Total Impulse Research Articles

Influences of various thermoplastic veil interleaves upon carbon fiber-reinforced composites subjected to low-velocity impact

Throughout their service life, composite materials may be subjected to impact loads, which can result in some damage mechanisms that cause degradation in mechanical and dynamic responses. Especially matrix-induced cracks and delamination can have significant effects on the final properties, and cause serious problems if the necessary precautions are not taken. In the current study, Carbon Fiber-Reinforced Polymer (CFRP) composites interleaved with Fine Glass (FG), Polyetherimide (PEI), Polyetheretherketone (PEEK), Polyimide (PI) and Poly-Phenylene Sulphide (PPS) thermoplastic veils were fabricated, and exposed to LVI tests under 25.2 J constant impact energy to determine how veils affect the dynamic properties. The selected veils are commercially available materials and are used for various purposes. In this regard, it was aimed to examine the usability of these commercially available veils as interlayers and to examine the impacts of the veils used as interlayers on the LVI characteristic of CFRP composites. According to the present study, it was found that veil interleaves significantly affect the composite stiffness, and accordingly, relevant LVI responses such as total impulse, bending stiffness, interaction times etc. For instance, approximately 21.2% reduction in the peak displacement and 73.23% increment in the bending stiffness were observed due to FG veil interleaves. On the other hand, when the effects of veil types were examined, the maximum and minimum variations in the LVI responses were observed for the FG and PEI interleaves, respectively, and FG veils were found to be the most effective veil types for the CFRP composites. It was also revealed that veil interleaves strengthen the interlaminar region between plies and delamination resistance, and thereby improved the Delamination Threshold Loads for all configurations.

On-orbit mission overview of the low power hall thruster propulsion system aboard venμs satellite

Venμs is a satellite launched in 2017, for super-spectral Earth imaging and Electric Propulsion System (EPS) demonstration. In this paper we overview EPS design and operation throughout all five mission phases, from open/closed-loop orbit control, through orbit descent (720 → 410 km), orbit maintenance under high drag environment, to orbit raising (410 → 560 km). The EPS consisted of two throttleable Hall thrusters, PPU, Propellant Management Assembly (PMA), and a 9 L propellant tank carrying 16 kg of Xenon. Both thrusters operated in the 300–550 W power range, generated a combined total impulse of 158.1 kN-sec and consumed all propellant. Two methods are described to compute the remaining propellant mass – “Bookkeeping” and “PTV” methods. The advantages and disadvantages of each method are discussed in light of the Venµs mission. Thruster performance was measured on-orbit using the “Orbit Determination” method and compared to laboratory experiments conducted on the ground with identical thrusters. The measured performance on-orbit was found to agree within the error bars with the performance measured on the ground. Lastly, we present several repeating events in which the propulsion system suffered from sudden beam-outs or ignition difficulties. We present the methods used to construct a solution and implement it.

Lifetime experiment and analysis of an electrowetting ionic liquid electrospray thruster

Ionic liquid electrospray thrusters are notable for their small size, low mass, and high specific impulse, making them ideal for use in micro/nano satellites. This study evaluates the lifetime of an electrowetting ionic liquid electrospray thruster. Experimental results indicate that the decrease in emission current is attributed to electrochemical reactions that increase the curvature of the emitter tips and the increased flow resistance. The online replenishment of insufficient propellant is achieved using an electrowetting device, which restores the emission current. Over the entire test period, the thruster operated for a total of 331.81 h, consuming 2.68083 g of propellant. This study offers valuable insights for improving the lifetime and total impulse of ionic liquid electrospray thrusters.

