The effects of blast induced imperfections on the energy absorption characteristics of square tubes

Word processed copy.Includes bibliographical references (p. 305-320).This investigation examines how blast-induced imperfections at opposite sides of a square tube affect the thin-wall structure and reduce its crush load when compressed in the axial direction i.e. its energy absorption characteristics

Deformation and tearing of uniformly blast-loaded quadrangular stiffened plates

Includes bibliographical references (leaves 131-134).An investigation into the deformation and tearing of stiffened quadrangular plates subjected to a uniform blast load is presented. A series of experimental results and numerical modelling using the finite element package; ABAQUS, on built-in quadrangular mild steel plates of different stiffener configurations and sizes subjected to a uniform blast load are reported. The main objectives of this investigation are to determine the dynamic response of stiffened quadrangular plates subjected to uniform blast loads, to assess the effect of the stiffener configuration and size on plate failure and to use a new approach that uses material properties that include temperature dependency to model the plate response. The experimental procedure consists of creating an impulsive load with the use of plastic explosive and measuring the resulting impulse using a ballistic pendulum. Explosive is centrally laid out in two concentric rectangular annuli on quadrangular plates of thickness 1.6mm with stiffeners of sizes; 3x3mm, 3x7mm, 4x3mm and 4x7mm; and configurations; none, single, double, cross and double cross; to provide the impulse required to give deformations up to plate tearing. In all the tests of Mode I category of large inelastic deformation, the plate profiles are characterised by a uniform global dome. The results of mid-point deflection versus impulse for the various stiffener sizes and configurations for Mode I show a generally linear relationship. In all the experiments, thinning mechanisms at the boundary are observed for all plates despite different stiffener sizes and configurations. Thinning, however, is not consistent all around the boundary. Thinning is also observed at the stiffener side closest to the boundary for double and double cross stiffened plates. There is, furthermore, a reduction in the stiffener width where two stiffeners cross each other perpendicularly

Deformation of thin plates subjected to impulsive load : Part III – an update 25 years on

In 1989, Nurick and Martin published two review papers on the deformation of thin steel plates subjected to impulsive air-blast loading. The state of the art has progressed significantly in the following 25 years, and this review paper restricts itself to experimental studies that investigate the response of monolithic metal plates subjected to air-blast loading generated by detonating plastic explosive. From the large number of experiments reported, it is shown that the failure progressions in circular and quadrangular plates are similar and can be adequately described by three “failure modes” – namely large plastic deformation (mode I), tensile tearing (mode II) and shearing (mode III) although the severity and location of these failures on the plates is primarily determined by spatial distribution of the blast loading across the plate surface, and that boundary conditions significantly influence the onset of shearing and tearing failures due to variation in the in-plane movement of the plate material. The non-dimensional analysis approaches used by Nurick and Martin have been expanded to include the effects of load localisation and stand-off distance, and show good correlation with the expanded sets of test data published since 1989. It is concluded that these approaches still hold merit as simple tools for evaluating the likely effect of a close proximity air blast load on a flat metal plate

Extreme cavity expansion in soft solids: damage without fracture

Cavitation is a common damage mechanism in soft solids. Here, we study this using a phase-separation technique in stretched, elastic solids to controllably nucleate and grow small cavities by several orders of magnitude. The ability to make stable cavities of different sizes, as well as the huge range of accessible strains, allows us to systematically study the early stages of cavity expansion. Cavities grow in a scale-free manner, accompanied by irreversible bond breakage that is distributed around the growing cavity, rather than being localized to a crack tip. Furthermore, cavities appear to grow at constant driving pressure. This has strong analogies with the plasticity that occurs surrounding a growing void in ductile metals. In particular we find that, although elastomers are normally considered as brittle materials, small-scale cavity expansion is more like a ductile process. Our results have broad implications for understanding and controlling failure in soft solids

Behaviour of a blast-driven ball bearing embedded in rear detonated cylindrical explosive

This paper presents insights into the flight characteristics of a ball bearing embedded in a rear detonated cylindrical charge, which represents an idealised piece of shrapnel from an improvised explosive device. A novel experimental technique was developed to quantify the loading from a blast-driven ball bearing. The impulse contributions from the blast pressure and the ball bearing impact were separately identifiable in the experimental data. Computational simulations, validated using experimental data, were used to elucidate additional detail about the momentum transfer and damage in the ball bearings during the blast event. The results show the critical influence of charge mass and aspect ratio on the development of the detonation pressure profile, its interaction with the embedded bearing, and the flight characteristics of the bearing. Length-to-diameter ratios below a critical value were more efficient in transferring momentum to the embedded bearings. These findings provide unique and detailed insights that will prove valuable to blast protection engineers considering the effects of embedded projectiles in improvised explosive devices

Influence of ball bearing size on the flight and damage characteristics of blast-driven ball bearings

This paper presents insights into the influence of ball size on the flight characteristics and damage of a ball bearing embedded in a rear detonated cylindrical charge. It includes results from a post-test damage analysis of ball bearings from previously reported experiments. Computational simulations using Ansys Autodyn were used to provide extra information about the velocity variation during flight and the damage sustained by the ball bearings during the blast event. The influence of bearing size (diameter and mass) was investigated using the validated simulation models to extend the dataset beyond the initial experimental work. The peak bearing velocity is influenced by the charge mass to ball bearing mass ratio and the aspect ratio of the charge. Larger ball bearings require extra momentum to accelerate them to higher velocities, but their higher surface area means a greater portion of the explosive charge is involved in transferring kinetic energy to the projectile. Tensile spalling was to be the major damage mechanism within the ball bearings. The charge aspect ratio also influenced the hydrostatic pressure propagation within the ball bearing itself, affecting the location and degree of internal cracking within the bearings. These findings will prove valuable to blast protection engineers considering the effects of embedded projectiles in improvised explosive devices

