The Effect of Fiber Orientation on Creep Behavior And Flextural Strength In Epoxy Composites

The creep behavior, flexural strength, shear stress was investigated in this paper for epoxy, epoxy composite reinforced with glass fibers: (chopped strand mat), woven roven (90 о -0 о ) and chopped strand mat together as a sandwich composite with volume fractio n (21, 25, 29) % for each typ e. The tests were done at c onstant temperature (room temperature (23 ± 2) о C. The results shown that the increasing in volume fraction increases the creep behavior, flextural streng th, shear stress for all samples also the results shown the effect of fiber orientation in increasin g the c reep behavior, flextural strength, sh ear stress in sandwich composites in comparession with the composites reinforced with randomly glass fibers.


Introduction
A composite may be defined as any multiple phase material that exhibits a significant proportion of the properties of both the constituent materials, a judicious combination of two or more distinct materials can provide better combination of properties.Fiber reinforced composites are those composites in which the dispersed phase is in the form of fibers, technologically, these composites are very important as they provide high strength and stiffness on a weight basis [1] .
Many researchers studied in this field, Balkees [2] showed that the orientation of fibers had a major role in increasing the creep  Houshyar [4] gave that the incorporation and increase of the fiber concentration gave rise to a considerable increase of tensile, flexural strength, the maximum improvement in properties was observed for the composite with W f = 50% which is equal to V f = 26%, is chosen as a critical fiber concentration, this was due to the reinforcement imparted by the fibers that allowed stress transfer from the matrix to the fibers.
Lee & Jyongsik [5] reported that as fiber content increased, the tensile and flextural modulus of the glass fiber composite showed a linear increment.
Another study by Abot & Yasmin [6] showed that the interface region between the matrix and glass fibers limited the mechanical properties of the composite.
Amorphous materials such as high polymers show high rate of deformation under relatively low stress and temperature because of their less   3) and ( 4) noticed that the strain increased rapidly in the beginning called initial instantaneous strain.The composite materials have different strain according to type of fiber, composition of fiber and adhesion between the fibers and the matrix in the interface region [14].Generally reinforcing the polymers increased the secondary stage in creep curve mean that needing more time to approach final fracture due to the role of fibers which absorbing the maximum part of the loads as a result the strain increased [15].

Conclusions
These results characterize the creep behavior and flextural strength, shear stress of composites with three volume percentages of an E-glass fiber in a room temperature curable epoxy matrix from them, the following conclusions can be drawn:-1.Change in volume percentage of fibre produces no change in mechanical properties.2. The creep rate in sandwich composite was higher than creep rate in random composite as a result the creep resistance of sandwich composite is lower than the creep resistance of random composite.
3. The creep constant (k) decreased in each type of composite with increasing the volume fraction of fibers.
[4]-Houshyar.R.A, Shanks.R.A, "The effect of fiber concentration on mechanical and thermal properties of fiber-reinforced poly The ability of a material to undergo flextural distortions without weakening or shattering is a key property for the use of polymers in many components and structural parts, the flextural strength calculated from the equation [flextural strength.p: applied load till failure occurs.L: span of the sample.b: width of the sample.t: thickness of the sample.While the shear stress predicted from the equation …….. (4) When τ: shear stress PDF created with pdfFactory Pro trial version www.pdffactory.com

FigureFigure ( 6 )
Figure (1) flextural strength of the composite reinforced with each type of glass fibers R: chopped strand mat S: Sandwich glass fibers

Eng. & Tech. Journal, Vol.28, No.7, 2010 The Effect of Fiber Orientation on Creep Behavior And Flexural Strength In Epoxy Composites 1283
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