Pressure-time Curve Research Articles

Experimental investigation on the vented flame and pressure behaviour of hydrogen-air mixtures

To explore the changes in pressure and flame propagation inside and outside the vessel when the pipe diameter does not match the vent diameter, and to check the conservatism of standards NFPA 68 and EN 14491 for this case, an experimental apparatus was utilized to investigate the influences of static activation pressure (0.7–1.75 bar) and vent diameter (30–70 mm) on the deflagration behavior of hydrogen–air mixtures (Φ: 0.6–1.4). The vented pressure, flame propagation, and pressure–flame interaction characteristics of hydrogen–air mixtures were observed and analyzed. Additionally, the conservatism of the calculated venting area under the experimental conditions of NPFA 68 and EN 14491 was verified. The results indicated that under an equivalence ratio of 0.6, the pressure-time curve inside the container exhibited only one peak (Pmax11). In the stoichiometric and fuel-rich states, the pressure-time curve inside the container exhibited two peaks attributed to the decrease in venting efficiency due to the secondary explosion inside the pipe, increasing the turbulence intensity within the container. When the static activation pressure is 0.7bar, the pressures of the three vent diameters of 30, 50 and 70 dropped by 11.34%, 24.38% and 26.86% respectively. And the Pmax11 at Φ= 1.0 and Φ= 1.4 are similar, while this phenomenon is not observed for other vent diameters. When the vent diameter was inconsistent with the duct diameter. the calculations of both standards were conservative. However, under these testing conditions (vent diameter: 30–70 mm, static activation pressure: 0.7–1.75 bar), the NPFA 68 calculations yield a conservatism range of 3.3 to 11, whereas EN14491 ranges from 1.6 to 15.7. The NPFA 68 results were more stable and concentrated, making these conditions more suitable for industry safety design in hydrogen venting.

The spatio-temporal evolution of shock wave pressure induced by laser: Effects of laser parameters and confinement layer

The spatio-temporal distribution of the shock wave pressure on the surface of the target is the key to the performance of laser shock processing (LSP), which is mainly determined by the laser parameters and the confinement layer. The two-dimensional kinetic simulations of the expansion process of the shock wave induced by irradiation of an aluminum target with nanosecond laser pulses are performed. It is found that by controlling the gap between the rigid confinement layer and the aluminum target, and the interval time between the double pulse laser pulses, multiple peaks appear on the shock wave pressure-time curve of the aluminum target surface, and the value and interval time of each peak will change.

Pressure Source Model of the Production Process of Natural Gas from Unconventional Reservoirs

This work is focused on developing a computational model to predict the production rate and pressure evolution of natural gas from unconventional reservoirs, particularly shale gas deposits. The model is based on the principle of conservation of mechanical energy and was developed from the transient solution of Bernoulli’s equation. This solution was obtained by computing the pressure evolution in the well resulting from the combined action of extracting the free gas and of gasification from kerogen. The transient behavior of gas production by hydraulic fracturing was calculated by numerically integrating Bernoulli’s equation. The curves representing gas flow evolution were considered as a series of stepwise steady states under a constant gas flow rate, similar to the pressure–time curves. These time steps were connected by instantaneous drops in pressure or gas flow rates. On the other hand, the delayed release of the adsorbed and dissolved gas in the kerogen was accurately calculated by introducing a semi-empirical gas pressure source term into the gas well pressure equation. The effect of this source is to gradually increase the gas pressure in the reservoir, emulating the gas release mechanisms from the organic matter. Model validation was based on production data from the unconventional reservoirs Eagle Ford, U.S.A., and Burgos basin, México. The initial measured gas production rate was used to determine a global friction factor of the gas flowing out from soil cracks and ducts. Additionally, measured production rate data were used to determine the coefficients of the source term function. Pearson correlation coefficients of 0.97 and 0.96 were obtained for Eagle Ford and Burgos basins data, respectively. In contrast, the corresponding coefficients calculated from the traditional Arps’ model were 0.89 and 0.5, respectively. The present pressure source model (PSM) represents a new approach to characterize the process of gas production from unconventional reservoirs, proving to be accurate in forecasting both the gas flow rate and pressure evolution during gas production. The postulated pressure source term was shown to mimic the desorption and diffusion kinetics, which release free gas from the kerogen.

