Progressive crushing of stitched glass/polyester composite cylindrical shells

This paper examines the effect of mode I interlaminar fracture toughness (GIc) on the specific energy absorption of stitched glass/polyester composite cylindrical shells under axial compression. The laminated composite cylindrical shells used as energy absorbers, absorb large amount of impact energy during collision. Since mode I delamination in the thin wall of axially collapsed shell is one of the major energy absorbing modes, contribution of GIc to specific energy absorption (SEA) of tubes is significant during collision. The GIc values are determined through double cantilever beam (DCB) test with stitched and unstitched planar specimens. The four and six-layered cylindrical tubes of D/t ratios 29.27 and 20, respectively, with GIc values ranging from 1.68 to 8.09 kJ/m2 are prepared by stitching and are subjected to quasi-static axial compression. Increasing GIc up to certain value leads to controlled progressive crushing, which is a good energy absorbing mechanism, beyond which failure is uncontrolled. Cylindrical tubes having GIc up to 6.34 kJ/m2 leads to 40% increase in SEA for four-layered tubes and 6.6% for six-layered tubes comparing with the corresponding unstitched tubes. When the tubes have GIc of 8.09 kJ/m2, four-layered tubes undergo unstable failure, but six-layered tubes undergo stable progressive crushing with 22% increase in SEA. Transition from stable to unstable failure depends upon the thickness of tubes. An analytical model is developed based on energy approach to predetermine the steady state mean crush load of cylindrical composite shells under axial compression. The model results are validated by experimental results, and show good agreement.