Function Of Impact Velocity Research Articles

Measurement of Dynamic Hardness by Controlled Sharp‐Projectile Impact

Impact of ZnS by a pyramidal projectile was used to provide a measurement of the dynamic hardness and to obtain direct comparison of the contact damage produced by static loading and impact. The dynamic hardness was evaluated from measurements of residual contact dimensions as a function of impact velocity, over the velocity range 5 to 40 m.s‐1. The value obtained (Hd=5.0 GPa) was higher than the static hardness (HS= 1.9 GPa). The higher hardness in impact causes more extensive cracking, an increase in the elastic recovery of the depth of the residual contact impression, and a smaller plastic zone surrounding the contact site. The relative extents of cracking in impact and static loading are predicted by a quasistatic indentation fracture mechanics analysis along with the appropriate values of hardness.

Transition of hertzian fracture to flexure fracture produced in glass plates by impact

The strength and fracture of a glass plate in a three-dimensional state of stress produced by the transverse impact of a spherical body is investigated. The plate is supported by a ring foundation whose radius is comparable to the thickness of the plate. A general impact theory is developed to determine the critical stresses in the plate as a function of impact velocity, plate thickness, and support span. Impact experiments were carried out to measure the impact velocity required to fracture a glass plate specimen as a function of support span. Hertzian fracture was observed at a short span of support whereas flexure fracture was observed at a larger support span. The impact velocity of fracture was measured to be increasing with increasing support span and its corresponding critical stress of fracture was also determined.

Systematics of the single and double electron scattering contributions to charge exchange

The authors examine the general charge transfer reaction in the first and second Born approximations for arbitrary initial (ZT,n'l'm') and final (ZP,nlm) states. The salient features of the first (single scattering) and second (single and double scattering) Born total cross sections are pointed out, with special emphasis on the possible dominance and detection of the double scattering contribution in charge exchange processes. The single scattering contribution is treated exactly and the double scattering contribution approximately as in a previous paper by the authors (1980). Representative distributions of cross sections are presented as a function of impact velocity and the various quantum numbers, thereby illustrating the characteristic trends of the two contributions.

Soybean Seed Quality as Affected by Impact Damage

ABSTRACT A centrifugal impactor was used to impact Beeson, Corsoy, and Williams varieties of soybeans at con-trolled velocities. Nine parameters used to measure seed quality of soybeans were determined as a function of im-pact velocity and soybean moisture content. Tests for seed quality included determining the percentages of split beans, fine material, seedcoat cracks, seed viability, Stein breakage, field emergence, warm and cold ger-mination, and yield. The percentages of split beans and fine material in-creased as the impact velocity was increased and as the seed moisture decreased from 17 to 8 percent. The varieties and moisture levels of soybeans which had low percentages of splits after impact also had high warm germination percentages. Of the varieties tested, Beeson was more susceptible to damage from impact than either of the other two varieties.

Multiple ionization of neon 2s- and 2p-electrons induced by ion atom collisions

Absolute cross sections for production of the 1s22s2p5 and 1s22s02p6 configurations of neon in collisions of H+, He+, and Ne+ with Ne and He have been measured by observation of radiative transitions in the spectral range of the vacuum ultraviolet for energies between 50 keV and 1 MeV. Projectile and target emission have been separated. The dependence of the cross sections upon impact velocity is discussed and compared with theoretical calculations. The relative population of the1P1 and3P2, 1, 0 and the3P2, 1, 0 fine structure levels of the 1s22s2p5 configuration is measured as function of impact velocity for the different projectile target combinations.

Strength Degradation of Glass Resulting from Impact with Spheres

The nature and extent of degradation incurred by glass surfaces impacted with spheres of steel and tungsten carbide were studied. The residual strength after impact depends on the velocity, radius, and density of the projectile; on the toughness and (indirectly) the hardness of the target; and, to a lesser degree, on the preexisting mechanical condition of the surface. The damage morphology involves modification of the basic Hertzian cone crack pattern by median (radial) cracks and crushed glass at the impact site. The essential features of the degradation may be predicted by a theoretical analysis of residual strength as a function of impact velocity as derived from indentation fracture mechanics. This study accounts, in particular, for a threshold velocity for significant strength loss, above which further strength decrease is relatively slight. Small, but significant, discrepancies between observed and predicted degradation characteristics are attributed to the departure from ideal Hertzian fracture geometry and to the dynamic nature of the contact. However, it is suggested that quasi‐statically based theory may be used for estimating the strength of structural ceramics in small‐particle impact situations.

On Fractures Produced by Low-Velocity Impact In Plexiglas Rods Simulating Drill Bits

Introduction The purpose of the present study was to arrive at a better understanding of the stress fields developed within drill bits under dynamic loading and the influence that these stress fields could have on the failure of the drill bits. Particular emphasis has been given to the influence that bit shape has on the establishment of highly localized, potentially destructive stress inhomogeneities within the bit. This paper covers one phase of a broad study involving three velocity regimes: impacts at very low velocities, 0 to 20 ft/sec, a velocity range in which dynamic effects are just beginning to be found; impacts at velocities ranging from 20 to several hundred ft/sec, a range commonly encountered in practical drilling operations; and impulsive loading through the detonation of explosives, a velocity range in which the dynamic effects are greatly exaggerated and made more identifiable. Specifically, fracturing which develops at the end of a cylindrical bar undergoing a shock produced by impact was experimentally investigated, the impacted area being the face of a truncated cone terminating the cylindrical bar. Fracture characteristics were looked at as a function of impact velocity, area of impacted face and cone angleparameters of considerable importance in the design of drill bit. EXPERIMENTS The specimens were made of Plexiglas, which enabled the fracture pattern to be easily observed. In Plexiglas, the velocity of a longitudinal wave is about 8,700 ft/sec, and the velocity of the transverse wave about 4,200 ft/sec. The specimens were impacted by a steel cylinder whose lower face was parallel to the terminal face of the experimental bit, as shown in Fig. 1. The impacting mass was shifted up and down on two steel rods, dropping from a maximum height of 11 ft, with the velocity varied between 0 and 6.5 m/sec. The initial mass of the cylinder was 4.1 kg, which could be increased by steps up to 8.8 kg by addition of steel plates. The velocity of the steel cylinder was determined by using an electric circuit; as the cylinder dropped, it contacted two steel wires, the first one starting and the second one stopping an electronic counter. Two similar counters connected in parallel were used to corroborate each other. The velocity was checked at each drop as it had been observed to vary somewhat from drop to drop. The two contact wires were located just above the top of the specimen so as to give a value of the instantaneous velocity of the steel cylinder at impact. The distance between the wires was 40 0.5 mm and the discrepancy between the counters was never more than 0.1 m/sec. Thus the velocity was known to within 3.25 per cent. This precision was sufficient with respect to the precision of the machining of the specimens. A very small lack of parallelism between the face of a specimen and that of the impacting hammer resulted in an oblique impact which required a much lower velocity to break the specimen. SPEJ P. 203^

A LABORATORY HULLER FOR SUNFLOWER SEED AND OATS

A laboratory huller of the centrifugal impact type is described and test data on sunflower seed and oats are given using percentage of seed hulled and meats broken as criteria of efficiency. It is shown that hulling efficiency is a function of impact velocity and moisture content of the seed. Low moisture levels give almost complete hulling with high meat breakage while higher moisture levels give practically no breakage of meats but lower levels of hulling.By selecting proper conditions of moisture and impact velocity it was possible to obtain 90 to 95% hulling with less than 10% of broken meats. It is suggested that improved efficiency might be obtained by flash drying to render the hulls more brittle without affecting the moisture level in the meats.