Analysis of formation of the Odessa crater

The impact of the meteorite that formed the Odessa crater is examined in this numerical study. Extensive information collected from excavation of the site has made it possible to use the Odessa crater as a code validation test, to the extent that a calculated impact can produce equivalent cavity dimensions and stratification. In addition, the calculations can be used to provide a better estimate of velocity and trajectory of the meteorite at impact. The initial set of simulations performed in this study suggests that original estimates of the impact conditions may not have been sufficient to produce a crater of the size and shape known from the Odessa site. Supplemental analysis was performed and suggested that the meteor impacted at a much larger obliquity angle and may have been much larger than originally speculated. Details of the analysis leading to these observations are presented.     

Penetration of semi-infinite AD995 alumina targets by tungsten long rod penetrators from 1.5 to 3.5 km/s

The performance of confined AD995 Alumina against L/D 20 tungsten long rod penetrators was characterized through reverse ballistic testing. The semi-infinite ceramic target was cylindrical with a diameter approximately 30 times the rod diameter. The target configuration included a titanium confinement tube and a thick, aluminum coverplate. The impact conditions ranged from 1.5 to 3.5 km/s with three or four tests performed at each of six nominal impact velocities. Multiple radiographs obtained during the penetration process allowed measurement of the penetration velocity into the ceramic and the consumption velocity, or erosion rate, of the penetrator. The final depth of penetration was also measured.

Primary penetration approaches 75% of the hydrodynamic limit. Secondary penetration is very small, even at 3.5 km/s. The effective R_t value decreased from 90 kbar to 70 kbar with increasing impact velocity over the range of velocities tested.

In tests in which the ratio of target diameter to penetrator diameter was reduced to 15, R_t, dropped by 30% to 50%. When a steel coverplate was used, total interface defeat occurred at 1.5 km/s.     

Fatigue in engine connecting rod bolt due to forming laps

An analysis was performed to asses the failure root cause of an automotive diesel engine which experienced collapse only 6 month after revision. The connecting rod bolts torque disassembly was monitored and fractured parts were selected to laboratory fracture analysis. It was verified with fatigue rupture of one of the fourth connecting rod bolt. Tensile tests were performed in four of the remaining connecting rod bolts. During this procedure, it was verified another bolt with fatigue crack propagation an indication that the first fatigued bolt did not have suffer torque relaxation. A finite element analysis was performed in connection with an analytical fracture mechanics approach aiming to evaluate the relation between tightening force and fatigue crack propagation in connecting rod bolts. The engine collapse occurred due to forming laps in the grooves of the bolt shank. Finally, some design improvements were suggested for avoid future failures: a gap in the groove length at the connecting rod cap interface, enough to avoid combination of forming laps and higher stress amplitude; increase of the bolt torque assembly to reduce stress amplitude.     

Jet-induced 2-D crater formation with horizontal symmetry breaking

We investigate the formation of a crater in a 2-D bed of granular material by a jet of impinging gas, motivated by the problem of a retrograde rocket landing on a planetary surface. The crater is characterized in terms of depth and shape as it evolves, as well as by the horizontal position of the bottom of the crater. The crater tends to grow logarithmically in time, a result which is common in related experiments. We also observe a horizontal symmetry breaking at certain well-defined conditions which, as we will demonstrate, could be of considerable practical concern for lunar or planetary landers. We present data on the evolution of these asymmetric states and attempt to give insights into the mechanism behind the symmetry-breaking bifurcation.     

Damage and rock-volatile mixture effects on impact crater formation

We explored simple geologic strength and material response models to determine which have the capability to simulate impact-induced faulting, complicated ejecta patterns and complex crater shapes. This led us to develop models for material damage, dilatancy, and inhomogeneous materials (mixtures). We found that a strength degradation (damage) model was necessary to produce faulting in homogeneous materials. Both normal and thrust ring faults may occur and extend relatively deeply into the planet during the transient cavity radial expansion. The maximum depth of fault development is about the depth of maximum penetration by the projectile. Dilatancy in geologic materials may reduce the final bulk density compared to the pristine state because of irreversible fracturing. When we include the effects of dilatancy, the radial position of faulting is displaced because of greater upward motions. In addition, the late time crater profile is shallower and the expression of features such as central peaks and rings may be more pronounced. Both damage and rock-ice mixtures effect the distribution of ejecta. The excavation flow field within the heavily damaged region is similar to flow fields in Mohr-Coulomb materials with no zero-pressure strength. In the outer, less damaged zone within the excavation cavity, the material trajectories collapse back into the crater. This effect creates a zone of reduced ejecta emplacement near the edge of the final crater. In the case of rock-ice mixtures, energy is preferentially deposited in the more compressible volatile component and the ejecta pattern is dependent upon the location of shock-induced phase changes in the volatile material.     

