Effect of fiber material on the energy absorption behavior of thermoplastic composite tubes

The primary objective of this work is to identify the effect of fiber material on the energy-absorption characteristics of thermoplastic composite tubes. PEEK matrix composite tubes reinforced with AS4 carbon fiber, IM7 carbon fiber, and S2 glass fiber have been investigated. Seven fiber orientations (theta) were used: unidirectional fibers parallel (0 degrees) to the axis of the tube, +/-5 degrees, +/-10 degrees, +/-15 degrees, +/-20 degrees, +/-25 degrees and +/-30 degrees. A 45 degrees chamfer was ground onto one end of each specimen to initiate progressive crushing. The +/-30 degrees AS4/PEEK, +/-30 degrees IM7/PEEK, and +/-25 degrees and +/-30 degrees S2/PEEK tubes failed catastrophically, whereas all the other tube specimens crushed progressively in splaying mode. The energy absorption capability of all three types of tubes varied with the fiber orientation. The carbon-tiber-reinforced tubes displayed 20% higher specific energy absorption capability than the glass-fiber-reinforced tubes. Among the carbon-fiber-reinforced tubes, for intermediate fiber orientations, the AS4/PEEK tubes absorbed slightly higher energy than the IM7/PEEK tubes. Efforts have been made to relate the energy absorption capability to the failure processes in the crush zone.