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Fracture behavior of VT22 near β titanium alloy produced by radial shear rolling and subsequent aging was studied in very high cycle fatigue tests with ultrasonic vibration frequency. This type of processing was shown to significantly increase the static and fatigue strengths of the alloy. According to fractographic analysis, the transition from very high cycle to high cycle fatigue failure occurs in the stress amplitude range of 850–900 MPa, which is almost two times higher than the fatigue limit of the conventionally produced VT22 titanium alloy. It was found that fatigue crack initiation in the very high cycle fatigue region is associated with the formation of a fracture facet inclined at an angle of less than 90° to the specimen axis. The facet exhibits a higher local concentration of interstitial impurities (carbon and oxygen) compared to the chemical composition of the surrounding material, which is due to diffusion mass transfer from the adjacent regions to the zone of highest compressive-tensile stresses.

The influence of consecutive shock-wave and gigacycle fatigue loads on the lifetime of titanium alloy VT6 (Ti-6A1-4V) was investigated. An experimental methodology for estimating the ultra-high cycle lifetime was developed with reference to accidental high-speed collision of solid particles with fan blades and subsequent fatigue failure under the flight cycle conditions normal for operating aircraft engines. The program of ultra-high cycle loading (the number of cycles is 107-109) of specially made specimens was implemented experimentally. In these experiments, massive flat targets made of titanium alloy VT6 after shock-wave loading were impacted by a flat striker (explosive generator method), which initiated controlled damage in the material. Ultra-high cycle loading tests were carried out on the Shimadzu USF-2000 ultrasonic testing machine, which made it possible to conduct fatigue loading tests up to 108-1010 cycles and frequency of 20 kHz. The "in situ" method of determining the accumulation of irreversible fatigue damage was applied. It is based on the analysis of nonlinear features of the feedback signal in a closed system of an ultrasonic fatigue installation, which allowed us to relate the microscopic mechanisms of fatigue with model representations, as well as to consider the stages of damage evolution based on the nonlinear kinetics of defect accumulation during cyclic loading in high - and gigacycle fatigue modes. In the mode of ultra-high cycle (gigacycle) fatigue, the material exhibits abnormalities of elastic properties, which lead to the effect of non-linearity in the oscillation amplitude.

Experiments on the dynamic loading of specimens from AMg6 alloy were conducted on a split Hopkinson–Kolsky bar and with target perforation. The thermodynamics of the deformation process was studied in situ by recording temperature fields using a CEDIP Silver 450M high-speed infrared camera in order to reveal the characteristic stages of strain localization. The temperature measurements in the localization zones do not confirm the traditional concept of the strain localization mechanism caused by thermoplastic instability. Dynamic tests of specimens made of Steel 3, AMg6, and D16 alloys of a special shape designed to study the localization of plastic deformation on a split Hopkinson–Kolsky bar were conducted using the StrainMaster noninvasive strain measurement system. The displacements and strain fields in these specimens are constructed. A comparison of the experimentally measured temperature and strain fields with the results of numerical simulation with allowance for the mesodefect accumulation kinetics in the material gives a satisfactory agreement within ~20%. In the specimens after the experiments, the surface relief was analyzed using a NewView-5010 optical surface profiler with subsequent processing of the 3D strain relief data and calculation of the scale invariant (Hurst index) and the spatial scale of the region on which the correlated behavior of mesodefects is observed. The data of the experiments and analysis of the surface relief of deformed specimens, as well as the data of numerical simulation taking the mesodefects accumulation kinetics in the material into account, suggest that one of the plastic strain localization mechanisms under high-speed loading is caused by jump-wise processes in the defect structure of materials.

The influence of dynamic preload on the fatigue endurance limit of AMg6 alloy has been experimentally studied in a range of 109 loading cycles. It is established that prestraining up to 10% deformation at 103 s–1 rate leads to a 22% decrease in the fatigue endurance limit. A mathematical model is proposed that can adequately predict fatigue fracture, including that after preload.

