Effect of impact and flexural loading on hybrid composite made of kevlar and natural fibers

In this work, four varieties of hybrid Fiber-Reinforced Polymer (FRP) panels made of kevlar-29 and natural fibers are studied. All panels have kevlar-29 face sheets and natural fiber core, such as jute, flax, sisal, and hemp. This research focuses on the behavior of these hybrid FRP panels under flexural and impact loading so that the panels can be explored for the structural/semi-structural members of army shelters, portable helipad, and roofing panels in high-altitude areas. Natural fibers are chemically treated with NaOH to improve hydrophobicity. The panels are vacuum bagged, the fiber volume fraction is 0.39, and the thickness is close to 4 mm. Three-point flexural loading using the universal testing machine and low-velocity impact loading up to 24 J under drop weight impact test setup is carried out to characterize the panels. Damage area, delamination, permanent deformation, indentation depth, energy absorbed, flexural strength, and modulus are measured. The hybrid flax/kevlar panel and hemp/kevlar panel, each resist impact with permanent deformation less than 0.5 mm up to 24 J. Without significant face sheet or core fiber breakage, the delamination is spread over a small radial distance of 18.5 and 24.5 mm, respectively. Interface matrix breakage causes delamination. The load vs deflection curve is almost linear under flexural loading, and specimens failed under compression at 240 MPa. The numerical simulation is also done using ANSYS and LS-DYNA for detailed study.