Theory Of The Fatİgue Test(İngİlİzce Rapor)

℮т℮яηαL · 29-04-07, 14:57

THEORY OF THE FATIGUE TEST
Fatigue failures can often be recognized from the appearance of the fracture. Two distinct zones can sometimes be distinguished; a smooth zone near the fatigue ***** itself which has been smoothed by the continual rubbing together of the *****ed surfaces, and a rough and crystalline-looking zone which is the final fracture. Occasionally the fatigue ***** shows roughly concentric rings which correspond to successive positions of the *****.
Labaratory fatigue tests can be carried out on four types of testing machine: (1) push-pull(axial loading); (2) rotating bending (rotating a cantilever beam with a stationary end load); (3) reversed bending (appliying an alternating bending moment to a flat plate specimen);(4) torsion (appliying torgue). The stress cycle is usually kept constant during the test and is often sinusiodal form owing to the nature of the testing machine. In practice, of course , the loading history may be more complicated than this-loading of an aeroplane fuselage is a typical example. Most tests are perpormed with the mean stress m =0. a series of specimens of the material are tested to failure at different values of the stress amplitude a and each test gives one point on a diagram of a versus the logarithm of the number of cycles to failure (known as the S-N curve )
Most materials have fatigue curves and the fatigue strength must be quoted relative to a specified number of cycles, the most common being the stress amplitude which will cause failure in 107 cycles. On the other hand , some materials e.g. , most steels and titanium alloys, have a fatigue curve. For such materials there is a definite value of stress amplitude below which fatigue will never occur and this value, the fatigue limit , is guoted in some material specifications.

29-04-07, 14:57	#1 (permalink)
℮т℮яηαL Hepimiz DeLiyiz , Hepimiz Fenerbahçe'Liyiz Giriş Tarihi: 03-11-2006 Yer: ۞ İsTaИbuL ۞ Yaş: 19 Mesajlar: 13,300 Blog Mesajları: 10 Rep Puanı: 3163602 Rep Gücü: 31794	Theory Of The Fatİgue Test(İngİlİzce Rapor) THEORY OF THE FATIGUE TEST Fatigue failures can often be recognized from the appearance of the fracture. Two distinct zones can sometimes be distinguished; a smooth zone near the fatigue *** itself which has been smoothed by the continual rubbing together of the *ed surfaces, and a rough and crystalline-looking zone which is the final fracture. Occasionally the fatigue * shows roughly concentric rings which correspond to successive positions of the ***. Labaratory fatigue tests can be carried out on four types of testing machine: (1) push-pull(axial loading); (2) rotating bending (rotating a cantilever beam with a stationary end load); (3) reversed bending (appliying an alternating bending moment to a flat plate specimen);(4) torsion (appliying torgue). The stress cycle is usually kept constant during the test and is often sinusiodal form owing to the nature of the testing machine. In practice, of course , the loading history may be more complicated than this-loading of an aeroplane fuselage is a typical example. Most tests are perpormed with the mean stress m =0. a series of specimens of the material are tested to failure at different values of the stress amplitude a and each test gives one point on a diagram of a versus the logarithm of the number of cycles to failure (known as the S-N curve ) Most materials have fatigue curves and the fatigue strength must be quoted relative to a specified number of cycles, the most common being the stress amplitude which will cause failure in 107 cycles. On the other hand , some materials e.g. , most steels and titanium alloys, have a fatigue curve. For such materials there is a definite value of stress amplitude below which fatigue will never occur and this value, the fatigue limit , is guoted in some material specifications.

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