Fragment Velocity Research Articles

New insights into real-time detection of tephra grainsize, settling velocity and sedimentation rate

Characterizing the size and settling velocity of pyroclastic fragments injected into the atmosphere during volcanic eruptions (i.e., tephra) is crucial to the forecasting of plume and cloud dispersal. Optical disdrometers have been integrated into volcano monitoring networks worldwide in order to best constrain these parameters in real time. Nonetheless, their accuracy during tephra fallout still needs to be assessed. A significant complication is the occurrence of particle aggregates that modify size and velocity distributions of falling tephra. We made the first use of the Thies Clima Laser Precipitation Monitor (LPM) for tephra-fallout detection at Sakurajima volcano (Japan), which is characterized by a lower size detection window with respect to more commonly used disdrometers (e.g., Parsivel2) and can more easily distinguish different falling objects. For the first time, individual particles have been distinguished from most aggregates based on disdrometer data, with the potential to provide useful grain-size information in real time. In case of negligible aggregation, LPM and collected sample-based estimates are in agreement for both grain-size and sedimentation rate. In case of significant aggregation, particle shape analyses and a dedicated drag equation are used to filter out aggregates from LPM data that also provide good agreement with collected tephra samples.

Lead spall velocity of fragments of ultra-high-performance concrete slabs under partially embedded cylindrical charge-induced explosion

When an explosion occurs close to or partially within the face of a concrete structure, fragments are rapidly launched from the opposite face of the structure owing to concrete spalling, posing a significant risk to nearby personnel and equipment. To study the lead fragment velocity of ultra-high-performance concrete (UHPC), partially embedded explosion experiments were performed on UHPC slabs of limited thickness using a cylindrical trinitrotoluene charge. The launch angles and velocities of the resulting fragments were the determined using images collected by high-speed camera to document the concrete spalling and fragment launching process. The results showed that UHPC slabs without fiber reinforcement had a fragment velocity distribution of 0–118.3 m/s, which are largely identical to that for a normal-strength concrete (NSC) slab. In addition, the fragment velocity was negatively correlated to the angle between the velocity vector and vertical direction. An empirical Eq. for the lead spall velocity of UHPC and NSC slabs was then proposed based on a large volume of existing experimental data.

The study on laser composite processing of pre-controlled crack in low carbon steel

To improve the initial velocity and damage effect of the pre-controlled fragments, and to ameliorate the processing method of the fragment shells, this study describes the laser composite experiment for processing low-carbon steel controlled-fragmentation by prefabricated cracks, and the cracks are used to realize the manufacture of pre-controlled fragments with low-carbon steel as the shell. The objective of this paper is to study the processing of prefabricated cracks on the surface of low carbon steel and the fracture mode of cracks. In the research, firstly, the low carbon steel was laser cladding brittle materials to modify the surface and obtain a brittle cladding layer, afterwards, laser alloying treatment was performed on the modified area to make the melting zone morphology uniform and symmetrical, and finally after the laser deep penetration treatment, metal cracks meeting the requirements were produced in the melting zone under the influence of multiple factors. The formation process and fracture mode of this kind of crack were studied, and the results show that the increase in carbon equivalent of the weld caused by the addition of alloy materials is the main reason for the cracks. The melting zone after laser treatment produced changes in metallographic structure, and the main structure in the melting zone is lath martensite, with an average hardness of 700–1000 HV, and cold cracks were produced under large residual stress. Research on the fracture surface found that the upper middle part of the melting zone containing Fe2W phase is the origin of cracks, its fracture feature is mainly quasi-cleavage fracture, and the crack propagation zone in the lower half of the melting zone is characterized by intergranular fracture. The crack ends in the heat-affected zone with lower hardness. This research has realized the controllable prefabricated crack manufacturing on the surface of low-carbon steel and provides technical and theoretical support for laser manufacturing of low carbon-steel controlled fragmentation.

