Particle and Long Bar Impact onto a Rigid Wall

Abstract

The chapter begins with an important case of a relatively weak normal impact of an elastic bar onto a rigid wall leading to propagation of elastic sound waves in the bar (Section 12.1). In such weak impacts significant deformations of the bar are absent. This technique is useful for material characterization, since not only purely elastic but also anelastic viscoelastic (viscoplastic) bars can be used in such impact experiments, which is briefly discussed in Section 12.1. Strong impacts of bars result in formation of plastic waves in such solid materials as metals and significant irreversible plastic deformations of such bars. These phenomena are also mentioned in Section 12.1. Section 12.2 is devoted to the impingement and break up of ice particles. Relatively Weak and Strong Impacts, the Split Hopkinson Pressure Bar: Propagation of Elastic Waves in Long Rods – Inertial Effects and Anelastic Material Properties. Strong Impacts and Irreversible Plastic Effects The present section considers impacts of solid rods weak enough not to cause significant irreversible plastic deformations, but rather wave propagation. The similarity with a weak drop impact onto a shallow liquid layer, when only capillary waves rather than crown-like splashing are generated (see Section 6.1 in Chapter 6), is quite transparent. The split Hopkinson pressure bar apparatus sketched in Fig. 12.1 is an important example of such a situation in solid–solid impacts. It is frequently used to measure anelastic dynamic material properties of a sample of interest in a wide range of frequencies, as was first proposed by Kolsky (1949). A short cylindrical specimen in question is located between two coaxial rods made of high-strength steel. A striker bar (on the left in Fig. 12.1) impacts onto the left-hand side steel rod and initiates a rectangular compressive stress pulse propagating through the rod as an elastic wave. It is accompanied by a wave of displacements of very small (in the elastic regime) but measurable amplitude. This wave reaches the specimen and is partially reflected and partially transmitted through it. Similarly, the wave propagating through the specimen is partially reflected and partially transmitted into the right-hand side steel rod. Strain gauges are used to analyze the elastic waves propagating in the rods, and their comparison yields information on the rheological behavior of the specimen, in particular, its anelastic viscoelastic (viscoplastic) properties, which definitely affect the transmitted wave.