Development of a composite crash cushion using computer simulations

The objective of this research is to develop a composite crash cushion that can absorb a vehicle's kinetic energy and bring the vehicle to a controlled stop. Crash cushions are installed in front of rigid structures with the intent to reducing occupants risk of injury during vehicle impact by gradually decelerating the vehicle at acceptable rates until eventually, it stops before impacting the rigid structure. The structural design and development of this crash cushion used in this research involved different innovative design concepts. These concepts made use of the presence of multiple overlapping cylinders filled with air placed within each cushion in the system. The air-filled cylinders contribute massively to the kinetic energy absorption of the vehicle by damping effect and thus reduce the velocity of the vehicle at safe rates. This crash cushion system consists of mainly six parts. They include the head container, middle containers, energy-absorbing tubes, cables, steel plates and rigid support. Only steel plates, cables and rigid support are made of structural steel S235 JR while the containers and energy absorbing tubes are made from Linear Low Density Polyehtylene (LLDPE).In occurrence of impact, the crash cushion components can be reusable, easy to repair and available at low cost. The energy absorbing technique presented is by far a better cost-effective alternative to other present energy absorbing techniques. Thus, making this a valid and efficient design. The performance of this crash cushion is evaluated by following the standard EN1317-3. EN1317-3 (Road restraint systems - Part 3: Performance classes, impact test acceptance criteria and test methods for crash cushions) is a European standard that was approved by the CEN and the TSE. This standard acts as a guideline to crash cushion tests. Over the years, full-scale crash tests have been used to test and evaluate the performance for the crash cushion but it is time-consuming and costly, thus testing and analysis of the performance of the design is done via finite elements analysis by using LS-DYNA software. The finite element method mainly comprises of development of finite element meshes of the entire crash cushion system and vehicle that divides the subjects into different parts and applies material properties, boundary conditions and other details. Next step is that the program derives the equations from the model and provides a valid solution in terms of simulations in which this solution will determine the dynamic response behavior of the crash cushion model. Three simulation tests were conducted. These tests include two head-on impact tests involving a 900 kg vehicle traveling at a speed of 50 kph and 100kph respectively. These tests evaluate the capability of the crash cushion to absorb kinetic energy of a vehicle. While the other test was a side impact test 15 degrees from the frontal centre. This involved a 1300 kg vehicle traveling at a velocity of 50 kph impacting the crash cushion at a third of the total length (L/3) from the front. This test evaluates the ability of the crash cushion to contain and redirect a vehicle. Results obtained from the tests were compared to the results from two full-scale crash tests for 50 kph. Their similarity means analysis is valid by using finite element analysis and this gives a green light to conduct more test simulations in reference to the EN1317-3. The test results show that even at high speeds such as 100kph the crash cushion can absorb kinetic energy at acceptable rates and reduce occupant's risk to injury.