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This study investigates changes in the peel strength of polyurea/monel 400 interfaces after prolonged exposure to saline water. The monel family of alloys is extensively used on marine structures d...

An experimental investigation through which the effects of low temperatures on the mechanical, fracture, impact, and dynamic properties of carbon- and E-glass-epoxy composite materials has been conducted. The objective of the study is to quantify the influence of temperatures from 20 °C down to −2 °C on the in-plane (tensile/compressive) and shear material properties, static and dynamic Mode-I fracture characteristics, impact/residual strength, and the storage and loss moduli for the materials considered. The low end of the temperature range considered in the study is associated with Arctic seawater as well as conditions found at extreme ocean depths (2 °C–4 °C). In the investigation, both carbon/epoxy and E-glass/epoxy laminates are evaluated as these materials are of keen interest to the marine and undersea vehicle community. The mechanical characterization of the laminates consists of controlled tension, compression, and short beam shear testing. The Mode-I fracture performance is quantified under both quasi-static and highly dynamic loading rates with additional flexure after impact strength characterization conducted through the use of a drop tower facility. Finally, dynamic mechanical analysis (DMA) testing has been completed on each material to measure the storage and loss moduli of the carbon fiber- and E-glass fiber reinforced composites. The findings of the study show that nearly all characteristics of the mechanical performance of the laminates are both material and temperature dependent.

An experimental study with corresponding numerical simulations was conducted to evaluate the blast response of composite plates after prolonged exposure to ultraviolet radiation. Two composite materials were used in this study, namely carbon fiber/epoxy and glass fiber/vinyl ester. The composite materials consisted of four unidirectional fiber plies oriented in a [± 45°]s layup. The plates were placed in a QUV Accelerated Weathering Tester for 500 h of exposure on each face, totaling 1000 h of ultraviolet radiation exposure, equivalent to 2.5 MJ/m2 of energy. The QUV Accelerated Weathering Tester was equipped with eight UVA-340 lamps to provide real service life exposure conditions. Material characterization experiments were performed on virgin specimens, as well as specimens exposed to ultraviolet radiation for 1000 h to determine its effect on the mechanical properties of the composites. Blast experiments were conducted on the composite plates to investigate the dynamic response before and after exposure to ultraviolet radiation. The plates were clamped on all edges and subjected to an air blast using a shock tube apparatus. Three-dimensional digital image correlation was coupled with high-speed photography to obtain full-field displacements of the specimens during blast loading. Furthermore, three piezoelectric pressure transducers were mounted on the shock tube apparatus and utilized to measure the pressure history of the shock wave loading. The quasi-static material characterization showed that the tensile modulus E1 had minimal change after exposure to ultraviolet radiation for 1000 h. However, matrix-dominated properties such as the in-plane shear modulus G12 increased after exposure to ultraviolet light for both the carbon and glass fiber composites, which resulted in lower out-of-plane displacements during blast loading. For the carbon fiber plates, the forced vibration frequency induced by the transverse blast load was higher in plates exposed to ultraviolet radiation when compared to virgin specimens. However, for the glass fiber plates exposed to ultraviolet radiation, the forced vibration frequency decreased when compared to virgin specimens. Finally, the finite element simulations were in good agreement with the experimental results. The simulations revealed that the glass fiber plates exposed to ultraviolet radiation had higher failure strains at the boundary than virgin specimens, despite having higher stiffness. A parametric study in which higher loading was simulated also showed that the glass fiber plates experienced more damage after 1000 h of ultraviolet radiation exposure.

The interaction between structures and bubbles generated by an underwater explosive (UNDEX) has been experimentally and computationally investigated. The problem analyzed consists of a flat steel plate adjacent to an explosive within an underwater environment. The experiments were performed for different standoff distances using high speed photography to capture the behavior of the underwater explosive gas bubble, and a series of pressure transducers, to record the emitted pressure histories. The numerical simulations were performed with the fully coupled Eulerian–Lagrangian fluid structure interaction code DYSMAS. The numerical simulations were validated with the experiments in terms of the detonation pressure, structural surface pressures, and UNDEX gas bubble growth and collapse. Results show that the UNDEX standoff distance greatly influences the gas bubble’s shape, migration speed, jetting behavior, and loading into its adjacent structure.

The response of composite materials and structures while subjected to highly transient loading in the form of underwater explosions has been studied through advanced experimental methods with corresponding computational simulations. The work conducted over approximately the past decade represents a progression in terms of loading conditions, structural geometries, and the effects of material ageing. The influence of elastomeric coatings has also been examined. Overall the research program was initiated through the study of curved composite plates subjected to far field underwater explosion (UNDEX) loading, and was followed by an investigation of flat plates undergoing near field blast loading. These efforts were followed by a detailed study into the highly complex loadings of cylindrical bodies subjected to near field blast conditions. Most recently, the effects of material ageing due to long term seawater immersion on the shock response of composites was considered. In each individual study, detailed experiments were conducted which subject the composite materials to controlled loading while capturing the response in real time through the use of high speed photography and optical methods. Furthermore, each individual study contains the development of detailed computational models which are shown to capture the complex fluid structure interactions while also accurately simulating the material response and damage characteristics.

