Effect of Fatigue Step Loading Sequence on Residual Strength

2000 ◽  
Vol 28 (3) ◽  
pp. 196-208 ◽  
Author(s):  
C. Sun ◽  
A. Gent ◽  
P. Marteny
Keyword(s):  
Residual Strength ◽  
Tensile Strain ◽  
Fatigue Tests ◽  
Rubber Compounds ◽  
Miner’S Rule ◽  
Step Loading ◽  
Step Down ◽  
Loading Sequence ◽  
Miner's Rule ◽  
Number Of Cycles

Abstract Miner's rule is often assumed to hold in accelerated fatigue tests. This rule implies that the order in which loads are applied is not significant. Whether particular loads are applied early in the test or later is unimportant; they are expected to cause the same amount of damage if they are imposed for the same number of cycles. In order to test this hypothesis, we have investigated the effect of loading sequence on residual strength using two levels of tensile strain and several representative rubber compounds. In all cases, a series of increasing strains was found to reduce the strength to a greater degree than the same strains applied in decreasing order. Thus, Miner's rule does not hold for the fatigue failure of these compounds. However, the relative rankings of the compounds remained the same in both step-up and step-down strain sequences.

Variable Loading Sequence Effect for Thermal Fatigue at a Mixing Tee

2019 ◽  
Author(s):  
Koji Miyoshi ◽  
Masayuki Kamaya
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Pipe Wall ◽  
Hot Spot ◽  
Fatigue Tests ◽  
Stress Fluctuation ◽  
Fluctuation Range ◽  
Miner’S Rule ◽  
Loading Sequence ◽  
Miner's Rule

Abstract Mixing flow causes fluctuations in fluid temperature near the pipe wall and may result in fatigue crack initiation. In a previous study, the authors reported the characteristics of the thermal stress to cause thermal fatigue at a mixing tee. A large stress fluctuation was caused by movement of the hot spot, at which the pipe wall was heated by hot flow from the branch pipe. According to a general procedure, fatigue damage is calculated by the linear damage accumulation rule. However, it has been reported that Miner’s rule does not always predict the fatigue life conservatively for variable stress amplitude. In this study, we investigated the change in fatigue life due to variable strain around the hot spot. The time histories of the strain around the hot spot were estimated by finite element analysis (FEA) for which the temperature condition was determined by wall temperature measured in a mock-up test. Strain-controlled fatigue tests were conducted using smooth cylindrical specimens made of stainless steel. The fatigue damage at failure of the specimen was calculated using Miner’s rule. The calculated fatigue damage around the hot spot became less than unity and the minimum value was 0.18. Therefore, Miner’s rule predicted non-conservative fatigue life. In addition, the calculated fatigue damage inside the hot spot was larger than those outside the hot spot and at the position of maximum stress fluctuation. Fatigue tests using strain with periodic overload were also conducted in order to investigate the effect of the loading history on fatigue life. It was shown that the strain with periodic overload reduced the fatigue life. The calculated fatigue damage for the strain at the maximum position of stress fluctuation range seemed to be smaller than those at other positions. This implies that the fatigue life can be estimated conservatively from the viewpoint of the loading sequence effect by calculating the fatigue damage using Miner’s rule for the strain at the maximum position of stress fluctuation range.

A First Investigation on Cumulative Fatigue Life for a Type 304-L Stainless Steel Used for Pressure Water Reactor

2009 ◽  
Author(s):  
A. Fissolo ◽  
J. M. Stelmaszyk
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Fatigue Tests ◽  
Operating Conditions ◽  
Damage Effect ◽  
Final Conclusion ◽  
Variable Loading ◽  
Miner’S Rule ◽  
Miner's Rule ◽  
Type 304

In order to estimate the crack initiation damage, and also the water leakage conditions on PWR pipes, uniaxial fatigue curves are often used. They were deduced from strain or stress load control tests using normalised cylindrical specimens. However, severe thermo-mechanical loading fluctuations are observed in operating conditions. Components may also be submitted to transient loadings. The purpose of the present work is to start investigation on the fatigue life with a variable loading, in order to examine cumulative damage effect in fatigue. In this frame, multilevel strain controlled fatigue tests have been performed on a Type 304-L stainless steel (elaborated in accordance with the RCC-M specifications). The experimental results show that linear Miner’s rule is not verified in our conditions. When the strains are applied in a decreasing order (High-Low strain sequence), the summation of cycle ratios is smaller than unity, whatever the number of applied levels, whereas this summation is higher than one for an increasing order (Low-High strain sequence). A loading sequence effect is clearly evidenced. Different cumulative fatigue damage theories, proposed in literature, have been also tested. Some of them have been given better estimation than the Miner’s rule. That is the case of the so-called “Hybrid Theory” proposed and tested before by Bui Quoc on a Type 304-L steel. Extension of a model proposed by S. Taheri would seem also promising. At this stage, final conclusion cannot be yet deduced, additional investigations are needed.

