Projectile Side Research Articles

Critical Velocity of High-Performance Yarn Transversely Impacted by Razor Blade

A ballistic parameter that influences the ballistic performances of a high-performance yarn is the critical velocity. The critical velocity is defined as the projectile striking velocity that causes instantaneous rupture of the yarn upon impact. In this study, we performed ballistic experiments to determine the critical velocity of a Twaron® yarn transversely impacted by a razor blade. A high-speed camera was integrated into the experimental apparatus to capture the in-situ deformation of the yarn. The experimental critical velocity demonstrated a reduction compared to the critical velocity predicted by the classical theory. The high-speed images revealed the yarn specimen failed from the projectile side toward the free end when impacted by the razor blade. To improve the prediction capability, the Euler–Bernoulli beam and Hertzian contact models were used to predict the critical velocity. For the Euler–Bernoulli beam model, the critical velocity was obtained by assuming the specimen ruptured instantaneously when the maximum flexural strain reached the ultimate tensile strain of the yarn upon impact. On the other hand, for the Hertzian contact model, the yarn was assumed to fail when the indentation depth was equivalent to the diameter of the yarn. The errors between the average critical velocities determined from experiments and the predicted critical velocities were around 19% and 48% for the Euler–Bernoulli beam model and Hertzian contact model, respectively.

Unsteady characteristics of cloud cavitating flow near the free surface around an axisymmetric projectile

The effect of free surface on unsteady cloud cavitation is important for high-speed surface vehicles, However, previously published experimental and numerical works regarding this topic are limited. In this paper, a typical launching experiment is performed with the presence of free surface. A numerical approach is established by using large eddy simulation and volume-of-fluid methods. Firstly, unsteady evolutions of the cavity and re-entry jet are obtained in both experimental and numerical results, which agree well with each other. Results indicate that the cavity evolution on the upper side of projectile is remarkably different compared to the lower side under the free-surface effect. For instance, on the upper side, cavity growth is slower, the velocity of the re-entry jet is higher, the cavity sheds faster, and the position of shedding cavity collapse is closer to the main cavity. Secondly, the effect of the free surface is studied by analyzing the constraint variation. Because the flow stream around the upper surface is thin, changing its direction under the effect of pressure difference inside and outside the cavity is easy. Non-axisymmetric collapse features generate a mass of strong vortexes on the cylindrical surface, and the non-uniform distribution of high pressure region is also one of the most important factors to induce lateral and vertical forces on the projectile. Finally, the heights of wave elevation in cases with and without cavitation are compared. The presence of cavitation leads to an increase in wave height, but the increment is about half the thickness of the cavity. This finding indicates that the actual constraint effect is between the effects of the infinite water field and the fully free condition.

Azimuthal Asymmetry of Pion-Meson Emission around the Projectile and Target Sides in Au+Au Collision at 1AGeV**Supported by the National Natural Science Foundation of China under Grant Nos 11421505 and 11220101005, and the National Basic Research Program of China under Grant No 2014CB845401.

The ratio of the number of emitted pions from the target side to that from the projectile side at target rapidity within the reaction plane is investigated for the study of the pion dynamics with an isospin-dependent quantum molecular dynamic model. The results show that high-energy pions are emitted preferentially towards the target side and, therefore, they are freezed out at the early stage of the collision. By contrast, low-energy pions are emitted predominantly in the opposite direction, which means that they are emitted in a later stage. This argument is based on the shadowing effect caused by the interaction of pions with the spectator matter in peripheral collisions at target or projectile rapidities. This phenomenon disappears in the central collision or at midrapidity due to the weaker shadowing effect. The calculated ratios are also compared with the experimental data.

