Improving Damage Tolerance of Composite Sandwich Structure Subjected to Low Velocity Impact Loading: Experimental Analysis

Abstract

Sandwich structures with composite face-sheets have seen its applications in variety of sectors including aerospace and automobile, owing to its high specific mechanical properties. However, there is a need to develop better damage tolerant sandwich structure as composite face sheets have low impact resistance in transverse direction. Composite sandwich structures with different impact resistant core materials were tested experimentally and numerically to develop light weight impact resistant and damage tolerant sandwich structure. Cores were made of the materials that claimed to absorb impact energy using variety of different energy dissipating mechanisms. Coupons of 4in. x 6in. dimensions were fabricated with 2X2 Twill weave carbon fiber reinforced polymer (CFRP) prepreg face-sheets and core material of Sorbothane®(energy absorption by dampening vibration),Nomex® honeycomb (conventional energy absorption through plastic deformation) and D3O® mesh (strain sensitivity to lock molecules and absorb energy) respectively. Moreover, coupons of CFRP-only and Aluminum sheet were tested for the relative comparison of energy absorption. Impact tests at various low velocities was performed using the Instron 9250 HV Impact Test Instrument with 6.64 kg of hemispherical indenter following ASTM D7136/D7136M standards. Also, Compression after Impact (CAI) test was performed on the impacted specimen following ASTM D7137/D7137M standards. Force, Energy and Displacement curves with respect to time was generated through drop weight impact testing. Specific energy absorption value was then obtained for each candidate isotropic, neat composite and composite sandwich structure by dividing respective energy absorbed values by respective sample mass. Similarly, specific stress vs. strain curve was obtained from CAI testing for all the impacted coupons. Relatively ductile compression failure in CAI tests of CFRP sandwich with D3O® mesh and Sorbothane® cores was observed compared to CFRP sandwich with Nomex® core. Moreover, CFRP sandwiches with D3O® mesh core absorbed more specific energy then its Nomex® and Sorbothane® counterparts at relatively higher impact speeds of 3.0 m/s.