Blast Experiments Research Articles

Dynamic response of polyurea coated thin steel storage tank to long duration blast loadings

Cylindrical steel storage tanks are often under the threat of long duration blast loadings induced by the explosion of flammable vapor clouds, and therefore the blast response and mitigation method of the tanks are of great importance to related industries. In the meantime, polyurea coating material, which has been proved to be effective in the blast mitigation of different structures, is employed in this study for the protection of steel storage tanks. Gas blast experiments, as well as numerical and theoretical models, are utilized to investigate the response and energy absorption mechanism of steel tanks and analyze the effect of polyurea coatings. The numerical results showed that the bending of the plastic hinge lines and the tension of the connect zone of the cylindrical shell are the main energy absorption ways of the tank. The modified beam-on-foundation model is then established and verified and the model indicates that the polyurea coatings mainly influence the displacements of the tanks by increasing the area density and bending moments of the tanks. Quantitative analysis on the effect of polyurea is conducted utilizing the response spectrum of the tank’s equivalent system and the range of displacement reducing ratio caused by polyurea and the appropriate spraying strategy of polyurea are acquired accordingly. At last, further numerical simulations are performed and give results that validate the theoretical predictions.

Equivalent SDOF Load Transformation Factors for One-Way Members Subjected to Air Blast Loading

The equivalent single-degree-of-freedom (SDOF) load transformation factor expressions of the simply supported, fixed end and simply-fixed one-way members subjected to air blast loading are derived by finite series-expansion method or finite point-fitting method. Moreover, figures are used to show the relative relationship between the load transformation factors KL and the ratio of stand-off distance to structural span (γ). The typical calculation conditions show that the load transformation factors are sensitive to the piecewise function of peak overpressure when γ is less than 0.5. The load transformation factor will be a smooth curve for peak overpressure adopting a single smooth continuous function. For the blast-resistant structural design, if the error of 3% in the elastic stage and 5% in the plastic stage can be allowed, γ = 1.0 is the demarcation point between near field blast and far field blast. In addition, if the error of 0.5% can be allowed, γ ≥ 2.0 can be treated as the far field blast. The calculation results of far field blast show that the values of KL of simply supported, simply-fixed, and fixed-end members are 0.64, 0.58, and 0.54, respectively, which means that the load transformation factor is insensitive to the selection of shape function in vibration mode function or static deflection curve function. The calculation accuracy of KL expression for simply supported beam structure in this paper has been verified through near field blast experiments. This paper provides a clear numerical definition for the distinction between near field and far field explosions. It provides qualification criteria for analyzing explosion categories in blast-resistant structural design and a reference for the selection of theoretical calculation formulas.

Experimental of Inverted-T Shape Reinforced Concrete Wall Subjected to Blast Load

Reinforced concrete (RC) widely used as the construction material for the main structural element for many significant structures such as bridge and building because of its relatively high strength and economical. However, there still lacks research published regarding the appropriate reinforcement steel arrangement in a complete RC structure subjected to blast load. Most of the published experimental works focused on the small rectangular or square RC panel. From the record search, the approved design by professional engineers, when RC wall subjected to the possibility of blast load, both RC wall details either retaining wall or shear wall implemented. Therefore, the full-scale blast experiment is vital to appraise the appropriate steel reinforcement arrangement in the RC wall. The blast experiment indicated, with different steel reinforcement arrangement in the RC wall, the better blast resistance with the number of cracks on the RC wall is significantly less from one another for the wall with the arrangement of horizontal flexural reinforcement tied-outside the vertical flexural reinforcement and the hooked-in direction of vertical flexural steel reinforcement into the wall base.

Wireless Transmission of Friedlander‐Type Signals for the Dynamic Measurement of Blast Pressure

AbstractDuring explosive detonation or air blast experiments, long cables are commonly used for transmitting signals delivered by pressure sensors to the safe place of the acquisition unit. While constant efforts are undertaken for enlarging the bandwidth of sensors in order to improve the measurement precision of the peak pressure, the limitations of the wired transmission of blast pressure signals delivered by these sensors are not addressed. We discuss here such limitations and propose a wireless new solution for the dynamic measurement of Friedlander‐type signals delivered by ultra‐wideband sensors (> ). Contrary to the wired solution, the distance between the sensor and the acquisition unit does not limit the measurement bandwidth of the wireless setup. Experimental results are reported for validation purposes and pave the way of the dynamic measurement of blast pressure variations occurring at the heart of the fireball generated during explosions.

