High-speed Deformation Research Articles

Twinning behavior and variant selection mechanism of b.c.c tantalum during dynamic plastic deformation

In this paper, the microstructure and twinning behavior of tantalum (Ta) during dynamic plastic deformation (DPD) were jointly analyzed in combination with impact experiments and molecular dynamics simulations, with a focus on the mechanism of variant selection for twinning. The results indicated that twins nucleate at grain boundaries and gradually grows with increasing deformation until it penetrates the entire grain. Due to the difference of grain boundary dislocation density, strain rate and deformation temperature have significant impacts on the quantity and distribution of twins. In addition, at room temperature, nearly half of the twin variants in DPD samples do not conform to Schmid law, and almost all the twin variants in liquid nitrogen samples do not follow to Schmid law. The activation of these non-Schmid variants is mainly affected by the strain coordination. Through this study, we have deepened our understanding of the dynamic microstructural response of Ta under high-speed deformation conditions.

Dynamic deformation behavior of Fe-0.22C-1.65Si-1.98Mn quenching and partitioning steel over a wide range of strain rates and constitutive model establishment

During traffic accidents, automobiles often experience rapid deformation at high strain rates spanning from 10² to 10³ s⁻¹. The dynamic deformation behavior and the constitutive model of the materials are crucial for precisely analyzing and simulating vehicle collisions and damage. This study focuses on a high-strength quenching-partitioning steel (Q&P steel) compositionally tailored for automotive applications, specifically Fe-0.22C-1.65Si-1.98Mn. Tensile tests were conducted under quasi-static (10⁻⁴–10⁻¹ s⁻¹) and dynamic (1–10³ s⁻¹) conditions to obtain stress-strain data, based on which the deformation behavior and instability mechanism of the Q&P steel were revealed. A Johnson-Cook (J-C) constitutive model was established to predict the stress-strain behavior. This model was further improved by incorporating the nonlinear influence of strain rate on stress, resulting in a significant reduction of prediction error by 60.9 % in the high strain rate range. Based on the modified J-C model, the finite element simulations of the high-speed collision for U-shaped and tubular components were conducted. The simulations exhibit excellent agreement with experimental results, thus confirming the accuracy of the model in predicting high-speed deformation behavior of the Q&P steel. This validation enables precise simulations of dynamic collision characteristics and energy absorption.

A novel mathematical-based approach to predict the high-speed deformation behavior of cryodeformed materials with varying stacking fault energies

Cryodeformed (CR) materials have complex microstructures containing nano-twins, dislocation clusters, tangles, and others, depending on the stacking fault energy (SFE). Such unique microstructure makes them suitable for several engineering applications under a high strain rate environment. The high-speed deformation (HSD) behavior of CR materials is difficult to understand due to their complex microstructure. The present work is focused on developing a novel mathematical modeling method to understand the high strain rate deformation of CR materials with varying SFE. The model equation correlates the microstructure-based variables to deformation-based variables like stress, strain, and strain rate. High-speed deformation was conducted using a crossbow test. Transmission electron microscopy (TEM) was conducted on these materials to validate the model output.

Enhanced dynamic-mechanical property and microstructural mechanism of a FeCoNiCrMo0.2 high-entropy alloy fabricated using powder bed fusion

