Metal Plasticity Research Articles

Plasticity resource of high-chrome 08Kh13N4M1F steel when pressing

The use of pipes made of high-chromium steel grades in developing oil and gas fields is an important task. The unique properties of the material make pipes indispensable under certain operating conditions in comparison with the same pipes made of carbon, low-alloy and alloy steel grades. However, at the same time, they have a reduced ductility during hot forming. In this work, in order to assess the probability of cracking during hot pressing of pipes made of high-chromium steel grades, the developed method of constructing diagrams of the plasticity of metals and alloys in the hot state for 08Kh13N4M1F steel grade is used. The technique was implemented using a modern testing complex Gleeble 3800. Compression, tensile and torsion tests were carried out at various temperatures. For each test, an assessment of the accumulated degree of deformation was carried out. The obtained data were put into the QForm 3D software package. Based on the processing of the computer simulation results, dependences were obtained that describe the change along the deformation zone when pressing of the stress state index, the intensity of the shear strain rates, and the temperature of the metal being pressed. On the basis of the data obtained, the curves of the dependence of the degree of plastic resource utilization on the deformation temperature were constructed. A metallographic study of 08Kh13N4M1F steel grade revealed the formation of δ-ferrite at hot deformation temperatures, which made it possible to draw conclusions about the most rational pressing temperature. The developed technical proposals, which ensure a decrease in the likelihood of cracking on the surface of hot-pressed pipes, were tested using computer modeling of the pressing process and during experimental pressing.

Determination of the plasticity of metals by impact indentation of a spherical indenter

The problems of measuring the plastic characteristics of metals are considered. It is shown that the characteristics of materials used to compare their plasticity are not comparable and depend in the different degrees on the values of strain, strain rate, and modulus of elasticity. At the same time, the value of plasticity is more physically substantiated, which is determined by the ratio of plastic strain to total strain. It is shown that one of the optimal methods for measuring plasticity (plasticity index) is indentation. The possibility of using impact microindentation for this purpose is studied and expressions are proposed that allow calculating the plasticity based on the results of a single indentation of a spherical indenter. The specialties of the calculation of strain for this type of testing are shown. It was found that the values of plasticity obtained from the ratios of the depths of the plastic and elastic penetration of the indenter are equivalent to the values calculated from the energy ratios upon impact. Experimental studies have been carried out on metals with different hardness and type of crystal lattice. For the first time, the effect of strain rate, deformation, and impact energy (initial impact velocity) on the calculated value of plasticity when a sphere is impressed with strain rates of ~ 103 s–1 is shown. It is shown that when the strain corresponding to the onset of full plasticity during indentation is reached, the maximum sensitivity of the measured plasticity parameter for various metals is achieved.

Covered self-expandable metallic stent versus plastic stent for preoperative endoscopic biliary drainage in patients with pancreatic cancer: a multi-center retrospective cohort study

Background Expanding indications for neoadjuvant chemotherapy (NAC) for resectable pancreatic cancer prolong the period from diagnosis to surgery. In resectable pancreatic cancer with malignant biliary obstruction (MBO), the biliary drainage method without any biliary events is ideally required to safely perform NAC as planned. Plastic stents (PS) have been traditionally used for preoperative biliary drainage; however, recently, covered self-expandable metallic stents (CSEMS) have emerged as a tool for preoperative biliary drainage. Aims To compare CSEMS with PS for preoperative biliary drainage in the management of resectable pancreatic cancer with MBO. Methods In this multicenter retrospective cohort study, we compared CSEMS with PS for preoperative biliary drainage in patients with pancreatic cancer at three tertiary care centers between 2008 and 2019. Results Of the 120 enrolled patients, 45 underwent CSEMS and 75 underwent PS. No significant difference was observed in the basic characteristics between the groups. The rate of recurrent biliary obstruction (RBO) was significantly lower and the time to RBO was significantly longer in the CSEMS group. In multivariate analysis, CSEMS was an independent factor for a longer RBO. However, pancreatitis and cholecystitis were more common in the CSEMS group. The surgery-related adverse events were not significantly different between the two groups, except for longer surgery time and time to discharge in the CSEMS group. Conclusions CSEMS for preoperative endoscopic biliary drainage in patients with pancreatic cancer reduced RBO, although the risk for pancreatitis or cholecystitis could be increased.

