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Rock materials are commonly endowed with anisotropic structures, like beddings, flaws and fillers, which makes it difficult to predict their strength, deformation and fracturing properties under dynamic loading. Considering the structural complexity and randomness in rock materials, it is difficult to obtain two rock specimens with exactly the same structures for experimental study. As an emerging method, 3D printing (3DP) shows some promise in being able to replicate the complicated meso-and micro-structures and repetitively fabricate identical "rock" specimens. In this study, 3D printed rock-like specimens are fabricated into bedded Brazilian discs (diameter: 50 mm and thickness: 25 mm) using extrudable geomaterials with an extrusion width of 1 mm and a layer thickness of 0.5 mm. By combining a split Hopkinson pressure bar and two high-speed cameras, Brazilian disc tests were conducted on 3DP specimens with bedding angles α (i.e. angle between impact direction and bedding orientation) of 0˚, 30˚, 60˚ and 90˚ to investigate their anisotropic mechanical and fracture properties under dynamic loading. Results show that the dynamic indirect tensile strength decreases as the bedding angle β increases from 0 to 30˚ and then increases when β is increased from 30˚ to 90˚. Failure patterns of 3DP specimens exhibit tensile dominated failure at bedding angles of 0˚ and 90˚, and the mixed tensile-shear failure in other bedding angles (30˚ and 60˚). The experimental results are consistent with a previous study using natural rock materials, indicating that the 3D printing technology is applicable to the replication study of rock-like materials under dynamic loadings, allowing an artificial design process and a repeatability in the structures, avoiding the inconsistencies in natural rock specimens. [ABSTRACT FROM AUTHOR]

We must know the construction characteristics so that the primary engine vibration can be distributed evenly. The analysis is carried out on the seamless structure, which is considered the ideal structure. The experimental Modal Analysis (EMA) method is used to see the characteristics of the dynamic load distribution in wooden ship construction. Simulation is used to find out which part of the construction has the highest stress concentration. Each construction part is grouped into the rigid base construction section (keel, floor, engine bed, and canal) and the elastic hull construction section (frame, hull board, and hull stringers). The simulation results show that in the radial direction of the fiber, with horizontal vibrations, the smallest amplitude occurs in the frame, while the largest occurs in the channel. In vertical vibrations, the smallest amplitude occurs at the keel and the largest in the hull board. In the tangential fiber direction, with horizontal vibrations, the smallest amplitude occurs in the hull board while the largest occurs in the engine bed area. In vertical vibrations, the smallest amplitude occurs at the keel while the largest occurs in the canal and engine bed. [ABSTRACT FROM AUTHOR]

In the framework of the current mathematical theory of growing solids, a nonclassical mechanical model is developed to trace the evolution of elastic technological stresses in cylindrical composite pieces during the additive processes of their manufacturing by the method of multi-layer power thread winding, taking into account the structure of the material being formed and an arbitrary law of changing the thread pre-tension. Based on the proposed model, the closed analytical dependencies are constructed. [ABSTRACT FROM AUTHOR]

Preventing fatigue damage and failure in components subjected to repeated impact loading is of great interest in many engineering applications. Quite often, material response during high-rate loading differs from quasi-static response due to the material’s strain rate sensitivity and adiabatic heating effects. Hence, experimental materials testing at realistic loading rates is important in many cases of impact fatigue. Impact loading tests involve an inherent challenge: since force equilibrium does not exist, the dynamic response of the whole load train must be properly accounted for in order to impose the desired loading on the specimen and to measure the specimen response. In the field of monotonic high strain rate materials testing, the Split Hopkinson Bar (SHB) technique has established itself due to its simplicity in terms of structural dynamics. However, traditional SHB setups require a long time to be reset/rearmed after the impact, and therefore they are ill-suited for cyclic impact loading studies. In this contribution, we present a modified SHB technique with fully automatized rapid resetting/rearming of the setup, which allows for controlled cyclic impact loading at a rate of 0.5 Hz. The applicability of the method is demonstrated in this paper with test results for a tempered steel. [ABSTRACT FROM AUTHOR]

It is sixty years since Cyril Stanley Smith's seminal paper describing the effects of shock loading on the structure / property behavior of metals. While numerous experimental observations have fostered the correlation of post-shock microstructural parameters, such as dislocations, point defects, deformation twins, shock-induced phase products, etc., with particular shock parameters, quantitative predictive capability of the defect generation and damage evolution in materials subjected to dynamic loading has yet to be realized. Broadly based defect generation/storage phenomenology presenting a unified view of the material structure/property aspects of shock-wave deformation for a wide range of crystal structures has proven very difficult. However, changes in design and manufacturing paradigms applied to events dominated by dynamic-loading processes have placed increased emphasis on developing physically- based predictive materials models of shock effects on materials as well as amazing innovations in in-situ shock diagnostics. In this paper, a survey of the evolution in the state-of-our-understanding of defect generation and damage evolution is discussed and thoughts on the evolving capabilities to move shock / dynamic behavior of materials research from observation to design and control is presented. Examples of how utilizing "real-time", post-mortem, and "in-situ" experimental approaches together are needed to facilitate quantification 4D processes during shock-wave loading including dislocation / defect generation, shock-induced phase transitions, and damage evolution and spallation. [ABSTRACT FROM AUTHOR]

