Quasi-static Pressure Research Articles

An experimental study of the effects of degrees of confinement on the response of thermoplastic fibre–metal laminates subjected to blast loading

A series of tests on the dynamic response of thermoplastic fibre–metal laminates (TFMLs) subjected to blast loading with three different degrees of confinement (unconfined, vented and fully confined) were performed. The deflection time histories, the residual deformation, the internal delamination and damage mode of the TFMLs were recorded or observed by employing the digital image correlation, the 3D scanning and X-ray computed tomography techniques. Based on equivalent material properties combined with dimensionless damage numbers φq, the deformation of fibre–metal hybrid structures of different configurations can be effectively predicted and verified by experimental data. In addition, the effective load applied to the hybrid structure within the saturation response time is a key factor in determining the blast performance at different degrees of confinement. Vented explosions can result in the same dynamic response as fully confined explosions with even more severe internal delamination. The presence of quasi-static pressure in fully confined explosions can contribute more than 20% to the final deformation. The results can provide a basis for further understanding of the dynamic response and failure behaviour of fibre–metal hybrid structures subjected to blast loading with different degrees of confinement.

Experimental study on internal explosion of thermobaric explosives containing metastable intermolecular composite (MIC) materials

In order to study the influence of metastable intermolecular composite (MIC) materials on the internal implosion properties of thermobaric explosive, the calorimetric bomb and closed chamber were used to measure the detonation heat, quasi-static pressure and energy impulse of five explosive formulations containing different MIC materials. Compared with the traditional aluminized warm compressed explosives, the energy release characteristics and output characteristics were analyzed. The results show that the explosive formula containing MIC material has lower detonation heat value in air and vacuum than that containing traditional Al powder; The quasi-static pressure and energy impulse of the former are higher than those of the latter, indicating that MIC materials can improve the output energy of thermobaric explosives. The results can be used to guide the formulation design of thermobaric explosives.

Effect of FOX-7 on Explosion Performances and Afterburning of HMX-Based Thermobaric Explosives

In this paper, confined explosions of HMX-based thermobaric explosives in a spherical chamber were studied. The effects of 1, 1-diamino-2, 2-dinitroethene (FOX-7) on the explosion performances and afterburning were obtained by changing its content. The results showed that the composition (HMX/FOX-7) enhanced the total impulse, but its effect on improving the initial energy and quasi-static pressure (QSP) was slight. The aluminum in thermobaric explosives burned incompletely, whereas FOX-7 promoted afterburning of aluminum particles. In addition, the promoting effect was more obvious with the increase of FOX-7 mass score in the composition. In conclusion, when the ratio of HMX to FOX-7 mass fraction in the composition was 3, the thermobaric explosive had low sensitivity and could maintain the energy level of the explosive.

Effect of CF on mechanical properties and ignition characteristics of Al/PTFE reactive materials under quasi-static compressive

The chopped carbon fiber (CF) was introduced into Al (aluminum) /PTFE (polytetrafluoroethylene) reactive materials, and Al/CF/PTFE reactive materials with different mass fractions of CF were prepared. In order to study the effect of CF on the mechanical properties and ignition characteristics of Al/PTFE reactive materials, quasi-static compression tests were carried out on different types of specimens. The fracture characteristics of the specimens were observed by SEM, and the ignition mechanism was analyzed by crack-induced hot spots. The results show that yield strength and elastic modulus increase while compressive strength and yield strain decrease with increasing CF mass fraction. The decrease in interfacial adhesion between CF and PTFE matrix, uneven load transfer of CF during compression and stress concentration lead to the decrease of mechanical properties of the material. The decrease of compressive strength of Al/CF/PTFE material and the failure of crack tip without ductile brittle transition are the main factors for the non ignition reaction in quasi-static compression. CF did not improve the quasi-static pressure properties of Al/PTFE, but decreased the quasi-static pressure sensitivity.

