High-speed Deformation Research Articles

Control of planar fabrics on the development of tensile damage zones under high-speed deformation: An experimental study with granite and gneiss

We have investigated the laboratory-scale, high-strain rate tensile failure processes responsible for Mode-I breccia dike formation in impact structures. Brazilian disc experiments with granite (isotropic) and gneiss (foliated) samples were performed on a Split Hopkinson Pressure Bar, equipped with high-speed photography. For the gneiss samples, the gneissic foliation was oriented (θ) at 0, 45 and 90° to the compression direction. Time-series images show the transient states of tensile rupture localization and propagation, leading to in situ fragmentation of the rocks. Granite samples produced a single incipient tensile rupture, accommodating pulverized clasts, whereas the gneisses underwent failure by way of major fracture and a network of secondary tensile fractures, forming large elongate clasts. For gneisses, θ greatly influenced the secondary crack growth, forcing propagation trajectories to orient preferentially either along or across the foliation. The two types of target rocks produced contrasting clast geometry in the fracture zones. The granite had mostly small clasts (<10 mm), with average aspect ratios around 1:2, whereas the gneisses produced larger clasts (<40 mm) with aspect ratios, 1:5, 1:4 and 1:4 for θ = 0, 45 and 90°, respectively. This study demonstrates that monomict breccia dikes could form in situ, rather than by a tensile dilation followed by infilling.

Влияние характеристик базальтового расплава на процесс образования волокон

In any production of products based on mineral fibers, one of the main types of equipment included in the line for the production of fiber products is installations for forming a basalt carpet, or the so-called fiberizing chambers. The quality of finished products depends on their perfection. Currently, there are several widely used in industry methods for producing mineral fibers from melt, which determine the various types and designs of fiberization chambers. In all chambers, the formation of mineral wool carpet occurs under the influence of hydrodynamic forces. Therefore, the study of such hydrodynamic characteristics as the rate of fall of individual fibers and clumps of these fibers and the hydrodynamic resistance of the carpet are of paramount importance in the design of new and reconstruction of old chambers. In this paper, we study the relationship between the strain rate and the viscosity coefficient of basaltic melt during fiber formation using a blow head developed by the authors. The substantiation of the process of fiber formation using a blowing head is given. Relations are obtained that establish the dependence of the strain rate in the fiber stream on the viscosity of the melt. Experimental data have been obtained that can be used to evaluate the effect of a basalt deposit on the dependence of the strain rate on the viscosity of a basalt melt. It was found that high-speed deformation of the melt greatly affects the quality of the fibers and the amount of waste in the production of fibers.

Structural Transformations in Copper during High-Speed Deformation upon the Convergence of a Massive Cylindrical Shell under Implosion

The deformation structure in copper that forms upon the convergence of a massive cylindrical shell into a cylinder is studied in this work. The shell in the deformation zone was subjected to high-speed deformation (~104 1/s) with large values of true strain (e varied from 0.8 to 2.0). It is shown that two types of structures were formed under deformation: regions containing disperse grains with high-angle boundaries and twins and regions with deformation cells having low-angle boundaries. It is found that the twins that arose at the early stages of deformation are distorted upon further deformation: their rectilinear boundaries are bent, the orientation relationships with the matrix are violated, and high-angle boundaries of arbitrary orientation are formed.

Research on the electromagnetic blanking based on force-free region deformation: simulation and experiments

Electromagnetic blanking (EMB) based on force-free region deformation is proposed to meet the no burr forming requirement of diaphragm parts for carrier rockets in the aerospace field. Deformation behaviors of the part were revealed along with the effects of key process parameters on the forming quality investigated. During the EMB process, the electromagnetic force, effective stress, and plastic strain were distributed in a rather uniform annular region and peaked near the edge of the die. High-speed deformation coupled tension and bending were evidenced. With the increase in discharge voltage, the diameter of the part reduced slightly, and the filling degree of the trimmed edge section reduced remarkably, while the thickness uniformity was improved. It was found that the filling degree was dependent on the deformation degree and the interaction between two different regions. Similar effects of initial blank diameter and discharge voltage were observed. The interaction was notable at a larger initial blank diameter, causing the sharper drop in the filling degree. The forming quality could be improved by using a blank holder, but an undesirable extra deformation zone would appear. In a word, the proposed EMB process is capable of forming no burr diaphragm part with high quality.