The article presents the operation of a system for monitoring the state of a structure made of polymer composite materials under dynamic loading of a carbon fiber sample with fiber-optic sensors based on Bragg gratings introduced at the manufacturing stage and installed on the surface. The results of a full-scale experiment were compared with the results obtained by mathematical modeling. [ABSTRACT FROM AUTHOR]

The paper presents a new testing technique for observing the real-time changes occurred in the elastic and dissipative bonds of a heavily loaded tribosystem of the splined coupling of MI-26 tail driver coupling. Unlike other non-destructive testing methods, the frequency transfer-function method can indirectly identify the ratio of the elastic, inertial and dissipative components of the frictional interaction of the splined coupling. The octave (1/3, 1/12, 1/24-fractional octave) spectral analysis of estimating the dissipative energy losses allows to identify the frequency ranges of natural vibrations and monitoring their changes of both the friction-mechanical subsystem and the lubricant used. The proposed dynamic quality criterion is applied both to observe of the changes in the frequencyse, transient in time, elastic-dissipative characteristics of the splined coupling and to actualize a short- or long-term forecast of their changes up to the "warning" and "danger" levels. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical calculations of dynamic loading of thin cylindrical targets with a ratio of cylinder heights to its diameter 1 : 1 and 5 : 1. The propagation of elastic waves in cylinders with different ratios of heights to the radius of the VZhM8 single-crystal nickel alloy with cubic symmetry of properties in order to determine the propagation velocities of rod waves in the [001], [011] and [111] directions was simulated in this paper. The problem of loading of a target from VZhM8 by a steel projectile with a starting velocity was carried out by the finite element method in a three-dimensional formulation. [ABSTRACT FROM AUTHOR]

The present paper studies the stress-strain state in the near-surface layer of the material under surface loading. The thickness of the layer is much larger than the average surface roughness. The material and its surface take into account the elements of the internal structure and the approach of physical mesomechanics to the description of its behavior. The stress-strain state is calculated with a finite-difference method for solving a set of equations that describe the mechanical behavior of the material under dynamic loading. It is shown that the used physical mesomechanics approach allows modeling an inhomogeneous stress-strain state with the formation of localized deformation bands and a block-like structure of the plastic flow. Modeling of the stress-strain state for near-surface layer allows estimating its thickness and the degree of influence on the overall deformation. [ABSTRACT FROM AUTHOR]

Experimental and theoretical studies on the mechanisms of plastic deformation localization under dynamic loading have been carried out. Experiments on the dynamic loading of specimens were performed on the split Hopkinson bar and on the ballistic system designed for target perforation. To study localized shear under high-speed loading, we used specimens of a specific shape developed for the performance of these particular experiments. The localization of plastic strain at high loading speeds was also investigated in the ballistic tests on the perforation of targets under the impact of a cylindrical projectile made of high-strength steel, which is accompanied by the formation and ejection of the plug. The mechanisms are associated with the collective effects in the ensemble of microdefects in spatially localized regions. In-situ infrared scanning of the instability zone followed by the study of the dislocation substructure provided supporting evidence for the assumption that the above processes play a significant role in the defect subsystem of the material during the development of localized plastic flow. Modeling of localization of plastic deformation is carried out using the equations that relate the non-equilibrium transitions to the mechanisms of structural relaxation and plastic flow. [ABSTRACT FROM AUTHOR]

Results of experimental and numerical studies of A57036, AISI 420 and AISI 321 steels under static and dynamic loading according to the theory of critical distances (TCD) are reported. The samples with different stress concentrators in high strain rate region 10²–10³ s–¹ using a split Hopkinson bar were tested. This study confirmed that the early-proposed modification of TCD can adequately estimate the strength of steel samples in case of dynamic loading. The error does not exceed ±20% regardless of the used method (point, line or area). [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical simulation of the dynamic loading of a target from an anisotropic aluminum alloy AA7010-T6 with an isotropic aluminum projectile with different velocities. The process of destruction of an anisotropic target material was simulated by applying the fracture criterion from accumulated plastic deformations. This criterion makes it possible to take into account the anisotropy of the strength characteristics of the target material and to simulate the process of accumulation of microdamages. To study the effect of anisotropy of the mechanical characteristics of the material on its deformation, two types of calculations were carried out: in the first case, the mechanical properties of the target material along the loading direction were minimal, and in the second case, maximal. This statement of the problem corresponds to the statement of the problem in natural experiments in which the direction of the material rolling is oriented parallel or perpendicular to the direction of the load. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical simulation of the dynamic loading of an target from an anisotropic aluminum alloy 2024 by an isotropic aluminum projectile. The process of spalling destruction of an anisotropic target material was modeled with the help of two models of elastoplastic deformation of the material, in the first case the fracture criterion from accumulated plastic strains. In the second case, the elastoplastic material deformation model is supplemented by a fracture criterion containing the ultimate porosity. The obtained results of the calculations were compared with the experimental data for the case of the initial shock loading rate of 630 m/s. Numerical modeling of spall destruction of target is performed by the finite element method in a three-dimensional formulation. [ABSTRACT FROM AUTHOR]