In the paper, we study the kinetics of fatigue crack growth in MMg6 and D16T aluminum alloys in the gigacycle fatigue mode under dynamic preloading. The relevance of the problem statement is determined by the critical applications—life estimation of materials and structural elements of aircraft gas turbine engines experiencing random dynamic effects under flight cycle conditions. Specimens were preloaded by dynamic tension using the split Hopkinson (Kolsky) pressure bar at strain rates up to ~103 s−1, with consecutive gigacycle loading on the Shimadzu USF-2000 ultrasonic testing machine. Quantitative fractography of fracture surfaces was performed using profilometry and scanning electron microscopy data. We propose an original form of the kinetic equation, which relates the fatigue crack growth rate to a change in the stress intensity factor. The scale invariance of defect structures responsible for the formation of the fracture surface relief under gigacycle fatigue loading is found to be related to the power exponent of the Paris law. The fracture surface morphology of an aluminum-magnesium alloy under consecutive dynamic and gigacycle loading is studied by the multifractal detrended fluctuation analysis method. It is found that a transition from the stage of formation of a fish-eye zone of localized deformation is caused by the generation of fracture sites and accompanied by a qualitative change of the nonlinear dynamics of the system—a transition from monofractal to multifractal dynamics characterized by broadening of a multifractal spectrum at the final crack growth stage, which leads to macrofracture.

An experimental methodology was developed for estimating a very high cycle fatigue (VHCF) life of the aluminum alloy AMG-6 subjected to preliminary deformation. The analysis of fatigue damage staging is based on the measurement of elastic modulus decrement according to “in situ” data of nonlinear dynamics of free-end specimen vibrations at the VHCF test. The correlation of fatigue damage staging and fracture surface morphology was studied to establish the scaling properties and kinetic equations for damage localization, “fish-eye” nucleation, and transition to the Paris crack kinetics. These equations, based on empirical parameters related to the structure of the material, allows us to estimate the number of cycles for the nucleation and advance of fatigue crack.

The purpose of this work is to provide theoretical framework and experimental supporting evidence for a crucial role of structural transitions in the ensemble of defects at the meso-level (microshears and microcracks), as one of the mechanisms of plastic strain localization in metals under high-rate loading. The investigation of the sample response to dynamic loading was carried out on the split Hopkinson pressure bar and in a series of target penetration tests. To identify the characteristic stages of strain localization, the thermodynamics of the deformation process was investigated "in-situ" by recording the temperature fields using a high-speed infrared camera CEDIP Silver 450M. The temperature measured in the localization zone does not confirm the generally accepted concept of the strain localization mechanism as the mechanism governed by a thermoplastic instability. The samples stored after the experiment were subjected to microstructural analysis, using an optical interferometer-profilometer and a scanning electron microscope. The structural analysis revealed a correlated behavior of the ensemble of defects, which can be classified as a structural transition providing strain localization. The data of experimental studies, the examination of the structure of deformed samples, as well as the data of numerical modeling taking into account the kinetics of accumulation of microdefects in the material suggest that one of the mechanisms of plastic strain localization at high loading rates is associated with the jump-like processes in the defect structure of a material.

The Foreign Object Damage problem is considered as the damage tolerance statement for consecutive loading tests, which include the shock-wave loading (by explosive generator) of massive planar targets (aluminum alloy AlMg6) to provide a billet for the specimen machining with controlled damage that is the analogous material of the fan blades subjected to high-speed collision with solid particles. These samples were used to perform high cycle fatigue and very high cycle fatigue tests with the ultrasonic testing machine, which allows fatigue loading for 108–1010 cycles with an amplitude of up to several tens of micrometers and a frequency of 20 kHz. It is shown that the fatigue strength of AlMg6 alloy specimens pre-loaded by shock in the 109 cycle regime reduces by 24%. The fatigue damage-failure transition and crack initiation were studied by the amplitude–frequency analysis of higher harmonics associated with the influence of defects on the effective elastic properties. The structural study of the fracture surface for the specimens after consecutive loading was conducted using the profilometry data to identify the roughness scale invariants induced by defects for corresponding areas responsible for the staging of fatigue damage-failure transition. The scale invariants and corresponding lengths were used for the formulation of the generalized Paris law for the crack advance in the damaged material.

