Velocity Limit Research Articles

Mechanism-driven analytical modelling of UHMWPE laminates under ballistic impact

Ultra-high molecular weight polyethylene (UHMWPE) fiber reinforced composite laminates have been widely used to defend against projectiles and fragments. Although the ballistic performance of UHMWPE composites has been extensively characterized both experimentally and numerically, analytical modelling remains a challenge. This study develops a mechanism-based analytical model of UHMWPE cross-ply laminates, with the progressive process of projectile penetration divided into two sequential stages of local failure and bulging deformation: the former is characterized with the strain concentration model under local shock compaction, and the latter is described using a modified membrane stretching model. Compared with existing energy-based models, the current model enables revealing physical mechanisms underlying the deformation/failure processes of UHMWPE laminate subjected to projectile impact, with relevant parameters correlated with material properties. Further, without using any fitting parameter, the proposed analytical model can predict both the ballistic limit and residual projectile velocity. For validation, the model predictions are compared with existing test data, with good agreement achieved for varying projectile mass, projectile size, laminate type, and laminate thickness. It is demonstrated that the maximum strain under a penetrating projectile is controlled by the thickness of un-penetrated laminate and the growth of bulge, and that the longitudinal wave speed and maximum tensile strain in the UHMWPE laminate dictate its ballistic limit.

Analysis of a Square Split-and-Recombined Electroosmotic Micromixer with Non-aligned Inlet-Outlet Channels

ABSTRACT In micro-scale sensitive medicinal and biochemical systems, improving mixing efficiency with small velocity limitations is critical. This work examines the influencing key parameters and their implications on mixing efficiency in a new two-dimensional electroosmotic micromixer (EM) with nonaligned input and outlet microchannels. The micromixer uses electroosmosis force generated by microelectrodes mounted on the walls of a square split and recombine (SSAR) mixing chamber to blend fluids of various concentrations, which enter into an intake microchannel from different inlets. The governing equations along with the specified boundary conditions are solved by the finite element-based solver. Thorough investigations are executed to explore how the mixing performance of the new microchannel mixer is affected by both flow (inlet velocity) and electric field (electrode potential arrangement, voltage magnitude, AC frequency, and phase difference) parameters. The results revealed that only adding electrode pairs always doesn’t increase the mixing efficiency of SSAR-EM, rather electrode polarity configuration along with an increase in electrode pair optimizes fluid mixing. Also, according to the present observations, the mixing performance of SSAR-EM is strongly sensitive to the input fluid velocity, the phase difference applied to the micro-electrodes, the AC frequency, and the amplitude of the alternating voltage. Corresponding to optimal parameters (i.e. velocity of 50 µm/s, AC-frequency of 8 Hz, voltage of 100 mV, and phase difference of 7π/36-radian), the mixing efficiency of SSAR-EM becomes 98.26%.

Directional polymer crystallisation with a fast-moving sink.

It has previously been shown that non-isothermal directional polymer crystallisation driven by local melting (Zone Annealing), has a close analogy with an equivalent isothermal crystallisation protocol. This surprising analogy is due to the low thermal conductivity of polymers-because they are poor thermal conductors, crystallisation occurs over a relatively narrow spatial domain while the thermal gradient spans a much wider scale. This separation of scales, which occurs in the limit of small sink velocity, allows replacing the crystallinity profile with a step and the temperature at the step acts as an effective isothermal crystallisation temperature. In this paper, we study directional polymer crystallisation under faster moving sinks using both numerical simulations and analytical theory. While, only partial crystallisation occurs, regardless, a steady state exists. At large velocity, the sink quickly moves ahead of a region that is still crystallizing; since polymers are poor thermal conductors, the latent heat dissipation to the sink becomes inefficient, eventually resulting in the temperature increasing back to the melting point thereby resulting in incomplete crystallization. This transition occurs when the two length scales measuring the sink-interface distance and the width of the crystallizing interface become comparable. For steady state and in the limit of large sink velocity, regular perturbation solutions of the differential equations governing heat transport and crystallization in the region between the heat sink and the solid-melt interface are in good agreement with numerical results.