The dynamics of a medieval tower, inside the Basilica of San Benedetto in Ferrara (Italy), subjected to transversal dynamic loadings has been analyzed by using a distinct element code which implements the Non-Smooth Contact dynamics method. Since the contact between blocks is governed by the Signorini's impenetrability condition and the dry-friction Coulomb's law, the tower exhibits discontinuous dynamics. The sliding motions of blocks are non-smooth functions of time. Numerical simulations are performed with the aim of investigating the influence of the friction coefficient but also of the amplitude and frequency of the excitation at the base. [ABSTRACT FROM AUTHOR]

In this article you may find information about the hybrid methodology for determining strain-rate-dependent constants for Johnson-Cook material model. This methodology is based on the use of experimental and numerical research. The methodology assumes the use of the Charpy hammer test with the notched and smooth samples for determining constants for plasticity and failure of the material. [ABSTRACT FROM AUTHOR]

Loading dynamics of a transmission line (TL) with a joint weight, wind and ice deposits loading is being studied. For exploring of icing restapling the equations of dynamics and heat conduction are resolved. The mechanism of the appearance of «the dance of wires» is revealed. [ABSTRACT FROM AUTHOR]

This study presents the multi-objective optimisation of empty and foam-filled double circular tubes under pure axial and oblique impact loading conditions. Thin-walled metal tube structures are utilised in vehicular bodies due to the increased energies that can be absorbed by lightweight material structures. Finite element analysis is performed with ABAQUS code, and then confirmed using applicable experimental tests. Optimised designs of crushing parameters, including minimum peak crushing forces and maximum specific energy absorptions, were conducted with Radial Basis and Non-dominated Sorting Genetic Algorithm-II functions. The findings demonstrate that aluminium foam-filled double circular tubes do feature increased crashworthiness over empty, unfilled versions when subject to impact loads. [ABSTRACT FROM AUTHOR]

The dynamic failure and fragmentation response of pressed metallic composites is investigated experimentally using a Kolsky bar and explosive loading. The composites are made of nominally brittle (tungsten) and ductile (aluminum) metal phases, in varying ratios, to explore the effect of composition on the material fragmentation behavior. Dynamic compression experiments at strain rates ~2000 s-1 are conducted on a Kolsky bar to apply controlled uniaxial deformation. High-speed images captured during the dynamic loading provide insight to the nature of the failure mechanisms activated (e.g. brittle vs. ductile fragmentation). Explosively-driven fragmentation experiments are conducted in a shock tunnel to investigate the fragmentation behavior under shock loading which produces higher rates and induces spall failure. These experiments incorporate high-speed schlieren imaging to track the explosively driven shock and resulting fragments as they travel down range. The high-speed images from both experimental setups are correlated with postmortem measurements of the resulting fragment size distributions, providing connections between the composition and fragmentation behavior. [ABSTRACT FROM AUTHOR]

The reverse Taylor impact is a common experiment to investigate the dynamical response of materials at high strain rates. To better understand the physical phenomena and to provide a platform for code validation and Uncertainty Quantification (UQ), a co-designed simulation and experimental paradigm is investigated. For validation under uncertainty, quantities of interest (QOIs) within subregions of the computational domain are introduced.When regions of interest can be identified, the computational cost for UQ can be reduced by confining the random variability within these regions. This observation inspired us to develop an asynchronous space and time computational algorithm with localized UQ. In every region of interest, high resolution space and time discretization schemes are used for a stochastic model. Apart from the regions of interest, low spatial and temporal resolutions are allowed for a stochastic model with low dimensional representation of uncertainty. The approach is exercised on a linear elastodynamics problem and shows a potential in reducing the UQ computational cost. [ABSTRACT FROM AUTHOR]