Towards an understanding of the effect of adding a foam core on the blast performance of glass fibre reinforced epoxy laminate panels

This paper presents insights into the blast response of sandwich panels with lightweight foam cores and asymmetric (different thicknesses) glass fibre epoxy face sheets. Viscously damped elastic vibrations were observed in the laminates (no core), while the transient response of the sandwich panels was more complex, especially after the peak displacement was observed. The post-peak residual oscillations in the sandwich panels were larger and did not decay as significantly with time when compared to the equivalent mass laminate panel test. Delamination was the predominant mode of failure on the thinner facesheet side of the sandwich panel, whereas cracking and matrix failure were more prominent on the thicker side (which was exposed to the blast). The type of constituent materials used and testing conditions, including the clamping method, influenced the resulting failure modes observed. A probable sequence of damage in the sandwich panels was proposed, based on the transient displacement measurements, a post-test failure analysis, and consideration of the stress wave propagation through the multilayered, multimaterial structure. This work demonstrates the need for detailed understanding of the transient behaviour of multilayered structures with significant elastic energy capacity and a wide range of possible damage mechanisms. The work should prove valuable to structural engineers and designers considering the deployment of foam-core sandwich panels or fibre reinforced polymer laminates in applications when air-blast loading may pose a credible threat

The effect of scaling building configuration blast experiments on positive phase blast wave parameters

Explosions in an urban setting can have a significant negative impact. There is a need to further understand the loading effects caused by the blast’s interaction with structures. In conjunction with this, the effects of scaling and understanding the limitations of laboratory experiments are equally important given the cost incurred for full-scale experiments. The aim of this study was to determine the scaling effects on blast wave parameters found for reduced-scale urban blast scenario laboratory experiments. This paper presents the results of numerical modelling and physical experiments on detonating cuboidal PE-4 charges and measuring the pressure in direct line of sight and at three distinct positions around the corner of a small-scale “building” parallel to the rear wall. Two scales were used, namely 75% and 100%. Inter-scaling between 75% and 100% worked fairly well for positions shielded by the corner of the wall. Additionally, the lab-scale results were compared to similar (but not identical) field trials at an equivalent scale of 250%. The comparison between lab-scale idealised testing and the larger-scale field trials published by Gajewksi and Sielicki in 2020, indicated sensitivity to factors such as detonator positioning, explosive material, charge confinement/mounting, building surface roughness, and environment

Lamivudine Therapy for Korean Children with Chronic Hepatitis B

PURPOSE: Lamivudine is known to be very effective in suppressing hepatitis B virus replication and virus induced necroinflammation. The aim of this study was to evaluate lamivudine therapy efficacy, predictive factors, breakthrough, prevalence of YMDD mutation, and relapse rate in Korean children with chronic hepatitis B. MATERIALS AND METHODS: Between August 1999 and February 2005, 60 children on lamivudine therapy for chronic hepatitis B were enrolled. Treatment response was defined as alanine aminotransferase (ALT) normalization, and HBeAg and HBV-DNA disappearance. RESULTS: Seroconversion rates of HBeAg and HBV- DNA were 42% and 53%, respectively, and ALT normalization rate was 88%. Seroconversion rates of HBeAg (60.0%) and anti-HBe (60.0%) were higher in patients younger than 6 years. Seroconversion rate of HBV-DNA (68.4%) and normalization rate of serum ALT (94.7%) were highest in patients between 6 and 12 years. Seroconversion rates of all HBV markers were lowest in patients older than 12 years. Predicted 3 year cumulative seroconversion rates, were 70%, 68% for HBeAg, HBV-DNA, respectively. These were calculated by Kaplan-Meier method. Cox proportional hazard regression model showed that pre-treatment ALT was a positive predictive factor for seroconversion of HBeAg and HBV-DNA. Breakthrough phenomenon was noted in 6 patients, and 3 had a YMDD mutation. CONCLUSION: Lamivudine therapy had a significant effect on HBeAg seroconversion and HBV-DNA disappearance, and ALT normalization for Korean children with chronic hepatitis B.ope

Towards an Understanding of the Effect of Adding a Foam Core on the Blast Performance of Glass Fibre Reinforced Epoxy Laminate Panels

This paper presents insights into the blast response of sandwich panels with lightweight foam cores and asymmetric (different thicknesses) glass fibre epoxy face sheets. Viscously damped elastic vibrations were observed in the laminates (no core), while the transient response of the sandwich panels was more complex, especially after the peak displacement was observed. The post-peak residual oscillations in the sandwich panels were larger and did not decay as significantly with time when compared to the equivalent mass laminate panel test. Delamination was the predominant mode of failure on the thinner facesheet side of the sandwich panel, whereas cracking and matrix failure were more prominent on the thicker side (which was exposed to the blast). The type of constituent materials used and testing conditions, including the clamping method, influenced the resulting failure modes observed. A probable sequence of damage in the sandwich panels was proposed, based on the transient displacement measurements, a post-test failure analysis, and consideration of the stress wave propagation through the multilayered, multimaterial structure. This work demonstrates the need for detailed understanding of the transient behaviour of multilayered structures with significant elastic energy capacity and a wide range of possible damage mechanisms. The work should prove valuable to structural engineers and designers considering the deployment of foam-core sandwich panels or fibre reinforced polymer laminates in applications when air-blast loading may pose a credible threat