الفهرس 
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Abstract
This work is concerned with study of the effect of fiber length and fiber volume fraction at different crosshead speeds on the mechanical properties and fracture toughness of randomly oriented glass fibers reinforced polyurethane elastomer composites. The modulus of elasticity and the yield strength increase with increasing the fiber volume fraction, the fiber length and the crosshead speed. The percentage increase due to the increasing of fiber volume fraction for10 mm fiber length is much higher than that for 5 mm fiber length. The percentage increase due to increasing of the crosshead speed for 10 mm fiber length is lower than that for 5 mm. The toughness of the failed specimens decreases with increasing the fiber volume fraction, the crosshead speed and fiber length. Additionally, the fracture toughness of these composites with notch to width ratio of 0.2 was investigated in Mode I fracture using single-edge notched tension test. The critical stress intensity factors (KIC) were determined using J-integral method. The rupture occurred for all notched specimens. For un-notched specimens, rupture occurred only at 500 mm/min crosshead speed for the two fiber lengths of 5 mm and 10 mm with 0.25%, 0.50% and 0.75% fiber volume fractions because of the limitation of the maximum stroke of the testing machine. At 500 mm/min, the JIC decreases with increasing glass fiber volume fraction and also decreases with increasing fiber length from 5 mm to 10 mm, while the KIC increases with increasing both glass fiber volume fraction and fiber length.