A Statistically Load-Weighted Probabilistic Fatigue Life Model

2008 ◽  
Vol 44-46 ◽  
pp. 51-56 ◽  
Author(s):  
Li Yang Xie ◽  
Wen Qiang Lin
Keyword(s):  
Fatigue Life ◽  
Stress Amplitude ◽  
Random Variable ◽  
Cyclic Stress ◽  
General Situation ◽  
Statistical Average ◽  
Underlying Principle ◽  
Model Configuration ◽  
System Of Units ◽  
Life Model

By interpreting traditional stress-strength interference model as a statistical average of the probability that strength (a random variable) is greater than stress (another random variable) over its whole distribution range, the same model configuration, which was conventionally applied only to the case of same system-of-units parameters (e.g., stress and strength, both are measured in MPa), was applied to more general situation of different system-of-units parameters. That is to say, the traditional model was extended to more general situations of any two variables, as long as one of the variables can be expressed as a function of the other. Further more, the probabilistic fatigue life under random stress can be predicted, with known probabilistic fatigue lives under several deterministic cyclic stress amplitudes and known distribution of the random cyclic stress amplitude. The underlying principle is that the fatigue life under random stress is equal to the statistical average of the fatigue lives under cyclic stress of deterministic amplitudes which can be considered as the samples of the random stress.

The Reliability of a Component Under Multiple Cyclic Stress Levels With Distributed Cyclic Numbers

2016 ◽  
Author(s):  
Xiaobin Le
Keyword(s):  
Fatigue Life ◽  
Probabilistic Models ◽  
Random Variable ◽  
Fatigue Loading ◽  
Cyclic Stress ◽  
Initial Crack ◽  
Stress Levels ◽  
Single Constant ◽  
Unsolved Issue ◽  
Loading Spectrum

Fatigue damage is initiated through some “defects” on the surfaces of and/or inside the component and induced by the fatigue cyclic loadings. These “defects” are randomly scattered in components, and one of these “defects” will be randomly “activated” and finally developed to become the initial crack which causes the final fatigue failure. Therefore, the fatigue strength is inherently a random variable and should be treated by probabilistic models such as typical P-S-N curves. The fatigue cyclic loading could be presented or described in any form. But the fatigue loading spectrum can generally be grouped as and described by these five models: (1) a single constant cyclic stress (loading) with a given cyclic number, (2) a single constant cyclic stress with a distributed cyclic number, (3) a distributed cyclic stress (loading) at a given fatigue life (cyclic number), (4) multiple constant cyclic stress levels with given cyclic numbers, and (5) multiple constant cyclic stress levels with distributed cyclic numbers. The approaches for determining the reliability of components under fatigue loading spectrum of the models 1∼4 are available in literature and books. But few articles and books have addressed an approach for determining the reliability of components under the fatigue loading spectrum of the model 5. This paper will propose two approaches for addressing this unsolved issue. Two examples will be presented to implement the proposed approaches with detailed procedures.

Investigating Discrepancies in Vibration Bending Fatigue Behavior of Additively Manufactured Titanium 6Al-4V

2018 ◽  
Author(s):  
Onome Scott-Emuakpor ◽  
Casey Holycross ◽  
Tommy George ◽  
Luke Sheridan ◽  
Emily Carper ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Sem Analysis ◽  
Concentration Effects ◽  
Bending Fatigue ◽  
Grain Structures ◽  
Life Model ◽  
Microscopic Features ◽  
Cold Rolled

The vibration bending fatigue life uncertainty of additively manufactured Titanium (Ti) 6Al-4V specimens is studied. In this investigation, an analysis of microscopic discrepancies between 10 fatigued specimens paired by stress amplitude is correlated to the bending fatigue life scatter. Through scanning electron microscope (SEM) analysis of fracture surfaces and grain structures, anomalies and distinctions such as voids and grain geometries are identified in each specimen. This data along with previously published results are used to support assessments regarding bending fatigue uncertainty. Corrections on stress and scatter based on microscopic features are implemented to the stress versus fatigue life comparisons. The results of this investigation show that the bending fatigue life uncertainty can be bounded by cold-rolled Ti 6Al-4V data when correcting the tested stress amplitude values with stress concentration effects and variation due to microstructure geometries. The understanding gained from this study is important for future development of a predictive vibration bending fatigue life model that will include the probability of geometry, density, and location of voids as an artifact of LPBF build parameters.