Pyrometry is an established technique used in high strain rate experiments (such as plate impact experiments) whereby the temperature of a sample is determined from the measurement of collected thermal radiation. By applying Planck's Law, radiometry data can be used to determine temperature. A significant source of uncertainty in applying pyrometry to high strain rate experiments is due to possible changes in emissivity after a sample has been shocked; thus it is desirable to determine emissivity during the experiment. Kirchhoff's Law, which states emissivity is the complement of reflectivity, can be a pplied to determine emissivity in high strain rate experiments. Ideally the sample's reflectivity would be measured at the same wavelength and on the same experiment as the pyrometry measurement. A diagnostic has been developed which produces a modulated reflectivity signal that is insensitive to tilt and surface finish. Following characterisation of the system in the laboratory, dynamic tests were conducted. During the dynamic tests, the reflectivity signal was multiplexed onto the radiance signal allowing simultaneous measurement of radiance and reflectivity. A description of the diagnostic, results from laboratory t esting and r esults and analysis from dynamic experiments are presented. [ABSTRACT FROM AUTHOR]

The STANAG 4496 Ed. 1 Fragment Impact, Munitions Test Procedure is normally conducted by gun launching a projectile for attack against a munition. The purpose of this test is to assess the reaction of a munition impacted by a fragment. The test specifies a standardized projectile (fragment) with a standard test velocity of 2530±90 m/s. The standard test velocity can be challenging to achieve and has several loosely defined and undefined characteristics that can affect the test item response. MSIAC performed and international review of the STANAG 4496 related to the fragment impact test. To perform the review, MSIAC created a questionnaire in conjunction with the custodian of this STANAG and sent it to test centers. Fragment velocity variation, projectile tilt upon impact, aim point variation and projectile material were identified as observed gun testing issues. These, as well as other gun testing issues, have significant implications to resulting IM response. [ABSTRACT FROM AUTHOR]

A large number of experiments have been conducted using the Cavendish single stage gas gun to investigate the dynamic properties of sand. The results included successful measurements of release in dry materials, demonstrating that this is markedly different to the loading path. The effect of moisture was examined and shown to be strongest where the material was close to saturation, at which point the microstructure of the exact sample configuration plays a significant role in the response. Finally, the effect of sample morphology was probed, and whilst it was found to be significant at low rates, in the shock regime impedance appears to be more strongly influenced by the presence of moisture or a fraction of small particle size debris. [ABSTRACT FROM AUTHOR]

Laser-driven shock loading is a versatile, low destructive method to study material dynamic behaviors with an effcient repetitive rate. In these experiments, compared with the more conventional high-explosive or impact-based techniques, all the scales are reduced (few ns shock duration, a few mm planar loaded area) while the shock pressure may reach several tens of GPa. This configuration makes possible the use of many diagnostics with limited exposition to generated fragments. We present recent experiments of material ejection under laser-driven shock loading. The target is a thin plate of Tin with periodical grooves of few tens of µm in its rear surface, in order to induce solid or liquid micro-jetting. These jets turn into a cloud of µm-sized particles. Depending on surface roughness, the velocity and the density of the cloud vary. The density of the cloud is estimated thanks to a new high-resolution X-ray imaging with a laser-driven source; while optical shadowgraphy observes the displacement of the fastest particles. Thus, µm-structures in the particles cloud and in the target can be revealed. [ABSTRACT FROM AUTHOR]

Necking of thin bodies (bars, plates) loaded in tension is one form of strain localization in ductile materials that may lead to failure. The phenomenon of necking has been studied extensively, initially for quasistatic loading and then for dynamic loading. Nevertheless, many issues concerning necking are still unclear. Among these are: 1) is necking a random or deterministic process; 2) how does the specimen choose the final neck location; 3) to what extent do perturbations (material or geometrical) influence the neck forming process; and 4) how do various parameters (material, geometrical, loading) influence the final neck location. Here we address these issues using computer simulations with a hydrocode. Among other things we find that: 1) neck formation is a semi deterministic process. Changing one of the parameters monotonously usually moves the final neck location monotonously as well, but there are exceptions; 2) final neck location is sensitive to the radial velocity of the end boundaries, and as this boundary condition is not fully controlled in tests, this may be the reason why neck formation is sometimes regarded as random; and 3) neck formation is insensitive to very small perturbations, but may be influenced by larger perturbations. [ABSTRACT FROM AUTHOR]

The response of particulate materials to impulsive loading includes complex interactions between grains due to fracture and comminution and the presence of interstitial material. The quasi-static strength of saturated powders is related to the concept of "effective stress" in which the fluid stiffens the material response and reduces the shear strength. However, detailed information regarding the effects of saturation under dynamic loading is lacking since static equilibrium between phases cannot be assumed and the interaction becomes more complex. Recent experiments on the IMPULSE (IMPact System for ULtrafast Synchrotron Experiments) capability at the Dynamic Compression Sector (DCS) of the Advanced Photon Source (APS) have captured in-situ X-ray phase-contrast images of shock loaded soda lime glass spheres in dry and saturated conditions. Previous investigations have observed reduction of fragmentation attributed to "cushioning" of an interstitial fluid in impact recovery experiments. The differences between the modes of deformation and compaction are compared with direct numerical simulations showing that the cause of fracture is different. In drained (dry) impact experiments at 300 m/s, the fractures initiate near the contact point between grains. In fully saturated experiments with identical impact conditions, spallation is observed during the incident stress-wave passage in the glass before the H2O has equilibrated. [ABSTRACT FROM AUTHOR]

