Studies of two-dimensional liquid-wedge impact and their relevance to liquid-drop impact problems

Abstract

In the initial stage of liquid-drop impact, the contact region expands faster than the wave speed in the liquid. This causes compressible behaviour in the liquid, and high transient pressures. High-velocity jetting results when the wave motion in the liquid overtakes the expanding contact edge and moves up the free surface of the drop. The detailed pressure fields in this early time history of impact have been calculated by Lesser ( Proc . R . Soc . Lond . 377, 289 (1981)) for both two and three-dimensional liquid masses and for targets of finite admittance. An important result is that the edge pressures exceed the central ‘water-hammer’ pressure 3ρ 0 CU i and at the time of shock-detachment approach ca . 3ρ 0 CU i . At this stage the edge pressures, for both spherical drops and two-dimensional liquid wedges, depend only on the impact velocity and the instantaneous angle between the liquid and solid surfaces. This suggests that the essential features of the early stage of liquid impact can be usefully studied by producing impacts with two-dimensional liquid wedges, and predicted data for pressures, shock angles and velocities are presented. Experiments are described for producing impacts with preformed shapes by using water-gelatine mixtures and observing the impact events with high-speed photography. The results confirm the main features of the model and give information on edge pressures, jetting, cavitation in the liquid and the effect of the admittance of the solid. The relevance of the results to the damage and erosion of materials subjected to liquid impact is discussed. In particular, it is possible to explain the apparently low damage-threshold of some materials, the form of damage and its development with repeated impact. The study highlights the importance of the detailed surface geometry in the region of contact.

Deformation and fracture of rocks due to high-speed liquid impingement

“…When jetting starts, its velocity can be several times the impact velocity (Bowden and Brunton, 1961;Field et al, 1964, Bourne andField, 1997). This phenomenon was investigated experimentally and analytically by Field et al (1985), and analytically more recently by Haller et al (2003). High-velocity jetting exploits surface asperities, which arise from damage (mainly cracks) introduced by the Rayleigh surface waves (see Section 3.1), resulting either in further extension of these cracks or in material removal due to chipping; this latter mechanism is illustrated schematically in Fig.…”

“…As a result side jetting of the compressed fluid occurs at velocities higher than the impact velocity. This phenomenon was investigated experimentally by Field et al (1985), and analytically more recently by Haller et al (2003). The jetting period lasts over the period of…”

Ballistic impact studies of a borosilicate glass

“…Early on in the impact process, the radius of the contact area between the rod and target expands more rapidly than compressive waves in the steel can travel [36] , precluding the possibility of release waves and leading to high compressive pressures as a volume of steel at the end of the rod is compressed. This mode of loading is roughly planar since the rod nose is flattened.…”

Cavitation erosion as a kind of dynamic damage

“…Multiple spall damage of target upon impact with a projectile was found Rinehart and Pearson (1954) to be accompanied by formation of longitudinal cracks under the contact zone, although no explanation was given. The depth of needle-like pits arising on the surface of steam turbine blades was reportedly to have a size of several drops Field et al (1985). Longitudinal damageability by drops and dust was found to be spall-related in its character.…”