Adaptation of the Iosipescu in-plane shear test method for high strength textile composites

In order to use the Iosipescu V-notch beam test for determining the in-plan e shear strength of high strength 2D 2 x 2 biaxial braided composites, two modifications were made to the specimen geometry. First, they were tabbed t o prevent buckling at the gage section and pinching of the specimen at grip sections. Tabbed specimens having gage sections of 0.50", 0.35", and 0.188 " were studied. Also, to reduce the load required for failure, the shear ar ea was decreased by deepening the V-notch. Failure modes of specimens havin g notch widths of 0.425", 0.350", 0.325", and 0.300" were examined. In this investigation, high toughness PR520 epoxy resin was selected to make panel s by resin transfer molding (RTM). An initial study was conducted to find t he best possible specimen,geometry using +/-45 degrees braid. Then, both +/ -45 degrees and +/-60 degrees braid angles were studied for the selected ge ometry. In order to investigate the cut direction effects on the +/-60 degr ees braid in-plane shear modulus and the strength, the specimens were cut i n both 0 degrees and 90 degrees directions of the panel. Tabbed specimens w ith a gage length of 0.188" demonstrated the highest average shear strength . The notch width of 0.325" produced acceptable failures. Thus, it was sele cted as the minimum notch width. Then, both +/-45 degrees and +/-60 degrees specimens having gage section of 0.188" and notch width of 0.325" were tes ted for shear properties. The tabs minimized the bending loads due to buckl ing and pinching of the specimens across the gage section. Modifications in creased the in-plane shear strength by about 33-55% for +/-45 degrees. The 0 degrees cut-direction specimens, which had +/-30 degrees fibers with resp ect to the loading path, had lower strength and modulus values than that of the 90 degrees cut-direction specimens. Modulus results for +/-60 degrees specimens were close to analytical predictions regardless of the cut direct ion.