The response of composite cylinders to near field underwater explosive (UNDEX) loading, including the effects of polyurea coatings, have been studied through experiments with corresponding computational simulations. Experiments were conducted on woven E-glass/epoxy roll wrapped cylinders in three unique configurations: (1) base composite, (2) base composite with a thin (100% composite thickness) coating, and (3) base composite with a thick (200% composite thickness) coating. Each cylinder configuration was subjected to near field underwater explosive loading in a large diameter test tank at charge standoff distances of 2.54 cm and 5.08 cm. The response of the cylinders on the non-loaded side was evaluated through high speed photography coupled with three-dimensional Digital Image Correlation (DIC). Transient deformation and Post-mortem damage comparisons were made to evaluate the effects of the applied coatings. The LS-Dyna finite element code has been utilized to conduct corresponding computational simulations of the experiments to allow for additional evaluations of the cylinder response. The simulations are shown to provide high correlation to the experiments in terms of pressure loading and final damage mechanisms. Results for the internal / kinetic energy levels and the material strains as determined through the simulations are presented. The experimental and numerical results show that the application of a polyurea coating is effective for significantly reducing damage in the cylinders. It is also shown that there is in increase in both material internal energies as well as overall strains with increasing coating thickness.

The Murray Lecture that was delivered in 2011 included a historical perspective on salient features of research conducted and published by Arun Shukla. A review of experimental work since the Murray Lecture is presented in this paper on the topic of imploding underwater structures. Specifically, the dynamic underwater collapse of metallic structures was studied under free-field and confined environments using novel applications of the Digital Image Correlation (DIC) technique. During these implosion experiments, the implodable volumes became unstable under hydrostatic and combined hydrostatic-explosive conditions. Moreover, there are two types of confinements explored in this paper. A semi-confinement, where a large tubular structure is open to a reservoir at one end and closed at the other end, which leads to water hammer waves on the closed end after implosions. Also, a full-confinement, where a large tubular structure is closed at both ends, which leads to limited hydrostatic potential energy during the implosion. For accurate displacement and velocity measurements of the collapsing structures, the 3D DIC technique is calibrated for underwater measurements in a small-scale setup for each experimental configuration. High-speed cameras are then used to record the dynamic implosion event while dynamic pressure transducers measure the emitted pressure pulses. The results of these experimental series show that the 3D DIC technique can be successfully used for displacement measurements of submerged objects by extracting intrinsic and extrinsic parameters using a submerged calibration grid. The implodable volume in an open-ended semi-confining structure displays a reduced collapse velocity with respect to a free-field configuration. This is primarily caused by a near-field pressure drop from the superposition of low-pressure implosion waves inside confining structure. Semi-confined implosion also exhibits high-pressure hammer pulses at the closed end. Implosions in fully confined vessels show significant reduction/delays in the implosion process due to limited energy present in the vessel. Lastly, during fully confined explosive experiments, the shock wave impact leads to structural vibrations in the implodable volume. The amplitude of these vibrations increases with higher hydrostatic pressures until the implodable volume shows an instability.

An experimental and computational study was conducted to evaluate the dynamic response of weathered biaxial composite plates subjected to near-field explosive/blast loadings. Naval structures are subjected to aggressive marine environments during their service life that can significantly degrade their performance over time. The composite materials in this study are carbon–epoxy composite plates with [0, 90]s and [45, − 45]s layups. The composites were aged rapidly through submersion in 65 $$^{\circ }$$ C seawater for 35 and 70 days, which through Arrhenius’ methodology, simulates approximately 10 and 20 years of operating conditions, respectively. Experiments were performed by clamping the composite plates to an air-backed enclosure inside an underwater blast facility. During the experiments, an RP-503 explosive was submerged, behind the composite specimen, and detonated. Meanwhile, transducers measured the pressure emitted by the explosive, and three high-speed cameras captured the event. Two of the cameras were placed facing the specimen to measure full field displacement, velocities, and strains through a 3D digital image correlation analysis. The third high-speed camera was used to record the explosive’s behavior and bubble-to-specimen interaction. Additional experiments were performed to obtain the non-weathered and weathered material properties as well as the residual strength post the blast experiments. Additionally, a coupled Eulerian–Lagrangian finite element simulation was conducted to complement the experimental findings. Results show that the diffusion of water into the composite material leads to a more prominent blast response as well as the degradation of mechanical properties, especially shear properties which are dominated by the epoxy matrix. Residual strength experiments also show a substantial decrease in the structural integrity post-blast loading for the weathered composites. Lastly, the numerical simulations showed substantial increase in maximum strains with relatively small decreases in mechanical stiffness. Hence, even past the saturation point, incremental changes in material properties can have a significant impact on mechanical performance.

An experimental study with corresponding numerical simulations was conducted to investigate the blast response of weathered Carbon-Epoxy composite plates. The dynamic behavior of the composite plates with and without prior exposure to an aggressive marine environment was explored using a shock tube apparatus coupled with a high speed photography system. In order to simulate prolonged exposure in an aggressive marine environment, specimens were submerged in an elevated temperature, 3.5% salt solution for 0, 30 and 60 days. The saline solution temperature was maintained at 65 °C to accelerate the aging process. Finite Element Modeling (FEM) for the blast loading experiments was performed using the Ls-Dyna code. Models have been developed for both the simply supported and fixed boundary condition cases. Tensile and four point bend tests were performed to characterize the quasi-static mechanical behavior of the composite material before and after prolonged exposure to aggressive marine environments. After 30 and 60 days of submergence, the tensile modulus decreased by 11% and 13%, the ultimate tensile strength decreased by 12% and 13%, and the ultimate flexural strength decreased by 22% and 22%, respectively. Dynamic blast loading experiments were performed on simply supported and fully clamped specimens, to determine the effects of the boundary conditions on the Carbon-Epoxy specimen response. The Weathered (30 and 60 days) and Non-Weathered (0 day) specimens displayed dramatically different behavior after being subjected to a blast load. For the simply supported case, Non-Weathered specimens displayed an average maximum out of plane displacement of 20 mm and recovered elastically. Weathered specimens, both 30 and 60 days exhibited similar initial transient behavior but failed catastrophically due to through thickness cracking at the point of maximum deflection. For the fixed boundary condition, the Non-Weathered specimens displayed an average maximum out of plane displacement of 5.57 mm, whereas the 30 day and 60 day weathered specimens displayed a maximum out of plane displacement of 6.89 mm and 6.96 mm, respectively. The corresponding numerical simulations matched well with the experimental data. However, for the fixed boundary case, the beam vibration of the simulation was off phase with the experimental results due to imperfect boundary conditions in the experiments.

