Blast Tests Research Articles

Strategic use of steel fibers and stirrups on enhancing impact resistance of ultra-high-performance fiber-reinforced concrete beams

In order to investigate the static and dynamic flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams, twelve half-scale beams (125 × 250 × 2438 mm) were fabricated and tested under quasi-static and drop-weight impact loading conditions. Four different volume fractions (vf) of steel fibers, i.e., 0, 0.5, 1.0, and 1.5%, and shear reinforcements were considered as test variables. Force-displacement relations and energy dissipating capacity were derived to evaluate and compare the impact resistance of the UHPFRC beams. The force-displacement curves, excluding inertial effects, were obtained by a proposed process using D'Alembert's dynamic equilibrium principle, and energy dissipating capacity was calculated by integrating the overlapped force-displacement curves of sequential impact tests. Furthermore, the equivalent blast load was converted from the impact force to extend the utilization of impact test results for substituting difficult blast tests on structural specimens. Lastly, the test results indicate that the addition of steel fibers and stirrups enhanced the static and impact resistances of the UHPFRC beams in terms of higher load carrying capacity, higher energy dissipating capacity, and lower maximum and residual displacements. As for specimens without steel fibers and stirrups, brittle shear failure occurred under static and impact loading conditions.

Thermally Conductive Study of Polyethylene/Al2O3 Composite Networks Cross-linked Pipes by Electron Beam Irradiation

The surface-modified Al2O3 particles were introduced into polyethylene(PE) to enhance the thermal conductivity, and PE/Al2O3 cross-linked networks with improved thermal and mechanical properties were prepared through electron beam(EB) irradiation technology. The incorporation of reactive irradiation sensitizer was useful in fabricating a high degree of cross-linking(DC) PE networks under a low irradiation dose. In the PE sample containing 2% sensitizer, DC ca.67.1% could be obtained under 60 kGy(1 kGy=1000 J/kg). EB-irradiation greatly improved the tensile stress of PE-based samples, and the tensile stresses of the samples with 0.2%—5% TMPTA(trimethylolpropane triacrylate) under 60 kGy were 24.61—27.77 MPa. All the EB-irradiated samples had higher Vicat softening temperatures than the samples without irradiation. After treatment at 120 kGy, the Vicat softening temperatures of PE-Al2O3-44/ TMPTA-2 increased from 127 °C to 130.4 °C. SEM images revealed that PE-Al2O3-50 samples with increased amount of Al2O3 particles showed a conduction “pathway,” and thermal conductivity reached 0.67 W/(m·K). Thus, high-performance pipes were successfully extruded, which could satisfy the static hydraulic blasting test and exhibit improved thermal conduction capability.

Blast-induced liquefaction in silty sands for full-scale testing of ground improvement methods: Insights from a multidisciplinary study

In the engineering geology field increased attention has been posed in recent years to potential liquefaction mitigation interventions in susceptible sand formations. In silty sands this is a major challenge because, as the fines content increases, vibratory methods for densification become progressively less effective. An alternative mitigation technique can be the installation of Rammed Aggregate Pier® (RAP) columns that can increase the resistance of the soil, accounting for its lateral stress increase and for the stiffness increase from soil and RAP composite response. To investigate the influence of these factors on liquefaction resistance, full-scale blast tests were performed at a silty sand site in Bondeno (Ferrara, Italy) where liquefaction was observed after the 2012 Emilia-Romagna earthquake. A multidisciplinary team of forty researchers carried out devoted experimental activities aimed at better understanding the liquefaction process at the field scale and the effectiveness of the treatment using inter-related methods. Both natural and improved areas were investigated by in-situ tests and later subjected to controlled blasting. The blast tests were monitored with geotechnical and geophysical instrumentation, topographical surveying and geological analyses on the sand boils. Results showed the RAP effectiveness due to the improvement of soil properties within the liquefiable layer and a consequent reduction of the blast-induced liquefaction settlements, likely due to soil densification and increased lateral stress. The applied multidisciplinary approach adopted for the study allowed better understanding of the mechanism involved in the liquefaction mitigation intervention and provided a better overall evaluation of mitigation effectiveness.

