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Effects of hole layout, braking torque and frictional heat on crack initiation from small holes in one-piece brake discs
Technical Paper
2000-05-0232
Sector:
Language:
English
Abstract
Brake discs have some holes in the flange for promoting heat
dissipation as well as refreshing the pad surfaces. One-piece brake
discs are desirable even for large sizes in order to reduce the
production cost. However, cracks exceptionally occurred from some
holes in the flange during braking under extremely severe test
conditions for one-piece brake discs. On the other hand, no cracks
were observed under the same condition for two-piece brake discs
consisting of a hub and a flange. The objective of the present work
is to show way cracks occur in the case of one-piece brake
discs.
Cyclic braking tests under extremely severe conditions were
carried out using large one-piece brake discs having some hole in
their flange. When the number of braking cycles was beyond 300,
some tiny cracks occurring around holes were found. They grew in
the radial direction of the brake discs. In order to examine
whether braking torque is a driving force for crack initiation or
not, the time interval was altered 10 times longer than the normal
condition. The experimental results showed that the number of total
cracks around holes after 300 times of braking decreased as the
braking interval was extended. The crack length also decreased.
These results indicate that the braking torque itself does have
less direct effect on crack initiation. Additional test results
indicated that heat cycles due to braking caused thermal cyclic
strain around holes and O-compression strain cycles acting discs
beyond the yielding stress in compression lead compression tension
cyclic stress. Such cyclic stress causes crack initiation around
holes.
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