الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Composites have became a material of intense research due to its increasing use in
the engineering industry. Since engineering structures are frequently subjected to cyclic
loading, during the past decades investigating fatigue performance, and developing fatigue
life prediction methodologies, have been the subjects of study for a large number of
researchers. This thesis studies the fatigue behaviour of woven - roving GFRP specimens,
with [0, 900hs , [30°, -600hs ,[±45°hs and [60°, -300b fibre orientations, under pure
bending, pure torsion and combined bending and torsional moments, with different
min. stress.
negative or positive stress ratios (R = ) .
max. stress
The results showed that under static bending and also under completely reversed
pure bending tests, the [0, 900b specimens have the higher bending strength than other
fiber orientations. While the [±45°b specimens have the lowest value. For static torsional
and completely reversed pure torsion tests, the [±45°b specimens have the highest
torsional strength and the [0, 900b specimens have the lowest one. The [300,-600b and
[60°,-300hs specimens have approximately the same bending and torsional strength under
pure bending or pure torsion.
Using the power formula: CJ max = aN b for combined bending and torsional loading
have proved its suitability by giving acceptable values for the correlation factor. The
deviation in the values of the power (b) for all cases of loading conditions was negligible
and it may be considered to be a material constant of - 0.123. For constant fiber orientation
angle, increasing the value of negative stress ratio (R) causes an increase in the
corresponding value of (a). While increasing the value of positive stress ratio causes a
decrease in the value of (a). On the other hand, for constant negative or positive stress
ratio, an increase in fiber orientation angle causes a decrease in the value of (a).
The validity of the SWT parameter (~(Jmax(Ja ) was examined for the present cas~
and it showed good validity for woven-roving GFRP for all fiber orientations under
combined bending and torsional fatigue loading. Performing only the completely reversed
(R=-I) fatigue test and using the S WT parameter wi II be sufficient to find out the strength
of the material. The modified SWT parameter, (Kw.ra CTm •. ,CT,,), was found to be constant
of 0.5471 and valid for woven-roving GFRP for all fiber orientations under combined
bending and torsional fatigue loading.
1 (I-R)1jI
Also, the validity of the modified fatigue strength ratio (’I’ = 21 ) was
i- (I+R);;
2
examined and the results showed that it has become a useful measure for establishing the
master S- relationship for woven-roving GFRP under combined bending & torsional
fatigue moments for all fiber orientations over a range of stress ratios.