Intraoperative right ventricular end-systolic pressure–volume loop analysis in patients undergoing cardiac surgery: A proof-of-concept methodology

BackgroundPerioperative right ventricular (RV) dysfunction is associated with increased morbidity and mortality in cardiac surgery patients. This study aimed to demonstrate proof of concept in generating intraoperative RV pressure–volume (PV) loops and conducting an end-systolic PV relationship (ESPVR) analysis using data obtained from routinely used intraoperative monitors. MethodsAdult patients undergoing cardiac surgery with the placement of a pulmonary artery catheter (PAC) between May 2023 and March 2024 were included prospectively. The PV loops were generated using 3-dimensional echocardiographic RV volume data and continuous RV pressure data obtained from a PAC. The volume–time and pressure–time curves were digitized using the semiautomatic WebPlotDigitizer program and synchronized to reconstruct an RV PV loop and analyze ESPVR using the previously validated single-beat method. ResultsIntraoperative RV PV loops were generated for 25 patients, including 17 patients with preserved RV systolic function (group 1) and 8 patients with reduced systolic function (group 2). Mean Ees, Ea, and Ees/Ea ratio were 0.63 ± 0.25 mm Hg/mL, 0.60 ± 0.23 mm Hg/mL, and 1.0 8 ± 0.31 mm Hg/mL, respectively, by the Pmax method and 0.56 ± 0.32 mm Hg/mL, 0.60 ± 0.23 mm Hg/mL, and 0.91 ± 0.21 mm Hg/mL, respectively, by the V0 method. Group 1 had a significantly higher Ees compared to group 2 regardless of the calculation method and a larger Ees/Ea ratio calculated by the V0 method. ConclusionsIt is clinically feasible to derive RV PV loops from routine hemodynamic and echocardiographic data. With further validation and technological support, this can be a potential real-time intraoperative RV function monitoring tool.

Effects of biomass feedstock and applied pressure on the binding mechanism and pellet qualities

To expand the sources of feedstocks for pelleting and enhance the applicability of the pelleting device, 7 types of feedstocks with representative chemical component contents from different resources were densified. The pressure-time (P-T) curves and energy consumption were used to analyze the densification process and binding mechanism. Specific energy density and densification effects were evaluated pellet qualities and classified feedstock types. Results showed that the densification process was first affected by the feedstock types and then applied pressure. Biomass chemical component contents significantly influence the densification process, the required time, and the final pellet length. Energy consumption in the compression stage is much more than in the extrusion stage. The exponential stage consumes more than 90 % of the total energy. Energy conversion efficiency varies from 62.19 % to 95.06 % with the feedstock types and applied pressures. Single pellet density, densification effects, and specific energy densities increased with the rising applied pressure. BB, SD, PN, CS, and SB can be used as primary feedstocks. SR and ROC act as secondary feedstocks or lubricants. Cellulose, hemicellulose, and lignin of plant cell walls are solid bridges. Extractives, fat, and protein in the plant cells are binders and lubricants to make the pellet surface smooth. This paper could provide further insight into various biomass feedstock densification and general design for pelleting devices.

Surface Chemistry of Cytosporone-B Incorporated in Models for Microbial Biomembranes as Langmuir Monolayers.

Cytosporone-B, a polyketide renowned for its antimicrobial properties, was integrated into Langmuir monolayers composed of dipalmitoylphosphoethanolamine (DPPE) and dioleoylphosphoethanolamine (DOPE) lipids, effectively emulating microbial cytoplasmic membranes. This compound exhibited an expansive influence on DPPE monolayers while inducing condensation in DOPE monolayers. This led to a notable reduction in the compressibility modulus for both lipids, with a more pronounced effect observed for DPPE. The heightened destabilization observed in DOPE monolayers subjected to biologically relevant pressures was particularly noteworthy, as evidenced by surface pressure-time curves at constant area. In-depth analysis using infrared spectroscopy at the air-water interface unveiled alterations in the alkyl chains of the lipids induced by cytosporone-B. This was further corroborated by surface potential measurements, indicating a heightened tilt in the acyl chains upon drug incorporation. Notably, these observed effects did not indicate an aggregating process induced by the drug. Overall, the distinctive impact of cytosporone-B on each lipid underscores the importance of understanding the nuanced effects of microbial drugs on membranes, whether in condensed or fluid states.