Experimental study on crack formation in sandstone during crater blasting under high geological stress

Crater blasting is widely used for rock excavation. In deep rock engineering projects, blasting is done in a high stress environment. To study the effects of high geological stresses on rock blasting, crater blasting tests on sandstone using an exploding electric wire were conducted under three different static load conditions. The evolution of the strain fields and the propagation of cracks on the surfaces of samples were recorded and subsequently analysed by digital image correlation. The rock fracturing mechanisms are discussed. The experimental results indicate that (1) the areas of major principal strain on the sample surfaces are circular under conditions of no static stress and symmetric biaxial stress loads, but the strain area is elliptical under a uniaxial load; (2) after blasting, the static stress state changes the crack initiation mode, crack propagation, and the distribution of the cracks in the crack network; and (3) static stress can increase the size of the blasting crater.

Study on Energy Output Characteristics of Explosives Containing B/Al in the Air Blast

It is a key problem to design and prepare metallized explosives of high energy and low sensitivity. In order to study the effect of the content of the boron/aluminum (B/Al) compound powder on the energy output property of metallized explosives in the air blast, three HMX-based explosives containing B/Al were designed and prepared. Air blast tests of cylindrical samples are performed, accompanied by numerical simulations by the finite element program LS-DYNA. The results show that the shock wave overpressures of explosives containing B/Al are higher than those of explosives containing Al under the same conditions. The deviations between the values calculated by the empirical equation and the measured values are smaller than 3.5 kPa, and the deviations between the values obtained in numerical simulations and the measured values are smaller than 4.9 kPa. Although the Al powder can enter the reaction with detonation products and air easier, the burning time of the boron powder is longer and the released energy is larger. Moreover, as the content of the B/Al compound powder increases, the burning time becomes longer, and the aftereffect work ability and the damage effect become stronger.

Prediction of blast pressure-duration capacity of monolithic Thermally Tempered Glass panes

Most standards and documents for blast-resistant design of glazing systems are based on simplified Single Degree Of Freedom (SDOF) models and triangular blast pressure time histories with no negative phase. Previous experimental studies have clearly indicated that pressure-duration or pressure-impulse design curves generated from such SDOF models may be overconservative, especially during impulsive blast scenarios. In this study, pressure-duration capacity curves for various monolithic Thermally Tempered Glass (TTG) panes are derived using Finite Element (FE) models. Moreover, the imposed blast pressure time histories include both positive and negative phases, which are deemed to be more realistic than considering the positive phase alone. Previous blast tests have shown that TTG panes can experience significant in-plane strain before fracture and exceeding the cracking strength does not necessarily mean fracture and disintegration of the pane. Accordingly, in the present study, glass fracture is judged based on the maximum principal strain rather than the stress criterion which has been widely used in earlier studies. The accuracy of the FE modeling technique and the abovementioned fracture criterion is verified using these blast test results on TTG panes. Pressure-duration curves of predicted capacity are obtained for TTG panes with different aspect ratios (1, 1.25, 1.5, 1.75, 2), different thicknesses (8 mm, 10 mm, 12 mm, 16 mm) and different widths (600 mm, 900 mm, 1,200 mm). Similar to current available standards, four edges of the adopted panes are restrained in the out-of-plane direction, but without in-plane or rotational restraints. The obtained pressure-duration capacity curves are compared with those provided by UFC 3-340-02. This shows that UFC's pressure-duration capacity curves are overconservative in both the impulsive and quasi-static regions.

Blast response of a thin oriented strand board wall

There has been a remarkable increase in the worldwide number of suicide bombing attacks in recent years. These attacks have left numerous victims as well as economic and psychological impacts on targeted locations. Developing new approaches to designing and constructing blast protection wall systems is an ever pressing need to partially mitigate the damaging effects of blast loadings. Several applications of simple blast protection wall systems have been considered for military purposes, but far fewer studies exist for non-military applications. The current study evaluates the overall performance of a thin oriented strand board (OSB) cantilever wall in response to the blast energy from explosive detonations. The study presents the results of open-space blast tests to measure the blast wave pressure in free air (without wall), and blast pressure (behind wall) at specified standoff distances. For the OSB response, a 3D dynamic finite element model was created using ABAQUS/Explicit software combined with the ConWep blast model to represent wall-blast wave interactions in free air to compare with the blast test results. Reductions in blast pressure behind the OSB wall of over 20 percent were observed. Good agreement between the test results and the numerical predictions was also found. The results of this work indicate the potential of using simple blast walls to partially mitigate blast loading at extremely low cost and minimal installation effort.