Powder bed fusion (PBF), along with subsequent heat treatment, plays a crucial role in enhancing the impact toughness of FeCoNiCrMo0.2 high-entropy alloys (HEAs) and expanding their potential applications in field for high-speed deformation. In this study, the dynamic-mechanical properties and microstructure of the as-built PBF–FeCoNiCrMo0.2 HEAs and quenched PBF–FeCoNiCrMo0.2 HEAs heated at 600–750 °C for 8 h were investigated. As the heating temperature increases, the columnar grains and cellular structures undergo coarsening and the dislocation density gradually decreases. Moreover, higher heating temperatures facilitate the precipitation of Mo-rich second phases. This occurrence can be primarily attributed to the segregation of Mo at the boundaries of the as-built specimens. Consequently, in the quenched specimens, the μ phases are predominantly distributed along the boundaries of the cellular structures. In the quenched Q700 specimen (heated at 700 °C for 8h), the size and volume fraction of the μ phases are measured to be 63.4 nm and 3.59%, respectively. Additionally, under the same condition, the Q700 specimens also exhibited a relatively slight increase in the size of the cellular structures. The impact energy absorption, dynamic yield strength, and dynamic compressive strength of the Q700 quenched specimens were found to be 210.1 MJ/m3, 1066 MPa, and 1649 MPa at a strain rate of 1840 s−1. These values represent a dramatic improvement of 38.1%, 52.7%, and 14.7% higher in comparison to those of the as-built specimens. Under impact deformation, the presence of the μ phases plays a significant role in impeding the movement of dislocations by acting as a pinning agent for the boundaries of the cellular structures, thereby enhancing the strength. Simultaneously, the cellular structures were significantly elongated to form the deformation bands and to coordinate the impact deformation, leading to good impact energy absorption. In combination, the synergistic strengthening and toughening effect of the μ phases and the elongated cellular structures contribute to a remarkable improvement in the impact toughness of the PBF-HEAs.

High-speed deformation behaviour of 45° extruded magnesium alloy under quasi-in-situ conditions

In this study, quasi-in-situ electron backscatter diffraction was employed to investigate the microstructural evolution and deformation behaviour of ZK60 magnesium alloy with an initial 45° extruded state orientation under two high-speed impacts. The experimental results demonstrated that the deformation of the alloy mainly depended on slip and [Formula: see text] tension twinning. With the increase of deformation, the [Formula: see text] tension twins nucleated continuously, and there were stretching twin variants that were 60° away from the original stretching twins. In addition, compared with the conventional orientation (extrusion direction), 45° samples were easier to activate various slips under high-strain rate deformation conditions, especially ⟨c + a⟩ slips.

High-speed Deformation Behavior of a SUS316LN Austenitic Stainless Steel with Heterogeneous-nano Structure

High-speed Deformation Behavior of a SUS316LN Austenitic Stainless Steel with Heterogeneous-nano Structure

Mechanically strong and fully transparent PMMA composite with greatly improved toughness and impact strength incorporating PEBA nanofibrils

Improving the tensile toughness and impact strength of poly(methyl methacrylate) (PMMA) involves a trade-off, the improvements often come at the expense of reduced tensile strength, stiffness, transparency, and other crucial properties. In this article, we report a facile method to enhance the tensile toughness and impact strength of PMMA simultaneously, without sacrificing its tensile strength, stiffness, transparency, glass transition temperature, and scratch resistance. We demonstrate that the inclusion of only 3 wt% of polyether block amide elastomer (PEBA) nanofibrils (diameters ranging from ∼ 20 to 164 nm) in PMMA and ∼ 0.6 wt% of a random ethylene-glycidyl methacrylate copolymer (E-GMA) selectively at the interface resulted in a remarkable increase of ∼ 169 % in its elongation at break, ∼188 % in tensile toughness, and ∼ 87 % in notched Izod impact strength. Importantly, by incorporating such a minimal content of rubbery materials, these improvements were attained without compromising any of its major properties. Herein, we also demonstrate that multiple crazing was the primary toughening mechanism in the composites at a slow deformation speed (i.e., tensile testing), while rubber cavitation and subsequent ductile shear yielding of the surrounding matrix (enabled by the presence of E-GMA at the interface) was the most dominant at a high deformation speed (i.e., notched Izod impact testing). The high-performance composites presented herein possess immense potential for use in applications requiring a unique combination of attributes such as high strength, stiffness, tensile toughness, impact strength, and optical transparency.

Structural Investigations and Rheology of Convergence of Thick-Wall Shells from Al–Mg Alloy

Abstract—The deformation behavior of thick-walled hollow cylindrical shells made of the AMg6 alloy (Al–6.1% Mg–0.6% Mn–0.1% Ti–0.2% Si, wt %) loaded according to an 8-point initiation scheme of an attached explosive is considered. The intensity of explosive loading was regulated by the amount of explosives. It has been established that, different scenarios for their convergence are observed depending on the intensity of the impact and the geometric characteristics of the shells. The conditions for the formation of spallation internal layers were determined, the evolution of the structure during high-speed deformation along the radius and along the length of the shells and the change in hardness along the radius of the shells were studied. X-ray photography of the dynamics of shell deformation processes was carried out at different time intervals. The speeds of movement of the outer and inner layers of the shells and the speed of their deformation for different amounts of explosives were determined.