Comparison of knee biomechanical characteristics during gait between patients with knee osteoarthritis and healthy individuals

ObjectiveThis study aim to quantify the differences in knee biomechanics during gait between knee osteoarthritis (KOA) patients and healthy individuals. MethodsTwenty KOA patients (4 males and 16 females, 66.2 ± 7.7 years) and twenty controls (16 males and 4 females, 64.8 ± 5.4 years) were recruited for gait test using the motion capture system and force-platform system. The spatiotemporal parameters, knee kinematics and kinetics, and tibiofemoral contact force (TFCF) were calculated using an improved musculoskeletal model. ResultsKOA patients walked with reduced speed (48.6 %), stride length (32.9 %), stride height (33.0 %), time proportions of single-support phases (19.2 %), increased gait cycle time (31.0 %), time proportions of stance (8.5 %) and double-support phases (57.7–75.9 %). KOA patients had significant smaller peak flexion angle (29.1 %), flexion ROM (50.6 %) and peak flexion moment (90.2 %), greater peak adduction moment (KAM) (40.7 %), peak rotation moments (KRM) (50.0 %), KAM impulse (106.2 %) and KRM impulse (126.0 %). In proximodistal direction, greater medial TFCF impulse (238 %), total and medial first-peak TFCF (9.6 % and 15.2 %), and smaller lateral peak TFCF (33.3 %) and TFCF impulse (38.4 %) were found in KOA patients. Besides, significant differences were found in the total, medial and lateral peak TFCFs and TFCF impulses in mediolateral direction, and the medial and lateral TFCFs and TFCF impulses in anteroposterior direction. ConclusionsSignificant differences were found in the spatiotemporal parameters, knee kinematics and kinetics, and TFCF between the two groups. The results of this study have important implication for clinicians and rehabilitation physicians. These quantified biomechanical differences can provide data support for the personalized and quantified rehabilitation strategies, give suggestions for the exercises of KOA patients, help monitor disease, evaluate surgical treatment, and develop more effective preoperative planning and postoperative rehabilitation strategies.

Comparison of the dynamic characteristics of GFRP, CFRP, and hybrid composites subjected to repeated low‐velocity impact

AbstractThe current study used the vacuum‐assisted hand lay‐up method (VAHLM) to manufacture glass fiber‐reinforced polymer (GFRP), carbon fiber‐reinforced polymer (CFRP), and glass/carbon fiber‐reinforced hybrid composites to examine the influences of fiber materials and hybridization on the repeated low‐velocity impact (LVI) responses. In this regard, the manufactured composites were exposed to repeated LVI loading at 3 m/s under 25.2 J impact energy, and thus dynamic characteristics such as total impulse, contact/bending stiffness, interaction time, peak force/displacement, and absorbed‐rebounded energies depending on the impact number were acquired. LVI tests were continued until penetration was observed in the composites, at which point the penetration threshold numbers for each composite type were acquired. Furthermore, the macro‐scale damage analyses depending on the impact number were gradually examined, and the impacts of hybridization and fiber material on the damage mechanisms were determined. The study found that GFRP, hybrid and CFRP composites had the highest impact resistance, respectively, and that glass fiber‐reinforcement is well‐suited for applications that require higher impact resistance. When the average penetration threshold numbers for the composites were examined, it was observed that GFRP composites had approximately five times higher penetration threshold numbers than CFRP composites and that hybrid specimens exhibited similar properties to CFRP composites in terms of impact resistance. This scenario was linked to the various deformation capabilities of glass and carbon fibers, and it was concluded that the high‐deformation capability of the fibers improved the penetration threshold numbers.Highlights Effects of hybridization and fiber material on LVI responses were examined. Fiber material has a significant influence on impact resistance. Penetration threshold number can be associated with the fibers' strain capability. The adhesion factor plays an active role in the damage of hybrid specimens.

Reliability of Quadriceps Twitch Muscle Properties and Explosive Voluntary Contractions at Different Knee Joint Angles