Enhanced water transportation on a superhydrophilic serial cycloid-shaped pattern.

Spontaneous and directional water transportation (SDWT) is considered as an ideal water transportation method and has a great prospect in the aerospace and ship fields. Nonetheless, the existing SDWT has the limitation of a slow water transportation velocity because of its geometry structure configuration, which hinders the practical application of the SDWT. To overcome this limitation, we developed a new superhydrophilic serial cycloid-shaped pattern (SSCP) which was inspired by the micro-cavity shape of the Nepenthes. First, we experimentally found that the water transportation velocity on the SSCP was faster than that on the superhydrophilic serial wedge-shaped pattern (SSWP) and analyzed the faster water transportation mechanism. Then, the influence of the SSCP parameters on the transportation velocity was investigated by a single-factor experiment. In addition, the water transportation velocity on the SSCP was enhanced to 289 mm s-1 by combining the single-factor experiment, orthogonal optimization design, streamline junction transition optimization, and pre-wet pattern, which was the fastest in the SDWT. Moreover, the SSCP demonstrated its superior capability in long-distance water transportation, gravity resistant water transportation, heat transfer, and fog collection. This finding shows remarkable application prospects in the high-performance fluid transportation system.

Real-time trajectory generation for dual-stage feed drive systems

Machine tools are designed using dual-stage feed drives with slow and fast stages when speed and accuracy must be delivered over large work-volume. The slow stage provides large-stroke positioning whereas the fast stage executes short-stroke accurate tool-tip placement. This paper presents a real-time trajectory generator (governor) that distributes reference motion commands so that coordinated high-speed dual-stage contouring motion can be realized. A novel dynamic command scaling (DCS) approach is developed to generate trajectories in real-time that fully utilize the stroke (range), velocity, acceleration and dynamic limits of the dual-stages drives. Demonstration in 2D laser patterning shows >2 times increase in productivity.

NMPC of Unmanned Aerial Manipulators Considering Obstacle Avoidance and Manipulability

Trajectory tracking and obstacle avoidance are essential features to ensure the safe navigation of unmanned aerial manipulators (UAMs) in unstructured environments. However, these techniques may not work effectively in complex scenarios; therefore, this work presents a novel method to control the end effector of an aerial manipulator that simultaneously maximizes the manipulability of the robotic arm and guarantees obstacle avoidance of the entire system using non-linear model predictive control (NMPC) formulations. The NMPC includes trajectory tracking, obstacle avoidance, and the manipulability index in the cost function, resulting in fast algorithm convergence. The controller considers system constraints, such as the actuators’ limitations, including the aerial platform's maneuverability velocity and joint limits in the articulated manipulator. The results of the simulations demonstrate that the NMPC formulation successfully achieves the desired tasks, which validates the effectiveness of our approach ensuring safe and flexible navigation of aerial manipulators in complex scenarios.

Upper Limits for Velocity, Momentum, and Energy of Motion

Upper Limits for Velocity, Momentum, and Energy of Motion

Numerical study on influence of target thickness on impact response of GFRP composites

Due to rise in threats like ballistic impacts, blast loading and vehicle collision in armored military vehicles, the demand for materials with high strength and enhanced energy absorption capacity has been increased. Applications of Fiber reinforced composites as armor material in military vehicles is being considered as one of the measures to reduce such threats. The focus of this work is to investigate the energy absorption capacity of a GFRP plates subjected to a rigid projectile with blunt-nosed at the intermediate velocity range by using non-linear finite element code LS-DYNA. It has been found that the numerically computed results of ballistic limit velocity and residual velocity, closely resemble the test results reported in the literature. With altering target thickness, it has also been explored how the energy absorption capacity, projectile's residual velocity, ballistic velocity limit and damage mechanism of composite. The numerical results make it evident that the target thicknesses have a significant impact on the target's ballistic resistance and delamination area.