The mechanical behavior of E-Glass/Epoxy and Carbon Fiber/Epoxy laminates when exposed to low temperature and prolonged submergence operating environments has been investigated through a detailed experimental study. The temperature range which was studied consisted of room temperature (20 °C) to −2 °C, the lowest temperature expected in a submerged ocean environment. Mechanical characterization of each material has been conducted through tensile, compression and short beam shear testing. Additionally, the influence of temperature on the Mode I fracture performance of these laminates was evaluated through Double Cantilever Beam (DCB) tests. Furthermore, a Dynamic Mechanical Analyzer (DMA) was employed to evaluate the structural behavior of these laminates under a range of frequency loading and temperatures. A transition between a matrix-dominated to laminate-dominated responses as functions of strain rate were identified. The current study has resulted in the mechanical characterization of E-Glass/Epoxy and Carbon Fiber/Epoxy laminates as a function of temperature ranging from room temperature to low temperature sea water conditions. The experimental results show a dependence on the static, fracture, and dynamic properties of these laminates.

An experimental investigation was carried out to determine the long term effects of exposure to a sea-floor depth ocean environment on the blast response of carbon-fiber/epoxy (CFE) laminates. By means of accelerated life testing (ALT), the behavior of laminates with and without exposure to high pressure saline water was explored using an air-blast shock tube facility and 3D-DIC technique coupled with high speed stereo photography. Specimens were tested in the unweathered condition and two durations of exposure: 14 days and 24 days immersed in a 70 °C, 3.5% NaCl solution pressurized to 41.3 MPa in a novel aging facility specifically designed to study the weathering behavior of composite materials at large ocean depths. From a diffusion study utilizing Arrhenius methodology, these cases simulate 8.9 and 15.3 years of service life, respectively. No statistically significant differences between the in-plane tensile elastic modulus, ultimate tensile strength, in-plane shear modulus, and ultimate shear strength were observed between any of the three cases. The flexural modulus of the laminates was observed to decrease by 13.2% and 20.8% for the two weathered cases, respectively. Dynamic air-blast experiments utilizing 3D digital image correlation (DIC) to track out-of-plane displacements revealed only marginal gains in normalized deflection of 5.1% and 2.0% for the two weathering cases, indicating no significant change in blast response with aging.

An experimental and computational investigation was conducted to study the interaction between bubbles generated by an underwater explosive (UNDEX) and a nearby steel plate structure. The experiments were performed for different standoff distances to investigate the interaction between the gas bubble and the rigid structure. High-speed photography was utilized to capture the underwater explosive gas bubble’s behavior, and a series of pressure transducers were used to record the emitted pressure histories. The numerical simulations were performed with the Dynamic System Mechanics Advanced Simulation software, which is a full y coupled Eulerian–Lagrangian fluid–structure interaction code. The numerical simulations were validated with the experiments in terms of the detonation pressure, structural surface pressures, and UNDEX gas bubble growth and collapse. Results show that the UNDEX standoff distance greatly influences the gas bubble’s shape, migration speed, bubble jetting behavior, and loading into its adjacent structure. Moreover, the impulse generated by the shock wave on the plate surface proved to be small in comparison to the impulse generated by the collapse of the UNDEX gas bubble. The magnitude of impulse depends on standoff distance, collapse symmetry, and relative collapse location.

An experimental investigation to understand the mechanisms of dynamic buckling instability in cylindrical structures due to underwater explosive loadings is conducted. In particular, the effects of initial hydrostatic pressure coupled with a dynamic pressure pulse on the stability of metallic cylindrical shells are evaluated. The experiments are conducted at varying initial hydrostatic pressures, below the critical buckling pressure, to estimate the threshold after which dynamic buckling will initiate. The transient underwater full-field deformations of the structures during shock wave loading are captured using high-speed stereo photography coupled with modified 3-D Digital Image Correlation (DIC) technique. Experimental results show that increasing initial hydrostatic pressure decreases the natural vibration frequency of the structure indicating loss in structural stiffness. DIC measurements reveal that the initial structural excitations primarily consist of axisymmetric vibrations due to symmetrical shock wave loading in the experiments. Following their decay after a few longitudinal reverberations, the primary mode of vibration evolves which continues throughout later in time. At the initial hydrostatic pressures below the threshold value, these vibrations are stable in nature. The analytical solutions for the vibration frequency and the transient response of cylindrical shell are discussed in the article by accounting for both (1) the added mass effect of the surrounding water and (2) the effect of initial stress on the shell imposed by the hydrostatic pressure. The analytical solutions match reasonably well with the experimental vibration frequencies. Later, the transient response of a cylindrical shell subjected to a general underwater pressure wave loading is derived which leads to the analytical prediction of dynamic stability.

