High Rate Deformation Research Articles

Manufacturing thin-walled 99.99% pure Zn tubes with ultrafine grained structures by flowforming

The last decade has seen several attempts to introduce bioresorbable prostheses in order to reduce the number of surgeries, but all the potentially interesting metallic alloys suffer of poor mechanical or chemical resistance. Zinc alloys are attracting more attention for producing temporary prosthesis devices thanks to their bioabsorbable characteristic in human environment, since they present a suitable corrosion resistance to human fluids. However, at the same time, they have extremely poor mechanical properties that make them still unsuitable for such applications. One possible way to increase mechanical performances is to refine the material grain using Severe Plastic Deformation (SPD) processes that can be traditionally used to obtain such refined microstructures through the application of high deformation rates under complex stress states. The paper focuses on the feasibility of using the backward tube flowforming process to obtain a significant grain refinement (below 1 µm) when applied to pure zinc alloy in order to increase its mechanical resistance to values suitable for load bearing temporary prostheses, starting from a 287 µm grain size material. A numerical FE simulation was adopted to understand the strain during the process while the influence of the process parameters, namely the reduction per pass, the mandrel speed and the feed rate, on the microstructural characteristics and related mechanical properties are shown and discussed.

Simulation of Uniaxial Deformation of Magnesium Nanocrystals of “Rigid” and “Soft” Orientations

Atomistic simulation of high-rate deformation ($${v}$$ = 3 × 108 s–1) by compressing perfect and defect (5% of vacancies and 5% of hydrogen impurity atoms) magnesium nanocrystals of “rigid” [0001] and “soft” [$$1\bar {1}01$$] orientations is performed at T = 300–375 K using three different interatomic interaction potentials. The free surface microrelief evolution of magnesium nanocrystals during plastic flow is shown. Stress σ–strain e diagrams are constructed. The strain dependences of the scalar dislocation density are determined; the dependences of the strain rate $$\dot {\varepsilon }$$ on the strain measure e are constructed. The potential energy variation during deformation is considered. The formation of barriers causing the anomalous behavior of the strain rate is discussed. The effect of vacancies and hydrogen atoms on the shape of stress–strain curves, dislocation structure, and scalar dislocation density is shown. Conclusions about the effect of the type of the interatomic interaction potential on calculated characteristics are made.

Direct Observation of Low Strain, High Rate Deformation of Cultured Brain Tissue During Primary Blast.

The Veterans Health Administration determined that over 250,000 U.S. service members were diagnosed with a traumatic brain injury (TBI) between 2008 and 2018, of which a great proportion were due to blast exposure. Although the penetrating (secondary) and inertia-driven (tertiary) phases of blast-induced TBI (bTBI) have been studied thoroughly and are known to be injurious, primary blast brain injury has been less studied. We investigated the biomechanics of primary bTBI in our previously developed in vitro shock tube model with a fluid-filled sample receiver. Using stereoscopic, high-speed cameras and digital image correlation (DIC), we mapped the deformation of organotypic hippocampal slice cultures (OHSCs) following a range of blast exposures to characterize the induced strains. As blast exposure increased, tissue strain increased, although the levels remained relatively low (maximum < 9%), with strains rates between 25 and 85s-1. Both strain magnitude and rate were highly correlated with the in-air blast impulse and in-fluid peak pressure parameters. Comparing biomechanical parameters to previously reported blast-induced electrophysiological dysfunction, a threshold for deficits in long-term potentiation (LTP) was observed for strains between 3.7 and 6.7% and strain rates between 25 and 33s-1. This is the first study to experimentally determine primary blast-induced strain and strain rates in hippocampal tissue.

Amorphous structure in single-crystal magnesium under compression along the c axis with ultrahigh strain rate

