MECHANICAL-PROPERTIES OF TRIAXIALLY BRAIDED COMPOSITES - EXPERIMENTALAND ANALYTICAL RESULTS

This paper investigates the unnotched tensile properties of two-dimens ional (2-D) triaxial braid-reinforced composites from both an experime ntal and an analytical viewpoint. The materials are graphite fibers in an epoxy matrix. Three different reinforcing fiber architectures were considered. Specimens were cut from resin transfer molded composite p anels made from each braid. There were considerable differences in the observed elastic constants from different size strain gage and extens ometer readings. Larger strain gages gave more consistent results and correlated better with the extensometer readings. Experimental strains correlated reasonably well with analytical predictions in the longitu dinal, 0-degrees, fiber direction but not in the transverse direction. Tensile strength results were not always predictable even in reinforc ing directions. Minor changes in braid geometry led to disproportionat e strength variations. The unit cell structure of the triaxial braid w as discussed with the assistance of computer analysis of the microgeom etry. Photomicrographs of braid geometry were used to improve upon the computer graphics representations of unit cells. These unit cells wer e used to predict the elastic moduli with various degrees of sophistic ation. The simple and the complex analyses were generally in agreement , but none adequately matched the experimental results for all the bra ids.