The fluid structure interaction phenomenon occurring in confined implosions is investigated using high-speed three-dimensional digital image correlation (DIC) experiments. Aluminum tubular specimens are placed inside a confining cylindrical structure that is partially open to a pressurized environment. These specimens are hydrostatically loaded until they naturally implode. The implosion event is viewed, and recorded, through an acrylic window on the confining structure. The velocities captured through DIC are synchronized with the pressure histories to understand the effects of confining environment on the implosion process. Experiments show that collapse of the implodable volume inside the confining tube leads to strong oscillating water hammer waves. The study also reveals that the increasing collapse pressure leads to faster implosions. Both peak and average structural velocities increase linearly with increasing collapse pressure. The effects of the confining environment are better seen in relatively lower collapse pressure implosion experiments in which a long deceleration phase is observed following the peak velocity until wall contact initiates. Additionally, the behavior of the confining environment can be viewed and understood through classical water hammer theory. A one-degree-of-freedom theoretical model was created to predict the impulse pressure history for the particular problem studied.

The dynamic behavior of Hastelloy® X plates subjected to normal and oblique shock loading was studied both experimentally and numerically. A series of experiments was conducted on Hastelloy® X plates at room temperature under fixed boundary conditions using a shock tube apparatus. High-speed digital cameras were used to obtain the real-time images of the specimen during the shock loading. Digital image correlation (DIC) technique was utilized to obtain 3D deformations of the plates using stereo-images of the specimen. The numerical modeling utilized the finite element software package Dynamic System Mechanics Analysis Simulation (DYSMAS), which includes both the structural analysis as well as the fluid–structure interaction to study the dynamic behavior of the specimen under given loads. Experimentally obtained pressure–time profiles were used as a reference in numerical modeling. It was observed that the lower angles of shock incidence caused more deformation on the specimen. Additionally for oblique shocked specimens, the deformation was observed to initiate from the edge nearer to the muzzle. The results from the numerical simulations were validated with the experimental data, and showed excellent correlation for all cases.

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.

The constitutive behavior of polyurea after prolonged exposure to aggressive marine environments, including saline water, UV radiation and combinations of both, was investigated in this study. A diffusion study was performed at several temperatures to determine the effect of temperature on saline water ingression into the polyurea using Crank's method. This diffusion data coupled with Arrhenius' methodology allowed for the calculation of an acceleration factor relating laboratory exposure time at elevated temperature to real-life service time. Cast cylindrical specimens were exposed to UV radiation, saline water, and various combinations of UV radiation and saline water. These combinations were: a) exposure to saline water followed by UV radiation, b) UV radiation followed by saline water, and c) saline water and then UV radiation followed by saline water. Uniaxial compressive experiments were conducted on both the virgin and exposed specimens at strain rates of 1.7 × 10 − 3 s − 1 and 2.6 × 10 3 s − 1 . Under quasi-static loading conditions, the elastic modulus of the polyurea dropped by 73% after 84 days of exposure to saline water at 85 °C. Specimens exposed to UV radiation showed a maximum increase in the elastic modulus of 64% after 20 days of exposure. When tested under dynamic loading conditions, specimens exposed to saline water for 84 days showed a 48% decrease in strain energy while those exposed to UV radiation showed a 45% increase.

This paper details a numerical study of the dynamic stability of a cylindrical shell structure under combined hydrostatic and dynamic pressure loading within a tubular environment as compared to the traditional loading of hydrostatic pressure alone. Simulations are executed using a coupled Eulerian–Lagrangian scheme, within the dynamic system mechanics advanced simulation (DYSMAS) code, to explicitly model the (1) structural response of a single unstiffened cylindrical shell to dynamic pressure loading and (2) the fluid flow field within the surrounding environment due to the shock and the shell structural response. Simulations involve a non-pressure-compensated aluminum 6061-T6 cylindrical structure with a length-to-diameter ratio, L/D, equal to 9.6. This structure is 31.8 mm (1.25-in) in outer diameter and is concentrically and longitudinally centered within the outer tube, which has an inner diameter of 177.8 mm (7.00-in) and total internal length of 2.13 m (84-in). Simulations are run at four hydrostatic tank pressures, which are categorized by percentage of measured critical collapse pressure, Pc, of the shell structure: 66% Pc, 80% Pc, 85% Pc, and 90%Pc. For each case, the shell structure is subjected to shock loading created by the detonation of a commercial blasting cap at a given standoff to the structure within the confining tube. Simulated pressure histories are compared to experimental pressure data at gage locations. The simulations and corresponding experiments produce the same overall result for three of four cases (i.e., survive: 66%Pc or implode: 85%Pc and 90%Pc). For the 80%Pc case, the overall result differs between simulation and experiment in that the specimen in the experiment survives but the simulated cylinder implodes. However, the discrepancy between the overall experimental result and corresponding simulation is not deemed a failure for the 80%Pc case; instead, this signifies a transitional case for the dynamic stability of the shell structure (i.e., collapse is sensitive to small deviations from assumed conditions in this regime).

