Lateral impact on a flexible viscoelastic tube

Abstract

An experimental investigation was undertaken to examine the effects of transverse normal impact of an essentially rigid striker on flexible viscoelastic tubes with resultant large deformations and large local strains. The tests were conducted on a medical-grade ester-plasticized compound of polyvinyl chloride with nominal inner and outer diameters of 4.76 and 7.94 mm (3/16 in and 5/16 in), respectively, suspended vertically with a free length of 1.3 m. The specimens were dynamically loaded by two projectiles striking the center of the span: (i) a 6.35 mm (1/4 in) diameter steel ball bearing travelling at initial velocities between 40 and 70 m/s, and (ii) a special configuration composed of Lexan with a cylindrical striking surface of 3.97 mm (5/32 in) radius travelling between 4 and 10 m/s with the axis of the contact surface, the axis of the tube and the direction of motion forming an orthogonal triad. The impact phenomena were observed by high-speed photography at a framing rate of 6500 pps. The displacement histories determined from the films were employed to compute an approximate force history using a nonlinear regression analysis. The pinching of the tube in the impact region, the velocity of propagation of the disturbance along the tube, the duration of contact and the rebound velocity of the striker were also measured. It was noted that the tube was completely closed by the striking sphere at higher velocities, while less pinching occurred when the plastic striker was utilized. It appears that the amount of pinching for a given tube is primarily determined by the initial energy of the striker and by the ratio of the initial velocity to the wave speed that characterizes the energy flow away from the impact point.