Granular layers on vibrating plates: Effective bending stiffness and particle-size effects

Acoustic methods of land mine detection rely on the vibrations of the top plate of the mine in response to sound. For granular soil (e.g., sand), the particle size is expected to influence the mine response. This hypothesis is studied experimentally using a plate loaded with dry sand of various sizes from hundreds of microns to a few millimeters. For low values of sand mass, the plate resonance decreases with added mass and eventually reaches a minimum without particle size dependence. After the minimum, a frequency increase is observed with additional mass that includes a particle-size effect. Analytical nondissipative continuum models for granular media capture the observed particle-size dependence qualitatively but not quantitatively. In addition, a continuum-based finite element model (FEM) of a two-layer plate is used, with the sand layer replaced by an equivalent elastic layer for evaluation of the effective properties of the layer. Given a thickness of sand layer and corresponding experimental resonance, an inverse FEM problem is solved iteratively to give the effective Young’s modulus and bending stiffness that matches the experimental frequency. It is shown that a continuum elastic model must employ a thickness-dependent elastic modulus in order to match experimental values

Granular layers on vibrating plates: Effective bending stiffness and particle-size effects

Acoustic methods of land mine detection rely on the vibrations of the top plate of the mine in response to sound. For granular soil (e.g., sand), the particle size is expected to influence the mine response. This hypothesis is studied experimentally using a plate loaded with dry sand of various sizes from hundreds of microns to a few millimeters. For low values of sand mass, the plate resonance decreases with added mass and eventually reaches a minimum without particle size dependence. After the minimum, a frequency increase is observed with additional mass that includes a particle-size effect. Analytical nondissipative continuum models for granular media capture the observed particle-size dependence qualitatively but not quantitatively. In addition, a continuum-based finite element model (FEM) of a two-layer plate is used, with the sand layer replaced by an equivalent elastic layer for evaluation of the effective properties of the layer. Given a thickness of sand layer and corresponding experimental resonance, an inverse FEM problem is solved iteratively to give the effective Young’s modulus and bending stiffness that matches the experimental frequency. It is shown that a continuum elastic model must employ a thickness-dependent elastic modulus in order to match experimental values

DEVELOPMENT, PARAMETERIZATION AND VALIDATION OF DYNAMIC MATERIAL MODELS FOR SOIL AND TRANSPARENT ARMOR GLASS

Despite the signing of several mine ban treaties in the 1990\u27s, it is widely recognized that there is a landmine crisis. The following are some of the main aspects of this crisis: (a) Millions of unexploded landmines remain deployed all over the world; (b) Thousands of civilians are killed or maimed every year by unintended detonations of the mines; (c) The cost of medical treatment of landmine injuries runs into the millions; (d) the ability of the international community to provide the humanitarian relief in terms of medical services, safe drinking water and food, etc., is greatly hampered by landmine contamination of the infrastructure in mine affected countries; and so on. To address the aforementioned landmine crisis, the research community around the world has taken upon itself the challenge of helping better understand the key phenomena associated with landmine detonation and interaction between detonation products, mine fragments and soil ejecta with the targets (people, structures and vehicles). Such improved understanding will help automotive manufacturers to design and fabricate personnel carriers with higher landmine-detonation survivability characteristics and a larger level of protection for the onboard personnel. In addition, the manufacturer of demining equipment and personnel protection gear used in landmine clearing are expected to benefit from a better understanding of the landmine detonation-related phenomena. The landmine detonation-related research activity can be broadly divided into three main categories: (a) shock and blast wave mechanics and dynamics including landmine detonation phenomena and large-deformation/high-deformation rate constitutive models for the attendant materials (high explosive, air, soil, etc.); (b) the kinematic and structural response of the target to blast loading including the role of target design and use of blast attenuation materials; and (c) vulnerability of human beings to post-detonation phenomena such as high blast pressures, spall fragments and large vertical and lateral accelerations. The present work falls primarily into the category (a) of the research listed above since it emphasizes the development of a large-deformation/high-deformation rate material model for soil. It is generally recognized that the properties of soil, into which a landmine is buried, play an important role in the overall effectiveness/lethality of the landmine regardless of the nature of its deployment (fully-buried, flush-buried or ground-laid). Therefore, in the present work, a series of continuum-level material models for soil of different types has been derived (using available public-domain data and various basic engineering concepts/principles), parameterized and validated against experimental results obtained from standard mine-blast testing techniques. Special attention is paid to improving the understanding of the effects of moisture, clay and gravel content on the different aspects of soil material behavior under blast loading conditions. Specifically, the effect of these soil constituents/conditions on the equation of state, strength and failure modes of the material response is investigated. The results obtained clearly revealed that: (a) the moisture clay and gravel contents of soil can substantially affect the response of soil under blast loading conditions as well as the extent of detonation-induced impulse transferred to the target structure/personnel; (b) over all, the models developed in the present work, when used in transient non-linear dynamics analysis of landmine detonation and detonation product/mine-fragment/ soil-ejecta interaction with the target structures/personnel, yielded results which are in reasonably good agreement with their experimental counterparts