The mechanical behavior of four unique blends of polyurea materials has been investigated through a combined experimental and computational study. Mechanical characterization of each material was evaluated under both tensile and compressive loading at strain rates ranging from 0.01 to 100 strains per second (1/s). Planar blast wave experiments utilizing a 40 mm light gas gun were also conducted which imparted strain rates up to 104 strains per second (1/s). The material testing results showed that stress-strain response is a function of loading, strain level, and strain rate. These results were utilized to define a non-linear rubber material model in Ls-Dyna which was validated against the test data through a series of “block” type simulations for each material. Each material model was shown to replicate both the tensile and compressive behavior as well as the strain rate dependence. The material models were subsequently extended to the simulations of the blast wave experiments. The blast wave simulations were shown to accurately capture wave propagation resulting from a shock type pressure loading as well as the stress magnitudes of the transmitted waves after passing through the respective polyurea materials. The current study has resulted in the mechanical characterization of four polyurea materials under tensile/compressive loading at increasing strain rates, a suitably validated numerical material model, and suitable correlations between experimental and simulation results.

The effect of plate curvature, plate thickness, and thickness distribution on the response of curved composite plates subjected to far field underwater explosion (UNDEX) loading has been studied through computational simulations. In this study five panels with increasing radii of curvature are considered. Furthermore, the effect of plate thickness is considered by investigating three plate thicknesses for a given radii of curvature. Finally, a comparison is made between a plate with a uniform thickness and a plate with equal mass but a thicker outer boundary and thinner midsection. The effects are assessed using the plate center point deflection, full field deformation evolution, and fluid structure wave interaction. The results show that when subjected to shock pressure loading the deformation mechanics of the plate is significantly affected by the amount of curvature, thickness, and thickness distribution.

An experimental study with corresponding numerical simulations has been conducted to evaluate the response of E-Glass / Epoxy composite plates, including polyurea coating effects, subjected to near field underwater explosion (UNDEX) loading. Experiments are performed in a water filled blast tank in which the including transient plate response during the UNDEX loading is measured utilizing high speed photography coupled with Digital Image Correlation. The experimental results show that the transient response of the plate is improved through the use of a thicker plate or through the application of a polyurea coating, although there is a weight penalty associated with the additional material which should be considered. Corresponding computational models of the experiments have been conducted with the commercial finite element code LS-Dyna. The simulations are shown to have a high level of correlation to the experimental data.

An experimental study is conducted to investigate the phenomenon of sympathetic underwater implosion of cylindrical metallic shells in a confining environment. Two aluminum 6061-T6 implodable volumes with different collapse pressures are placed inside a confining tube with one end open to the environment and are hydrostatically loaded up to the weaker implodable volumes’ critical collapse pressure. Experiments show that implosion of the weaker implodable volume (critical pressure=Pc) inside the confining tube leads to the subsequent sympathetic implosion of the stronger implodable volume (critical pressure=1.2Pc). Implosion of the weaker implodable volume produces strong oscillating water hammer waves with 1.6Pc peak over-pressure, which initiates the implosion of the stronger implodable volume. Pressure histories recorded within the confining tube indicate that the sympathetic implosion of the stronger implodable volume generates low pressure high frequency implosion waves. The superposition of the low pressure waves with the high pressure water hammer waves mitigates to a great extent the later cyclic water hammer loading within the confining tube.

An experimental study was conducted to evaluate the response of weathered unidirectional composite plates subjected to near-field blast loading. The composite materials in this study are carbon-epoxy composite plates with a [45, −45]s layup and was subjected to simulated marine aging through submersion in seawater baths for 70 days at 65 degrees Celsius in order to simulate approximately 20 years of real life operating conditions. Experiments were performed by fully clamping the specimen plates to an air-backed enclosure in a water tank. An RP-503 explosive was placed underwater behind the composite structure to be loaded. During the experiments, transducers measured the pressure emitted by the explosive, and three high-speed cameras captured the entire event. Two of the cameras were placed apart facing the specimen to measure full-field displacements through 3-D Digital Image Correlation analysis. Results show that the diffusion of water into the composite material leads to degradation of the blast response behavior as well as a loss of flexural strength and modulus.

A fundamental experimental investigation, with corresponding computational simulations, was conducted to understand the physical mechanisms of implosions of cylindrical shells occurring within a tubular confining space which has a limited potential energy reservoir. In particular, attention was focused on studying the generation of pressure waves from the implosion, the interaction of the pressure waves with the confining tube walls and end caps, and the collapse mechanisms of the implodable volume. Experiments were conducted with three implodable volume geometries which had similar critical collapse pressures. The implodable volumes were aluminum 6061-T6 cylindrical tubing and were placed concentrically within the confining tube. Pressure histories recorded along the length of the confining tube during the experiments were utilized to analytically evaluate the deformation of the implodable volume using fluid–structure coupled deformation models. Computational simulations were conducted using a coupled Eulerian–Lagrangian scheme to explicitly model the implosion process of the tubes along with the resulting compressible fluid flow. The numerical model developed in this study is shown to have high correlation with the experimental results and will serve as a predictive tool for the simulation of the implosion of different cylindrical geometries as well as various tube-in-tube implosion configurations. The experimental results show that the limited hydrostatic potential energy available in a confined environment, as compared to a free field, significantly influences the implosion process. The wall velocities of the implodable volume during the collapse, as well as the extent of the collapse progression, are largely affected by the sudden decrease in the available hydrostatic potential energy. This energy is shown to be partially transformed into elasto-plastic strain energy absorbed in the deformation of the implodable volume, as well as the kinetic energy of the water during the implosion process. Experiments also show that the extent of the collapse progression of an implodable volume can potentially be inhibited within a closed environment, which can lead to the arresting of an implosion event prior to completion for larger implodable volumes. The pressure waves generated during collapse comprise of waves emitted due to the impact of the implodable volume walls, the arrest of rushing water and contact propagation along the walls. These processes later evolve into water hammer type axial wave behavior.