Subjected to a dynamic traction, a ceramic material will eventually fail as a consequence of the triggering, propagation and coalescence of a distribution of microcracks. The DFH (Denoual-Forquin-Hild) anisotropic damage model considered in this study is based on a description of three physical phenomena activated all along the fragmentation process occurring in brittle materials. The first one concerns the activation of the population of preexisting defects distributed in the material, described by a Weibull law. The second one corresponds to the propagation of microcracks at a constant velocity. The last one is the so-called occultation phenomenon. It is based on the observation that in the vicinity of a crack, tensile stresses are relaxed, hence precluding the triggering of another crack in the same direction. The performance of DFH model has been assessed with the aim of improving the modeling of damage associated to spalling in ceramic materials. Dynamic tensile loadings have been performed at different strain rates, by means of a plate impact and a quasi-isentropic compression followed by a release wave. The characteristics of different patterns of damage observed experimentally have been accurately reproduced by means of three-dimensional Lagrangian calculations. [ABSTRACT FROM AUTHOR]

The tensile response of ductile, polycrystalline metals is often accompanied by the formation of pores within the material, which coalesce and fail a plane within a metal. This large deformation process is broadly progressive, with a physical path consisting of nucleation, growth, coalescence, and failure, which occur individually over short periods of time. Thus distinct micro-mechanisms operate, each influenced by microstructure, loading path, and loading profile, which remains a significant challenge to represent and predict numerically at the macroscale. In a previous study, the influence of loading path on damage evolution in high-purity tantalum has been presented; in this paper, complimentary measurements are made on a pure, FCC copper. Samples were shock loaded to three different peak stresses using both symmetric impact, and two different composite flyer plate configurations, such that upon unloading, the three samples were subject to nearly identical tensile loading. The damage evolution in the soft-recovered copper samples was then quantified using optical metallography and electron-back-scatter diffraction. We shall compare metallurgical observations, velocimetry histories and simulations to discuss the dynamic failure mechanics observed. [ABSTRACT FROM AUTHOR]

The effect of loading direction on the spall strength and damage in Lean Duplex Stainless Steel 2101 (LDSS 2101) has been investigated. Experiments were conducted in a single stage gas-gun to test the spall strength of LDSS 2101 along the Rolling Direction (RD), Transverse Direction (TD) and Normal Direction (ND). Microstructural examinations were conducted using optical microscopy and Electron Backscatter Diffraction (EBSD). LDSS 2101 showed similar spall strength in all considered directions. However, the amount of spall damage was dependent on the loading direction. Moreover, most of the spall damage was accommodated within the ferrite phase. [ABSTRACT FROM AUTHOR]

The dynamic response of polymeric materials has been widely studied with the effects of degree of crystallinity, strain rate, temperature and sample size being commonly reported. This study uses a simple PMMA structure, a right cylindrical sample, with structural features such as holes. The features are varied in a systematic fashion. Samples were dynamically loaded using a Split Hopkinson Pressure Bar up to failure at room temperature. The resulting stressstrain curves are presented showing the change in sample response. The strain to failure is shown to be relatively unaffected by the presence of holes, while failure stress is changes significantly. The fracture patterns seen in the failed samples, varies with loading; tensile cracks, cone cracks and radial fracture. Shear effects are the dominant initial form of failure for the different holes sizes and geometries. The samples were prepared by laser cutting and checked for residual stress before experiment. This presentation of empirical results will be used to develop new failure surfaces for PMMA and validate predictive model predictions where material, structure and damage are included. [ABSTRACT FROM AUTHOR]

Recent advancements in coupling dynamic loading platforms with third generation light sources are providing new means to study materials at extreme conditions. Diagnostics such as X-ray diffraction (XRD) and X-ray phase contrast imaging (PCI) are being employed in-line with dynamic loading platforms for studying dynamic phenomena such as phase transitions, microstructural evolution, etc. Here we study the well-known polymorphic phase transformation (α- ε phase) in polycrystalline iron through front-surface plate impact experiments using dynamic X-ray diffraction techniques at the Dynamic Compression Sector at the Advanced Photon Source (APS) The impact stress state of the iron samples were measured using optical velocimetry techniques The window correction for Lexan™ was also investigated since this material was used as the impact surface and optical window in the experimental configuration described here, and has been shown to be useful as a window material for other dynamic XRD measurements. X-ray diffraction data show that at impact stresses near the known transition stress for polycrystalline iron (13 GPa), we begin to see evidence of the transition to the higher pressure epsilon phase (hcp). Although additional experiments are needed to observe the complete transformation to the ε-phase, this work provides the first XRD data for iron obtained in plate impact experiments that provide insight into this well-known transition. [ABSTRACT FROM AUTHOR]

