scholarly journals Low Cycle Fatigue Failure of a Sitka Spruce Tree in Hurricane Winds

2014 ◽  
Vol 40 (5) ◽  
Author(s):  
Warren Leigh
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Wind Speed ◽  
Fatigue Failure ◽  
Low Cycle Fatigue ◽  
Failure Prediction ◽  
Picea Sitchensis ◽  
Cycle Fatigue ◽  
Hurricane Wind ◽  
The Impact

Pine plantations are prone to stem breakage due to high cyclic stress levels associated with hurricane force winds. Stress analytical and finite element simulation models were constructed of a representative profile of a (Sitka) Picea sitchensis tree. The profile surface stress (S) was determined due to the combined load of tree self-weight and hurricane wind speed. The results were complemented by reference to two other studies by other researchers that investigated the impact of fatigue cycles on failure (N) of pine wood and tree sway cycles to present a stem fatigue life prediction. The position of maximum surface profile stress and trunk fracture initiation location was ascertained from a non-uniform stress response. No stress uniformity along the trunk profile was observed for any wind-load case examined. The analytical model and finite element analysis of the P. sitchensis tree trunk profile revealed a statically adequate strength reserve factor of 1.4, which suggested another mode of failure was responsible. Fatigue life failure prediction was examined under cyclic and same-stress amplitude related to the hurricane wind speed of 33 m s-1. Predicted trunk fracture occurred in 2.6 hours, which dramatically reduced to two minutes with an increase in wind speed of only 1 m s-1. The calculated exposure time was similar to that recorded during Hurricane Hugo’s transit in 1989. The time-to-failure prediction obtained by the method of analysis provided in this study seemed plausible, and that the profile associated with the P. sitchensis tree would suffer trunk breakage by low cycle fatigue failure.

Prediction of the Low-Cycle Fatigue Life of HY-100 Undermatched Welds in Marine Structures

1995 ◽  
Vol 11 (02) ◽  
pp. 71-80
Author(s):  
Rahul S. Shah ◽  
Kuo-Chiang Wang ◽  
Mary Jane Kleinosky
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Analytical Models ◽  
Cyclic Behavior ◽  
Beam Specimen ◽  
Cycle Fatigue ◽  
Marine Structures ◽  
Surface Plasticity

Finite-element and analytical models are used in this study to predict the low-cycle fatigue life of undermatched (lower yield strength) weldments of HY-100 steel. The objective was to determine the feasibility of replacing conventional overmatched welds in marine structures. Fatigue tests were performed on standard, smooth specimens, notched cylindrical specimens and a four-point-bend test on a full-scale butt beam specimen. Numerical analyses were conducted using finite elements, with a two-surface plasticity algorithm to simulate the cyclic behavior of the individual materials. The stress and strain concentrations at the notches were also evaluated using two analytical models: the Neuber and Glinka relations. The finite-element predictions compared well with experimental data and produced detailed predictions of the strain distributions, which were then used to assess the crack initiation life. Glinka's relation demonstrated superior predictive capabilities for local strains over Neuber's relation.

Analysis on Torsional Fatigue Life of Turbo-Generator Shafts

2011 ◽  
Vol 467-469 ◽  
pp. 1858-1863 ◽  
Author(s):  
Yu Jiong Gu ◽  
Tie Zheng Jin
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Circuit Simulation ◽  
Short Circuit ◽  
Cycle Fatigue ◽  
Two Phase ◽  
Torsional Fatigue ◽  
Turbo Generator ◽  
The Impact

Both low-cycle fatigue and high-cycle fatigue exist during torsional vibrations, but the impact of high-cycle fatigue has rarely been considered. In this paper, a torsional fatigue life analyzing method used for torsional vibration of turbo-generator shafts has been developed based on Manson-Coffin equation and high-cycle fatigue theory. The method has been used to estimate the torsional fatigue life in the most dangerous section of the shafts in a power plant. The cumulative torsional fatigue damage under two-phase short circuit simulation has been predicted.

scholarly journals Numerical modeling of the low cycle fatigue: effect of manufacturing imperfections caused by machining process

2021 ◽  
Vol 349 ◽  
pp. 02011
Author(s):  
Ikram Abarkan ◽  
Abdellatif Khamlichi ◽  
Rabee Shamass
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Machining Process ◽  
Loading Conditions ◽  
Cycle Fatigue ◽  
Maximum Shear Strain ◽  
Element Analysis ◽  
The Impact

The majority of mechanical components in nuclear power plants must be designed to withstand extreme cyclic loading conditions. In fact, when these components are subjected to low cycle fatigue, machining imperfections are considered one of the most significant factors limiting their service life. In the present work, using finite element analysis, a methodology has been suggested to predict the fatigue life of cylindrical parts made of 316 SS, at ambient temperature, under nominal strain amplitude ranging from ± 0.5 to ±1.2% with various surface roughness conditions. Two different multiaxial strain-life criteria have been considered to estimate the fatigue life, namely Brown-Miller and maximum shear strain. The comparison between the predicted and the experimental fatigue lifetimes has revealed that the adopted multiaxial strain life criteria can successfully estimate the fatigue life of 316 SS grade under uniaxial loading conditions. Furthermore, it has been found that the fatigue life decreases as the surface roughness average value increases, which indicates that surface regularities have a significant impact on low cycle fatigue life. Therefore, the proposed methodology is found to be capable of assessing the impact of surface roughness on the fatigue life of this specific steel in the low cycle fatigue regime.

