ANALYTICAL METHODS FOR TEXTILE COMPOSITES
While crimp effects on shear are small, they can sometimes give consistent
variations. Figure 3-3 shows that the length of the float (the uncrimped length of yarn
between cross-over points) in satin weaves affects shear strength. In this figure, the Oxford
weave has the shortest float, followed by the 5-harness satin, and the 8-harness satin. The
shear strength increases as the float length increases.
Shear Strength (MPa)
Figure 3-3. Comparison of in-plane shear strengths of various T300/934 weaves,
showing effect of crimp. (From [3.6].)
3.4.2 2D Braids
As for 2D weaves, the relationship between fiber architecture and strength for 2D
braids must also involve the degree of waviness of the primary load bearing tows. In
addition, braids introduce several further variables, whose roles are still poorly understood.
These include the relative sizes of inlaid tows and braider tows, the spacing of inlaid tows,
and the size of the unit cell.
The tensile strengths of two triaxial carbon/epoxy braids and equivalent tape
laminates are compared in Fig. 3-4. The braid notation is defined in Section 2.3.1.3. The
unnotched strength of the braids is 10-30% less than that of the tape laminates. However,
the notched strengths are much closer, with the braids in one case even being superior. The
braids overall are considerably less notch sensitive.
