Internal Blast Loading Research Articles

Effective Impulse for Fully Clamped Rectangular Plates Under Internal Blast Loading

Effective Impulse for Fully Clamped Rectangular Plates Under Internal Blast Loading

Theoretical and Numerical Analysis of Blasting Pressure of Cylindrical Shells under Internal Explosive Loading

Cylindrical shells are principal structural elements that are used for many purposes, such as offshore, sub-marine, and airborne structures. The nonlinear mechanics model of internal blast loading was established to predict the dynamic blast pressure of cylindrical shells. However, due to the complexity of the nonlinear mechanical model, the solution process is time-consuming. In this study, the nonlinear mechanics model of internal blast loading is linearized, and the dynamic blast pressure of cylindrical shells is solved. First, a mechanical model of cylindrical shells subjected to internal blast loading is proposed. To simplify the calculation, the internal blast loading is reduced to linearly uniform variations. Second, according to the stress function method, the dynamic blast pressure equation of cylindrical shells subjected to blast loading is derived. Third, the calculated results are compared with those of the finite element method (FEM) under different durations of dynamic pressure pulse. Finally, to reduce the errors, the dynamic blast pressure equation is further optimized. The results demonstrate that the optimized equation is in good agreement with the FEM, and is feasible to linearize the internal blast loading of cylindrical shells.

Review of the damage and protection of warship structures under internal blast loading

Review of the damage and protection of warship structures under internal blast loading

Dynamic instability of fiber composite cylindrical shell with metal liner subjected to internal pulse loading

Thin-walled cylindrical shells are commonly used structures in explosion containment vessels. When subjected to internal blast loading, these cylindrical shells are prone to dynamic buckling failure.In this work the dynamic stability of cylindrical fiber composite shells with metal liner subjected to uniform internal pressure pulse was investigated through both finite element simulations and theoretical modelling. In particular, pulse buckling of the inner metal liner and vibrational buckling of the outer fiber composite shell were observed and studied. Dynamic, Implicit analysis in ABAQUS Standard considering the initial geometric imperfections were conducted to study the mechanisms for the dynamic buckling of the inner metal liner and outer fiber composite shell. The simulated buckled shape using a simplified two-dimensional model could successfully reproduce the previous experimental results. The dynamic pulse buckling of the metal liner was found to occur during the plastic compression process. The effect of the buckling amplitude of the inner metal liner on the dynamic stability of the outer fiber composite shell was also revealed using numerical simulations. Instead of preventing the outer fiber composite shell from buckling instability, severely buckled metal liner with large buckling amplitude may even accelerate the growth of unstable mode of the fiber composite shell. The theoretical solution for the radial deformation of the metal liner was established by modelling the growth of the buckling mode as the amplification of the initial geometric or velocity imperfection. The most amplified mode and corresponding amplification were determined by the derived amplification function. The solutions for the radial deformation of the outer fiber composite shell were represented by a set of Mathieu differential equations. The dynamic instability of the fiber composite shells was determined from the Mathieu stability charts. The dependence of the dynamic instability of the bilayer composite shells on various parameters such as composite layup, thickness-to-radius ratio and impulse of pressure pulse loading was theoretically predicted and compared with the finite element simulation results.

Equivalent scaling method on the dynamic response of box-shaped structures under internal blast

Scaled-down experiments are one of the main approaches to represent the dynamic response and damage characteristics of full-scale prototype. While, it is well known that structures subjected to dynamic loads do not follow the usual scaling laws due to the size effects and strain rate sensitivity. The present study proposes a new procedure to equivalent scale the dynamic response of steel box structures subjected to internal blast loading. The present equivalent scaling method based on a new dimensionless number and considered the influence of both the size effects of structural dimension and the strain rate sensitivity on material resistance. This method also has an advantage of convenient engineering application. Moreover, two field tests designed according to the present scaling method were conducted to examine the effective of this method. The experimental results show that the smaller scale specimen presents similar damage mode and features with the larger scale one according to the comparison of the test results. In addition, discussions on the similarity of internal blast load and on the larger scale scaling were conducted through numerical simulations. The numerical results show that the similarity of the explosive pressure load inside the structure is related to the complexity of the structure. The difference of the pressure peaks exceeds 10% at the box corner when according to Hopkinson scaling law. The deformation results show that the scaling is more perfectly when the present scaling method is applied.