Analysis of impact pressure, rock-breaking effect, and ground vibration induced by the disposable CO2 fracturing tube

The technology of expansion fracturing with liquid CO2 (EFLCO2) has attracted increasing attention due to reduced vibration and damage. The disposable fracturing tube has been developed and is gradually replacing the Cardox tube. However, there is a lack of impact pressure testing of disposable tubes under real working conditions, selection of gas explosion design parameters, and systematic analysis of blasting vibration. This limitation has constrained the widespread application of disposable fracturing tubes in engineering. A joint monitoring of the pressure-time curves in the disposable tubes and boreholes was conducted. The rock-breaking effect of varying hole spacing parameters in the EFLCO2 design was analyzed, and a systematic study was carried out on the vibration peak value, frequency, and energy characteristics. The results show that (1) the pressure distribution characteristics, stress peak value, and duration in the disposable tubes are different from those of Cardox tubes, which show multi-peak distribution, low-pressure peak value, and short duration. The correlation between the pressure in the disposable tube, filling pressure, and liquid CO2 weight is established, and a theoretical calculation method for the borehole wall pressure is proposed; (2) The hole spacing in rocks of different hardness is suggested; and (3) At the same scale distance, the peak particle velocity (PPV) caused by EFLCO2 (PPVCO2) is significantly smaller than that caused by blasting (PPVexplosive). The ratio of PPVexplosive to PPVCO2 is a power function related to scale distance, and a distance-related zonality exist in this relationship. The frequency composition of the vibration signal caused by EFLCO2 is relatively simple with a narrow frequency band. Its PPV and energy are mainly concentrated in the low-frequency band. This research contributes to the optimization of disposable fracturing tubes, gas explosion design, and vibration hazard control.

The dynamic response of composite auxetic re-entrant honeycomb structure subjected to underwater impulsive loading

The researches on dynamic responses of underwater impulsive loading have been conducted. However, the previous study mainly concentrated on metal sandwich structure and fixed supported boundary. The relative research on composite auxetic re-entrant honeycomb structure and simply supported boundary are rarely. In this paper, the effect of the gradient form and relative density on impact resistance performance of composite auxetic re-entrant honeycomb structure was experimentally and numerically investigated. The one-stage light gas gun was applied to provide initial kinetic energy of the fly plate, and the diffuser-type shock tube was utilized to generate and propagate exponential decaying shock wave. The pressure–time curve was respectively amplified and recorded by the charge amplifier and oscilloscope. The response speed, final deflection of rear panel and failure mode of cores and panels were used to evaluate impact resistance of composite auxetic re-entrant honeycomb structures. Moreover, acoustic-structure interaction algorithm was applied to simulate impact course of specimens in Abaqus/Explicit. The results between experiment and numerical simulation exhibited good consistency. The results indicated that the positive gradient form could excessively slow down response speed of rear panel by dissipating energy of shock wave, and the average gradient demonstrated smaller final displacement of rear panel and less failure compared with graded structures.

Research on the blockage effect in a shock tube

The shock tube is a crucial experimental apparatus in the field of explosive impact. Limited research has been conducted on the visualization of the internal flow field in shock tubes under blockage conditions, and there is a lack of comprehensive understanding of the mechanisms behind blockage effects. This paper presents experimental and numerical investigations into the propagation of shock waves inside a shock tube and their interaction with obstructive elements. Blockage effect experiments were conducted on a shock tube test platform, where pressure data were obtained through a pressure monitoring system. Additionally, schlieren imaging technology was employed to visualize the evolution of shock wave fronts. A two-dimensional numerical model of the shock tube was established using Fluent software, and the computed results exhibited excellent agreement with the experimental data, confirming the accuracy of the numerical model. The mechanism of the blockage effect was revealed through analysis of pressure-time curves and images depicting the evolution of shock wave fronts. Furthermore, adjustments to parameters on the validated numerical model allowed for analysis and comparison of different blockage ratios. The results indicate that the disturbance to the flow field caused by the blockage effect is primarily due to the reflection of shock waves between the front surface of the obstructive element and the shock tube wall. This reflection leads to differences in pressure curves compared to free-field conditions, and such differences increase with higher blockage ratios.