Reconstruction of ejecta field based on photon Doppler velocimetry from shock-loaded samples in vacuum

Photon Doppler velocimetry (PDV) has been extensively used to measure the velocity of single objection or fragments under the impact; however, with the PDV measurement, how to recover the ejecta field, which is a high-velocity multiple-particles system, remains a challenge. Mie theory is applied to describe the light-particle scattering process, and Monte Carlo algorithm is introduced to simulate PDV spectrums. By the simulations, how the PDV spectrum is qualitatively influenced by the velocity profile, particle size, and total area mass of ejecta is revealed. Then a novel optical model is proposed to derive the quantitative relationships between these ejecta parameters and PDV spectrum characteristics. With this model, the ejecta parameters can be extracted from PDV spectrum directly. Estimated values of the ejecta parameters from experimental spectrum are in good agreement with those measured by piezoelectric probe.

Effect of Aluminum Powder Content on Air Blast Performance of RDX-Based Explosive Grenade Charge

For aluminized explosive, the charge performance of explosive grenade is very significant for promoting their application. Firstly, the detonation performance of cyclotrimethylenetrinitramine (RDX) based explosives with different aluminum powder (0%, 20%, 25%, 30%, 35%, and 40%, respectively) content was investigated. Next, the air blast tests of RDX-based aluminized explosives were carried out. Then, RDX-based explosive grenade charges of L-1 and L-2 where the aluminum powder content was 20% and 25% were selected for air blast and static blasting fragments velocity tests. Finally, the energy release mechanism of the air blast was deduced via calculation. The results show that RDX-based aluminized explosives have higher detonation heat, detonation velocity, and detonation volume when the aluminum powder content is 20%, and the shock wave over pressure as well as impulse keep a high level at the same time within 4.5 m. The air blast performance of L-1 is better than L-2 within 2.2 m. As the distance increases, the air blast energy of L-1 is mainly used for shell rupture and fragment acceleration, while the contribution of L-2 is less than that of L-1. This study demonstrated that the explosion power of RDX-based explosive grenade charge is the most powerful where the content of aluminum powder is about 20%.

Velocity characteristics of fracture fragments of mica-crystal materials under high-speed impact

Determination of the velocity of individual fragments of a fragmented matter following an impact is necessary for studying the dynamic mechanical properties of materials. Various models descriptive of specific collision cases are used to predict the fragmentation parameters including the velocity of fragments. The models have been mostly designed to describe metallic materials. The research aims at experimental determination of the fragments destruction velocity following an impact against hard-melting non-metallic silicate material (potassium fluorphlogopite). Potassium fluorphlogopite targets have been shaped as flat plates sized 280x160x15 mm. The 23 mm steel ball (Steel 20) was used as a projectile. Four impact tests have been conducted with the following parameters: ball velocity 230 m/s and collision angle 90°; ball velocity 120 m/s and collision angle 90°; ball velocity 230 m/s and collision angle 30°; ball velocity 120 m/s and collision angle 30°. Velocity of burst fragments was determined on the basis of a video recording with Photron Fastcam SA5 high-speed camera. The video has been processed using frame-by-frame image analysis in ImageJ-FiJi software (TrackMate module). The experiment determined the velocities of individual burst fragments following an impact against hard-melting non-metallic silicate material, specifically potassium fluorphlogopite. It has been established that the change in the velocity of fragments in time corresponds to the hyperbolic function; a coefficient has been proposed to calculate the change in the velocity of potassium fluorphlogopite fragments break-off in time.