Mechanisms of plastic strain localization under the dynamic loading of specially shaped specimens made of the AMg6 aluminum alloy and intended for tests under conditions close to a pure shear on a split Hopkinson–Kolsky pressure bar are studied theoretically and experimentally. The mechanisms of plastic flow instability are related to collective effects in the ensemble of microdefects in spatially localized regions visualized in situ using a CEDIP Silver 450M high-speed infrared camera. The calculation corresponding to the experimental loading scheme is implemented using wide range constitutive equations reflecting the dependence of structural relaxation mechanisms—manifestation of the collective behavior of microdefects—on the evolution of the localized flow shear instability. Microstructure analysis of deformed specimens included the study of the spatial relief (porosity) scaling by the data of a NewView-5010 microscope-interferometer in regions of plastic strain localization. An increase in the structural scaling exponent (Hurst exponent) reflected the degree of the multiscale correlated behavior of defects and the porosity induced by them in regions of localized plasticity. Infrared scanning of the strain localization region and numerical simulation followed by an estimate of the defect structure corroborated the hypothesis that effects of thermal softening do not play a decisive role in the process of plastic shear localization in the tested material under the considered loading regimes. A new, one of the possible ones, mechanism of plastic strain localization under dynamic loading is justified. It is caused by the multiscale collective behavior of mesodefects—structure-scaling transitions—and establishes the stadiality of the localized shear evolution.

The paper presents the results of fatigue-testing ultrafine-grained and coarse-grained Ti-45 wt.% Nb alloy samples under very high cycle fatigue (gigacycle regime), with the stress ratio R = −1. The ultrafine-grained (UFG) structure in the investigated alloy was formed by the two-stage SPD method, which included multidirectional forging (abc–forging) and multipass rolling in grooved rollers, with further recrystallization annealing. The UFG structure of the Ti-45 wt.% Nb alloy samples increased the fatigue limit under the high-cycle fatigue conditions up to 1.5 times compared with that of the coarse-grained (CG) samples. The infrared thermography method was applied to investigate the evolution of temperature fields in the samples under cyclic loading. Based on numerical morphology analysis, the scale invariance (the Hurst exponent) and qualitative differences for UFG and CG structures were determined. The latter resulted from the initiation and propagation of fatigue cracks in both ultra-fine grained and coarse-grained alloy samples under very high-cycle fatigue loading.

An experimental and theoretical study of fracture mechanisms of the AMg6 alloy at different structural levels was carried out under consecutive dynamic and fatigue tests associated with conventional catastrophic events of aircraft engine components (fan blades) due to the foreign object damage and the life-time decrease in the presence of a corrosive environment. The AMg6 alloy samples were preloaded dynamically using the split Hopkinson-Kolsky bar at the strain rates ∼103 s−1 and then subjected to the VHCF test up to 108–109 cycles at the Shimadzu USF-2000 resonance testing machine (the load frequency is 20 kHz) with the cooling by abundant compressed-air and salt fog (3% NaCl). The scaling analysis of fracture surface roughness was conducted to characterize quantitatively specific areas associated with the stages of damage-failure transition in the presence of the corrosion.

The phenomenon of plastic strain localization in alloys under dynamic loading was experimentally studied on a Hopkinson–Kolsky bar and during target penetration tests. The temperature fields generated during deformation were studied in situ using a CEDIP Silver 450M high-speed infrared camera with the aim to identify the characteristic stages of localized shear. The temperature field distribution obtained at different time allowed us to trace the evolution of plastic strain localization. Microstructural analysis of the post-test samples was carried out using an optical interferometer-profilometer and electron microscopes. The structural analysis provided evidence for the correlated behavior of the ensemble of defects, which can be classified as a structural transition responsible for the strain localization. The results of experimental studies, the study of the deformed sample structure, as well as the data of numerical simulation made with consideration for the evolution of microdefects in the material, suggest that one of the mechanisms of plastic strain localization in alloys under high-speed loading is caused by jump-wise processes in the defective structure of materials.

