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The nonlinear self-refraction of acoustic pulsed beams, which include shock fronts, is studied. The medium of sound propagation is a gas where thermodynamically non-equilibrium processes take place, such as exothermic chemical reaction or excitation of vibrational degrees of a molecule's freedom. Comparative analysis of the features of sound propagation over gases where pure nonlinear attenuation of the shock wave occurs, and gases with non-equilibrium and equilibrium processes, is performed. PACS Nos.: 43.25, 43.35.Fj. Nous etudions l'auto-refraction non lineaire d'un faisceau acoustique pulse qui inclut une onde de choc. Le milieu de propagation du son est un gaz dans lequel se produisent des transformations thermodynamiquement hors d'equilibre, comme des reactions chimiques exothermiques ou l'excitation des degres de liberte vibrationnels des molecules. Nous completons avec une analyse comparative des caracteristiques de propagation du son dans des gaz ou l'onde de choc est soumise a une pure attenuation non lineaire et dans des gaz ou on trouve des transformations hors d'equilibre et a l'equilibre. [Traduit par la Redaction], 1. Introduction There are different kinds of self-action of sound, which have been observed in experiments, among them nonlinear self-action and inertial types of self-action. The first kind reflects the [...]

A simple semi-empirical model for predicting the peak overpressure field that results when a shock emerges from a circular shock tube is presented and validated. By assuming that the shape of the expanding shock remains geometrically similar after an initial development period, an equation that describes the peak overpressure field in the horizontal plane containing the shock tube's centerline was developed. The accuracy of this equation was evaluated experimentally by collecting peak overpressure field measurements along radials from the shock tube exit at 0 deg, 45 deg, and 90 deg over a range of shock Mach numbers from 1.15 to 1.45. It was found that the equation became more accurate at higher Mach numbers with percent differences between experimental measurements and theoretical predictions ranging from 1.1% to 3.6% over the range of Mach numbers considered. (1) Shocks do propagate in a geometrically similar manner after some initial development length over the range of Mach numbers considered here. (2) The model developed here gives reasonable predictions for the overpressure field from a shock emerging from a circular shock tube. (3) Shocks are expected to be completely symmetric with respect to the shock tube's centerline, and hence, a three dimensional overpressure field may be predicted by the model developed here. (4) While there is a range of polar angle at which the shock shape may be described as being spherical with respect to the shock tube's exit, this range does not encompass the entirety of the half space in front of the shock tube, and the model developed here is needed to accurately describe the entire peak overpressure field. [DOI: 10.1115/1.4002183] Keywords: shock tube, pressure field, semi-empirical

Shock-wave interaction with an elastic structure is investigated using a coupled numerical analysis approach, which considers solid-fluid interaction within an arbitrary Lagrangian-Eulerian framework. The analysis is performed considering a compressive shock wave, where the shock front is followed by constant pressure. An analysis procedure, which considers the change in the fluid domain due to the deformation of the solid and changes in the overpressure due to the movement of the elastic structure, is developed. Approximate numerical procedures for solving the Riemann problem associated with the shock are implemented within the Godunov finite volume scheme for the fluid domain. The influences of parameters such as structural stiffness and mass of the system on the displacement, velocity, and energy of the elastic structure following the shock-wave incidence are investigated. Immediately after the contact of the shock wave with the solid surface the pressure at the face of the elastic solid rises to a value which is equal to that obtained off of a fixed rigid wall. Subsequently, the motion of the piston produces changes in the applied pressure. The overpressure applied to the elastic system does not have a fixed profile but it depends on its elastic stiffness and structure mass. It is shown that there is a continuous exchange of energy between the air and the moving elastic structure, which produces a damped motion of the solid. The effect of damping is considerable for the cases of low elastic stiffness and low structural mass, where the resulting motion of the solid is nonoscillatory. The conventional analysis procedure, which ignores the energy exchange between the air and the moving solid, predicts an undamped oscillatory response of the structure for all cases considered. It is shown that neglecting the interaction between the air and solid can produce significant error in the total energy of the structure and the dynamic load factor when the resulting motion is nonoscillatory. DOI: 10.1061/(ASCE)AS.1943-5525.0000022 CE Database subject headings: Blasting; Elastic structures; Structural response; Fluid-structure interactions. Author keywords: Shock; Blast; ALE; Riemann; Overpressure; Transient; Dynamic; Structure.

