Three dimensional weft knitted sandwich composites under drop-weight impacts in different energy levels

In this study the behavior of a novel 3D integrated weft knitted sandwich composite (3DIWKSCs) were investigated. The weft knitted spacer fabrics produced by E-glass fibers on a flat knitted machine with tow cross-sectional shapes (rectangular and triangular). The 3DIWKSCs manufactured by use of the vacuum assisted resin transfer molding (VARTM). The results of the 3DIWKSCs with tow cross-sectional shapes under drop-weight impact tests in three energy levels showed that the triangular-shape of 3DIWKSC has the higher strength in all energy levels of impact than the rectangular-shape of 3DIWKSC. Furthermore the contact force of 3DIWKSCs was increased by increasing of the energy level of impacts. The main damage modes of 3DIWKSCs under impacts were the transverse cracks on the upper face-sheets and the cracks on the connecting layers of the core. Also, by increasing the energy level, cracks occurred in the lower face-sheets as the curved area and the local indentation were created underneath the impactor. There is no any de-bonding between the core-face of the 3DIWKSCs under drop-weight impact tests.