Numerical study of fatigue damage under random loading using Rainflow cycle counting

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Tayeb Kebir ◽  
José A.F.O. Correia ◽  
Mohamed Benguediab ◽  
Abilio M.P. De Jesus
Keyword(s):  
Fatigue Damage ◽  
Numerical Study ◽  
Scientific Work ◽  
Stress Effect ◽  
Mean Stress ◽  
Random Loading ◽  
Content Type ◽  
Rainflow Cycle Counting ◽  
The Mean ◽  
Rainflow Counting

PurposeThe purpose of this scientific work is to simulate the fatigue damage under random loading, taking into account the mean stress effect on fatigue lifetime and using the Rainflow counting technique to assess the fatigue damage by the Ansys software. The used material is aluminum alloy 6082-T6. A comparison with literature results has confirmed this investigation in this paper.Design/methodology/approachThe study of fatigue under random loading is based on the same concepts as constant loading with the addition of damage summation. The proportion of damage caused by a stress cycle depends not only on the alternating stress but also on the mean stress.FindingsAnalysis of the fatigue damage shows that the number of relative damage due to each cycle.Originality/valueThis paper aims to simulate the fatigue damage under random loading for aluminum alloys.

Numerical study of fatigue damage under random loading using rainflow cycle counting

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Tayeb Kebir ◽  
José Correia ◽  
Mohamed Benguediab ◽  
Abilio M.P. de Jesus
Keyword(s):  
Fatigue Damage ◽  
Numerical Study ◽  
Hysteresis Loops ◽  
Scientific Work ◽  
Simulation Method ◽  
Stress Effect ◽  
Mean Stress ◽  
Random Loading ◽  
Content Type ◽  
The Mean

PurposeThe purpose of this scientific work is to simulate the fatigue damage under random loading taking into account the mean stress effect on fatigue lifetime and using the rainflow counting technique to assess the fatigue damage.Design/methodology/approachThe study of fatigue under random loading is based on same concepts which as constant loading with addition of damage summation. The damage of materials due a stress cycle depends not only on the alternating stress but also on the mean stress.FindingsThe cycles counting simulation method allows quantifying the hysteresis loops, even if for small amplitude stresses.Originality/valueThe cycles are low or medium; the damage occurs most often, the higher values of alternating stresses cause the most failure of materials.

Fatigue Life Prediction of Vortex Reducer Based on Stress Gradient

2018 ◽  
Author(s):  
Yanbin Luo ◽  
Yanrong Wang ◽  
Bo Zhong ◽  
Jiazhe Zhao ◽  
Xiaojie Zhang
Keyword(s):  
Fatigue Life ◽  
Size Effect ◽  
Stress Gradient ◽  
Fatigue Crack Initiation ◽  
High Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Notched Specimens ◽  
Life Model ◽  
The Mean

The effects of stress gradient and size effect on fatigue life are investigated based on the distributions of stress at notch root of the notched specimens of GH4169 alloy. The relationship between the life of the notched specimens and the smooth specimens is correlated by introducing the stress gradient effect factor, and a new life model of predicting the notched specimens based on the Walker modification for the mean stress effect is established. In order to improve the prediction precision of life model with the equation parameters having a definite physical significance, the relationships among fatigue parameters, monotonic ultimate tensile strength and reduction of area are established. Three-dimensional elastic finite element (FE) analysis of a vortex reducer is carried out to obtain the data of stress and strain for predicting its life. The results show that there is a high-stress gradient at the edge of the air holes of the vortex reducer, and it is thus a dangerous point for fatigue crack initiation. The prediction result of the vortex reducer is more reasonable if the mean stress, stress gradient and size effect are considered comprehensively. The developed life model can reflect the effects of many factors well, especially the stress concentration. The life of the notched specimens predicted by this model give a high estimation precision, and the prediction life data mainly fall into the scatter band of factor 2.

Time-Variant Reliability Assessment of FPSO Hull Girder With Long Cracks

2006 ◽  
Vol 129 (2) ◽  
pp. 81-89 ◽  
Author(s):  
Efrén Ayala-Uraga ◽  
Torgeir Moan
Keyword(s):  
Brittle Fracture ◽  
Fatigue Cracking ◽  
Stiffened Panel ◽  
Stress Effect ◽  
Mean Stress ◽  
Stiffened Panels ◽  
Hull Girder ◽  
Mean Stress Effect ◽  
Hull Structure ◽  
The Mean

An efficient time-variant reliability formulation for the safety assessment of an aging floating production storage and offloading (FPSO) vessels with the presence of through-thickness cracks (i.e., long cracks), is presented in this paper. Often in ship structures, cracks are detected by means of close visual inspection when they have already propagated through the thickness. The propagation of long cracks in stiffened panels is therefore considered, as they may be present in critical details of the deck and/or bottom plating of the vessel. Although it has been found that stiffened panels are tolerant to fatigue cracking, the safety of such structural components with the presence of long cracks may be threatened when exposed to overload extreme conditions, i.e., brittle or ductile fracture may occur. The probability of brittle fracture of an aging hull structure, i.e., a stiffened panel at the bottom plating with the presence of long cracks is studied in this paper. The mean stress effect due to the continuously varying still-water loading as well as residual stresses is explicitly accounted for in the crack growth calculation procedure presented herein. An analytical model is established for determining the equivalent long-term stress range including the mean stress effect. The continuously varying still-water load effects due to the operational nature of FPSOs introduce additional uncertainties in the estimation of fatigue damage as well as in the likelihood of fracture failure mode. In the present case study it is found that the time-invariant approach is a good approximation when dealing with the time-variant reliability problem. One of the main conclusions drawn from this study is that the still-water mean stress has a significant effect on the failure probabilities of stiffened panels with long cracks under brittle fracture mode.