Experimental determination of fragment dynamics of refractory non-metallic silicate material under high-velocity impact

The individual velocity of rupture fragments after impact is necessary to evaluate how dangerous they are after dispersion. The aim of the study is to experimentally determine the velocity of rupture fragments upon impact on a refractory non-metallic silicate material (potassium fluorophlogopite). The targets made from potassium fluorophlogopite were shaped in the form of flat plates with a size of 280x160x15 mm. A steel ball with a diameter of 23 mm was used as a projectile. Four impact experiments were performed with the following parameters: ball speed of 230 m/s and collision angle of 90°; ball speed of 120 m/s and collision angle of 90°; ball speed of 230 m/s and collision angle of 30°; ball speed of 120 m/s and collision angle of 30°. The velocity of the rupture fragments was determined through video recording obtained using a high-speed Photron Fastcam SA5 camera. The video was processed by analyzing frame-by-frame images using the ImageJ-FiJi. The velocities of individual rupture fragments upon impact on a refractory non-metallic silicate material are experimentally determined using the example of potassium fluorophlogopite. It is established that the nature of the change in the fragment velocity relative to time corresponds to a hyperbolic function and depends on the kinetic energy of the fragments. A coefficient for calculating the change in the velocity of rupture fragments of potassium fluorophlogopite relative to time is proposed.

Measurement of ejection velocity of rock fragments under dynamic compression and insight into energy partitioning

High-speed three-dimensional digital image correlation (3D-DIC) technique was utilised to examine the ejection velocity characteristics of rock fragment in dynamic compression tests . The fragment velocity components of fragment were extracted from velocity fields distributed within the fragment area. By identifying the peak resultant velocity, the initial fragment ejection velocity was determined. The kinetic energy of fragments was evaluated with the initial ejection velocity and the mass of the fragments in each size group. Results show that the fragment movement is successively accelerated by stress-wave propagation, crack opening and Poisson's effect which contribute to the axial, circumferential and radial velocity component of fragment, respectively. The variance in circumferential velocity of two neighbouring fragment areas indicates the formation of fragments. The peak value of radial velocity , which is the chief component in ejection velocity reveals the time when ejection taking place. The initial ejection velocity of fragment gradually decreases with increasing size, but increases significantly as strain rate increases . The kinetic energy of fragments ejection comprises 12%∼24% of absorbed energy at strain rate of 69∼100 s -1 , and the percentage further increases with increasing strain rates. Ignoring the kinetic energy of fragments will lead to overestimation of dissipated energy consumed by rock fragmentation in dynamic compression. • High-speed 3D-DIC was applied to identify three-dimensional velocity patterns of rock fragments under dynamic compression. • Strain recovery, fragment formation and ejection were revealed by velocity components of fragments, respectively. • Ejection velocity of fragment gradually decreases with increasing size, but increases significantly as strain rate increases. • Kinetic energy of fragments ejection takes more than 20% of absorbed energy with the strain rate above 85 s -1 .

Preformed Fragment Velocity Distribution of Elliptical Cross-section Projectile

In the field of warhead design, non-cylindrical warhead, especially elliptical cross-section warhead, has received considerable attention. In this study, the initial velocity and distribution characteristics of the preformed fragments of a columnar projectile with an elliptical cross-section were examined. To obtain the velocity distribution of the fragments in this kind of projectile, three elliptical cross-section projectiles with different geometric sizes were test based on the static detonation tests. Then, the numerical models of the elliptical cross-section projectile have been established and validated according to the experiment results. Besides, two kinds of initiation types were studied by the simulation model, and the results indicate that not only the geometric size but the initiation type do great influences on the fragment velocity distribution in the direction of the axis. An empirical model was proposed based on the fragment two-step acceleration progress, and it was in good accordance with numerical results.

Analiza efikasnosti bojnih glava parčadnog dejstva protiv "mekih" ciljeva

The efficiency of the weapon system has been usually studied by altering the guidance and control or aerodynamics of the missile. This research investigated methods of enhancing the efficiency of the weapon system against soft targets based on the fragmentation warhead design. Different warhead geometric configurations, initiation points, as well as premade fragment material and shapes have been studied to enhance overall weapon efficiency against soft target. The study considered the static fragment distribution and velocity as the base for the analysis. A new vulnerability code has been developed based on the mean area of effectiveness to prove the study using both simulations and field tests. There were significant improvements on the weapon efficiency by altering the warhead parameters. The simulated results showed good correspondence with the test results. The newly developed vulnerability code can be considered as an additional system engineering analysis tool for the calculations of weapon efficiency.

