الفهرس 
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Abstract
Studying the fatigue behavior represents one of the most important targets for any
new material before being used. This is because; fatigue behavior cannot be predicted and
the fatigue failure cannot be expected as in the case of static yielding. This thesis studies
the fatigue behavior of wove-roving glass fiber reinforced polyester (GFRP) under
combined bending and torsional moments, out-of-phase, with different fluctuating stresses.
Fatigue tests were conducted on two fiber orientations, [0,90h and [±45h, thin-walled
tubular specimens with 45° and 90° phase shift between bending and torsional moments at
a certain ratio of the flexural stress(A) to the torsional shear stress (B); NB=2 for [0,90h
specimens and AlB= I for [±45h specimens. To study the effect of mean stress of fatigue
. . c. . d diff . (R min .stress )
behavior, specimens were ratigue teste at I erent stress ratros = , R = -I,
max.stress
-0.75, -0.5, -0.25 for both fiber orientations at the two phase angles.
The results showed that the [0,90h specimens have higher bending strength than
the [±45h specimens, while the [±45h specimens have higher torsional strength than the
[0,90h specimens. And The endurance limit, calculated at N=2* 1 06 cycles, of pure
bending (Se) is 3.2 times the endurance limit of pure torsion (Ses) for [0,90h and 1.8 times
the endurance limit of pure torsion (Ses) for and [±45h specimens. Also, at high stress level
increasing the presence of non-zero out-of-phase angles between bending moment and
twisting moment decreases the specimen life, while at lower stress level the life increases.
This trend is independent ofthe effect oftested fiber orientations.
The validity of The Smith-Watson-Topper parameter {SWT=J(O”m.pJ} was
examined and it showed good validity for both fiber orientations; i.e. performing only the
completely reversed (R=-l) fatigue test and using the SWT parameter will be sufficient to
find out the strength of the material under any negative stress ratio. Using the power
formula SWT = al bl has resulted in having a nearly constant ratio between (a.) and the
corresponding static strength for both fiber orientations. Also, the validity of the modified
.!.(I-R)y
fatigue strength ratio {If’ = 2 } was examined for the present case and the
1- .!.(1 + R)y
2
results showed that it has become a useful measure for establishing the master S-N
relationship for woven-roving GFRP with [0,90h and [±45h fiber orientations under
combined bending and torsion in-phase and out-of-phase fatigue loading with negative
stress ratios. Using the power formula If’ = a2 N b2 has proved its suitability for [0,90h and
[±45h specimens. And the value of (b2), at different loading conditions for both fiber
orientations [0,90h and [±45h, may be considered to be material constant. The value of
(a2) was found to be nearly equal to the ratio (a/ su), where S, is the static strength in fiber
direction and (a) is the constant of (CYmax. = a Nb) at completely reversed load (R= -1) for
each specified loading condition.