Safety Factor in Fatigue Under Fluctuating Stresses

1987 ◽  
Vol 109 (4) ◽  
pp. 397-401 ◽  
Author(s):  
V. A. Avakov
Keyword(s):  
Safety Factor ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Static Strength ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Safety Factors ◽  
Generalize Expression ◽  
Allowable Stresses ◽  
Number Of Cycles

It is common to assume identical allowable safety factors in static strength [m], defined by mean stress (Sm), and in fatigue [a], defined by stress amplitude (Sa), in order to find the full safety factor (F) under asymmetrical cycles, or to plot any type of the Sm–Sa diagram of allowable stresses. Here additional modification is considered to generalize expression of the full factor of safety in fatigue under asymmetrical stresses, utilizing unequal allowable safety factors in static strength (by mean stress) and in fatigue (by stress amplitude): ([a] ≠ [m]). We assume that loading is stationary, and cumulated number of cycles is large enough to consider high cycle fatigue.

Proposed ASME Code High Cycle Fatigue Design Curves for Austenitic and Ferritic Steels

2017 ◽  
Author(s):  
Sampath Ranganath ◽  
Hardayal S. Mehta ◽  
Nathan A. Palm ◽  
John Hosler
Keyword(s):  
High Cycle Fatigue ◽  
Ferritic Steels ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Design Curve ◽  
Fatigue Design ◽  
Asme Code ◽  
The Mean ◽  
Number Of Cycles ◽  
Fatigue Evaluation

The ASME Code fatigue curves (S–N curves) are used in the fatigue evaluation of reactor components. For the assessment of high frequency cyclic loading (such as those produced by flow-induced vibrations), where the number of cycles is expected to be very large and cannot be estimated, the stresses are evaluated by comparison with the fatigue limit1 at 1011 cycles. Other high cycle events of finite time duration (e.g. safety relief loading), where the number of cycles is large but well defined, the fatigue evaluation is performed by comparing the calculated stress with the allowable values defined by the high cycle fatigue design curve. This paper discusses the development of fatigue design curves for austenitic and ferritic steels when the number of cycles is in the range 106 – 1011 cycles. The first part of the paper addresses austenitic stainless steel components which are used for reactor internals. Specifically, the approach described here uses temperature dependent properties (cyclic yield strength, cyclic ultimate strength) for the mean stress correction and the correction for the modulus of elasticity. The high cycle fatigue design curve is developed by applying the mean stress and the E correction on the reversing load mean data curve and applying a factor of 2 on stress. The generic methodology developed for austenitic steel was applied to carbon and low alloy steels also. The proposed fatigue design curves are part of a draft ASME Code Case being considered by the ASME Code Subgroup on Design Methods. This paper describes the technical basis for the proposed ASME Code Case for the high cycle fatigue design curves for austenitic and ferritic steels.

Uniaxial Ratcheting and Low-Cycle Fatigue Failure of U75V Rail Steel

2016 ◽  
Vol 853 ◽  
pp. 246-250 ◽  
Author(s):  
Tao Fang ◽  
Qian Hua Kan ◽  
Guo Zheng Kang ◽  
Wen Yi Yan
Keyword(s):  
Fatigue Life ◽  
Strain Amplitude ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Rail Steel ◽  
Low Cycle Fatigue ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Ratcheting Strain ◽  
Cyclic Straining

Experiments on U75V rail steel were carried out to investigate the cyclic feature, ratcheting behavior and low-cycle fatigue under both strain- and stress-controlled loadings at room temperature. It was found that U75V rail steel shows strain amplitude dependent cyclic softening feature, i.e., the responded stress amplitude under strain-controlled decreases with the increasing number of cycles and reaches a stable value after about 20th cycle. Ratcheting strain increases with an increasing stress amplitude and mean stress, except for stress ratio, and the ratcheting strain in failure also increases with an increasing stress amplitude, mean stress and stress ratio. The low-cycle fatigue lives under cyclic straining decrease linearly with an increasing strain amplitude, the fatigue lives under cyclic stressing decrease with an increasing mean stress except for zero mean stress, and decrease with an increasing stress amplitude. Ratcheting behavior with a high mean stress reduces fatigue life of rail steel by comparing fatigue lives under stress cycling with those under strain cycling. Research findings are helpful to evaluate fatigue life of U75V rail steel in the railways with passenger and freight traffic.

scholarly journals High Cycle Fatigue Appearance of 10wt% cr steel and Dissimilar Metal Weld

2021 ◽  
Vol 9 (VI) ◽  
pp. 2185-2202
Author(s):  
Hilal Ahmad Shah
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Cycle Fatigue ◽  
Crack Initiation And Propagation ◽  
R Ratio ◽  
Initiation And Propagation ◽  
Different Temperatures ◽  
Fracture Surface Analysis ◽  
Metal Weld

The present study deals with the high cycle fatigue (HCF) behavior of a ten wt% Cr steel at ambient also as high temperatures (300–853 K). S–N curves were created at unlike temperatures using an R-ratio of −1. Outcome of mean stress was established over and done with Haigh diagram at 853 K using different R-values. Fatigue life was found to decrease with upsurge in test temperature and stress amplitude. Fatigue life was attempted using Basquin equation. Detailed fracture surface analysis was performed to study the crack initiation and propagation modes towards empathetic the mechanisms of failure at different temperatures.