Response of Fully Prefabricated Subway Stations Subjected to Internal Blast Loading

A new kind of fully prefabricated subway station is developed in Changchun, China. This study investigates the failure mechanisms of these stations subjected to medium internal blast loading. A series of numerical simulations are carried out using the finite element program LS-DYNA. From the results, the damage and failure of the station are progressive and occur when the main event of blast loading is over. The distribution of casualties is presented in the subway station. Results show that the joints of the fully prefabricated stations can help reduce the damage of the underground stations.

Protective Effects of Ventilation Shaft in Tunnel Structures Subjected to Internal Blast Loading

Terrorist attacks on tunnels result in massive economic and societal losses. A new approach to simulate blast loading using LS-DYNA was introduced to investigate the influence of ventilation shaft on circular cast-iron tunnels in saturated soil subjected to internal blast loading. The combined effect of reduced blast pressure and modified lining vibration characteristics was observed to depend on the magnitude of blast loading. Ventilation helped to mitigate lining damage when the blast loading was low. Thus, ventilation shaft could be used as an effective mitigation method for tunnels.

Experimental Study on Ground Vibration Caused by the Blast Loading of an Explosion Vessel

To investigate the ground vibration caused by the internal blast loading of an explosion vessel while evaluating the damage caused by vibration propagation to surrounding buildings, a series of explosion vibration tests were carried out using an explosion vessel. The blasting vibration monitors recorded the vibration parameters, and the vibration velocity frequency distributions were analyzed by the Hilbert–Huang transform (HHT) method. The results show that the explosion vibration velocity is closely related to the explosive charge and propagation distance. The effect of an explosive charge and propagation distance on the vibration amplitude at frequencies of 20–60[Formula: see text]Hz is not apparent, but at frequencies of 5–10[Formula: see text]Hz, low-order frequencies are noticeable. Furthermore, the energy amplitude and vibration action duration increase with increasing explosive charge and decrease with increasing propagation distance. The results provide an essential reference for studying the propagation law and effects on ground vibration waves produced by blast loading in an explosion vessel.

A review on internal blast damage effects of multi-box type structures

The damage mechanisms of structures under internal blast are important for the prediction and evaluation of damage effects of conventional weapons and the design of anti-explosion structures of buildings and ships. The researches status and existing problems are discussed in this paper, based on the following four aspects as the internal explosion loads on structures, the plastic responses of structures to internal explosion loads, the damage modes of box-wall structures under internal explosion loads, and the damage modes and distribution of multi-box structures under internal explosion loads. With respect to an internal blast load, it is recognized that the blast model can be divided into dynamic high-pressure stage and quasi-static pressure stage. The former is formed by the initial shock wave and reflection wave while the latter is mainly composed of expansion of detonation gas and chemical energy released by explosion. In regard to the plastic response of the structure under the internal blast load, the studies have shown that quasi-static pressure plays an important role in the response process. With respect to the damage mode of the internal blast loaded structure, the damage mode is greatly affected by the pressure relief mode and pressure relief speed, studies on the damage modes of the beam and plate were introduced. As regards the damage mode and distribution of multi-box structures under the internal blast load, the internal explosion damage of the metal box structure of ships was mainly introduced. Most of the current researches focus on the damage features and there is rarely systematic understanding and analysis for the damagemechanisms. Through the review of the research on the damage and damage of the structures under the internal blast load, suggestions are provided for further researches on: (1) the models to describe the internal explosion loads on more complex structures and the corresponding damage effects; (2) the mechanisms of dynamic response of the box walls to internal blast load; (3) the coupling effect of multi-box structures with internal explosion waves and detonation products; (4) the methods to quickly and accurately predict the damage mode, damage range and damage degree of structures under internal explosion loads.