Kelvin-Helmholtz instability in high-energy heavy-ion collisions

The dynamical development of collective flow is studied in a (3+1)-dimensional fluid dynamical model, with globally symmetric, peripheral initial conditions, which take into account the shear flow caused by the forward motion on the projectile side and the backward motion on the target side. While at $\sqrt{{s}_{NN}}=2.76A$ TeV semiperipheral $\text{Pb}+\text{Pb}$ collisions the earlier predicted rotation effect is visible, at more peripheral collisions, with high resolution and low numerical viscosity, the initial development of a Kelvin-Helmholtz instability is observed, which alters the flow pattern considerably. This effect provides a precision tool for studying the low viscosity of quark-gluon plasma.

Low-mass dilepton production through transport processes in a quark-gluon plasma

The dynamical development of collective flow is studied in a (3+1)D fluid dynamical model, with globally symmetric, peripheral initial conditions, which take into account the shear flow caused by the forward motion on the projectile side and the backward motion on the target side. While at $\sqrt{s_{NN}} = 2.76A$\,TeV semi-peripheral Pb+Pb collisions the earlier predicted rotation effect is visible, at more peripheral collisions, with high resolution and low numerical viscosity the initial development of a Kelvin-Helmholtz instability is observed, which alters the flow pattern considerably. This effect provides a precision tool for studying the low viscosity of Quark-gluon Plasma.

Unitarity at small Bjorken x

This paper presents a solution to the nonlinear small- x “projectile side” evolution equations as derived by Balitskii in 1996. The solution is based on functional Fokker–Planck methods. The fixed point at small x is explicitly calculated and all correlation functions in this limit are determined. They show clear saturation and unitarization properties. Scaling laws that hold during the saturation phase and throughout the whole course of the evolution are established. The corresponding Langevin equations are given as a basis for numerical simulations opening the field for future studies of dynamical issues of the evolution not analytically accessible. The methods used may be extended to the “target side” equations of Jalilian-Marian, Kovner, Leonidov and Weigert.

衝撃圧接における接合面形成過程について

It is well known that two metallic plates are bonded momentarily at a high velocity impact. It is guessed that the plastic work occurring on the contacting surface is converted into heat so that the bonding proceeds due to the heat. Although this phenomenon is observed on an explosive welding, it is considered that the bonding mechanism of the dynamic compaction is also the same. The exposive welding and the dynamic compaction have been already used industrially. However, the bonding mechanism is not clarified sufficiently.The aim of this paper is to investigate the formation of bonding area at the impact welding using a longitudinal impact test. In the longitudinal impact test, a projectile accelerated by a gas gun collides with a target so that the welding occurs at the interface between two metals. The material used for the projectile is a commercial pure aluminum and the target materials are mild steel, copper and stainless steel. The bonding area is observed using a scanning acoustic tomograph and the bonding strength is examined by a quasi-static tension test. Additionally, the profile of the crater on the target after impact is also measured.It appears that the formation of the bonding area is dependent on the deformation processes of the projectile and the target, as indicated by the following results. The radial deformation of the impact face of the projectile is very restricted by the friction force at the interface or the deformation of the target so that the bulging accompanied with the folding of the projectile side occurs and the mushrooming profile appears after impact. Although a few areas considered to be bonding ones are found from an ultrasonic image after the bonding, the bonding force of the central part is much stronger than that of the other parts. Subsequently, it is presumed that the bonding mechanism of the copper target differs from those of the other targets.

Preferential emission of pions in asymmetric nucleus-nucleus collisions.

