Short beam shear performance of spread-tow woven stitched composite with anti-sandwich structure

Spread-tow woven fabrics (STW) have attracted considerable attention because of their ultrathin structure and low porosity, which benefit the design and application of STW composites. Little is known about how the thickness relationship between the middle and surface layers affect the mechanical properties of sandwich structures. Therefore, this study developed an anti-sandwich stitched composite with STW in the center and a nonwoven felt/STW hybrid on both sides. The interlayer shear behavior and damage mode transformation of STW composites with different middle-layer thicknesses were studied using short-beam shear tests, digital image correlation (DIC) full-field strain nephograms and micro-computed tomography (micro-CT). The results showed that the anti-sandwich structure improved the shear strength, particularly when the middle layer thickness was four times that of the surface layer. As the middle layer thickness ratio decreased, the synergistic effect of the anti-sandwich structure was weakened, and the damage mode changed from ductile to brittle. Furthermore, the hybrid ratio of the STW/nonwoven fabric in the surface layer had little effect on the performance because of the good interfacial adhesion between the STW and nonwoven fabric. The anti-sandwich structure that can improve the properties and stability of STW composites provides a reference for the structural design of STW composites in engineering applications.Highlights An anti-sandwich composite was developed by spread tow woven fabrics. Nine types of anti-sandwich composite were designed and fabricated. The thickness of the middle layer affected the synergistic mechanisms. The optimal anti-sandwich structure has a 4.59% increase in shear strength. The specific shear strength is 14.86% higher over pure spread tow laminates. Shear performance evaluation of anti-sandwich composite. image