It is well known that twinning deformation plays an important role in the plastic deformation of hexagonal close-packed (HCP) metals because of the insufficient independent slip systems in HCP metals. However, recent works show twinning deformation does not happen in compression in the $c$ axis of the magnesium (Mg) single crystal, and it is not clear that how it deforms with limited dislocation glide in absence of twinning deformation. In the present work, molecular dynamics simulations with well validated modified embedded-atom method potential for Mg are performed to reveal the microscopic deformation behaviors of Mg single crystal compressed in the $c$ axis. We focus on the microstructures and the evolution during both the deformation and the relaxation of the Mg single crystal. Twinning deformation is not observed in the simulations as expected, and dislocations and the amorphous regions are found to be dominant under different loading conditions. The amorphous regions are dominant in the deformation under ultrahigh strain rate, and it results in more homogenous deformation and lower flow stress than dislocation glide. The dislocation glide is dominant under lower strain rate, and the insufficient dislocations may lead to quite inhomogeneous plastic deformation. Furthermore, it is revealed that the amorphous regions consist of irregularly distributed atoms with higher per-atom potential than those in the crystalline state. The amorphous regions thus annihilate rapidly once the high-rate deformation is stopped. The annihilated amorphous regions turn into crystalline ones with dense dislocation networks. The annihilation rate of the amorphous regions decreases with increasing pressure, while it hardly depends on temperature.

Impact of interseismic deformation on phase transformations and rock properties in subduction zones

Phase transformations greatly affect physical properties of rocks and impose a first-order control on geodynamic processes. Under high deformation rates, rheological heterogeneities cause large spatial variations of stress in materials. Until now, the impact of higher deformation rates, rock heterogeneity and stress build up on phase transformations and material properties is not well understood. Here we show, that phase transitions are controlled by the stress build-up during fast deformation. In a deformation experiment (600 °C, 1.47 GPa), rock heterogeneity was simulated by a strong elliptical alumina inclusion in a weak calcite matrix. Under deformation rates comparable to slow earthquakes, calcite transformed locally to aragonite matching the distribution of maximum principal stresses and pressure (mean stress) from mechanical models. This first systematic investigation documents that phase transformations occur in a dynamic system during deformation. The ability of rocks to react during fast deformation rates may have serious consequences on rock rheology and thus provide unique information on the processes leading to giant ruptures in subduction zones.

Adaptive-Partial Template Update with Center-Shifting Recovery for High Frame Rate and Ultra-Low Delay Deformation Matching

Adaptive-Partial Template Update with Center-Shifting Recovery for High Frame Rate and Ultra-Low Delay Deformation Matching

Converging criteria to characterize crack susceptibility in a micro-alloyed steel during continuous casting

The ductility drop and decrease in strength that lead to crack formation during continuous casting of steel is typically investigated by means of the hot ductility test. In this study, hot ductility tests are performed by using a thermo-mechanical Gleeble system to simulate the deformation of steels at high temperatures and low deformation rates similar to those during continuous casting. Thus, temperature was varied between 600 and 1000°C while strain rates covered a range from 0.001 to 0.1s−1. Tests are carried out to identify the temperature range at which the steel is susceptible to crack formation as well as the effect of strain rate. Characterization of fractured surfaces and phase transformation after thermo-mechanical tests are conducted in the SEM and Optical Microscope. The combination of these techniques makes possible to formulate cracking mechanisms during hot processing which show critical strain for failure at temperatures between 700 and 900°C based on the convergence of three different criteria: I) Reduction of area, II) True fracture strength-ductility and III) True total energy. This approach provides a better understanding of crack formation in steels at the high temperatures experienced during continuous casting. This information is key to productivity losses and avoid defect formation in the final cast products.

Structural Transformation of the Surface of a High-Strength Steel after Hydroabrasive Action

High-strength steel subjected to hydroabrasive action is studied. Contamination of the cut surface with fragments of abrasive particles is revealed. The cut-surface relief is described. The microhardness of the cut surface and the depth of the cold-hardened layer are determined. Structural transformation near the surface is studied using X-ray diffraction analysis and transmission electron microscopy. It is found that plastic deformation of the surface layer occurs by both slipping and twinning, which is due to the high rate of deformation occurring under conditions of compressive stresses.

Application of trilateration and Kalman filtering algorithms to track dynamic brain deformation using sonomicrometry

Trilateration and Kalman filtering algorithms have been used in many tracking applications ranging from Global Positioning Systems to biomechanics experiments to track rigid body motion and position. Recently, a technique called sonomicrometry was used to measure the deformation of human brain tissue during an injurious impact by measuring distances between sensor pairs embedded in the parenchyma and skull. The array of measured distances were used to calculate the position of each sensor at high sampling rates to quantify brain dynamic deformation. However, non-linear trilateration and Kalman filtering algorithms, which are traditionally used to track object positions, have not been investigated for the unique application of high-rate, small displacement, and dynamic deformation data collected using sonomicrometry. The objective of this study was to compare eight trilateration and Kalman filtering algorithms to determine the most suitable method for sonomicrometry trilateration. The algorithms were tested using experimental brain deformation sonomicrometry data in which random measurement errors were intentionally introduced to evaluate the effect and robustness on tracking dynamic position. The results showed that linear least squares trilateration methods performed poorly compared to the non-linear methods. Maximum Likelihood Estimate and Kalman filtering were the best performing algorithms. The Kalman filtering method was the most suitable for tracking dynamic brain deformation using sonomicrometry because it provided an accurate estimation of dynamic position and the estimated position was insensitive to the chosen initial parameters. The algorithms and error analysis can be extended to a variety of positioning applications using sonomicrometry or similar high-rate dynamic deformation tracking.

