Page 60 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
38
Table 2.4 Intensify factors by various surface treatments [10].
Diameter, Intensify
Surface treatments Specimen d mm −1 factor, q
Induction quenching Without stress concentration 7∼20 1.3∼1.6
30∼40 1.2∼1.5
With stress concentration 7∼20 1.6∼2.8
30∼40 1.5∼2.5
Nitriding (depth 0.1∼0.4 mm) Without stress concentration 8∼15 1.15∼1.25
30∼40 1.10∼1.15
With stress concentration 8∼15 1.9∼3.0
30∼40 1.3∼2.0
Carbonizing (depth 0.2∼0.6 mm) Without stress concentration 8∼15 1.2∼2.1
30∼40 1.1∼1.5
With stress concentration 8∼15 1.5∼2.5
30∼40 1.2∼2.0
Rolling Without stress concentration 7∼20 1.2∼1.4
30∼40 1.1∼1.25
With stress concentration 7∼20 1.5∼2.2
30∼40 1.3∼1.8
Shot peening Without stress concentration 7∼20 1.1∼1.3

30∼40 1.1∼1.2
With stress concentration 7∼20 1.4∼2.5
30∼40 1.1∼1.5

factors can be found in reference [10] and abridged data used in this book are listed in
Table 2.4.
The effect of these factors can be evaluated by a combined influence factor K ,

expressed in the formula as [14]
( )
k 1 1
K = + − 1 (2.20)

q
These discussions relate to the endurance limit of materials subjected to normal tensile
stress only, that is, tensile stresses resulting from bending or axial tension. Cases involv-
ing fluctuating torsional shear stresses are comparable to normal stresses, and tensile
stress can be substituted with shear stress directly.
The actual endurance limit of a machine element will then be
−1
= (2.21)
−1e
K

Considering these factors, the actual endurance limit diagram of an element is then
obtained by moving line ACF proportionally to line A C F , while keeping EF as it is, as
1 1
1
shown in Figure 2.5. Points on lines A F E characterize endurance limits corresponding
1 1
to a stress ratio between −1and +1.