TECHNICAL ARTICLE ‘‘Crash Pendulum’’ Energy Absorption Test System M. Ucar and A. Cengiz Mechanical Design and Manufacturing Department, Kocaeli University, Kocaeli, Turkey Keywords Crash, Energy Absorption, Test System, Momentum, Dynamic Testing, Materials Behaviors, Structural Testing Correspondence A. Cengiz, Mechanical Design and Manufacturing Department, Kocaeli University, Kocaeli, Turkey Email: akcengiz@kocaeli.edu.tr Received: December 21, 2009; accepted: August 14, 2010 doi:10.1111/j.1747-1567.2010.00693.x Abstract In this study, a novel ‘‘crash pendulum’’ test system which enables the observa- tion of energy absorption capabilities of the materials/structures was developed. The system works with two simple pendulum principles and allows free mass collision axially. On the system, each mass block fixed to pendulum arm has an energy capacity of 4 kJ and moves at a velocity of 8 m/s. The data for the veloc- ity of the mass block versus time were derived from the data for the angular displacement versus time. Kinetic energy was calculated by processing the velocity–time data with momentum equations. Restitution coefficient (e) of materials/structures on the contact region and mean impulsive force can also be calculated. In this study, steel and foam materials, whose restitution coefficient had already been known, were tested to validate the system. Finally, charac- teristics of a cylindrical aluminum tube were measured and then compared with the values which are available in the literature. Introduction Determination of the energy absorption characteris- tics of a part/system which is subjected to crushing force is very crucial for crash energy management such as design studies of crashworthy vehicles. For this reason, a number of test techniques with different principles were developed. In the literature, drop hammer test is mostly used for measuring response of laminates. 1,2 Drop tower facilities are suitable for axial and off-axis crashing test for tubular geometries. 3 Rigid wall crash tests can be realized by means of striking the mass blocks to a rigid stationary surface by a pneumatic or hydraulic thruster for several types of crush applications. 4–6 Moreover, there are specific applications for deter- mining the crashing responses of the structures. Such additional apparatus may be mounted into the clas- sical systems to increase the deformation speed with high strain rate effects. 7 Another one is the single arm pendulum developed for motorcycle tire assembly. 8 In this study, ‘‘Crash Pendulum’’ test facility was established in order to carry out the dynamically loaded crash experiments. The system has several advantages compared to drop-weight tower test sys- tems. Vertical falling of the rigid mass under gravity, such as in drop towers, can result in high inertial force which is not truly in real-world crashes. Inertia can also cause the spring back effect particularly during collision if the mass is heavy. On the contrary, pen- dulum system minimizes these disadvantages since each arm can travel freely around on their path after it reached its limit before collision phase. In crash pendulum system, basic energy absorption character- istics such as absorbed energy, mean crushing force (impulsive force), and restitution coefficient can be easily defined by momentum equations. Configuration of the Test System The system was designed to produce an axially impact loading without gravity effect during impact. Thus, the system has double simple pendulum illustrated schematically in Fig. 1. Each arm of the system can carry adjustable mass block between 0 and 250 kg and move them with a velocity up to 8 m/s. As shown in Fig. 1, the startup potential energy can be adjusted with mass value (m) of blocks and initial height (h) of them. Therefore, the system has a wide range of potential energy which is completely converted into kinetic energy just before impact. Experimental Techniques 36 (2012) 33 – 38  2011, Society for Experimental Mechanics 33