scholarly journals A novel model for low-cycle multiaxial fatigue life prediction based on the critical plane-damage parameter

2020 ◽  
Vol 103 (3) ◽  
pp. 003685042093622
Author(s):  
Jianhui Liu ◽  
Xin Lv ◽  
Yaobing Wei ◽  
Xuemei Pan ◽  
Yifan Jin ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Failure Mechanism ◽  
Fatigue Failure ◽  
Prediction Accuracy ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Multiaxial Fatigue ◽  
Fatigue Life Prediction ◽  
Cycle Fatigue ◽  
Classic Model

Multiaxial fatigue of the components is a very complex behavior. This analyzes the multiaxial fatigue failure mechanism, reviews and compares the advantages and disadvantages of the classic model. The fatigue failure mechanism and fatigue life under multiaxial loading are derived through theoretical analysis and formulas, and finally verified with the results of multiaxial fatigue tests. The model of multiaxial fatigue life for low-cycle fatigue life prediction model not only improves the prediction accuracy of the classic model, but also considers the effects of non-proportional additional hardening phenomena and fatigue failure modes. The model is proved to be effective in low-cycle fatigue life prediction under different loading paths and types for different materials. Compared with the other three classical models, the proposed model has higher life prediction accuracy and good engineering applicability.

An Application of Metal Plasticity in Finite Element Modeling to Predict the Low-Cycle Fatigue Life of a High-Pressure Steam Turbine Casing

2014 ◽  
Author(s):  
Zachary Dyer ◽  
George C. Altland
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Steam Turbine ◽  
Fatigue Damage ◽  
Low Cycle Fatigue ◽  
Total Strain ◽  
Cycle Fatigue ◽  
Steam Turbines ◽  
Elastic Plastic ◽  
Turbine Casing

In the current market for large steam turbines, customers increasingly want to aggressively cycle their equipment to accommodate electrical grids that include fluctuating supplies of green energy. Increased and aggressive cycling leads to higher probability of low-cycle-fatigue cracking and provides motivation for the design of new steam turbines that are robust enough to withstand this demanding working environment yet still meet the operational and cost expectations of potential customers. ASME BPVC Section III Subsection NH provides a calculation for fatigue damage assessment using either an elastic method or an inelastic method. This paper describes how the inelastic method can be applied to large steam turbines — calculating low-cycle fatigue damage by using commercial finite element software and plastic material models to directly determine elastic-plastic strains throughout the cycle, rather than approximating them using the results of an elastic analysis. The inelastic method is applied to a steam turbine casing during startup cycles — the total strain through the cycle is calculated directly by the elastic-plastic finite element analysis (FEA) then the delta equivalent total strain is calculated using equations in Subsection NH. For comparison, an elastic method is applied to the same analysis — the maximum elastic stress is calculated by the linear-elastic FEA then the delta equivalent total strain is approximated using Neuber’s rule. The inelastic method calculates a smaller delta equivalent total strain, which leads to significantly increased fatigue life. This more sophisticated method could lead to steam turbine components with less cost, more durability, and better performance. This paper also discusses some issues in using the inelastic method, such as shakedown and ratcheting.

Finite element simulation technique for evaluation of opening stresses under high plasticity

2021 ◽  
pp. 1-21
Author(s):  
Ans Al Rashid ◽  
Ramsha Imran ◽  
Zia Ullah Arif ◽  
Muhammad Yasir Khalid
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Finite Element Simulation ◽  
Crack Closure ◽  
Low Cycle Fatigue ◽  
Simulation Technique ◽  
Experimental Results ◽  
High Plasticity ◽  
Cycle Fatigue ◽  
Element Simulation

Abstract The crack closure phenomenon is important to study as it estimates the fatigue life of the components. It becomes even more complex under low cycle fatigue (LCF) since under LCF high amount of plasticity is induced within the material near notches or defects. As a result, the assumptions used by the linear elastic fracture mechanics (LEFM) approach become invalid. However, several experimental techniques are reported on the topic, the utilization of numerical tools can provide substantial cost and time-saving. In this study, the authors present a finite element simulation technique to evaluate the opening stress levels for two structural steels (25CrMo4 and 30NiCrMoV12) under low cycle fatigue conditions. The LCF experimental results were used to obtain kinematic hardening parameters through the Chaboche model. The finite element analysis (FEA) model was designed and validated, following the fatigue crack propagation simulation under high plasticity conditions using ABAQUS. Crack opening displacement vs. stress data was exported from ABAQUS, and 1.5% offset method was employed to define opening stress levels. Numerical simulation results were compared with the experimental results obtained earlier through the digital image correlation (DIC) technique. To conclude, FEA could be a valuable tool to predict crack closure phenomena and, ultimately, the fatigue life of components. However, analysis of opening stresses using crystal plasticity models or extended finite element method (XFEM) tools should be explored for a better approximation in future studies.

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