Hypervelocity impact of rod projectiles with L/D from 1 to 32

Beside a short remark on the “hydrodynamic theory of rod projectiles”, the paper deals with the terminal ballistic behaviour of cylindrical projectiles against semi-infinite targets. Experimental data of EMI, completed by results of some other authors, are presented. Crater parameters like depth, diameter and volume and their dependence on projectile velocity (up to 5000 m/s), projectile and target material properties, as well as L/D-ratios (1–32), will be discussed. Mainly the projectile materials steel and tungsten sinter-alloys are considered. Target materials are mild steel and high strength steel, an Al-alloy and a tungsten sinter-alloy. The results show that the influence of material density on the crater dimensions is considerably greater than the influence of strength. The L/D ratio determines the velocity dependence of crater depth, diameter and volume. At high velocities in the hydrodynamic regime, the crater depth of short cylinders (L/D 1) is approximately proportional to v_p^2/3 (V_p=projectile velocity). With increasing L/D-ratio, the slope of the penetration curves decreases and converges for rods (L/D 1) versus a saturation, i. e. becomes nearly independent on v_p. A consequence of this saturation is the existence of a so-called “tangent velocity”, above which an optimal increase of efficiency is only realized by increasing the projectile mass and not the velocity. Furthermore, ballistic limits of real targets like single plates and symmetric double plates meteorite bumper shield) are taken into account. The expected better performance of “segmented rods” is also discussed.     

Debris fragment characterization in oblique hypervelocity impacts

A case history in debris characterization is presented for oblique impacts of chunky tungsten projectiles against thin plates. The integrated approach of scaled experiments and hydrocode simulations led to a semi-analytic model of behind the plate debris fragment distributions. This debris distribution model agreed quite well with the experimental fragment distributions derived from witness plate measurements. The 1/4 scale test program included three projectile masses, two target geometries (single and dual plates), a velocity range of 4–7 km/s and a strike angle range of 15–55 degrees. Close correlation of measured and predicted fragment distributions encouraged the extension of the model to higher velocities not currently obtainable in the laboratory.

The paper also includes discussions of critical features of debris in oblique hypervelocity impact, the scalability of fragment data, and the utilization of the derived fragment models in semi-analytic damage assessment codes.     

Electrostatic BEM for MEMS with thin conducting plates and shells

Micro-electro-mechanical systems (MEMS) sometimes use beam or plate shaped conductors that can be very thin-with h/L≈O(10⁻²−10⁻³) (in terms of the thickness h and length L of the side of a square pate). Conventional Boundary Element Method (BEM) analysis of the electric field in a region exterior to such thin conductors can become difficult to carry out accurately and efficiently—especially since MEMS analysis requires computation of charge densities (and then surface tractions) separately on the top and bottom surfaces of such plates. A new boundary integral equation (BIE) is derived in this work that, when used together with the standard BIE with weakly singular kernels, results in a powerful technique for the BEM analysis of such problems. This new approach, in fact, works best for very thin plates. This thin plate BEM is derived and discussed in this work. Numerical results, from several BEM based methods, are presented and compared for the model problem of a parallel plate capacitor.     

Standing-wave solutions of the Enneper (sine-Gordon) equation

The present paper investigates the real solutions of the partial differential equations (∂²ω/∂u²) − (∂²ω/∂ν²) = sin ω (Enneper or sine-Gordon equation) that are of the FORM = F(|₁(u) · |₂(ν)). In the application of the Enneper equations to crystal physics such solutions may represent standing waves. A complete classification of these solutions and its degenerate cases is given.     

Development of the high-velocity gas-dynamics gun

The subjects of this paper are the historical overview and development of the high-velocity gas-dynamics gun. These are guns that derive their energy from a reservoir of compressed gas. Other 3uns derive their energy from electricity or from high explosive. Their historical overviews and developments are covered in papers by Mr. William Weldon and Mr. Alex Wenzel.