The shock jump relations for gradients of flow variables are presented in the case of a uniform steady freestream with a curved shock that may trigger an endothermic or exothermie chemical reaction. The rich information that can be obtained from these is used in order to derive field information for flow variables as well as details about the sonic line. This presentation collects, reviews, and extends work that has been published previously in various places. Comparisons with experiment and with numerical computation are given in some cases. The gradient -jump relations are likely to be useful for higher-order numerical schemes that use shock fitting. DOI: 10.2514/1.39993

The characteristics of the flow and the noise of shock-containing jets have been studied for nearly three decades. It is now established that broadband shock-associated noise is generated by the interaction of the downstream-convecting coherent structures of the jet flow with the shock cells in the jet plume. Past analyses of far-field data have been carried out with the total measured noise, which contains both the turbulent mixing noise and shock noise. In this study, these two components are first separated and extracted from the total spectra. Both convergent and convergent-divergent nozzles are considered. The decomposition is made possible by a recently developed scaling methodology for turbulent mixing noise, which provides excellent collapse of the mixing noise spectra from jets at all velocities but at a fixed temperature ratio. The characteristics of the shock component alone are investigated. A surprising effect of jet temperature on shock noise is established for the first time: the levels increase as the jet is first heated; however, the levels do not increase with further increase in jet temperature. The physical phenomenon responsible for this saturation of levels is not known at this time. The intensity for shock noise in the forward quadrant does not scale as the fourth power (shock exponent) of [square root of [absolute value of [M.sup.2.sub.j] - [M.sup.2.sub.D]]] but spans a range from 2.9 to 6.17, depending on the radiation angle and the jet temperature ratio. It is not straightforward to collapse the shock spectra. It is also established for the first time that nonlinear propagation effects are manifested at lower radiation angles, in which the shock component is dominant. The physical phenomenon that triggers the onset of nonlinear propagation for the shock noise could not be identified. The characteristics of the correlation functions at the lower inlet angles for subsonic and supersonic jets are different, attesting to the different noise generation mechanisms. DOI: 10.2514/1.38521

The interaction of shocks with multimaterial interfaces can occur in several applications, including high-speed flows with droplets, bubbles, and particles and hypervelocity impact and penetration. To simulate such complicated interfacial dynamics problems, a fixed Cartesian grid approach in conjunction with level-set interface tracking is attractive. In this regard, the ghost fluid method has been widely used to capture the interface dynamics. However, ghost fluid method experiences difficulties, particularly when strong shocks impinge on the interface. It has been shown that an accurate representation and decomposition of the wave systems (by solving a Riemann problem at the interface) significantly alleviates the shortcomings confronted by the ghost fluid method. Variants of the ghost fluid method proposed in the past differed in the way in which this Riemann problem was invoked at the interface. In this work, a simple, robust, and multidimensional procedure to construct the Riemann problem at the interface is presented. The work focuses primarily on resolving interface dynamics due to strong shocks interacting with embedded fluid-fluid interfaces (gas-gas and gas-liquid interfaces) in compressible flows. Several one- and two- dimensional problems involving moderate-to-very-large deformation of the embedded interface have been computed. The numerical examples demonstrate the flexibility, stability, and versatility of the approach in successfully resolving the embedded material interface. DOI: 10.2514/1.43148

Numerical simulation of shock waves interacting with multimaterial interface is immensely challenging, particularly when the embedded interface is retained as a sharp entity. The challenge lies in accurately capturing and representing the interface dynamics and the wave patterns at the interface. In this regard, the ghost fluid method has been successfully used to capture the interface conditions for both fluid-fluid and solid-fluid interfaces. However, the ghost fluid method results in over/underheating errors when shocks impact interfaces, and hence must be supplemented with numerical corrective measures to mitigate these errors. Such corrections typically fail for strong shock applications. Variants and extensions of the ghost fluid method have been proposed to remedy its shortcomings with mixed success. In this paper, the performance of approaches based on the ghost fluid method, in the case of strong shocks impinging on immersed solid boundaries in compressible flows, is evaluated. It is found that (from the viewpoint of simplicity, robustness, and accuracy) a reflective boundary condition used in conjunction with a local Riemann solver at the interface proves to be a good choice. The method is found to be stable, accurate, and robust for wide range problems involving strong shocks interacting with embedded solid objects. DOI: 10.2514/1.43153

In order to study the deformation mechanisms during ultrahigh strain rate deformation of face centered cubic metals, laser shock peening of a 304L stainless steel is systematically investigated. Two deformation modes--microtwins and microbands--and their interrelationship during high strain rate deformation are discussed in detail. Transmission electron microscopy and selected area electron diffraction are employed to study the deformation modes. It is found that twinning rakes place even when the shock pressure is much less than the critical twinning stress ill stainless steels. Theoretical critical twinning stress is not the only criteria to decide the deformation modes of twinning or slip. The formation of twinning and slip can be affected by the factors such as loading profile, loading stress/strain rate, stacking fault energy, grain sizes, and cell substructures. Factors that influence twin-slip transition in shock loading are discussed. The formation of dislocation structure is compared with those predicted using 3D dislocation dynamic simulation. [DOI: 10.1115/1.4000099] Keywords: stainless steel, high strain rate deformation, dislocation substructures, low energy dislocation structure, twins, microbands, laser shock peening

