For fiber glass polyester , the orientation of fibers at [0/90] degree in a ply showed a stronger mechanical properties compared to a [+- 45] orientation. The chopped strand mat (CSM) showed a mechanical properties greater than the [+-45] but lower than the [0/90] orientation. It seem that the [0/90] orientation is the strongest among the 3 orientation. BUT I need to understand the reasons.
In the attachment, I provided the mechanical properties of the orientations from tensile test.
Think about it in terms of fabric. The matrix is not as rigid as the fibres (for steel, carbon or glass). Therefore, when loaded in the direction of the fibres (0,90) the fibre stiffness dominates. When the loading is at +/- 45, the matrix stiffness dominates.
I think this results related to the shear stress between glass fiber and the chains structure of polyster.The shear stress changes with the orientation angles and the stucture polymer type.
Chopped strand mats impart isotropic behavior to the laminate. angled ply laminates are highly anisotropic . Pl go thru Mechanics of composites book by Gibson / Jones / Kaw / Meyers
Consult: Composite Materials: Design and Applications, Third Edition
Daniel Gay
You can find the analyses of FRCM in details in the book of Jones - Mechanics of composite materials ....... Good Luck
Thank you for all the answers, I am sure that I almost find a concrete justification for my current situation/question.
The strength of the ply is at its highest when the fibres are oriented in the 0 degree direction (ie the material is tested in the direction of the fibres). It has been observed that when the fibres are oriented in the 45 degree direction, the strength drops to 10% of the strength of the ply with fibres in the 0 degree direction. For the 90 degree orientation, the strength drops to about 7-8%. I attach a graph showing this. For simplicity one can assume that the fibres oriented at 45 to 90 degrees will only contribute 10% of the strength. If you know the volume fraction of each ply, you can calculate the theoretical strength. If you have only two plies in the composite as in [0/90], the volume fraction of each is 0.5. From this, the strength of the [0/90] composite will be about 55% that of a [02] composite. If the orientation, is [+-45], the strength will be only 10% that of the [02]. I have demonstrated this to my students many times in the lab. We have been running the lab for about 30 years and I can confirm that the approximation is fairly accurate.
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