Strain rate dependent mechanical response for monoclinic NiTi shape memory alloy: Micromechanical decomposition and model validation via neutron diffraction

Design of shape memory alloy based structure in high–frequency or dynamic applications needs to build on a luminous comprehension for high speed deformation mechanisms of the corresponding material. In present work, dynamic responses and bulk texture evolutions are studied in martensitic NiTi through multi–scale characterization efforts. The objective is to quantitatively decompose the macroscopic strain according to deformation mechanisms and construct a phenomenological constitutive model. This study uses quasi–static in–situ and dynamic ex–situ neutron diffraction techniques to follow the evolution of bulk texture, twin volume fraction, and active twinning modes under various strain rates. It is demonstrated that the mechanical responses are strongly rate sensitive. The observation is attributed to the variation in slip activity. A distinct twinning mode change during compression is captured through in–situ neutron diffraction, and the shear induced reorientation is well described. Based on experimental observations, a constitutive model that includes effects of elasticity, reorientation of accommodation twinning, and plasticity is constructed and validated in a wide strain rate range. The overall results provide insights into strain rate dependent mechanical response of martensitic NiTi in both experiment and model aspects. This work will guide the design and application of shape memory alloys, especially in dynamic condition.

Shear behavior of woven and non-crimp fabric based thermoplastic composites at near-processing conditions

In intra-laminar shear testing of continuous fiber reinforced thermoplastic composites at near-processing conditions, several factors influence the measured forces in picture frame tests. These influences mostly result from tight clamping of the specimen in the frame and, depending on the heating strategy, possible unmelted areas near the clamping regions, yielding in a shift of the point of rotation of the fibers. An approach to compensate these effects has recently been suggested, but generally valid compensation settings could not yet be deducted. In addition, research on the shear properties of continuous fiber reinforced thermoplastics has been limited to quasi-static deformation speeds and thermodynamically stable temperature levels. This study examines the effect of high deformation speeds and temperature levels in the transitional region between melting point and recrystallization on the intra-laminar shear behavior of different types of continuous fiber reinforced thermoplastics to deduct a material behavior, which better resembles actual processing behavior by using a custom-built picture frame setup. The edge effects are analyzed to deduct generally recommendable compensation settings using a statistical approach. In addition, variations of the pathways of individual fibers in pre-forms are measured, revealing elongation reserves of 0.4–0.5%, which can be confirmed in picture frame tests. The results furthermore show the importance of performing material tests at near-processing conditions to deduct reliable material data for usage in forming simulation. Further research is necessary to understand the complex deformation behavior in the transitional region below melting point and before recrystallization is complete.

High-speed Deformation and Failure of Titan Alloy

The paper presents the results of a study of the dynamic properties of 3M titanium alloy under tension, carried out using the Kolsky method, as well as the results of determining the spall strength obtained using a VISAR laser interferometer. The experiments using the split Hopkinson pressure bar were carried out in the range of strain rates of 700 - 1500 s_1. In this experiments, dynamic strain diagrams were obtained, according to which the yield strength σ0.2 and the tensile strength were determined. The yield strength of the studied material increases with increasing strain rate from 700 MPa to 800 MPa. Since the 3M alloy does not experience hardening with increasing strain, fracture begins at stress close to yield strength. The tensile strength of this alloy under uniaxial tension (temporary tensile strength) also grows slightly from 700 MPa to 800 MPa with increasing strain rate. The ultimate plastic fracture characteristics of a titanium alloy (elongation and relative narrowing after rupture) are practically independent of the strain rate. In plane-wave experiments, spall strength was studied in the range of strain rates of 2 · 104 - 5 · 104s-1. The obtained values of spall strength lie in the range of 1.6 - 4 GPa, which significantly exceeds the values obtained under static loading and the values obtained in experiments using the Kolsky method, which is apparently associated with both the influence of the strain rate and the influence volumetric stress state in a plane-wave experiment.