ABSTRACT Background Measures that assess muscle strength and its development, either voluntarily or involuntarily, are important in the clinical and research context. The main aim of this study was to verify the interday reliability and the minimum detectable change (MDC) of the knee extensors muscles torque using evoked contractions and explosive voluntary contractions (EVC), across six different joint angles. Methods 20 participants, 16 men and 4 women (26.5 ± 6.6 years; 174.5 ± 11.1 cm; 73.7 ± 11.3 kg), participated in this study. Evoked twitch contractions and voluntary explosive contractions of the knee extensors were performed in 2 days (test-retest) at 20, 40, 70, 90, 105 and 115 degrees. Results The most reliable twitch parameters were peak torque (PT), contraction time (CT), half relaxation-time (½ time), total impulse and peak rate of torque development (RTDPeak), with coefficient of variation (CV) ranging from ~ 8% at 20° to 5% at 115° angle. It was verified that CT and ½ time become more reliable as the knee angle changed from 20 to 115 degrees, from shorter to longer muscle lengths (7.3 to 2.7% and 8.8% to 4.0%, respectively). The more reliable parameters for voluntary contraction were PT, RTD250 ms, RTDPeak and impulse250 ms (CV from around ~ 8% at 20°/115° and 5% at 70°/90°). For voluntary contractions, all measures performed at 70° angle were more reliable compared to the other angles. Conclusion It was concluded that for the knee extensor muscles, evoked twitch contractions presented greater reliability across knee angles, with lower CV values when compared to the voluntary measures for the same time windows. Specifically, for the evoked twitch contractions, angles from 70 to 115 degree proved to be highly reliable. On the other hand, for the voluntary contractions, the central angles (70 and 90 degree) were the most reliable.

The influence of background co-flow on the propulsive characteristics of starting jets

The influence of uniform background co-flow on the propulsive characteristics of starting jets with stroke ratios (length to diameter ratio, L/D) from 1 to 5 and velocity ratios (ratio of co-flow velocity to maximum jet velocity, Rv) from 0 to 0.6 has been investigated numerically. The total impulse generated increases with increasing Rv for L/D<1.5, but increases initially and then decreases for 1.5≤L/D≤3.5. Furthermore, it decreases with increasing Rv for L/D>3.5. The co-flow affects the generation of total impulse mainly by modifying the development of pressure thrust FP(t). The influence on FP(t) can be divided into three stages. During the initial and final stages, FP(t) decreases with increasing Rv, and increases during the middle stage. These three stages are explained by the influence of co-flow on wake vortex ring, leading vortex ring and stopping vortex ring, respectively. Transition between stages can also be related to the instantaneous velocity ratio Rv(t), which is the ratio of co-flow velocity to instantaneous jet velocity. The negative influence of co-flow on the generation of impulse can be mitigated by the velocity program with faster acceleration and shorter deceleration duration, which is equivalent to reducing the average value of Rv(t).

Research on the Combustion Mode and Thrust Performance of Rotating Detonation Scrarmjet Engines

Decades of research in hypersonic science and engineering have shown that scramjet engines are the preferred choice for powering hypersonic vehicles. In these engines, oblique shock combustion and rotating detonation combustion are two common combustion modes. This article primarily focuses on the numerical simulation and theoretical analysis of these two combustion modes. The research indicates that as the combustible mixture injected into the combustion chamber increases, the combustion mode transitions from deflagration combustion to self-sustaining detonation combustion and then to forced detonation combustion to maintain stable combustion in the chamber. Under self-sustaining detonation combustion mode, as the amount of combustible mixture injected into the chamber increases, the number of detonation waves gradually increases from one to multiple and the angle between the detonation waves and the inflow changes from acute to right angles. In the forced detonation combustion mode, the minimum shock wave intensity required to initiate detonation combustion can be obtained by drawing a tangent from the Rayleigh line. The structure generating oblique shock waves in the combustion chamber needs to match the shock wave intensity. In the detonation combustion mode, both the exit total temperature and specific impulse of the combustion chamber increase with the increase in Mach number at the inlet, while the pressure ratio decreases. This article provides a reference for the design of the combustion chamber in supersonic combustion ramjet engines.

Radial ablation uniformity of cathode and design of double anode micro-cathode arc thruster

