Pulse Loading Research Articles

Analysis of Anomalous Dynamic Responses of Fiber Metal Laminates Under Pulse Loading

Composed of metallic layers and composite plies, fiber metal laminates (FMLs) combine inherent advantages of metals and composites. The phenomenon of anomalous response behavior, in which the permanent deformation is in the opposite direction to the incoming pressure wave, has been discovered in dynamic responses of monolithic plate subjected to impulsive loading. In this study, dynamic responses of FML plates of various configurations are examined and compared against the responses of a monolithic plate using finite element analysis. It is found that under the load condition in which an anomalous dynamic behavior of an aluminum plate is observed, FMLs oscillate a few cycles before resting on permanent deformation, and the laminate thickness strongly affects the final deflection, which could be in the counter-intuitive direction or near the initial position of zero deflection depending on configuration and specification of FMLs. In addition, interaction of damage accumulation with deflection responses is investigated. The findings of this study can be useful for optimal design of FMLs intended for usage under extreme loadings.

Design features of negative feedback and power smoothing filter of the DC / DC converter with pulse loads for transmitter-receiver modules of active electronically scanned arrays

The fundamental difference of the voltage converter of the secondary power supply source for the transmitter-receiver modules of active electronically scanned arrays with impulse load and variable duty cycle from traditional voltage converters that constantly consume power from the primary network is shown. Methods for improving the quality of transient processes in voltage converter with constant power consumption during start-up by soft start are not applicable to improve the quality of transients in periodic current pulses caused by a pulsed load. Since any ripples, noises, instabilities in the power supply of the transmitter-receiver modules of active electronically scanned arrays operating in a linear mode lead to parasitic amplitude modulation of the emitted signal and to a deterioration in the quality of selection and target tracking, very strict requirements are imposed on the quality of the transmitter-receiver modules supply voltage (voltage ripple kп ≤ 0,5 %, the amount of overshoot of the output voltage sU ≤ 2 %, etc.). The article shows that such a quality of the output voltage with a pulsed load of the transmitter-receiver modules of active electronically scanned arrays can be obtained using a lower-type voltage converter, with a double-circuit negative feedback for the output voltage and current of the inductor, with a storage capacitor and with a power smoothing filter with the characteristics of Chebyshev and Butterworth. The work investigated the influence of the negative feedback depth on the output voltage and current of the smoothing filter choke, the value of the storage capacitor capacity, the type and parameters of the smoothing filter, and recommendations were given to select their optimal values, at which the required quality of the supply voltage for the transmitter-receiver modules of active electronically scanned arrays was ensured, taking into account the minimization of their dimensions.

Features of synthesis of ekranoplane control systems

The article deals with the theory of designing ekranoplane control systems, taking into account the features of their dynamic properties and operating conditions. Flying at low altitude over an uneven surface is accompanied by powerful periodic and pulse loads caused by the roughness of the underlying surface. In addition, with small changes in altitude, the controllability and stability of the ekranoplane changes significantly up to loss of stability. For the synthesis of the ekranoplane control system, a new method for calculating a nonlinear mathematical model of an ekranoplane based on the CFD Comsol Multiphysics and Matlab programs is proposed. The results of simulation are presented.

Beams destruction by explosion of non-contact charges of condensed explosives in water

The analysis of effects of the hydrodynamic field created by the explosion of condensed explosive charge on the simplest construction element in the form of beams in the water is performed. The features of the load due to the location of the beam in the water are taken into account by the attached mass introduction. The classical condition of the element destruction is used, according to which it is necessary that the stress in the element is greater than the ultimate resistance of the material and refined of O.E. Vlasov’s formula on the proportionality of the bending moment to the acting explosive load pulse is used.

Usability of Ultrasonic Frequency Testing for Rapid Generation of High and Very High Cycle Fatigue Data.