Shock Wave Physics as Related to Primary Non-Impact Blast-Induced Traumatic Brain Injury.

Blast overpressure exposure, an important cause of traumatic brain injury (TBI), may occur during combat or military training. TBI, most commonly mild TBI, is considered a signature injury of recent combat in Iraq and Afghanistan. Low intensity primary blast-induced TBI (bTBI), caused by exposure to an explosive shock wave, commonly leaves no obvious physical external signs. Numerous studies have been conducted to understand its biological effects; however, the role of shock wave energy as related to bTBI remains poorly understood. This report combines shock wave analysis with established biological effects on the mouse brain to provide insights into the effects of shock wave physics as related to low intensity bTBI outcomes from both open-air and shock tube environments. Shock wave peak pressure, rise time, positive phase duration, impulse, shock velocity, and particle velocity were measured using the Missouri open-air blast model from 16 blast experiments totaling 122 mice to quantify physical shock wave properties. Open-air shock waves were generated by detonating 350-g 1-m suspended Composition C-4 charges with targets on 1-m elevated stands at 2.15, 3, 4, and 7 m from the source. All mice sustained brain injury with no observable head movement, because of mice experiencing lower dynamic pressures than calculated in shock tubes. Impulse, pressure loading over time, was found to be directly related to bTBI severity and is a primary shock physics variable that relates to bTBI. The physical blast properties including shock wave peak pressure, rise time, positive phase duration, impulse, shock velocity, and particle velocity were examined using the Missouri open-air blast model in mice with associated neurobehavioral deficits. The blast-exposed mice sustained ultrastructural abnormalities in mitochondria, myelinated axons, and synapses, implicating that primary low intensity blast leads to nanoscale brain damage by providing the link to its pathogenesis. The velocity of the shock wave reflected back from the target stand was calculated from high-speed video and compared with that of the incident shock wave velocity. Peak incident pressure measured from high sample rate sensors was found to be within 1% of the velocity recorded by the high-speed camera, concluding that using sensors in or close to an animal brain can provide useful information regarding shock velocity within the brain, leading to more advanced knowledge between shock wave physics and tissue damage that leads to bTBIs.

Development of a Daily Epidemiological Model of Rice Blast Tailored for Seasonal Disease Early Warning in South Korea.

Early warning services for crop diseases are valuable when they provide timely forecasts that farmers can utilize to inform their disease management decisions. In South Korea, collaborative disease controls that utilize unmanned aerial vehicles are commonly performed for most rice paddies. However, such controls could benefit from seasonal disease early warnings with a lead time of a few months. As a first step to establish a seasonal disease early warning service using seasonal climate forecasts, we developed the EPIRICE Daily Risk Model for rice blast by extracting and modifying the core infection algorithms of the EPIRICE model. The daily risk scores generated by the EPIRICE Daily Risk Model were successfully converted into a realistic and measurable disease value through statistical analyses with 13 rice blast incidence datasets, and subsequently validated using the data from another rice blast experiment conducted in Icheon, South Korea, from 1974 to 2000. The sensitivity of the model to air temperature, relative humidity, and precipitation input variables was examined, and the relative humidity resulted in the most sensitive response from the model. Overall, our results indicate that the EPIRICE Daily Risk Model can be used to produce potential disease risk predictions for the seasonal disease early warning service.

Blast wave interaction with structures: an application of exploding wire experiments

The purpose of this research study is to build upon prior shock dynamics research to create an improved experimental setup that can be used to better understand the interaction of shock waves with structures. Large-scale blast wave experiments pose a risk to the individuals running the experiments, the surroundings, and the institution funding them. In contrast, small-scale blast experiments are able to decrease the danger and amount of funding needed associated with each experiment while producing valuable data. Simulations of blast wave–structure interaction may, on the other hand, result in extensive computational times and results that need verification. The exploding wire setup used in this research study has been optimized to consistently produce results at a run-time of less than 100 s per experiment. The adaptable exploding wire setup has a discharge voltage range of 10–40 kV. The configuration includes three main components: the driver, the experimental apparatus, and an ultrahigh-speed imaging system. The original makeup of the exploding wire apparatus allows for flexible adjustments of specifications such as initial detonation, shock wave origin, and magnitude in two and three dimensions. A recent advancement in algorithm tracking has allowed for automated detection of the individual shock fronts. In this instance, the exploding wire apparatus was adapted to simulate city-scale explosions in two dimensions, and the results were compared with numerical simulations.