The gas dynamics gun is viewed first from the standpoint of modern technology. An idealized configuration, the “Reference Gun”, is analysed in order to quantify the effects of gun diameter and length, projectile mass, and propellant gas pressure and composition. The analysis assumes that the propellant is an ideal gas, and formulae are derived for the base pressure and velocity of the projectile as functions of the size and loading parameters of the gun. The analysis demonstrates that the prime requirements for high velocity are a high gas pressure, a low molecular weight gas, a light projectile, and a long gun.

The history of guns is reviewed briefly from 14th century black-powder muzzle-loaders to 20th century, nitrocellulose -propellant, breech-loaded guns. The velocity limit of the modern gun is shown to be around 3 km/s, if the gun is loaded with nitrocellulose propellant and is very long (200 calibers). However, if the gun is loaded with hydrogen and the length doubled, it is shown that the velocity limit can be increased to 7 km/s, thus approaching current needs.

The problem of using hydrogen has been solved by the invention of the piston-compression light-gas gun (PCLGG). However, the limited strength of the fragile, sabot-model projectiles of experimental research has capped the maximum acceleration and has placed a demand on the gun's operating cycle to generate a constant pressure at the base of the projectile for the launching run. This second problem has been partially solved by the invention of a modification to the PCLGG known as the piston-compression, accelerated-reservoir, light-gas gun (PCARLGG). Both the PCLGG and the PCARLGG are described. The performance of the PCARLGG has been analyzed by a hydrocode developed for this purpose, and the results of the calculations are presented and compared with experiment.

The concept of a frictionless, adiabatic “Ideal Gun” is introduced in order to simplify the analysis of performance. It is shown that the performance of any ideal gun is given by a simple equation involving two dimensionless parameters that relate the projectile's velocity to its mass, its average base pressure, and the diameter and length of the gun. Based on the ideal gun equation, the maximum operating velocity of the gas-dynamics gun is estimated to be about 12 km/s.     

A novel gamma-ray imaging concept using “edge-on” microchannel plate detector

The “edge-on” illuminated microchannel plate (MCP) position-sensitive detector (PSD) is used for gamma-ray imaging for the first time. The superior position resolution of the MCP is combined with high detection efficiency due to the “edge-on” illumination mode. The results of imaging a 15 μCi ¹³⁷Cs source (662 keV quantum energy) are presented.     

Hypervelocity impact simulation experiments on LDEF°-foils

A variety of space environmental effects can be studied on many experiments having been exposed on the LDEF-satellite.

Among others the thermal blankets of the Ultra-Heavy Cosmic Ray Nuclei Experiment (“UHCRE”, Exp. A0178) displayed many micrometeoroid / space debris impact features.

In an effort to understand their nature and characteristics, an experimental impact simulation program has been carried out.

UHCRE-spare foils have been impacted by glass, aluminium, and iron projectiles with masses ranging from about 30 nanograms up to several milligrams. Impact velocities range between about 3 km/s and 13 km/s.

Characteristic impact craters and perforation holes have been produced. Their sizes and morphologies have been related with respective projectile impact parameters.

“Halo zones” around perforation holes, as they had been observed in the exposed LDEF-foils, have also been obtained experimentally. They were found to be delamination effects within the foil layers caused by the propagation of impact shock waves.     

Mechanical and machining properties of X38CrMoV5-1/Al2O3 metal matrix composites and components

Large plates and discs of X38CrMoV5-1/Al₂O₃ metal matrix composites (MMCs) were produced via Ti-activated pressureless melt infiltration. After machining the plates were characterised using non-destructive testing methods (X-ray and ultrasonic C-scans) in order to investigate the quality of infiltration before preparing bars for four-point-bending tests. Subsequently, parts of the plates were used for machining tests, including sawing, welding and spark erosion. Furthermore, MMC discs were prepared for wear tests. The as-infiltrated MMC discs show a low wear rate of 1.6 × 10⁻¹⁰–2.2 × 10⁻¹⁰ m/s, which is 2–3 times better than the hardened steel itself, or 12–17 times better compared to X38CrMoV5-1 in the annealed state. As a first component a wire-drawing die was fabricated and successfully tested for drawing Al alloy AA6082 and steel 16MnCr5.     