Questing behavior of adult Amblyomma americanum (L.) in a laboratory setting</p >

Tick-borne diseases are on the rise globally; however, information is lacking about tick questing behavior. In this laboratory study, we explored tick preferences for stem type (plastic grass, wooden, and metal), questing height, and head orientation. Using 60 Amblyomma americanum adults over three 72-hour replicates, we determined that 21.7% of ticks quested at any given time and that ticks exhibited a strong preference to quest with their heads oriented downwards, irrespective of stem type. Individual ticks tended to quest on only one stem in this study, and a maximum of three. Nonetheless, ticks appeared to prefer questing on wooden and plastic grass stems over metal stems. We did not find an effect of time of day on tick questing rates. Increased understanding of tick questing behavior can improve vector control efforts.

Plasticity of Metal-Organic Framework Glasses.

Metal-organic framework (MOF) glasses provide new perspectives on many material properties due to their unique chemical and structural nature. Their mechanical properties are of particular interest because glasses are inherently brittle, which limits their applications as structural materials. Here we perform strain-rate-dependent uniaxial micropillar compression experiments on agZIF-62, agZIF-UC-5, and agTIF-4, a series of MOF glasses with different substituting linker molecules, and find that these glasses show substantial plasticity, at least on the micrometer scale. At a quasi-static strain rate of 0.001 s-1, the micropillars yielded at approximately 0.32 GPa and subsequently deformed plastically up to 35% strain, irrespective of the type of substituting linker. With increasing strain rate, the yield strength of agZIF-62 evolved with the strain-rate sensitivity m = 0.024 to reach a yield strength of 0.44 GPa at a strain rate of 510 s-1. On the basis of this relatively low strain-rate sensitivity and the absence of serrated flow, we conclude that structural densification is the predominant mechanism that accommodates such extensive plasticity.

Modified Embedded‐Atom Method Potentials for the Plasticity and Fracture Behaviors of Unary HCP Metals

AbstractModified embedded‐atom method (MEAM) potentials have been widely used in molecular dynamics (MD) simulations to describe the interatomic interactions in metallic systems. However, conventional MEAM potentials are almost exclusively fit to a limited number of key single‐value properties, limiting the predictability of MD simulations, especially for complex hexagonal‐close‐packed (HCP) metals with multiple slip systems. Here, three MEAM potentials for unary HCP metals (Mg, Co, and Ti) are fit to conventional target properties, as well as continuous‐energy curves and their gradients obtained from density‐functional theory calculations. These targets include the lattice parameters, cohesive energy, elastic constants, and surface energies as well as the cohesive energy curve, basal plane decohesion energy curve, and generalized stacking fault energy curves for basal, prismatic, pyramidal I, and pyramidal II planes. These interatomic potentials demonstrate excellent reproduction of relevant properties and enable accurate MD simulations of volumetric and plastic deformations, as well as fracture in Mg, Co, and Ti HCP metals. Importantly, the interatomic potentials demonstrate better performance than all existing EAM/MEAM potentials readily available from the literature.

Plasticity Model for Structural Steel with Lode Angle Dependence

In recent years, the Lode angle was found to have a significant effect on plasticity and fracture strain of ductile metal under shear dominant loading, and the classical J2 plasticity theory generally overestimates the cases under shear dominant loading. In practice, shear dominant loading is common, that is, fillet-welded joints, partial-penetration welded joints, and metallic shear dampers. Therefore, it is important to study plasticity of structural steel under shear dominant loading and develop corresponding plasticity models for accurate evaluation of the plasticity and fracture of metallic structures. A plasticity model considering the effect of the Lode angle was simplified based on previous studies. Eight types of specimens with different configurations were designed to generate different initial stress states. Three different material tests were conducted to figure out little anisotropy in different locations of steel plate. The integration process for the simplified plasticity model were studied, and a user-defined subroutine in ABAQUS was developed for the model. A postnecking modification method for the true stress–true strain was recommended to evaluate the postnecking behaviors of structural steel through comparison of experimental and numerical simulation results. The simplified single parameter plasticity model proved to have high accuracy for specimens under various stress states, and a detailed calibration process for the material parameter was also introduced.