Micro-cathode arc thruster offers promising applications in micro–nanosatellite space missions owing to its simple structure, high specific impulse, and low power consumption. However, the non-uniform ablation of the cathode poses a significant limitation on the total impulse of micro-cathode arc thruster. This non-uniformity can be categorized into circumferential and radial types, with previous research primarily focusing on the influence of circumferential ablation non-uniformity. Nevertheless, it has been observed that radial ablation non-uniformity also affects the stability of the thruster, despite the lack of studies in this area. To investigate the mechanism behind the cathode radial ablation, a slice model has been designed to study the motion process of the cathode spots during a single discharge using a high-speed camera. From this analysis aims to identify the root cause of uneven cathode radial ablation. Building upon these findings, a double anode micro-cathode arc thruster has been devised to enhance the uniformity of cathode ablation. Experimental verification has been conducted to assess the performance of the double anode micro-cathode arc thruster. The results indicate that in the traditional micro-cathode arc thruster discharge process, the cathode spots do not migrate towards the outer layer covered by the shell. Instead, they extend to the surface of the shell along the contact area between the shell and cathode. This leads to unequal ablation between the inner and outer layers of the cathode. The double anode micro-cathode arc thruster effectively addresses these issues by providing two discharge channels that maintain the dynamic balance of electrode resistance and increase the ablation amount on the outer layer of the cathode. Consequently, the total impulse of the thruster improved significantly while ensuring the desired performance index.

Study on a hybrid-produced magnetic-field Hall thruster

The increasing interest in all-electric, low-Earth orbit satellite constellations has stimulated the rapid development of electric propulsion technology, particularly low-power Hall thrusters. In this study, the difficulties in magnetic field design were analyzed in low-power Hall thrusters, and a new and efficient hybrid production technique is proposed. Hybrid production combines the advantages of coil and permanent magnet production; the main magnetic field is generated by permanent magnets, and the regulating magnetic field is generated by coils in parallel. Accordingly, a prototype of a 600-W hybrid-produced magnetic field Hall thruster, HPHT-600, was designed and tested. The HPHT-600 has a small size (channel outer diameter 54 mm), light weight (1.2 kg), low area–volume ratio (0.148), and low magnetic power. In addition, it exhibits a power envelope of 300–1000 W and a total efficiency of 53.5 % at the discharge voltage of 300 V, anode volume flow rate of 35 sccm, and total specific impulse of 1900 s at 500 V and 20 sccm.

A reinforced concrete shear wall building structure subjected to internal TNT explosions: Test results and numerical validation

When an explosion occurs within reinforced concrete shear wall (RCSW) structures, the overpressures and duration of blast loads will be amplified by the confining effects of enclosed walls, which can cause more severe damage to the structure than a free air explosion (FAE). However, research on RCSW structures subjected to internal explosions (IEs) are still limited and no benchmark tests exist. To provide a benchmark for studying the blast resistance of RCSW structures subjected to IEs, three Trinitrotoluene (TNT) IE field tests were conducted in this study on a 2-story, 3 × 3-bay, 1/3 scaled RCSW substructure, in which the overpressures, displacements, and crack patterns of RCSWs were recorded. The three tests were performed consecutively after each other on the same structure at TNT loads of 95.3 g (Test-1), 253 g (Test-2), and 400 g (Test-3). The test results showed that the floor slab directly above the explosion and one of the RCSW confining the explosion failed in flexure (i.e., the support rotation angle exceeds 2°) in Test-2 with the scaled distance of 1.53, whilst the other three neighboring RCSWs failed in flexure in Test-3 with the scaled distance of 1.31. In addition, a detailed finite element model was established using LS-DYNA and was validated against the test results. The numerical simulation results showed that the energy released from TNT in IE scenarios (14.5 GJ/m3) was 1.95 times that in FAE scenarios (7.43 GJ/m3). The total blast loads applied to the RCSWs increased with the decrease of the area of opening. The average impulse applied to the four RCSWs were similar in IE scenarios, and the average impulse could be represented by the impulse at the center of each of the RCSWs (excluding the RCSW with window opening, as the opening is at the center). The shock and gas overpressure impulses at the center of RCSWs accounted for approximately 19.4 % and 80.6 % of the total impulse, respectively. Furthermore, the peak overpressures at the wall centers and the total blast loads experienced by the RCSWs under IE scenarios were 1.79 times and 11.13 times higher than those under FAE scenarios, respectively. This was due to the confinement of enclosed walls under IE scenarios. Consequently, the displacements and damage levels of the RCSW substructure under IE scenarios were much larger than those under FAE scenarios.