An assessment of blast modelling techniques for injury biomechanics research.

Blast-induced traumatic brain injury (TBI) has been affecting combatants and civilians. The blast pressure wave is thought to have a significant contribution to blast-related TBI. Due to the limitations and difficulties of conducting blast tests on surrogates, computational modelling has been used as a key method for exploring this field. However, the blast wave modelling methods reported in current literature have drawbacks. They either cannot generate the desirable blast pressure wave history or they are unable to accurately simulate the blast wave/structure interaction. In addition, boundary conditions, which can have significant effects on model predictions, have not been described adequately. Here, we critically assess the commonly used methods for simulating blast wave propagation in air (open-field blast) and its interaction with the human body. We investigate the predicted blast wave time history, blast wave transmission, and the effects of various boundary conditions in three-dimensional (3D) models of blast prediction. We propose a suitable meshing topology, which enables accurate prediction of blast wave propagation and interaction with the human head and significantly decreases the computational cost in 3D simulations. Finally, we predict strain and strain rate in the human brain during blast wave exposure and show the influence of the blast wave modelling methods on the brain response. The findings presented here can serve as guidelines for accurately modelling blast wave generation and interaction with the human body for injury biomechanics studies and design of prevention systems.

Improved SDOF and numerical approach to study the dynamic response of reinforced concrete columns subjected to close-in blast loading

In this study, the blast performance of steel reinforced concrete (RC) columns was experimentally and analytically investigated. The experiments consisted of 11 one-half-scale columns subjected to different levels of blast loading using TNT explosives. The experimental results show that when the scaled distance is relatively large, less damage occurs to steel RC columns with higher axial loads than to columns with smaller axial loads at the same blast level. As the scaled distance decreases, the axial load increases the level of damage to RC columns. In addition, the equivalent single-degree-of-freedom (SDOF) approach for determining the dynamic response of RC columns against combined axial and blast-induced transverse loads was improved. Nonlinear section and member analyses were incorporated into the suggested SDOF method by considering the effect of axial load and complex features of the material behavior, the high strain-rate effect and the column geometry. The SDOF model was validated by comparing the maximum displacements obtained from the SDOF analysis with experimental data from blast testing of RC columns. Parametric studies were also performed to investigate the effects of axial load, the longitudinal reinforcement ratio, transverse reinforcement ratio, aspect ratio and boundary conditions. In order to consider the local damage effect, the numerical study was undertaken to investigate the effects of transverse reinforcement spacing on the blast resistance of RC columns using LS-DYNA.

Effect of specific yoga mudras on respiratory efficiency in asthma patients

Effect of specific yoga mudras on respiratory efficiency in asthma patients - IJCAP- Print ISSN No: - 2394-2118 Online ISSN No:- 2394-2126 Article DOI No:- 10.18231/j.ijcap.2019.077, Indian Journal of Clinical Anatomy and Physiology-Indian J Clin Anat Physiol

Blast Testing and Numerical Simulation Analysis of Diversion Tunnel Upper Section for Qianping Reservoir

This paper expounds the basic theory of rock mass blasting technology, the rock blasting excavation of Qianping reservoir project was taken as an example, by means of numerical simulation and experimental research, the finite element model for rock blasting excavation in Qianping reservoir is established. The rock blast on the upper section of the diversion tunnel for Qianping reservoir is simulated by using the dynamic analysis module LS-DYNA in the finite element method analysis software ANSYS, through the comparative analysis of blast testing and numerical simulation results. The results show that, the dynamic analysis results are in good agreement with the field test, the correctness and validity of the finite element model are proved, finite element dynamic analysis model is a general calculation model, rock mechanics parameters in the model can be adjusted in the calculation process, it can be used to simulate the blasting excavation process of different rock properties.

Bursting Analysis Of GFRP Composite Pipline Used In Oil & Gas Applications

The goal of this trial study was to research the impacts of low speed effect stacking on the weight bearing limit of the E-Glass and Epoxy Composite Pipe. In this investigation we are looking at the Burst Test Results of both PVC Pipe and FRP Pipe. The examples were loaded up with water and exposed to blast test until particular spillage disappointment is watched.