High-Cycle Fatigue Behavior of Type 4340 Steel Pressurized Blocks Including Mean Stress Effect

2019 ◽  
Author(s):  
Elie A. Badr ◽  
Joanne Ishak
Keyword(s):  
Stress Ratio ◽  
Fatigue Behavior ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Ultimate Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Test Results ◽  
Linear Correction ◽  
The Mean

Abstract Mean stress effects in pressurized steel blocks were examined under constant amplitude fatigue loading. The tests were performed to provide experimental data needed to study the effect of mean stress on fatigue lives of subject specimen, and to substantiate the use of analytical expressions to account for the mean stress. The mean stress was the result of subjecting the specimens to an autofrettage pressure which induced compressive residual stresses at the crossbore intersection of the specimens. Fatigue tests were carried out under both tensile and compressive mean stress levels. Test results were compared to several mean stress accounting relationships such as the Smith-Watson Topper, Bergmann and Seeger, modified Goodman, Gerber and Soderberg. Test results indicated that the modified Goodman equation is favorable in accounting for the effect of both tensile and compressive mean stresses on fatigue life (up to a compressive mean stress to ultimate stress ratio of −0.2). The behavior under compressive mean stress to ultimate stress ratio of less than −0.2 indicated that a linear correction relationship was required.

Mean Stress Effect on Fatigue Properties of Type 316 Stainless Steel: Part II — In PWR Primary Water Environment

2017 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Effective Strain ◽  
Strain Range ◽  
Stress Effect ◽  
Mean Stress ◽  
316 Stainless Steel ◽  
Mean Stress Effect ◽  
Primary Water ◽  
The Mean

The mean stress effect on the fatigue life of Type 316 stainless steel was investigated at 325°C in simulated PWR primary water. It was shown that, as shown in high-temperature air environment, the fatigue life was extended by applying the mean stress under the same stress amplitude. An increase in the maximum peak stress by applying the mean stress induced additional plastic strain and this hardened the material. On the other hand, the fatigue life was shortened by the mean stress for the same strain range. The ratcheting strain caused by applying mean stress accelerated crack mouth opening and reduced fatigue life. It was also shown that the fatigue life in the simulated PWR primary water was shorter than that in air even without the mean stress. The magnitude of the reduction depended on the strain range. The reduction in fatigue life was the maximum when the strain range was 0.6%. The environmental effect disappeared when the effective strain was less than 0.4%.

Development of New Design Fatigue Curves in Japan: Discussion of Best-Fit Curves Based on Fatigue Test Data With Small-Scale Test Specimen

2018 ◽  
Author(s):  
Yun Wang ◽  
Hisamitsu Hatoh ◽  
Masato Yamamoto ◽  
Motoki Nakane ◽  
Akihiko Hirano ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Fatigue Tests ◽  
Small Scale ◽  
Stress Effect ◽  
Mean Stress ◽  
Mean Stress Effect ◽  
Scale Test ◽  
The Mean ◽  
Best Fit ◽  
Good Agreement

Based on the precedent design fatigue curves and recent fatigue data obtained from materials with different mechanical properties, new design fatigue curves with high general versatility in air have been developed by The Japan Welding Engineering Society (JWES). Structural materials with different tensile strength are utilized in fatigue tests to verify the validity of these design fatigue curves and discuss the mean stress effect. The materials employed in this study are austenitic stainless steel (SS) SUS316LTP, carbon steel (CS) STPT370, low-alloy steels (LASs) SQV2A and SCM435H, all of which are used in the structural components of nuclear power plants of Japan. The best-fit curves (BFCs) are formulated by using the parameter of tensile strength to describe the relationship between strain (stress) amplitude and fatigue life [1]. The results of fully reversed axial fatigue tests conducted with small-scale test specimens of those materials in air at ambient temperature show good agreement with the developed BFCs. The results of fatigue tests also indicate that the mean stress effect is remarkable in materials with higher tensile strength. The applicability of Modified Goodman and Smith-Watson-Topper (SWT) approaches to the design fatigue curves is compared and discussed when considering mean stress effect. The correction of mean stress effect with SWT approach shows a good agreement with the developed BFCs.

scholarly journals Study on the Elastic–Plastic Correlation of Low-Cycle Fatigue for Variable Asymmetric Loadings

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2451 ◽  
Author(s):  
Junhong Zhang ◽  
Weidong Li ◽  
Huwei Dai ◽  
Nuohao Liu ◽  
Jiewei Lin
Keyword(s):  
Low Cycle Fatigue ◽  
Strain Ratio ◽  
Stress Effect ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Ratcheting Strain ◽  
Asymmetric Loading ◽  
Pressure Tubing ◽  
Proposed Model ◽  
The Mean

The mean stress effect in fatigue life varies by material and loading conditions. Therefore, a classical low cycle fatigue (LCF) model based on mean stress correction shows limits in asymmetric loading cases in both accuracy and applicability. In this paper, the effect of strain ratio (R) on LCF life is analyzed and a strain ratio-based model is presented for asymmetric loading cases. Two correction factors are introduced to express correlations between strain ratio and fatigue strength coefficient and between strain ratio and fatigue ductility coefficient. Verifications are conducted through four materials under different strain ratios: high-pressure tubing steel (HPTS), 2124-T851 aluminum alloy, epoxy resin and AZ61A magnesium alloy. Compared with current widely used LCF models, the proposed model shows a better life prediction accuracy and higher potential in implementation in symmetric and asymmetric loading cases for different materials. It is also found that the strain ratio-based correction is able to consider the damage of ratcheting strain that the mean stress-based models cannot.

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