Thermo-Mechanical Response of Hybrid Polymer Composites During Tensile Loading

The fiber reinforced polymers are candidate materials for critical applications in view of the high strength, stiffness characteristics; however, they are highly anisotropic and have complex failure mechanisms. Thermo-mechanical response characterization is one of the means of identifying damage progression in these materials. In this study, tensile tests were conducted on the hybrid composite laminates and Infrared thermographs were used to capture the thermal response of the specimen for the entire range of loading till failure. The tests were conducted on natural fiber composite specimens and hybrid (natural + synthetic fiber) composite specimens. The natural fibers used were in the form of uni-directionally stitched mats of Sunhemp, Kenaf and Flax fiber. The synthetic fibers used were bi-directionally woven Carbon fiber mat and Glass fiber mat. All the laminates were prepared using the hand lay-up technique. Four different configurations of the laminates were prepared. The natural fiber composite laminate comprised of Sunhemp fiber mat in a polyester resin system. The Sunhemp fiber mat was also used with woven Glass fiber mat on one side to prepare an unsymmetrical hybrid laminate. The Kenaf fiber mat was placed between layers of woven Glass fiber mats whereas the flax fiber mat was placed between the woven carbon fiber mats; Epoxy LY 556 and hardener Araldite® was used as the matrix. The finished laminate thickness was 2.1 mm and dog-bone tensile specimens were extracted using a CNC router. Some of the specimens were impacted at low velocities from two different heights to study the change in thermo-mechanical response, post-impact, during tensile test. Temperature response as a function of applied stress, failure strain and work done suggests that there is a correlation between the fracture events that take place during tensile test with the temperature response. In cases where there was a ply-drop failure, the rate of temperature change could identify the failure events, even though the resultant peak temperature was less. When the specimen failed by a single mode of failure (delamination/fiber failure), the temperature rise was found to be proportional to the input work done during tensile testing.