Endurance testing and characterization of a novel candidate for CubeSat propulsion: The Advanced Cusp Field Thruster (ACFT)

In recent years, there has been a notable push for cost reduction in space applications, aligning with the growing interest in CubeSats. To unlock their full capabilities, propulsion is essential for executing complex missions. However, many propulsion technologies struggle to combine a low power-to-thrust ratio (PTTR), delivering sufficient total impulse, and providing high thrust, all within the limited space of a CubeSat. In this context, the Advanced Cusp Field Thruster (ACFT) emerges as a novel candidate, encapsulating all these crucial characteristics. To validate its performance of the thruster without the integration of a dedicated feeding system and a Power Processing Unit (PPU), a miniaturized development model of an ACFT underwent a 1650-hour endurance test, followed by a subsequent end-of-test characterization. This led to the achievement of a total impulse of 4400Ns and a maximum thrust of 1522±41μN at a specific impulse of 1035±41.4s, a PTTR of 29.5±0.8W/mN (without neutralizer), and an overall efficiency of 17.2±1.1% using krypton.

Surrogate-assisted differential evolution using manifold learning-based sampling for high- dimensional expensive constrained optimization problems

To address the challenges of high-dimensional constrained optimization problems with expensive simulation models, a Surrogate-Assisted Differential Evolution using Manifold Learning-based Sampling (SADE-MLS) is proposed. In SADE-MLS, differential evolution operators are executed to generate numerous high-dimensional candidate points. To alleviate the curse of dimensionality, a Manifold Learning-based Sampling (MLS) mechanism is developed to explore the high-dimensional design space effectively. In MLS, the intrinsic dimensionality of the candidate points is determined by a maximum likelihood estimator. Then, the candidate points are mapped into a low-dimensional space using the dimensionality reduction technique, which can avoid significant information loss during dimensionality reduction. Thus, Kriging surrogates are constructed in the low-dimensional space to predict the responses of the mapped candidate points. The candidate points with high constrained expected improvement values are selected for global exploration. Moreover, the local search process assisted by radial basis function and differential evolution is performed to exploit the design space efficiently. Several numerical benchmarks are tested to compare SADE-MLS with other algorithms. Finally, SADE-MLS is successfully applied to a solid rocket motor multidisciplinary optimization problem and a re-entry vehicle aerodynamic optimization problem, with the total impulse and lift to drag ratio being increased by 32.7% and 35.5%, respectively. The optimization results demonstrate the practicality and effectiveness of the proposed method in real engineering practices.

The significant role of passive oxide layer on reactive metal combustion: insights into composite solid propellant with superior performance

ABSTRACT Passive oxide layer could expose a significant impact on reactive metal combustion. Boron and aluminum experience combustion enthalpy of 59.3 and 31.1 KJ/g and passive oxide layer of 200 and 7 nm, respectively. In this study, surface oxygen of born and aluminum particles (10 µm) was quantified via EDAX analysis. Boron and aluminum demonstrated surface oxygen content of 14.6 and 7.2 wt %, respectively. Reactive particles were integrated into ammonium perchlorate (AP) oxidizer. While boron demonstrated decrease in AP decomposition enthalpy by −14.8%; aluminum offered an increase in AP decomposition enthalpy by 60.8% using DSC. Whereas, aluminum oxide layer could be pealed out more effectively; boron passive oxide layer could melt with the evolution of an insulating barrier. Aluminum particles offered decrease in AP apparent activation energy by 68%, 105%, and 76% using Kissinger, Kissinger-Akahira-Sunose (KAS), and Flyn and Wall (FWO) models, respectively. Solid propellant formulations were developed; ballistic performance was assessed using small-scale rocket motor. Aluminum particles demonstrated stable combustion process with enhanced specific impulse and total pressure impulse compared with boron. Additionally, aluminum particles demonstrated stable burning with pressure exponent of 0.19 compared with 0.4 for boron particles.