In order to study the uniaxial and quasi-biaxial mechanical properties of aging solid propellants under low temperature and high strain rate, stress-strain curves and tensile fracture surfaces of HTPB propellant were obtained in a wide range of temperature (-30,25 °C) and strain rates (0.4,4.0 and 14.29 s-1), respectively, by means of uniaxial and biaxial tensile tests and electron microscopy scanning on the fracture cross section. The results indicate that the quasi-biaxial tensile mechanical properties of aging HTPB propellant is same as the uniaxial tensile mechanical properties influenced distinctly by temperature and strain rate. With decreasing temperature and increasing strain rate, the mechanical properties gradually strengthen. The damage for HTPB propellant changes from "dehumidification" to grain fracture. The initial elastic modulus E and maximum tensile stress σ of the uniaxial and biaxial tensile increase gradually with decreasing temperature and increasing strain rate, and well present linear-log function relation with strain rate. The ratio of quasi-biaxial and uniaxial stretching under different loading conditions was obtained so that the researchers could predict the quasi-biaxial tensile mechanical properties of the propellant based on the uniaxial test data. [ABSTRACT FROM AUTHOR]

This work presents studies the effect of ultrafine-grained (UFG) structure on impact toughness and dynamic compression of pure copper M1 (99.9%). The UFG structure was provided by means of equal-channel angular pressing (ECAP) on the Conform scheme with four and eight passes. Impact toughness tests on samples with U-shaped notch were performed using a drop weight impact machine. Dynamic compression test of cylindrical samples were performed with a setup with the Split-Hopkinson pressure bar (SHPB-20) by the Kolsky method. The results showed that the impact toughness of the UFG copper states was not less than that of the coarse-grained (CG) counterpart. Moreover, the fracture process of the UFG material requires more energy. An increase of compression strain rate by 6 orders resulted in the well-known strain-rate dependence of the yield strength for the CG material and the UFG material after eight ECAP passes. The yield strength of the material after four ECAP passes remained at the level corresponding to a quasi-static loading. [ABSTRACT FROM AUTHOR]

Work is reported on model-based defect characterization in CFRP composites. The work utilizes computational models of ultrasound interaction with defects in composites, to determine 1) the measured signal dependence on material and defect properties (forward problem), and 2) an assessment of defect properties from analysis of measured ultrasound signals (inverse problem). Work is reported on model implementation for inspection of CFRP laminates containing multi-ply impact-induced delamination, in laminates displaying irregular surface geometry (roughness), as well as internal elastic heterogeneity (varying fiber density, porosity). Inversion of ultrasound data is demonstrated showing the quantitative extraction of delamination geometry and surface transmissivity. Additionally, data inversion is demonstrated for determination of surface roughness and internal heterogeneity, and the influence of these features on delamination characterization is examined. Estimation of porosity volume fraction is demonstrated when internal heterogeneity is attributed to porosity. [ABSTRACT FROM AUTHOR]

The paper deals with the verification of various numerical models in relation to the pilot-phase measurements of a rail bridge subjected to dynamic loading. Three types of FEM models were elaborated for this purpose. Static, modal and dynamic analyses were performed. The study consisted of measuring the acceleration values of the structural components of the object at the moment of the train passing. Based on this, FFT analysis was performed, the main natural frequencies of the bridge were determined, the structural damping ratio and the dynamic amplification factor (DAF) were calculated and compared with the standard values. Calculations were made using Autodesk Simulation Multiphysics (Algor). [ABSTRACT FROM AUTHOR]

The paper describes the results of poorly studied interrelated unstable oscillations of friction disks - lateral thermoelastic oscillations perpendicular to the disk plane and parametric oscillations in the plane of the disk. [ABSTRACT FROM AUTHOR]

Orthotropic cylindrical shell panels under dynamic loading (the load has a linear time dependency) are examined in this paper. Relationships of a mathematical model of their deformation are presented in view of the geometric nonlinearity, transverse shears and orthotropy of the material. The Kantorovich method is applied to form a system of ordinary differential equations. The derived system is solved by the Rosenbrock method. The stability of several types of orthotropic panels of modern materials (fiberglass, carbon fiber reinforced plastic, etc.) is studied and critical load values are obtained. [ABSTRACT FROM AUTHOR]

The theory of critical distances (TCD) is one of the most promising approaches to the prediction of material fracture, in which the stress concentration effect is taken into account. To date, the TCD has proven itself as a successful method for assessing the fatigue, static and dynamic strength of components with stress concentrators. However, for dynamic loading the theory was verified only on a small list of materials. This paper confirms that the application of the theory of critical distances to specimens made of structural steel 08X18H10T with different geometry features under dynamic deformation is a successful technique for estimating dynamic strength, and it allows a substantial reduction in the program of experiments in determining the ultimate loads. [ABSTRACT FROM AUTHOR]