Hypervelocity crater formation in aluminum alloys at low temperatures

The penetration and perforation of three kinds of aluminum alloys at room temperatures and low temperatures in the velocity range from about 0.5 to about 3.7 km/s were investigated experimentally. Main interests were focused on the depth and diameter of craters and their relations to the impact velocity. As a result, very distinctive features of the temperature effect on the shape and size of craters were found. Also, the effect of impact-induced phase transition of projectiles on the crater formation was examined about carbon steel, aluminum alloy and NaCl projectiles.     

The effects of a random off-axis velocity component on the penetration achieved by long rod kinetic energy penetrators and shaped charge jets

The impact of long rod kinetic energy penetrators and shaped charge jets on homogeneous targets is investigated. In particular the effects of a random off-axis velocity component on the penetration achieved are analyzed. The aim of this study is to consider the case where the off-axis velocity component takes a uniform value W along the rod or jet.

It is assumed that penetration takes place according to the classical hydrodynamic penetration law, and that it continues either until the projectile material is exhausted or until a side wall collision occurs. The penetration is evaluated as a function of a reference coordinate q defined along the projectile, and the corresponding crater radius distribution R(q) calculated, on the assumption that W is zero. The locus of the penetration stagnation point S corresponding to the true value of W is then determined as a function of q and a revised crater profile is calculated with radius R(q), centred on S. We determine whether a side-wall collision occurs, and calculate the final penetration, P. The probability that P exceeds a given value P_o is found. We then determine the expected value of P and investigate parameter variations to maximize this value.     

Dynamic elastic-plastic buckling phenomena in a rod due to axial impact

Dynamic elastic-plastic buckling phenomena which might develop in a rod from an axial impact loading are studied in order to identify the conditions for quasi-static behaviour. A discrete model for dynamic elastic-plastic buckling, which retains the axial and the lateral inertia forces, is proposed, and the relationship between the model parameters and the characteristics of an actual structure is given. Examples of different external loadings and boundary conditions are considered in order to clarify the influence of elastic-plastic axial wave propagation on the buckling process. The critical time for the initiation of buckling is obtained and the post-buckling behaviour of the model is analysed. Particular attention is paid to the role of the striking mass on the characteristics of the buckling process and on the development of the buckling shape. The numerical study reveals that the inertia of the striking mass affects considerably the development of the buckling shape causing different patterns of axial strain distributions at the initiation of buckling. The comparisons which are made between the model predictions and some previously published experimental data show that the buckling process is governed by the impact velocity as well as by the external loading history provided by the experimental technique.     

Dynamic recrystallization-induced flow phenomena in tungsten–tantalum (4%) [001] single-crystal rod ballistic penetrators

Deformation-flow microstructures associated with [001] W–4% Ta penetrator fragments in a rolled homogeneous steel armor target exhibit dynamic recrystallization. The equiaxed, recrystallized grain structure observed in the deformed penetrator is also associated with soft zones in corresponding microhardness maps. Microstructure evolution is also examined by transmission electron microscopy (TEM) and selected-area electron diffraction (SAED).     

Atomic force microscope study of crater formation in ion bombarded polymer

Polyimide Kapton films with a thickness of 62 m were bombarded by Ar+, N+, He+ and D+ ions at energies from 10–50 keV. After bombardment at room temperature, the surface topographic changes of the polymer were investigated using an atomic force microscope (AFM). The most common feature of the ion-bombarded Kapton surface is the formation of craters which often have circular shape and rims. The crater sizes suggest they are unlikely to have been caused by a single ion but by the collective effects including diffusion and trapping of gas atoms and gas molecules in ion-bombarded polymer. A model for the formation of these craters is proposed.     

On the optimal performance of long-rod penetrators subjected to transverse accelerations

The paper deals with theoretical considerations on the conception and optimization of long-rod penetrators with regard to bending strain and penetration efficiency. In a first step we describe a method allowing to design long penetrators in such a manner that given values of bending stress and deflection are met if the rods are subjected to lateral forces. On the assumption of a constant lateral acceleration this results in rods with various dimensions; the aspect ratio remarkably does not remain constant. Then these penetrators are examined for maximum penetration efficiency while considering rods of equal energy. For the case studied the procedure results in an optimum velocity of about 2700 m/s. This demonstrates a fundamental difference in comparison to the optimization process with L/D-scaled penetrators where a much lower optimum velocity (2300 m/s) is obtained. In comparison to the reference penetrator (L/D=34, V=1800 m/s) the optimum penetrator — still at constant stress level and at an impact velocity of 2700 m/s — has of course a reduced mass, but also a reduced length and diameter showing an aspect ratio of 40. The perforation power could be increased by some 17%. On the other hand, the linearly scaled penetrator at constant energy only shows an increase of about 7% in penetration capability if the impact velocity reaches its optimum value at 2300 m/s. The optimization procedure of the energy-efficient penetration of constant-stress projectiles leads to an optimal velocity well in the hypervelocity regime. Furthermore, the special design of the penetrators with constant stress level results in a gain of penetration efficiency.     

