Glass Fibre Composite (GFRP)

Family

Composites

Category

composite

Density

2.1 g/cm³ · 2100 kg/m³

Fibre / matrix

E-glass · Epoxy

Fibre volume fraction

55%

Tensile strength, along the fibres

1,080 MPa

Tensile strength, across the fibres

39 MPa · 28× lower than along them

Modulus, along the fibres

39 GPa · 8.6 GPa across

Compressive strength, along the fibres

620 MPa · Poisson’s ratio 0.28

Values are for a unidirectional laminate of E-glass in epoxy at 55% fibre volume fraction, from fib Bulletin 40 (FRP reinforcement), unidirectional laminate values. Longitudinal means load along the fibres, transverse means load across them; change the fibre fraction or the layup and every figure here changes with it.

Machining

Cut and drilled with ordinary woodworking tooling, though the dust is abrasive and the fibres blunt high-speed steel quickly — carbide or diamond is the practical choice.

Joining

Bolted joints need the load spread over a large area: use washers and generous edge distance, because the laminate bears the load poorly through a hole. Bonding generally beats bolting here.

Durability

The matrix, not the glass, is what ages — UV yellows and embrittles it, and water diffuses in slowly. Gelcoat or paint is the protection, and for immersion it is not optional.

As with the wood and metal pages, these lines are not measurements. The longitudinal figures above assume the load arrives along the fibres; a bolted joint is usually the place where it does not, which is why the joining note is the one to read first.

• Figures are for a unidirectional laminate at the stated fibre volume fraction
• Isotropic only in the plane of the fibres — across them it is a fifth as strong
• The matrix, not the fibre, sets the temperature limit: typically 80–120 °C