Multiple-line-of-sight tunable diode laser absorption measurements of the shock-train structure inside a model scramjet isolator are described. Understanding the shock train is important when considering the design of isolators to prevent unstart as well as dealing with heat transfer. Results from experimental studies such as this one can be used to help reline and validate the computational fluid dynamics models that are used in isolator design. Interpretation of the data collected is complicated because of the unsteady nature of the shock train. First, the gigabytes of acquired data are integrated on a scan-by-scan basis to form absorption-versus-time plots that can be used to determine the shock oscillation power spectrum and amplitude. The shock train is found to oscillate about its mean position with a peak-to-peak amplitude nearly equal to the equivalent duct diameter of 5.75 cm and with a power spectrum largely confined below 100 Hz. Next, developing an understanding of fundamental features of the flow requires that some form of intelligent feature extraction is used. This is difficult because the flow features are not simply periodic but involve a multitude of frequencies. Here, k-means data clustering is used to reduce the information to shock structures corresponding to various shock-front locations in the scramjet isolator as a function of backpressure. These clustered data sets are then used to extract path-averaged (transverse direction) static temperatures, static pressures, and water concentrations as a function of streamwise position that can be compared with path-averaged computational fluid dynamics computations. The results indicate that the computational fluid dynamics overestimates the shock spacing by 45% and that the path-averaged temperatures and pressures show a factor-of-2 variation more than indicated by the computational fluid dynamics simulations. These results can be used to help improve the computational fluid dynamics computations of the shock-train structure. DOI: 10.2514/1.41077

The process of laser shock peening induces compressive residual stresses in a material to improve material fatigue life. For micron sized laser beams, the size of the laser-target interaction zone is of the same order of magnitude as the target material grains, and thus the target material must be considered as being anisotropic and inhomogeneous. Single crystals are chosen to study the effects of the anisotropic mechanical properties. It is also of interest to investigate the response of symmetric and asymmetric slip systems with respect to the shocked surface. In the present study, numerical and experimental aspects of laser shock peening on two different crystal surfaces (110) and (114) of aluminum single crystals are studied. Lattice rotations on the top surface and cross section are measured using electron backscatter diffraction, while residual stress is characterized using X-ray microdiffraction. A numerical model has been developed that takes into account anisotropy as well as inertial terms to predict the size and nature of the deformation and residual stresses. Obtained results were compared with the experimental finding for validation purpose. [DOI: 10.1115/1.3106034]

The DOE/OCDO sponsored Ultrasupercritical Steam Boiler Consortium is conducting thermal shock tests on austenitic and nickel-based materials to assess their use in thick-section boiler components. This paper describes the tests on CCA617 (a controlled chemistry version of IN617) and Super 304H thick-walled tubes. Details are given of the metallurgical analyses of the observed cracking in the bore and on the outside diameter of the samples, and of the thermal-mechanical analyses to explain the results. Elastic-plastic and elastic-plastic-creep analyses are used to calculate damage based on rupture life and creep strain accumulation. The results of the metallurgical and mechanical analyses are compared, and conclusions are drawn as to the accuracy and effectiveness of available high temperature life prediction techniques. The test conditions bear no relation to expected operating conditions. They are chosen to generate failure data. [DOI: 10.1115/1.3120265]

The aim of this research is to improve the robustness of the air gap controller for solid immersion lens (SIL)-based near-field recording (NFR) servo systems against dynamic disturbances such as external shocks. Stable control is essential in these systems because the air gap distance between the SIL and the rotating disk is less than 100 nm. To detect gap error and read-out signals for the SIL and the disk, the air gap control performance must be increased to avoid collisions due to external shocks. We propose an anti-shock air gap control system using a disturbance observer (DOB) and a dead-zone nonlinear controller. Experimental results demonstrate that a DOB with a Q filter bandwidth of 500 Hz reduced the minimum air gap distance due to an external 1 g@10 ms shock by 70.1%. A DOB and a dead-zone nonlinear controller maintained the optical head distance for a 2 g@ 10 ms shock. Thus the control performance in the presence of external shocks was improved. Index Terms--Anti-shock control, dead-zone nonlinear controller, disturbance observer (DOB), gap error signal (GES), near-field recording (NFR).