Control of a purely elastic symmetry-breaking flow instability in cross-slot geometries

The cross-slot stagnation point flow is one of the benchmark problems in non-Newtonian fluid mechanics as it allows large strains to develop and can therefore be used for extensional rheometry measurements or, once instability arises, as a mixing device. In such a flow, beyond a critical value for which the ratio of elastic force to viscous force is high enough, elasticity can break symmetry even in the absence of significant inertial forces (i.e. creeping flow), which is an unwanted phenomenon if the device is to be used as a rheometer but beneficial from a mixing perspective. In this work, a passive control mechanism is introduced to the cross-slot by adding a cylinder at the geometric centre to replace the ‘free’ stagnation point with ‘pinned’ stagnation points at the surface of the cylinder. In the current modified geometry, effects of the blockage ratio (the ratio of the diameter of the cylinder to the width of the channel), the Weissenberg number (the ratio of elastic forces to viscous forces) and extensibility parameters ($\unicode[STIX]{x1D6FC}$ and $L^{2}$) are investigated in two-dimensional numerical simulations using both the simplified Phan-Thien and Tanner and finitely extensible nonlinear elastic models. It is shown that the blockage ratio for fixed solvent-to-total-viscosity ratio has a stabilizing effect on the associated symmetry-breaking instability. The resulting data show that the suggested modification, although significantly changing the flow distribution in the region near the stagnation point, does not change the nature of the symmetry-breaking instability or, for low blockage ratio, the critical condition for onset. Using both numerical and physical experiments coupled with a supporting theoretical analysis, we conclude that this instability cannot therefore be solely related to the extensional flow near the stagnation point but it is more likely related to streamline curvature and the high deformation rates towards the corners, i.e. a classic ‘curved streamlines’ purely elastic instability. Our work also suggests that the proposed geometric modification can be an effective approach for enabling higher flow rates to be achieved whilst retaining steady symmetric flow.

Experimental and Numerical Investigation of the Effect of Different Temperature and Deformation Speeds on Mechanical Properties and Springback behaviour in Al-Zn-Mg-Cu Alloy

Thanks to their low density and high strength, the 7XXX series aluminum alloys are widely used as a support/beam parts in the aerospace industry. This alloy is target in the lightening studies of the automotive industry and surveys for sheet metal are still in progress. It is a series of alloys that can be applied to the aging process and has the most effect on mechanical properties. As formability is quite weak, methods are investigated. In this study, tensile test, bending test and Erichsen tests are performed at different deformation rates and temperatures. As a result of the experiments, it has been seen that the formability increases at high temperature and low deformation rates. If paint baking time is long, there will be no loss of strength. Also, the bending process is modeled with the help of the finite element analysis programs and the springback estimations are examined. It is seen that the results of the modeling process are quite successful. The effect of the strain rate sensitivity is determined.

INTERFEROMETRIC POINT TARGET ANALYSIS (IPTA) FOR LANDSLIDE MONITORING

Abstract. By the advent of Persistent Scatterer Interferometry (PSI) time-series analysis, this technique has demonstrated high performance in producing accurate measurements of ground displacements. However, due to several limitations such as high deformation rate, lack of man-made features and rough topographic characteristic, the efficiency of the PSI significantly decreases. The main goal of this paper is to illustrate the potential of one of the PSI methods namely the Interferometric Point Target Analysis (IPTA) to measure the deformation caused by landslide. The landslide occurs in an area lacking man-made features with rough topography. To this end, 28 Sentinel-1A SLC images spanning from October 14 2014 to October 27 2016, were used to generate single-master interferograms. The PS pixels were identified using amplitude dispersion and spectral diversity criteria. The PS pixels were unwrapped considering a linear model for the deformation behavior in an iterative manner. The residual topography and atmospheric contributions were estimated in each iteration and subtracted from the PS pixels phases. The results were finally compared to those extracted from conventional Small Baseline Subset (SBAS) time series analysis applied on the same datasets. A good agreement existed between two methods in some locations whereas unwrapping errors probably due to improper deformation model were observed in a couple of points.

