In order to allow members of the RA section of the team to reach their goal, build a solar energy UAV, they must characterize the material they will use for the structure through FEM analysis. However, to make this possible, you must have the data relating to the material itself. For this reason the guys have carried out in these days a tensile test, in this way achieving the complete stress-strain curve of the material.

But what is a tensile test and what are the curves mentioned above ? The tensile test is a static test in which a test piece is subjected to a load, which is progressively increased until the part is broken. During this test the mechanical behaviour of the material is observed;
each material will obviously have its own and therefore its own sigma-epsilon curve.

Generally, as the load increases, different behaviours are observed. Firstly there is a proportionality between effort and deformation. Then, once the sigma of proportionality has been reached (or yield point, in case of materials that present this phenomenon), this is going to be lost: once this load is exceeded, the famous law of Hooke loses its validity. Therefore, We pass from the field of elastic behavior to the plastic one. As a result, continuing further in the increase of the load we will finally reach the rupture of the test piece.

Let’s now see together what were the highlights of the experience carried out by our guys. After having purchased the carbon fibre fabric and the liquid two-component resin, two plates were laminated from which were cut out two batches of specimens, one with fibers at 0-90º and one at +-45º. After that, the test pieces were prepared by gluing the strain gauges to measure the elongations. At that point the test pieces were pulled up to the breaking load to obtain, as mentioned above, the complete stress-deformation curve. This was done in accordance with the legislation.

At the end of this experience, we can only thank the engineer Massimiliano Mattone who allowed the members of this section of the team to carry out these tests.