Validation and calibration of a lateral confinement model for long-rod penetration at ordnance and high velocities

In designing targets for laboratory long-rod penetration tests, the question of lateral confinement often arises, “How wide should the target be to exert enough confinement?” For ceramic targets, the problem is enhanced as ceramics are usually weak in tension and therefore have less self-confinement capability. At high velocities the problem is enhanced even more as the crater radius and the extent of the plastic zone around it are larger. Recently we used the quasistatic cavity expansion model to estimate the resistance of ceramic targets and its dependence on impact velocity [1]. We validated the model by comparing it to computer simulations in which we used the same strength model. Here we use the same approach to address the problem of lateral confinement.

We solved the quasistatic cavity expansion problem in a cylinder with a finite outside radius “b” at which σ_r (b) = 0 (σ_r = radial stress component). We did this for three cases: ceramic targets, metal targets, and ceramic targets confined in a metal casing. Generally, σ_r (a) is a decreasing function of “a” (“a” = expanding cavity radius, and σ_r (a) = the stress needed to continue opening the cavity). In the usual cavity expansion problem b → ∞, σ_r (a) = const., R =−σ_r (a) (R = resistance to penetration). For finite “b” we estimate R by averaging σ_r (a) over a range o ≤ a ≤ a_r, (where a_r, the upper bound of the range, is calibrated from computer simulations).

We ran 14 computer simulations with the CTH wavecode and used the results to calibrate a_r for the different cases and to establish the overall validity of our approach.

We show that generally for D_t/D_p > 30, the degree of confinement is higher than 95% (D_t = target diameter; D_p = projectile diameter; and degree of CONFINEMENT = R/R_∞; R∞ = resistance of a laterally infinite target). We also show the tensile strength of ceramic targets (represented by the spall strength P_min) has a significant effect on the degree of confinement, while other material parameters have only a minor effect.     

Variation of crater geometry with projectile L/D for L/D ≤ 1

A series of hydrocode calculations and terminal ballistics experiments were performed to investigate the penetration mechanics of projectiles with L/D ≤ 1. Projectile L/D ranged from 1/32 to 1; impact velocity ranged from 1.5 to 5 km/s. Projectiles were tungsten or tungsten alloy, targets were RHA. The paper concentrates on the effect of projectile L/D on the size and geometry of the target crater. Normalized crater depth (or penetration) increases with decreasing projectile L/D and achieves a maximum at about L/D=1/8 for 1.5 km/s and 1/16 for 3 km/s, and then decreases with further decrease in L/D. For 5 km/s, P/L increases with decreasing L/D over the entire range studied. P/L scales with impact velocity as P/L V^f(L/D) where, we believe, f(L/D) approaches 2 as L/D 0. The ratio of crater to projectile diameter D_c/D decreases with decreasing L/D and approaches a value of 1 as L/D approaches zero for all velocities studied. The crater shape measured by P/D_c decreases with decreasing L/D; i.e., as L/D decreases, the crater changes from approximately hemispherical for L/D = 1 to a very shallow disk shape. The kinetic energy required per unit crater volume, KE/V_c, increases with decreasing L/D for L/D < 1/4. That is, cratering efficiency decreases with decreasing projectile L/D. For the impacts studied, KE/V_c increases from about 5 kJ/cm³ to 12 kJ/cm³ as projectile L/D is reduced from 1 to 1/32.     

