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As one of the main modes of damage caused by gas explosions in industrial production, the debris generated by the explosion threatens the safety of surrounding personnel and buildings. By means of experimental research and theoretical modelling, the debris generated by the vented component was experimentally studied, and a predictive model of the scattering range of explosion-induced debris was proposed. Through experiments using a self-designed explosion test apparatus, it is found that the gas explosion exerts a quasi-static pressure, and the vented plate is cracked by the plastic hinge under deflagration load. According to the force and the motion equation of the debris, the predictive model of the debris trajectory was proposed by differentiating the scattering process. The distribution of random variables in the model was determined by experimental data, and the scattering range of explosive debris was obtained using the Monte Carlo method. By comparing the calculated results with experimental data gathered under three typical conditions, the model values were seen to agree with the experimental values, and this model can predict the scattering range of debris. The proposed prediction model for debris scattering can provide a reference for the design of works used to protect against debris damage and subsequent domino effect.

Knowledge of vented flame propagation is of significance in the design of protective work against the effects of a gas explosion. Since there is little attention paid to the damage caused by the vented flame, the propagation characteristics of a vented flame in an external space were studied. Vented explosion experiments were conducted in a custom-designed chamber under three concentrations of ethylene/air mixtures and numerical simulation was also used. The propagation of a vented flame in an external space mainly depends on the combustion with unburnt gas and four typical flame profiles due to the effect of Darrieus–Landau flame instability and diffusional-thermal instability are observed. At different stages of propagation, characteristics such as velocity, stretch rate, and distance are all different. The reach of the vented flame can be expressed as an exponential relationship with time and the acceleration exponent is 0.65, which indicates that the vented flame is essentially undergoing spherical decelerating propagation under unconfined deflagration conditions. The numerical simulation applied is in good agreement with the experiments, which provides a basis for the analysis of the external flow field.

The opening model of a hinged rotating cover was presented and validated by experiments conducted in a custom-designed test system. Good agreement was found in both internal overpressure and opening behaviour. The effect of a rotating cover on vented explosion was studied experimentally and compared with that of a bursting cover. Experimental results show that, as the concentration increases to the stoichiometric value, the reaction becomes more intense and the rate of combustion increases. Meanwhile, the rotating cover opens faster and causes the release rate to increase, so the peak overpressure decreased. Compared with a bursting vent cover, the rotating cover has a slower opening process. So the venting and turbulence caused by the rotating cover are weaker than those when using a bursting cover, which causes a higher overpressure and a lower rate of pressure build-up. Through the use of high-speed photography, four typical stages of formation of a vented flame: cellular flame, jet flame, quenching flame, and internal combustion were observed under both rotating venting and bursting venting. The smooth opening of a rotating cover can reduce the turbulence caused by the venting itself, thus reducing the duration of the vented flame propagating outside and the occurrence of secondary explosions in the chamber.

The results of dynamic compression tests of the rock revealed that the actual working pressure ranged from 5 GPa to 20 GPa when the penetration velocity ranged from 1000 m/s to 4000 m/s. The region is exactly the transition area where the compression state changes from elastoplasticity to hydrodynamics, and the rock is subject to restricted internal friction. Also the region lacks accurate representation in existing penetration theories. A study of the hydrodynamic was performed by using the internal friction theory. Equations were systematically presented which covered and linked up the elastoplasticity-semifluid with internal friction and hydrodynamic pressure. And the essential connections and differences between the penetration of hypervelocity kinetic energy bombs and common penetrating bombs were illuminated. Furthermore the velocity region of hypervelocity was demarcated theoretically, illuminating the transformation of the target medium with the increased penetration velocity from elastoplasticity to semifluid with internal friction and hydrodynamics. The calculations revealed the characteristic phenomenon that the decrease of penetration depth in that the abrasion of the bomb mass and the existence of a limitation depth. In conclusion the formulas to calculate the depth and diameter of the crater were presented.

To study the theoretical calculation method of the HEL for hard rock, the major factors determining the strength of rock under dynamic loadings are firstly discussed. Secondly, the calculation method of the HEL of hard rock is suggested based on the Lundborg strength criterion, and the parameters influencing the HEL are analyzed and discussed. Thirdly, the HEL obtained by theoretical calculation, numerical modeling, and experiments are compared. Fourthly, the abnormal decreasing or increasing of the HEL in plate impact experiments of hard rock is explained. This research shows that the HEL increases with Poisson’s ratio, the shear strength at zero pressure, the coefficient of internal friction and the plastic limit, and Poisson’s ratio and the plastic limit could be the most important factors. The simplified model of this work can give a rational and practical prediction of the HEL of hard rock in theory, and the complicated interaction between the “damage front” and the diffuse elastic precursor is assumed to explain two special effects of the HEL in plate impact experiments of hard rock, where Poisson’s ratio related to damage levels seems to be the dominant factor.

