Fatigue limit

Fatigue limit, endurance limit, and fatigue strength are all expressions used to describe a property of materials: the amplitude (or range) of cyclic stress that can be applied to the material without causing fatigue failure.cite book
title = Mechanics of Materials
edition = Second edition
last = Beer
first = Ferdinand P.
coauthors = E. Russell Johnston, Jr.
year = 1992
publisher = McGraw-Hill, Inc.
id = ISBN 0-07-837340-9
pages = 51
] Ferrous alloys and titanium alloys cite web
url = http://www.roymech.co.uk/Useful_Tables/Fatigue/Fatigue.html
title = Metal Fatigue and Endurance
accessdate = 2008-04-18
] have a distinct limit, an amplitude below which there appears to be no number of cycles that will cause failure. Other structural metals such as aluminium and copper, do not have a distinct limit and will eventually fail even from small stress amplitudes. In these cases, a number of cycles (usually 107) is chosen to represent the fatigue life of the material.

Definitions

ASTM defines "fatigue strength", "SNf", as the value of stress at which failure occurs after "Nf" cycles, and "fatigue limit", "Sf", as the limiting value of stress at which failure occurs as "Nf" becomes very large. ASTM does not define "endurance limit" but implies that it is similar to fatigue limit.cite book
title = Metal Fatigue in Engineering
edition = Second edition
last = Stephens
first = Ralph I.
year = 2001
publisher = John Wiley & Sons, Inc.
id = ISBN 0-471-51059-9
pages = 69
]

Some authors use "endurance limit", "Se", for the stress below which failure never occurs, even for an indefinitely large number of loading cycles, as in the case of steel; and "fatigue limit" or "fatigue strength", "Sf", for the stress at which failure occurs after a specified number of loading cycles, such as 500 million, as in the case of aluminium. cite book
title = Advanced Strength and Applied Stress Analysis
edition = Second edition
last = Budynas
first = Richard G.
year = 1999
publisher = McGraw-Hill, Inc.
id = ISBN 0-07-008985-X
pages = 532-533
] cite book
title = The Science and Engineering of Materials
edition = Fourth edition
last = Askeland
first = Donald R.
coauthors = Pradeep P. Phule
year = 2003
publisher = Brooks/Cole
id = ISBN 0-534-95373-5
pages = 287
] Other authors do not differentiate between the expressions even if they do differentiate between the two types of materials.cite book
title = Mechanics of Materials
edition = Fifth edition
last = Hibbeler
first = R. C.
year = 2003
publisher = Pearson Education, Inc.
id = ISBN 0-13-008181-7
pages = 110
] cite book
title = Mechanical Behavior of Materials
edition = Second edition
last = Dowling
first = Norman E.
year = 1998
publisher = Printice-Hall, Inc.
id = ISBN 0-13-905720-X
pages = 365
] cite book
title = Intermediate Mechanics of Materials
last = Barber
first = J. R.
year = 2001
publisher = McGraw-Hill
id = ISBN 0-07-232519-4
pages = 65
]

Typical values

Typical values of the limit ("Se") for steels are 1/2 the ultimate tensile strength, to a maximum of 100 ksi (690 MPa). For irons, aluminums, and copper alloys, "Se" is typically 0.4 times the ultimate tensile strength. Maximum typical values for irons are 24 ksi (165 MPa), aluminums 19 ksi (131 MPa), and coppers 14 ksi (96.5 MPa).

History

The concept of "endurance limit" was introduced in 1870 by August Wöhler.W. Schutz (1996). A history of fatigue. "Engineering Fracture Mechanics" 54: 263-300. [http://dx.doi.org/10.1016/0013-7944(95)00178-6 DOI] ] However, recent research suggests that endurance limits do not actually exist, that if enough stress cycles are performed, even the smallest stress will eventually produce fatigue failure. cite journal
journal = Fatigue & Fracture of Engineering Materials & Structures
volume = 22
issue = 7
year = 1999
pages = 559–565
title = There is no infinite fatigue life in metallic materials
last = Bathias
first = C.
doi = 10.1046/j.1460-2695.1999.00183.x
]

ee also

*fatigue (material)

References


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