EFFECT OF FIBER ARCHITECTURE PARAMETERS ON DEFORMATION FIELDS AND ELASTIC-MODULI OF 2-D BRAIDED COMPOSITES

The effects of various braiding parameters for 2-D triaxially braided textile composites were systematically investigated both experimentall y and analytically. Four different fiber architectures designed to pro vide a direct comparison of the effects of braid angle, yam size and a xial yam content were tested. Moire interferometry was employed to stu dy the effect of these parameters on the surface strain fields in the material. Moire results for the surface strain fields were found to be strongly influenced by all of the three parameters. Larger yam sizes led to higher normal strains and led to early cracking under transvers e loading. Increasing the axial yarn content by using larger axial yar ns also led to premature cracking under transverse loading. The mechan ical tests showed that stiffness properties were not a function of yar n size. However, they were strongly influenced by braid angle and axia l yam content. A simple analysis that explicitly models the fiber arch itecture was developed. The analysis technique successfully predicted mechanical properties and also the trends in die test data. Increasing the braid angle led to decreasing longitudinal modulus, increasing tr ansverse modulus, and in-plane shear modulus values that peaked for a braid angle of +/-45-degrees. Increasing the axial yarn content led to increasing longitudinal modulus, decreasing in-plane shear modulus an d Poisson's ratio values. Out-of-plane Young's modulus and shear modul i were insensitive to variations in braid angle and axial yarn content . Composite properties were found to be more sensitive to variability in braid angle than to variations in axial yarn content.