scholarly journals Simplified calculation method for coupled thermal--mechanical stress of drum using beam elements

2021 ◽  
Author(s):  
yanjun Li ◽  
zhenhua Zhang ◽  
qingpeng Zeng ◽  
chenshuo Li ◽  
jianxin Shi ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Mechanical Stress ◽  
Low Cycle Fatigue ◽  
Complex Structure ◽  
Operating Conditions ◽  
Life Assessment ◽  
Systematic Evaluation ◽  
Beam Elements ◽  
Simplified Method ◽  
Dual Action

The drum is the core part of a supercharged boiler that is prone to fatigue damage due to the dual action of thermal and mechanical stress. However, owing to its complex structure, complete modeling calculation of the drum requires considerable computational resources. Therefore, based on the basic theory of beam elements, we propose a simplified method using beam elements in place of solid tubes and evaluate the feasibility of this method. The results demonstrate that the simplified method reduced the overall mesh number of the model by 67.19% and the calculation time by 68.08%. Moreover, compared to the solid model, the maximum relative errors of stress and displacement were only 3.44% and 5.16%. Considering the dispersion of low-cycle fatigue life, we applied a statistical approach to the fatigue life assessment of the drum, and obtained the probability of failure corresponding to the fatigue life of the drum under the given operating conditions. This method provides an important basis for the systematic evaluation of fatigue life under various operating conditions and the prediction of failure occurrence.

Life Assessment of a Coke Drum by Using the Thermal-Mechanical Fatigue Properties and Laser Scanning Approach

2020 ◽  
Author(s):  
Zhiyuan Han ◽  
Guoshan Xie ◽  
Zengchao Wang ◽  
Jianzhong Yin ◽  
Jin Shi
Keyword(s):  
Fatigue Life ◽  
Laser Scanning ◽  
Low Cycle Fatigue ◽  
Complex Loading ◽  
Operating Conditions ◽  
Life Assessment ◽  
Fatigue Properties ◽  
Element Analysis ◽  
Thermal Mechanical Fatigue ◽  
Mechanical Fatigue

Abstract Coke drums are critical equipments in delayed coking plants, which are operated under severe thermal-mechanical conditions by cyclic heating and quenching processes. Cracks are usually developed during service because of severe plastic deformation and low-cycle fatigue. Thus, the assessment of the deformation severity and remaining life is important for safety operating of the coke drums. This study investigated the bulging damage and fatigue life of 6 coke drums after 16 years and 22 years of service in China. A thermal-mechanical fatigue test were first performed to simulate complex loading condition experienced by the coke drum. The thermal-mechanical fatigue life curve of the fabrication material was obtained. Then, a internal laser scanning was employed to measure the deformation and bulges of drum shells. The finite element analysis was developed to calculate the cyclic stress and strain and bulging severity based on the laser mapping and operating conditions. The fatigue life of the coke drum was assessed by the Coffin-Manson-Basquin’s relationship. The life evaluation results of different methods were compared and analyzed. The results showed that a reasonable life of the coke drum can be obtained by using the thermal-mechanical fatigue properties and laser scanning approach.

Assessment of Fatigue Life for High-Temperature Pipeline Welds Using X-Ray Diffraction Technique

2007 ◽  
Vol 353-358 ◽  
pp. 130-133
Author(s):  
Keun Bong Yoo ◽  
Jae Hoon Kim
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Diffraction Method ◽  
Life Assessment ◽  
Fatigue Properties ◽  
X Ray Diffraction ◽  
X Ray

The objective of this study is to examine the feasibility of the X-ray diffraction method for the fatigue life assessment of high-temperature steel pipes used for main steam pipelines, re-heater pipelines and headers etc. in power plants. In this study, X-ray diffraction tests were performed on the specimens simulated for low cycle fatigue damage, in order to estimate fatigue properties at the various stages of fatigue life. As a result of X-ray diffraction tests, it was confirmed that the full width at the half maximum (FWHM) decreased with an increase in the fatigue life ratio, and that the FWHM and the residual stress due to fatigue damage were algebraically linearly related to the fatigue life ratio. From this relationship, a direct assessment of the remaining fatigue life was feasible.

Transition From Low Cycle to High Cycle in Uniaxial Fatigue

2013 ◽  
Author(s):  
Mohamed E. M. El-Sayed
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Uniaxial Stress ◽  
Life Assessment ◽  
Elastic Behavior ◽  
Cycle Fatigue ◽  
Fatigue Life Assessment ◽  
Component Development

Fatigue is the most critical failure mode of many mechanical component. Therefore, fatigue life assessment under fluctuating loads during component development is essential. The most important requirement for any fatigue life assessment is knowledge of the relationships between stresses, strains, and fatigue life for the material under consideration. These relationships, for any given material, are mostly unique and dependent on its fatigue behavior. Since the work of Wöhler in the 1850’s, the uniaxial stress versus cycles to fatigue failure, which is known as the S-N curve, is typically utilized for high-cycle fatigue. In general, high cycle fatigue implies linear elastic behavior and causes failure after more than 104 or 105 cycles. However. the transition from low cycle fatigue to high cycle fatigue, which is unique for each material based on its properties, has not been well examined. In this paper, this transition is studied and a material dependent number of cycles for the transition is derived based on the material properties. Some implications of this derivation, on assessing and approximating the crack initiation fatigue life, are also discussed.