Ultrasonic fatigue testing is an increasingly used method to study the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of materials. Specimens are cycled at an ultrasonic frequency, which leads to a drastic reduction of testing times. This work focused on summarising the current understanding, based on literature data and original work, whether and how fatigue properties measured with ultrasonic and conventional equipment are comparable. Aluminium alloys are not strain-rate sensitive. A weaker influence of air humidity at ultrasonic frequencies may lead to prolonged lifetimes in some alloys, and tests in high humidity or distilled water can better approximate environmental conditions at low frequencies. High-strength steels are insensitive to the cycling frequency. Strain rate sensitivity of ferrite causes prolonged lifetimes in those steels that show crack initiation in the ferritic phase. Austenitic stainless steels are less prone to frequency effects. Fatigue properties of titanium alloys and nickel alloys are insensitive to testing frequency. Limited data for magnesium alloys and graphite suggest no frequency influence. Ultrasonic fatigue tests of a glass fibre-reinforced polymer delivered comparable lifetimes to servo-hydraulic tests, suggesting that high-frequency testing is, in principle, applicable to fibre-reinforced polymer composites. The use of equipment with closed-loop control of vibration amplitude and resonance frequency is strongly advised since this guarantees high accuracy and reproducibility of ultrasonic tests. Pulsed loading and appropriate cooling serve to avoid specimen heating.

Load Characteristics in Taylor Impact Test on Projectiles with Various Nose Shapes

This study focused on the impact load produced by a projectile and its potential application in the Taylor impact test. Taylor impact tests were designed and carried out for projectiles with four types of nose shapes, and the impact deformation characteristics and variation of the impact load as a function of the nose shape and impact velocity were studied. The overall high g loading experienced by the projectile body during the impact was discussed, and based on classical Taylor impact theory, impact analysis models for the various nose-shape projectiles were established and the causes of the different impact load pulse shapes were analyzed. This study reveals that the nose shape has a significant effect on the impact load waveform and pulse duration characteristics, while the impact velocity primarily affects the peak value of the impact load. Thus, the loading of specific impact environments could be regulated by the projectile nose shape design and impact velocity control, and the impact load could be simulated. Research results support the assumption that the Taylor impact test can be applied to high g loading test.

Random vibration of pretensioned rectangular membrane structures under heavy rainfall excitation

This paper analytically and experimentally investigates the random vibration problem of pretensioned rectangular membrane structures under heavy rainfall. An analytical model is firstly proposed. In this model, the heavy rainfall is modeled as a series of discretized pulse load whose amplitude follows the non-Gaussian distribution; then, the nonlinear governing equation and corresponding Fokker Planck Kolmogorov (FPK) equation of membrane structures are derived and solved by the perturbation method, considering both the geometrical nonlinearity of structure and the non-Gaussian type of load; consequently, the analytical solutions of the probability density function (PDF), mean and standard deviation of displacement response can be obtained. An artificial heavy rainfall experimental system is then developed. This system is used to (i) verify the analytical model and (ii) evaluate the effects of rainfall intensity, pretension level, and material properties. The results show that the displacement follows the significant non-Gaussian distribution and proves strong nonlinear characteristics with increasing rainfall intensity and pretension. The proposed analytical model can guide engineers to design membrane structures from the perspective of probability.

Wind-Induced Vibration Control of High-Rise Structures Using Compound Damping Cables

Based on the vibration reduction mechanism of compound damping cables, this study focuses on the wind-induced vibration control of high-rise structures with additional mass at the top. The differential equation of motion of the system under the action of the composite damping cable is established, and the analytical solution of the additional damping ratio of the structure is deduced, which is verified by model tests. The vibration response of the structure under the action of simple harmonic vortex excitation and randomly fluctuating wind loads is studied, and the effect of different viscous coefficients of the dampers in the composite damping cable and different installation heights of the damping cable on the vibration control is analyzed. The results show that a small vortex excitation force will cause large vibrations of low-dampened towering structures, and the structure will undergo buffeting under the action of wind load pulse force. The damping cable can greatly reduce the amplitude of structural vibration. The root means square of structural vibration displacement varies with damping. The viscosity coefficient of the device and the installation height of the main cable of the damping cable are greatly reduced.

Linear–Nonlinear Optimal Step Control for 1-kV SiC LLC Converters With Pulse Loads

The linear–nonlinear step load control is proposed to meet the requirements of the pulse load. The nonlinear optimal step control from absolute no-load to full-load is able to force the converter to reach the full-load steady-state operation point with the minimum output voltage drop and minimum settling time. The key is to calculate the initial switching frequency and the duty cycle of the first switching period depending on the load condition. The proposed method is realized by analytic geometry analysis on the state trajectory and confirmed in a 6.6-kW 1-kV/48-V SiC <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter. From no-load to full-load, the output voltage drops by 2.24 V and the settling time is 0.76 ms, which reduce by 18.8% and 79.3% compared with the conventional linear control, respectively. Under 100-Hz pulse load with the duty cycle of 30%, the output voltage drop is limited within 2.30 V and overshoot by 1.68 V.