Underwater blast loading of partially submerged sandwich composite materials in relation to air blast loading response

The research presented in this paper focusses on the underwater blast resilience of a hybrid composite sandwich panel, consisting of both glass-fibre and carbon-fibre. The hybrid fibres were selected to optimise strength and stiffness during blast loading by promoting fibre interactions. In the blast experiment, the aim was to capture full-field panel deflection during large-scale underwater blast using high-speed 3D Digital Image Correlation (DIC). The composite sandwich panel was partially submerged and subjected to a 1 kg PE7 charge at 1 m stand-off. The charge was aligned with the centre of the panel at a depth of 275 mm and mimicked the effect of a near-field subsurface mine. The DIC deflection data shows that the horizontal cross-section of the panel deforms in a parabolic shape until excessive deflection causes core shear cracking. The panel then forms the commonly observed “bathtub” deformation shape. DIC data highlighted the expected differences in initial conditions compared to air-blast experiments, including the pre-strains caused by the mass of water (hydrostatic pressure). Furthermore, water depth was shown to significantly influence panel deflection, strain and hence damage sustained under these conditions. Panel deformations and damage after blast was progressively more severe in regions deeper underwater, as pressures were higher and decayed slower compared to regions near the free surface.An identical hybrid composite sandwich panel was subjected to air blast; one panel underwent two 8 kg PE7 charges in succession at 8 m stand-off. DIC was also implemented to record the panel deformations during air blast. The air and underwater blast tests represent two different regimes of blast loading: one far-field in air and one near-field underwater. The difference in deflection development, caused by the differing fluid mediums and stand-off distances, is apparent from the full-field results. During underwater blast the panel underwent peak pressure loading of approximately 52.6 MPa whilst during air blast the panel was subjected to 67.7 kPa followed by 68.9 kPa peak pressure loads in succession. The two experiments demonstrate the response of the same hybrid composite sandwich panel under two differing blast regimes.The post-blast damage and strength of the hybrid panels following air and underwater blasts were evaluated. Post-blast testing revealed that the underwater blast causes significantly more damage compared to air blast, particularly debonding between the skins and core. The air blast panel sustains no visible rear skin/core debonding, whereas 13 regions of rear-face debonds are identified on the underwater blast panel. Sustaining no front-skin breakage was advantageous for retaining a high proportion of the compressive modulus for this hybrid layup following underwater blast. Damage mechanisms were interrelated. Determining the most detrimental type is not straightforward in real explosive and non-idealised experiments, however debonding was understandably shown to be significant. A further study to isolate failure modes and improve in situ instrumentation is ongoing.

Experimental and numerical studies on the dynamic response of stiffened plates under confined blast loads

Abstract Stiffened plate widely exists in ships, steel girders and wing of airplanes for its good bending resistance and lighter weight. The main purpose of this work is to investigate the dynamic response of stiffened plate subjected to confined blast loading through both experimental and numerical approaches. Firstly, several field blast experiments of box-shaped specimens with different dimensions and different explosive weight were conducted. The damage features of both inner-stiffened and outer-stiffened plate were obtained and investigated. Then, numerical models were built and validated by the experimental results, and the dynamic response processes were analyzed. Both the experimental and numerical results show that outward deformations produced in both inner-stiffened and outer-stiffened plate, while the ultimate deflection of outer-stiffened plate is smaller than that of inner-stiffened. In the meantime, overall bending deformations are observed in the outer stiffeners, while in-plane bulking of the flanges and instability failure of the web are observed in the inner stiffeners. In addition, the different dynamic response of stiffened plate under confined and unconfined blast loading were analyzed and compared using the validated numerical method, and the tendency of the dimensionless deflection of inner and outer stiffened plates subjected to confined blast were discussed.