The mechanical performance and a rate-dependent constitutive model for Al3Ti compound

The Al3Ti compound has potential application in the high temperature structure materials due to its low density, high strength and stiffness. The mechanical behaviors of the material under different loading rates were studied using compression tests. The results indicate that Al3Ti is a typical brittle material and its compressive strength is dependent on the strain rate. Therefore, a series of rate-dependent constitutive equations are needed to describe its mechanical behaviors accurately. However, it is still short of professional research on the material model for Al3Ti. In this study, the material model was developed on the basis of JH-2 constitutive equations using the experimental data. The model was then applied in simulating the impact process of Ti/Al3Ti metal-intermetallic laminate composites so as to validate the established model. Good agreement between simulation and experiment results shows the constitutive model predict the material responses under high rate and large deformation accurately. This work provides more support for the theoretical and numerical research on the intermetallic.

Progressive tilting of salt-bearing continental margins controls thin-skinned deformation

Abstract As a primary driving force, margin tilting is crucial for gravity-driven thin-skinned salt tectonics. We investigated how instant versus progressive margin tilting mechanisms influence salt tectonics using an analogue modeling setup where tilting rate could be controlled. Instant tilting resulted in initially high deformation rates, triggering widely distributed upslope extension and downslope contraction. Later, both the extensional and contractional domains migrated upslope as early extensional structures were successively deactivated, while deformation rates decreased exponentially. In contrast, progressive tilting led to downslope migration of the extensional domain by sequentially formed, long-lived normal faults. Contraction localized on a few, long-lived thrusts before migrating upslope. We attribute the distinct structural evolution of thin-skinned deformation, especially in the extensional domain, in the two tilting scenarios mainly to mechanical coupling between the brittle overburden and underlying viscous material. The coupling effect in turn is largely controlled by the deformation rate. By demonstrating the spatiotemporal variations of structural style and kinematic evolution associated with instant versus progressive tilting, we suggest that such variation is identifiable in nature and therefore can provide a new way to analyze margin tilting histories.

Understanding Flow Behavior and Microstructure Evolution during Thermomechanical Processing of Mill-Annealed Ti-6Al-4V Titanium Alloy

Abstract Titanium alloy in the mill-annealed condition has a significant store of energy because it is not fully recrystallized and the grains possess a very high dislocation density. It is well established that the extent of softening mechanisms like dynamic recrystallization/recovery (DRX/DRV) are dependent on the stored energy during hot deformation. In this case, stored energy in the prior worked material may facilitate the softening. The hot deformation behavior of mill-annealed Ti-6Al-4V is studied by hot compression tests in the temperature range of 750°C–950°C and strain rate (ε˙) range of 0.001–10 s−1 for 60 % deformation. The true stress-strain curve of the compression tests exhibits the variation in flow stress (σ) characteristics in a wide range of temperature and strain rate (T,ε˙). The activation energy calculated from the phenomenological constitutive equation is significantly higher than the self-diffusion activation energy, which suggests DRX as the main softening process. However, α → β phase transformation below the β-transition temperature during hot deformation substantiates the occurrence of a mechanism other than DRX. In the lower temperature regime T(&amp;lt; 850°C), softening is caused by the DRX process at a lower deformation rate ε˙ (&amp;lt; 0.01 s−1), whereas at a higher deformation rate, the grains are more deformed with very high grain average misorientation. In the high temperature regime, where α → β phase transformation is very pertinent, it subsequently forms the transformed microstructure. The processing map shows the highest efficiency in the lower ε˙ and temperature regime, whereas the least efficiency with instability is observed at high ε˙. Microstructure analyses reveal that the DRX/DRV and phase transformation–assisted microstructure evolution in mill-annealed Ti-6Al-4V are the major deformation mechanisms.

