ISO 10300-3:2023

INTERNATIONAL ISO
STANDARD 10300-3
Third edition
2023-08
Calculation of load capacity of bevel
gears —
Part 3:
Calculation of tooth root strength
Calcul de la capacité de charge des engrenages coniques —
Partie 3: Calcul de la résistance du pied de dent
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols, general subscripts and abbreviated terms . 2
5 General rating procedure . 6
6 Gear tooth rating formulae — Method B1 . 7
6.1 Tooth root stress formula . 7
6.2 Permissible tooth root stress . 8
6.3 Calculated safety factor . 9
6.4 Tooth root stress factors . 9
6.4.1 Tooth form factor, Y . 9
Fa
6.4.2 Stress correction factor for load at tooth tip, Y . 14
Sa
6.4.3 Contact ratio factor, Y . 14
ε
6.4.4 Bevel spiral angle factor, Y . 15
BS
6.4.5 Load sharing factor, Y . 16
LS
6.5 Permissible tooth root stress factors . 16
6.5.1 Relative surface condition factor, Y . 16
R,relT-B1
6.5.2 Relative notch sensitivity factor, Y . 17
δ,relT-B1
7 Gear tooth rating formulae — Method B2 .19
7.1 Tooth root stress formula . 19
7.2 Permissible tooth root stress . 19
7.3 Calculated safety factor . 20
7.4 Tooth root stress factors .20
7.4.1 General .20
7.4.2 Stress parabola according to Lewis . . 21
7.4.3 Basic formula of geometry factor, Y . 21
J
7.4.4 Geometry factor, Y , for bevel gears (for hypoid gears, see 7.4.5) .22
J
7.4.5 Geometry factor, Y , for hypoid gears . 26
J
7.4.6 Additional tooth strength parameters (for bevel and hypoid gears) . 35
7.4.7 Root stress adjustment factor, Y .38
A
7.5 Permissible tooth root stress factors .38
7.5.1 Relative surface condition factor, Y .38
R,relT-B2
7.5.2 Relative notch sensitivity factor, Y .38
δ,relT-B2
8 Factors for permissible tooth root stress common for method B1 and method B2 .39
8.1 Size factor, Y . 39
X
8.1.1 General .39
8.1.2 Structural and through hardened steels, spheroidal cast iron, perlitic
malleable cast iron.39
8.1.3 Case, flame, induction hardened steels, nitrided or nitro carburized steels .39
8.1.4 Grey cast iron and spheroidal cast iron (ferrit structure) .39
8.2 Life factor, Y .39
NT
8.2.1 General .39
8.2.2 Method A . . .40
8.2.3 Method B . .40
Bibliography .43
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 60, Gears, Subcommittee SC 2, Gear
capacity calculation.
This third edition cancels and replaces the second edition (ISO 10300-3:2014), which has been
technically revised.
The main changes are as follows:
— Table 1 has been inserted;
— Table 2 has been inserted;
— Figure 4 — surface condition factor, Y , for permissible stress number relative to standard test
R,relT
gear dimensions has been removed;
— Figure 5 — relative notch sensitivity factor with respect to standard test gear dimensions has been
removed;
— new Figure 5 — life factor, Y (standard reference test gears) has been added;
NT
— Figure 7 — size factor, Y , for permissible tooth root stress has been removed.
X
A list of all parts in the ISO 10300 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
When ISO 10300:2001 (all parts) became due for its first revision, the opportunity was taken to include
hypoid gears, since previously the series only allowed for calculating the load capacity of bevel gears
without offset axes. The former structure is retained, i.e. three parts of the ISO 10300 series, together
with ISO 6336-5, and it is intended to establish general principles and procedures for rating of bevel
gears. Moreover, ISO 10300 (all parts) is designed to facilitate the application of future knowledge and
developments, as well as the exchange of information gained from experience.
In view of the decision for ISO 10300 (all parts) to cover hypoid gears also, it was agreed to include
a separate clause: “Gear tooth rating formulae — Method B2” in this document, while the former
methods B and B1 were combined into one method, i.e. method B1. So, it became necessary to present a
new, clearer structure of the three parts, which is illustrated in ISO 10300-1:2023, Figure 1.
NOTE ISO 10300 (all parts) gives no preferences in terms of when to use method B1 and when to use
method B2.
Failure of gear teeth by tooth root breakage can be brought about in many ways; severe instantaneous
overloads, excessive macropitting, case crushing and bending fatigue are a few. The strength ratings
determined by the formulae in this document are based on cantilever projection theory modified to
consider the following:
— compressive stress at the tooth roots caused by the radial component of the tooth load;
— non-uniform moment distribution of the load, resulting from the inclined contact lines on the teeth
of spiral bevel gears;
— stress concentration at the tooth root fillet;
— load sharing between adjacent contacting teeth;
— lack of smoothness due to a low contact ratio.
The formulae are used to determine a load rating, which prevents tooth root fracture during the design
life of the bevel gear. Nevertheless, if there is insufficient material under the teeth (in the rim), a fracture
can occur from the root through the rim of the gear blank or to the bore (a type of failure not covered
by this document). Moreover, it is possible that special applications require additional blank material to
support the load.
...