Towards better understanding supersonic impact-bonding behavior of cold sprayed 6061-T6 aluminum alloy based on a high-accuracy material model

Supersonic impact deformation-induced bonding is at the heart of the cold spray (CS) process, and therein lies the difficulty of clearly understanding CS behaviors. In this study, the supersonic impact-bonding behavior was systematically investigated by accurately reproducing the CS process using a newly developed material model (Ma-Wang material model) with 6061-T6 aluminum alloy (Al6061-T6) as the target material. First, the material properties of the Ma-Wang material model were identified using general flow stress data. Then, the high-fidelity modeling was fully confirmed by comparing the simulated and experimental coefficients of restitution and microparticle deformations over a wide range of impact velocities. More importantly, the rebound origin and bonding features of supersonic impacts between identical and dissimilar materials (Al6061-T6/Al6061-T6 and Al6061-T6/sapphire) were thoroughly explored, revealing that regardless of the substrate type, metallic plastic deformation is the main pathway for energy dissipation (dissipating approximately 90% of the energy). In addition, the rebound of metallic microparticles is highly dependent on the elastic recovery of the substrate. The difference is that during the supersonic impact between dissimilar materials, interfacial friction can be another important pathway for energy dissipation (dissipating approximately 10% of the energy). The coordinated deformation between microparticles and substrate favors supersonic impact-bonding. Further, the distinct features due to jetting and energy can be regarded as precursors to CS bonding.

Plastic mulches reduce adult and larval populations of Drosophila suzukii in fall-bearing raspberry

The invasive spotted-wing drosophila, Drosophila suzukii, is a major pest of fruit crops worldwide. Management of D. suzukii relies heavily on chemical control in both organic and conventional systems, and there is a need to develop more sustainable management practices. We evaluated the efficacy of three colors of plastic mulches at reducing populations of D. suzukii in fall-bearing raspberry and assessed the mulches’ impacts on canopy microclimate factors relevant to D. suzukii. Black, white, and metallic plastic mulches reduced adult D. suzukii populations by 42–51% and larval populations by 52–72% compared to the grower standard. The mulches did not change canopy temperature or relative humidity, but metallic mulches increased canopy light intensity compared to the black mulch. Radiance in the visible spectrum (401–680 nm) was higher for the white and metallic mulch plots, but the black mulch plots did not differ from the control. In the UV spectrum (380–400 nm), all three plastic mulches had higher radiance than the control plots. Future studies will determine whether changes in radiance are associated with the observed reduction in D. suzukii populations. Plastic mulches are a promising cultural practice for managing D. suzukii since they can reduce adult and larval populations and could be incorporated into an integrated pest management program in both organic and conventional systems.

Modeling the Stress-Induced Transformation Behavior of Shape Memory Alloys under Multiaxial Loading Conditions

A large number of criteria to model the onset of plasticity for ductile metals have been proposed by researchers in the last century. Strangely, very few researchers have tried to model the stress-induced crystalline phase transformation of Shape Memory Alloys (SMAs) according to yield criteria. This paper focuses on the question: is a yield criterion originally proposed for describing the plastic behavior of metals suitable to model the “pseudoelastic” behavior of SMAs? To answer this question, two yield criteria originally proposed by the present author are used to predict the initial surface of transformation onset of two different SMAs: Cu-Al-Be and Ni-Ti alloy. The predicted initial transformation onset surfaces of the two SMAs are compared with experimental results and existing theories reported in the literature and some significant conclusions and recommendations are given.