Dynamic response and failure behaviour of thermoplastic fibre–metal​ laminates subjected to confined blast load

Due to the confinement effect, the blast load from a confined space explosion tends to cause more severe damage to structures. When subjected to this type of confined explosion, thermoplastic fibre–metal laminate (TFML) panels would experience repeated shock waves and relatively longer durations of quasi-static pressure. A better understanding of the dynamic response and damage mechanism of TFMLs under confined blast loading can greatly benefit the design of composite structures with improved blast resistance. In the present work, TFMLs with seven different configurations were designed and fabricated. Confined-blast experiments with various masses of trinitrotoluene (TNT) were performed on these TFMLs. The experimental results, including deflection time histories and X-ray computed tomography (CT) images, have been applied to the development of a method for predicting the dynamic response of laminates under confined blast loads. The findings of this work will assist in the rapid assessment of the deformation of fibre–metal laminates and assist in the pre-design of laminate structures in confined explosions.

TNT equivalency method in confined space based on steel plate deformation

TNT equivalency has been a widely accepted concept in engineering. However, as a fuel-rich explosive, the afterburning effect of detonation products would be remarkable when TNT is detonated in a confined space. The additional energy release from the burning of detonation products makes the traditional TNT equivalency to be more complicated. In this paper, in order to reveal the influence of afterburning effect of detonation products under the condition of confined blast, a series of TNT detonation tests in a confined chamber filled with four different atmospheres, air, nitrogen, water mist, and combined nitrogen and water mist were performed. The temperature, pressure-time histories and deflection of blast loaded steel plate were recorded. It is found that the pressure, temperature and the dynamic response of the blast loaded plate in nitrogen and water mist atmosphere were significantly lower than those in the air conditions, due to different mechanisms of energy release and absorption. In addition, the relation between deflection of target plate and the released energy from explosive was established. Furthermore, the method of determining TNT equivalency in confined explosion considering the afterburning effect was proposed and was employed to determine the TNT equivalency of a cased charge. By comparing the present TNT equivalency method with the method based on quasi-static pressure, the potential application of the method has been illustrated.

Computational modeling of confined blast waves with focus on interaction with structures

Blast loading is a critical extreme loading condition for most engineering structures. Modeling such scenarios is challenging due to the intrinsic non-linearities. Recent numerical methods can capture the physics governing blast waves and their interaction with structures in a more accurate way than established empirical methods. This article is intended as a proof of concept that state-of-the-art CFD and FE software can be combined to set up high-fidelity uncoupled simulations. Computational fluid dynamics is exploited in this work to map the pressure field developed during a detonation reaction in a Eulerian domain. Then, such pressure time history is applied in the finite element framework to perform Lagrangian simulations. The methodology is used to compare the structural response of blast-loaded plates in fully confined environments to that in free-field scenarios. It turns out that confined blast waves are more severe than blast waves in unconfined scenarios, mainly due to the multiple reflections and residual quasi-static pressure. Moreover, on the one hand, the quasi-static pressure appears to contribute to further increasing the plate out-of-plane deflection, while on the other hand, it prevents plates from undergoing reverse buckling or oscillations around the initial equilibrium configuration. Experimental tests are required to provide further evidence about the latter contribution.

Dynamic response prediction of prototype from scale-down model for I-core sandwich panels subjected to internal explosion

Cabin scale-down model experiments are an effective approach to investigate the dynamic response of I-core sandwich panels subjected to internal explosion. However, it is difficult to guarantee the complete geometrical similarity in terms of plate thickness for I-core sandwich panels between the scale-down model and prototype due to manufacturing process restriction and thickness specifications of commercially available plates. To resolve the above issue, a new and more reasonable dynamic response prediction method with high accuracy for prototype based on scale-down model test was proposed in the present work. The feasibility and accuracy of proposed prediction method were theoretically, experimentally, and numerically verified. The effects of TNT charge mass, correction method of TNT charge mass, and quasi-static pressure load were investigated. Results show that the proposed prediction method from the energy point of view has high accuracy and good feasibility when the plate thickness of scale-down model distorts. In the proposed approach, the TNT charge mass is corrected through specific impulse correction. Higher accuracy is gained by using the proposed prediction method in the case of internal explosion with large TNT charge mass. Directly correcting the TNT charge mass on the basis of geometrical similarity still underestimates the dynamic response of incomplete scale-down model when plate thickness distorts. It is not reasonable to ignore the effect of quasi-static pressure load, because the specific impulse of quasi-static pressure load is much larger than that of shock wave load. This work can provide practicable and accurate application guidance for the design of internal explosion scale-down model experiments for I-core sandwich panels.