堆载对邻近高铁桩基变形影响的数值分析研究

堆载对邻近高铁桩基变形影响的数值分析研究

ІМІТАЦІЙНЕ МОДЕЛЮВАННЯ РУЙНУВАННЯ ТИПОВИХ ЕЛЕМЕНТІВ КРІПЛЕННЯ ПІД ЧАС ДЕТОНАЦІЇ

A number of precautions are used to prevent injuries to people and industrial equipment during accidents at chemical plants. One of them is based on the use of protective containers for the storage of explosives. A typical container consists of a main structure and a lid of the loading hole. This cover is fixed to the container with fasteners based on bolted connections. To ensure the normative strength of such a connection at the design stage, an analysis of its dynamic strength is performed and the critical loads that cause the destruction of the structure are determined. To reduce the cost of design work, it is advisable to replace a number of experimental tests with numerical studies and simulate the process of destruction. Therefore, the development of methods for numerical analysis of dynamic strength and integrity of typical fasteners based on bolted joints is an urgent problem. Simulation of the destruction of composite structures based on bolted joints should adequately reflect the complex of mechanical loads. First, it is a static load due to the assembly of the bolted connection. Secondly, it is high-speed dynamic loads due to the action of a detonation shock wave. For mathematical modeling of such processes, it is necessary to take into account the influence of the load speed on the mechanical properties of metals in the bolted joint. An important role in modeling the destruction process is played by the correct choice of the criterion of destruction of the structural material. According to the analysis of previous studies, the criterion of maximum plastic deformation was chosen. For the numerical implementation of the developed mathematical model of high-speed deformation and destruction of the folded fastening structure on the basis of bolted connection taking into account nonlinear properties of mechanical characteristics of materials and influence of previous loadings during assembly of a design the finite element method is chosen. The application of the proposed technique at the design stage of protective containers allows to reduce the number of experimental tests and thus reduce the development time and to reduce its cost.

The development of a mathematical complex for modeling the progress of destruction of composite structures based on hight-speed deformation models

Today, there is a risk of destruction for a large number of buildings from various emergencies. Modern regulatory framework for the design and operation of buildings, contains many years of experience in analyzing the causes of collapse, takes into account a large number of impacts on structures (dynamic loads, climatic effects, temporary and permanent) during the entire service life. However, the increasing number of accidents with varying degrees of destruction, both of individual parts and of the entire structure, suggests that the impact that caused the destruction was not taken into account in the regulatory documents on the basis of which the object was designed. Therefore, there is a need for accurate calculation algorithms, modern reliable and cost-effective methods for the structural strengthening of supporting frames of buildings. The article considers existing methods for predicting the effects of fracture and solving problems for determining the stress-strain state based on a specially developed RHT (Riedel- Hiermaier-Thoma) strength model for high-speed deformation of reinforced concrete under dynamic loading conditions. A model problem is considered using a variational approach based on the construction of a functional for calculating the elastic deformation power, taking into account the power of inertia forces for a spherical explosive charge located directly in front of the structure. All calculations were performed in the ANSYSLS-DYNA environment, the results were obtained in the form of graphs of strain rates and stress fields.

Influence of non-metallic inclusions on the formation of the structure of the steel matrix in explosive loading

Purpose . The goal of this work was to study the localization of deformation near inclusions in steels with various types of metal matrix and the behavior of the inclusions themselves under pulsed loading. Methodology . Dynamic loading of the samples of steels E3 and 08H18N10T was carried out according to the scheme of throwing a thin plate. The calculated pressure was 80...90 GPa, strain rate 100 s -1 , exposure time 1.5 · 10 -6 s. The studies were carried out by several methods: metallographic (Neophot-21), electron microscopic (JSM-35). Findings . The features of local changes in the structure of the steel matrix near non-metallic inclusions under pulsed loading were studied. The processes of localization of deformation near inclusions in steels with various types of metal matrix and the behavior of the inclusions themselves under pulsed loading are discussed. The influence of the physical features of high-speed deformation on the formation of the structure of steels and the processes of its localization near inclusions were analyzed. It was established that stresses localized in a steel matrix near the inclusions cause their destruction. Scientific novelty . The analysis of plastic relaxation zones in a steel matrix was carried out, which made it possible to confirm the formation of regions with various orientations, which indicates a shear-rotational reorientation of these stress relaxation zones near inclusions as a result of plastic deformation having a wave nature. The general patterns of structure formation were determined and the influence of the crystal lattice type of the matrix of steels E3 and 08H18N10T on the development of localization of deformation processes near inclusions was shown. Practical relevance . Using the results obtained will allow us to develop pulsed pressure treatment regimes that allow you to influence the formation of the structure near non-metallic inclusions in various steels.