An experimental and numerical study has been conducted to evaluate the underwater blast response of E-Glass/epoxy composite plates with polyurea coatings. The goal of the study is to determine the effects of these elastomeric coatings on the dynamic response of the plates, specifically the influence of coating thickness, location, and plate natural frequency. The composite material is a 0°/90° biaxial layup and the coatings are applied to either the loaded or non-loaded faces. A conical shock tube facility which produces shock loading conditions representative of the underwater detonation of an explosive charge is used to impart the shock loading to the plates during the experiments. The transient response of the plates is recorded using a three-dimensional (3D) digital image correlation system, consisting of high-speed photography and specialized post processing software. Computational models of the experiments are developed using the LS-DYNA finite element code. The simulations are shown to have a high level of correlation to the experimental data in terms of center point displacements and full field deformation profiles. Additional parametric studies using the correlated model show that the transient response of the composite plates is improved with increasing coating thickness, and that polyurea coatings located on the back face of the panels provide better performance than when located on the loaded surface.

The effects of polyurea coatings on the response of E-Glass/Vinyl ester curved composite panels subjected to underwater explosive loading has been studied. The thickness and location of the polyurea coating has been varied to determine how these parameters affect the transient response. The composite material is a 0°/90° biaxial layup and the coatings are applied to either the loaded or non-loaded faces. The current work utilizes a conical shock tube facility which produces shock loading conditions equivalent to the underwater detonation of an explosive charge. The transient response of the plates is recorded using a three-dimensional (3D) Digital Image Correlation system, consisting of high-speed photography and specialized post processing software. The results show that for a given polyurea thickness, better performance is obtained when the back face of the panel is coated. Similarly the performance is improved as the coating thickness is increased; however this comes at a cost in terms of increased areal weight. The results show that there is likely an optimal coating thickness, that when located on the back face, provides a balanced tradeoff between panel performance and weight increase.

Experiments were conducted on woven E-glass/epoxy roll wrapped cylinders in three configurations; base composite, and base composite with a thin (100 % composite thickness) and thick (200 % composite thickness) polyurea coating. Each cylinder configuration was subjected to near-field UNDEX loading at charge standoff distances of 2.5 cm and 5.1 cm inside of a large diameter test tank. Results show that the application of a polyurea coating is effective for reducing damage in the cylinders.

This study experimentally investigates fluid structure interactions occurring during confined implosions using high-speed digital image correlation (DIC). Aluminum tubular specimens are placed inside a confining cylindrical structure with one end open to a pressurized environment. These specimens are exposed to hydrostatic pressure, which is slowly increased until they collapse onto themselves. The implosion event is viewed through an acrylic window on the confining structure. Full field deformation and velocities are captured with DIC and are synchronized with the pressure history. Experiments show that implosion inside a confining structure leads to extremely high oscillating water hammer effects. Both peak structural velocities and hammer impulses increase linearly with increasing collapse pressure.

Background & Aims: Interactions between mucosal cell types, environmental stressors, and intestinal microbiota contribute to pathogenesis in inflammatory bowel disease (IBD). Here, we applied metaproteomics of the mucosalâluminal interface to study the disease-related biology of the human colonic mucosa. Methods: We recruited a discovery cohort of 51 IBD and non-IBD subjects endoscopically sampled by mucosal lavage at 6 colonic regions, and a validation cohort of 38 no-IBD subjects. Metaproteome data sets were produced for each sample and analyzed for association with colonic site and disease state using a suite of bioinformatic approaches. Localization of select proteins was determined by immunoblot analysis and immunohistochemistry of human endoscopic biopsy samples. Results: Co-occurrence analysis of the discovery cohort metaproteome showed that proteins at the mucosal surface clustered into modules with evidence of differential functional specialization (eg, iron regulation, microbial defense) and cellular origin (eg, epithelial or hemopoietic). These modules, validated in an independent cohort, were differentially associated spatially along the gastrointestinal tract, and 7 modules were associated selectively with non-IBD, ulcerative colitis, and/or Crohnâs disease states. In addition, the detailed composition of certain modules was altered in disease vs healthy states. We confirmed the predicted spatial and disease-associated localization of 28 proteins representing 4 different disease-related modules by immunoblot and immunohistochemistry visualization, with evidence for their distribution as millimeter-scale microgeographic mosaic. Conclusions: These findings suggest that the mucosal surface is a microgeographic mosaic of functional networks reflecting the local mucosal ecology, whose compositional differences in disease and healthy samples may provide a unique readout of physiologic and pathologic mucosal states. Keywords: Inflammatory Bowel Disease, Mucosal, Networks, Ecology, Metaproteomics

The effect of preloading on thin composite plates subjected to underwater explosive loading has been studied through computational simulations. In this study the effects of three types of in plane preloading are considered: (1) directly applied compression, (2) indirectly applied compression, and (3) directly applied tension. The effects of the preloading conditions are assessed using the plate center point deflection, material damage, and delamination evolution. The results show that for thin composite plates subjected to underwater shock loading conditions there is a minimal effect of preload on the response of the plates or the amount of damage and delamination sustained.