Interface Formation and Bonding Mechanisms of Laser Welding of PMMA Plastic and 304 Austenitic Stainless Steel

Laser welding experiments involving amorphous thermoplastic polymer (PMMA) and 304 austenitic stainless steel plates were conducted to explore the influence of laser welding process parameters on plastic–metal joints. A high-speed camera was applied to record the dynamics of the molten pool and the formation of bubbles to reveal the bonding mechanisms of the hybrid joints. The influence of process parameters on the joints was analyzed using temperature measurements performed with thermocouples. The microstructure morphology of joints was observed using SEM. The mechanical characterization of the hybrid joints was carried out to understand the effect of the welding conditions on the weld morphology, flaws and shear stress. Different interface temperatures resulted in two types of bubbles and led to different weld morphology characteristics. A stable hybrid joint with the best shear stress was produced with a laser line energy of 20.16 J/mm2, a temperature of 305 °C and small bubbles. The shear stress of the effective joint under the maximum mechanical resistance was 4.17 MPa. The chemical bonds (M-O, M-C) and mechanical anchoring that formed on the steel’s surface contributed to the joint bonding. Range analysis provided guidance for identifying the impact of individual factors in the shear stress for the laser welding of plastic–metal.

Interventional endoscopic treatment in acute pancreatitis

Acute pancreatitis (AP) represents a frequent gastrointestinal diseases. Approximately 80% of patients have amild course of the disease and conservative treatment is sufficient; however, 20% of patients develop asevere AP with local and systemic complications. This article focuses on the currently recommended endoscopic management of severe AP. Classification of AP by the revised Atlanta classification and the occurrence of local or systemic complications. Summary of current evidence with respect to endoscopic management. Inspection of the current literature from specialist journals and current guidelines. The AP is classified as mild, moderate or severe based on systemic (hypotension, renal failure, lung failure) and/or local complications, such as acute peripancreatic fluid collections (APFC), peripancreatic pseudocysts (PPC), acute necrotic collections (ANC) and walled-off necrosis (WON). In recent years the staged endoscopic treatment of infected ANC, WON and PPC has become established. The initial step is the endoscopic ultrasound-guided puncture and drainage with plastic or lumen-apposing metal stents. For solid components or insufficient drainage, atransgastric endoscopic necrosectomy is recommended. The treatment of severe AP requires an interdisciplinary management in specialized centers and regular re-evaluation of the therapeutic efficacy. Interventional endoscopy has become established as the standard for treatment of severe AP.

Operating Parameters of Electric Pulse Activation for Internal Tapping-Screw Operations and its Justification

The processes of intensification of thread-cutting opera-tions by electric current have been known since the 70s of the last century. Internal threading operations are associated with the mechanism of plastic deformation, and, accordingly, with high values of forces and torques. This reduces the reliability of the process and requires additional measures to reduce power ten-sion. The use of the energy of short stimulating current pulses makes it possible to solve such problems due to the so-called electro-plastic effect (EPE). It is manifested due to additional stresses that cause an increase in the plasticity of metals in the presence of an electric potential and a temperature field in the de-formation center. At present, there is still no clear understanding of the phys-ical processes that determine the change in the VAT of a metal when an electric current is passed. The article presents an analysis of information in this area, which allows us to establish a number of physical phenomena, which are formed into three theories that explain the essence of EPE in metals: electron-dislocation interaction, joule heating, and magnetoplasticity. A description of experiments and equipment for electro-pulse stimulation of the threading operation is presented. The author offers a number of indicators that evaluate the possibilities of electric pulse action on the formation of internal threads when rolling threads, screwing thread-pressing parts, etc. A system of calculated coefficients evaluating the efficiency of the pulse current, its parameters and modes is established.

