CFRP Crash Absorbers in Small UAV: Design and Optimization

The high number of hull losses is a main concern in the UAV field, mostly due to the high cost of on-board equipment. A crashworthiness design can be helpful to control the extent and position of crash impact damage, minimizing equipment losses. However, the wide use of composite materials has recently put the accent on the lack of data about the behavior of these structures under operative loads, such as the crash conditions. This paper presents the outcome of a set of tests carried out to achieve a controlled crush of UAV structures, and to maximize the Specific Energy Absorption. In this work, a small-scale experimental test able to characterize the energy absorption of a Carbon-fiber-reinforced polymer under compression was developed introducing self-supporting sinusoidal shape specimens, which avoid the need for complex anti-buckling devices. The specimens were produced with different auto-triggering configurations and fibers' continuity was interrupted in selected position and for different extent in order to investigate the Specific Energy Absorption of the weakened laminates. The auto-triggering configuration was able to control the position of the initial failure of the specimen without any decrease in safety performance. This new kind of very light crash absorber can be used in small UAV to reduce the crash loads in the avionic and payload bay. With reference to a small UAV designed and manufactured at University of Bologna, an optimization of the crash absorbers positions has been carried out in order to achieve the best results in terms of energy dissipation.