Experimental and numerical studies were conducted to understand the effect of plate curvature on blast response of aluminum panels. A shock tube apparatus was utilized to impart controlled shock loading to aluminum 2024-T3 panels having three different radii of curvatures: infinity (panel A), 304.8 mm (panel B), and 111.8 mm (panel C). Panels with dimensions of 203.2 mm × 203.2 mm × 2 mm were held with mixed boundary conditions before applying the shock loading. A 3D Digital Image Correlation (DIC) technique coupled with high speed photography was used to obtain out-of-plane deflection and velocity, as well as in-plane strain on the back face of the panels. Macroscopic postmortem analysis was performed to compare the yielding and plastic deformation in the three panels. The results showed that panel C had the least plastic deformation and yielding as compared to the other panels. A dynamic computational simulation that incorporates the fluid-structure interaction was also conducted to evaluate the panel response. The computational study utilized the Dynamic System Mechanics Analysis Simulation (DYSMAS) software. The model consisted of the shock tube wall, the aluminum plate, and the air (both internal and external) to the tube walls. The numerical results were compared to the experimental data. The comparison between the experimental results and the numerical simulation showed a high level of correlation using the Russell error measure.

Background: Host–microbe interactions at the intestinal mucosal–luminal interface (MLI) are critical factors in the biology of inflammatory bowel disease (IBD). Methods: To address this issue, we performed a series of investigations integrating analysis of the bacteria and metaproteome at the MLI of Crohn's disease, ulcerative colitis, and healthy human subjects. After quantifying these variables in mucosal specimens from a first sample set, we searched for bacteria exhibiting strong correlations with host proteins. This assessment identified a small subset of bacterial phylotypes possessing this host interaction property. Using a second and independent sample set, we tested the association of disease state with levels of these 14 “host interaction” bacterial phylotypes. Results: A high frequency of these bacteria (35%) significantly differentiated human subjects by disease type. Analysis of the MLI metaproteomes also yielded disease classification with exceptional confidence levels. Examination of the relationships between the bacteria and proteins, using regularized canonical correlation analysis (RCCA), sorted most subjects by disease type, supporting the concept that host–microbe interactions are involved in the biology underlying IBD. Moreover, this correlation analysis identified bacteria and proteins that were undetected by standard means-based methods such as analysis of variance, and identified associations of specific bacterial phylotypes with particular protein features of the innate immune response, some of which have been documented in model systems. Conclusions: These findings suggest that computational mining of mucosa-associated bacteria for host interaction provides an unsupervised strategy to uncover networks of bacterial taxa and host processes relevant to normal and disease states. (Inflamm Bowel Dis 2012;)

The response of E-Glass/Vinyl ester curved composite panels subjected to underwater explosive loading has been studied. Three laminate constructions have been investigated to determine their relative performance when subjected to shock loading. These constructions are: (1) a baseline 0°/90° biaxial layup, (2) a 0°/90° biaxial layup that includes a thin glass veil between plies, and (3) a 0°/90° biaxial layup that has a coating of polyurea applied to the back face. The work consists of experimental work utilizing a water filled, conical shock tube facility. The samples are round panels with curved midsections, and are approximately 2.54 mm in thickness. The transient response of the plates is measured using a three-dimensional (3D) Digital Image Correlation (DIC) system, including high speed photography. This ultra high speed system records full field shape and displacement profiles in real time. The results show that the performance of the baseline laminate is improved when coated with the polyurea material, but conversely, is degraded by the inclusion of the glass veils between plies.

The diagnosis of acute rejection is suspected by clinical presentation and confirmed by biopsy. Serum creatinine levels increase during allograft dysfunction, but this measure is neither sensitive nor specific for acute rejection (1, 2). The gold standard for diagnosing rejection is needle biopsy, which is invasive, painful, and as sociated with patient morbidity (1–4). It would be advantageous to develop a noninvasive test that could detect rejection, improve transplant outcomes, and reduce the cost of care. The use of human plasma for biomarker discovery provides a means to monitor disease states in a relatively noninvasive manner (5, 6). Plasma comes in contact with tissues which are apt to release protein components that reflect the disease-altered state of the tissue (6). The SELDI ProteinChip System (Bio-Rad, Hercules, CA) uses solid phase extraction of proteins and peptides from biological mixtures followed by detection using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. ProteinChip arrays use a variety of chromatographic and biological surfaces to bind subsets of proteins from complex biological samples (7). The bound proteins are used to generate protein profiles used for biomarker discovery (7, 8). Urine protein profiles from renal allograft rejection patients have identified potential biomarker candidates and generated valuable insight into the biology of graft injury (9–15). The utilization of plasma for finding candidate bio-markers of renal allograft rejection holds promise as a biological fluid that can provide informative proteomic signatures of renal allograft rejection (16). This study analyzes the plasma proteomes of renal transplant patients by SELDI. Twenty-two proteins/peptides had significant differences when comparing plasma during rejection with postrejection. The combination of two candidate proteins had a high discriminatory value for detecting rejection. Two of the 22 candidates were identified and one, apolipoprotein A1 (Apo A1), was validated by enzyme-linked immunosorbent assay (ELISA) in the original and a larger independent cohort.

