Increase in hardening of 2024-T42 aluminum with fatigue stress amplitude

1990 ◽  
Vol 14 (1) ◽  
pp. 43-47 ◽  
Author(s):  
Th.B. Kermanidis ◽  
S.P. Pantelakis ◽  
D.G. Pavlou
Keyword(s):  
Stress Amplitude ◽  
Fatigue Stress

A Nonlinear Least Squares Logistic Fit Approach to Quantifying Uncertainty in Fatigue Stress-Life Models and an Application to Plain Concrete

2018 ◽  
Author(s):  
Jeffrey T. Fong ◽  
N. Alan Heckert ◽  
James J. Filliben ◽  
Paul H. Ziehl
Keyword(s):  
Least Squares ◽  
Endurance Limit ◽  
Stress Amplitude ◽  
Plain Concrete ◽  
Cyclic Stress ◽  
Logistic Function ◽  
Fatigue Stress ◽  
Least Squares Fit ◽  
Horizontal Asymptote ◽  
Number Of Cycles

A large number of fatigue life models for engineering materials such as concrete and steel are simply a linear or nonlinear relationship between the cyclic stress amplitude, σa, and the log of the number of cycles to failure, Nf. In the linear case, the relationship is a power-law relation between σa and Nf, with two constants determined by a linear least squares fit algorithm. The disadvantage of this simple linear fit of fatigue test data is that it fails to predict the existence of an endurance limit, which is defined as the cyclic stress amplitude at which the number of cycles is infinity. In this paper, we introduce a nonlinear least square fit based on a 4-parameter logistic function, where the curve of the y vs. x plot will have two horizontal asymptotes, namely, y0, at the left infinity, and y1, at the right infinity with y1 < y0 to simulate a fatigue model with a decreasing y for an increasing x. In addition, we need a third parameter, k, to denote the slope of the curve as it traverses from the left horizontal asymptote to the lower right horizontal asymptote, and a fourth parameter, x0, to denote the center of the curve where it crosses a horizontal line half-way between y0 and y1. In this paper, the 4-parameter logistic function is simplified to a 3-parameter function as we apply it to model a fatigue sress-life relationship, because in a stress-log (life) plot, the left upper horizontal asymptote, y0, can be assumed as a constant equal to the static ultimate strength of the material, U0. This simplification reduces the logistic function to the following form: y = U0 − (U0 − y1) / (1 + exp(−k (x − x0)), where y = σa, and x = log(Nf). The fit algorithm allows us to quantify the uncertainty of the model and the estimation of an endurance limit, which is the parameter, y1. An application of this nonlinear modeling technique is applied to fatigue data of plain concrete in the literature with excellent results. Significance and limitations of this new fit algorithm to the interpretation of fatigue stress-life data are presented and discussed.

High Frequency Fatigue and Using Frequency Domain Techniques

2020 ◽  
Author(s):  
Benjamin Francis ◽  
David Mair
Keyword(s):  
Frequency Domain ◽  
Maximum Stress ◽  
Stress Amplitude ◽  
Equivalent Stress ◽  
Phase Relationship ◽  
Maximum Amplitude ◽  
Time History ◽  
Complex Stress ◽  
Fatigue Stress ◽  
Frequency Domain Techniques

Abstract In recent years API 579 has provided the analyst with a detailed outline of the Wang-Brown algorithm (WBCC) for the cycle counting. The WBCC algorithm has become the generally accepted core of cycle counting implementations whenever multi-axial non-proportional fatigue stress histories are encountered. However, for vibration based fatigue, in the absence of any time history at all; it is common in industry to assess fatigue using frequency domain techniques. This paper presents special considerations for determination of the spectral stress fatigue in the spirit of API 579. In the frequency domain the stress cycles are counted a priori as a set of complex vectors. These complex stress vectors may represent the full stress tensor of a reduced set in an appropriate sub-space. The phase relationship between the vectors represents the time delay between the stress components of the stress field. This paper presents some of the actions that are necessary in order to accurately capture the phase relationships. It is often the case that the physics of the driving loads are either unknown or too complex to practically model. This is the case for complex fluid and particle interactions with vessel shells, piping or other wetted surfaces. This paper presents some tools and techniques that can be applied in order to characterize the loading spectrum in a manner which is specifically designed to capture the important fatigue characteristics. Any fatigue estimation technique must convert the stress vector set into a singularly dimensioned scalar metric that represents the stress amplitude of a cycle. However, the maximum stress amplitude from the cycle is not immediately accessible from the complex stress vectors. While a number of papers present techniques that are intended to calculate the maximum stress amplitude in the case where the stress metric is the equivalent stress this paper provides a slightly more general relation for the phase of the maximum amplitude. Finally the analyst must compare their calculated fatigue stress amplitudes to the API 579 fatigue curves. Closed form expressions for mono-linear spectral fatigue have been extensively investigated in the literature but more complex fatigue curves do not have such simple solutions. To this end this paper investigates the smooth bar carbon steel fatigue curves of ASME VIII-2.