The Fatigue Behavior of Steel Structures under Random Loading

2008 ◽  
Vol 378-379 ◽  
pp. 3-16
Author(s):  
Henning Agerskov
Keyword(s):  
Fracture Mechanics ◽  
Fatigue Test ◽  
Steel Structures ◽  
Fatigue Tests ◽  
Test Series ◽  
Test Results ◽  
Random Loading ◽  
Mechanics Analysis ◽  
Miner’S Rule ◽  
Miner's Rule

Fatigue damage accumulation in steel structures under random loading has been studied in a number of investigations at the Technical University of Denmark. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part of the investigation, fatigue test series with a total of 540 fatigue tests have been carried through on various types of welded plate test specimens and full-scale offshore tubular joints. The materials that have been used are either conventional structural steel or high-strength steel. The fatigue tests and the fracture mechanics analyses have been carried out using load histories, which are realistic in relation to the types of structures studied, i.e. primarily bridges, offshore structures and chimneys. In general, the test series carried through show a significant difference between constant amplitude and variable amplitude fatigue test results. Both the fracture mechanics analysis and the fatigue test results indicate that Miner’s rule, which is normally used in the design against fatigue in steel structures, may give results, which are unconservative, and that the validity of the results obtained from Miner’s rule will depend on the distribution of the load history in tension and compression.

Effect of Strain Amplitudes and Mean Strain Values on Fatigue Life at Elevated Temperature

2013 ◽  
Author(s):  
Shin-ichi Watanabe ◽  
Koh-ichi Imamura ◽  
Osamu Watanabe ◽  
Akihiro Matsuda
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Amplitude ◽  
Evaluation Method ◽  
Mean Value ◽  
Random Wave ◽  
Miner’S Rule ◽  
Miner's Rule ◽  
Number Of Cycles ◽  
Mean Strain

This paper shows randomness effects of loading amplitude and mean value of displacement-controlled loading history for perforated plates made of SUS304 stainless steel at elevated temperature of 550°C. Under the random wave of strain amplitude, the fracture behavior at elevated temperature environment is clarified by measuring the load-deflection curve at all cycles. The data of experiments were evaluated by Miner’s rule, which has been established as an evaluation method for load variation problem. Number of cycles to fracture is compared to show the good agreement with the Best Fit Fatigue curve (BFF). Peak count method also was used in calculating frequency of the strain in order to evaluate Miner’s rule, and the local strain concentration is calculated based on Stress Redistribution Locus (SRL) method. The other object of this study is to evaluate effect of mean value of strain in loading diagram on fatigue life. The mean strain were used for the cases of R = −0.0, −0.2, −0.4, −0.8 and −1.0. The crack length is measured by using photographs with the CCD video camera at a constant frequency. From the measurement, it is found that the number of cycles to failure is reduced when the absolute of value of mean strain is decreased. And cracks develop at both sides around the hole, but the growth of each crack may not be symmetric. By using these inelastic strain amplitude and crack initiation cycle, the experimented results are shown at the present study.

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.

Fatigue Characteristics of Vulcanized Natural Rubber for Automotive Engine Mounting

2007 ◽  
Vol 353-358 ◽  
pp. 178-181 ◽  
Author(s):  
S. Shibata ◽  
K. Ochi ◽  
Y. Aono ◽  
Hiroshi Noguchi ◽  
Hideki Oshima
Keyword(s):  
Fatigue Crack ◽  
Natural Rubber ◽  
Crack Length ◽  
Early Stage ◽  
Fatigue Cracks ◽  
Fatigue Tests ◽  
Miner’S Rule ◽  
Fatigue Characteristics ◽  
Stress Ratios ◽  
Miner's Rule

In order to investigate fatigue characteristics of vulcanized natural rubber (NR), fatigue tests are carried out under various stress ratios R (R = minimum stress / maximum stress). It was considered that the fatigue cracks were initiated from flaws in very early stage of total life. The fatigue damage process was almost the fatigue crack propagation process and it is independent of R. The crack growth rate was proportional to the crack length to about the first power, when the crack length was defined as the length of the direction perpendicular to the loading direction. Miner’s rule was examined to observe the fatigue crack behavior and checked by using two-step loading fatigue tests experimentally. It seems Miner’s rule has a possibility to predict fatigue lives.