Effects of content and particle size of cenospheres on the detonation characteristics of emulsion explosive

ABSTARCT Cenospheres are the main component of industrial waste of fly ash and taking full advantage of them has good economic and environmental values. In this paper, cenospheres sensitized emulsion explosive was prepared by adding cenospheres into the emulsion matrix as the sensitizers. The effects of content and particle size of cenospheres on detonation performance of emulsion explosives were studied, and the optimum formula was determined by comparing its detonation performance with glass microspheres (GMs) sensitized emulsion explosive. The optimum content and particle size of cenospheres were 12 mass% and 83 μm, and the brisance and detonation velocity were 18.34 mm and 4970 m/s, respectively, which were close to the maximum values of the traditional GMs sensitized emulsion explosive. Air blast experiments indicated that the influence of particle size of cenospheres on the work capability of emulsion explosive was consistent with its explosion power. Shelf-life test and optical microscope results showed that cenospheres sensitized emulsion explosives had good storage stability. Therefore, cenospheres could be a promising physical sensitizer for emulsion explosives.

Effect of strength matching on failure characteristics of polyurea coated thin metal plates under localized air blast loading: Experiment and numerical analysis

Abstract A favorable strength matching can be very beneficial for improving the performance of polyurea coated thin metal plates to resist blast loads. This study made an attempt to elucidate the effects of material and interface strengths, including steel and polyurea strengths, and interface normal (NFLS) and shear strengths (SFLS), on the failure characteristics of polyurea coated steel (PCS) plates under localized air blast loading. First, air blast experiments were conducted to identify the deformation and failure of PCS plates with different steel strengths. Subsequently, elaborative numerical simulations were performed to analyze the dynamic response and energy absorption characteristics of PCS plates. Finally, the effects of material and interface strengths on the failure characteristics of PCS plates were numerically evaluated. The results show that the kinetic energy of polyurea fragments significantly contributed to the total energy absorption of polyurea backing layer (PBL) that failed due to spalling. The steel strength had a significant effect, whereas the polyurea and interface strengths had marginal effect on the deformation of front steel layer (FSL). Increase in polyurea strength led to a dramatic decrease in the energy absorption proportion (EAP) of kinetic energy of polyurea fragments, but this EAP slightly varied by changing the steel strength or interface strength for PBLs that failed by spalling. The dominant energy absorption mechanisms of PBLs changed with the variation in steel and polyurea strengths, but did not vary with interface strength, including NFLS and SFLS.

Hydrothermally degraded carbon fiber / epoxy plates subjected to underwater explosive loading in a fully submerged environment

An experimental and computational investigation was conducted to evaluate the underwater blast response of fully submerged carbon fiber composite plates after prolonged exposure to saline water. The material was a biaxial carbon fiber/epoxy composite with a [±45°] fiber orientation layup. The plates were placed in a saline water bath with a temperature of 65 °C for 35 and 70 days, which simulates approximately 10 and 20 years of operating conditions in accordance to Fick's law of diffusion coupled with Arrhenius's Equation and a reference ocean temperature of 17 °C. Underwater blast experiments were performed in a 2.1 m diameter pressure vessel. The composite plates were placed in the center of the vessel while fully submerged in water, and an RP-85 explosive was detonated at a standoff distance of 102 mm from the center of the plate. Two cases of fluid hydrostatic gage pressures were investigated: 0 MPa, and 3.45 MPa. Two high speed cameras were utilized for three-dimensional Digital Image Correlation, which provided full-field displacements and velocities of the composite plates during underwater blast loading. A third high speed camera captured the behavior of the explosive gas bubble. Moreover, the pressure fields generated by the explosive detonation and resulting gas bubble were recorded with tourmaline pressure transducers. A water diffusion study was completed which showed that the diffusion of water into the composites reached a point of complete saturation after 35 days of exposure. Quasi-static material characterization tests were performed before and after prolonged exposure to saline water. The properties obtained from quasi-static testing also served as material inputs for the numerical models. The quasi-static test results showed that the tensile modulus E1,2 does not change with exposure to saline water, whereas the in-plane shear modulus G12 decreases with saline water exposure. During blast loading, for the case of 0 MPa hydrostatic gage pressure, the gas bubble interacts with the composite plate substantially. In such an event, the out of plane displacement increased for saline water exposed plates when compared to virgin structures. For the case of 3.45 MPa hydrostatic gage pressure, the gas bubble does not visibly interact with the composite plate. In this case, the out of plane displacement for specimens exposed to saline water was similar to the virgin specimen. A fully coupled Eulerian–Lagrangian fluid structure interaction simulation was performed by using the DYSMAS code. The numerical simulations showed that the displacement of fully submerged composite plates is driven by the displacement of fluid, as well as the size of the gas bubble formed by the explosive rather than the peak pressure generated by the explosive. The numerical simulations were in agreement with the experimental findings in terms of pressure history and plate deformation.