Fatigue Stress Analysis of Diaphragm Cap Hole in Orthotropic Steel Bridge Decks

2012 ◽  
Vol 204-208 ◽  
pp. 3265-3269
Author(s):  
Mu Ye Yang ◽  
Rong Liu ◽  
Bo Hai Ji ◽  
Han Jiang Xu ◽  
Ce Chen ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Yangtze River ◽  
Bridge Deck ◽  
Stress Amplitude ◽  
Steel Bridge ◽  
Fatigue Stress ◽  
Model Method ◽  
Local Stresses ◽  
Center Position ◽  
Improve Fatigue

Influence of diaphragm parameter on stress amplitude and fatigue damage of diaphragm details were investigated based on Tai Zhou Yangtze River Bridge. FEM of steel bridge deck and diaphragm detail were established. Boundary conditions of the diaphragm details FEM were interpolated by sub-model method, and the accurate local stresses of diaphragm details correspond to different lateral distribution of wheels were calculated. Results show the stress amplitude of diaphragm details reach maximum when wheel off-center position is 150mm, and it decreases with the increase of wheel off-center position greatly. The stress amplitude of diaphragm details increase with the increase of the distance of diaphragms, and increasing diaphragm’s thickness can improve fatigue stress of steel bridge deck.

Comparative study of the effective parameters on residual stress relaxation in welded aluminum plates under cyclic loading

2020 ◽  
Vol 21 (5) ◽  
pp. 505
Author(s):  
Yousef Ghaderi Dehkordi ◽  
Ali Pourkamali Anaraki ◽  
Amir Reza Shahani
Keyword(s):  
Residual Stress ◽  
Cyclic Loading ◽  
Stress Relaxation ◽  
Stress Amplitude ◽  
Cyclic Plasticity ◽  
Mean Stress ◽  
Effective Parameters ◽  
Perfect Plasticity ◽  
Residual Stress Relaxation ◽  
Aluminum Plates

The prediction of residual stress relaxation is essential to assess the safety of welded components. This paper aims to study the influence of various effective parameters on residual stress relaxation under cyclic loading. In this regard, a 3D finite element modeling is performed to determine the residual stress in welded aluminum plates. The accuracy of this analysis is verified through experiment. To study the plasticity effect on stress relaxation, two plasticity models are implemented: perfect plasticity and combined isotropic-kinematic hardening. Hence, cyclic plasticity characterization of the material is specified by low cycle fatigue tests. It is found that the perfect plasticity leads to greater stress relaxation. In order to propose an accurate model to compute the residual stress relaxation, the Taguchi L18 array with four 3-level factors and one 6-level is employed. Using statistical analysis, the order of factors based on their effect on stress relaxation is determined as mean stress, stress amplitude, initial residual stress, and number of cycles. In addition, the stress relaxation increases with an increase in mean stress and stress amplitude.

scholarly journals Fatigue Stress-Life Model of RC Beams Based on an Accelerated Fatigue Method

2019 ◽  
Vol 4 (2) ◽  
pp. 16
Author(s):  
Eljufout ◽  
Toutanji ◽  
Al-Qaralleh
Keyword(s):  
Cyclic Loading ◽  
Fatigue Testing ◽  
Three Dimensional ◽  
Rc Beam ◽  
Rc Beams ◽  
Testing Methods ◽  
Load Range ◽  
Fatigue Stress ◽  
Life Model ◽  
Prediction Band

Several standard fatigue testing methods are used to determine the fatigue stress-life prediction model (S-N curve) and the endurance limit of Reinforced Concrete (RC) beams, including the application of constant cyclic tension-tension loads at different stress or strain ranges. The standard fatigue testing methods are time-consuming and expensive to perform, as a large number of specimens is needed to obtain valid results. The purpose of this paper is to examine a fatigue stress-life predication model of RC beams that are developed with an accelerated fatigue approach. This approach is based on the hypothesis of linear accumulative damage of the Palmgren–Miner rule, whereby the applied cyclic load range is linearly increased with respect to the number of cycles until the specimen fails. A three-dimensional RC beam was modeled and validated using ANSYS software. Numerical simulations were performed for the RC beam under linearly increased cyclic loading with different initial loading conditions. A fatigue stress-life model was developed that was based on the analyzed data of three specimens. The accelerated fatigue approach has a higher rate of damage accumulations than the standard testing approach. All of the analyzed specimens failed due to an unstable cracking of concrete. The developed fatigue stress-life model fits the upper 95% prediction band of RC beams that were tested under constant amplitude cyclic loading.