3D Feature-Based Sampled-Data Visual Tracking*

3D feature-based Visual Servoing (VS) on the one hand shows attractive peculiarities, on the other hand it suffers from drawbacks related to the existence of local minima, which may affect the convergence character of the VS control loop. Furthermore, the performance of the visual tracking module may constitute a bottleneck enforcing severe constraints on the workspace and visual task execution speed. In this paper we introduce a novel sampled-data model of the 3D feature-based VS, and, in order to avoid drawbacks due to local minima, we plan the target reference trajectory in the feature space with the aim to constraint the feature error dynamics to remain close to the desired equilibrium point. Then, we propose a novel feature generation based on the homography provided by a template matching algorithm based on the Zero mean Normalized Cross Correlation (ZNCC) and the design of a visual tracking scheme by resorting to the Extended Kalman Filter (EKF) and Lyapunov direct method, which explicitly takes into account the camera velocity limits, while ensuring stability.

Stability with respect to domain of the low Mach number limit of compressible heat-conducting viscous fluid

We investigate the asymptotic limit of solutions to the Navier-Stokes-Fourier system with the Mach number proportional to a small parameter $\rightarrow 0$, the Froude number proportional to $\sqrt{}$ and when the fluid occupies large domain with spatial obstacle of rough surface varying when $\rightarrow 0$. The limit velocity field is solenoidal and satisfies the incompressible Oberbeck–Boussinesq approximation. Our studies are based on weak solutions approach and in order to pass to the limit in a convective term we apply the spectral analysis of the associated wave propagator (Neumann Laplacian) governing the motion of acoustic waves.

Numerical investigation of ballistic impact on multilayered ceramic/metal target plate with or without air gap

The present work is based on numerical simulations of the ballistic behavior of multilayered alumina/aluminum armor plates of varying thicknesses against normal impacts of ogive-nosed steel projectiles. The numerical simulation and the associated models have been validated against published experimental results. A total of nine distinct combinations of ceramic–metal armor plates are impacted normally at different strike velocities, ranging from 200 to 1200 m/sec to determine the residual velocities and ballistic limit velocities of the projectile for each combination of target plate. In a few circumstances, a small air gap has been considered in a combination to compare its ballistic performance to that of a target without an air gap. The optimal ratio of ceramic in a ceramic metal bilayered target plate is determined numerically. This article visualizes the progressive damage of target plates and projectiles at various strike velocities to explore the effects of thicknesses and relative positions of ceramic layers in ceramic/metal armors of a given total thickness in terms of ballistic limit velocity, deformation, and damage of the projectile and target plate.

Experimental-numerical study on ballistic impact behavior of 316L austenitic stainless steel plates against blunt and ogival projectiles

316L austenitic stainless steel (ASS) is the standard reference material in fabricating pressurized hydrogen storage tanks due to its low hydrogen embrittlement sensitivity and excellent corrosion resistance. Ballistic performance of such tanks is of course a concern of safety. In this study, ballistic impact behavior of 316L ASS was studied against blunt and ogival nose shaped projectiles within impact velocity range of 160.3–324.1 m/s. Ballistic impact behavior of 316L ASS is sensitive to nose shapes of projectiles. For targets against blunt projectile, shear plugging with ejected plugs is observed, and target deflection is limited; for targets against ogival projectile, failure mode is ductile hole enlargement, small bulge and some fragments are observed on front and rear sides of targets, respectively. Ballistic limit velocities (BLVs) for two projectiles are respectively 180.9 m/s and 333.5 m/s, indicating better energy absorption against ogival projectile. Numerical simulations of ballistic impact tests were carried out using either the Lode independent MJC or the Lode dependent modified Mohr-Coulomb (MMC) fracture criterion. Numerical prediction by the latter is more accurate than the former as ballistic impact tests are dominated by stress state where Lode parameter is strong enough to cause a big difference between MMC and MJC criteria, and fracture behavior is accurately predicted by the latter but overestimated by the former.

Failure analysis of composite plate under ballistic impact

Numerical models were used to evaluate the ballistic impact of common armour steel plates of medium thickness by give-nosed bullets travelling at explosive velocity. To understand the behaviour and breakdown of the material under impact situations, Johnson-Cook material and failure models have been employed. The model constants were derived using data from the authors' prior experimental work done. ANSYS 2019 R3 was used to simulate the situation. The penetration phases have been anticipated. The simulation findings were used to establish residual velocities, ballistic limit velocity, and perforation timings, which matched experimental data.