A solid immersion lens (SIL)-based near field recording (NFR) device is regarded as the next generation optical storage device that can achieve an areal density over 100 GB/[in.sup.2]. However, the NFR system is very weak for the external shock due to the extremely small gap between a SIL and a disc. Many researches using a gap servo control were carried out, but the results were too insufficient to satisfy needs of the industry. To solve this problem, we propose a new method using air bearing surface (ABS) to avoid a collision between the SIL and the disc occurred by the external shock. In this paer, we check a feasibility of a ABS on shock resistance in NFR system due to many reasons such as a large mass of moving part, a protrusion of the SIL and a low stiffness of wire. We also design an ABS to avoid effectively the collision between the SIL and the disc and to improve shock resistance of SIL based NFR system. Finally, we investigate the effect of the ABS on shock resistance of optical head for SIL based NFR system. Index Terms--Air bearing surface, near field recording, shock resistance, solid immersion lens.

MACHINES Compressors 07-1501 Wang, S. Compressor noise control. Proceedings of the Thirteenth International Congress on Sound and Vibration, Vienna, Austria: PS004, July 2-6, 2006 (www.iiav.org). KEYWORDS: automobiles, compressors, design, noise [...]

Four classical support conditions are investigated for beams with distributed loading, which has a temporal form of rectangular pulse. First, a simple calculation is presented, using algebraic equations of momentum and energy conservation to derive approximate deflection results. Then, exact relationships, derived from work by others and describing a total of five regimes of motion, are quoted and discussed. These relations were developed using a popular, rigid-plastic material model. On the other hand, there is an elastic-perfectly plastic material model, which represents a more realistic description of material properties. When solutions are obtained by means of a numerical simulation, employing the better material model, it is found that the simpler solutions developed here provide more accurate results of final deflections. DOI: 10.1061/(ASCE)0733-9399(2007)133:3(320) CE Database subject headings: Dynamic loads; Australia; Beams; Inelastic action.

Manganin stress gauges are used to monitor the behavior of pure tungsten under conditions of one-dimensional shock loading, which are mounted in longitudinal and lateral orientations. The results have shown that the decrease in shear strength behind the shock front is related to both the innate influence of the high Peierls stress in tungsten on dislocation generation, motion and storage and the nucleation and growth of grain boundary cracks that gradually degrade the material's strength.

MACHINES Compressors 07-0001 Marscher, W.D., and J.J. McGinley. Vibration troubleshooting of an air compressor. S/V, Sound and Vibration (United States) 40(5):12-15, May 2006 (sv@mindspring.com). KEYWORDS: bearings, case histories, compressors, diagnostic [...]

1. Introduction Several system reliability models subject to shocks can be found in the literature. Generally, the models studied assume that the shocks arrive at random times, causing damages of [...]

A series of techniques has been assembled to characterize the unreacted Hugoniot of candidate explosives. Particle velocity gauges have been proven for inclusion into the material.

Aeroelastic mesoflaps for recirculating transpiration have been investigated in an effort to control shock/boundary-layer interactions (SBLIs) through passive cavity recirculation. The mesoflap concept utilizes a matrix of small flaps covering an enclosed cavity that are designed to undergo local aeroelastic deflection to achieve proper mass bleed or injection when subjected to gasdynamic pressure loading. Experiments were performed to investigate the applicability of the mesoflap concept for oblique shock interaction by employing shadowgraph flow visualizations, surface pressure measurements, and mean and fluctuating velocity measurements, along the spanwise midplane of the shock intersection. The experiments were conducted in a Mach 2.41 supersonic wind tunnel operating at a unit Reynolds number of 57 x [10.sup.6] [m.sup.-1]. With the thickest mesoflap arrays in place, the leading shock formed at the location of the first flap and the boundary-layer thickness at shock impingement was greater due to flow injection through the upstream flaps. However, the thinnest mesoflap arrays yielded a somewhat reduced boundary-layer thickness downstream of the interaction as a result of the tangential bleeding by the last flaps. Stagnation pressure profiles for the thinnest arrays also showed improved recovery downstream of the SBLI as compared to the solid-wall case. However, further study is needed to investigate three-dimensional effects and to determine whether this control strategy provides significant performance improvements for flow conditions more consistent with actual inlets.