Numerous investigations recorded a dramatic decrease in penetration depth at hypervelocity. The decrease is due to the severe mass loss of the projectile. The mechanics of mass loss are complicated, so the entirely theoretical model is still absent. In this paper, we derive a semitheoretical formula for mass loss by solving the equation of motion of the projectile during penetration. The result shows that the decrease in projectile mass at hypervelocity accords with the power law. Furthermore, we obtain a continuous formula for depth of penetration in the entire velocity domain. The theoretical results agree well with experimental data. The formula for the critical velocity of depth decreasing is also obtained as a by-product of the solving procedure.

Local damage on concrete slab subjected to a contact explosion includes explosive cratering on the front face and spalling or perforating on the back face. It is a subject that has been studied by many investigators for many years for many purposes. However, computational methods on explosive spallation or perforation are rare while they are significant for the design of warhead, the protective structure and engineering blasting. In this paper, the dynamic behavior of material was described by rigid-plastic model, and the material resistance of concrete slab subjected to contact explosions was derived by utilizing limit equilibrium theory. Combined with the initial and boundary conditions, the formulae of the threshold thickness have been derived, which can predict the categories of local damage on concrete slab under contact explosion loads. Besides, a non-dimensional impact factor was derived, which reflects the integrated nature of explosive sources and material resistance. Finally, analysis study of the results of numerical simulation and the derived equations proved the rationality of the proposed calculation methods.

Considering that the foundation soil (calcareous sand) of offshore platforms is subjected to wave loadings of different heights in a long time, cyclic triaxial tests are conducted on the Nanhai Sea calcareous sand under different loading conditions, i.e., amplitude, initial effective confining pressure, frequency, and waveform. Test results indicate that the failure of Nanhai Sea calcareous sand under cyclic loading is not only governed by the gradual development of excess pore water pressure but also by the accumulation of axial strain. There is a dilative tendency in loose or dense Nanhai Sea calcareous sand inhibiting the full liquefaction, which leads to the failure type of cyclic liquefaction. The effect of loading conditions on the excess pore water pressure, the axial strain, the secant modulus, and the cycle numbers to failure was investigated. The effect of loading amplitude, effective confining pressure, and waveform is profound, while the effect of frequency is not obvious. The cycle numbers to failure at different cyclic stress ratios demonstrated that the liquefaction resistance of Nanhai Sea calcareous sand is larger than that of calcareous sand in other sea areas.

For gas explosion accidents occurring in buildings, the explosion characteristics may be affected by the presence of the equipment and furniture, and the temperature produced by the vented explosion threatens the safety of surrounding personal and buildings. To investigate the internal overpressure and external temperature behaviors, explosion venting tests of methane-air mixtures were conducted in a self-designed 4.5-m3 square chamber, by changing the solid obstacles, ignition positions, and initial turbulence levels. The results showed that P1 is generated due to the venting rate exceeding the volume growth rate of products after vent opening; with increasing flame propagation, flame front increases and more folds are present on the surface during venting, when the rate of combustion product exceeds the venting rate again, then P2 forms. Ignition position and obstacles have little effect on P1, but affect the Helmholtz oscillation and high-frequency pressure oscillation (P4). Front ignition leads to the longest duration of Helmholtz oscillation and central ignition results in the largest P4. In the presence of obstacles, P4 is eliminated and strengthened in the cases of rear and front ignitions, respectively. P4 decreases and then increases as a function of the number of obstacles. Front ignition leads to the lowest temperature peak, rear and central ignition results in the same temperature peak. The length of the high-temperature field is the shortest under four obstacles and front ignition, respectively. Under strong initial turbulence, the overpressure peak, length and duration of the high-temperature field are the largest.

Analogue material with appropriate properties is of great importance to the reliability of geomechanical model test, which is one of the mostly used approaches in field of geotechnical research. In this paper, a new type of analogue material is developed, which is composed of coarse aggregate (quartz sand and/or barite sand), fine aggregate (barite powder), and cementitious material (anhydrous sodium silicate). The components of each raw material are the key influencing factors, which significantly affect the physical and mechanical parameters of analogue materials. In order to establish the relationship between parameters and factors, the material properties including density, Young’s modulus, uniaxial compressive strength, and tensile strength were investigated by a series of orthogonal experiments with hundreds of samples. By orthogonal regression analysis, the regression equations of each parameter were obtained based on experimental data, which can predict the properties of the developed analogue materials according to proportions. The experiments and applications indicate that sodium metasilicate cemented analogue material is a type of low-strength and low-modulus material with designable density, which is insensitive to humidity and temperature and satisfies mechanical scaling criteria for weak rock or soft geological materials. Moreover, the developed material can be easily cast into structures with complex geometry shapes and simulate the deformation and failure processes of prototype rocks.