Testing device for aerodynamic alternating loads on a train cabin

In high-speed train operations, especially during the passage of two trains or when passing through tunnels, the surface of the train experiences intense transient alternating pressure. The resulting alternating aerodynamic loads can lead to fatigue damage in the train's structure. To address this issue, an experimental device is developed in this study to accurately replicate the alternating aerodynamic loads experienced by trains. In this research, a novel method for simulating variable loads using triangular pressure wave patterns is proposed. Validation tests are conducted to assess the effectiveness of the device in replicating the desired load profiles. Furthermore, a noise suppression mechanism is incorporated into the device design. By incorporating noise source analysis and optimization techniques, the device design effectively controls the noise level within 85 dBA during the loading process. The experimental results demonstrate that the proposed device can achieve a triangular wave loading frequency of 2.5 cycles per minute, with a pressure range of ±3000 Pa for a 250 m3 high-speed train cabin. The pressure load output stability has high consistency in the pressure‒time curves at various measurement points inside the tested object, with a maximum difference of 0.99%. The experimental device designed in this study meets the requirements for simulating the aerodynamic loads on the surface of high-speed trains travelling at speeds of up to 350 km/h.

Coronary hemodynamic simulation study.

In this paper, a two-way fluid-structure coupling model is developed to simulate and analyze the hemodynamic process based on dynamic coronary angiography, and examine the influence of different hemodynamic parameters on coronary arteries in typical coronary stenosis lesions. Using the measured FFR pressure data of a patient, the pressure-time function curve is fitted to ensure the accuracy of the boundary conditions. The average error of the simulation pressure results compared to the test data is 6.74%. In addition, the results related to blood flow, pressure contour and wall shear stress contour in a typical cardiac cycle are obtained by simulation analysis. These results are found to be in good agreement with the laws of the real cardiac cycle, which verifies the rationality of the simulation. In conclusion, based on the modeling and hemodynamic simulation analysis process of dynamic coronary angiography, this paper proposes a method to assist the analysis and evaluation of coronary hemodynamic and functional parameters, which has certain practical significance.

A parameter determination method of powder burn model based on Levenberg-Marquardt optimization

ABSTRACT The powder burn model is a mathematical model used to characterize the combustion behavior of energetic materials. In this paper, a parameter determination method for the powder burn model is proposed based on the Levenberg-Marquardt (L-M) optimization algorithm, establishing connections between internal ballistics parameters and powder burn model parameters. Taking a 4/1 single-base propellant as an example, the detailed fitting process is presented, and error analysis is conducted. The fittings of the gas state equation and reaction rate equation of powder burn model converge at the 15th and 22nd iterations, respectively. Both fittings displayed a high level of accuracy, with an R-squared value of 0.999. The comparison with the results of the closed bomb experiments demonstrates excellent agreement between pressure-time curves calculated by the powder burn model and the internal ballistics model, confirming their suitability for describing the combustion behavior of propellants. This method provides a foundation for numerically simulating the internal ballistics combustion behavior of energetic materials.

Influence of water coupling coefficient on the blasting effect of red sandstone specimens

This study investigates the impact of different water coupling coefficients on the blasting effect of red sandstone. The analysis is based on the theories of detonation wave and elastic wave, focusing on the variation in wall pressure of the blasting holes. Using DDNP explosive as the explosive load, blasting tests were conducted on red sandstone specimens with four different water coupling coefficients: 1.20, 1.33, 1.50, and 2.00. The study examines the morphologies of the rock specimens after blasting under these different water coupling coefficients. Additionally, the fractal dimensions of the surface cracks resulting from the blasting were calculated to provide a quantitative evaluation of the extent of rock damage. CT scanning and 3D reconstruction were performed on the post-blasting specimens to visually depict the extent of damage and fractures within the rock. Additionally, the volume fractal dimension and damage degree of the post-blasting specimens are calculated. The findings are then combined with numerical simulation to facilitate auxiliary analysis. The results demonstrate that an increase in the water coupling coefficient leads to a reduction in the peak pressure on the hole wall and the crushing zone, enabling more of the explosion energy to be utilized for crack propagation following the explosion. The specimens exhibited distinct failure patterns, resulting in corresponding changes in fractal dimensions. The simulated pore wall pressure–time curve validated the derived theoretical results, whereas the stress cloud map and explosion energy-time curve demonstrated the buffering effect of the water medium. As the water coupling coefficient increases, the buffering effect of the water medium becomes increasingly prominent.

