The mechanical strength of FRP depends on the combined effect of the glass fibre reinforcement content and orientation, as well as on the type of resin and the accuracy of processing.
As the percentage of glass reinforcement increases, so does the breaking load — both in tension and bending — and impact resistance.
As for fibre orientation, maximum strength is achieved when all the strands are arranged parallel to one another (unidirectional layout); if the strands are arranged equally at right angles to each other, strength is lower but still considerable (orthogonal layout); if the strands are arranged with no preferential orientation, strength is equal in all directions (isotropic layout).
The more orderly the fibre arrangement, the higher the achievable glass content, and therefore the greater the mechanical strength.
The density of FRP is about 1/5 that of steel.
Mechanical strength ranges from 0.5 to several times that of steel, depending on the composition of the FRP and the orientation of the reinforcement within the composite. There are FRP formulations with strongly oriented reinforcement in which, along the main direction of the glass fibres, strength exceeds that of other materials even for the same cross-section.
The absolute elastic moduli of FRP are lower than those of metals; however, when considering the modulus-to-density ratio, strongly oriented structures can achieve values in the same order of magnitude as metals.
FRP also has considerable impact resistance, as it distributes the impact load and does not deform permanently, unlike steel, which can undergo permanent deformation (plastic phase).