Моделирование одноосной деформации нанокристаллов магния "жесткой " и "мягкой" ориентировок

Abstract. Atomistic modeling of high-speed deformation by compression of ideal, defective (5% vacancies, 5% impurity hydrogen atoms) magnesium nanocrystals with "hard" and "soft" orientations at T = 300 – 375 K was carried out. Three interatomic interaction potentials were used. The evolution of the microrelief of the free surface of magnesium nanocrystals in the process of plastic flow is shown. Diagrams "stress σ – deformation ε" are constructed, deformation dependences of the scalar dislocation density are determined, and the strain rate dependences on the degree of deformation ε are constructed. The influence of vacancies and hydrogen atoms on the shape of deformation curves, dislocation structure and scalar dislocation density is shown. Evolution of typical dislocation structures is shown, some typical dislocation reactions are given. Conclusions are drawn on the influence of the type of interatomic interaction potential on the calculated characteristics.

High-Speed Deformation of Pinless FSWed Thin Sheets in AA6082 Alloy

The high-speed deformation behavior of friction stir-welded thin sheets in AA6082-T6 aluminum alloy, under biaxial balanced stretching, was investigated by means of a hemispherical punch test carried out using direct tension-compression Split Hopkinson Bar. The friction stir welding process was performed on thin sheet blanks using a pinless tool; the rotational and welding speeds were kept constant during process. The dynamic tests were carried out, with a punch speed of 4500 mm/s, at different punch stroke values until failure of the friction stir welded sample. It was seen that failure occurs along the welding line at a dome height about 11% higher than that at the onset of necking. Fractographic analysis shows that deformation is localized in the fracture zone. The results were compared with those obtained on friction stir welded blanks deformed under quasi-static condition in order to evaluate the influence of the loading rate on the weld deformation and fracture mechanisms. It was shown that joints deformed under dynamic loading condition are characterized by a dome height at the onset of necking significantly higher than the one measured under quasi-static condition.

Influence of the Guinier–Preston Zones on the Concentration Dependence of the Yield Point of the Aged Two-Component Alloys in Conditions of High-Speed Deformation

The glide of an ensemble of edge dislocations at the high-speed deformation of an aged binary metal alloy is theoretically analyzed. The yield stress of the alloy is a nonmonotone function of the second component concentration, which has a maximum and a minimum under certain conditions. The maximum corresponds to the transfer from the dominating influence of dislocation collective interaction on creation of a spectral gap to the prevalence of the influence of collective interaction of atoms of the second component. The minimum of the obtained curve corresponds to the transfer from the prevalence of the drag of the dislocation by the Guinier–Preston zones to the prevalence of its drag by the atoms of the second component.

Graphics processing unit assisted diffraction phase microscopy for fast non-destructive metrology

For non-invasive deformation metrology using optical interferometry based techniques, reliable phase retrieval is an important problem. This paper proposes a graphics processing unit assisted fast and robust phase retrieval technique based on signal subspace method. The effectiveness and efficiency of the proposed method is shown using numerical simulations. For processing a fringe pattern of size 1024 by 1024 pixels, our proposed implementation provided improvement in computational efficiency by a factor of more than 150 as compared to the conventional sequential method. The practical viability of this approach is demonstrated for high speed deformation testing in an experimental configuration based on diffraction phase microscopy.

Численный анализ управляемой потери устойчивости пологих менисковых облицовок при высокоскоростном обжатии

Experimental and analytical research methods of losses of stability of meniscal form liners at their high-speed deformation, i.e., collapse, by products of detonation of explosive have limited opportunities. They are caused by the complicated nature of liner thickness change to control the operated loss of stability --- folding, high-speed deformations of liners, intensive drop of pressure acting on them and some other features. The paper introduces an approach to numerical three-dimensional modeling of collapse of meniscal form liners with variable thickness in the circumferential direction in the area of their periphery, the modeling being carried out by the finite element method in Lagrange coordinate system in LS-DYNA software package. The study also shows the main stages of implementing this approach and describes the key parameters of the materials models used, as well as the type of the final element and mechanism of adaptive updating of the computational grid. By the method of numerical simulation, we found the main regularities of liners collapse and folding of the afterbody of high speed elements formed during the collapse of the liners. The results of numerical calculations are confirmed by experimental data. The studies done are of interest to specialists involved in the analysis of the loss of stability of various structures under dynamic loads, as well as to specialists in the field of explosion and impact physics.