Intestinal transplantation (ITx) offers a potential way of survival for patients with intestinal failure who have developed life-threatening complications (1). Overall, patient and graft survival rates have improved significantly over the past several years (2, 3). Nonetheless, acute cellular rejection (ACR) continues to pose major challenges in these patients, occurring in up to 50% of recipients and accounting for the majority of grafts loss. Currently, endoscopic biopsy is the only way for clinical assessment of ACR (4). Limitations of endoscopy include that it is invasive and associated with risks of bleeding, infection, or perforation. In addition, ACR is also often patchy (missed by ~30% of endoscopies) (5), and confounded by its presentation, which may be similar to infection. This creates challenges to both clinical management and biologic research (6). New noninvasive techniques to analyze ACR are thus needed to further advance the ITx field. The intestine is the largest immune organ in the body, with 80% of the total immune cells (7). Study of ITx recipients is further complicated by the presence of an immunogenic chimeric donor cell population (8, 9), and the underlying biology of ACR remains unclear. Recently, an underappreciated role of the innate immune system has been suggested in solid organ transplantation with evidence from both mouse models and human studies (10). Upregulation of proinflammatory mediators has been shown to occur independently of adaptive immunity, even before the T-cell response (11–14). Moreover, the profile of this early cytokine upregulation suggests it might be due to the epithelial stress response to tissue injury (12, 15). High-throughput proteomics allows simultaneous detection of a panel of proteins, which are differentially expressed in healthy and disease states. This technology has been successfully applied to profile proteins from different forms of clinical specimens (16), and protein combinations provide potentially innovative biomarkers which are useful in diagnosis or disease monitoring. In the search of biomarkers for ACR, various metabolites and proteins have been suggested as potential biomarkers for allograft monitoring in both human and mouse study (6, 17, 18). The purpose of this study was to evaluate the feasibility of using protein profiles of ostomy effluents as a strategy to monitor ACR, in particular those related to innate immune activation, which may represent a precondition of the graft for rejection. We used both high-throughput proteomic analysis and candidate immunoassay protein detection of ostomy effluents to search in a noninvasive manner for molecular profiles of epithelial stress and innate immunity during ACR. Our analyses uncovered several proteins that appeared to differ among patients with early ACR, notably the elevation of antimicrobial peptides and cytokines characteristic of early innate immune activation.

The effect of underwater shock loading on an E-Glass/Epoxy composite material has been studied. The work consists of experimental testing, utilizing a water filled conical shock tube and computational simulations, utilizing the commercially available LS-DYNA finite element code. Two test series have been performed and simulated: (1) a reduced energy series which allowed for the use of strain gages and (2) a series with increased energy which imparted material damage. The strain gage data and the computational results show a high level of correlation using the Russell error measure. The finite element models are also shown to be able to simulate the onset of material damage by both in-plane and delamination mechanisms.

A comprehensive experimental/numerical study on the implosion of longitudinally off-centered cylindrical implodable volumes was conducted within a tubular confining space. In particular, the aim of this study was to examine the changes in the implosion mechanics and in the nature of pressure waves, arising from the longitudinally off-centered location of the implodable volume. Experiments were conducted with 31.8 mm outer diameter, cylindrical aluminum 6061-T6 implodable volumes placed concentrically within the confining tube. Three longitudinal offset locations were chosen within the confining tube, such that distance from the center of the implodable volume to the center of confining tube is equal to: (a) zero, (b) 3/7 of the half-length of confining tube (L), and (c) 5 L/7. Pressure transducers mounted on the inner surface of the confining tube were used to capture the pressure waves released during the implosion event. Computational simulations were performed using a coupled Eulerian–Lagrangian scheme to explicitly model the implosion process of the tubes along with the resulting compressible fluid flow. The experiments revealed that the longitudinal asymmetric placement of the implodable volume enhances the strength of hammer pressure waves generated during the implosion process. The off-centered location of the implodable volume causes a pressure imbalance in the entire length of the confining tube. Hence, the water particle velocity shifts toward the implodable volume producing high pressure region at the end-plate near the implodable volume, while the other end-plate experiences significantly longer cavitation due to low pressure. This far end-plate cavitation duration is also found to increase with increasing longitudinal offset, even though the total combined cavitation duration at both the end-plates is approximately same for all offset locations. With high correlation observed between the experiments and simulations, computation models were further used to correlate the longitudinal offset and the signature of pressure waves at various interpolated locations. Simulations show that there is increase in both the peak pressure and the impulse of the hammer wave with increasing longitudinal offset of the implodable volume. Simulations also show that the collapse rate of the implodable volume decreases with the increasing longitudinal offset.

We present a narrowband interference (NBI) canceller that suppresses spectral leakage in an orthogonal frequency-division multiplexing (OFDM)-based system caused by a narrowband (NB) signal. We assume that the spectrum of the NB signal is within the spectrum of the OFDM signal. This can be the case, e.g., on digital subscriber lines (DSL) and in new unlicensed frequency bands for radio transmission. The canceller makes linear minimum mean-square error estimates of the spectral leakage by measuring the NBI on a few modulated or unmodulated OFDM subcarriers. It uses a model of the NB signal's power spectral density as a priori information. Using a frequency invariant design, it is possible to cancel NBI from signals that are changing their frequency location with significantly reduced complexity overhead. The operational complexity of the canceller can be lowered by using the theory of optimal rank reduction and using the time-bandwidth product of the NB signal. Analytical performance evaluations, as well as Monte Carlo simulations, show that, without perfect a priori information, this canceller can suppress the spectral leakage from a strong NB signal (e.g., with equal power as the OFDM signal) to well below the background noise floor for typical applications where it causes negligible signal-to-noise ratio and symbol error rate degradation. Validerad; 2003; 20070109 (ysko)