Microstructural evolution and deformation behavior of an interstitial TRIP high-entropy alloy under dynamic loading

The mechanical properties and microstructural evolution under dynamic loading conditions are of paramount importance in the development and utilization of interstitial high-entropy alloys (iHEAs). This study focuses on the investigation of a currently trending material, C-doped TRIP-assisted HEA Fe49.5Mn30Co10Cr10C0.5 (at.%). By subjecting the alloy to uniaxial quasi-static and dynamic tensile loading, the study systematically elucidates mechanical property testing under different strain states, characterizes the microstructural evolution during deformation, analyzes deformation mechanisms, and delves into the essence of mechanical responses. Particularly, by employing digital image correlation (DIC) techniques, local severe deformation regions under high-speed deformation conditions are sampled to investigate microstructural changes under extreme deformation conditions. The results indicated that, in comparison to quasi-static tensile deformation, the dynamic tensile deformation of the HEA demonstrated a slight increase in yield strength, a decrease in ultimate tensile strength, and a trend toward an increase in total elongation. Specifically, at a strain rate of 103 s−1, the tensile strength was ∼825.5 MPa, and at a strain rate of 10 s−1, the elongation was ∼57.7 %. In quasi-static deformation, the TRIP and TWIP effects served as the primary deformation mechanisms. In dynamic deformation, the proportion of ε-martensite phase transformation was significantly reduced, with deformation twinning (DT) and dislocations becoming the dominant mechanisms, originating from the impact of adiabatic heating on the stacking fault energy (SFE). Furthermore, in the locally severe deformation region, multiple twinning systems were activated, coupled with a substantial accumulation of dislocations. A minor presence of dual-oriented martensite also contributed to this complex mechanism. Additionally, the carbides formed through C-doping exerted a significant hindrance on dislocation slip during high-speed deformation and under high-strain conditions. Simultaneously, they promoted the activation of multiple twinning systems, making an indispensable contribution to maintaining the strain hardening rate (SHR) of the HEA.

Microstructure and dynamic-mechanical property of a selective laser melting AISI 316 L stainless steel

Dynamic mechanical properties are the key indicators for the application of the selective laser melting AISI 316 L stainless steel (SLM AISI 316 L SS) in impact-related fields. The σ precipitate can improve the dynamic mechanical properties of the SLM AISI 316 L SS during high-speed deformation, and promote the application of the SLM AISI 316 L SS in field of the high-speed deformation. Dynamic mechanical properties of the as-built and quenched specimens are tested by using a split Hopkinson pressure bar (SHPB). The specimens exhibit excellent impact energy and ultimate compressive strength, reaching 210.33 MJ/m3 and 1411 MPa, respectively. Microstructure of the SLM AISI 316 L SS is observed by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The melt pool boundary and cellular substructure disappear, and the rod-like σ precipitates are mainly distributed at the columnar grain boundary after quenching process. Quantitative analysis of the σ precipitate is obtained by small angle neutron scattering (SANS). Size and volume fraction of the σ precipitates in the quenched specimens can reach 31.5 nm and 2.7%, respectively. Quenched specimens after dynamic deformation mainly produce deformation bands with about 20 µm width. The σ precipitates distributing at the columnar grain boundaries suppress grain growth and dislocation movement by pinning grain boundaries and dislocations, leading to the optimization of the dynamic mechanical properties of the SLM AISI 316 L SS. This work provides theoretical guidance for the strengthening and toughening of dynamic mechanical properties of the SLM AISI 316 L SS.

