EXPERIMENTAL RESEARCH OF CHARACTERISTICS OF SHOCK ABSORBERS OF IMPACT ENERGY OF PASSENGER COACHES T he subject of this work is the experimental character- ization of three types of elements for collision energy absorption of railway coaches operating on tube crushing, expansion, and compaction principles. 1–3 The absorber’s role is to absorb as much of the collision kinetic energy as possible by controlled deformation in order to protect the structure 4–6 behind the absorption elements from deforma- tion to the highest degree possible and thus protect the passen- gers and coach. The first type of absorber consists of tubes with a square cross-section to which the kinetic energy is transferred at the moment of impact. The tube loses its stability by bending and during the deformation process absorbs a certain amount of collision energy. 2,7 The second type of absorber consists of a seamless tube and cone-like impactor. At the moment of impact, the kinetic energy is transferred to the impactor that widens the tube and thus absorbs part of the collision kinetic energy. 1,8 The third type of absorber consists of a seamless tube and cone-like ring. In this case, at the moment of impact, the kinetic energy is transferred to the ring that starts to shrink the tube. 3 During controlled plastic deformation of the tube, absorp- tion of part of the collision kinetic energy occurs. The last two types of elements absorb energy by elastic–plastic deformation of the tube and friction between the impactor or ring and the tube. The total absorbed energy depends on the material qual- ity (the material should have a high plasticity), manufacturing quality, and construction parameters of the tube and ring (impactor). The space available for a collision energy absorber, in an agreement with a standard European rail vehicle buffer, is the limiting factor for designing an absorption device. Dimen- sioning of absorption devices is performed according to the installation point limitations (dimensions of the buffer and fron- tal part of the main structure, between which comes collision energy absorber), required amount of absorbed energy, 9 and experience obtained analyzing frontal rail vehicle collisions. 10 The purposes of the article were to investigate the suitability and justifiability of the proposed construction of a collision energy absorber of a passenger coach using experimental meth- ods and to design a solution that is more efficient and suitable for application in the construction of passenger coaches. EXPERIMENTAL RESEARCH OF ENERGY ABSORBERS WORKING ON THE PRINCIPLE OF SQUARE CROSS-SECTION TUBE CRUSHING The shape and dimensions of elements used for the experi- mental research of steel square cross-section absorbers of collision energy are given in Fig. 1. Investigations were per- formed using quasi-static axial pressure on a press. Details of the investigation have been given in previous work. 2 Figure 2a shows a force versus stroke diagram for five sam- ples of type 1 (with one circular opening), while Fig. 2c shows a diagram for the other two sample types. Figure 2b shows the sample of type 1 after the deformation process. The basic disadvantage of this type of absorber is the large force increase at the start of the strain, which is caused by the moment of stability loss by tube deformation. This increase at the start of the deformation is the consequence of the locali- zation of deformation due to buckling. Therefore, the large portions of the absorber elements remained almost non- deformed in the impact zones. This feature is not desired because the absorption should be performed by the whole absorbers’ volume, leading to much higher absorbed energy. Further research conducted on one sample showed that use of the absorption elements predeformed to stroke of about 10 mm, shown in Fig. 2c, avoid the initial undesired force maximum. EXPERIMENTAL RESEARCH OF ENERGY ABSORBERS OPERATING ON THE TUBE-WIDENING PRINCIPLE Experimental investigations were performed following the same procedure as in the previous case using the quasi-static pressure loading method. The shape and dimensions of the elements used for the experimental research of steel tube absorbers of collision energy are given in Fig. 3b. The impac- tor was made of C45E quality steel, diameter of 90 mm, impac- tor head height 32 mm, and slope angle of 138. Tube elements were produced from standard 88.9 3 4–mm seamless tubes of P235T1 quality. Seven tube samples were investigated. Six of those samples were identical, 150-mm long (denoted as S1–S6 in Fig. 4). The 7th sample was 304-mm long (denoted as S7 in Fig. 4). Figure 3a shows these six elements and two impactors used. Figure 3b shows initial position of impactor–tube cou- ple. The axial force F versus stroke h was measured. 1 Figure 4 shows force versus stroke for all seven investigated absorption couples. All tested samples show initial force increase much more gradual than square cross-section tube crushing– type elements. Force scattering between different samples in this stage can be primarily explained by the fact that two impac- tors (denoted as I1 and I2 in Fig. 4) were used in several consec- utive tests with new tubes without minor surface damage repair. Stochastic friction coefficient conditions, initial misalignment of the impactor and the tube, etc., have influenced this scatter too. After the initial stage, the force of all samples tended to an average value of 200 kN 6 10%. The tube length of 150 mm was a little bit tight to see this clearly. Therefore, to check the uniformity of the force after the stage of primary increase and TECHNIQUES by G. Simic´ , V.Lucˇanin, J. Tanaskovic´, and N. Radovic´ Dr. G. Simic´(gsimic@mas.bg.ac.yu) is a professor and Dr. V. Lucˇanin (vlucanin@ mas.bg.ac.yu) is a professor at the University of Belgrade–Faculty of Mechanical Engineering, Department of Railway Mechanical Engineering, Belgrade, Serbia. J. Tanaskovic´ (jovant@eunet.yu) is in the ‘‘GOS ˇ A Institute’’ d.o.o., Smederevska Palanka, Belgrade, Serbia. Dr. N. Radovic´ (nenrad@tmf.bg.ac.yu) is a professor at the University of Belgrade–Faculty of Technology and Metallurgy, Department of Metallurgical Engineering, Belgrade, Serbia. doi: 10.1111/j.1747-1567.2008.00470.x  2009, Society for Experimental Mechanics July/August 2009 EXPERIMENTAL TECHNIQUES 29