No, under compression the fibers are not under tension. If the fibers are more or less aligned with the load and the matrix is stiff enough, they can also carry compressive loads. Since the fibers are way stiffer than the matrix, they do most of the work. The composite has a lower strength under compression than tension but is still higher than without reinforcement.
Also, if you only put fibers on the tension side of a beam, doe to the difference in stiffness, you neutral fiber goes closer to the fibers and you can not load them so much. At the same time, the compressive side will be overloaded
No, under compression the fibers are not under tension. If the fibers are more or less aligned with the load and the matrix is stiff enough, they can also carry compressive loads. Since the fibers are way stiffer than the matrix, they do most of the work. The composite has a lower strength under compression than tension but is still higher than without reinforcement.
Also, if you only put fibers on the tension side of a beam, doe to the difference in stiffness, you neutral fiber goes closer to the fibers and you can not load them so much. At the same time, the compressive side will be overloaded