Blast resistance evaluation of urban utility tunnel reinforced with BFRP bars

To improve corrosion-resistance of shallow-buried concrete urban utility tunnels (UUTs), basalt fiber reinforced polymer (BFRP) bars are applied to reinforce UUTs. As the UUT must have excellent survival capability under accidental explosions, a shallow-buried BFRP bars reinforced UUT (BBRU) was designed and constructed. Repetitive blast experiments were carried out on this BBRU. Dynamic responses, damage evolutions and failure styles of the BBRU under repetitive explosions were revealed. The tunnel roof is the most vulnerable component and longitudinal cracks develop along the tunnel. When the scaled distance is larger than 1.10 m/kg1/3, no cracks are observed in the experiments. When the BBRU is severely damaged, there are five cracks forming and developing along the roof. The roof is simplified as a clamped-supported one-way slab, proved by the observation that the maximum strain of the transverse bar is much larger than that of the longitudinal bar. Dynamic responses of the roof slab are predicted by dynamic Euler beam theory, which can consistently predict the roof displacement under large-scaled-distance explosion. Compared with the UUT reinforced with steel bars, the BBRU has advantages in blast resistance with smaller deflections and more evenly-distributed cracks when the scaled distance is smaller than 1.260 m/kg1/3 and the steel bars enter plastic state. Longer elastic defamation of the BFRP bars endows the UUT more excellent blast resistance under small-scaled-distance explosions.

Air blast pressure characteristics of moving charge

Air blast pressure between moving charge and static charge are obviously different, however, due to the limitation of testing means, most blast or impact experiments were conducted under static state, which bring risks to evaluate safety of the target structures. In this paper, based on the finite element software and theoretical analysis, we investigated characteristics of the air blast pressure of moving charge. By introduced the toroidal distribution coefficient and radial distribution coefficient, a calculation model, used to calculate the overpressure with scope of relative distance at range of 0.4∼2 m/kg1/3 around blast center was established. The model could quickly calculate overpressure distribution around the blast center. Furthermore, isobars lines of moving charge were obtained by solving the model, some other phenomena were also analyzed.

Experimental and numerical study on dynamic response of V-shaped hull subjected to mine blast

Detonation of an anti-tank (AT) mine or improvised explosive device (IED) yields a shock wave, which can result in a severe damage to a vehicle and its personnel. Blast mitigation techniques play important role in dissipating and reflecting incoming blast waves as well as decreasing damage potential. This study set out to investigate the blast mitigation performance of V-shaped hull design of a military vehicle, both from numerical and experimental viewpoint. LS-DYNA was used in numerical studies. Results show that numerical simulation is in accord with blast experiment and maximum deviation percentage between measured and calculated displacements is 15%. Communicated by Prof. Corina Sandu.

Experimental study of blast loading behind a building corner

The paper presents unique blast experiments in reference to scientific literature and official standards. Experimental scenarios reflect a hypothetical realistic combat situation of a human being covered from a blast wave behind a rigid building corner. In the scenario assumed, the overpressure loads affect the lungs while the person is standing or the eardrums while the person is kneeling at the aiming position. The paper presents 27 free-field experiments measuring the overpressure loads. All the measurements were taken behind the right angle of the rigid wall. Two masses of TNT were considered: 200 g and 400 g. In the selected cases, a low test-to-test variability of the measured data was observed. Detailed plots of overpressure versus time are presented for various distances behind the building corner and TNT charge masses. Peak overpressure versus positive impulse plots are also demonstrated. Furthermore, the safety thresholds regarding different locations behind the building corner are defined for the considered explosive masses.