Pion production in Ne on Pb collisions at a beam energy of 800 MeV/nucleon is studied by solving a coupled set of transport equations for the phase-space distribution functions of nucleons, deltas, and pions. The experimentally observed preferential emission of pions away from the interaction zone towards the projectile side in the transverse direction is found to be due to the stronger pion absorption by the heavier target spectator. A model calculation of the pion transverse momentum distribution in the reaction plane agrees with that of the experimental data. The existence of a collective How signature among the final-state baryons of relativistic heavy-ion collisions at beam energies around I GeV/nucleon has been firmly established by the in-plane transverse momentum analysis [l]. Due to the small mass of pions compared to that of baryons, it has been pointed out that the pions might serve as a good probe of any hydrodynamical Row [2]. Moreover, as pions are mainly corning from the decay of b resonances in the relativistic heavy-ion collisions, the remnant of the collective flow carried by 6 resonances might be seen in the final-state pions. Looking for Aow signatures among pions, several groups [2 — 4] have studied the transverse momentum distribution in the reaction plane for pions (average transverse momentum in the reaction plane (p ) versus rapidity y). One of the most striking results from the DIOGENE Collaboration [2] is that the in-plane transverse momentum of pions is always positive even for backward rapidities, for the asymmetric (Ne or Ar)+(Nb or Pb) systems. However, the intranuclear-cascade model predicts values compatible with zero over the whole range of rapidity [2]. The quantum-molecular-dynamics model calculation of the pion transverse momentum distribution [5] indicates that the introduction of the mean field describes some of the experimental effect, but the model predicts less asymmetry than observed experimentally. Therefore, the question whether the experimentally observed preferential emission of pions away from the interaction zone towards the projectile side in the asymmetric nucleusnucleus collisions is due to the collective Bow of pions or due to the shadowing effect of the heavier target spectator has not been resolved. In this article we report on the results of a study using I a hadronic transport model [6— 8]. The preferential emission of pions toward the projectile side in the transverse direction in the reaction Ne+Pb at a beam energy of 800 MeV/nucleon is found to be due to the stronger absorption of pions by the heavier target spectator. The calculated transverse momentum distribution of pions in the reaction plane agrees with that of the experimental data. The calculations were performed by numerically solving a coupled set of transport equations for the phasespace distribution functions of nucleons, deltas, and pions. The transport equation for the particular state b of the baryon (nucleon and delta) reads [7,8] dfb(xp) + V„fb (xp) V„U(x ) V fb— (xp)

Multiple-ionization collision dynamics.

The 1.4-MeV/u ${\mathrm{U}}^{32+}$+Ne collision system is studied in detail in order to elucidate the dynamics of multiple ionization in energetic, heavy-ion--atom collisions. Differential cross sections versus recoil-ion charge state, calculated by the n-body classical-trajectory Monte Carlo method, are presented for the \ensuremath{\theta} and cphi angle dependences of the projectile, recoil ion, and ejected electrons. The calculations show a high degree of ejected-electron asymmetry towards the projectile side of the target nucleus which strongly effects the transverse-momentum balance between the heavy particles. Experimental and calculated cross sections differential in the recoil-ion charge state and transverse momentum are found to differ by orders of magnitude from those for the projectile, providing evidence for the importance of explicitly considering the ejected electrons' momenta in the determination of the heavy-particle (both the projectile and the recoil-ion) angular differential cross sections. Polarization of the target electrons and screening of the recoil ion by the ejected electrons lead to \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}6}$-rad negative-angle deflections of the projectile for recoil-ion charge states up to 4+. The angular scattering of the recoil ion departs significantly from that predicted for a two-body collision, and is found to be nearly isotropic for low recoil-ion charge states and peaked to angles \ensuremath{\theta}>90\ifmmode^\circ\else\textdegree\fi{} for high recoil-ion charge states. A stopping-power calculation for this system is in good agreement with the experimental value. Stopping powers differential in impact parameter and for energy deposition to \ensuremath{\delta} electrons and multiple ionization are given to further describe the projectile energy loss.

Nuclear collective flow and charged-pion emission in Ne-nucleus collisions at E/A = 800 MeV.

Triple-differential cross sections of charged pions were measured for collisions of Ne projectiles at E/A = 800 MeV with NaF, Nb, and Pb targets. The reaction plane was estimated event by event from the light-baryon momentum distribution. For heavy targets, preferential emission of charged pions away from the interaction zone towards the projectile side was observed in the transverse direction. Such a preferential emission, which is not predicted by cascade calculations, may be attributed to a stronger pion absorption by the heavier spectator remnant.