The Metallographic Study of High-Speed Deformation and Convergence of Thick-Walled Cylindrical Copper Shells under Explosive Loading

Abstract—Metallographic method investigated the process of convergence of thick-walled cylindrical copper shells under the action of an explosion. The explosion was initiated from eight points evenly spaced in a circle on the surface of the explosive surrounding the shell. At the intermediate stage of convergence, eight outliers formed on the inner surface of the shell. The convergence of the shells into the cylinder is completed by expanding and closing the emissions. The formation of outliers is explained by the occurrence of plastic (cumulative) jets at the deformation front. Jets occur when adjacent deformation projections collide. Areas of localized deformation were found inside and around the ejections, which is associated with this method of initiating an explosion. It is established that high-speed deformation of copper during the convergence of shells is accompanied by the formation of a large number of twins. There are more twins in the outer zones of the shells than in the inner ones.

A multifunctional soft robotic shape display with high-speed actuation, sensing, and control

Shape displays which actively manipulate surface geometry are an expanding robotics domain with applications to haptics, manufacturing, aerodynamics, and more. However, existing displays often lack high-fidelity shape morphing, high-speed deformation, and embedded state sensing, limiting their potential uses. Here, we demonstrate a multifunctional soft shape display driven by a 10 × 10 array of scalable cellular units which combine high-speed electrohydraulic soft actuation, magnetic-based sensing, and control circuitry. We report high-performance reversible shape morphing up to 50 Hz, sensing of surface deformations with 0.1 mm sensitivity and external forces with 50 mN sensitivity in each cell, which we demonstrate across a multitude of applications including user interaction, image display, sensing of object mass, and dynamic manipulation of solids and liquids. This work showcases the rich multifunctionality and high-performance capabilities that arise from tightly-integrating large numbers of electrohydraulic actuators, soft sensors, and controllers at a previously undemonstrated scale in soft robotics.

Effects of hydrogen on the dynamic mechanical properties and microstructure of 7055 and 7A52 aluminum alloys

In the present work, the effect of hydrogen on the impact resistance of the 7055 and 7A52 aluminum alloys have been experimentally investigated by using split Hopkinson pressure bar (SHPB) and electrochemical hydrogen charging technique. It was first found that hydrogen induced stress chase after yield deformation in 7055 and 7A52 alloys. Meanwhile, hydrogen reduced the yield strengths of the two alloys. Besides, the evolution of microstructures including cracks, particles and dislocations has been quantitatively analyzed by polarizing microscope (PM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). It has been found that both two aluminum alloys are sensitive to hydrogen embrittlement under high-speed deformation conditions. The hydrogen causes hydrogen compression cracks at grain boundaries, pores, and Al2Cu particles in the material, and the hydrogen cracking of both aluminum alloys after impact appeared to be layered, and the lower layer cracking was flat, which indicated that the hydrogen made the alloy embrittle to some extent. Besides, hydrogen reduces the hindering effect of copper-containing phase and large η phase on dislocation movement, which makes the dislocations distribution inside the 7055 alloy grains more uniform. The results show that 7000-series aluminum alloys are sensitive to hydrogen embrittlement under high-speed deformation conditions.

Dynamic Behaviour of Selective Laser Melted 316L Steel - Mechanical Properties and Microstructure Changes

316L steel specimens with three different shear zones made by SLM (Selective Laser Melting) were subjected to dynamic tests using the Split Hopkinson Pressure Bar method. The effect of high-speed deformation on changes in microstructure was analyzed. In addition, the stress-strain relationship was determined from the SHPB results. To visualize the deformation process of the specimens during the tests, a camera with a high frame rate was used. It was shown that as the plastic deformation increases, the hardness of the material increases. Microstructural analysis of dynamically loaded areas revealed numerous defects. Twinning was found to be the main deformation mechanism. Large plastic deformation and many other microstructural changes such as shear bands, cracks and martensite nucleation were also observed.

High-Speed Deformation Measurement with Event-Based Cameras

High-Speed Deformation Measurement with Event-Based Cameras

Особенности высокоскоростной деформации состаренных сплавов

The sliding of an ensemble of edge dislocations under high-speed deformation (high strain rate deformation) of an aged binary alloy is theoretically analyzed. An analytical expression of the dependence of the dynamic yield strength on the dislocation density is obtained. The conditions under which this dependence is nonmonotonic and has a minimum and maximum are obtained. The minimum occurs during the transition from the dominance of dynamic braking (drag) of dislocations by point defects to the dominance of braking by other dislocations (Taylor hardening). The position of the maximum corresponds to the value of the dislocation density, at which their contribution to the formation of the spectral gap becomes dominant.