Quasi-Static Pressure Characteristics of Explosion Venting Vessel Under Confined Explosion

Quasi-Static Pressure Characteristics of Explosion Venting Vessel Under Confined Explosion

Deformation response research on aluminum sheets with different central pre-cracked defects under quasi-static hydraulic pressure loading

The crack behavior and bending deformation of pre-cracked sheet are coupled under the pressure loading. Two theoretical methods (SCMLD and PTELD) were used to compare and verify the bulge test data of intact aluminum alloy sheets, and the applicability of the two methods in equilibrium bulge test were discussed. ABAQUS extended finite element method (XFEM) and the parameters of fracture energy based on experiments were used to simulate the bulging deformation and failure behavior of pre-cracked sheet, the results agreed with the experimental test data well. What is more, the slope of h−p curve reflects the equivalent bending stiffness, which is affected by the crack shape length rather but not the crack shape.

High Quasi-static Pressure Measurement of Explosion in Closed Container

To develop a method for determining the parameters of the final equation of state (EOS) of detonation products of aluminized explosives, an explosion quasi-static pressure measurement system in closed containers with a large mass-to-volume ratio is developed. The influence of domestic and foreign typical charge piezoelectric pressure sensors, sensor buffer adjustment structures, container tightness, grounding operation, weather, and other factors on the long-time measurement of high quasi-static pressure are comparatively studied. The test methods and conditions for obtaining standard quasi-static pressure-time curves are clarified. The influence of the mass of different aluminized explosives on the static pressure is obtained. The result shows that the foreign 113B03 type sensor is more suitable for measuring quasi-static pressure with a leakage effect in a humid environment. An appropriate sensor buffer adjustment structure and reliable grounding operation can significantly reduce the high-frequency oscillation of the signal.

Szilard Engines and Information-Based Work Extraction for Active Systems

The out of equilibrium nature of active systems can be exploited for the design of information-based engines. We design two types of an active Szilard engine that use a Maxwell demon to extract work from an active bath composed of noninteracting active Brownian particles. The two engines exploit either the quasistatic active pressure of active Brownian particles or the long correlation time of their velocities. For both engines the active bath allows us to overcome the Landauer principle and to extract larger work compared to conventional Szilard engines operating in quasithermal equilibrium. For both of our engines, we identify the optimal regimes at which the work extracted and the efficiency are maximized. Finally, we discuss them in the context of synthetic and biological active systems.

Dynamic damage characteristics of rock under multiple loads during high-voltage pulse fragmentation

To analyze the damage characteristics of rocks during high-voltage pulse fragmentation (HVPF), two kinds of loads, shockwave and cavity, are determined by optical observation, and the pressure–time characteristics of these two and their mechanism of damage to rocks in mesoscopic view are analyzed. A model of dynamic damage characteristics of brittle rock under multiple loads is established, which includes numerical calculation and discrete element simulation. In the discrete element simulation, the rock is simplified as a circular region without reflection boundary with a certain size of the circular hole inside, and the grains in the region are discretized as rigid spheres with a definite bonding relationship. The shockwave is considered the time-varying pressure loaded to the grains of the circular hole, and the cavity is considered the quasi-static pressure loaded to the grains on both sides of the fracture. The results of the model show that shear cracks and tensile cracks are produced during the shockwave action, but tensile cracks are predominant. The shockwave acts as a preload for the expansion of cracks, and the damage radius is small. Most of the cracks in HVPF are caused by the cavity. A comparison of the numerical calculation results with the discrete element simulation results shows that the model can describe the distribution characteristics of cracks under multiple loads, which lays a foundation for further analysis of the internal mechanism of HVPF.