Influence of the Surface Structure and Properties on the Fatigue Strength of Electromechanically Strengthened Quenched Steel

Abstract—For the example of quenched carbon steel 45 and U8 steel, the influence of surface hardening (electromechanical treatment, surface plastic deformation, nonabrasive ultrasonic finishing, and various combinations) on the surface structure and microhardness, the cyclic durability of the hardened samples, and the mechanisms of fatigue failure is analyzed. Research by means of optical and scanning electron microscopy, microhardness measurement, and fatigue tests shows that, for the quenched carbon steels, high-speed pulsed thermal deformation in the course of electromechanical treatment increases the surface microhardness (by more than 50%) and decreases the fatigue limit (by 20–30%). That is associated with the formation of hard nonequilibrium ultradisperse phases of nonuniform chemical composition in the surface layer. The quenched structure close to the surface is tempered, with the formation of softening zones and the appearance of residual tensile stress. Accordingly, the microhardness in these zones declines and the fatigue limit falls. Such decrease in performance of the steel on surface hardening merits further study, along with potential technologies for improving its performance. Surface hardening of carbon steels by some combination of electromechanical treatment, surface plastic deformation, and nonabrasive ultrasonic finishing permits adjustment of the structure and phase composition and the stress–strain state of surface and subsurface layers of the steel by varying the temperature and deformation. By that means, balanced strength and fatigue characteristics of the samples may potentially be obtained by appropriate preliminary heat treatment. Intense surface plastic deformation and nonabrasive ultrasonic finishing after electromechanical hardening may be used to smooth the surface, mend subsurface defects, and correct the stress–strain state of the steel. That increases the microhardness in the tempering zone by 20–25% and the fatigue limit of the samples by 25–30%.

Rapid deformation analysis in digital holographic interferometry using graphics processing unit accelerated Wigner-Ville distribution.

High-speed measurement of temporally varying displacement derivatives of a deformed object is an important and challenging problem in precision metrology. This paper proposes an approach for temporal deformation analysis using digital holographic interferometry, where a series of digital holograms is recorded corresponding to a test object subjected to variable load. Numerical reconstruction followed by superposition of these holograms provides a huge stack of interference or fringe pattern data, which needs to be processed to extract the displacement derivative information. This operation involves great computational complexity, and we propose a highly efficient Wigner-Ville distribution method based on a graphics processing unit to address the challenge. Experimental results clearly demonstrate the viability of the proposed approach for high-speed deformation analysis in digital holographic interferometry.

Simulation and experimental study on the effect of abrasive size, rotational speed, and machining gap during ultra-precision polishing of monocrystalline silicon

Monocrystalline silicon wafers are the key materials for micro-electro-mechanical-systems. These wafers require high surface quality with damage-free subsurface. Because of the high-speed deformation during the ultra-precision polishing of these wafers, Smoothed Particle Hydrodynamics (SPH) which is a meshless method with good self-adaptability can be useful in the simulation of the polishing process. In this work, SPH analysis model of Magnetic Abrasive finishing (MAF) is established according to the principle of the polishing process. Moreover, experiments are done to reveal the effects of polishing variables on the reduction in surface roughness (ΔRa) and material removal (MR). Also, verification of simulation results is done with experiments. Our findings showed that MR and ΔRa value increase with increasing abrasive size, rotational speed and, decreasing machining gap. According to our experimental findings, maximum ΔRa and MR are 0.65 and 39.09 mg, respectively. Finally, it is possible to optimize polishing parameters and provide the theoretical guidance for production.

Constitutive parameters identification based on DIC assisted thermo-mechanical tensile test for hot stamping of boron steel

Hot stamping of Boron steel is a thermal-mechanical and phase transformation coupled process. The reliable testing and parameter identification method of the constitutive behavior is crucial for accurate simulation on hot stamping. The imprecise strain and strain rate calibration due to the inevitable temperature gradient along the gauge length in the Gleeble tensile test has been a great challenge to the accurate description on constitutive behavior at elevated temperatures. In the present work, a novel design of grips is developed to flexibly regulate the length of Uniform Temperature Zone (UTZ) along the specimen gauge length. A system with new speckle preparation method and great optical anti-interference ability is developed for the accurate strain calibration at elevated temperature and high-speed deformation based on digital image correlation (DIC). The influence of the length of UTZ and the strain measurement methods on the accuracy of parameters identification is further investigated. The DIC based calibration method on full-field strain and strain rate makes the parameter identification more robust on the length variation of UTZ, that is, the identified parameters are nearly the same using different UTZ length of specimen. The appropriate UTZ length should be satisfied to prevent the ends of gauge length from blue brittleness and the undesirable end failure. The identified constitutive parameters are verified by comparison between simulation and experiments of the hot stamping hat-type parts. It shows that the newly developed DIC-based method is the most precise within the context of the tested approaches to determine constitutive parameters of hot stamping process.