Temperature dependence of the growth of gallium oxide on CoGa(100)

The oxidation of a CoGa(100) surface at high temperatures has been studied by scanning tunnelling microscopy (STM) and auger electron spectroscopy (AES). When CoGa(100) is oxidised at a sufficiently high temperature (>600 K), an ordered Ga₂O₃ film is formed. The stability of the film depends on the sample temperature and partial oxygen pressure of the ambient gas. At negligible oxygen pressure (<10⁻¹¹ mbar) the oxide is stable up to 850 K. At an oxygen pressure of 10⁻⁶ mbar the oxide is stable up to 930 K and some of the oxide remains present up to 970 K. The oxide film is found to be very uniform. The thickness of the film is constant and independent of the oxidation temperature (600 K<T<930 K), oxygen pressure (<10⁻⁶ mbar), and exposure (10⁻⁴–10⁻² mbar.s≈10²–10⁴ L). We find a clear improvement of the order of the oxide film surface with increasing oxidation temperature. In STM images, a domain structure of the oxide film is observed. The size of the domains increases by a factor of 5–10 when the oxidation temperature is increased from 700 to 900 K.     

Measured charge generation by small mass impact at velocities between 1 and 45 km/s

The electrical charge that is generated by the impact of a small mass at velocities between 1 and 45 km/s was investigated using the Electrostatic Dust Accelerator of the Max-Planck-Institut in Heidelberg (MPI) and the Plasma Accelerator of the Lehrstuhl fu¨r Raumfahrttechnik (LRT) of the Technische Universita¨t Mu¨nchen (TUM). Glass beads were accelerated, and the targets were of different materials i.e., (Au, W, Fe, Al). The mass/velocity range of the accelerated small masses was: MPI: 10⁻¹⁵g−10g/ 1km/s−10g−5g/ 2km/s±_total of both polarities can be described by the empirical formula: Q^±_total =Cmv^β[Coulomb], C being a function of the density ratio of target/projectile, is approximately unity and β between 2.92 and 3.77. The charge detector is described and the results that were obtained in test series at both facilities are discussed in relation to the empirical formula.     

A kinetic model for the degradation of benzothiazole by Fe3+-photo-assisted Fenton process in a completely mixed batch reactor

The degradation of benzothiazole in aqueous solution by a photo-assisted Fenton reaction has been studied in a batch reactor in the pH range 2.0–3.2 and for H₂O₂ and Fe(III) concentrations respectively between 1.0×10⁻³–1.5×10⁻¹ and 1.0×10⁻⁶–4.0×10⁻⁶ M.

A kinetic model has been developed to predict the decay of benzothiazole at varying reaction conditions. The use of kinetic constants from the literature in the model allows to simulate the system behavior by taking into account the influence of pH, hydrogen peroxide, Fe(III) and sulfate concentrations and the ionic strength.     

Influence of laser sources with different spectral properties on the performance of vapor cell atomic clocks based on lin‖lin CPT

We evaluate the influence of 2 types of laser sources with different spectral profiles on the performance of vapor cell atomic clocks based on lin‖lin coherent population trapping (CPT) resonances. We show that a short-term stability of 1 − 2 · 10⁻¹¹τ{−1/2} may be reached in a compact system using a modulated vertical cavity surface-emitting laser. Here the stability is limited by the detection noise level and can be improved up to a factor of 4 by increasing the lock-in detection frequency to several tens of kilohertz, which is not possible in standard double resonance atomic clocks. We compare these results with CPT prepared under the same experimental conditions, using 2 phase-locked extended cavity diode lasers, with which we predict a challenging short-term stability of 1 − 3 · 10⁻¹³τ^−1/2, comparable to the state-of-the-art laser-pumped Rb-clocks.     

The CPLEAR electromagnetic calorimeter

A large-acceptance lead/gas sampling electromagnetic calorimeter (ECAL) was constructed for the CPLEAR experiment to detect photons from decays of π⁰s with momentum p_π⁰ ≤ 800 MeV/c. The main purpose of the ECAL is to determine the decay vertex of neutral-kaon decays K⁰ → π⁰π⁰ → 4γ and K⁰ → π⁰π⁰π⁰ → 6γ. This requires a position-sensitive photon detector with high spatial granularity in r−, −, and z−coordinates. The ECAL - a barrel without end-caps located inside a magnetic field of 0.44 T - consists of 18 identical concentric layers. Each layer of 1/3 radiation length (X₀) contains a converter plate followed by small cross-section high-gain tubes of 2640 mm active length which are sandwiched by passive pick-up strip plates. The ECAL, with a total of 6X₀ has an energy resolution of and a position resolution of 4.5 mm for the shower foot. The shower topology allows separation of electrons from pions. The design, construction, read-out electronics, and performance of the detector are described.     