Vibration Measurements of the Gerbil Eardrum Under Quasi-static Pressure Sweeps.

Tympanometry provides an objective measurement of the status of the middle ear. During tympanometry, the ear-canal pressure is varied, while the response of the ear to sound pressure is measured. The effects of the pressure on the mechanics of the middle ear are not well understood. This study is a continuation of our previous work in which the vibration response of the gerbil eardrum was measured in vivo under quasi-static pressure steps. In this study, we delivered a continuous pressure sweep to the middle ear and measured the vibration response at four locations for six gerbils. Vibrations were recorded using a single-point laser Doppler vibrometer and glass-coated reflective beads (diameter ~ 40µm) at the umbo and on the mid-manubrium, posterior pars tensa and anterior pars tensa.The vibration magnitudes were similar to those in the previous step-wise pressurization experiments. Most gerbils showed repeatability within less than 10dB for consecutive cycles. As described in the previous study, as the frequency was increased at ambient pressure, the vibration magnitude on the manubrium increased slightly to a broad peak (referred to as R1) and then decreased until a small peak appeared (referred to as R2), followed by multiple peaks and troughs as the magnitude decreased further. The low-frequency vibration magnitude (at 1kHz) decreased monotonically as the pressure became more negative except for a dip (about 500Pa wide) that occurred between - 700 and - 1800Pa. The lowest overall magnitude was recorded in the dip at mid-manubrium. The vibration magnitudes also decreased as the middle-ear pressure was made more positive and were larger than those at negative pressures. R1 was only visible at negative and small positive middle-ear pressures, while R2 was visible for both positive and negative pressures. R2 split into multiple branches after the middle-ear pressure became slightly positive. No magnitude dip was visible for positive middle-ear pressures.The low-frequency vibration magnitudes at negative middle-ear pressures on the pars tensa were higher than those on the manubrium. R1 was not visible for large negative middle-ear pressures on the pars tensa. R2 appeared as a multi-peak feature on the pars tensa as well, and a higher-frequency branch on the posterior pars tensa appeared as a trough on the anterior pars tensa. The magnitude dip was not present on the pars tensa. The largest overall magnitude was recorded at the R2 peak on the posterior pars tensa.The results of this study expand on the findings of the step-wise pressurization experiments and provide further insight into the evolution of the vibration response of the eardrum under quasi-static pressures.

High-Speed Infrared Radiation Thermometer for the Investigation of Early Stage Explosive Development and Fireball Expansion.

The understanding of blast loads is critical for the development of infrastructure that protects against explosions. However, the lack of high-quality experimental work on the characterisation of such loads prevents a better understanding of many scenarios. Blast loads are typically characterised by use of some form of pressure gauge, from which the temperature can be inferred from a pressure measurement. However, such an approach to temperature measurement is limited; it assumes ideal gas laws apply throughout, which may not be the case for high temperature and pressure scenarios. In contrast, infrared radiation thermometers (IRTs) perform a measurement of temperature based upon the emitted radiance from the target object. The IRTs can measure fast changes in transient temperature, making them seemingly ideal for the measurement of a fireball’s temperature. In this work, we present the use of a high-speed IRT for the measurement of early-stage explosive development and fireball expansion within a confined blast, with the temperature of the explosive fireball measured from its emitted radiance. The temperature measured by the IRT was corroborated against the temperature inferred from a pressure gauge measurement; both instruments measured the same temperature from the quasi-static pressure (QSP) point onwards. Before the QSP point, it is deduced that the IRT measures the average temperature of the fireball over a wide field-of-view (FOV), as opposed to that inferred from the singular shocks detected by the pressure gauge. Therefore, use of an IRT, in tandem with a pressure gauge, provides a potential invaluable measurement technique for the characterisation the early stages of a fireball as it develops and expands.

