Deformation mechanisms of dry textile preforms under mixed compressive and shear loading

Elementary analyses of a standard compression test and a new test configuration for combined compression and shear illuminate the mechanisms of deformation of dry fiber bundles in fiber preforms under multi-axial loads. Such stress states arc central to fiber bundle behavior in thick preforms that are being manipulated in pressurized tools. Sliding, buckling, compression, and shear deformation mechanisms are observed to operate at the single fiber bundle (tow) level. Shear includes deformation transverse to the axis of a tow (changes in cross-sectional shape) and axial shear (shear deflection of a tow segment acting as a short beam). Not all of these mechanisms have been addressed before in the extensive literature on textile deformation. The presence of multiple mechanisms complicates the quest for simple experiments that could be treated as standards for data acquisition. The need for new tests to be invented and standardized is highlighted.