PSBs and Non-Propagation of Small Surface and Interior Cracks in Polycrystalline Copper

2013 ◽  
Vol 592-593 ◽  
pp. 777-780 ◽  
Author(s):  
Stefanie E. Stanzl-Tschegg ◽  
Bernd M. Schönbauer
Keyword(s):  
High Cycle Fatigue ◽  
Fatigue Loading ◽  
Cycle Fatigue ◽  
Lower Stress ◽  
Small Surface ◽  
Loading Method ◽  
Very High Cycle Fatigue ◽  
Small Cracks ◽  
Number Of Cycles ◽  
Very High

PSB formation and its relevance for an eventual fatigue limit of polycrystalline electrolytic copper was studied in the very-high cycle fatigue regime with the ultrasound fatigue loading method. PSBs are formed at much lower stress/strain amplitudes than reported in earlier literature, if a high enough number of cycles is applied. Fatigue fracture takes place at approximately 50% higher amplitudes than needed for PSB formation, which is likewise in contrast to former literature results. Non-propagation of small cracks, originating from intrusions or PSB-induced non-propagating grain-boundary cracks are made responsible for this different material response.

scholarly journals The effect of mean stress and stress biaxiality in high-cycle fatigue

2017 ◽  
Vol 41 (2) ◽  
pp. 440-455 ◽  
Author(s):  
Imade Koutiri ◽  
Daniel Bellett ◽  
Franck Morel
Keyword(s):  
High Cycle Fatigue ◽  
Mean Stress ◽  
Cycle Fatigue

Strength Analysis of Diesel Engine Crankshaft Based on Flexible Multi-Body Dynamics

2014 ◽  
Vol 654 ◽  
pp. 65-68
Author(s):  
Ling Jin Wang ◽  
Dan Li ◽  
Xiu Xia Lu ◽  
Pei Fan Li ◽  
Ying Jun Jia
Keyword(s):  
Diesel Engine ◽  
High Cycle Fatigue ◽  
Dynamics Simulation ◽  
Strength Analysis ◽  
Cycle Fatigue ◽  
Safety Factors ◽  
Body Dynamics ◽  
Dynamics Calculation ◽  
Multi Body ◽  
Engine Crankshaft

Crankshaft is one of the key parts of the diesel engine. Several causes would be lead to the failure of the crankshaft. A novel strength analysis method is used for crankshaft high cycle fatigue simulation of the diesel engine based on flexible multi-body dynamics in this paper. In order to investigate the fatigue strength of other parts of the diesel engine at the same time, a complete coupled dynamic model of diesel engine crankshaft and block is built and coupled dynamics simulation is carried out. Then dynamics calculation results of each part is extracted for high cycle fatigue analysis and the reliability research of the crankshaft, The simulation results show that, the minimum safety factors of the crankshaft is 1.301, it meet the strength requirements, the safety factors of the block and the cap could be calculated at the same time. These suggest that this method can guide the design of the diesel engine crankshaft and has gained significant importance in practical study.

High Cycle Fatigue Behavior of Cold Forging Die Steel

2009 ◽  
Vol 417-418 ◽  
pp. 225-228 ◽  
Author(s):  
Ryuichiro Ebara ◽  
R. Nohara ◽  
Rintaro Ueji ◽  
A. Ogura ◽  
Y. Ishihara ◽  
...  
Keyword(s):  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cold Forging ◽  
Propagation Mode ◽  
Cycle Fatigue ◽  
Die Steel ◽  
Initiation And Propagation ◽  
Number Of Cycles ◽  
Forging Die

High cycle fatigue behavior of the representative cold forging die steel, YXR3 with Rockwell C scale hardness number of 60.0 is investigated. Axial fatigue strength of plane and notched bar specimens with stress concentration factor, Kt of 1.5, 2.0 and 2.5 is presented. The emphasis is placed upon the subsurface crack initiation observed on notched specimens failed at number of cycles over than 106 cycles. Crack initiation and propagation mode of cold forging die steel is discussed with respect to fracture surface morphology.

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