Nanostructure formation due to impact of highly charged ions on mica

Muscovite mica was irradiated with slow highly charged Ar^q+ (charge state q = 12, 16) and Xe^q+ (q = 23, 27) ions in a kinetic energy range of 150-216 keV and subsequently observed by contact mode atomic force microscopy. Surprisingly, on samples irradiated with Xe ions nano-sized hillock-like structures were found well below the charge state threshold reported in earlier experimental investigations. However, the structures found are not the result of a true topographic surface modification induced by the ion bombardment, because the absence of these nanostructures in tapping mode images and the dependence of the detected structures on scan conditions points towards a surface modification which manifests itself only in frictional forces and therefore in height measurement artifacts. Furthermore the generated defects are not stable but can be erased by continuous scanning.     

The segmented bidirectional single-loop topology for material flow systems

This paper introduces the segmented bidirectional single-loop (SBSL) flow topology for carrier-based material handling systems. This configuration is based on a single-loop flow-path structure that is divided into non-overlapping segments, each containing a single carrier operating in a bidirectional mode. The design procedure comprises a 0 - 1 mixed-integer formulation to determine the single-loop including the pickup and delivery station location. The second stage is a segmentation procedure to determine the non-overlapping segments in the loop. Finally the performance of the SBSL is evaluated by means of simulation.     

Determination of complex formation constants of lipophilic neutral ionophores in solvent polymeric membranes with segmented sandwich membranes

A potentiometric method to determine ionophore complex formation constants in solvent polymeric membrane phases, proposed originally by Russian researchers, is critically evaluated and compared to other established methods. It requires membrane potential measurements on two-layer sandwich membranes, where only one side contains the ionophore. The resulting initial membrane potential reflects the ion activity ratio at both aqueous phase--membrane interfaces and can be conveniently used to calculate complex formation constants in situ. This method is potentially useful, since it does not require the use of a reference ion or second ionophore in the measurement. In this paper, the five ionophores valinomycin, BME-44, ETH 2120, tert-butylcalix[4]arene tetraethyl ester, and S,S'-methylenebis(diisobutyldithiocarbamate) are characterized in poly(vinyl chloride) (PVC) plasticized with dioctyl sebacate (DOS) and compared with other established methods. The resulting formation constants correspond well to literature values. The influence of varying membrane concentrations and different anionic site additives is studied and found to be relatively small. Experiments are also performed with and without lipophilic inert electrolytes and with ionophore-free sandwich membranes to illustrate the effect of ion pairing and the membrane internal diffusion potential on the response of such sandwich membranes. These experiments suggest that ions are completely associated in PVC-DOS membranes, but that such ion pairs are rather nonspecific. Diffusion potentials seem to play a minor role with these systems. The results are explained with theory. This work indicates that the characterization of electrically charged ionophores, anion-selective ionophores, and ionophores in membrane matrixes other than PVC plasticized with DOS may now be experimentally accessible.     

Approximate solution by frontal method of two-dimensional problem on formation of crater in a metal by a laser pulse

The two-dimensional formation of a crater in a metal by a laser pulse is studied by the frontal method. The problem is reduced to a set of transcendental equations for the evaporation constants and to an equation of the first order for the frontal surface. Calculations are made for Al, Cu, and Fe targets for laser energy flux densities from 10⁶ to 10⁸W/cm².Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 3, pp. 540–545, March, 1976.     

Thaumasite formation due to atmospheric SO2–hydraulic mortar interaction

The objective of this paper was to reproduce the formation of thaumasite due to the reaction of atmospheric SO₂ with hydraulic mortars. The research was carried out on mortars made with ordinary Portland cement (OPC), mineralized white Portland cement, hydraulic lime and a mixture of lime and pozzolana. Mortars underwent sulfation by exposing the samples to 300 ppm SO₂ at 25 °C and 95% RH for 2 days. Subsequently, half of the sulfated samples were kept for 6 and 12 months in a chamber with 0.3 ppm, SO₂ as pollutant (0.50 l min⁻¹ flow gas velocity), 5 °C and 95% RH. The other halves of the sulfated samples were kept partially immersed in water at 5 °C for 4, 9 and 14 months.

The process of thaumasite formation in hydraulic mortars due to the interaction of the material with atmospheric SO₂ was reproduced in all the hydraulic mortars kept partially immersed in water at low temperature, except in the lime–pozzolana mixture. Gypsum was the first reaction product formed as a result of that interaction. Subsequently, gypsum reacted with calcium carbonate and C–S–H gel resulting in the formation of thaumasite. The formation of thaumasite was easier and quicker in sulfated samples kept at low temperature partially immersed in water. Only in OPC mortars was thaumasite formation observed in samples exposed to 0.3 ppm of SO₂ for 12 months.     

Investigation on the response of segmented concrete targets to projectile impacts

The study of penetrator performance without free-surface effects can require prohibitively large monolithic targets. One alternative to monolithic targets is to use segmented targets made by stacking multiple concrete slabs in series. This paper presents an experimental investigation on the performance of segmented concrete targets. Six experiments were carried out on available small scale segmented and monolithic targets using instrumented projectiles. In all but one experiment using stacked slabs, the gap between slabs remained open. In the final experiment design, grout was inserted between the slabs, and this modification produced a target response that more closely represents that of the monolithic target.