3D optical diagnostics for explosively driven deformation and fragmentation

High-speed, optical imaging diagnostics are presented for three-dimensional (3D) quantification of explosively driven metal fragmentation. At early times after detonation, Digital Image Correlation (DIC) provides non-contact measures of 3D case velocities, strains, and strain rates, while a proposed stereo imaging configuration quantifies in-flight fragment masses and velocities at later times. Experiments are performed using commercially obtained RP-80 detonators from Teledyne RISI, which are shown to create a reproducible fragment field at the benchtop scale. DIC measurements are compared with 3D simulations, which have been ‘leveled’ to match the spatial resolution of DIC. Results demonstrate improved ability to identify predicted quantities-of-interest that fall outside of measurement uncertainty and shot-to-shot variability. Similarly, video measures of fragment trajectories and masses allow rapid experimental repetition and provide correlated fragment size-velocity measurements. Measured and simulated fragment mass distributions are shown to agree within confidence bounds, while some statistically meaningful differences are observed between the measured and predicted conditionally averaged fragment velocities. Together these techniques demonstrate new opportunities to improve future model validation.

Characteristics of micro-explosive dispersion of gel fuel particles ignited in a high-temperature air medium

The characteristics of processes developing during the ignition and combustion of single gel fuel particles with a mass of 10 mg in a high-temperature motionless air medium were investigated by means of a hardware and software system. The system featured a high-speed video camera, LED spotlights and a laptop with commercial and custom software. A group of fuel compositions was derived from oil-filled cryogels alone and with the addition of fine solid combustible components. Polyvinyl alcohol with 10 wt% in an aqueous solution was used as an organic polymer thickener. When exposed to rapid heating, fuel compositions (oil + aqueous solution of PVA + emulsifier; oil + coal dust + aqueous solution of PVA + emulsifier) were characterized by the micro-explosive dispersion of particles. The velocities of fine fragments after the micro-explosive dispersion of a fuel melt droplet were established when the air temperature was varied in the range of 700–1000 °C. The gas–vapor mixture temperature in the region of the fuel gas-phase combustion was determined using the original two-color pyrometry technique.

Critical behavior for impact fragmentation of spherical solid bodies sensitive to strain rate

We consider the impact fragmentation of two spherical solid bodies sensitive to the strain rate in a three-dimensional setting. We use both dimensional analysis and numerical simulations by the smoothed-particle hydrodynamics (SPH) method to shed light on this problem. The key point of the work is the assumption of complete self-similarity of the problem under consideration with respect to the effective strain rate parameter , which is verified by numerical simulations. As a result, we consider the two cases corresponding to high-velocity and low-velocity loading. The size of the system may be characterized by the total number of SPH particles N tot approximating each sphere. It is shown that for the finite system the critical velocity of fragmentation at high-velocity loading exceeds that at low-velocity loading, i.e. V c∞ > V c0. With an unlimited increase in the system size, these velocities become the same. It is shown that V c∞ and V c0 depend on the system size in a quadratic manner, i.e. where ν is a correlation length exponent.

Acceleration of DNA Replication of Klenow Fragment by Small Resisting ForceSupported by the National Natural Science Foundation of China (Grant Nos. 11674381, 21991133, 11774407, 11874415, 11874414, and 31770812), the Key Research Program on Frontier Science (Grant No. QYZDB-SSWSLH045), the National Key Research and Development Program of China (Grant No. 2016YFA0301500), the CAS Strategic Priority Research Program (Grant No. XDB37010100), and

