Abstract

In this study the influence of machined surface texture on the fatigue strength of a Graphite/Bismaleimide (Gr/Bmi) laminate was examined. Rectangular beam specimens were machined to achieve specific surface roughness 0.2Ra10.0μm and then subjected to fully reversed four-point flexural fatigue. The surface texture resulting from machining was evaluated using contact profilometry and the standard surface roughness parameters were used in estimating the effective stress concentration K¯t and effective fatigue notch K¯f factors for the machined surfaces according to models reported in the open literature. Fully reversed flexural fatigue loading of the laminate was conducted at two separate maximum bend loads corresponding to Tsai-Hill ratios for first ply failure of 0.75 and 0.9. It was found that the reduction in stiffness of the Gr/Bmi laminate at both levels of fatigue loading increased with the magnitude of surface roughness. The apparent fatigue stress concentration factors Kf of the machined surfaces determined from experimental results ranged from 1.0 to 1.2. The effective fatigue notch factors estimated using the Arola-Ramulu model for the machined specimens were within 10% of the corresponding Kf determined from experiments.

1.
Abrate
,
S.
, and
Walton
,
D. A.
,
1992
, “
Machining of Composite Materials. Part I: Traditional Methods
,”
Compos. Manuf.
,
3
, No.
2
, pp.
75
83
.
2.
Abrate
,
S.
, and
Walton
,
D. A.
,
1992
, “
Machining of Composite Materials. Part II: Non Traditional Methods
,”
Compos. Manuf.
,
3
, No.
2
, pp.
85
94
.
3.
Howarth, S. G., and Strong, A. B., 1990, “Edge Effects with Water Jet and Laser Beam Cutting of Advanced Composite Materials,” Proceedings of the 35th International SAMPE Symposium, pp. 1685–1697.
4.
Colligan, K., 1993, “Machined Edge Effects on the Compression Strength of Graphite/Epoxy Composite,” Masters Thesis, University of Washington.
5.
Arola
,
D.
, and
Ramulu
,
M.
,
1998
, “
Net-Shape Manufacturing and the Process-Dependent Failure of Fiber-Reinforced Plastics Under Static Loads
,”
ASTM J. Compos. Technol. Res.
,
20
, No.
4
, pp.
210
220
.
6.
Arola
,
D.
, and
Ramulu
,
M.
,
1997
, “
Net-Shape Manufacturing and the Performance of Polymer Composites Under Dynamic Loads
,”
Exp. Mech.
,
37
, No.
4
, pp.
379
385
.
7.
Neuber, H., 1958, Kerbspannungsleshre, Springer-Verlag, pp. 159–163.
8.
Zahavi, E., and Torbilo, V., 1996, Fatigue Design: Life Expectancy of Machine Parts, 1st Edition, CRC Press, pp. 193.
9.
Arola, D., 1996, “The Influence of Net-Shape Machining on the Surface Integrity of Metals and Fiber Reinforced Plastics,” Ph.D. dissertation, University of Washington.
10.
Arola
,
D.
, and
Ramulu
,
M.
,
1999
, “
An Examination of the Effects from Surface Texture on the Strength of Fiber Reinforced Plastics
,”
J. Compos. Mater.
,
33
, No.
2
, pp.
102
123
.
11.
Kapur, K. C., and Lamberson, L. R., 1977, Reliability in Engineering Design, Wiley, pp. 291–332, NY.
12.
Gibson, R. F., 1994, Principles of Composite Materials Mechanics, McGraw Hill, NY.
13.
Charewicz, A., and Daniel, I. M., 1986, “Damage Mechanisms and Accumulation in Graphite/Epoxy Laminates,” Composite Materials: Fatigue and Fracture, ASTM STP 907, pp. 274–297.
14.
Camponeschi, E. T., and Stinchcomb, W. W., 1982, “Stiffness Reduction as an Indicator of Damage in Graphite/Epoxy Laminates,” Composite Materials: Testing and Design (Sixth Conference), ASTM STP 787, pp. 225–246.
15.
Gibbins, M. N., and Stinchomb, W. W., 1982, “Fatigue Response of Composite laminates with Internal Flaws,” Composite Materials: Testing and Design (Sixth Conference). ASTM STP 787, pp. 305–322.
16.
Peterson R. E., 1974, Stress Concentration Factors, Wiley, New York.
17.
Ramulu
,
M.
,
Wern
,
C. W.
, and
Garbini
,
J. L.
,
1993
, “
Effect of Fiber Direction on Surface Roughness Measurements of Machined Graphite/Epoxy Composite
,”
Compos. Manuf.
,
4
, No.
1
, pp.
39
51
.
You do not currently have access to this content.