Interaction between Hydraulic Fracture and Pre-Existing Fracture under Pulse Hydraulic Fracturing

Summary Pulse hydraulic fracturing technology can greatly improve the effect of fracture propagation in rock and form complex fracture networks in reservoirs. The interaction mechanism between hydraulic fractures and pre-existing fractures under pulse hydraulic pressure is unclear. The induced laws of pre-existing fractures on the propagation direction of hydraulic fractures under different pulse frequencies and pulse hydraulic pressures are revealed in this work. We have carried out traditional hydraulic fracturing (THF) tests and pulse hydraulic fracturing tests with rock-like specimens. We compared the interaction between hydraulic fractures and pre-existing fractures in the two hydraulic fracturing tests. Acoustic emission (AE) characteristics of the interaction between hydraulic fractures and pre-existing fractures during pulse hydraulic fracturing are analyzed. The results show that pre-existing fractures in the rock-like specimen can induce the direction of propagation of hydraulic fractures. The influence of pre-existing fracture tips on hydraulic fracture propagation is greater with low pulse frequencies than with traditional hydraulic pressures and high pulse frequencies. When the pulse frequency is 1 Hz, hydraulic fractures are easily induced by pre-existing fracture tips. With increasing pulse frequency, the hydraulic fracture propagation direction gradually moves away from the pre-existing fracture tips and extends perpendicularly to the direction of the minimum principal stress. Under pulse hydraulic loading, more hydraulic fractures are generated around the wellbore than under THF and extend to the pre-existing fracture, and more hydraulic fractures around the wellbore are created with low-frequency pulse loading than with high-frequency pulse loading. Compared with traditional hydraulic pressures, hydraulic fracture propagation with low pulse frequencies (1 and 3 Hz) is more complex than hydraulic fracture propagation with traditional hydraulic pressures and high pulse frequencies (5 Hz). Under high pulse hydraulic pressure and pulse frequency, hydraulic fractures easily extend along the direction perpendicular to the direction of the minimum principal stress like propagation under traditional hydraulic pressure. The study of the interaction mechanism between hydraulic fractures and natural fractures under pulsating hydraulic pressure can provide a method for the formation of fracture network systems in large-scale fracturing and may improve the fracturing efficiency.

Nanostructuring of Iron Disulfide Cathode Materials for Enhanced Thermal Batteries

For the U.S. Department of Defense, high-performance power sources are a critical technology for current and future gun-fired munitions. Molten salt thermal batteries are the reserve power source of choice for many weapon systems due to their high power density, proven long shelf life, and capability to function across a wide range of operating environments. The incorporation of nanomaterials into thermal battery components offers the potential to produce batteries with performance improvements, such as higher voltages at increased current densities. In this study, nanoscale iron disulfide (FeS2) was synthesized using a fully scalable, high energy milling method, and characterized utilizing SEM, XRD, ICP-OES, BET surface area analysis, TGA-DSC, and other techniques. Nanostructured cathode mixtures containing the nanoscale FeS2 and LiCl-KCl eutectic salt electrolyte were pressed into electrode pellets. Their electrochemical performance was then characterized as compared to standard FeS2 cathode electrode pellets currently used in industry. Single cell thermal battery discharge testing, polarization type scans, and pulse load capability were used to compare cell performance for better understanding of best-use applications for these materials. Compared to control cells, the cells utilizing nanostructured cathodes provided higher power response, with respect to both voltage and runtime.

Comparison of Laplacian based explicit and implicit gradient elasticity with reference to one-dimensional problems in statics and dynamics

It has been shown previously, that Laplacian based explicit and implicit gradient elasticity models can be derived as particular cases of Mindlin’s gradient elasticity and Mindlin’s micro-structured (or equivalently Eringen’s micromorphic) elastic materials. Also, they can be established as counterparts of viscoelastic solids, in view of an analogy to linear viscoelasticity based on mechanical elements. The present paper aims to compare responses predicted by the gradient elasticity counterpart of the three-parameter viscoelastic solid with those predicted by the gradient elasticity counterpart of the viscoelastic Kelvin model and by the classical elasticity. The comparison is mainly based on closed form solutions of one-dimensional problems in statics and dynamics. Specifically, the analysis includes static loading, axial vibrations and tension step pulse loading of a bar.