Mechanical properties of Nomex honeycombs filled with tubes of carbon fibre reinforced vinyl ester resin composites

The Nomex honeycomb structures filled with carbon fibre reinforced vinyl ester resin composite tubes (NHFCT) were proposed to improve the energy absorption capacity of Nomex honeycombs. Thereafter, the mechanical properties of the NHFCT structures were explored based on the quasi-static pressure test, finite element simulation, and a theoretical model. The test result showed that the NHFCT structures enable increased SEA while retaining the energy absorption performance of Nomex honeycombs. When applying a certain load on the NHFCT structures, the Nomex honeycombs are folded; the CFRP tubes are torn and expanded, and the embedded cells bulge. The established finite element simulation model was used to simulate the deformation of NHFCT structures and the theoretical model was employed to predict their energy absorption performance. Tests applicable to the practical application revealed that NHFCT structures of a large area present more stable performance and the superimposed NHFCT structures are subjected to step-wise gradient deformation. The CFRP tubes suffer slight indentation on the panel between layers and they are torn in a funnel shape under the effect of the panel stiffness. The research provides reference for improving the mechanical properties of Nomex honeycomb structures and broadening their range of application.

Airfoil Anemometer With Integrated Flexible Piezo-Capacitive Pressure Sensor

Demand is expected to accelerate for autonomous air vehicles that transport people and goods, making wind sensors on these vehicles and in the air space where they operate critical to ensure safe control of many simultaneous take-offs and landings. Conventional anemometers such as pitot tubes as well as rotating, heated-element, acoustic, and drag technologies have drawbacks for small and micro-aerial vehicles including high power consumption, high aerodynamic drag, complex signal processing, and high cost. This paper presents an airfoil-shaped anemometer that provides low drag while integrating sensors for measuring wind speed and direction on tethered kites, balloons, and drones. Wind speed is measured by an integrated dual-layer capacitive pressure sensor with a polyvinylidene fluoride (PVDF) diaphragm while wind direction is measured by a 3D digital magnetometer that senses the orientation of the airfoil relative to the earth’s magnetic field. A model is presented for a dual-layer capacitive sensor and validated through quasistatic pressure chamber testing. The capacitive sensor as well as a commercial digital magnetometer are integrated into a NACA 2412 profile airfoil and tested in a laboratory-scale wind tunnel. The capacitive sensor provides a sensitivity of 1.84 fF m2s−2 and the airfoil exhibits a unique stable angle-of-attack to within ±2° as measured by the magnetometer.

ORAL ADMINISTRATION OF METHYLGLYOXAL ELEVATES BLOOD PRESSURE, BUT NOT ARTERIAL STIFFNESS, IN MICE

Objective: Methylglyoxal (MGO), a highly reactive dicarbonyl compound, is associated with diabetes and other age-related diseases such as hypertension. In these diseases, MGO may accelerate arterial stiffening. In the present study, we investigated the effect of elevated plasma MGO concentrations on arterial stiffness measured in- and ex vivo. Design and method: Eight-week-old male C57BL/6 mice were randomly allocated to control (n = 22) and treatment (n = 22) groups. Treatment started at age 10 weeks and consisted of 50 mM MGO in the drinking water for 13 weeks. Blood pressure (tail-cuff) and tonometric carotid-to-femoral pulse wave velocity (PWV) were recorded after 0, 5, and 11 weeks. After 15 weeks, mice were euthanised and their left common carotid arteries (CCAs) harvested for ex vivo bi-axial biomechanical testing. First, CCAs were stretched to in vivo length and exposed to quasi-static pressure inflation from 0–200 mmHg. Second, a 5 Hz pulsatile pressure of 120/80 mmHg was applied, to enable calculation of single-point PWV (Bramwell-Hill). Third, a structural axial stiffness coefficient was determined by performing quasi-static axial stretch sweeps at constant pressures of 60/100/140/200 mmHg. Finally, a four-fibre family strain energy function was fitted to the dataset to allow for calculation of material stiffness variables. Results: Plasma MGO levels at 15 weeks in the treatment group were 2.2-fold higher than the control group (879 ± 274 nM vs. 399 ± 45 nM, mean ± standard deviation, p < 0.001). After 11 weeks, systolic and diastolic blood pressures were elevated in the treatment group (systolic 110 ± 3 vs 105 ± 7 mmHg, p = 0.015, diastolic 85 ± 3 vs 80 ± 7 mmHg, p = 0.019). No differences in carotid-to-femoral PWV were observed at any time point (Figure). Ex vivo PWVs were not significantly different; neither were the axial stiffness coefficients. CCAs from treated mice showed a non-significant smaller inner radius and thickness than controls. Material stiffness, as assessed by constitutive modelling at a reference pressure of 100 mmHg, did not show any difference between groups. Conclusions: Higher plasma MGO levels are associated with an increase in blood pressure, but not an increase in arterial stiffness.

