiding principles run through both isothermal low cycle fatigue (LCF) and thermomechanical fatigue (TMF) under general conditions. This paper presents a methodology using mechanism-based constitutive equations to describe the cyclic stress–strain curve and the nonlinear damage accumulation equation incorporating (i) rate-independent plasticity-induced fatigue, (ii) intergranular embrittlement (IE), (iii) creep, and (iv) oxidation to predict LCF and TMF lives of ductile cast iron (DCI). The complication of the mechanisms and their interactions in this material provide a good demonstration case for the model, which is in good agreement with the experimental observations.

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