A Review on Capturing Twin Nucleation in Crystal Plasticity for Hexagonal Metals

Owing to its ability to incorporate Schmid’s law at each integration point, crystal plasticity has proven a powerful tool to simulate and predict the slip behavior at the grain level and the ensuing heterogeneous stress/strain localization and texture evolution at the macroscopic level. Unfortunately, notwithstanding substantial efforts during the last three decades, this remarkable capability has not been replicated for materials where twinning becomes a noticeable deformation mechanism, namely in the case of low-stacking fault energy cubic, orthorhombic, and hexagonal close-packed structures. The culprit lies in the widely adopted unphysical pseudo-slip approach for capturing twin formation. While the slip is diffuse, twinning is a localized event that occurs as a drastic burst of a confined number of partial twinning dislocations establishing an interface that pursues growth through a thread of perfect twinning dislocations in the sense of bicrystallography. Moreover, at earlier stages, twin nucleation may require atomic diffusion (Shuffling) and faceting, generally demanding higher stress levels not necessarily on the twin shear plane, while triaxiality at adequate sites might be needed or preferred such as lower grain boundary misorientations or other twin boundaries. Identifying a mathematical framework in the constitutive equations for capturing these twin formation sensitivities has been a daunting challenge for crystal plasticity modelers, which has stalled ameliorating the design of key hexagonal materials for futuristic climate change-related industries. This paper reviews existing approaches to incorporating twinning in crystal plasticity models, discusses their capabilities, addresses their limitations, and suggests prospective views to fill gaps. The incorporation of a new physics-based twin nucleation criterion in crystal plasticity models holds groundbreaking potential for substantial progress in the field of computational material science.

Large rotations of the grain-scale stress tensor during yielding set the stage for failure

The stress-state within individual grains in a polycrystal determine the fate of the aggregate including mechanical failure. By tracking the evolution of the stress tensor throughout the elastoplastic transition, large rotations of the stressstate, which have long been theorized to occur, are observed experimentally for the first time. These stress rotations (∼15°) are more than an order of magnitude larger than the concomitant crystallographic lattice reorientations (∼0.9°) well-known to occur during metal plasticity. Furthermore, these rotations are accompanied by a decrease in stress triaxiality within certain grains, promote strain softening, and set the stage for failure at an early stage of deformation. These results provide a completely new perspective through which to contemplate the question of “hot-spots” responsible for failure of high-performance structural materials.

Interface Characteristics and Bonding Performance of the Corrugated Mg/Al Clad Plate.

In this paper, a corrugated Mg/Al clad plate was successfully manufactured by an upper corrugated roller and a lower flat roller at 400 °C rolling temperature and 35% reduction ratio. Interface bonding performance of the corrugated Mg/Al clad plate was studied by tensile-shear test. The finite element method was used to simulate the corrugated rolling process. Experiment results revealed that the Mg/Al clad plate fabricated by corrugated roller had a tight bonding interface, no crack, and no intermetallic compounds. The transverse tensile-shear strength at the trough position reached 31.22 MPa, and the tensile-shear strength at the peak position was 17.61 MPa. It can be found that the stress and strain of interface metal at the trough position were the largest through numerical simulation results. Two cross-shear zones can be formed in the rolling deformation zone of the corrugated Mg/Al clad plate, which can accelerate the metal plastic flow and promote interface close bonding.

Effects of pin morphology on the interface defects of the FSWed lap joints of 2A12 aluminum alloy

The current work aims to study the effects of stirring pin morphology on the FSWed lap joints defects and mechanical properties. The 2A12 aluminum alloy friction stir welding lap joints were obtained using two shapes and three thread lengths of stirring pins by experiments. Besides the interface defects forming mechanism were studied by joints plastic metal flow numerical simulation. The results show that the conical pin can lead to uniform and continuous plastic metal velocity field which forms a Hook defect with sharp end, smaller deflection angle (minimum 8°) and larger size (maximum 0.18mm). It also will lead to a larger failure load (maximum is 9.5kN), and the fracture position easily occurs at the Advancing side (AS) of lower plate. The three section pin has a periodic shearing effect causing velocity difference between the arc edge and cutting section of the pin which forms a Hook defect with thicker end, larger deflection angle (maximum 42°) and smaller size (minimum 0.06mm). It also causes discontinuous wavy debris forms in the AS. The three section pin leads to a lower failure load (maximum is just 7.6kN), and the fracture position turns to occur at the lap interface. The increase of the thread length can promote the exchange of plastic metal in the thickness direction and interface materials flow velocity. So the angle (from 20°to 150°) and size (from 0.1mm to 0.6mm) of Hook increases but the height of Cold Lap reduces (increasing the effective sheet thickness of retreating side from 0.69mm to 0.95mm). In addition, the increase of the thread length can make the periodic shear effect of three section pin gradually weak. It is also found that the fracture position is closely related to the shape and the thread length of pins. When using conical pin, the fracture occurs at AS of lower plate or Retreating Side of Nugget Zone (NZ-RS) of upper plate; When using three section pin, the fracture occurs at the bonding interface. And with the increase of the thread length, the fracture position changes from the bonding interface to the NZ-RS of upper plate, and finally to the AS of lower plate.

