In continuously coupled blade structures, fretting fatigue and wear have to be considered as supposed failure modes at the contact surface of the shroud cover, which is subject to steady contact pressure from centrifugal force and the vibratory load of the blade. We did unique fretting tests that modeled the structure of the shroud cover, where the vibratory load is only carried by the contact friction force, i.e., a type of friction. What was investigated in this study are fretting fatigue strength, wear rate, and friction characteristics, such as friction coefficient and slip-range of 12%-Cr steel blade material. The friction-type tests showed that fretting fatigue strength decreases with the contact pressure and a critical normal contact force exists under which fretting fatigue failure does not occur at any vibratory load. This differs from knowledge obtained through pad-type load carry tests that fretting fatigue strength decreases with the increase of contact pressure and that it almost saturates under a certain contact pressure. Our detailed observation in the friction-type tests clarified that this mechanism was the low contact pressure narrowing the contact area and a resulting high stress concentration at a local area. The fretting wear rate was explained by the dissipated energy rate per cycle obtained from the measured hysteresis loop between the relative slip range and the tangential contact force. It was found that the fretting wear rate is smaller than the wear rate obtained by one-way sliding tests, and the former is much smaller than the latter as the dissipated energy decreases. Finally, to prevent fretting fatigue and wear, we propose an evaluation design chart of the contact surface of the shroud cover based on our friction-type fretting tests.

References

References
1.
Nagata
,
K.
,
Matsuda
,
T.
, and
Kashiwaya
,
H.
,
1987
, “
Effect of Contact Pressure on Fretting Fatigue Strength
,”
Trans. Jpn Soc. Mech. Eng., Ser. A
,
53
(
486
), pp.
196
199
.10.1299/kikaia.53.196
2.
Hattori
,
T.
,
Nakamura
,
M.
, and
Watanabe
,
T.
,
2000
, “
A New Approach to the Prediction of the Fretting Fatigue Life that Considers the Shifting of the Contact Edge by Wear
,” ASTM STP Paper No. 1367, pp. 19–30.
3.
Niho
,
S.
,
Kubota
,
M.
,
Sakae
,
C.
, and
Kondo
,
Y.
,
2003
, “
Effect of Relative Slip Amount on Initiation Site and Propagation Condition of Fretting Fatigue Crack
,”
Proceedings of the 56th Kyushu Branch Regular Meeting of the Japan Society of Mechanical Engineers
, Kyushu, Japan, March, Paper No. 038-1, pp.
11
12
.
4.
Nishioka
,
K.
, and
Hirakawa
,
K.
,
1968
, “
Study on Fretting Fatigue (4th Report)
,”
Trans. Jpn Soc. Mech. Eng., Ser. A
,
34
(
266
), pp.
1644
1649
.10.1299/kikai1938.34.1644
5.
Kondo
,
Y.
, and
Bodai
,
M.
,
2001
, “
The Fretting Fatigue Limit Based on Local Stress at the Contact Edge
,”
Fatigue Fract. Eng. Mater. Struct.
,
24
, pp.
791
801
.10.1046/j.1460-2695.2001.00449.x
6.
International Institute of Welding,
2003
, International Institute of Welding Document No. XIII-1965-03/WV-1127-03, pp. 25–27.
7.
Shima
,
M.
, and
Satoh
,
J.
,
1986
, “
Studies of Fretting (Part 4)
,”
Junkatsu
(Lubrication),
31
(
7
), pp.
507
514
.
8.
Material Mechanics
,”
1991
, Society of Material Science, Japan, pp. 168–169.
9.
Fouvry
,
S.
,
Kapsa
,
P.
, and
Vincent
,
L.
,
2000
, “
Fretting Wear and Fretting Fatigue: Relation Through a Mapping Concept
,” ASTM STP Paper No. 1367, pp.
49
64
.
You do not currently have access to this content.