Gear Crack Propagation Path Studies-Guidelines for Ultra-Safe Design

TITLE AND SUBTITLE:
Gear Crack Propagation Path Studies-Guidelines for Ultra-Safe Design

AUTHOR(S):
David G. Lewicki

REPORT DATE:
July 2001

FUNDING NUMBERS:
WU-712-30-13-00
1L162211A47A

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
John H. Glenn Research Center
Cleveland, Ohio 44135-3191
and
U.S. Army Research Laboratory
Cleveland, Ohio 44135-3191

PERFORMING ORGANIZATION REPORT NUMBER:
E-12912

SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Washington, DC 20546-0001
and
U.S. Army Research Laboratory
Adelphi, Maryland 20783-1145

REPORT TYPE AND DATES COVERED:
Technical Memorandum

SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA TM-2001-211073
ARL-TR-2468

SUPPLEMENTARY NOTES:
Prepared for the 57th Annual Forum and Technology Display sponsored by the American Helicopter Society,
Washington, DC, May 9-11, 2001. Responsible person, David G. Lewicki, organization code 5950, 216-433-3970.

ABSTRACT:
Design guidelines have been established to prevent catastrophic rim fracture failure modes when considering gear tooth bending fatigue. Analysis was performed using the finite element method with principles of linear elastic fracture mechanics. Crack propagation paths were predicted for a variety of gear tooth and rim configurations. The effects of rim and web thicknesses, initial crack locations, and gear tooth geometry factors such as diametral pitch, number of teeth, pitch radius, and tooth pressure angle were considered. Design maps of tooth/rim fracture modes including effects of gear geometry, applied load, crack size, and material properties were developed. The occurrence of rim fractures significantly increased as the backup ratio (rim thickness divided by tooth height) decreased. The occurrence of rim fractures also increased as the initial crack location was moved down the root of the tooth. Increased rim and web compliance increased the occurrence of rim fractures. For gears with constant pitch radii, coarser-pitch teeth increased the occurrence of tooth fractures over rim fractures. Also, 25° pressure angle teeth had an increased occurrence of tooth fractures over rim fractures when compared to 20° pressure angle teeth. For gears with constant number of teeth or gears with constant diametral pitch, varying size had little or no effect on crack propagation paths.

SUBJECT TERMS:
Gears; Crack propagation; Fracture mechanics; Finite element method; Design

NUMBER OF PAGES:
16

PDF AVAILABLE FROM URL:
2001/TM-2001-211073.pdf
( 1,465 KB )

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