Influence of standoff distance on the deformation of square steel plates subjected to internal blast loadings

This study presents a combining experimental and numerical efforts on elucidating the influence of the standoff distance on large inelastic deformation of square steel plates subjected to the fully-confined internal blast loading from TNT detonation. Experimental results reveal that increasing standoff distance could lead to a monotonic increase of permanent central displacement of the target plate, which contradicts the well-known free-air blast scenarios. Detailed three-dimensional finite element simulations using LS-Dyna are carried out to provide additional insights into the pressure evolution and transient response of the ductile plates. The numerical results are validated against experimental data where they were found to be in reasonable agreements. Numerical predictions reveal that complex pressure wave interactions within the blast chamber, and the saturated impulse effect attribute, in part, or combination, to the aforesaid phenomenon. The discussions on the limitation of the current findings are also provided, highlighting its dependency on the confinement’s geometry.

The scaling laws of cabin structures subjected to internal blast loading: Experimental and numerical studies

This paper presents a combination of experimental and numerical investigations on the dynamic response of scaling cabin structures under internal blast loading. The purpose of this study is to modify the similar relationship between the scaled-down model and the prototype of the cabin structures under internal blast loading. According to the Hopkinson’s scaling law, three sets of cabin structure models with different scaling factors combined with different explosive masses were designed for the experimental study. The dynamic deformation process of the models was recorded by a three-dimensional digital imaging correlation (DIC) method and a 3D scanning technology was used to reconstruct the deformation modes of the specimen. In addition, a finite element model was developed for the modification of the scaling law. The experimental results showed that the final deflection-to-thickness ratio was increased with the increase of the model size despite of the similar trend of their deformation processes. The reason for this inconsistency was discussed based on the traditional scaling law and a modified formula considering of the effects of size and strain-rate was provided.

Review of methods for prediction of internal blast loading

A review of internal blast loads on structures modeling methods is presented in the paper. Also, numerical simulations of the internal explosion were done in software Ansys Autodyn. Critical areas of confined spaces were identified for this type of explosion event. Recommendations were given regarding the use of numerical simulations in blast wave parameter prediction, as well as suggestions for further research.

Review of methods for prediction of internal blast loading

A review of internal blast loads on structures modeling methods is presented in the paper. Also, numerical simulations of the internal explosion were done in software Ansys Autodyn. Critical areas of confined spaces were identified for this type of explosion event. Recommendations were given regarding the use of numerical simulations in blast wave parameter prediction, as well as suggestions for further research.

Effect of blast inside tunnel on surrounding soil mass, tunnel lining, and superstructure for varying shapes of tunnels

In this study, a finite element (FE) analysis of shallow tunnels exposed to a blast inside the tunnel, with soil as surrounding medium and a structure at ground level, was performed. The ConWep program, developed by the US Army, was used to simulate blast loading using ABAQUS/Explicit®. Drucker–Prager (D–P) plasticity model, concrete damage plasticity (CDP), and Johnson–Cook (J–C) plasticity models were used to define the behavior of the soil, concrete, and reinforcement, respectively. FE analysis was carried out to compare the damages to the superstructure with variation in the cross-sectional shapes of the tunnel under internal blast loading. Three tunnel shapes (circular, rectangular, and horseshoe cross-sections) were considered in the FE analysis. An explosive of 100 kg TNT was located at the center of the cross-section of the tunnel. The response of the tunnel in terms of displacement and stress at critical locations was computed. The results showed that changes in the cross-section of the tunnel affect the stability of the tunnel, even when keeping all other factors constant. It was observed that the intensity of the stresses was the highest for a rectangular tunnel and lowest for a circular tunnel. Furthermore, it was also determined that the tunnel with a rectangular cross-section experienced the maximum displacement in the reinforced concrete (RC) lining compared with the horseshoe and circular tunnels. The displacement measured at critical structural members of the superstructure was found to be the highest for the tunnel with a rectangular cross-section and lowest for the tunnel with a circular cross-section.