Investigating Discrepancies in Vibration Bending Fatigue Behavior of Additively Manufactured Titanium 6Al-4V

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Onome Scott-Emuakpor ◽  
Casey Holycross ◽  
Tommy George ◽  
Luke Sheridan ◽  
Emily Carper ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Fatigue Life ◽  
Scanning Electron Microscope ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Sem Analysis ◽  
Bending Fatigue ◽  
Grain Structures ◽  
Life Model ◽  
Scanning Electron

The vibration bending fatigue life uncertainty of additively manufactured titanium (Ti) 6Al-4V specimens is studied. In this investigation, an analysis of microscopic discrepancies between ten fatigued specimens paired by stress amplitude is correlated with the bending fatigue life scatter. Through scanning electron microscope (SEM) analysis of fracture surfaces and grain structures, anomalies and distinctions such as voids and grain geometries are identified in each specimen. These data along with previously published results are used to support assessments regarding bending fatigue uncertainty. The understanding gained from this study is important for the future development of a predictive vibration bending fatigue life model.

A Statistical Load Weighted Average Fatigue Reliability Model for Uncertain Constant Amplitude Cyclic Load

2007 ◽  
Vol 353-358 ◽  
pp. 2497-2500
Author(s):  
Li Yang Xie ◽  
Xue Hong He
Keyword(s):  
Cyclic Load ◽  
Weighted Average ◽  
Random Variable ◽  
Amplitude Distribution ◽  
General Situation ◽  
Fatigue Reliability ◽  
Constant Amplitude ◽  
Statistical Average ◽  
Assigned Value ◽  
The Individual

The present paper interpreted the traditional stress-strength interference model as an equation expressing the statistical average of the probability of strength preponderating over stress. Thus, the same equation, which was traditionally applicable only in the situation of same-measure parameters, can be applied to more general situation of different-measure parameters. In other words, the traditional model was extended to the situation of any two variables, as long as one variable can be expressed as a function of the other. With a specific load amplitude distribution, the method is to calculate the statistical average of the probability that fatigue life random variable under the individual constant amplitude cyclic load is greater than an assigned value. The extended interference analysis method can be applied directly to calculate fatigue reliability under constant amplitude cyclic load with uncertainty in the stress range.

Fretting fatigue behavior and failure characteristics of 35CrMoA steel under elliptical loading path

2021 ◽  
Vol 73 (6) ◽  
pp. 922-928
Author(s):  
Ziao Huang ◽  
Xiaoshan Liu ◽  
Guoqiu He ◽  
Zhiqiang Zhou ◽  
Bin Ge ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Contact Pressure ◽  
Wear Debris ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Fretting Fatigue ◽  
Cyclic Stress ◽  
Loading Path ◽  
Fatigue Wear ◽  
Content Type

Purpose This study aims to understand the multiaxial fretting fatigue, wear and fracture characteristics of 35CrMoA steel under the elliptical loading path. Design/methodology/approach By keeping the contact pressure and torsional shear cyclic stress amplitude unchanged; the axial cyclic stress amplitude varied from 650 MPa to 850 MPa. The fretting fatigue test was carried out on MTS809 testing machine, and the axial cyclic strain response and fatigue life of the material were analyzed. The fretting zone and fracture surface morphology were observed by scanning electron microscope. The composition of wear debris was detected by energy dispersive X-ray spectrometer. Findings In this study, with the increase of axial stress amplitude, 35CrMoA steel will be continuously softened, and the cyclic softening degree increases. The fretting fatigue life decreases unevenly. The fretting scars in the stick region are elongated in the axial direction. The area of fracture crack propagation zone decreases. In addition, the results indicate that wear debris in the slip region is spherical and has higher oxygen content. Originality/value There were few literatures about the multiaxial fretting fatigue behavior of 35CrMoA steel, and most scholars focused on the contact pressure. This paper reveals the effect of axial cyclic stress on fretting fatigue and wear of 35CrMoA steel under the elliptical loading path.