The vibration of linear mechanical systems with arbitrary damping is known to pose challenging problems to the analyst, for these systems cannot be analyzed with the techniques pertaining to their undamped counterparts. It is also known that a class of damped systems, called proportionally damped, can be analyzed with the same techniques, which mimic faithfully those of single-degree-of-freedom systems. For this reason, in many instances the system at hand is assumed to be proportionally damped. Nevertheless, this assumption is difficult to justify on physical grounds in many practical applications. What this assumption brings about is a damping matrix that admits a simultaneous diagonalization with the stiffness matrix. Proposed in this paper is a decomposition of the damping matrix of an arbitrarily damped system allowing the extraction of the proportionally damped component, which, moreover, approximates optimally the original damping matrix in the least-square sense. Finally, we show with examples that conclusions drawn from the proportionally damped approximation of an arbitrarily damped system can be dangerously misleading. [DOI: 10.1115/1.1483832]

Radiation loading on a vibrating structure is best described through its radiation impedance. In the present work the modal acoustic radiation impedance load on an infinitely long cylindrical source harmonically excited in circumferentially periodic (axially independent) spatial pattern, while positioned concentrically within a fluid cylinder, which is embedded in a fluid-saturated unbounded elastic porous medium, is computed. This configuration, which is a realistic idealization of an acoustic logging tool suspended in a fluid-filled borehole within a permeable surrounding formation (White, J. E., 1983, Underground Sound Application of Seismic Waves, Elsevier, Amsterdam, Fig. 5.29, p. 183), is of practical importance with a multitude of possible applications in seismo-acoustics and noise control engineering. The formulation utilizes the Biot phenomenological model to represent the behavior of the sound in the porous, fluid-saturated macroscopically homogeneous and isotropic surrounding medium. Employing the appropriate wave-harmonic field expansions and the pertinent boundary conditions for the given boundary, configuration, a closed-form solution in the form of an infinite series is developed and the resistive and reactive components of modal radiation impedances are determined. A numerical example for a cylindrical surface excited in vibrational modes of various order, immersed in a water-filled cavity which is embedded within a water-saturated Ridgefield sandstone environment, is presented and several limiting cases are examined. Effects of porosity, frame stiffness, source size, and the interface permeability condition on the impedance values are presented and discussed. [DOI: 10.1115/1.1488664]

A procedure to calculate the natural frequencies of in-plane loaded, thin, slightly curved, simply supported rectangular plates is presented, with numerical results. This includes the solutions to von Karman's static equilibrium equation and the linear shell vibration equation using Galerkin's method. The compatibility equations are given in terms of Airy stress functions which satisfy the 'shear free' and 'constant normal displacement' in-plane edge conditions. This procedure is an extension to the method presented by Hui and Leissa, the difference being the use of a multiterm Fourier series representation for the initial imperfection, the static deflection and the vibratory modes. [DOI: 10.1115/1.1489449]

Drop tests are often substituted in qualification or life testing of microelectronic and optoelectronic products by shock tests. The existing (e.g., Telcordia) qualification specifications require that a short term load of the given magnitude and duration (say, an 'external' acceleration with the maximum value of 500 g, acting for 0.001 s) is applied to the support structure of the product under test. The natural frequencies of vibration are not taken into account. The objective of our study is to develop simple analytical ('mathematical') predictive models for the evaluation of the dynamic response of a structural element in a microelectronic or an optoelectronic product/package to an impact load occurring as a result of drop or shock tests. We use the developed models to find out if a shock tester could be 'tuned' in such a way that the shock tests adequately mimic drop test conditions. We suggest that the maximum induced curvature and the maximum induced acceleration be used as suitable characteristics of the dynamic response of a structural element to an impact load. Indeed, the maximum curvatures determine the level of the bending stresses, and the maximum accelerations are supposedly responsible for the functional (electronic or photonic) performance of the product. We use the case of an elongated rectangular simply supported plate as an illustration of the suggested concept. We show that in order to adequately mimic drop test conditions, the shock test loading should be as close as possible to an instantaneous impulse, and that the duration of the shock load should be established based on the lowest (fundamental) natural frequency of vibrations. We show also that, for practical purposes, it is sufficient to consider the fundamental mode of vibrations only, and that the shock load does not have to be shorter than, say, half the quarter of the fundamental period. We demonstrate that, if the loading is not short enough, the induced curvatures and accelerations can exceed significantly the curvatures and accelerations in drop test conditions. Certainly, the results of such shock tests will be misleading. After the appropriate duration of the shock impulse is established, the time dependence and the maximum value of the imposed ('external') acceleration in shock tests should be determined, depending on the most likely drop height, in order to adequately mimic drop test conditions. We demonstrate that the application of a probabilistic approach can be helpful in understanding the mechanical behavior and to ensure high short- and long-term reliability of an electronic or photonic device that might be or will be subjected to an accidental or expected impact loading. We conclude that although it is possible to 'tune' the shock tester, so that the drop test conditions are adequately reproduced, actual drop tests should be conducted, whenever possible. The results of the analysis can be helpful in physical design and qualification testing of microelectronic and photonic products, experiencing dynamic loads of short duration. [DOI: 10.1115/1.1487356]

A study of the shock response of a hard disk drive dropped from a height onto a surface with a specific contact stiffness is presented. A finite element model of the hard disk drive was developed and transient response analysis of the model was performed to evaluate the shock problem. The study shows why a disk drive is particularly sensitive to shock inputs with narrow pulse widths in the order of 0.5 to 1 millisecond.

