Energy Dissipation in Impact Absorber1 S. Ekwaro-Osire2, I. Durukan, F.M. Alemayehu Mechanical Engineering Department Texas Tech University Lubbock, TX 79409-1021 J.F. Cardenas-Garcia, United States Patent and Trademark Office ABSTRACT Impact absorbers are effective in passively absorbing and dissipating excessive energy in a primary system. They perform through momentum transfer by collision and dissipation of kinetic energy as sound and heat energy. The performance and dynamics of the impact absorber is highly dependent on the surface nature of the impact wall and ball. The impact surface material affects the effective coefficient of restitution. The objective of this research was to study and compare the total energy dissipation for different combinations of impact wall material and mass of impact ball. An experimental setup of single-unit impact absorber with different materials for the impact wall was designed and constructed. The exact locations of the impact ball(s) and the response of the primary structure were simultaneously tracked using a novel image processing technique. Based on the tracked motion of the ball and primary structure, two-way ANOVA is implemented to study the effect of variation in wall material and ball mass. It was shown that impact wall material selection is critical to obtain a best configuration for optimal total energy dissipation. INTRODUCTION Impact vibration absorbers have been used extensively to control vibrations of mechanical systems. These systems generally consist of solid mass or masses, placed in the primary system in such a way that the impact ball/s are free to move between two surface ends of the impact wall, rigidly attached to the primary system. They are effective in passively absorbing and dissipating excessive energy in a primary system by which vibration amplitude of the primary system will be limited to an acceptable level. IVAs work in such a way that the Kinetic energy of the primary system is being transformed in to the kinetic energy of the ball by collision [1]. Initially, the system has a higher kinetic energy while the ball is almost at rest, hence a kinetic energy close to zero. Then, when the ball is being impacted by the wall the first time, the ball gets its maximum kinetic energy right after impact taking some energy of the system; and then, the ball tries to slow down, and that is when the second wall comes and hits the ball in to motion. This repeats as long as the system continues to be externally excited. It is a fact that elastic collisions have better separation capabilities than plastic collisions. Hence, having a bigger coefficient of restitution between the ball and the wall that is close to one will facilitate the occurrence of more number of collisions by which more energy will be absorbed by the ball. That is, the bigger the coefficient of restitution, the closer the restitution impulse will be to the deformation impulse. This way, a consistent transfer of momentum by impact will take place. This paper presents the energy dissipation capabilities of a single-unit IVA, considering varying ball mass and impact wall material. Three steel balls with 28.1 g, 35.7 g and 44.0 g combined with steel, aluminum and brass (9 different combinations) for a fixed clearance has been studied. The objective of this research was to study the energy absorption performances for an optimal configuration. In this experimental study, an image processing technique has been used to track the position of the primary system and the ball; using a high speed camera 1 The views expressed in this paper are those of the author and do not necessarily reflect the official policy or position of the United States Patent and Trademark Office or the U.S. Government. 2 Corresponding author: stephen.ekwaro-osire@ttu.edu T. Proulx (ed.), Optical Measurements, Modeling, and Metrology, Volume 5, Conference Proceedings of the Society for Experimental Mechanics Series 9999999, DOI 10.1007/978-1-4614-0228-2_40, © The Society for Experimental Mechanics, Inc. 2011 331
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