Treatment of Low Stresses in Fatigue Design of Girth Welds Under Spectrum Loading

2008 ◽  
Author(s):  
Stephen J. Maddox
Keyword(s):  
Fatigue Tests ◽  
Test Results ◽  
Welded Steel ◽  
Steel Pipes ◽  
Fatigue Design ◽  
Conflicting Evidence ◽  
Miner’S Rule ◽  
Miner's Rule ◽  
Girth Welds ◽  
Spectrum Loading

Although the use of Miner’s rule for calculating the cumulative damage due to spectrum loading is well established, there is conflicting evidence as to how stresses below the constant amplitude fatigue limit (CAFL) should be assessed. They are known to be damaging under spectrum loading, but the extent of that damage is not clear. Since such stress levels potentially contribute the majority of the fatigue damage from wave motion and vortex-induced vibration in risers, this issue is highly significant both economically and with respect to safety. Therefore, fatigue tests were performed on strip specimens cut from girth-welded steel pipes under constant and variable amplitude loading to investigate this issue. The test results were assessed on the basis of Miner’s rule used in conjunction with various methods of extrapolating the S-N curve beyond the CAFL to establish the most suitable for correctly representing the damaging effect of stress ranges below it. A fracture mechanics fatigue crack growth analysis was also performed to calculate the fatigue lives expected under the test loading spectrum.

scholarly journals Fatigue Properties of AZ31B Magnesium Alloy Processed by Equal-Channel Angular Pressing

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1191
Author(s):  
Ryuichi Yamada ◽  
Shoichiro Yoshihara ◽  
Yasumi Ito
Keyword(s):  
Magnesium Alloy ◽  
Equal Channel Angular Pressing ◽  
Low Cycle Fatigue ◽  
Annealed Sample ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Angular Pressing ◽  
Fundamental Research ◽  
Number Of Cycles ◽  
Biodegradable Magnesium

A stent is employed to expand a narrowed tubular organ, such as a blood vessel. However, the persistent presence of a stainless steel stent yields several problems of late thrombosis, restenosis and chronic inflammation reactions. Biodegradable magnesium stents have been introduced to solve these problems. However, magnesium-based alloys suffer from poor ductility and lower than desired fatigue performance. There is still a huge demand for further research on new alloys and stent designs. Then, as fundamental research for this, AZ31 B magnesium alloy has been investigated for the effect of equal-channel angular pressing on the fatigue properties. ECAP was conducted for one pass and eight passes at 300 °C using a die with a channel angle of 90°. An annealed sample and ECAP sample of AZ31 B magnesium alloy were subjected to tensile and fatigue tests. As a result of the tensile test, strength in the ECAP (one pass) sample was higher than in the annealed sample. As a result of the fatigue test, at stress amplitude σa = 100 MPa, the number of cycles to failure was largest in the annealed sample, medium in the ECAP (one pass) sample and lowest in the ECAP (eight passes) sample. It was suggested that the small low cycle fatigue life of the ECAP (eight passes) sample is attributable to severe plastic deformation.

Effects of T5 and T6 Heat Treatments Applied to Rheocast A356 Parts for Automotive Applications

2008 ◽  
Vol 141-143 ◽  
pp. 237-242 ◽  
Author(s):  
Mario Rosso ◽  
Ildiko Peter ◽  
R. Villa
Keyword(s):  
Fatigue Behaviour ◽  
Cyclic Stress ◽  
Industrial Applications ◽  
Fatigue Tests ◽  
Controlled Cooling ◽  
Test Analysis ◽  
Heat Treated ◽  
Mechanical Performances ◽  
Semi Solid ◽  
Number Of Cycles

The correlation between the evaluation of the mechanical and of the fatigue behaviour of the rheocast, T5 and T6 heat treated SSM A356 aluminium alloy with respect to the microstructures of the component has been investigated. The study has been carried out on a suspension arm injected in a rheocasting 800 tons plant in Stampal S.p.A. The new rheocasting is a process that allows obtaining the alloys in a semisolid state directly from the liquid state, by controlled cooling of the molten alloys. The resulting microstructures are very fine, free from defects and homogeneous: these characteristics improve the mechanical properties of the alloys and specially the response to cyclic stress, an important issue for a suspension component. After a preliminary tensile test analysis, axial high frequency fatigue tests have been carried out at room temperature on specimen cut out from the suspension arm to determine the Wöhler curve and the number of cycles to failure. The results of this work allow a comparison of the effects of heat treatment process, T5 or T6, on Semi-Solid components for industrial applications in the automotive field. On the basis of these analysis the correlation between microstructure and mechanical performances can be established.

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