A unified viscoplastic model and strain rate–temperature equivalence of frozen soil under impact loading

Based on the double-pulse shaping technology, a method for obtaining long rising edge loading pulse by using the structural response of a pulse shaper is proposed. The traditional split Hopkinson pressure bar (SHPB) was improved to be suitable for testing the dynamic mechanical properties of low wave impedance materials. The dynamic mechanical properties of frozen soil at different temperatures and strain rates were tested using the improved SHPB equipment. The increase in the strength of frozen soil was associated with a decrease in temperature and increase in strain rate. The strain rate–temperature equivalence of frozen soil is proposed by regression analysis of the experimental data. The relationship between the temperature and strain rate of frozen soil satisfied the Arrhenius equation and could be explained by the thermal activation mechanism. The thermal softening characteristics of frozen soil caused by the adiabatic heating under impact loading were analyzed, and described by the damage variable driven by the adiabatic heating. The damage dynamic constitutive model is proposed based on the unified viscoplastic theory. The comparison between the model and experimental results indicate the applicability of the model.

Current Sensorless Microcontroller-Based Battery Management System with SOC and Active Cell Balancing

Battery management system (BMS) has become an important research topic following the trend and development of the electric vehicle. Although research on Active Cell Balancing, SOC, and current estimation has been carried out, the previous work mostly focused on comparing and developing methods. In this research, we demonstrate the process of designing BMS hardware using a low-cost microcontroller and without using a current sensor. The SOC simulation results produce an RMSE of 0.0832% for the 100% -10% SOC-OCV curve, and the current estimation simulation produces an RMSE of 0.2576 A, while for testing using a 6-ohm pulse load, the RMSE error value is 0.3960 A. The Active Cell Balancing method was successfully performed in simulation with Simulink. Furthermore, our simulation and test results suggest that complex battery models and multiple SOC-OCV curves can be used for better current and OCV estimation results. Our experimental results are also useful to develop a guideline to design a microcontroller-based BMS.

Швидкість деформації, рухливості атомів і механічні властивості металів

The dependences of diffusion coefficients in metals with different crystal lattice (b.c.c., f.c.c., h.c.p., b.c.t.), subjected to pulse effects by different types of processing in a wide range of strain rates (10-2 - 106 s-1) without heating and at T &lt; 0,5 Tpl. studied by m ethods based on the use of radioactive indicators 55Fe, 95Nb, 60Co, 65Zn, 63Ni, 26Al, 44Ti (layer-by-layer radiometric analysis of residual integral activity, macro- and microautoradiography). Used such types of processing as ultrasonic shock treatment, diffusion welding, shock load, magnetic pulse processing, etc. On the same materials subjected to the same types of processing, mechanical characteristics (impact strength, microhardness, tensile strength, etc.) were determined. In addition, literature data related to the determination of some mechanical characteristics in the deformation of metals at different speeds were used. It turned out that with increasing the rate of plastic deformation there is not only an increase in the mobility of atoms, but also a decrease in differences in the values of the diffusion coefficients of intrinsic atoms and other diffusers in different metals. Despite the large difference in melting temperatures, in particular zinc and niobium, their self-diffusion coefficients in the migration of atoms without heating at a rate of 106 s-1 differ only 1.5 times, while at 1 s-1 the difference in the mobility of atoms is 4 orders of magnitude. It is shown that the velocity dependences of diffusion and mechanical characteristics can be rectilinear, have extremum or inflection, but they will be approximately the same for diffusion coefficients and parameters that characterize the mechanical properties of metals under impulse loads. Establishing the type of velocity dependences for diffusion and mechanical characteristics makes it possible to determine intermediate and extrapolated values for both characteristics, as well as on the schedule of one dependence to predict the shape of the other with a certain accuracy. Keywords: radioactive isotopes, self- and heterodiffusion, pulse loads, strain rate, mechanical characteristic.

Pulsed-Power Load Monitoring for an All-Electric Ship: Utilizing the Fourier Transform Data-Driven Deep Learning Approach

Future Naval Advanced Weapon and sensor loads require high power density power electronic distribution systems (PEDs) to be viable. The mission-defined electronic loads, such as advanced radar and pulsed-power weapons, tend to have an irregular power draw, consume a significant amount of power, and would require significant additional generation equipment well beyond the existing power system. A legacy low-voltage ac power grid on a destroyer is already at capacity and because space is at a premium, it is unlikely that any new power-hungry pulse load could be included without a significant paradigm shift. Furthermore, most of the potential power within the vessel is locked to the mechanical drive system and not readily usable as electrical power. As such, the all-electric ship is the intended option to unlock the mechanical power for various high power pulse loads.

