Fatigue Life Prediction for Variable Strain at a Mixing Tee by Use of Effective Strain Amplitude

2020 ◽  
Author(s):  
Koji Miyoshi ◽  
Masayuki Kamaya
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Effective Strain ◽  
Single Overload ◽  
Loading Sequence

Abstract Mixing flow causes fluid temperature fluctuations near the pipe walls and may result in fatigue crack initiation. The authors have previously reported the loading sequence effect on thermal fatigue in a mixing tee. The fatigue damage around the hot spot, which was heated by the hot jet flow from the branch pipe, obtained by Miner’s rule was less than 1.0. Since the strain around the hot spot had waveforms with periodic overload, the loading sequence with periodic overload caused reduction of the fatigue life around the hot spot. In this study, the effect of a single overload on the fatigue crack growth rate was investigated in order to clarify the reduction of the fatigue life at the mixing tee due to strain with periodic overload. In addition, the prediction method of the fatigue life for the variable thermal strain at the mixing tee was discussed. It was shown the crack growth rate increased after an overload for both cases of tensile and compressive overloads. The effective strain amplitude increased after the application of a single overload. The fatigue life curve was modified by considering the increment of the effective strain range. The fatigue damage recalculated using the modified fatigue life curve was larger than 1.0 except in a few cases. The fatigue life could be assessed conservatively for variable strain at the mixing tee using the developed fatigue curve and Miner’s rule.

Fatigue Life Assessment for Variable Strain in a Mixing Tee by Use of Effective Strain Range

2021 ◽  
Author(s):  
Koji Miyoshi ◽  
Masayuki Kamaya
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Effective Strain ◽  
Strain Range ◽  
Life Assessment ◽  
Miner’S Rule ◽  
Loading Sequence ◽  
Miner's Rule

Abstract Mixing flow causes fluctuations in fluid temperature near a pipe wall and may result in fatigue crack initiation. Movement of the hot spot, at which the pipe inner surface was heated by hot flow from the branch pipe, causes thermal stress fluctuations. In this study, the effect of the loading sequence on thermal fatigue in a mixing tee was investigated. In addition, the prediction method of the fatigue life for the variable thermal strain in the mixing tee was discussed. The time histories of the strain around the hot spot were estimated by finite element analysis for which the temperature condition was determined by wall temperature measured in a mock-up test. The accumulated fatigue damage around the hot spot obtained by Miner's rule was less than 1.0. Since the strain around the hot spot had waveforms with periodic overload, the loading sequence with periodic overload caused reduction of the fatigue life around the hot spot. Crack growth tests showed that a single overload decreased crack opening strain and increased the effective strain range. The increment of the effective strain range accelerated the crack growth rate after the overload. The accumulated fatigue damage for the strain in the mixing tee was calculated using Miner's rule and the strain ranges which added the maximum increment of the effective strain range. The accumulated fatigue damage was larger than 1.0 under most conditions. The proposed procedure is suitable to predict the conservative fatigue life in a mixing tee.

Effects of a Single Overload on Fatigue Crack Growth of Type 316 Stainless Steel

2021 ◽  
Author(s):  
Koji Miyoshi ◽  
Masayuki Kamaya
Keyword(s):  
Growth Rate ◽  
Stainless Steel ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Opening ◽  
Constant Amplitude ◽  
Single Overload ◽  
Tensile Overload

Abstract The effect of a single overload on the fatigue crack growth rate was investigated for Type 316 stainless steel. Fatigue crack growth tests were conducted by controlling strain and load. Tensile and compressive overloads were applied during constant amplitude cycling. The overload ratio, which was defined as the ratio of overload size to baseline constant amplitude, was also changed. The constant amplitude tests were conducted at the strain or the stress ratio of −1.0 which was defined as the ratio of the minimum value to the maximum value. The crack opening point was obtained by the unloading elastic compliance method. The crack growth rate increased after the single compressive overload. The accelerating rate increased with the overload ratio. In contrast, not only the acceleration but also the retardation of the crack growth rate was observed for some tensile overload cases. The crack growth rate increased for relatively small tensile overload cases and decreased for relatively large tensile overload cases. The change in the crack opening level was examined. The crack growth rates after tensile and compressive single overloads correlated with the effective strain and stress intensity factor ranges both for load and strain controlling modes.

Experiment and Modeling of Fatigue Crack Growth With Altering Loading Direction

2009 ◽  
Author(s):  
Wenfeng Tu ◽  
Xiaogui Wang ◽  
Zengliang Gao
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Growth Behavior ◽  
Cyclic Plasticity ◽  
Crack Growth Behavior ◽  
Loading Direction

The experiments of mixed Mode I-II fatigue crack growth with altering loading direction were conducted with compact specimens made of 16MnR steel. The specimens were tested under three loading steps. When the crack reached a certain length in the first step, the loading direction was switched to a certain angle. Finally, the loading direction was returned to the original orientation. The crack grow direction had a tendency perpendicular to the loading axis. Right after the loading direction was changed, the crack growth rate was retarded. A new approach developed was used to predict the crack growth behavior. The elastic-plastic stress analysis was performed using the finite element method with the implementation of a cyclic plasticity model. Based on the stress-strain response, fatigue damage near the crack tip was determined by a multi-axial fatigue criterion. Both the crack growth rate and cracking direction were obtained according to the maximum fatigue damage distribution on the critical material plane. The predictions for the crack growth behavior including the crack growth rate and crack growth path were in agreement with the experimental data.