Paper presents the “in situ” method for determining of irreversible fatigue damage accumulation, based on the analysis of nonlinear manifestations of the feedback signal in a closed system of an ultrasonic fatigue system. During very high cycle (gigacycle) fatigue, the anomalies of the elastic properties of the material are appear, which leads to a nonlinearity effect in the amplitude of oscillations. This effect increases with the initiation and growth of fatigue cracks. The technology was applied to samples of AMG-6 alloy with preliminary dynamic deformation at various levels of average stress to determine the moment of initiation and growth of the fatigue crack in very high cycle fatigue regime. This method is applicable for the early detection of fatigue cracks both on the surface and inside the material under cyclic loading in the ultrasonic mode. On the basis of wide-range defining relations for a deformable solid body with mesoscopic defects, a mathematical model has been proposed that can adequately describe behavior of the material during fatigue failure. The results of mathematical modeling are in good agreement with the experimental data

An experimental and theoretical study of plastic shear localization mechanisms observed under dynamic deformation using the shear–compression scheme on a Hopkinson–Kolsky bar has been carried out using specimens of AMg6 alloy. The mechanisms of plastic shear instability are associated with collective effects in the microshear ensemble in spatially localized areas. The lateral surface of the specimens was photographed in the real-time mode using a CEDIP Silver 450M high-speed infrared camera. The temperature distribution obtained at different times allowed us to trace the evolution of the localization of the plastic strain. Based on the equations that describe the effect of nonequilibrium transitions on the mechanisms of structural relaxation and plastic flow, numerical simulation of plastic shear localization has been performed. A numerical experiment relevant to the specimen-loading scheme was carried out using a system of constitutive equations that reflect the part of the structural relaxation mechanisms caused by the collective behavior of microshears with the autowave modes of the evolution of the localized plastic flow. Upon completion of the experiment, the specimens were subjected to microstructure analysis using a New View-5010 optical microscope–interferometer. After the dynamic deformation, the constancy of the Hurst exponent, which reflects the relationship between the behavior of defects and roughness induced by the defects on the surfaces of the specimens is observed in a wider range of spatial scales. These investigations revealed the distinctive features in the localization of the deformation followed by destruction to the script of the adiabatic shear. These features may be caused by the collective multiscale behavior of defects, which leads to a sharp decrease in the stress-relaxation time and, consequently, a localized plastic flow and generation of fracture nuclei in the form of adiabatic shear. Infrared scanning of the localization zone of the plastic strain in situ and the subsequent study of the defect structure corroborated the hypothesis about the decisive role of non-equilibrium transitions in defect ensembles during the evolution of a localized plastic flow.

In the paper, we study the influence of consecutive dynamic and gigacycle fatigue loads on the lifetime of VT6 titanium alloy. The relevance of the problem statement is determined by the critical applications – life estimation of materials and structural elements of aircraft gas turbine engines experiencing random dynamic effects under flight cycle conditions. The samples were preloaded dynamically by the split-Hopkinson bar device. Fatigue tests of preloaded samples were conducted on Shimadzu USF-2000 ultrasonic fatigue testing machine

Experimental studies on the response of samples to dynamic loading were performed using a split Hopkinson-Kolsky bar and in a series of perforation tests. In-situ investigations of the thermodynamics of deformation processes made it possible to identify the characteristic deformation localization stages. Temperature fields were recorded with a high-speed infrared camera CEDIP Silver 450M, and strain localization in the samples was evaluated with a strain noninvasive measurement system StrainMaster. Temperature measurements made in the localization zone did not support a generally accepted concept that the strain localization mechanism is the mechanism governed by thermoplastic instability. The microstructural analysis of the samples stored after the experiment was carried out using an optical interferometer-profilometer and a scanning electron microscope. The analysis revealed the correlated behavior of the ensemble of defects, which can be classified as a structural transition providing strain localization. The data of experimental studies, the examination of the structure of deformed samples, as well as the data of numerical modeling performed with consideration of the kinetics of accumulation of microdefects in the material suggest that one of the mechanisms of plastic strain localization at high loading rates is associated with the jump-like processes in the defect structure of the material.