Mechanisms of Superplastic High-Rate Deformation in the Al–Mg–Zn–Fe–Ni–Zr–Sc Alloy

The microstructure and acting superplastic deformation mechanisms in the high-strength Al–7.0% Zn–2.7% Mg–1.0% Ni–0.9% Fe alloy low-doped with Sc and Zr upon deformation at a temperature of 480°С and a strain rate of 1 × 10–2 s–1 at a stable flow stage in a true strain range of 1.1 to 1.6 have been investigated. To evaluate the contributions of superplastic deformation mechanisms to the total elongation, marker grids have been applied on the surface by ion etching, and microstructural changes of the surface have been analyzed. Grain boundary sliding and intragranular deformation play dominant roles. The contribution of each mechanism is 35–40%. The remaining 25% belongs to the diffusional creep mechanism, which is determined from the size of striated zones formed at the transverse grain boundaries on the surface of a deformed sample.

Numerical and experimental investigation of simply supported steel beams under drop‐weight impact tests

ABSTRACTDue to the increase in terroristic attack and catastrophic events, the engineering structures are more and more likely to be subjected to abnormal loading conditions. Moreover, exceptional and unpredictable fatalities (extreme wind actions, explosions, car impacts…etc.) could lead to dreadful consequences, such as the partial or total progressive collapse of the structures. In view of this, it is required for engineers and researchers to have a better knowledge of all the phenomena associated to such exceptional loadings on structures.The behaviour of structures under impact, which is the main topic of the present paper, is a complex phenomenon and the response of a structure depends on a large number of variables such as the sensitivity of the materials to high rates of deformation, imperfection of the system, type and velocity of the impacting body among others.The present paper presents the behaviour of simply supported beams under impact loads. In particular, nine drop‐weight impact tests have been performed at different level of impact energy. Within the proposed paper, the experimental impact tests conducted on simply support beams will be first presented. Then, exploiting the power of FEM analyses performed using the commercial software Abaqus/CAE© and validated against experimental evidences, different modelling techniques, along with several material models, are examined and compared. From these results, the ability of a detailed FE modelling to predict the response of impacted beams, when a proper modelling of the material behaviour at high rate of deformation is ensured, is discussed and a first estimation of the dynamic increase factor (DIF) for beam under impact loadings is given.

Features of mechanical behavior of EV battery modules under high deformation rate

We report on changes in material behavior of electric vehicle (EV) Li-ion battery cell modules when the loading speed increases from quasi-static to high speed (close to 1 m/s). A series of out-of-plane indentation experiments were performed on stacks of pouch cells placed in the specially designed enclosure to represent conditions in battery modules. Over one hundred of large format automotive pouch cells were tested under displacement rates differing by orders of magnitude. The details of internal failure were studied by X-ray tomography (XCT). We observe a shift in the force–displacement response from a parabolic behavior characteristic of particulate materials under compression to the response typical of fully dense materials with yield point. This shift is associated with dynamic effects in active materials which result in deep propagation of damage into the battery module, despite the fact that the internal short circuit is triggered when the displacement of the indenter is one half of that under the slow displacement rate.

Novel MIMO‐SAR system applied for high‐speed and high‐accuracy deformation measurement

As a novel system, multiple-input multiple-output synthetic aperture radar (MIMO-SAR) has achieved rapid development in the past years. Based on the MIMO technique, multiple transmitting and receiving antennas could be utilised to compose a specific geometrical structure and acquire a large aperture. The MIMO-SAR system can be utilised to take deformation measurement to scenes with high deformation rate and can avoid the problems of phase errors caused by the antennas' vibration on the rail. This study introduces the basic principle of the MIMO technique and the key problems in the system design. Experimental datasets are acquired with the MIMO-SAR and GB-SAR (ground-based SAR) systems simultaneously. Comparisons of the imaging results indicate that the MIMO-SAR system has a better repeat-track interferometry performance than the GB-SAR system. In addition, deformation measurement results validate the high-accuracy measurement ability of the MIMO-SAR system.

Stepwise shock compression of aluminum at room and elevated temperatures

With the aim of expanding the measurable range of high-rate deformation, experiments were conducted in which AD1 aluminum [A199.3 under the international classification and AA1135 in the USA (American National Standards Institute)] was subjected to stepwise shock compression at both room temperature and in the range of 498–530 °C. Measurements of the width of the plastic shock waves revealed that the anomalous thermal hardening at strain rates exceeding 105 s−1 is maintained upon increasing the deformation up to at least 6.5%. The hysteresis during shock compression and unloading cycles of the elastic–plastic body was analyzed. The results indicated that determination of the stress states behind the plastic shock wave utilizing this method requires higher than usual measurements and calculation accuracies.