Modeling of Fatigue Crack Growth Based on Two Cyclic Plasticity Models

2008 ◽  
Vol 44-46 ◽  
pp. 111-118
Author(s):  
Wen Feng Tu ◽  
Xiao Gui Wang ◽  
Zeng Liang Gao
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Fatigue Crack Growth Rate ◽  
Cyclic Plasticity ◽  
Plasticity Model ◽  
Stress Strain

Based on two different cyclic plasticity models, fatigue crack growth for 16MnR steel specimens is simulated by using the same multi-axial fatigue damage criterion. The first plasticity model is the Jiang and Sehitoglu model and the second plasticity model is the simple nonlinear kinematic hardening model. The elastic-plastic stress-strain field near the crack tip is obtained respectively by using the two plasticity models. According to the same fatigue criterion, different fatigue damage near the crack tip is determined on the basis of stress-strain responses. The first plasticity model can accurately capture cyclic plasticity deformation behavior and predictions of fatigue crack growth rate are in agreement with the experimental results. However, lots of material constants in the model need to be fitted and more experimental tests should be conducted. The second plasticity model is very simple. The parameters of the model can be acquired easily by uniaxial fatigue tests. Compared with experimental data, the prediction results of fatigue crack growth rate lead to some errors by adopting the second plasticity model.

scholarly journals Fatigue crack growth in aluminum alloy from cold expanded hole with preexisting crack

2020 ◽  
Vol 99 (3) ◽  
pp. 5-16
Author(s):  
P. Yasniy ◽  
O. Dyvdyk ◽  
O. Semenets ◽  
V. Yasnii ◽  
A. Antonov
Keyword(s):  
Growth Rate ◽  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Residual Lifetime ◽  
Aircraft Structure ◽  
Edge Notch

The fatigue life of aircraft structure elements with operational damage in the vicinity of the hole was investigated. The plates 60 mm wide and 6 mm thick made of D16chT aluminum alloy with a central hole were taken for the study. Fatigue damage was examined with an corner quarter-elliptical fatigue crack with a length of 1,25 mm, which was initiated from an edge notch of 0,5 x 0,5 mm. The fatigue crack growth rate on the surface of the plate after mandrel hole with cold expansion degree i = 2,7% increases up to15 times and residual lifetime in three times compared to the virgin plate.

Improvement of Pipeline Fatigue Life Estimation

2016 ◽  
Author(s):  
Sanjay Tiku ◽  
Aaron Dinovitzer ◽  
Vlad Semiga ◽  
Mark Piazza ◽  
Tom Jones
Keyword(s):  
Numerical Simulation ◽  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Life Estimation ◽  
Fatigue Life Estimation

Fracture mechanics methodologies for calculating fatigue lives have been successfully applied by pipeline operators to estimate integrity reassessment intervals. Their application in the definition of pipeline system fatigue lives has been overly conservative in actual practice. The source and magnitude of the conservatism inherent in the calculated fatigue life estimates needs to be identified so operators have a better indicator of when reassessments should take place. The pipe life estimation is especially critical for Electric Resistance Weld (ERW) and Electric Flash Weld (EFW) pipeline systems with longitudinally oriented defects. Prior work on improving fatigue life was initiated through studies completed by Pipeline Research Council International, Inc. (PRCI) to evaluate the sources of differences between fatigue life estimates produced by industry fatigue analysis software and different metallurgists. Two significant sources of conservatism in the fatigue life estimation process were identified: the fatigue crack growth rate (da/dN) and the bulging correction factor applied to axial surface flaws. The experimental and numerical simulation techniques considering the impact of these factors on rate of fatigue crack growth of pipeline axially oriented defects are described in this paper. Finite element modeling was used to simulate pipe bulging in the presence of axial flaws. The effect of the pipe thickness, diameter and flaw geometry was compared with treatments included in existing defect assessment standards. The results illustrate that for longer and deeper flaws existing treatments over represent the local bending due to pipe wall bulging. This results in unnecessarily conservative (shorter) fatigue life estimates. The crack growth rate (da/dN) was measured in a compact tension specimen material fatigue testing program. The test results included a range of ERW and EFW pipe materials with varying vintages and grades. The measured fatigue crack growth rate for the materials tested was found to be lower than that recommended by existing industry standards. This adds to the over conservatism of current approaches. The numerical simulation and materials testing results and related recommendations presented in this paper are compared to existing codified treatments to quantify the level of conservatism inherent in the current state of practice. Recommendations are provided to enhance the precision and better manage conservatism in fatigue crack growth rate calculations. Increased accuracy serves to improve integrity management and would be of interest to pipeline operators, consultants and regulators.

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