Effects of ignition location and vent area on the external explosion in vented hydrogen explosions

In the current study, effects of vent area and ignition location on vented stoichiometric hydrogen-air mixture explosion were experimentally and numerically investigated. Internal and external pressure-time curves and flame behavior were focused. For low vent coefficient Kv = 4, the maximum internal pressure results from the vent rupture for front ignition and the external explosion for center ignition and rear ignition. The maximum internal pressure for IL4 is larger than those for other ignition locations. The maximum internal pressure is induced by the internal chemical reaction and increases monotonically with Kv for different ignition locations, and the maximum internal pressure occurs at center ignition as Kv ＞ 4. Mach disk in external flame begins to appear when Kv increases to 12.75 for front ignition and 8.65 for other ignition locations. External pressure histories show two pressure peaks P1 and P2 for center and rear ignitions. Although the pressure peak P1 results from the leading pressure wave, the pressure peak P2 is induced by the venting flame and external explosion for center ignition and rear ignition, respectively. Only one pressure peak was recorded for center ignition. For front ignition and IL2, the maximum external pressure increases with Kv while it firstly increases and then decreases for center ignition, IL4 and rear ignition, the critical value is Kv = 17.36 for center ignition and IL4 while it is Kv = 8.65 for rear ignition.

Gas breaktrough behavior of the Spanish reference bentonite


 The Spanish concept for the geological disposal of radioactive waste implies the use of pre-compacted bentonite, as a main component of the engineering barrier system. The reference bentonite, called FEBEX bentonite, is composed mainly of montmorillonite, has a maximum grain size of 5 mm and a hygroscopic water content of ~14.5%. The aim of this work was to determine the gas breakthrough (BT) pressure on saturated samples of this buffer material.
 Samples (20 mm length, 38/50 mm diameter) were uniaxially compacted at 1.5 and 1.6 g·cm-3 dry densities (DD), directly in the test cell. Their water content were from hygroscopic to around 26% (full saturation at 1.6 DD), most of them on the wet side of optimum. Compaction pressures ranged between 7 and 1.4 MPa, depending on target DD, water content and granulometry of the bentonite. To check the effect of the as-compacted macrostructure, we tested three grain size distributions (full <5 mm, 1.18<x<2.0 mm, and 2.83<x<4.7 mm) with similar water content (hygroscopic); and the full grain size distribution with different water contents (around 18, 22 and 26%). Mercury intrusion porosimetry (MIP) on small compacted samples (for different DD and granulometric fractions) showed that the main differences between them were macrostructural, with minor effect on mesostructure.
 A series of long-term gas injection tests were carried out to determine, by constant pressure steps, the BT pressure. Some improvements were introduced in the experimental gas breaktrough (BT) setup and the testing protocol described in [1], including different configurations of gas up and downstream volumes (~150, 75 and 50 cm3), where actual pressure (inlet or outlet) is measured (Fig. 1a). A measurement of gas permeability (on the as-compacted sample) and two injection phases (on the fully saturated sample) configure the BT protocol. Each injection phase consists of a water permeability measurement and a long-term gas injection at increasing/decreasing pressures. The gas injection is intended to elicit at least two BT events (Fig 1b). The cells kept the samples in isochoric conditions during the test: after the saturation phase, the swelling pressure is expected to prevent preferential gas flows between the sample and the cell body. Once the gas injection starts no more water was supplied.
 Gas permeability was measured on as-compacted samples with the high-pressure steady-state setup described in [2, 3]. The measurements of gas outflow and other variables, including RH/Temperature, permit to calculate the gas permeability and to estimate the sample drying induced by gas flow during the test. In these samples, there was a linear relationship of gas flow with the difference of square pressures for all dry densities tested. From these measurements, intrinsic permeability ranged from 10-14 m2 to 10-17 m2 (for 1.5 DD and 1.6 DD).
 The water permeability measurement before the first gas injection phase allows to obtain a base-line value; the one after gas injection allows to determine if the sealing capacity was compromised by the previous BT events. Average values were in the range (0.7 – 2.0)·10-18 m2.
 After [1], the air entry pressure for the FEBEX compacted bentonite is around 25 MPa (for DD 1.6). BT pressures determined in this work were much lower than this value and close to the upper range of the expected swelling pressure, that controls the gas entry and the breakthrough events. Local variations in the swelling pressure due to several factors (material heterogeneity, change in suction, temperature, stress) can direct the high-pressure gas through preferential local paths.
 The BT events on pressure-time curves showed a consistent and systematic repetition of BT values (Fig 1b); they had different shapes depending on whether the injection pressure was greater than, close to or just less than the actual BT pressure; and changes in the slope of the curves could indicate different types of flow and the underlying physical concept (from microfracturing, in the case of the instantaneous episodes, to microscopic pathway dilation for the gradual ones).
 BT pressures increased with increasing dry density and water content (initial saturation degree) at compaction (considered as initial microstructural state); and the geometry of the sample (decreasing L/D ratio). The BT behavior is considered as a characteristic of a given liquid-solid system (sample): related to the initial state after compaction and the preservation of their structure during the test, at a specified temperature. Changes affecting the structure will affect the BT pressure.
 Gas migration in saturated FEBEX bentonite at DD<1.6 was interpreted to occur by the formation and propagation of dilatant pathways.