Mechanisms of plastic shear localization in a material under dynamic loading are studied theoretically and experimentally. These mechanisms are associated with collective effects occurring in the ensemble of microdefects in spatially localized regions. In-situ infra red scanning of the instability zone and a subsequent analysis of the dislocation substructure lend support to the supposition that nonequilibrium transitions in defect ensembles play a decisive role in the development of localized plastic flow. The equations relating nonequilibrium transitions to the mechanisms of structural relaxation and plastic flow are used to simulate localizations of plastic deformation. [ABSTRACT FROM AUTHOR]

In this study, molecular dynamic simulations of high-velocity impact of a spherical 3C-SiC cluster, with a wide range of velocities (from 100 to 2600 m/s) and with a rigid wall, were performed. The analysis of the final structure shows that no structural phase transformation occurred in the material, despite the high pressure during the collision process. [ABSTRACT FROM AUTHOR]

The article considers the strength of a dynamically loaded pipeline at hydraulic blow. We propose, in diagnosing the pipeline quality, to determine the pipe material stress-strain state based on the wave problem solution on the distribution of radial pressure waves in the pipe, both taking into account the falling radial compressive stress waves and the interference of falling and reflected stress waves that form on the free surface. It is shown that the mechanical pressures from the loaded surface to the free surface significantly reduced. The calculations results of the necessary pipe wall thickness the are given at averaging the effective stresses for various transport environments. [ABSTRACT FROM AUTHOR]

The paper addresses the problem of plastic deformation of circular membranes and shallow axisymmetric membrane shells under high-intensity loading considering rotary inertia. The resolving equations systems are obtained, the numerical implementation program and algorithms are developed. The research methods used in the paper include finite difference method, differential-incremental method of the second and fourth orders of accuracy, the Fourier series solutions with Bessel functions. The results are obtained confirming reasonability of considering rotary inertia. [ABSTRACT FROM AUTHOR]

The paper presents investigation of the dynamic behavior of composite bridges with open web girders. The bridge span is made of reinforced concrete layers with a metal pan underneath. The dynamic tests of the bridge structure are carried out using the multichannel vibrodiagnostic test kit for measuring the eigenfrequency. The software application LIRA is used to develop the finite element model (FEM) of the bridge after its mathematical simulation. The FE model is subjected to loads identical to the experimental ones, and the dynamic behavior of the bridge is simulated to measure the multimode eigenfrequences. A careful comparison between the calculations and experimental results shows good agreement for the investigated parameters of the bridge structure. [ABSTRACT FROM AUTHOR]

Civil and industrial buildings and structures have lately become more frequently exposed to dynamic impacts caused by emergencies. Such loads are random in nature and are characterized by high intensity and short duration of action. In this regard, protection of structures from these impacts comprises an important scientific and practical problem. One of the ways of possible improvement of structural resistance to dynamic loads of great intensity is the use of yielding supports. This article presents the results of research of reinforced concrete slabs placed on yielding supports. Yielding supports are presented in the form of deformable elements of ring cross-section, which are characterized by three phases of deformation: elastic, elastoplastic, and elastoplastic with hardening. The present research considers behavior of the slab in elastic phase, while behavior of supports is analyzed in elastoplastic and elastoplastic with hardening phases. Conducted studies allowed evaluating the influence of rigidity of yielding supports in the plastic stage of deformation. Research results also allowed explaining the influence of the nature of distribution of rigidities along the perimeter of the slab and the level of deformations of yielding supports at the moment of transition to the stage of plastic deformations on behavior of concrete slabs. According to the results of performed calculations, physical and mechanical parameters of supports have been revealed enabling to get the maximum effect to reduce the stress-strain state parameters of structures. [ABSTRACT FROM AUTHOR]

Extreme events, both natural and man-made, have become more frequent. Explosions, falling or impact of bodies influence buildings and structures causing occurrence of high intensity inertia forces. Due to dynamic nature of the mentioned impacts they are to be considered in design calculations. The paper studies behavior of oblique sections of reinforced concrete (RC) beams under transverse dynamic loading; it describes the potential of using yielding supports, presented as inserted elements with ring cross-section. Experimental study included tests of 24 RC beams under shortterm dynamic impact of falling weight (265 kg). The behavior of RC beams was analyzed by measuring deformation of reinforcement and concrete, the value of supports reaction and impulse acting on a structure. The paper considers separate and joint effect of yielding supports and longitudinal compression on strength and deformability of RC beams. Longitudinal compressive force and yielding supports are proved to influence significantly the stress-strain state of oblique sections of RC beams under dynamic loading. Time of deformation is significantly prolonged in case of extended plastic component in yielding supports. [ABSTRACT FROM AUTHOR]