In this work we investigated the influence of consecutive dynamic and gigacycle fatigue loads on the lifetime of aluminum-magnesium alloy AlMg6. Preloading of samples was achieved during dynamic tensile tests in the split-Hopkinson bar device. Fatigue tests were conducted on Shimadzu USF-2000 ultrasonic fatigue testing machine. This machine provides 10 9 -10 10 loading cycles with the amplitude from 1 to several dozens of microns and frequency of 20 kHz, which reduces dramatically the testing time in the comparison to the classical fatigue testing machines. The New-View 5010 interferometer–profiler of high structural resolution (resolution of 0.1 nm) was used for quantitative fracture surface analysis, which provided the data allowing us to find correlation between mechanical properties and scale-invariant characteristics [1] of damage induced roughness formed under dynamic and gigacycle fatigue loading conditions. Original form of the kinetic equation was proposed, which links the rate of the fatigue crack growth and the stress intensity factor using the scale invariant parameters of fracture surface roughness. The scale invariance characterizes the correlated behavior of multiscale damage provides the link of crack growth kinetics and the power exponent of the modified Paris law. The comparative analysis of the scaling characteristics of samples loaded under conditions of high - and gigacycle fatigue shows a significant decrease in the range of spatial scales, where the Hurst exponent remains constant for dynamically loaded samples in the «fish-eye» (0.5-10.9 mkm) zone. This result confirms our assumption that mentioned characteristic scales L pz and l sc [2-3] play an important role in the list of variables for the kinetic equation fatigue of crack growth and can be used for the identification of phenomenological parameters (power index) providing self-similar law for the crack path. References 1. Bouchaud E. Scaling properties of cracks // J. Phys. Condens. Matter. – 1997. – 9. –P. 4319– 4344. 2. Vladimir Oborin, Mikhail Bannikov, Oleg Naimark, Mikhail Sokovikov, Dmitry Bilalov Multiscale study of fracture in aluminum-magnesium alloy under fatigue and dynamic loading // Frattura ed Integrita Strutturale. – 2015. – Vol.34 – P.479-483 3. V. Oborin, M. Bannikov, O. Naimark and T. Palin-Luc. Scaling invariance of fatigue crack growth in gigacycle loading regime // Technical Physics Letters. – 2010. – Vol. 36. – No. 11. – P. 1061-1063.

The research is focused on simulation and experimental investigation of high-strain rate loading to study the mechanisms of plastic flow localization and failure mode transition in metals (AlMg6). The task of breaking down barriers by metal shell was examined. Model based on the statistical-thermodynamic description of deformation of solids with mesoscopic defects (microshears and micro-cracks) was used to simulate the behavior of metals under dynamic loading. Experimental studies were also carried out. The real-time lateral surface temperature was measured by high speed infrared camera CEDIP Silver 450M. The consistent result of “in-situ” experiment is the elevated temperature of strain localization area that doesn’t exceed 72°C. The results of numerical simulation are in a good agreement with the in-situ measured infrared experimental data. Experimental and theoretical (numerical) study of dynamic strain localization allowed us to establish the structure induced mechanism of plastic strain localization as possible mechanism of transition to the adiabatic shear failure. Evaluated temperature in the strain localization area (72°C) will not support conventionally used mechanisms of plastic strain localization as autocatalytic temperature control visco-plastic phenomena. Structural study of defect induced scaling properties revealed the correlated behavior of microshear ensemble that can be classified as structural transition providing the dynamic strain localization.

