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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]

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]

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]

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]

Mechanical behavior of stochastic metal-ceramic composites with the aluminum matrix under high-rate deformation at shock-wave loading is numerically simulated with consideration for structural evolution. Effective values of mechanical parameters of metal-ceramic composites Al-B4C, Al-SiC, and Al-Al2O3 are evaluated depending on different concentration of ceramic inclusions. [ABSTRACT FROM AUTHOR]

Hydroforming has a rapid development recently which has good forming quality and less cost. However, it still cannot meet the requirements of forming complex parts with small features just like convex tables, or bars which are widely employed in automotive and aircraft industries. The impact hydroforming technology means the most features are formed by hydroforming and the small features are rapidly reshaped by high intensity impact energy in a very short time after the traditional hydroforming. The impact pressure rises to the peak in 10ms which belongs to dynamic loading. In this paper, impact hydroforming process is proposed. The generation and transmission of impact hydroforming energy and impact shock wave were studied and simulated. The deformation process of the metal disks under the dynamic impact loading condition presented impact hydroforming is an effective technology to form complex parts with small features. [ABSTRACT FROM AUTHOR]

A new recovery method for investigating material response to shockless (ramped) loading paths is described. The work makes use of a laser generated plasma piston that produces ramped loading at high strain rates (>≈107/s). Large sample sizes are utilized to prevent reflected wave interactions. The overall deformation path is characterized by two transients: one at very high strain rate on the 5–10 nanosecond time scale and one at a lower strain rate occurring over a 1–2 microsecond timescale. It was found that a sufficiently large region of material experiences shockless loading conditions enabling recovery based characterization. The presence of two strain transients makes the method more applicable to comparative assessments between shockless and shock loading conditions. [ABSTRACT FROM AUTHOR]

The new data are presented on relaxation of an elastic precursor in unalloyed depleted uranium and two its alloys. Results were obtained under low-intense explosive loading. Statistic thermofluctuational model was used for approximation of experimental data. The inversion of strength properties of the tested U-Mo and U-Fe-Ge alloys at their quasi-static and high-rate loading was revealed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

G. I. Taylor showed that dynamic material properties could be deduced from the impact of a projectile against a rigid boundary. The Taylor anvil test became very useful with the advent of numerical simulations and has been used to infer and/or to validate material constitutive constants. A new experimental facility has been developed to conduct Taylor anvil impacts to support validation of constitutive constants used in numerical simulations. A 37-mm diameter Hopkinson bar apparatus was adapted to conduct the Taylor anvil experiments. An adaptor was designed to ensure impact planarity of the projectile onto the anvil, which is made from VascoMax steel, backed by a 1.82-m steel bar to provide inertial mass to the anvil and ensure deceleration of the projectile solely from elastic waves within the projectile. A digital imaging system was adapted to determine radial deformation as a function of length. Details of the experimental techniques, along with examples of experiments using 6061-T6, are discussed. Numerical simulations are used to complement the experimental results. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

In the current study we are developing an experimental fracture material property test method specific to dynamic fragmentation. This test method allows the study of fracture fragmentation in a reproducible laboratory environment under well-controlled loading conditions. Motion and fragmentation of the specimen are diagnosed using framing camera, VISAR and soft recovery methods. Fragmentation properties of several steels, nitinol, tungsten alloy, copper, aluminum, and titanium have been obtained to date. The values for fragmentation toughness, and failure threshold will be reported, as well as effects in these values as the material strain-rate is varied through changes in wall thickness and impact conditions. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

One of the current challenges facing researchers in the field of dynamic properties of materials is the need for a predictive modeling capability for damage and fragmentation. A series of small-scale, explosively-driven experiments were designed and executed in order to gain a better understanding of the nucleation and growth of damage under explosive loading. The interaction of varying obliquity detonation waves with the test articles was of particular interest. The material in these tests experiences a combination of hydrostatic and deviatoric stresses that is spatially and temporally varying. Variations in shot geometries and explosive load causes direct variations in the nature of the resulting damage fields in the recovered samples. The characterization of a number of samples from a test series of tantalum discs will be presented and compared to numerical analyses of the experiments. Insights gained from the post-mortem examination of the discs and the accompanying simulations will be presented. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Accurate material constitutive modeling is critical for the quality and reliability of the simulation of dynamic impact processes. Under dynamic loading ductile structural components can experience very large deformation that, in terms of equivalent plastic strain, can be well beyond the strain at which necking would occur in uniaxial tensile tests. Unfortunately, the material flow curve for ductile metals can only be measured over a limited strain range while at large strain it is either extrapolated or corrected in some way. In this paper the role of the approximation of the material flow law in the post-necking range is investigated with particular reference to the Taylor test. Result seems to indicate that the flow law governs the shape of the mushroom region while temperature and strain rate have a more important role in the resulting deformed shape of the intermediate and rear portion of the specimen geometry. In particular, the temperature effect exponent in the J&C expression can be calibrated based on the final length of the impacted cylinder. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The response of shocked materials in the pressure range 100 GPa reveals self-similar features that could be linked with collective properties of typical mesodefects (dislocation substructures, microcracks, microshears). The statistical approach was developed that allowed us to specify the Ginzburg-Landau theory for tensor order parameter of the mesodefect density and to establish the existence of self-similar solutions as specific collective modes in mesodefect ensemble related to the plastic strain and damage localization. The subjection of relaxation properties of dynamically loaded materials to mentioned collective modes provides the self-similar behavior of materials that experimentally were observed as the universality (fourth power law) of steady-state plastic front and delayed failure (failure wave) phenomenon as the resonance excitation of blow-up damage localization areas. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

High-strength constructional 38KhN3MFA steel and 02H18К9M5-BИ maraging steel were tested to determine the yield stress under dynamic loading. The 38KhN3MFA steel was used as central test material to work out the experimental technique. For both kinds of steel the results obtained in the plane shock tests under uniaxial strain condition show approximately the identical yield stress values as those obtained in Taylor tests. Cracking of maraging steel occurs along the shock-induced austenite bands where microhardness is much smaller than that for the rest of the matrix. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Uniaxial loading experiments have been conducted on PBS9501. This material is highly packed, of the order of 94 % by weight, with sugar having a 3:1 granulated to powdered sugar ratio. With the aim of developing a valid optical-based fracture test for PBX materials, strain rate and sample size have been investigated in the material. The results show that PBS9501 has a strain rate sensitivity similar to that observed in polymers, while the response to compression suggests a failure criterion that is similar to that seen in granular materials. Samples placed in compression are observed to fail by the localisation of shear deformation along slip planes. The fracture test under development will employ digital image cross correlation to track displacements as the test sample is loaded. From knowledge of the displacement fields, the stress and strain fields can be extracted allowing such fracture parameters as Rice’s J-integral to be evaluated. Such data are extremely useful for the development and validation of computational models. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]