The Role of Graphene Admixtures in the Stability of Aluminum Oxide to Brittle Fracture under Pulsed Electrophysical Actions

We report the results of testing the dynamic strength of Al2O3 nanoceramics with different concentrations of five-layer graphene under the action of a high-current nanosecond electron beam and a high-voltage electric discharge of the same nanosecond duration. It is found that, under pulsed loading, an increase in the graphene content in the composite increases the brittleness of the nanocomposite.

Rectangular current pulse generator to test varistors with pulsed electrical load

A brand-new circuit of a rectangular pulse current generator is presented. As a rule, generators consisting of 6-10 LC cells connected in series are used to obtain rectangular current pulses. Such units are very cumbersome and complicated in the selection of element parameters and adjustment, so a new scheme of pulse current generator was proposed. The main difference from the classical circuit is the method of generating a rectangular current pulse, i.e. by adding the currents from two parallel circuits connected to the load. The first circuit at discharge generates an aperiodic current pulse, the second generates an oscillatory current pulse. The total current pulse flowing through varistor has constant amplitude for some time. In a specified period of time, while the current pulse has a constant amplitude, there is an interruption of current with the help of a switching device. The given circuit solution is possible to implement when using fundamentally new switching devices of the IGBT module. A connection diagram of a pulse current generator for testing varistors with a classification voltage to 1200 V with adjustable pulse duration of 50, 1000, 2000 µs is proposed. The parameters of the generator circuit elements are determined. The measures aimed at suppression of overvoltages arising at break of current in circuits with high inductance as well as the tests confirming the operability of the designed circuit are carried out.

Equipment and materials for shock-intermittent cutting

The article considers the shock-intermittent processing method, which is used for cutting blind threads M12x1.5 in nuts made of steel grade X18N9T. Compared to the conventional method, it allows increasing the processing productivity; the durability of the thread taps has increased to 300 holes (with manual thread cutting, the durability of the taps is 100 holes). The method allows mechanizing labor-intensive threading operations. The optimal conditions of processing by this method are determined based on ensuring sufficient strength of the cutting wedge of the tool under repeated loading and, at the same time, creating the most intense impact on the material of the cut layer of the workpiece. The destruction of the processed material on impact most easily occurs at critical deformation rates, which, for instance, equal 60 m/s for corrosion-resistant steel. This leads to an overestimation of the impact pulse values, and consequently, chipping of the cutting edges of the tool. Therefore, for these processing conditions, there is an optimal value of the pulse load transmitted by the spindle to the tool. For threads M10 and M12 with pitches of 1.25 and 1.5 in parts made of steel grades X18N10T, the best results are achieved at loads corresponding to the increment of the dynamic moment of the driven bushing with the tool. At high pulse loads, the durability of the working tool is sharply reduced, and at lower loads, the cutting performance is reduced. One of the positive features of shock-intermittent cutting is the presence of breaks that facilitate the operation of the cutting wedge due to the better penetration of the coolant. Therefore, shockintermittent cutting is carried out at more intensive modes than conventional continuous cutting. However, the tool life does not decrease as a result, but even increases. The relative length of the cutting area, determined by the angle, should be chosen based on the fact that the temperature in the cutting area does not have time to reach its steady value, equal to the cutting temperature during the normal long-duration cutting, carried out continuously.

Experimental analysis of dual-rotor-support-casing system with blade-casing rubbing

Vibration features of inner rotor and casing of a dual-rotor-support-casing (DRSC) system with rubbing existing between blade and casing are analyzed in this work. First, an improved model for analyzing rubbing between blade and casing is presented, in which the kinetic energy of the blade, the deformations of blade and casing are considered. Second, a finite element model of the DRSC system is built as well as the motion equations, where unbalance and time-varying pulse load is considered. Third, natural frequencies and modes, acceleration responses of the casing, and inner rotor of the system with blade-casing rubbing faults are obtained. Finally, the blade-casing rubbing experiments are implemented on the dual-rotor-support-casing test rig, compared with dynamics analysis. The results indicate that (i) the improved rubbing model is more accurate in describing the impact of rubbing between blade and casing; and (ii) the components of impact frequency and the coupling frequencies are prominent when blade-casing rubbing occurs and validated by the experimental results.