Interlimb kinetic asymmetries during the tuck jump assessment are more exposed following kinetic stabilization

ObjectiveTo analyse interlimb kinetics and asymmetries during the tuck jump assessment (TJA), before and after kinetic stabilization, to identify injury risk in healthy female athletes. DesignCross-sectional study. SettingLaboratory. ParticipantsTwenty-five healthy females (age 21.0 ± 1.83 yrs; height 1.68 ± 0.06 m; body mass 69.4 ± 10.7 kg). Main outcome measuresKinetics were measured during 10-s trials of the TJA and absolute asymmetries compared, before and after kinetic stabilization using paired sample t-tests. Statistical parametric mapping (SPM) compared vertical ground reaction force (VGRF) data for each limb during the jumping cycles before and after stabilization. ResultsSmall to moderate increases in interlimb asymmetries were observed after stabilization for VGRF, relative vertical leg stiffness, average loading rate, total and propulsive impulse, peak braking and propulsive force (p < 0.05). SPM revealed significant interlimb differences between 77-98% and 83–99% of ground contact for the jumping cycles pre- and post-stabilization respectively. ConclusionsLarger asymmetries were evident after kinetic stabilization, with increased VGRF in the non-dominant limb. We speculate that participants sacrificed interlimb landing symmetry to achieve kinetic stability, which may reflect a primal landing strategy that forgoes movement quality. Assessing lower limb biomechanics using the TJA should involve examining kinetic stability and interlimb kinetic asymmetries.

Correlations to estimate the ground loading from small scale propane BLEVE experiments

This paper presents small-scale propane BLEVE (Boiling Liquid Expanding Vapor Explosion) experiments coupled with an investigation into ground loading dynamics. The experiments utilized cylindrical aluminum pressure vessels, with a diameter of 50 mm and a length of 300 mm. The controlled variables included burst pressure, liquid fill level, and weakened length. Both high and low-speed measurements of internal pressure and ground force were conducted during the experiments. The dependent variables analyzed were peak total ground load, force duration, and impulse. The findings from the study show trends in ground force and impulse with alterations in failure pressure, fill level and weakened length. Specifically, ground force and impulse exhibit an upward trend with increasing failure pressure, fill level and weakened length (cut length). For the first time, comprehensive correlations have been developed, incorporating the controlled variables, as well as theoretical boiling wave speed and vapor speed, to estimate the dependent variables, which represents a significant contribution in the field. However, the study does acknowledge the presence of scatter in the data, which are believed to be associated with the intricacies of the vessel opening process. It should be noted that this correlation has not been validated for larger scales. Once validated on a larger scale, these correlations can be directly applied in the design and practice of civil infrastructure to enhance the structural integrity. Additionally, the research has direct implications for industrial applications, allowing for the quantitative assessment of risks associated with bridge collapse during the transportation of PLGs.

Analysis of Pushing Forces During the Water Polo Eggbeater: Reliability and Validity of a Novel Approach.

Water polo players benefit from greater odds of success when maintaining their tactical position against their opponents. This study evaluated the reliability and validity of a water-based resistance test to replicate this skill.Thirty-three water polo players participated in this study (19 males and 14 females, 14 from senior and 19 from junior national teams). Data were collected during two regular training sessions, separated by one week, using a load cell to instrument a weight stack resistance setup on the pool deck. Performance parameters such as mean force, maximum force, mean peak force and total impulse were defined with custom Python scripts. Test-retest reliability was assessed using intra-class correlations (ICC3,1). Group comparisons were explored between male and female players. Level of significance was set at p < 0.05. The reliability findings were high to very high for the mean force, maximum force, mean peak force, inter-stroke range, and total impulse (ICC 0.85-0.93, p < 0.01). Group comparisons showed significantly greater values in male players for these variables (p < 0.01, ES = 1.05-9.36) with large to very large effect sizes. However, there was no significant difference in endurance measured between sexes (p = 0.88, ES = 0.04). This study presents a methodology with satisfactory metrological qualities for field applications using simple and affordable equipment. The testing apparatus presented in this study can readily be replicated in a variety of training environments by practitioners working with water polo teams. Coaches can use this approach to evaluate individual player progress or to compare performance across a group of water polo players.

