دراســـــة الخواص الميكانيكية للمادة المركبة المقواة بواسطة الياف احادية الاتجاه

Mechanical properties Investigation of Composite material reinforced by uni-directional fibers

Abstract

In this work, the effect of fiber orientation and layers sequence on the properties will be studied Mechanical (strength, stiffness and fatigue) of carbon/epoxy composite material. The laminated composite materials were manufactured using Hand lay-up in vacuum technique with a volume fraction of 30%. This work consists of selecting the appropriate failure theory by comparing the experimental tensile test results of composite materials’ lamina (carbon/epoxy) with different orientations (0° to 90°)with the five failure theories (Maximum stress theory, Maximum strain theory, Tsai-Hill theory, Tsai-Wu theory, and Ha shin’s theory), a theoretical study of the effect of stacking sequence of layers with angles (0°,30°,60°,75° and 90°), on tensile strength using Hashin’s theory, The laws of elasticity for composite materials and classical laminate theory to get the best sequence using the MATLAB program. The tensile test was performed for three sequences, where the sequence [60/30/0/90/75] represented the highest tensile value, the sequence [30/90/0/60/75] is represented the middle tensile value, and the sequence [0/30/60/90/75] is represented the minimum tensile value. The percentage difference between the theoretical and experimental tensile value results of the sequence [60/30/0/90/75] was 6.64%, while the percentage of the difference between the theoretical and experimental tensile value results of the sequence [30/90/0/60/75] was 9.34%. As for the sequence [0/30/60/90/75], the percentage of difference was 27%, and the fatigue properties of three stacking sequence laminated composite mentioned above have been measured experimentally under a constant stress ratio of R=-1 as a fully reversed bending load. The results showed that the sequence [60/30/0/90/75] that has the higher tensile strength had had better fatigue limits (60.08MPa and Nf > 106). Finally, the scanning electron microscope analysis (SEM) was used for investigating the morphology microstructure of the failed specimens of three sequence and mention above under the influence of fatigue test, such as fibers breaking, matrix breaking, deboning between matrix and fiber, delamination, and transverse crack appearing, and that the failure shape were somewhat similar in all the sequences, but differed in the beginning of the damage from one layer to another due to the location of that layer in laminate, and its get away from center load.