DNA polymerases are an essential class of enzymes or molecular motors that catalyze processive DNA syntheses during DNA replications. A critical issue for DNA polymerases is their molecular mechanism of processive DNA replication. We have proposed a model for chemomechanical coupling of DNA polymerases before, based on which the predicted results have been provided about the dependence of DNA replication velocity upon the external force on Klenow fragment of DNA polymerase I. Here, we performed single molecule measurements of the replication velocity of Klenow fragment under the external force by using magnetic tweezers. The single molecule data verified quantitatively the previous theoretical predictions, which is critical to the chemomechanical coupling mechanism of DNA polymerases. A prominent characteristic for the Klenow fragment is that the replication velocity is independent of the assisting force whereas the velocity increases largely with the increase of the resisting force, attains the maximum velocity at about 3.8 pN and then decreases with the further increase of the resisting force.

A detailed study on the micro-explosion of burning iron particles in hot oxidizing environments

As a promising carbon-free fuel, iron powder can directly combust with air and has great potential to provide clean and high-grad heat for various applications. The combustion characteristics of iron particles are of great significance for developing iron combustion model, designing efficient combustor, and optimizing combustion technologies. In this work, the micro-explosion behavior of burning iron particles was experimentally investigated based on optical diagnostics. With two high-speed cameras operating at 10,000 frames per second, the three-dimensional (3D) motion and mean surface temperature of burning iron particles during the micro-explosion process were measured using the stereo imaging technique and two-color pyrometry, respectively. The probability of micro-explosions in different oxidizing environments were statistically studied. Three distinct micro-explosion modes have been observed. The results showed that the micro-explosion of burning iron particles heavily depended on oxygen concentration. The micro-explosion would slightly reduce the particle surface temperature by 30–70 K within 0.5 ms, since a lot of smaller fragments were produced. In addition, the 3D velocity of most fragments would sharply increase to 2–6 times within 0.2 ms after the micro-explosion occurred. Regarding the mechanism of the micro-explosion, three types of potential gas sources inside the particle were discussed. The sharp gradients of gas temperature and oxygen concentration may facilitate the rapid increase of the internal pressure in the particle, which eventually causes the micro-explosion.

Experimental and numerical simulation study on polyurea-coated fuel tank subjected to combined action of blast shock waves and fragments

Fuel tanks, as core fuel components of many types of mechanical equipment, are highly vulnerable to strong dynamic loads, such as those from explosions and fragments. In this paper, two types of polyurea materials (AMMT-53 and AMMT-55) were designed to enhance the damage resistance of fuel tanks. The mechanical parameters and performance differences of the two polyurea materials were first obtained. On this basis, a series of experiments study on fuel tanks coated with different thicknesses polyurea subjected to a combination of blast waves and fragments were performed. The results showed that these two types of polyurea materials had different protective abilities. The AMMT-53 polyurea could effectively reduce the perforation rate but could not prevent the liquid leakage, while the AMMT-55 polyurea could not significantly reduce the perforation rate, but the self-healing property could effectively prevent the leakage of liquid. The whole process of the shock wave and the fragments acting on the fuel tank was revealed by numerical simulations. From the change of the fragment velocity, the strength of the shock wave in the liquid, and the energy change of the polyurea layer, it was proven that the coated polyurea layers had good protective effects on the fuel tank.

Experimental study on the cavity evolution and liquid spurt of hydrodynamic ram

In research of the characteristics of the cavity evolution, the pressure, and the liquid spurt in hydrodynamic ram, the experiment of the high-velocity fragment impacting the water-filled container had been conducted. The relationships between the above three characteristics have been researched. The evolution of the cavity can be divided into three processes according to its shape characteristics. The first liquid spurt occurred in Process Ⅱ and the rest of it occurred in Process Ⅲ. The duration of the second liquid spurt is longer than the first liquid spurt. When the impact velocity of the fragment is less than 996 m/s, the velocity of the second liquid spurt is the highest. When the velocity of the fragment is greater than 996 m/s, the velocity of the first liquid spurt is the highest. The maximum velocities of the first and second liquid spurt are 111 m/s and 94 m/s respectively. The pressure fluctuated sharply in Processes Ⅰ and Ⅲ. The maximum peak pressures in the shock and the cavity oscillation phases are 15.51 MPa and 7.96 MPa respectively. The time interval of the two adjacent pressure pulses increases with the increase of the fragment velocity.