Особенности динамики дислокаций в состаренных сплавах

The high-speed deformation of aged alloys containing alloying elements has been theoretically analyzed. An expression for the contribution of the Guinier-Preston zones to the value of the dynamic yield strength has been obtained. Dynamic effects have a significant influence on the motion of dislocation ensembles. The dynamic yield strength under certain conditions does not depend on the rate of plastic deformation. The concentration dependence of the dynamic yield strength is determined by the competition between the interaction of dislocations with alloying elements and dislocations of the ensemble. If the interaction with alloying elements dominates, the dynamic yield strength decreases with increasing their concentration. If the collective interaction of dislocations dominates, the yield strength decreases as their density increases.

Disaster Precursor Identification and Early Warning of the Lishanyuan Landslide Based on Association Rule Mining

It is the core prerequisite of landslide warning to mine short-term deformation patterns and extract disaster precursors from real-time and multi-source monitoring data. This study used the sliding window method and gray relation analysis to obtain features from multi-source, real-time monitoring data of the Lishanyuan landslide in Hunan Province, China. Then, the k-means algorithm with particle swarm optimization was used for clustering. Finally, the Apriori algorithm is used to mine strong association rules between the high-speed deformation process and rainfall features of this landslide to obtain short-term deformation patterns and precursors of the disaster. The data mining results show that the landslide has a high-speed deformation probability of more than 80% when rainfall occurs within 24 h and the cumulative rainfall is greater than 130.60 mm within 7 days. It is of great significance to extract the short-term deformation pattern of landslides by data mining technology to improve the accuracy and reliability of early warning.

Structure formation and physical-mechanical properties of Al-Mg alloy with microadditions of graphene

Composites based on Al-Mg alloy, reinforced with graphene nanofilms, were obtained by in situ synthesis under a layer of salt melt. Using SEM and HRTEM, the morphological and dimensional characteristics of the structural components of composites with different contents of graphene were studied. An experiment on dynamic compression of composites by the Kolsky method was carried out, dynamic properties were measured, and the evolution of a cast structure during high-speed deformation was considered. For the first time, the dynamic properties of composites under loading by plane shock waves have been determined. The dynamic properties of aluminum matrix composites are compared depending on the properties of the non-reinforced alloy.

An innovative solid state manufacturing approach for developing high performance Al/Cu bimetals

Al/Cu bimetals are extensively used in various sectors like electronics and electrical, cookware and decorative industries to make parts and components. The bimetallic components developed by most of the existing manufacturing processes often shows both poor interfacial bond strength and inferior tensile strength. The present work explores an alternate microstructural engineering based novel manufacturing approach to improve the product performance of Al/Cu bimetals via a hybrid manufacturing process consisting of: (a) cryorolling + short-term annealing to engineer microstructural variation in parent materials and (b) laboratory plane strain bonding process for joining/bonding. Four different microstructural combinations are engineered in Al and Cu parent materials (such as ultrafine grained, bimodal/heterogeneous grained, fine grained and coarse-grained microstructures) and the influence of such microstructural combinations on joining potential of Al/Cu bimetals at wide range of process parameters are established. Among all microstructural combinations, ultrafine grained Al + bimodal grained Cu combination has shown excellent bond quality due to dual advantage of high ductility from its coarse-grained counterparts and interfacial strain localization from the UFG counterparts. When deformed at high deformation speed, the bimodal material shows signatures of excellent bonding in the form of microscopic waves and swirls. A possible mechanism is cyclic interaction between the back stress and forward stress arising due to the differences in the strain accommodation capabilities between the fine and coarse grains in this microstructure. This cyclic strain provides a ratcheting effect which results in exceptionally high shear strain at interface and facilitates enhanced bond quality due to wave-like material interlocking. Fine element simulations are also in agreement with experimental results when upscaled to industry scale roll bonding process.