Thermite and intermetallic projectiles examined experimentally in air and inert gas environments

Intermetallic (aluminum and zirconium) and thermite (aluminum and molybdenum trioxide) projectiles were launched using a high velocity impact ignition testing system. The experiments were designed to simulate reactivity in high (argon) and low (air) altitude environments. The projectiles were launched into a chamber that included a steel target plate for projectile penetration before impacting a rear witness plate. The chamber was semi-sealed and instrumented for quasi-static pressure data. The results provide an understanding of energy release from the projectile materials and of the environmental influence on performance. The transient pressure traces provide insight into reaction kinetics. A bifurcation in transient pressure rise was an indication of a shift in reaction kinetics from the inherent reactive material to metal oxidation with the environment. The bifurcation was delayed by about 0.15 ms for the intermetallic relative to the thermite, evidence that the thermite reaction proceeded faster upon impact than the intermetallic. The two-step process (impact ignition of the reactive material followed by metal oxidation) was shown to produce higher energy conversion efficiencies than projectiles composed of pure fuel (i.e., aluminum) reported previously. Both reactive materials showed energy conversion efficiencies greater than 30% (for air) and 50% (for argon), and an explanation of underestimated efficiency and energy losses is provided. These results have implications for advancing formulations for ballistic applications. Structural reactive materials can be used to modify the effective reactivity of metal-containing formulations in varied atmospheric environments.

Experimental Study on the Probability of Different Wave Impact Types on a Vertical Wall with Horizontal Slab by Separation of Quasi-static Wave Impacts

When the fundamental natural frequency of marine structures is comparable to the dominant frequency of incident waves, the response of the load on the structure will be amplified. Accurately quantifying how wave loads can be amplified by incident wave conditions must thus be considered in any structural analysis, given how sensitive these characteristics are to different wave impact types. Systematic physical model tests of wave impacts on the simple horizontal plate and the vertical wall with a horizontal overhanging cantilever slab were performed. By first comparing quasi-static wave load estimates along a simple horizontal plate (obtained by low-pass filtering the pressure time series at different cut-off frequencies) with quasi-static uplift pressures from established predictive formulations, a cut-off frequency of 7 Hz was found to accurately separate the quasi-static component from impulsive wave impacts. By applying the low-pass filtering approach with the selected cut-off frequency to the pressure measurements for the vertical wall with a horizontal cantilever slab case, the impulsive and quasi-static peaks were attained, which were then used to quantify the probabilities of individual impulsive, dynamic, and quasi-static wave impacts. Incoming wave conditions and structural clearance had a significant effect on the probabilities of different wave impacts. With the increasing wave height and wave steepness, wave impacts on the horizontal slab and vertical wall were increasingly of the impulsive type and less frequently of the quasi-static type, while the probability of dynamic impact types were relatively stable. As the overhanging slab was shifted from elevated to submerged, the dominant type of wave impact on the structure was variable, ranging from impulsive to dynamic to quasi-static as its elevation was lowered. The results indicated that up to 90% of the impacts were of the impulsive type when the overhanging slab was on or slightly over the still water level. Moreover, the presence of the vertical wall increased the magnitude of wave loads and the occurring frequency of impulsive wave impacts for the horizontal slab.