Energy and blast performance of beryllium in a model thermobaric composition in comparison with aluminum and magnesium

A direct comparison is made between the effectiveness of Al, Mg, and Be powders as additional fuels in model thermobaric compositions containing 20% fuel, 20% ammonium perchlorate, and 60% RDX (1,3,5-Trinitro-1,3,5-triazacyclohexane) passivated with wax. Experimentally determined calorimetric measurements of the heat of detonation, along with the overpressure histories in an explosion chamber filled with nitrogen, were used to determine the quasi-static pressure (QSP) under anaerobic conditions. Overpressure measurements were also performed in a semi-closed bunker, and all blast wave parameters generated after the detonation of 500 g charges of the tested explosives were determined. Detonation calorimetry results, QSP values, and blast wave parameters (pressure amplitude, specific and total impulses) clearly indicate that Be is much more effective as an additional fuel than either Al or Mg in both anaerobic post-detonation reactions as well as the subsequent aerobic combustion. The heat of detonation of the RDXwax/AP/Be explosive mixture is over 40% and 50% higher than that of the mixture containing aluminum and magnesium instead of beryllium, respectively. Moreover, the TNT equivalent of the Be-containing composition due to the overpressure in the nitrogen-filled explosion chamber is 1.66, while the equivalent calculated using an air shock wave-specific impulse at a distance of 2.5 m is equal to 1.69. The high values of these parameters confirm the high reactivity of beryllium in both the anaerobic and aerobic stages of the thermobaric explosion.

Equation of State of Autoclaved Aerated Concrete-Oedometric Testing.

This paper aims at investigating the triaxial behavior of Autoclaved Aerated Concrete (AAC) under extremely high pressures, and experimentally determine Equation of State (EOS) for several different AAC densities. Oedometric tests were carried out using a home-made high-pressure triaxial apparatus, and pressures up to ~500 MPa were applied. The complete pressure-bulk strain relationships were measured, and new findings and insights were obtained. The paper presents the testing set-up and the measurement system. The data processing method accounting for the AAC pronounced shortening during the ongoing test is described using a weighted functions procedure for the circumferential strains' calculation, with which the confining pressure was determined. The boundary conditions effects on the test results were investigated, and a new technique for specimen insulation was suggested to ensure loading without friction and the prevention of local shear failure. The experimental EOS for different AAC densities were obtained. EOS curves for different specimens with the same density demonstrated good to very good repeatability of the EOS curves over the entire pressure range. Based on the tests results and the density's span, three classes of AAC are proposed. A preliminary attempt to apply the newly obtained EOS curves has been carried out to examine the energy dissipation for three different dynamic load levels. Although this is a preliminary stage that is beyond the objective of this paper, early interesting results were observed where an optimal AAC density, for which the highest energy has been absorbed, was identified. This finding encourages inclusion of that preliminary study as a closure section. Numerical simulations of wave propagation through ACC layers of different densities, laid on rigid supporting slabs, was carried out. The minimum total impulse imparted to the rigid slab was found for the optimal AAC density that has been determined above.

Hetero‐blast from a structural reactive material cylinder under explosive loading

AbstractA structural reactive material (SRM) cylinder is considered here as a limiting case of a dense metallic energetic system in which a mixture of metal particles is consolidated to the theoretical maximum density excluding porosity, to possess both high energy density and mechanical strength. Dynamic fragmentation and free‐field explosion of a 103 mm inner diameter SRM cylinder charge is experimentally studied, with a wall thickness varying in a range of metal‐to‐explosive mass ratio M/C=1.3 to 4.0. Under explosive loading, the SRM cylinder produces a designated fragment size distribution divided into two groups: fine fragments with sizes on the order of 102 μm and below, and coarse fragments with sizes on the order ranging between 100‐101 mm. Prompt detonation shock‐induced reaction (DSIR) of the expanding cloud of high‐concentration fine fragments supplements the energy to enhance the primary blast as it propagates, while the coarse fragments form a high‐speed, high‐concentration metal momentum flux crossing the fireball and blast front to contribute to the total impulse loading to a nearby structure. Rapid impact‐induced reaction (IIR) of the secondary fragments from high‐speed coarse SRM fragments further enhances the reflected blast loading or generates a high interior explosion pressure as fragments perforate into the structure. The above distinctive characteristics of a unique hetero‐blast are coupled effectively in the near‐field range.