The influence of various loading rates on concrete fracture surface areas

The fracture surface areas of concrete prisms that were tested in bending under various loading rates are presented in this paper. Loading rates corresponding to quasi-static, impact and blast were applied to cover a wide range of load action that may be applied on a concrete structure over its lifetime. It was verified experimentally that the fracture surface tends to decrease with increasing loading rate from quasi-static to hard impact. However, fracture surface gained under the blast experiments do not follow this trend as there are probably other factors governing the response to the blast. It seems that the inertia or the stress concentration at the crack tip are the governing factors for the dynamic increase factor (DIF) and less for the fracture surface, while the different physical characteristics of the testing method for blast versus quasi-static or impact loading may also influence the results.

Experimental investigation on the performance of PVC foam core sandwich panels subjected to contact underwater explosion

This paper presents a blast experiment to investigate the performance of sandwich panels with metallic face sheets and ungraded/graded polyvinyl chloride (PVC) foam cores subjected to contact underwater explosion. The deformation and failure modes of the sandwich panels were identified and classified. The protective effect of sandwich panel was also evaluated by setting a witness plate. Particular attention was concentrated on the effects of the charge weight, face-sheet configuration, core height, and core gradation. Experimental results reveal that the panel front face suffered severe petalling failure and generated structural fragments; the PVC foam experienced spider-web-like crack failure and perforation failure; while the back face failed into petalling mode or plastic deformation without fracture. The increase of charge weight worsened the panel failure level as expected, yet did not affect the failure mechanisms. Adopting a thick core would benefit sandwich panel in terms of both the energy absorption enhancement and the damage level reduction. The panel system with a thick back face and a thin front face performed better in protecting the witness plate than the one with reverse configuration. Moreover, through designing the graded core with high/middle/low configuration, the panel performance could be further improved.

Polymer infused composite metal foam as a potential aircraft leading edge material

The leading edge of aircraft wings must be free from three-dimensional disturbances caused by insect adhesion, ice accretion, and particle wear in order to improve flight performance, safety, and fuel efficiency of the aircraft. An innovative solution was explored in this work by infusing stainless steel composite metal foam (S-S CMF) with a hydrophobic epoxy resin system. S-S CMF was made with 100% stainless steel using a powder metallurgy technique. The infused epoxy filled the macro- and microporosities, unique to S-S CMF’s structure, creating a product with a density similar to that of aluminum. The contact angle, wear rate, erosion resistance, and insect adhesion of the novel infused composite metal foam were measured and compared to aluminum, epoxy and stainless steel. The infusion process was determined to fill up to 88% of the pores within the S-S CMF and was found to reduce wettability and insect residue accretion. The contact angle of the infused S-S CMF was 43% higher than its parent material, stainless steel, and 130% higher than aluminum. Insect residue maximum height and areal coverage were reduced by 60 and 30%, respectively, compared to aluminum. Grit blast experiments to simulate erosion resulted in a greater roughness increase for aluminum than for the parent epoxy resin or the resin-infused S-S CMF. These results suggest that the durability and performance of infused S-S CMF was superior compared to aluminum, which is the current leading edge material of choice. Based on the promising results under relevant wear and erosion conditions, it is concluded that the infused S-S CMF can offer a potential tailored replacement to aluminum leading edge material.

Visualization and analysis of concrete specimens damage after fire and blast experiments

The paper is focused on visualization and analysis of concrete specimen damage after fire and blast experiments. A data visualization tool, based on an in-house MATLAB code, is described and its applicability and versatility are illustrated. In the first illustrative example, concrete spalling of fire exposed floor slab panels made of various types of concrete (without fibres, with polypropylene fibres, with steel fibres) is analysed. In the second example, the results of ultrasonic pulse velocity measurements of concrete bridge decks before and after blast experiments are shown in order to investigate the blast resistance of the decks made of different types of materials and to illustrate the damage of the decks in the form of the material degradation, surface spalling and puncture. The developed data visualization tool has been included in a freely available scientific computer program with a graphical user interface.