Initial Stage Of Impact Research Articles

A mathematical model for the initial stages of fluid impact in the presence of a cushioning fluid layer

In this paper we formulate a mathematical model for initial stages of the impact of a rigid body onto a fluid in the presence of a cushioning fluid layer between them. Some numerical and analytical solutions are obtained in appropriate asymptotic limits, and numerical solutions are obtained to the full leading order problem. Finally, we compare our model with the work of other authors.

Observations on impact attrition of granular solids

Results of preliminary experiments investigating attrition of granular solids by impaction are reported. Solution-grown sodium chloride crystals, 1.2 mm cubes, were accelerated in an air eductor and impacted on to a target plate at a velocity of 29 m s −. The initial stages of impact were recorded using an image converter camera, at a speed of 50 000 frames per second. Qualitative analysis of the results indicates that the macroscopic surface features of these particles created during the crystallization process play a dominant role in determining the characteristics of the resulting debris. The fracture morphology, however, is similar to that for a more perfect melt-grown crystal under quasi-static compression.

The impact of a soft metal sphere on a hard metal target II. Deformation of the target

Abstract The variation is reported of the depth, diameter and profile of indentations in a quenched-and-tempered steel target due to the normal impact of aluminium, phosphor bronze and brass spheres at velocities up to 280 ms−1.A critical velocity for the onset of plastic flow in the target was determined. A quasi-static analysis modified by the effect of strain rate was unable to predict a contact pressure high enough to cause yield in the target. It is suggested that a state of uniaxial strain compression exists at the centre of the contact zone during the initial stages of impact. The pressure may then be determined as a function of velocity using appropriate one-dimensional strain-rate-independent wave theory. Relevant uniaxial strain compression data were estimated from the elastic constants available in the literature and from uniaxial stress-strain curves determined from quasi-static hardness measurements. When the Vickers hardness of the undeformed sphere is less than about 0·4 times the Vickers hardness H t of the target, plastic flow in the target arises solely from the initial contact pressure; the corresponding critical pressure at the centre of the contact zone causing yield in the target may then be calculated from the critical impact velocity. The critical impact pressure is found to be (0·33 ± 0·03)H t when the target is lubricated with a thin layer of molybdenum disulphide grease and (0·27 ± 0·03)H t when the target surface is unlubricated. The residual impressions in the target are much larger than the contact area at the first arrival of release waves in the sphere at the sphere-target interface.

Siderophile-rich particles in the melt rocks at the E. Clearwater impact structure, Quebec: Their characteristics and relationship to the impacting body

The composition of the sampled melt rocks at the 22 km diameter E. Clearwater impact structure indicates the presence of ∼8% C-1 material. The meteoritic component is fractionated with refractory siderophiles, up to 30 times C-1 abundances, concentrated in ten to hundred micron-sized, magnetic particles. These particles consist of the Ni-sulphide, millerite, and what is assumed to be a mixture of refractory silicates and magnetite with grain sizes of <1 μm. The larger particles have a core-rim structure with millerite and occasionally very minor galena and possibly pentlandite in the core. An origin as a combination of altered meteoritic metal and condensed meteoritic silicate is favored for the origin of the siderophile-rich particles. If 8% meteoritic material is taken as the average meteoritic contamination in the melt, then the E. Clearwater projectile may have impacted with a velocity of 17 km s−1. Peak shock pressures would have been of the order of 300 GPa, sufficient to vaporize the silicate component but only melt the metal component of the projectile. As the meteoritic material was being driven down into vaporized/ melted target rocks during the initial stages of impact, the melted Fe, Ni metal underwent oxidation, Fe was removed, and meteoritic silicate material recondensed on the cooler, essentially Ni metal. As cavity excavation proceeded, these Ni metal, silicate-oxide particles were incorporated in the melt, their refractory nature prevented thermal digestion and sulphur in the melt reacted with the metal to produce millerite on final equilibration. If this hypothesis is correct, it suggests that the E. Clearwater projectile was a C-2 or C-3 chondrite, both of which are compatible with the trace element composition of the melt rocks. Clearwater Lake is a twin impact structure formed by an asteroid pair. It is still not clear, however, what type of projectile formed the 32 km diameter western structure, where the surface melt rocks contain no identifiable meteoritic signature.

Interaction of a liquid layer with a membrane during the initial stage of impact

Interaction of a liquid layer with a membrane during the initial stage of impact

Dynamic contact stresses produced by the impact of an axisymmetrical projectile on an elastic half-space

The dynamic contact stresses between an axisymmetric projectile and an elastic half-space are obtained by solving three-dimensional equations of motion. These stresses are written as the sums of the Hertz contact stresses and wave-effect integrals. In terms of the contact radius, the Hertz theory is shown to be a good approximation in determining total applied force. However, for calculating the maximum radial surface stress at the maximum contact radius, the Hertz theory applies only when the contact time is longer than approximately 40 μsec. The discrepancy between the Hertz radial stress and the corresponding value obtained here is greater at the initial stage of impact than at the middle of the contact time.

Hydrodynamic Theories of Ship Slamming Review and Extension

A critical review and evaluation of existing hydrodynamic theories of body-water impact is presented. It is shown, partly by comparison with available experimental data, that fitting methods are adequate only for bodies of reasonably large deadrise angle during later stages of the impact process. The ellipse-fitting technique is extended to a much broader class of body forms and more accurate formulations of the general problem are proposed that avoid linearization of the free-surface boundary condition and can account for compressibility effects during the initial stage of impact, although numerical procedures must be employed.