日本金属学会誌

J. Japan Inst. Metals, Vol. 15, No. 9 (1951),
pp. 402-407

On the Relation between Structure and Strength (II) On the Fatigue Failure of Steel and Cast Iron

F. Matsumoto


Abstract:

The author proposed the general formula for the fatigue strength as follows:

σnWn-k1τ, ·····(1)
where σnW and σn mean the fatigue strength,respectively,with or without diminishing the effect caused by repeated load having the stress difference τ in shearing,and k1 is a coefficient depending on micro-slip-path besides τ. In other words, σn correspends to the separating strength discussed Previously.
For steel,k1 is about 2.8~3.3 and σt is equal to (2.3 ~ 2.7)σu,where σu indicates the fatigue limit in single blow tension. Furthermore,the following expressions were derived, respectively: σW,fatigue limit in tension and compression=(0.53 ~ 0.68)σu, σW', fatigue limit in bending: (1.1 ~ 1.3)σW, τu, fatigue limit in single flow torsion: σW, and τW, fatigue limit in double blow torsion=(0.3 ~ 0.4)σu. With the same conception, for cast iron, σu', σW', σW'', τu' and τW' which correspond to σu, σW, σW', τu and τW respectively, for steel, were expressed using stress concentration factor αkt (in tension) or αkt (in shearing), correcting factor k2 against k1 and factor δ in bending. For an example, for σW' the following formula was derived :
αktσW'=σt-k1k2kt/2+αks/2)σW' ·····(2)

For steel containing x% of carbon, an approximation was put forward empirically as follows:
σWx'=(0.6 ~ 0.9){σfs+(σpsfs)(x/0.9)2/3} ·····(3)

where σfs and σps indicate the yceld point of firrite and pearlite, respectively. This idea could be applied also to the carburized steel, which is considered to be composed of harder outer case and softer inner part. Furthermore, the author discussed the outer notch effect on fatigue.


(Received 1950/12/18)

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