Table 2-8. Maximum principal stresses of a macro model for various graphite/epoxy
composite systems.
Sample Orientation, Laminate Plate Theory
Sample Orientation, 9
OL (MPa) GT (MPa) YLT (MPa)
A 0 0 0 0
0 -24.9 46.4 0
90 -92.9 49.9 0
0 -54.3 43.1 7.76
C 45 16.2 39.5 -2.85
90 -136 47.3 -7.76
Table 2-9. Maximum principal stresses in the fiber and matrix phases of a unit cell for
various graphite/epoxy composite systems from micro-analysis.
Square Cell Hexagonal Cell
Sample 0 Fiber (MPa) Matrix (MPa) Fiber (MPa) Matrix (MPa)
CY1 2 C1 C2 C1 C2 C1 C2
A 0 1.78 -36.9 39.4 -20.7 3.29 -33.8 41.3 -10.1
0 54.3 -104 63.4 -35.5 51.2 -91.0 63.4 -21.8
90 59.0 -217 65.4 -36.3 55.2 -204 66.6 -22.9
0 50.8 -155 69.2 -34.2 47.7 -147 68.4 -21.4
C 45 45.3 -33.5 61.3 -33.4 43.3 -23.4 61.3 -19.7
90 55.9 -291 71.4 -35.4 52.2 -283 71.1 -22.7
Table 2-10. Percentage difference of principal stresses estimated by square and hexagonal
unit cells. The negative sign indicates that micro-stress result estimated by the
hexagonal unit cell is lower.
Fiber (MPa) Matrix (MPa)
Sample 0
C 1 (%) G2 (%) 1 (%) 2 (%)
A 0 84.7 -8.56 4.76 -51.2
0 -5.60 -12.1 -0.10 -38.5
90 -6.33 -5.99 1.87 -37.0
0 -6.16 -4.92 -1.19 -37.5
C 45 -4.57 -30.1 0.03 -41.2
90 -6.61 -2.85 -0.39 -36.1
The laminate stresses are estimated by stress-strain relation for various laminate
samples with principal material directions (L and T) in Table 2-8. The micro-stresses in
fiber and matrix phases are estimated using the micromechanics methods and the
principal stresses or and o-2 are calculated based on the micro-stress results in Table 2-9.