Plate perforation by deformable projectiles — A plastic wave theory

A one-dimensional wave propagation model of plate perforation is developed for cylindrical projectiles impacting plates at normal obliquity. This theory assumes that the projectile and plate materials are rigid-linearly strain-hardening and rigid-perfectly plastic respectively, with respect to engineering stress and strain. During penetration, the projectile deforms and a plug forms in the plate. The plug which is sheared from the plate is larger than the initial cross-section of the projectile. Residual velocity, plug mass and final plug thickness are determined for this model and compared with experiments on ductile metal plates impacted at velocities larger than the minimum perforation velocity.     

n型SnS热电材料的制备与性能研究

SnS由低毒、廉价、高丰度的元素组成, 在热电研究领域受到广泛关注。采用机械合金化(MA)结合放电等离子烧结(SPS)工艺制备了n型SnS_1-xCl_x(x=0, 0.02, 0.03, 0.04, 0.05, 0.06)多晶块体热电样品, 并研究了Cl^-掺杂量对SnS物相、微观结构以及电热输运性能的影响。结果表明: Cl^-的引入会提高电子浓度, 使SnS由本征p型转变为n型半导体。随着Cl^-掺杂量的增加, n型SnS半导体室温下的霍尔载流子浓度从6.31×10¹⁴ cm^-3 (x=0.03)增加到7.27×10¹⁵cm^-3 (x=0.06)。x=0.05样品在823 K取得最大的电导率为408 S·m^-1, 同时具有较高的泽贝克系数为-553 μV•K^-1, 使其获得最大功率因子为1.2 μW·cm^-1·K^-2。Cl^-的掺入会引入点缺陷, 散射声子, 使晶格热导率κ_lat由0.67 W·m^-1·K^-1(x=0)降至0.5 W·m^-1·K^-1 (x=0.02)。x=0.04样品在823 K获得了最大ZT为0.17, 相比于x=0样品(ZT~0.1)提高了70%。     

Investigation of the dependence of the contact resistance on the external gold layer in AuNiGeAu/n-GaAs

The contact resistance of an Au/Ni/Ge/Au metallization system on n-GaAs exhibits a drop in contact resistance from 13.3 × 10⁻⁶ ω cm² to 8.6 × 10⁻⁶ ω cm² when the external gold layer is varied from 800 Å to 6000 Å in thickness. Secondary ion mass spectroscopy indicates that the improvement in contact resistance is due to the gold's “regulating” the amount of NiAs formed, leading to an increase in the area fraction covered by the Ni₂GeAs. The result shows that the external gold layer deposited to improve bonding should be optimized in thickness. This role played by the external gold layer of the metal system in affecting the contact resistance has not been previously studied.     

Impact flash and debris cloud expansion of high-pure metal foils

Results of 2 mm aluminum spheres perforating Al, Cu, Mo, Au, Sn, and Zn metal foils of a purity > 99.9 % with thicknesses between 0.1 mm and 2.0 mm, densities of up to 20 g/cm³, melting temperatures of 500 – 3000 K and specific heats of fusion of 20 – 350 kJ/kg at impact velocities between v_p = 4.5 km/s and v_p = 9 km/s are presented. The influence of target thickness, target material properties and impact velocity on the perforation hole diameter, impact flash duration and expansion velocity, fragmentation and debris cloud formation at nearly constant areal density is demonstrated. The dependence of impact crater pattern at witness plates on target material density, thickness, impact velocity and areal density ratio between projectile and target material is discussed. For tin and lead evidence is given for the ability of digital scanning electron microscope analysis as an effective tool for indicating change of aggregation from solid into liquid and for the determination of relative projectile and target material quantities.