Determining the hot forming limits of titanium alloy sheet under different strain paths by constant equivalent strain rate hot gas bulging tests

This study aims to determine the hot forming limit diagram (FLD) of titanium alloy sheet using constant equivalent strain rate hot gas bulging tests. A novel method was proposed to calculate pressure-time curves under different strain paths, ensuring that the equivalent strain rate during hot deformation remains constant. The key of this method is the development of a VUMAT material subroutine that accurately reflects anisotropic hardening and r-value evolution, and the pressure loading curves under different strain paths were determined by coupling with the VUAMP amplitude subroutine embedded with a PID control algorithm. Based on dies with different cavity structures and unbonded double-layer samples, the FLDs of TA32 titanium alloy sheet under linear and nonlinear strain paths were obtained by carrying out hot gas bulging tests at 800 ℃ with a strain rate of 0.001 s-1. The results demonstrate that the proposed approach is applicable for determining the pressure-time curves under various complex strain paths, and it is experimentally verified that the equivalent strain rate of the sample apex is maintained near the target value during the bulging process. Furthermore, the significant effects of anisotropy and strain path change on the forming limits were quantitatively analyzed. The developed method is not only beneficial for testing the hot biaxial mechanical properties of materials, but also useful for controlling the strain rate during the hot forming of complex thin-walled components to improve the formability of materials.

Experimental and numerical study on the blast resistance of C-shaped doubled steel concrete slab (C-DSCS) with L-shaped connectors

This study aims to explore the blast resistance of C-shaped doubled steel concrete slabs (C-DSCS) with L-shaped connectors. These slabs utilize the superior compressive strength of concrete and enhance the load-bearing capacity by following a load path similar to that of arch structures. The dynamic behaviors and energy dissipation of the C-DSCS with L-shaped connectors were experimentally and numerically investigated under near-field explosion. Firstly, the pressure–time curve of the explosion was obtained by the pressure sensor in the test. Then, a finite element model (FEM) of the C-DSCS specimen was established through the LBE algorithm, and the accuracy of the finite element model was experimentally validated. Finally, parametric analyses was carried out to investigate the steel plate thickness, explosion distance and spacing of connectors on the dynamic response of the C-DSCS. The results indicated that the C-DSCS specimen had good integrity without failing or severe destruction under the explosion. A small number of oblique cracks appeared in the concrete infill near the free side of L-shaped connectors, which can effectively exert the compressive strength of the concrete. Concrete and bottom steel plate were the main energy-consuming component for C-DSCS and dissipated more than 78% of the explosive energy. In addition, L-shaped connectors also played a certain role in absorbing explosive energy, which can effectively reduce the maximum deflection of the specimens by decreasing the spacing of connectors. This paper provides a basis for theoretical analysis of dynamic response of C-DSCS subjected to close-in explosion, laying a foundation for further design methods.