Effect of inflow conditioning for dry powder inhalers

The transport of pharmaceutical dry powder inside an optically accessible inhaler-like device is studied using both macro- and microscopic high-speed imaging. The investigation aims to systematically study the effect of inflow modifications on the dispersion characteristics of agglomerates inside a dry powder inhaler (DPI) geometry. An inhaler device was designed with geometrical features akin to commercial inhalers used in the current market and research oriented inhalers such as the Twincer®: two offset inlet channels (one with a powder pocket), a clockwise swirling chamber and a single outlet channel. At the device outlet, a vacuum pump was fitted with an actuator and calibrated to achieve a steady state inhalation with a peak flowrate of 85 and 125 L/min. Airflow conditions at the intake of the device were strategically perturbed in order to induce powder fluidisation and dispersion using turbulence grids and through physically obstructing channel streams in order to achieve changes in flow behaviour (e.g., flow separation). Complete fluidisation of the powder bed was observed with image processing enabling statistics on de-agglomerated fragment size and velocity. A range of behaviour was noted including local turbulence through introduction of a grid, bimodal fragment size behaviour for cohesive mannitol powder, as well as introduction of low velocity zones in the device through flow splitting. The geometry enables simple systematic study of inflow conditions into a DPI-like device with the data being useful for study of a given powder formulation (mannitol) and validation of computational models.

Double casing warhead with sandwiched charge to produce multiple fragment groups for sequential hits: Concept and analysis of fragment velocity

This work introduces a novel fragmentation warhead that can produce two groups of fragments with different velocity characteristics and strike the target sequentially. The two groups of fragments come from two separate casings in one warhead, and the different velocities of fragments from different groups are attained by having a charge compartment sandwiched between the two casings in the warhead. A theoretical analysis formula is established to predict the maximum velocity of fragment from each casing based on energy balance. The results of X-ray radiography experiment and 3D smooth-particle hydrodynamics numerical simulation indicate that the proposed formula is accurate and reliable in calculating the fragment velocity as long as the thickness of the inner casing is less than 30% the radius of the inner charge. The fragment velocities of warheads with different structure are further analyzed, and the results show that the fragments of the two casing exhibit greater disparity in their maximum velocity when more charge is packed in the sandwiched compartment instead of enclosed in the inner casing.

Research on Damage Characteristics of Brick Masonry under Explosion Load

As the main structural component of partition wall or load-bearing wall, brick masonry has been widely used in construction engineering. However, brick and mortar are all brittle materials prone to crack. Nowadays, fireworks, gas stoves, high-pressure vessels, and other military explosives may explode to damage nearby structures. Many explosion casualties had shown that the load-bearing capacity of brick masonry decreased dramatically and cracks or fragments appeared. Previous studies mainly focused on noncontact explosion in which shock wave is the main damage element. In fact, the response and damage effect of brick masonry wall under contact explosion are more complex, which attracts more attention now. In order to explore the damage characteristics of brick masonry under explosion load, a series of simulations and verification experiments are conducted. RHT and MO granular material models are introduced to describe the behaviour of brick and masonry, respectively, in simulation. The combination effect of front compressive wave and back tensile wave are main factors influencing the breakage of masonry wall. The experimental results are well in accordance with the simulation results. The front cross section dimension of crater is closely related to the radius of spherical explosive charge. A power function predictive model is developed to express the relationship between the radius of hole and the radius of explosive. Furthermore, with increasing the quantity of explosive charge, the number and ejection velocity of fragments are all increased. The relationship between maximum ejection velocity and the quantity of explosive also can be expressed as a power function model.