Effect of pre-impact waves in an elastic rod on coefficient of restitution

• Published in: International journal of impact engineering 2021-05, Vol.151, p.103816, Article 103816
• Main Authors: Lundberg, B., Rastemo, T., Huo, J.
• Format: Article
• Language: English
• Subjects: Coefficient of restitution; Elastic cylinders; Percussive drilling; Pre-impact waves; Rigid walls; Rod; Stiffness; Super rebound; Transit time; Wave equations
• ISSN: 0734-743X; 1879-3509; 1879-3509
• DOI: 10.1016/j.ijimpeng.2021.103816

•Impact between a uniform elastic rod and a linear elastic or bilinear inelastic spring supported by a fix rigid wall is studied.•The spring may represent, e.g., the stiffness of a small elastic cylinder with flat ends or the inelastic bit-rock interaction in percussive drilling.•Acceleration of the rod to its impact momentum by a force generates pre-impact waves in the rod.•Such waves have significant effect on the coefficient of restitution (COR) if the duration of the force is short relative to the wave transit time through the rod.•A mechanism leading to super rebounds with COR up to 1.4261 is described in terms of pre-impact waves. The effect of pre-impact waves on the coefficient of restitution (COR) in longitudinal impact of a uniform elastic rod on a linear elastic or bilinear inelastic spring supported by a fix rigid wall is studied. The spring models may represent the quasi-static response of, e.g., a small elastic cylinder or the inelastic bit-rock interaction in percussive drilling. The rod is accelerated to its impact momentum either by a force of relatively short duration which generates significant pre-impact waves in the rod (pre-impact wave case) or by a force of long duration which does not generate such waves (reference case). Analytical and numerical results based on the 1D wave equation are presented in dimensionless form. It is shown that the work performed by the accelerating force is much larger in the pre-impact wave case than in the reference case, and that the COR generally depends on spring stiffness, elasticity parameter, initial rod-spring separation, and wave transit time. In the pre-impact wave case, the COR may be significantly larger or smaller than in the reference case. It may also be significantly larger or smaller than unity. A pre-impact wave mechanism leading to super rebounds with COR up to 1.4261 is described.