The High Cycle Fatigue and Fracture Behavior of Friction Stir Welded Aluminum Alloy 2024

2008 ◽  
Vol 378-379 ◽  
pp. 175-206 ◽  
Author(s):  
T.S. Srivatsan ◽  
Satish Vasudevan ◽  
Lisa Park ◽  
R.J. Lederich
Keyword(s):  
Fatigue Life ◽  
Fracture Behavior ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Tensile Ductility ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Friction Stir ◽  
Final Fracture ◽  
Microstructural Effects

In this research paper, the cyclic stress amplitude controlled fatigue response and fracture behavior of an Al-Cu-Mg alloy (Aluminum Association designation 2024) is presented and discussed. The alloy was friction stir welded in the T8 temper to provide two plates one having high tensile ductility and denoted as Plate A and the other having low tensile ductility and denoted as Plate B. Test specimens of the alloy, prepared from the two plates, were cyclically deformed under stress amplitude control at two different load ratios with the primary objective of documenting the conjoint influence of magnitude of cyclic stress, load ratio and intrinsic microstructural effects on cyclic fatigue life and final fracture characteristics. The high cycle fatigue resistance of the alloy is described in terms of maximum stress, R-ratio, and microstructural influences on strength. The final fracture behavior of the friction stir welded alloy is discussed in light of the concurrent and mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the alloy microstructure, magnitude of cyclic stress, and resultant fatigue life.

Effect of Contact Pressure and Cyclic Stress Amplitude on Fretting Fatigue of 45-Carbon Steel

2007 ◽  
Vol 353-358 ◽  
pp. 134-137
Author(s):  
Wei Ming Sun ◽  
Shui Sheng Chen ◽  
Li Qun Tu
Keyword(s):  
Fatigue Life ◽  
Carbon Steel ◽  
Contact Pressure ◽  
Main Crack ◽  
Stress Amplitude ◽  
Fretting Fatigue ◽  
Cyclic Stress ◽  
Outer Edge ◽  
Middle Portion ◽  
Contact Pressures

The effect of contact pressure on fretting fatigue in quenched and tempered 45-carbon steel is studied. With an increase in contact pressure, fretting fatigue life is decreased quickly at low contact pressures; however it almost unchanged at high contact pressures. With an increase in cyclic stress amplitude, fretting fatigue life decreased. In the test, concavity is formed at the fretted area accompanying wear. The main crack is initiated at the outer edge corner of the concavity at high contact pressures, and initiated at the middle portion of the fretted area at low contact pressures.

Numerical investigation of the fatigue performance of elastic rail clips considering rail corrugation and dynamic axle load

2020 ◽  
pp. 095440972092601
Author(s):  
Ping Wang ◽  
Jun Lu ◽  
Caiyou Zhao ◽  
Mingming Chen ◽  
Mengting Xing
Keyword(s):  
Fatigue Life ◽  
Stress Amplitude ◽  
Cyclic Stress ◽  
Maximum Speed ◽  
Analysis Method ◽  
Vibration Acceleration ◽  
Intrinsic Frequency ◽  
Rail Corrugation ◽  
Naturally Occurring ◽  
Coupling Dynamic