Explosion venting trials were conducted in a 4.5 m3 stainless chamber to investigate the effects of ignition position and vent area on the explosion characteristics of 9.5 vol% methane-air mixtures using a high-speed camera and three pressure transducers under standard conditions (P0 = 100 kPa, T0 = 298 K). This work provides a basic understanding of the relationship between flame behaviors and internal pressure under different experimental conditions. The results show that hydrodynamic instability, diffusive-thermal instability, and R-T instability stimulate the cellular structure and oscillations of the flame front, and the increase of the internal pressure promotes the instability of the flame front. P1 forms owing to the rate of combustion products and dynamic characteristics of the vented plate. The coupling of the flame front, reflected wave on the walls and the acoustic wave, results in violent flame oscillations during venting, corresponding to P4. Ignition position has almost no effect on the flame front speed before vented plate failure. Helmholtz oscillation process is more violent for ignition near the vent but disappears with decreasing vent area. Central ignition always leads to the maximum pressure peak, only two pressure peaks are observed for front or central ignition, three pressure peaks occur after rear ignition. As the vent area decreases, P1 and P4 are the dominant peak pressures in the cases of rear and central ignitions, respectively. The maximum pressure peak is equal in the front and rear ignition cases when the vent area is greater than, or equal to 0.36 m2.

The testing of vented explosion of methane-air mixtures was conducted in a custom-designed 4.5-m3 steel chamber. Methane concentrations in the mixed gas varied between 7 and 13 vol% and the static hysteresis time was set as 0, 1, and 5 min to characterize strong, medium and weak turbulence levels. The effects of concentration and initial turbulence on pressure characteristics and flame development were investigated. It is found that the quasi-static pressure in the chamber during vented explosion can be divided into three stages: pressure release, Helmholtz oscillation, and acoustic oscillation. The Helmholtz oscillation at a frequency of about 20–40 Hz is produced after the peak pressure P1 caused by the pressure release at all concentrations; however, the acoustic oscillation at a frequency of about 300 Hz only occurs after Helmholtz oscillation when the concentration is near the optimum. In the early stage of internal flame development, the cellular structure is generated due to hydrodynamic instability and diffusive-thermal instability, and the flame front is distorted owing to the instability caused by venting. Initial turbulence distorts the flame front, significantly increases the peak pressure, and stimulates the generation of acoustic oscillation at the upper and lower limits of concentration. Under the influence of initial high turbulence, the internal flame propagation distance has a power function relationship with time, and the turbulence acceleration factor and distance also show a power function relationship.

Micro carbonaceous spheres have been successfully synthesized from watermelon via a one-pot hydrothermal reaction. After a quick annealing process to remove the surface oxygen groups, the as-prepared spheres presented an excellent microwave absorption performance at the Ku band (12–18 GHz), with a loading ratio of 25 wt% in a paraffin-based composite at 2.0 mm thickness.

A structural model experiment was carried out on a buried scaled-down reinforced-concrete arch structure subjected to underground close-in explosions. The aim of the experiment is to provide believable results of dynamic responses of large-span structures, including the dynamic loads, deflections, strains and failure modes. To achieve this objective, blast experiments were carried out under 0.6 kg, 3 kg, 6 kg and 17.4 kg TNT charges, respectively. Distribution laws of the applied dynamic loads, deflections, strains, accelerations and the failure modes of the arch were revealed. Different from the quasi-uniform distribution style subjected to far-field explosions, the dynamic loads applied on the buried arch subjected to close-in explosions have tense local effects and render a triangle-like distribution style. According to the tested deformations and strains, it can be concluded that subjected to close-in explosions, the buried arch deforms at a dominant flexural mode, companying with compression mode. Spalling, tensile cracks and shear failures of the concrete and yielding of the steel bars are the main failure modes of the blast-loaded arch. The arch will collapse after four or five plastic hinge lines formed. The experimental data are helpful for engineers and well support further theoretical analysis.

A facile self-assembled polymerization method has been used to form pyrrole to an ultralight three-dimensional (3D) polypyrrole (PPy) aerogel. It exhibits an effective electromagnetic absorption (EA) bandwidth (deeper than −10 dB), which was characterized as 6.2 GHz when the filler loading is only 7 wt. % in paraffin based composite. This 3D-PPy aerogel can be considered as a light weight, low adjunction, thin thickness, and high performance EA material.