EPS foam blast attenuation in full-scale field test of reinforced concrete slabs

Predicting explosion parameters is an important step when planning for blast tests or the design of blast resistant buildings. This paper presents a comparison of recorded pressure that was reflected on the surface of reinforced concrete slabs with and without EPS (Expanded Polystyrene) foam retrofit measured from a detonation of 2.7 kg of non-confined plastic explosive. Two 50 MPa reinforced concrete slabs measuring 1.0x1.0x0.08 m, simply supported on two sides were tested. The explosive was suspended at a distance of 2.0 m from the upper surface of the slabs; one of the slabs had 5.0 cm thick foam on the top side. Eight piezoelectric pressure sensors were positioned at a distance of 2.0 m from the explosive. Results showed that the foam retrofit reduced the reflected pressure by approximately 57% when compared to the slab without EPS foam retrofit.

Damage assessment and mitigation measures of underwater tunnel subjected to blast loads

The damage prediction and protective measures of tunnels subjected to blast loads have gained importance in recent years due to increasing accidental events and terrorist attacks. This paper performs numerical modeling to assess the damage characteristics of an underwater tunnel subjected to blast loads and explore the potential mitigation measures. Firstly, a three-dimensional numerical model of an underwater tunnel based on coupled Lagrange and Euler (CLE) method is developed. The accuracy of the CLE method and material models is verified with blast testing data. Subsequently, the dynamic response and damage evolution of the tunnel subjected to underwater explosions are investigated. Potential failure patterns due to various underwater blast loads are explored. Intensive numerical simulations are then carried out to investigate the damage levels of the tunnel. Based on numerical data, empirical relations are suggested to predict the tunnel damage levels based on charge weight and standoff distances. CFRP (carbon fiber reinforced polymer) cloth is used to improve the resistance of the tunnel to underwater explosions. Mitigation effects of different strengthening schemes are investigated, and the optimum strengthening thickness of the CFRP cloth is recommended. The results show that the rigidity and load carrying ability of the tunnel are significantly improved by bonding the CFRP cloth. The recommended thickness of the CFRP cloth is 0.5–0.835 mm.

Internal Fractures After Blasting Confined Rock and Mortar Cylinders

Blast-induced fines in rock negatively influence multiple aspects of raw-mineral sustainability. The Austrian Science Fund (FWF) sponsored a project to investigate the cause of the fines by studying blast fragmentation through small-scale blast tests and numerical simulations. The paper covers the experimental part of the project focusing on internal blast-induced fracturing and related mechanisms. The blast tests were done by blast-loading confined granite and mortar cylinders. The blast-driven dynamic cracking at the end face of the cylinder opposite to the initiation point was filmed with a high-speed camera. Following analyses covered internal crack patterns, fracture surfaces, and sieving of the blasted cylinders to quantify the amount of fine material created. The internal crack patterns and fracture surfaces were analysed by means of computer tomography (CT) and scanning-electron microscopy (SEM). The CT scans show that the amount of explosive charge affects the changing of the topological features of the crack patterns along the cylinder. They also depict different deformation zones around the blast-hole wall with respect to the blasted material and the amount of charge. Although fracture surfaces of larger fragments do not clearly differ in measured roughness and curvature, the SEM scans of smaller fragments show clear difference in fracture surfaces with respect to the blasted material and the amount of charge. SEM scans of thin sections extracted from the blasted cylinders show different fracture features that could be related to the branching/merging mechanism.

The effects of high strain-rate and in-plane restraint on quasi-statically loaded laminated glass: a theoretical study with applications to blast enhancement

Laminated glass panels are increasingly used to improve the blast resilience of glazed facades, as part of efforts to mitigate the threat posed to buildings and their occupants by terrorist attacks. The blast response of these ductile panels is still only partially understood, with an evident knowledge gap between fundamental behaviour at the material level and observations from full-scale blast tests. To enhance our understanding, and help bridge this gap, this paper adopts a ‘first principles’ approach to investigate the effects of high strain-rate, associated with blast loading, and the in-plane restraint offered by blast-resistant frames. These are studied by developing simplified analytical beam models, for all stages of deformation, that account for the enhanced properties of both the glass and the interlayer at high strain-rates. The increased shear modulus of the interlayer results in a composite bending response of the un-fractured laminated glass. This also enhances the residual post-fracture bending moment capacity, arising from the combined action of the glass fragments in compression and the interlayer in tension, which is considered negligible under low strain-rates. The post-fracture resistance is significantly improved by the introduction of in-plane restraint, due to the membrane action associated with panel stretching under large deflections. This is demonstrated by developing a yield condition that accounts for the relative contributions of bending and membrane action, and applying the upper bound theorem of plasticity, assuming a tearing failure of the interlayer. Future work aims to complete the theoretical framework by including the assessment of plate-action and inertia effects.