Quantitative 29Si NMR spectra of single-crystal [Alpha]-quartz, shock compressed to 12-38 GPa and recovered, provide new information about the complex response of quartz to shock loading. Spectra from samples recovered from shock pressures of 12-20 GPa show a broadening of the 29Si NMR peak and the development of asymmetry toward lower NMR frequency (indicating an increase in the mean Si-O-Si intertetrahedral bond angle). NMR spectra of samples shock compressed above [approximately]25 GPa show increasing amounts of a separate amorphous phase of Si[O.sub.2] with a mean Si-O-Si bond angle roughly 5 [degrees] narrower, and 10-15% denser, than fused Si[O.sub.2]. Small amounts of crystalline material remain with a mean Si-O-Si bond angle up to 3 [degrees] larger than unshocked [Alpha]-quartz. The recovery of dense glass indicates that post-shock temperatures were sufficiently low to also preserve stishovite, had any been created in our experiments. The paucity of stishovite or [6]Si in an amorphous phase in our recovered samples suggests that the formation of stable, high-coordinated Si is kinetically hindered in shock compression experiments up to about 3540 GPa, except in regions of high temperature, such as planar deformation features (PDFs), microfaults (pseudotachylites), or voids.

Pulsed lasers were used to induce plane shocks of short duration in iron samples of different thicknesses. Polymeric piezoelectric transducers were used to collect transmitted wave measurements. Findings indicated a decrease of the elastic precursor amplitude with increasing propagation distance and a stress relaxation behind the elastic wave front. Significant twin formations were found by postshock examinations of recovered specimens.

A theory regarding the response of R lines in ruby crystals subjected to deformations was evaluated through experimental measurements of the shifts of ruby R lines for shock loading along the low symmetry r direction. The predictive capability of the theoretical model was seen based on experimental results showing good agreement with the calculated values based on symmetry adapted irreducible strains. Validation of the model implied that oriented ruby chips can now be utilized in diamond anvil cell experiments.

Presented in this paper is the study of the effect of panel stiffness on the resistance of cladding panels subjected to blast loading. In many situations the size of a cladding panel has largely been decided by architects, leaving engineers to design the cross section, which directly influences the panel stiffness. By introducing the concept of a deformed shape function that is independent of panel stiffness and loading levels, the relative effect of panel stiffness, the material properties, and blast loading levels on panel deformation and forces transferred to fixings can be assessed without the need to actually specify the deformed shape function. It was found that these relative effects of panel stiffness and loading levels also depend on whether the panel is in the impulsive or quasi-static loading range. The theoretical predictions were compared with results from finite element analyses using DYNA3D, and good agreement was obtained. Though the mathematical derivation is complex, the findings are easy to use and have wide practical applications.

The design of expandable polystyrene foam buffers, used as protective packaging for a range of goods, is by and large steeped in heuristics because the design procedures have not been formalized. This paper discusses the application of Taguchi's Method of Parameter Design to the determination of the key design parameters of expandable polystyrene foam end cap buffers. An [L.sub.18] orthogonal array was adopted for the planned experiments. The eight design parameters considered critical in the design of the cushioning buffers were product centroid-to-buffer centroid distance, cushioning area, buffer thickness, wall thickness, material density, rib configuration, rib width, and rib spacing; of these, only buffer thickness, wall thickness and buffer density were found to be significant at a 99% confidence interval. The height of the ribs, being the difference between the buffer and wall thicknesses, is the single most important factor. The buffer cushioning area was found to be not as important as its distribution over the entire load-bearing area and the buffer configuration. The buffers were designed in Unigraphics II, and the post-processing of the NC part program for machining on the Hamai vertical machining center. The impact shock testing of the end cap buffers was conducted on the Lansmont Model 65/81 Shock Test System., INTRODUCTION Protective packaging shields goods from damage by shock and vibration during handling, distribution, or transit (1). The different protective packaging configurations fulfill this primary function in a cost-effective way [...]

Research has established a mechanical model to describe the dynamics of vibration absorbers with motion-limiting stops. The chaotic vibrations, lower damping and nonlinear effects are described through the use of refined contact-noncontact criteria. Numerical analysis is given to illustrate theoretical observations regarding chaotic responses.