A Simple Approximate Simulation Using Coupled Eulerian–Lagrangian (CEL) Simulation in Investigating Effects of Internal Blast in Rock Tunnel

The need for faster and safer means of land transportation has increased due to scarcity of land. The number of terror attacks on the underground metro tunnels has increased in the past couple of decades. These events have presented the increased need for blast resistant design of metro tunnels. The stability of underground metro tunnels constructed in the different rocks has been analysed in the present paper. The analysis of impact loading has been carried out using nonlinear finite element technique. The coupled Eulerian–Lagrangian which is an advanced method of modelling for trinitrotoluene (TNT) and air inside the tunnel has been used. The explosive charge has been assumed at the centre of the tunnel having 100 kg mass, and the analysis is carried out for 30 ms of duration. The nonlinear behaviour of TNT has been simulated by using Jones–Wilkins–Lee material model of the equation of state. The nonlinear behaviour of the different rocks, i.e. Quartzite, Quartz-Schist, Sandstone, Shale and Dolomite, has been considered through the Mohr–Coulomb constitutive model. The rock model has 30 m × 30 m × 35 m dimension having an opening of 5 m at the centre of the model. The tunnel has 12.5 m of the depth of overburden and tunnel lining has 0.35 m of thickness. The tunnel lining has been reinforced with steel bars of Fe415 steel grade, and concrete has M30 grade. The rock tunnel constructed in Shale is susceptible to a higher magnitude of damage as compared to other rocks in this paper when exposed to internal blast loading. The Quartzite rock tunnel is the most suitable choice for constructing the blast-resistant tunnel. It has been concluded that Quartzite has higher safety against an internal blast loading caused by 100 kg TNT explosive charge. Heaving has been observed for all the cases on the ground above the location of TNT.

Dynamic response of stiffened plate under internal blast: Experimental and numerical investigation

Stiffened plates are the basic units of ships, aircraft and other structures. The purpose of this paper is to investigate the dynamic response of stiffened plates under internal blast loading. A combined experimental and numerical investigation was carried out on the cabin structures with unstiffened, single-stiffened and double-stiffened plates. The characteristics of internal blast wave, the effects of stand-off distance and the stiffener position on the deflection and failure modes of stiffened plates were sequentially analyzed. It was interestingly found that the deflection first decreased and then increased with the increase of stand-off distance. Additionally, despite of the reinforcement on the deformation resistance, the stiffeners tended to reduce the damage tolerance of the target plates. This research provides the basic data and theoretical support for the blast resistance design of ships, aircraft and other structures.

Experimental and numerical studies of tubular concrete structures subjected to blast loading

The E39 coastal highway route along the west coast in Norway is envisioned a future without ferries. A submerged floating tube bridge built in concrete has been suggested as a means of crossing wide and deep fjords, and an internal blast load against this structure could have disastrous consequences. To investigate the response of tubular concrete structures subjected to blast loading, standard off-the-shelf concrete pipes were tested using live explosives. The tests were monitored by high-speed cameras and pressure sensors. Three different positions for the explosive charges were used and the charge size was varied for each position. It was found that a contact charge detonated from the outside requires approximately twice the explosive amount to breach the pipe than a contact charge detonated from the inside, suggesting a significant confinement effect. Charges placed in the centre of the cross-section produced longitudinal cracking and fragmentation. Measurements show that the pressure inside the pipe is notably higher than immediately outside. As one would expect, reinforcement increased the blast capacity of the pipes significantly. Material test specimens (cubes and cylinders) were cut from the pipes and tested quasi-statically to determine the mechanical properties. The material tests were used to calibrate a concrete material model for finite element simulations, where the blast load was described by a particle-based method. The structural response from the simulations showed good agreement with the experimental data. This applied to the contact charges as well although no special measures were taken to account for the contact detonation.

