Composite Materials

· For a graphite fiber reinforced epoxy matrix (gfrp) with: V_f = 0.80, σ_ym = 60 MPa, E_f = 300 GPa, and E_m = 2.0 GPa, the tensile yield stress in the direction parallel to the fibers is: σ_yC = 7.2 GPa >> σ_ym
· Composites behave well in tension but less well in compression where the buckling of the fibers and composite yield can occur.

· In uniaxial compression, the fiber buckling mode depends upon the fiber volume fraction as illustrated.
· At low volume fractions "out-of-phase" buckling (a) can occur. At large V_f only the "in-phase" mode is possible.

From: Hull, "Introduction to Composite Materials," Cambridge (1992)