Finite element modelling of the explosive blast response of carbon fibre-polymer laminates

A finite element (FE) modelling methodology is presented to analyse the dynamic response of carbon fibre reinforced polymer laminates when loaded by the shock wave generated by an airborne explosive blast. An FE model is developed to calculate the out-of-plane deformation of laminates over the entire duration of an explosive blast loading event. The FE model can also predict the initiation and propagation of delamination cracking and ply rupture in laminates. The response of the composite target plates to explosive blast loading was modelled in the FE program Abaqus using an explicit solver. The explosive air blast load was modelled using the ConWep algorithm. The accuracy of the FE model is assessed using experimental data obtained from small-scale far-field and near-field explosive blast tests performed on carbon-polyester and carbon-vinyl ester laminates. The FE model can predict the dynamic deformation of the laminates to within an accuracy of ~10%. The model can also accurately determine delamination cracks and broken plies.

Experimental study on rock-like materials fragmentation by electric explosion method under high stress condition

High stress is the main feature of deep mining. The in situ stress plays a large part in rock fragmentation. In this study, an electric explosion system was developed to study the fragmentation behaviour of rock under high stress conditions. A series of test experiments, including electric blasting tests of copper wires in air and rock-like materials, and blasting crater tests under different stress loading conditions, were conducted. The dynamic evolution of the strain field, and crack propagation process during rock-like materials fragmentation were monitored by digital image correlation (DIC) technique. The results indicate: the electric explosion method is reliable and can provide a clean energy source for rock-like materials fragmentation. Besides, the static stress significantly affects the evolution of the strain field in specimens under electric explosion loading, and in turn changes the crack propagation behaviour, and the final shape and size of the fracture zone.

Modeling and simulation of carbon composite ballistic and blast behavior

The design of the next generation of aeronautical vehicles is driven by the vastly increased cost of fuel and the resultant imperative for greater fuel efficiency. Carbon fiber composites have been used in aeronautical structures to lower weight due to their superior stiffness and strength-to-weight properties. However, carbon composite material behavior under dynamic ballistic impact and blast loading conditions is relatively unknown. For aviation safety consideration, a computational constitutive model has been used to characterize the progressive failure behavior of carbon laminated composite plates subjected to ballistic impact and blast loading conditions. Using a meso-mechanics approach, a laminated composite is represented by a collection of selected numbers of representative unidirectional layers with proper layup configurations. The damage progression in a unidirectional layer is assumed to be governed by the strain-rate-dependent layer progressive failure model using the continuum damage mechanics approach. The composite failure model has been successfully implemented within LS-DYNA® as a user-defined material subroutine. In this paper, the ballistic limit velocity (V50) was first established for a series of laminates by ballistic impact testing. Correlation of the predicted and measured V50 values has been conducted to validate the accuracy of the ballistic modeling approach for the selected carbon composite material. A series of close-in shock hole blast tests on carbon composite panels were then tested and simulated using the LS-DYNA® Arbitrary-Lagrangian-Eulerian (ALE) method integrated with the Army Research Laboratory (ARL) progressive failure composite model. The computational constitutive model has been validated to characterize the progressive failure behavior in carbon laminates subjected to close-in blast loading conditions with reasonable accuracy. The availability of this modeling tool will greatly facilitate the development of carbon composite structures with enhanced ballistic impact and blast survivability.

The impact of various types of steel fibres on the strength parameters and blast resistance of high – performance concrete

The paper describes composition proposals and subsequent optimization and testing of developed fibre-reinforced UHPC mixtures, which seem to be optimal as construction material for the blast and ballistic protective systems, such as mobile blast-resistant walls and covers, which are the expected outcomes of the presented research project. Methods of laboratory testing and optimization of developed UHPC mixtures, with the aim of achieving the best possible values of physical-mechanical parameters, are described in this paper. In connection with laboratory verification, field blast tests of UHPC board samples and consequently of the entire blast-resistant wall system were realized and resistance to dynamic stress was investigated.