NOVEL SIDE-VENT-CHANNEL BASED BLAST MITIGATION CONCEPT FOR LIGHT TACTICAL VEHICLES

A new concept solution for improving survivability of the light tactical military vehicles to blast-loads resulting from a shallow-buried mine detonated underneath such vehicles is proposed and critically assessed using computational engineering methods and tools. The solution is inspired by the principle of operation of the rocket-engine nozzles, in general and the so called \u27pulse detonation\u27 rocket engines, in particular, and is an extension of the recently introduced so-called \u27blast chimney\u27 concept (essentially a vertical channel connecting the bottom and the roof and passing through the cabin of a light tactical vehicle). Relative to the blast-chimney concept, the new solution offers benefits since it does not compromise the cabin space or the ability of the vehicle occupants to scout the environment and, is not expected to, degrade the vehicle\u27s off-road structural durability/reliability. The proposed concept utilizes properly sized and shaped side-vent channels attached to the V-shaped vehicle underbody. The utility and the blast-mitigation capacity of this concept is examined in the present work using different (i.e. coupled Eulerian/Lagrangian and coupled finite-element/discrete-particle) computational methods and tools. To maximize the blast-mitigation potential of the proposed solution, standard engineering optimization methods and tools are employed for the design of side-vent-channels. It is shown that, by proper shaping and sizing of the side-vent-channels, venting of ejected soil and supersonically-expanding gaseous detonation products can be promoted, resulting in an increase in the downward thrust on the targeted vehicle. Furthermore, it is found that optimization of the geometry and size of the side-vent-channel solution for the maximum blast-mitigation performance, requires consideration of a tradeoff between the maximum reductions in the detonation-induced total momentum transferred to, and the acceleration acquired by, the target vehicle. The results obtained farther confirmed theblast-mitigation effects of the side-vent-channels, although the extent of these effects is relatively small (3-4%)

The detection of vertical cracks in asphalt using seismic surface wave methods

Assessment of the location and of the extension of cracking in road surfaces is important for determining the potential level of deterioration in the road overall and the infrastructure buried beneath it. Damage in a pavement structure is usually initiated in the tarmac layers, making the Rayleigh wave ideally suited for the detection of shallow surface defects. This paper presents an investigation of two surface wave methods to detect and locate top-down cracks in asphalt layers. The aim of the study is to compare the results from the wellestablished Multichannel Analysis of Surface Waves (MASW) and the more recent Multiple Impact of Surface Waves (MISW) in the presence of a discontinuity and to suggest the best surface wave technique for evaluating the presence and the extension of vertical cracks in roads. The study is conducted through numerical simulations alongside experimental investigations and it considers the cases for which the cracking is internal and external to the deployment of sensors. MISW is found to enhance the visibility of the reflected waves in the frequency wavenumber (f-k) spectrum, helping with the detection of the discontinuity. In some cases, by looking at the f-k spectrum obtained with MISW it is possible to extract information regarding the location and the depth of the cracking

Seismicity and Ground Motion Simulations of the SW Iberia Margin

In this study, we focus on the region between Gorringe Bank and the Horseshoe Fault located in the SW Iberia margin, which is believed to be the site of the great 1755 earthquake. We model ground motions using an extended source located near the Horseshoe scarp to generate synthetic waveforms using a wave propagation code, based on the finite-difference method. We compare the simulated waveforms using a 3-D velocity model down to the Moho discontinuity with a simple 1-D layered mod- el. The radiated wave field is very sensitive to the velocity model and a small number of source parameters; in particular, the rupture directivity. The rupture directivity (controlled by the rupture initiation location), the strike direction and the fault di- mensions are critical to the azimuthal distribution of the maximum amplitude oscilla- tions. We show that the use of a stratified 1-D model is inappropriate in SW Iberia, where sources are located in the oceanic domain and receivers in the continental do- main. The crustal structure varies dramatically along the ray paths, with large-scale heterogeneities of low or high velocities. Moreover, combined with the geometric li- mitations inherent to the region, a strong trade-off between several parameters is of- ten observed; this is particularly critical when studying moderate magnitude earth- quakes (M< 6), which constitute the bulk of the seismic catalogue in SW Iberia

Optical wave evolution due to interaction with elastic wave in a phoxonic crystal slab waveguide

Phoxonic crystal as a means of guiding and confining electromagnetic and elastic waves has already attracted attentions. Lack of exact knowledge on how these two types of waves interact inside this crystal and how electromagnetic wave evolves through this interaction has increased this field complexity. Here we explain how an elastic wave affects an electromagnetic wave through photo-elasticity and interface displacement mechanisms in a phoxonic crystal slab waveguide. We obtain a master equation which can describe electromagnetic wave evolution. In this equation we define a coupling parameter and calculate its value for different modes of electromagnetic and elastic waves and show it vanishes for some types of modes . Finally we solve the master equation for a typical phoxonic crystal slab waveguide and illustrate the electromagnetic wave evolution