Blast analysis of tunnels in Manhattan-Schist and Quartz-Schist using coupled-Eulerian–Lagrangian method

The tunnels are the lifeline of urban centers and play a significant role in the mass transportation of goods and services. They are the locales of accident and target for subversive activities, including terror attacks. Society needs to be well aware of such accidents and mitigation methods. We have carried out the analysis of internal blast loading using finite element analysis for two different rock tunnels constructed in Manhattan-Schist and Quartz-Schist rock employing Abaqus. The coupled-Eulerian–Lagrangian method has been considered for advanced modeling of the air inside the tunnel and 100 kg of Trinitrotoluene (TNT) explosive. TNT has been considered as material for better results by using Jones–Wilkins–Lee model and Eulerian volume fraction tool in the Abaqus have been used. This study concludes that rocks having a higher angle of friction are more resistant to blast loading. Further, rocks having lower cohesion are more blast resistant. However, if the design of tunnel support remains constant in rocks, then, damage in the tunnel lining remains the same, but deformations vary.

Effect of unconfined compressive strength of rock on dynamic response of shallow unlined tunnel

Tunnels and underground space have been evolved as an integrated part of sustainable transportation infrastructure of both the developed and developing countries. Tunnels also have strategic importance in the defence sector of the nation. In recent decades, tunnels have been subjected to several events of intentional and unintentional blast incidents. The present study investigates the response of shallow unlined rock tunnels subjected to an internal blast. The effect of different unconfined compressive strengths (UCS) of rock on the extent of damage produced due to blast loading has been investigated. UCS representing dolomite, shale, sandstone, granite, basalt and quartzite medium has been investigated through a three-dimensional finite element model having dimensions of 30 m × 30 m in cross section and 35 m in length generated in Abaqus. The diameter of the unlined tunnel has been taken as 5 m having overburden depth of 12.5 m. Coupled-Eulerian–Lagrangian modelling has been adopted to simulate the blast loading. Nonlinear Mohr–Coulomb failure criteria have been adopted for different rock media. Trinitrotoluene (TNT) explosive has been used to simulate the blast loading, and Jones–Wilkins–Lee material model has been adopted to model the characteristics of TNT. Subsequently, a relation has been proposed to understand the damage caused by TNT blast loading in a shallow unlined tunnel. The total induced energy due to internal blast loading has been found to be maximum and minimum in dolomite and quartzite, respectively.

Fitness-for-Service Strategies for Impulsively Loaded Vessels

Abstract High-explosive containment vessels are often designed for repeated use, implying predominately elastic material behavior. Each explosive test imparts an impulse to the vessel wall. The vessel subsequently vibrates as a result of the internal blast loading, with amplitude diminishing exponentially in time after a few cycles due to structural damping. Flaws present in the vessel, as well as new flaws induced by fragment impact during testing, could potentially grow by fatigue during these vibrations. Subsequent explosive tests result in new sequences of vibrations, providing further opportunity for flaws to grow by fatigue. The obvious question is, How many explosive experiments can be performed before flaws potentially grow to unsafe limits? Because ASME Code Case 2564-5 (Impulsively Loaded Pressure Vessels) has just been incorporated in Section VIII, Division 3 of the 2019 ASME Boiler and Pressure Vessel Code, evaluation of remaining life and fitness-for-service of explosive containment vessels now draws upon two interrelated codes and standards: ASME Section VIII-3 and API-579/ASME FFS-1. This paper discusses their implementation in determining the remaining life of dynamically loaded vessels that have seen service and are potentially damaged. Results of a representative explosive containment vessel are presented using actual flaw data for both embedded weld flaws and fragment damage. Because of the potentially large number of flaws that can be detected by modern nondestructive inspection methods, three simplifying assumptions and a procedure are presented for conservatively eliminating from further consideration the vast majority of the flaws that possess considerable remaining life.