Experimental and numerical investigation of combustion characteristics of carbon-free NH3/H2 blends in N2O

A detailed experimental and numerical investigation of the combustion characteristics of carbon-free NH3/H2 blends in N2O was performed in the present work. The experiments with various hydrogen fractions (α = 0–1.0) and equivalence ratios (φ = 0.6–1.4) were performed at ambient pressure (1 atm) and temperature (283 K) in a standard 3.375-L cubic combustion vessel. The explosion behaviors (maximum explosion pressure Pmax and maximum pressure rise rate (dp/dt)max) were obtained from the pressure-time curves. Further, the combustion characteristics (e.g. laminar burning velocity (SL), thermal expansion ratio (σ), flame thickness (δ), effective Lewis number (Leeff) and Markstein length (Lb)) were calculated numerically by means of chemical kinetic analysis using Zhang's mechanism (Zhang et al., Combust. Flame, 2017, 182: 122–141). Besides, sensitivity analyses of the explosion pressure and laminar burning velocity were performed to identify the contribution of dominant elementary reactions. The results show that, for combustion supported by N2O, the flame instability and the potential of deflagration to detonation transition (DDT) should be considered for the evaluation of Pmax and (dp/dt)max. Moreover, the hydrodynamic instability of premixed H2/NH3/N2O flame reaches its peak near the stoichiometric ratio and increases monotonously with the hydrogen fraction. The diffusion-thermal instability is more significant in the leaner mixture, and it is not invariably enhanced with the increase of hydrogen fraction but is relevant to the composition of the mixture. In addition, the sensitivity analysis of explosion pressure demonstrates that R80 (N2O + H2N2+H2O) and R70 (N2O+(M) = N2+O (+M)) are the most dominant reactions contributing to the pressure rise. The sensitivity analysis of laminar burning velocity shows that R70 (N2O+(M) = N2+O (+M)), R71 (N2O + HN2+OH) and R80 (N2O + H2N2+H2O) are the most dominant reactions enhancing laminar burning velocity.

Densification mechanism of ZnO ceramics prepared by cold sintering with molten zinc acetate dihydrate as the transient liquid medium

The transportation of Zn2+ in acetic acid (HOAc) or Zn(OAc)2 water solution was considered crucial for the successful cold sintering of ZnO ceramics. However, our work shows that ZnO ceramics can even be densified by cold sintering with the aid of solid Zn(OAc)2·2 H2O without introducing extra free water. DSC-TG analysis reveals that pure Zn(OAc)2·2 H2O is dehydrated completely into solid Zn(OAc)2 during heating in an open environment, while it melts in ZnO-Zn(OAc)2·2 H2O mixture or a high-pressure and semi-closed circumstance due to the strongly suppressed dehydration. Consequently, molten Zn(OAc)2·2 H2O acts as the transient liquid medium for the dissolution-precipitation process at over 100 °C, and plays a dominant role in the densification, microstructural evolution, and mechanical robustness of the cold-sintered ZnO ceramics. The densification mechanism is confirmed by the pressure-time curves, and reveals a novel strategy for cold sintering of water-insoluble ceramics by introducing molten hydrated salt or alkali as the transient liquid medium.

Finite element simulations and experimental investigations on formability of magnesium alloys in superplastic forming

The paper presents the formability aspects of magnesium alloy (AZ31B) sheets into regular and intricate shapes during Super Plastic Forming (SPF). Finite Element (FE) simulations are performed at specific strain rates within the superplastic temperature range. The formability of 1 mm sheet into conical, cylindrical, box and groove shaped dies are simulated. The simulated Pressure-Time (P-T) curve is given as pressure control algorithm to form the shapes experimentally. Thickness strains of the experimentally formed components validated with simulation results are found to be in close agreement with each other. It is demonstrated by the analysis that regular shapes posses uniform thickness distribution throughout the profile. The components with complex intricate shapes recorded unevenness in thinning behavior. The unevenness in thinning is influenced by the Grain Boundary Sliding (GBS) and diffusion kinetics. GBS is well controlled by optimum P-T algorithm to produce sharp intricate shapes with uniform thickness.