Arc-shock interaction in a supersonic nozzle has been investigated for a current range from 200 to 1500 A and for three pressure ratios. The adverse pressure gradient associated with the shock causes flow separation and a broadening of arc cross section. Compared with the shock position in the absence of the arc, the shock center is moved toward upstream and to a region close to the wall. The shock is no longer plane. The center of the shock is not very sensitive to the current, but the shock strength reduces when the current is increased. V-I characteristics under shock conditions are slightly modified. Index Terms - Arc characteristics, arc-shock interaction, circuit breaker, supersonic nozzle.

Low-energy impact tests were performed on a polyamide 6 using a dart test technique with a 20-mm-diameter hemispherical striker. Partial penetrations at controlled and increasing energies allowed to visualize the different steps of the deformation. The evolution of the deformation is described, taking into account the shape and the thickness of the samples, the crystalline orientation, the microstructure and the resulting mechanical properties of the polymer. The deformation results from several steps, which are revealed by the evolution of the force measured on the striker. The deformation induces important and inhomogeneous changes in the microstructure and the orientation of the polymer. Variations may be abrupt. The resulting mechanical behavior is strongly dependent on this evolution and, as a consequence, depends on the location in the sample. These observations confirm that it is impossible to predict such a complex behavior using data from simple tensile tests., INTRODUCTION The impact resistance of polymers determines their usefulness in many applications. Consequently, there is an increasing demand for tests that accurately simulate end-use conditions. In the past, the most [...]

Experiments on the use of N(sub 2)O to increase shock tunnel test time were performed in the electric arc-driven shock tube at the NASA Ames Research Center. A total of 29 tests were conducted, 17 with air in the driven tube, 10 with N(sub 2)O/N(sub 2) in the driven tube and 1 with argon in the driven tube. Results reveal that the test times estimated from light histories increased by 60-100% when substituting N(sub 2)O/N(sub 2) for air in the driven tube and when operating at overtailored conditions.

The unstable loading response of convex shells is responsible for the differences in the plate and convex shell responses to transverse loading. The plate and the convex shell responses differ in terms of trends in the response parameters, and the damage extent and distribution. The instability helps the convex shells in dissipating impact energy through structural deformation, thus minimizing the impact damage. This concept of instability has implications for the designing of tolerant aerospace components.

A Hugionot equation of state (EOS) model for characterizing the shock compression response of porous materials over the full pressure range was developed based on a thermodynamic EOS describing changes in the thermodynamic variables along isobaric paths. The model was applied to 2024 aluminum, copper and tungsten. The resulting Hugoniot EOSs showed good agreement with empirical data.

The impact of viscous damping on the maximum displacement and maximum acceleration or deceleration of a one-degree-of-freedom linear system experiencing a shock load during accidental drop or drop tests was investigated. Consequently, the results, which showed that both events occur only in undamped systems, were correlated to the use of smart materials with high-energy absorption characteristics in microelectronic applications.

An analytic impact force function facilitates the investigation of the dynamic response of orthotropic composite cylindrical shells to low-velocity impact by a solid striker. A normal impact accommodating solution, based on a higher order shear deformation theory, allows the examination of the induced strains for such impacts. Experimental results suggest that maximum strains occur at the impact point during contact. Relationship of the history and location of the contact force with the strain magnitudes is discussed. Strain responses to central and noncentral impact are detailed.

In this study, stress intensity factors for axial cracks in hollow cylinders subjected to thermal shock are determined by using the thermal weight function method. The thermal weight function is a universal function for a given cracked body and can be obtained from any arbitrary mechanical loading system. The thermal weight function may be thought of as Green's function for the stress intensity factor of cracked bodies subject to thermal loadings. Once the thermal weight function for a cracked body is determined, the stress intensity factor for any arbitrary distributed thermal loading can be simply and efficiently evaluated through the integration of the product of the temperature and the correspondent thermal weight function. A numerical boundary element method for the determination of thermal weight functions for axial cracks in hollow cylinders is used in this study to evaluate the transient stress intensity factor. As a demonstration, some examples of axial cracks in hollow cylinders subjected to thermal shock are solved by using the thermal weight function method, and the results are compared with available results in the published literature.

Vibratory energy transmitted through propagating waves generated by machine foundations can be detrimental to adjacent structures or sensitive equipment operating nearby. Most of the vibratory energy affecting structures nearby is carried by surface waves that propagate in a zone close to the ground surface. Thus, for machine foundations vibrating at moderate to high frequencies, vibration amplitudes in the vicinity of the foundation can be reduced significantly by installing an annular in-filled trench wall around it. An in-filled trench wave barrier reduces the ground motion by interception, scattering, and diffraction of the surface waves. This approach of isolating a vibrating machine foundation from its surroundings is known as active isolation. This paper presents a numerical investigation on active isolation of machine foundation by in-filled trench wave barriers in a three-dimensional viscoelastic half-space. A rigorous boundary element method (BEM) algorithm for dynamic analysis of three-dimensional solids has been used to study the effects of various geometric and material parameters on the performance of the in-filled trench barriers. Important dimensionless parameters have been identified and design guidelines are presented.