Fatigue Life of the Human Teeth: A Continuum Damage Approach

2019 ◽  
Vol 43 ◽  
pp. 1-19
Author(s):  
Theddeus Tochukwu Akano
Keyword(s):  
Fatigue Life ◽  
Damage Mechanics ◽  
Stress Amplitude ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Elastoplastic Model ◽  
Human Teeth ◽  
Proposed Model ◽  
Number Of Cycles ◽  
Cycles To Failure

Normal oral food ingestion processes such as mastication would not have been possible without the teeth. The human teeth are subjected to many cyclic loadings per day. This, in turn, exerts forces on the teeth just like an engineering material undergoing the same cyclic loading. Over a period, there will be the creation of microcracks on the teeth that might not be visible ab initio. The constant formation of these microcracks weakens the teeth structure and foundation that result in its fracture. Therefore, the need to predict the fatigue life for human teeth is essential. In this paper, a continuum damage mechanics (CDM) based model is employed to evaluate the fatigue life of the human teeth. The material characteristic of the teeth is captured within the framework of the elastoplastic model. By applying the damage evolution equivalence, a mathematical formula is developed that describes the fatigue life in terms of the stress amplitude. Existing experimental data served as a guide as to the completeness of the proposed model. Results as a function of age and tubule orientation are presented. The outcomes produced by the current study have substantial agreement with the experimental results when plotted on the same axes. There is a notable difference in the number of cycles to failure as the tubule orientation increases. It is also revealed that the developed model could forecast for any tubule orientation and be adopted for both young and old teeth.

A new design of cable anchor for ultra-high fatigue stress cable net of largest telescope in the world

2020 ◽  
pp. 107280
Author(s):  
Wanxu Zhu ◽  
Kefei Jia ◽  
Feng Fu ◽  
Dongqiu Lan ◽  
Kai Qian
Keyword(s):  
Fatigue Stress ◽  
The World ◽  
High Fatigue

scholarly journals Aluminide Thermal Barrier Coating for High Temperature Performance of MAR 247 Nickel Based Superalloy

Coatings ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 48
Author(s):  
Mateusz Kopec ◽  
Dominik Kukla ◽  
Xin Yuan ◽  
Wojciech Rejmer ◽  
Zbigniew L. Kowalewski ◽  
...  
Keyword(s):  
High Temperature ◽  
Stress Amplitude ◽  
Aluminide Coating ◽  
Chemical Vapor ◽  
Fatigue Tests ◽  
Protective Atmosphere ◽  
X Ray ◽  
Nickel Based Superalloy ◽  
Barrier Coating ◽  
Aluminide Layer

In this paper, mechanical properties of the as-received and aluminide layer coated MAR 247 nickel based superalloy were examined through creep and fatigue tests. The aluminide layer of 20 µm was obtained through the chemical vapor deposition (CVD) process in the hydrogen protective atmosphere for 8 h at the temperature of 1040 °C and internal pressure of 150 mbar. A microstructure of the layer was characterized using the scanning electron microscopy (SEM) and X-ray Energy Dispersive Spectroscopy (EDS). It was found that aluminide coating improve the high temperature fatigue performance of MAR247 nickel based superalloy at 900 °C significantly. The coated MAR 247 nickel based superalloy was characterized by the stress amplitude response ranging from 350 MPa to 520 MPa, which is twice as large as that for the uncoated alloy.

scholarly journals Tension-Tension Fatigue Behavior of High-Toughness Zr61Ti2Cu25Al12 Bulk Metallic Glass

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2815
Author(s):  
Yu Hang Yang ◽  
Jun Yi ◽  
Na Yang ◽  
Wen Liang ◽  
Hao Ran Huang ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Shear Band ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Fatigue Resistance ◽  
Metallic Glasses ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Bulk Metallic Glasses ◽  
High Toughness

Bulk metallic glasses have application potential in engineering structures due to their exceptional strength and fracture toughness. Their fatigue resistance is very important for the application as well. We report the tension-tension fatigue damage behavior of a Zr61Ti2Cu25Al12 bulk metallic glass, which has the highest fracture toughness among BMGs. The Zr61Ti2Cu25Al12 glass exhibits a tension-tension fatigue endurance limit of 195 MPa, which is higher than that of high-toughness steels. The fracture morphology of the specimens depends on the applied stress amplitude. We found flocks of shear bands, which were perpendicular to the loading direction, on the surface of the fatigue test specimens with stress amplitude higher than the fatigue limit of the glass. The fatigue cracking of the glass initiated from a shear band in a shear band flock. Our work demonstrated that the Zr61Ti2Cu25Al12 glass is a competitive structural material and shed light on improving the fatigue resistance of bulk metallic glasses.

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