The behavior of specimens dynamically loaded during the split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in-situ using a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time allowed one to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infra-red camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profiler and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically.

The paper focuses on the experimental and theoretical study of instability of plastic strain and its localization in materials subjected to high-velocity perforation. The online study of the specimen surface was made using the high-speed infrared camera CEDIP Silver 450M. The distribution of the temperature field obtained at different instants of time allows getting insight into the evolution of the process of plastic strain localization. After testing, the structure of the specimen material was examined by scanning electron microscopy. In our investigation, the mechanisms of plastic shear instability and localization of plastic strain (in the three-dimensional statement) have been simulated numerically, and the peculiarities of the kinetics of microshear accumulation in the material have been analyzed.

We investigated the influence of consecutive shock-wave and gigacycle fatigue loads on the lifetime of aluminum-magnesium alloy AlMg6. An experimental methodology for estimating the ultra-high cycl...

The influence of consecutive dynamic and gigacycle fatigue loads on the lifetime of aluminum-magnesium alloy AlMg6 (5083) has been studied to analyze the fracture surface morphology (roughness scaling) and generalized fatigue crack kinetics, taking into account the correlated behavior of defects at the crack tip area (process zone). The samples were dynamically preloaded by a split-Hopkinson bar device. Fatigue tests of the preloaded samples were conducted on a Shimadzu USF-2000 ultrasonic fatigue testing machine. A New-View 5010 interferometer-profiler of high structural resolution (resolution of 0.1 nm) was used for quantitative fracture surface analysis. The analysis provided data for finding the correlation between mechanical properties and scale-invariant characteristics of damage-induced roughness formed under dynamic and gigacycle fatigue loads.

The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the size of grains is ~300nm. Rotational deformation modes give rise to the high angular disorientations of grains. The development of plastic shear instability regions has been simulated numerically. For this purpose, we use a recently developed theory, in which the influence of microshears on the deformation properties of materials has been studied by the methods of statistical physics and thermodynamics of irreversible processes. The results of theoretical and experimental studies suggest that one of the mechanisms of the plastic shear instability and localization of plastic strain at high-velocity perforation is related to structural and kinetic transitions in microshear ensembles.&nbsp

The objective of this work is to provide the link between the fatigue behaviour of pre-strained aluminium alloys and the scaling properties of damage induced on the fracture surface. Fatigue tests performed on pre-strained aluminium alloys revealed a large difference in their residual fatigue resistance linked to the material: the Al–Cu alloy demonstrated a sharp decrease of HCF life-time due to the pre-straining whereas the insensitivity of the Al–Mg alloy was clear. For the Al–Cu alloy, the investigations made at a ‘mechanical’ scale allow us to associate the strain energy absorbed during the prior loading with the aspect of the surface and the residual HCF life-time. The statistical characterization of the fatigue damaged zone was done from the measurement of the surface roughness. Scaling properties were established that allowed the conclusion of the universality of HCF damage kinetics as the mechanism controlling the sensitivity of Al–Cu alloy whatever the pre-straining history.

In this paper we investigate the influence of consecutive dynamic and gigacycle fatigue loads on the lifetime of the aluminum-magnesium alloy AlMg6. Preloading of specimens is achieved during dynamic tensile tests in the split Hopkinson bar device, and quasi-static loadings are carried out on a servo hydraulic tensile machine (Biss Bi-00-100 series). Fatigue tests are conducted on a Shimadzu USF-2000 ultrasonic fatigue testing machine. This machine provides 109–1010 loading cycles with the amplitude from 1 to several dozens of microns and frequency of 20 kHz; this reduces dramatically the testing time in comparison with the classical fatigue testing machines. A New-View 5010 interferometer–profiler of a high structural resolution (0.1 nm) is used for qualitative fracture surface analysis, which provides the data allowing us to find a correlation between mechanical properties and scale-invariant characteristics of damage-induced roughness formed under dynamic and gigacycle fatigue loading conditions.