To analyze the reasons for rail clip fracture, the characteristics of rail corrugation were first measured using a rail corrugation meter. The vibration acceleration of the fastener clips at the sections with/without rail corrugation was measured, and the effects of rail corrugation on the clip vibration were analyzed. After this, a vehicle--track coupling dynamic model and a refined model for the fastener system were established in order to study the effects of rail corrugation on the vibration acceleration and stress on critical points. Finally, the rail grinding limits were determined based on the fatigue analysis method and the damage accumulation theory from the aspect of the fatigue life of the clip. The results of the study showed that the main wavelength of rail corrugation at the rail clip fracture section was approximately 40 mm. The vibration acceleration of the clip caused by rail corrugation was too large. Under normal installation conditions, the maximum clip stress was 1490 MPa at the small circular arc on the rear arch, which was identical to the on-site fracture location. The intrinsic frequency of the clip was approximately 810 Hz. Rail corrugation excited and triggered the forced vibration of the clip, and induced resonance at a speed of 120 km/h and a wavelength of 40 mm. The large cyclic stress amplitude of the clip with rail corrugation increased from 44 MPa to 68 MPa when compared with the clip without rail corrugation. Rail clip fracture was caused by the naturally occurring resonance fatigue arising from rail corrugation. For metro lines designed with a maximum speed of 120 km/h, it was suggested to control the rail corrugation amplitudes with a wavelength of 40 mm, 50 mm, 30 mm, 120 mm and 160 mm to below 0.04, 0.08, 0.16, 0.19 and 0.2 mm, respectively, taking into account the fatigue life of the clip.

An Investigation of the Cyclic Fatigue and Final Fracture Behavior of a Titanium Alloy

2008 ◽  
Vol 378-379 ◽  
pp. 271-298 ◽  
Author(s):  
T.S. Srivatsan ◽  
Mithun Kuruvilla ◽  
Lisa Park
Keyword(s):  
Titanium Alloy ◽  
Fatigue Life ◽  
Fracture Behavior ◽  
Stress Amplitude ◽  
Load Ratio ◽  
Cyclic Fatigue ◽  
Cyclic Stress ◽  
Fatigue Properties ◽  
Final Fracture ◽  
Stress Load

In this technical manuscript the cyclic stress amplitude controlled fatigue properties and fracture behavior of an emerging titanium alloy (referred to by its designation as ATI 425TM by the manufacturer) is presented and discussed. The alloy was provided as rod stock in the fully annealed condition. Test specimens of the as-received alloy were cyclically deformed under total stress amplitude control at two different stress ratios (R = 0.1 and R = 0.3) with the purpose of establishing the conjoint and mutually interactive influences of magnitude of cyclic stress, load ratio and intrinsic microstructural effects on cyclic fatigue life, final fracture behavior and viable mechanisms governing failure at the microscopic level. The high cycle fatigue resistance of this titanium alloy is described in terms of maximum stress, load ratio, and maximum elastic strain. The final fracture behavior of the alloy under cyclic loading conditions is discussed in light of the mutually interactive influences of intrinsic microstructural features, magnitude of cyclic stress, load ratio and resultant fatigue life.

An Investigation of the High Cycle Fatigue and Final Fracture Behavior of Aluminum Alloy 2219

2008 ◽  
Vol 378-379 ◽  
pp. 207-230 ◽  
Author(s):  
T.S. Srivatsan ◽  
Satish Vasudevan ◽  
Lisa Park ◽  
R.J. Lederich
Keyword(s):  
Fatigue Life ◽  
Fracture Behavior ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Load Ratio ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Final Fracture ◽  
Stress Load ◽  
Microstructural Effects

In this research paper, the cyclic stress amplitude controlled fatigue response and fracture behavior of an Al-Cu (Aluminum Association designation 2219) is presented and discussed. The alloy was provided as a thin sheet in the T62 temper in the fully anodized condition. A small quantity of the as-provided sheet was taken and the surface carefully prepared to remove the thin layer of anodized coating. Test specimens of the alloy, prepared from the two sheets (anodized and non-anodized), were cyclically deformed under stress amplitude control at two different load ratios with the primary objective of establishing the conjoint influence of magnitude of cyclic stress, load ratio and intrinsic microstructural effects on cyclic fatigue life and final fracture characteristics. The high cycle fatigue resistance of the alloy is described in terms of maximum stress, load ratio, and microstructural influences on strength. The final fracture behavior of the alloy sheet is discussed in light of the concurrent and mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the alloy microstructure, magnitude of cyclic stress, and resultant fatigue life.

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