Page 59 - Analysis and Design of Machine Elements

Figure 2.6 Size factors for bending and torsion [10]. Strength of Machine Elements 37

Table 2.3 Surface condition factors by different manufacturing
methods [13].

Fabrication methods /MPa
b
400 800 1200
Mirror-polished 1 1 1
Fine-ground 0.90 0.90 0.85
Machined 0.80 0.75 0.68
Hot-rolled 0.74 0.50 0.40
As forged 0.55 0.38 0.28

are limited, the surface codification factor for shear can be selected as approximately

equal to that for tension .

Intensify Factor, q Although surface treatment does not have much influence on static
strength, it can significantly increase fatigue strength of an element. Surface treatment
refers to surface heat treatment and cold work hardening. The former includes flame
quenching, induction quenching, carburizing and nitriding; while the latter includes
cold rolling, shot peening, hammer peening and so on. The effect of surface treatment
on the fatigue strength is measured by intensify factor . Detailed data on intensify
q