Atomistic simulations of distortion-limited high-speed dynamics of antiferromagnetic skyrmions

In antiferromagnetic (AFM) materials, localized self-sustaining states called solitons, namely, domain walls (DWs) and skyrmions, can be efficiently driven by currents and achieve velocities of several kilometers per second. These solitons are massive particles and therefore cannot travel faster than a limiting velocity akin to the speed of light for the material. The specifics of these high-velocity dynamics, in which solitons begin to display relativistic effects, have been well understood for the case of DWs (single-dimensional particles). Here, we perform an extensive and systematic atomistic study of both one-dimensional and two-dimensional soliton dynamics in chiral magnetic materials, both at and away from angular momentum compensation. We develop an elastic restorative force model to explain the dynamic skyrmion deformations, supported by simulation data. We claim that these deformations arise from a local imbalance of gyrotropic forces. We also present an outlook on the role of skyrmion compactness in their deformation patterns, velocity limits, as well as the absence of behaviors similar to ones observed in relativistic DWs. We claim that limits on skyrmion compactness also impede their ability to reach the velocity regime where relativistic effects begin to occur in rapidly moving DWs, due to the critical skyrmion breakdown behavior. These results could prove to be significant to the field of spintronics, as well as the potential applications of skyrmions for novel logic and memory devices.

Effect of ignition energy on combustion characteristics of flammable working fluids

Working fluids with low global warming potential (GWP) will play an important role in the research and development of alternative working fluids for organic Rankine cycles and refrigeration cycles. However, the flammability of low GWP working fluid limits their development, and the energy of typical fire sources has a significant impact on their safe application. At present, there is a lack of relevant research on the effect of ignition energy on their flammability. In this paper, the effect of ignition energy on the combustion characteristics for propane (R290), fluoroethane (R161), 1,1-Difluoroethane (R152a), and 3,3,3-Trifluoropropene (R1243zf) was studied using a variable ignition energy system. The initial flame propagation process, flammability limit, and burning velocity were tested and analyzed in the range of 50 mJ to 20 J. The results showed that with the increase of ignition energy, the lower flammability limit (LFL) decreased and the upper flammability limit (UFL) increased, but their rate of change decreased with the increasing ignition energy. The effect of ignition energy on the flammability limit of R1243zf was significantly greater than that of the other three working fluids. In addition, the effect of ignition energy on flame propagation was mainly limited to the initial stage, and the burning velocity was independent of ignition energy. The mechanism of ignition energy on combustion characteristics was obtained. The research results have guiding significance for the safe application of flammable working fluids.

Ballistic resistance of high-strength armor steel against ogive-nosed projectile impact

The advanced high-strength armor steel with the superior strength-to-weight ratio can extremely improve the ballistic resistance and mobility of military equipment and structures. Aiming to assess the ballistic resistance including the ballistic limit and failure modes of two types of advanced high-strength armor steels, the projectile perforation test and numerical simulations were conducted. Firstly, ten shots of 15 mm-caliber ogive-nosed projectile perforation test were performed under the initial impact velocities of 164–428 m/s. The failure mode and out-of-plane displacement (OPD) response of target plate were recorded by utilizing the high-speed 3D digital image correlation system. Then, the classical finite element (FE) and mesh-free Smoothed Particle Galerkin (SPG) methods were adopted to conduct the numerical simulations, respectively. The predicted residual velocities of projectile were compared with the test data to verify the accuracy of the calibrated constitutive model parameters and numerical analysis approaches. By further comparing the failure modes and OPD–time histories of target, it was drawn that the FE method is preferable to reproduce the failure mode of target, while the SPG method is recommended to quickly predict the residual velocity of projectile. Finally, by adopting the validated numerical analysis approach, the residual velocities for two types of high-strength armor steels under the initial impact velocity range of 150–600 m/s were obtained. The reliabilities of the existing seven analytical models in predicting the ballistic limit and residual velocity for high-strength armor steels were further evaluated.