Effects of segmented thermal-vibration stress relief process on residual stresses, mechanical properties and microstructures of large 2219 Al alloy rings

Large 2219 Al-Cu alloy transition rings are extensively employed in propellant tanks of heavy launch vehicles. These rings have a diameter exceeding 5 m or even reaching 10 m, with a less than 2% thickness-to-radius ratio, and low stiffness which can cause machining deformation due to the residual stress. Thus, residual stress relief of these rings is necessary in their extreme manufacture. A novel effective method is thermal-vibration stress relief (TVSR), which integrates the conventional thermal stress relief (TSR) and vibratory stress relief (VSR); however, the existing TVSR equipment cannot meet the requirements of large rings, and the underlying mechanisms of TVSR remain unclear and a quantitative interpretation is still lacking. Therefore, a segmented TVSR (STVSR) process suitable for large rings was proposed and the corresponding experiment was carried out with a self-made STVSR experiment platform. Then this study investigated the evolution and distribution laws of the residual stresses, tensile properties, Vickers hardness, dislocations, precipitated phases and metallography during STVSR. Based on the experimental results, multi-scale mechanics theory and strengthening mechanisms were applied to quantitatively reveal the underlying mechanisms of residual stress relief by STVSR. The results showed that the circumferential and axial residual stress relief rates can reach 44.43% and 45.14% after STVSR, respectively. The residual stress relief after STVSR is attributed to the dynamic evolution of dislocations and precipitated phases in the material. The improvement of mechanical properties mainly depends on the precipitated phases and is also affected by the residual stress. The findings confirm the significant effects of STVSR on metal plasticity and provide valuable insight into the underlying mechanisms of TVSR.

Shear induced deformation twinning evolution in thermoelectric InSb

Twin boundary (TB) engineering has been widely applied to enhance the strength and plasticity of metals and alloys, but is rarely adopted in thermoelectric (TE) semiconductors. Our previous first-principles results showed that nanotwins can strengthen TE Indium Antimony (InSb) through In–Sb covalent bond rearrangement at the TBs. Herein, we further show that shear-induced deformation twinning enhances plasticity of InSb. We demonstrate this by employing large-scale molecular dynamics (MD) to follow the shear stress response of flawless single-crystal InSb along various slip systems. We observed that the maximum shear strain for the (111)[11bar 2] slip system can be up to 0.85 due to shear-induced deformation twinning. We attribute this deformation twinning to the “catching bond” involving breaking and re-formation of In–Sb bond in InSb. This finding opens up a strategy to increase the plasticity of TE InSb by deformation twinning, which is expected to be implemented in other isotypic III–V semiconductors with zinc blende structure.

Theoretical investigation of the 70.5[formula omitted] mixed dislocations in body-centered cubic transition metals

The low-temperature plasticity of body-centered cubic (bcc) metals is governed by 12〈111〉 screw dislocations due to their compact, non-planar core. It has been proposed that 70.5° mixed (M111) dislocations may also exhibit special core structures and comparably large Peierls stresses, but the theoretical and experimental evidence is still incomplete. In this work, we present a detailed comparative study of the M111 dislocation in five bcc transition metals on the basis of atomistic simulations. We employ density functional theory and semi-empirical interatomic potentials to investigate both the core structure and the Peierls barrier of the M111 dislocation. Our calculations demonstrate that reliable prediction of M111 properties presents not only a very stringent test for the reliability of interatomic potentials but is also challenging for first-principles calculations for which careful convergence studies are required. Our study reveals that the Peierls barrier and stress vary significantly for different bcc transition metals. Sizable barriers are found for W and Mo while for Nb, Ta and Fe the barrier is comparably small. Our predictions are consistent with internal friction measurements and provide new insights into the plasticity of bcc metals.