Static and Dynamic Behavior of Composite Sandwich Bars with Crushed Corn Cob Core

For this research we have built some composite sandwich bars in this way: the core is made from crushed corn cob and the samples faces are made from natural fabrics: cotton, flax and silk. The connection of these elements (core and the faces) is made by using epoxy resin Resoltech 1050 with its hardener Resoltech 1058 s. All the samples are molded at room temperature (20–23 ℃) and there was waited 48 h for the resin polymerization with its hardener. From the plates obtained there were cut samples to be tested by three methods: tensile test and bending on universal testing machines (for the tensile test there was used an Instron machine and for the bending there was used an LBG Testing Equipment machine) and free vibrations by clamping the bars at one end and leaving the other end free. From the static tests there were determined the Young modulus values, breaking strength (both tensile and bending), elongation at break and maximum force. From the free vibrations, by applying Euler–Bernoulli theory, the next dynamic parameters were obtained: the eingenfrequency for the first eigenmode, damping factor, dynamic Young modulus, dynamic stiffness and loss factor. The general conclusion obtained from all the tests was that the samples reinforced with cotton had the best mechanical properties no matter the applied test (static or dynamic).