Polymethylmethacrylate (PMMA) is used widely in shock experiments as a window material and in explosive characterization tests, e.g. gap tests, as a shock mitigation material. In order to simulate the complex loading present in a gap test, the constitutive response of the PMMA must be well understood. However, it is not clear what characterization must be done when the PMMA material is changed, e.g. changing supplier, and the Rohm and Haas Type II UVA PMMA, which was used for many of the calibration experiments, is no longer available. In this paper, we will present characterization results on legacy Rohm and Haas Type II UVA in comparison with a new PMMA grade proposed for use in gap tests. Planar shock experiments are performed to determine the compression and release response. [ABSTRACT FROM AUTHOR]

Use of polymers in defense, aerospace and industrial applications under extreme loading conditions makes prediction of the behavior of these materials very important. Crucial to this is knowledge of the physical damage response in association with phase transformations during loading and the ability to predict this via multi-phase simulation accounting for thermodynamical non-equilibrium and strain rate sensitivity. The current work analyzes Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) experiments on polytetrafluoroethylene (PTFE). In particular, the phase transition during loading and subsequent tension are analyzed using a two-phase rate sensitive material model implemented in the CTH hydrocode. The calculations are compared with experimental high-speed photography. Deformation patterns and their link with changing loading modes are analyzed numerically and correlated to the test observations. It is concluded that the phase transformation is not as critical to the response of PTFE under Dyn-Ten-Ext loading as it is during the Taylor rod impact testing. [ABSTRACT FROM AUTHOR]

Shock-reshock and shock-release experiments were performed on silicon nitride ceramics above and below its phase transition pressure. Experimental results clearly show the occurrence of elastic-plastic transition and phase transition during initial shock loading. The HEL and phase transition stress are determined as 11.6 and 34.5 GPa, respectively. Below the phase transition stress, the reshock profile consists of the single shock with short rise time, while the release profile shows the gradual release followed by rapid one. Above phase transition stress, reshock and release behavior varies with the initial shock stress. In the case of reshock and release from about 40 GPa, the reshock structure is considerably dispersed, while the release structure shows rapid release. In the reshock profile from about 50 GPa, the formation of the shock wave with the small ramped precursor is observed. And, the release response from same shocked condition shows initial gradual release and subsequent quite rapid one. These results would provide the information about how phase transformation kinetics effects on the reshock and release behavior. [ABSTRACT FROM AUTHOR]

Shock compression experiments were performed on amorphous Ce3Al melt-spun ribbons using the 50 J laser shock loading system at the Omega laser facility. A multi-layered sample of 2mm total thickness with 1 mm x 1.5 mm width and 40 μm thick ribbons sandwiched with 6 μm epoxy was used as the target in order to study the effects of varying pressures (due to attenuation) on the transformation behavior. The shock-induced changes were characterized post-mortem via synchrotron XRD analysis. Comparisons of the initial amorphous, thermally devitrified (at 500°C), and shock compressed samples indicate devitrification under high pressure shock compression into the thermodynamically stable hexagonal α-Ce3Al intermetallic phase, similar to the thermally devitrified samples. [ABSTRACT FROM AUTHOR]

Understanding the impact response of aluminium foams is essential for assessing their energy absorption capacity under dynamic loading. In this paper, the dynamic compaction behavior of closed-cell aluminium foam (CYMAT™) has been tested using the plate-impact technique. Post-impacted samples have been examined using optical microscopy to observe the microstructural changes with the objective of elucidating the pore-collapse mechanism. [ABSTRACT FROM AUTHOR]

Prediction of survivability of encapsulated electronic components subject to impact relies on accurate modeling, which in turn needs both static and dynamic characterization of individual electronic components and encapsulation material to generate reliable material parameters for a robust material model. Current focus is on potting materials to mitigate high rate loading on impact. In this effort, difficulty arises in capturing one of the critical features characteristic of the loading environment in a high velocity impact: multiple loading events coupled with multi-axial stress states. Hence, potting materials need to be characterized well to understand its damping capacity at different frequencies and strain rates. An encapsulation scheme to protect electronic boards consists of multiple layers of filled as well as unfilled polymeric materials like Sylgard 184 and Trigger bond Epoxy # 20-3001. A combination of experiments conducted for characterization of materials used Split Hopkinson Pressure Bar (SHPB), and dynamic material analyzer (DMA). For material which behaves in an ideal manner, a master curve can be fitted to Williams-Landel-Ferry (WLF) model. To verify the applicability of WLF model, a new temperature-time shift (TTS) macro was written to compare idealized temperature shift factor with experimental incremental shift factor. Deviations can be readily observed by comparison of experimental data with the model fit to determine if model parameters reflect the actual material behavior. Similarly, another macro written for obtaining Ogden model parameter from Hopkinson Bar tests can readily indicate deviations from experimental high strain rate data. Experimental results for different materials used for mitigating impact, and ways to combine data from DMA and Hopkinson bar together with modeling refinements are presented. [ABSTRACT FROM AUTHOR]