The electrophoretic motion of cylindrical macroions inside a nanochannel using molecular dynamics simulation

This paper examines the electrophoretic motion of a cylindrical macroion floating in a solution of water and NaCl inside a silicon nanochannel using molecular dynamics simulation. The aim is to investigate the effects of parameters like free movement, initial orientation, shape, aspect ratio, surface charge density and initial electrical charge of macroion on the electrophoretic motion. Findings suggest that any increase in surface charge density could give a rise to electrophoretic velocity of the solution. Considering the macroion free to move around, initial orientation does not play significant role in final results. Results also imply that macroion’s velocity does not change steadily by variations in surface charge density which is because of the multilayer structure of the Stern layer. Finally, average electrophoretic velocity of the solution for all scenarios in this study is witnessed to be the same. However, maximum electrophoretic velocity could be four times greater than average values. This must be taken into account in applications with limited maximum velocity.

Ballistic perforation resistance of elastomer-metal laminate plates

This study investigates the effect of polyurea coating on the ballistic resistance of polyurea-steel laminate plates. Ballistic tests are carried out to compare the residual velocities and failure modes of the monolithic steel plate and polyurea-steel laminate plates on an equal mass basis. Experimental results show that polyurea coating could lead to an enhanced ballistic resistance of the laminate plate (with 5.2% greater ballistic limit velocity), but only when applied at the impact-receiving face. Finite element simulations are performed to provide insights into the penetration process and the energy partitioning to reveal the enhancing mechanisms of the frontal polyurea coating. Excellent agreement was obtained between the numerical simulations and the experimental results. Simulation results suggest that the frontal polyurea-coating has a cushioning effect to alleviate and redistribute the total contact force acting on the substrate steel layer, which helps to spread the local impact to a far-field response. The polyurea-coating on the impact-receiving face provides additional ballistic resistance by promoting greater energy dissipation of the steel layer through global deformation.

Experimental and numerical study on ballistic resistance of aluminum foam sandwich panel considering porosity and dimensional effect

Sandwich panels have been widely used in various industries due to their high strength and energy absorption capacity. In this study, the ballistic behavior of a sandwich panel comprised of two aluminum face-sheets and an aluminum foam as the sandwich core is studied. The panels are constructed and subjected to the blunt-nosed projectile. The experimental test consists of a sandwich panel with three different ranges of foam densities and two thicknesses for the panels beside hardened steel projectiles. Then, numerical simulations of the projectile perforation in the panels are conducted that are in good agreement with the experiments. The failure mechanism of the sandwich panels is investigated and the role of foam core is discussed. Failure mechanism and the amount of plug depends on foam density and projectile velocity, such that different failure mechanisms such as plugging, petaling, and dishing occurred for the face-sheets. After that, the ballistic limit velocity (VBL) of sandwich panels was calculated via experiments and finite element simulations. The experiments and simulations showed that increasing the density and thickness of the foam core generally leads to an increase in VBL. Finally, we study the panels with the constant mass and (or) constant height with different foam densities and the effect of foam density is investigated in these cases.

Ballistic tests on hot-rolled Ti-6Al-4V plates: Experiments and numerical approaches

Superior ballistic performance and the lightweight character of Ti alloys are considered as main reasons for their use in armour applications against a broad spectrum of ballistic threats, e.g. bullet, fragment or blast impact. Because dynamic loading caused by typical penetrators is characterized by high strain rates, only specific test methods allow a closer investigation of the respective material behaviour. In the present study, quasi-static and dynamic compression tests as well as ballistic tests were conducted on a two-phase α+β alloy Ti-6Al-4V (in m%) manufactured by hot-rolling. Post-deformation heat treatments, influencing microstructure and mechanical properties were applied in order to compare three different microstructural configurations: as-rolled, mill-annealed and bimodal. While, on the one hand, ballistic tests were employed for the determination of the ballistic limit velocity v50, compression tests, on the other hand, delivered essential input parameters for the application of the Johnson-Cook constitutive model in a finite element simulation of the impact event. The comparison of experimental results to simulation results was supplemented by means of microstructural characterization of tested samples with the focus set on the prevalently observed deformation and damage mechanisms, as for example adiabatic shearing.