We have studied, both experimentally and theoretically, the mechanisms of plastic shear localization during the dynamic deformation (adiabatic shear band formation) of metals. Instability mechanisms are frequently associated with collective effects in microdefect ensembles in spatially localized regions. Infrared in-situ scanning of instability regions and further investigation of a dislocation substructure confirm that non-equilibrium transitions play a key role in defect ensembles during the evolution of a localized plastic flow. The use of equations reflecting a relationship between non-equilibrium transitions and plastic flow has made it possible to perform simulations for plastic shear localization.

The research is focused on the simulation and experimental investigation of high-strain rate loading to study the mechanisms of plastic flow localization in metals (AlMg6) using a ballistic installation. Unique results of experiments are given in the paper. Numerical simulation using wide-range constitutive equations is done. The paper also shows the results of structural studies.

Fatigue (high- and gigacycle) crack initiation and its propagation in titanium alloys with coarse and fine grain structure are studied by fractography analysis of fracture surface. Fractured specimens were analyzed by interferometer microscope and electronic microscope to improve methods of monitoring of damage accumulation during fatigue test and verify the models for fatigue crack kinetics. Fatigue strength was estimated for high cycle fatigue (HCF) regime using the Luong method [1] by “in-situ” infrared scanning of the sample surface for the step-wise loading history for different grain size metals. Fine grain alloys demonstrated higher fatigue resistance for both HCF and gigacycle fatigue regimes. Fracture surface analysis for cylindrical samples was carried out using optical and electronic microscopy method. High resolution profilometry (interferometerprofiler New View 5010) data of fracture surface roughness allowed us to estimate scale invariance (the Hurst exponent) and to establish the existence of two characteristic areas of damage localization (different values of the Hurst exponent). Area 1 with diameter ~300 ?m has the pronounced roughness and is associated with damage localization hotspot. Area 2 shows less amplitude roughness, occupies the rest fracture surface and considered as the trace of the fatigue crack path corresponding to the Paris kinetics.

In this paper we investigated the influence of consecutive dynamic and gigacycle fatigue loads on the lifetime of aluminum-magnesium alloy AlMg6. Preloading of samples was achieved during dynamic tensile tests in the split-Hopkinson bar device. Fatigue tests were conducted on Shimadzu USF-2000 ultrasonic fatigue testing machine. The New-View 5010 interferometer-profiler of high structural resolution (resolution of 0.1 nm) was used for qualitative fracture surface analysis, which provided the data allowing us to find correlation between mechanical properties and scale-invariant characteristics of damage induced roughness formed under dynamic and gigacycle fatigue loading conditions. Original form of the kinetic equation was proposed, which links the rate of the fatigue crack growth and the stress intensity factor using the scale invariant parameters of fracture surface roughness. The scale invariance characterizes the correlated behavior of multiscale damage provides the link of crack growth kinetics and t...

The behavior of specimens dynamically loaded during split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in-situ using a high-speed infrared camera CEDIP Silver 450M. The temperature field distribution obtained at different time allowed one to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infrared camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profiler and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically.

The research is focused on simulation and experimental investigation of high-strain rate loading to study the mechanisms of plastic flow localization of metals (AlMg6) using the Kolsky bar compression test. Unique results of the experiments on the samples of the special form were given in the article. Numerical simulation using wide-range of constitutive equations was done. The paper also shows the results of structural studies.

The behavior of specimens dynamically loaded during the split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infra-red camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically.

The role of the collective behavior of defect ensembles at the crack tip and the laws of fatigue crack propagation in aluminum-magnesium alloy AMg6 (5056) have been studied under conditions of symmetric tension-compression gigacycle loading at 20 kHz using ultrasonic fatigue testing machine Shimadzu USF2000. 3D New View 5010 interferometer profiler high resolution data of defect induced roughness in the crack process zone under fatigue crack path revealed the existence of two characteristic scales: the scale of the process zone and the correlation length that is the scale when the correlated behavior of defect induced roughness has started.