Shock veins in the Sixiangkou (L6) chondrite contain two high-pressure assemblages: (i) majorite-pyrope solid solution plus magnesiowustite that crystallized at high pressures and temperatures from a shock-induced silicate melt of bulk Sixiangkou composition and (ii) ringwoodite plus low-calcium majorite that were produced by solid-state transformation of olivine and low-calcium pyroxene. The morphology and chemistry of the majorite-pyrope garnet and the size of the magnesiowustite crystals indicate a longer duration at high pressure and temperature than predicted by impact scenarios. This pressure-temperature regime is constrained by the olivine-ringwoodite and orthopyroxene-majorite phase transformations, fusion of the meteorite constituents, and crystallization of majorite-pyrope solid solution plus magnesiowustite from that melt under high pressure., Forsteritic olivine [Fe/(Fe+Mg) < 0.26] transforms into the denser polymorphs modified spinel (wadsleyite, β phase) and spinel (ringwoodite, γ phase) in the Earth's transition zone (1-4) and dissociates at pressures [...]

We use three-dimensional surface topography analysis for evaluating waterjet generated surfaces. The waterjet generated surface is separated into smooth and striation zones, where striation influence is negligible in the smooth zone. It is found that the smooth zone has a random, moderately isotropic texture, with the height distribution nearly Gaussian. The effects of cutting speed, depth of cut, and abrasive size on the surface roughness are studied for the smooth zone and striation zone separately. This provides useful information for controlling process parameters to obtain smooth finished surfaces. Spectral analysis is used to investigate the surface striation and machine structure vibration. It is found that forced vibration of the mechanical structure strongly influences striations generated in the waterjet machining system.

This paper deals with the regenerative chatter vibration occurring in cutting tools with different side cutting edge angles. The occurrence of regenerative chatter vibration of the cutting tool is influenced by two factors, which are closely related to the vibratory energy supply or consumption. One factor is the interference effect between the tool flank and the workpiece. Of course, this factor exists in the primary chatter, too. The other is the regenerative effect. The influence of both factors on the regenerative chatter vibration of cutting tools with different side cutting edge angles is examined experimentally. The vibratory energy supply is simulated, considering the dynamic cutting process. As a result, the property of the regenerative chatter vibration and the influence of the side cutting edge angle on the regenerative chatter vibration are clarified.

A study shows that low-speed impact damage-initiation of thick laminated composite plates occurs at the impact site and the plate surface opposite to the impact site. The tensile fracture on the plate surface opposite to the impact site causes impact damage-initiation in thin plates. Three-dimensional stress states enable the analyses of the low-speed impact damage-initiation characteristics. The study is conducted on quasi-isotropic and orthotropic graphite-epoxy and graphite-bismaleimide laminated plates.

A mathematical model of the time-dependent response of a fully clamped, isotropic, homogenous, linear elastic rectangular plate to transverse impact events uses a closed-form solution to generate simulated sensor-response data that can evaluate potential neural network-based impact location. Fast Fourier transform of the strain integrated over frequency is utilized in deriving the most successful impact location methodology.

The melting of chondrule precursors in an accretional shock reprocesses the bulk of chondrule solid material. Accretional shock leads to a cooling process in the gas during solid grain melting. This results in the enhancement of intensity drag while heating the large grains of the chondrule. Accretional shock heats the chondrules more than the adiabatic shock effects in the gas.

The objective of this paper is to evaluate the ability to accurately predict the motions, structural response, and failure modes of internal structural components subjected to high-intensity airblast and ground shock loading. The cases of interest involve a surface flush, buried reinforced concrete cylinder that is expected to experience negligible damage, within which are contained aluminum and steel structures that may or may not be shock-isolated at the internal attachment points. The structures and subsystems are modeled in detail using the FLEX three-dimensional nonlinear transient analysis code. The analyses were carried out using the soil island approach to represent the local airblast-induced, direct-induced, and crater-related ground shock from a simulated nuclear explosion. A test involving only local airblast effects with hard-mounted internal substructures was conducted. Comparisons of data from this test with calculations will be presented. Calculations will also be included that show potential failure mechanisms for the internal subsystems and their causes.

Ultrasonic wave velocity measurements of longitudinal and shear modes help determine the equation of state of aluminium nitride. A combination of equation of state and shock Hugoniot data on AlN helps determine the strength of AlN under plane shock wave compression. A comparative study of static high-pressure examination of wurtzite to rock salt structure transition in AlN helps understand the existing shock Hugoniot coordinates above the transition stress.