3D Crack Growth Analysis and Its Correlation With Experiments for Critical Turbine Components Under an International Collaborative Program

2008 ◽  
Author(s):  
J. Hou ◽  
J. Dubke ◽  
K. Barlow ◽  
S. Slater ◽  
L. Harris ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Operating Conditions ◽  
Cycle Fatigue ◽  
3D Crack Growth ◽  
International Collaborative ◽  
2D And 3D ◽  
Growth Analyses ◽  
Stress Analyses

Following a reanalysis of the original material data plus supplementary Low Cycle Fatigue (LCF) specimen testing, an Original Equipment Manufacturer (OEM) reduced the low cycle fatigue life limits for a number of turbine components. To ascertain the validity of the new life limits, an international collaborative spin rig test program was initiated to provide more accurate low cycle fatigue life limits. The program covered a broad range of activities including, Finite Element (FE) stress analyses, cyclic spin rig testing, fractographic assessment and fatigue crack growth (FCG) analyses. This paper describes the 2D and 3D crack growth analyses of critical turbine components in a turboprop gas turbine engine, comparison of predicted results obtained using different software and also correlations with spin test results from the program. First, FE stress analyses of selected turbine components were carried out under both engine operating conditions and spin-rig test configurations in order to determine the maximum and minimum operating speeds required to match the stress ranges at the critical location specified by the OEM under engine operating conditions. Second, 2D and 3D crack growth analyses were performed independently by three organisations for a disk bolthole using the state-of-the-art software. Third, the predictions from different software were compared, and the relative technical merits of each software were evaluated. Finally, the predicted results were correlated against the striation counts determined by the OEM from the results of spin rig tests.

scholarly journals Fatigue life assessment method of in-service mechanical structure

2021 ◽  
Vol 13 (2) ◽  
pp. 168781402199652
Author(s):  
Xiqiang Ma ◽  
Fang Yang ◽  
Jishun Li ◽  
Yujun Xue ◽  
Zhiqiang Guan
Keyword(s):  
Elastic Modulus ◽  
Fatigue Life ◽  
Modulus Of Elasticity ◽  
Evaluation Model ◽  
Assessment Method ◽  
Operating Conditions ◽  
Life Assessment ◽  
Model Parameters ◽  
Mechanical Structure ◽  
Proposed Model

The most usual failure mode of any mechanical structure is fatigue, which is characterized by an important feature of the decrease of elastic modulus of the material. In this paper, a fatigue life evaluation model based on equivalent elastic modulus is proposed for in-service mechanical structure. In the proposed model, parameters that represent the operating conditions of the mechanical structure, such as load, vibration, and shaft torque, etc., are used as the generalized load. To replace the fatigue stress, the statistical method is used here, which is also used in the conventional fatigue analysis method. The structural strain is also measured simultaneously. Using the statistical theory, the equivalent modulus of elasticity is formulated based on the relationship of stress, strain, and modulus of elasticity. To validate the proposed model, an online fatigue damage experiment has been conducted. The experimental results have been compared with that of the fatigue life prediction model with good agreement. It is expected that the methodology proposed in this paper will be widely used.

Low Cycle Fatigue Behavior of Welded Components: A New Approach — Experiments and Numerical Simulation

2012 ◽  
Author(s):  
Eliane Lang ◽  
Jürgen Rudolph ◽  
Thomas Beier ◽  
Michael Vormwald
Keyword(s):  
Fatigue Life ◽  
Thermal Loading ◽  
Weld Seam ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Strain Curve ◽  
Life Assessment ◽  
New Approach ◽  
Elastic Plastic ◽  
Weld Seams

Nuclear power plant components are often subjected to local plastic deformations due to low cycle operational thermal loading conditions. The fatigue behavior of weld seams is of particular interest in this context. Applicable design codes for fatigue life assessment use factors (e.g. Fatigue strength reduction factors – FSRF) within the simplified elastic-plastic or general elastic-plastic analysis in connection with the design fatigue curves for non-welded components. This way, the influence of the weld seam on the fatigue behavior is approximately considered. Emanating from this status quo ideas for a new approach considering the particularities of the fatigue behavior of the weld seam in more detail are developed. The proposed approach is based on material mechanics and constitutes a combination of experimental findings and numerical calculations in order to determine the local strains and the fatigue relevant influence of geometrical and metallurgical notches induced by the weld seam. Experiments on welded specimens provide the fatigue life as well as the stabilized cyclic stress-strain curve as relevant input parameters for the finite element analyses. The proposed model is capable of considering the exact geometry of the weld seam obtained by 3D scanning with very high resolution and the different material strengths due to the weld. The consideration of the principal influences on the fatigue behavior of weld seams paves the way to the application of established damage parameters such as PJ with the future objective to transfer the results also on arbitrary proportional and non-proportional loadings with variable amplitudes.

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