A Braking System for Tests with a Prescribed Deceleration Pulse

Tests with a prescribed deceleration pulse are fundamental to the development and certification of crashworthy structures. At the Politecnico di Milano Laboratory for the Safety of Transports these tests are carried out using a horizontal impact-sled facility. Test articles are mounted on a trolley which is launched down a rail and then arrested by means of a braking system that allows prescribed deceleration pulses to be obtained. The oleo-pneumatic braking system customarily used in these tests is difficult to use and user-defined time-histories of the deceleration pulse cannot be obtained. In an effort to overcome these limits, a new braking system was developed. The idea was to arrest the trolley by means of a number of beams that varied in length and that were positioned at variable distances from each other. Experimental tests and numerical simulations were carried out in parallel to verify the feasibility of the new system and improve on the initial design. A mathematical model and genetic algorithm were also developed and used as part of a method to find the test set-up that allowed user-defined deceleration pulses to be obtained. A full-scale test with the deceleration pulse prescribed for small airplane seat certification was carried out to assess the performance of the braking system. The test revealed a weakness of the braking system that was then further developed before being put into full operational service.