Metal Plasticity Research Articles

The Influence of Tool Shape on Plastic Metal Flow, Microstructure and Properties of Friction Stir Welded 2024 Aluminum Alloy Joints

In this paper, the effect of different shapes of tool pin on the plastic flow of 2024-T6 aluminum alloy during friction stir welding was studied. In order to observe the plastic flow of materials more clearly, we chose the method of friction stir welding of dissimilar materials, considering the different corrosive characteristics of aluminum alloys made of different materials when exposed to the same corrosive liquid. By studying and comparing the temperature field, macro and microstructure, microhardness and tensile properties of welded joints, the results indicated that the metal in the weld nugget zone (WNZ) mainly came from the base metal of the advancing side, the thread being the driving force of the downward movement of the FSW plastic metal. The deep groove thread tool pin had the strongest ability to drive the metal downward. The conical cam thread tool pin had the strongest stirring effect on materials and the best metal fluidity. The macroscopic morphology, microstructure, mechanical properties and fracture morphology of different joints were analyzed, and the results showed that all joints could form an excellent union, with an onion ring pattern appearing in cross-section. The minimum grain size of the WNZ formed by the conical cam thread stirring head was 7~12 μm; the hardness was least at the junction of the heat affected zone (HAZ) and the thermo-mechanically affected zone (TMAZ). However, the hardness of the weld formed by the conical cam thread at this point was higher than that of other stirring heads; the tensile strength of all joints was more than 80% of the BM, and the maximum tensile strength of the joint welded by the conical cam thread tool pin was 364.27 MPa, accounting for 86.73% of the base metal (BM). The elongation after break was 14.95%. Tensile fracture morphology analysis showed that all joints were fractured by plastic fracture.

Мultifunctional Inhibitors of "INCORGAZ" and "AMDOR" Series against Hydrosulfide and Carbon Dioxide Corrosion of Steel

Protective efficiency of inhibitors of the "INCORGAZ" and "AMDOR" series is analyzed in relation to carbon steel corrosion in model stratum waters of oil and gas fields saturated with hydrogen sulfide and carbon dioxide separately and together. The bactericidal properties of the inhibitors with respect to sulfate-reducing bacteria, reduction of steel hydrogenation, influence on the preservation of metal plastic properties are evaluated. The contributions of the inhibitor and the shielding film of corrosion products to the total protective effect are considered. The inhibitors under study provide a decrease in the corrosion rate of carbon steel to a value much less than 0.05 mm/year, according to the data of 240-hour exposure in hydrogen sulfide environments.

Synchronous involvement of topology and microstructure to design additively manufactured lattice structures

This article presents a methodical approach to optimize microstructure (e.g., the crystallographic texture) and topology (e.g., unit cell and struts) concurrently to improve the mechanical properties of additively manufactured metallic lattice structures (AMLS), i.e., yield strength and plastic flow stress. Full-field elasto-viscoplastic Fast Fourier Transform (EVP-FFT) crystal plasticity (CP) simulations are employed to determine the optimal microstructure. The CP model parameters were calibrated to measured macroscopic stress–strain response and microstructural data for polycrystalline samples of additively manufactured (AM) Inconel 718 with solution treated and aged (STA) microstructure. Since the crystallographic orientation of the constituent single-crystal grains with respect to the loading direction has a significant impact on the mechanical behavior of the material, stress projection factor analysis was used to determine four candidate textures to explore in for a given unit cell topology. Full-field crystal plasticity simulations were used to determine macroscale yield surface parameters for each of the considered textures, thereby enabling macroscale lattice unit cell simulations that account for the underlying microstructure. The calibrated microstructure-dependent yield surfaces are used to investigate the effect of different microstructures on the mechanical response of different LS topologies with the same relative density. The results show that in a texture with <111> crystallographic direction, parallel to the loading direction, the tensile and compressive yield strength are 20% and 58% larger, respectively compared to the AM STA IN718 texture. Furthermore, when this texture is used in conjunction with the Rhoctan topology, the results demonstrate 50% improvement in both the yield strength and modulus of elasticity relative to previously optimized AMLS designs that did not directly account for microstructure. This simultaneous consideration of microstructure and topology during optimization, thus, significantly enhances the structural integrity of the AMLS.

Obtaining a lower estimate of the fatigue limit of metals by a simplified quantitative thermometric approach in a low-cost one-specimen test

The plasticity of metals leads to an internal heat generation during fatigue testing. Therefore, qualitative and quantitative thermography are widely accepted for assessing fatigue damage. The onset of significant heat generation and temperature rise is usually attributed to the fatigue limit of a material. Now, a 40-year-old but just rarely used measurement technique using NTC thermistors is used to reveal the temperature profile in a specimen. A direct comparison with modern thermographic methods exposes the much higher resolution of this simple and inexpensive method. This method provides the much desired ability to assess fatigue limit rapidly and efficiently with only one specimen, even for homogeneous materials and materials conditions with high thermal conductivity or even for small specimen volumes, in a valid and very reliable manner.

Effect of Arc Length on Oxygen Content and Mechanical Properties of Weld Metal during Pulsed GMAW

Pulsed gas metal arc weld (GMAW) was widely used for the advantages of controllable heat input, all-position welding, and no spatter. In order to obtain an ideal welding process, the stability of the arc length was studied in many researches, but the influence of arc length on the properties of weld metal was ignored. In this paper, the effect of arc length on oxygen content and mechanical properties of weld metal during pulsed GMAW was studied. Q690 high strength steel was selected as the base metal, and ER69-G solid wire, with a diameter of 1.2 mm, was used as the electrode wire. Additionally, the shielding gas and the wire feed rate were 82% Ar + 18% CO2 and 4 m/min, respectively. The results showed that as the arc length raised from 2.9 mm to 9.2 mm, the oxidation reacted more completely in the droplet transfer zone, and the oxygen content of the weld metal increased significantly. The tensile strength of the weld metal reduced but the −40 °C impact energy heightened. Due to the longer arc, the proportion of acicular ferrite (AF) in the microstructure decreased, but the proportion of lath bainite (LB) and granular bainite (GB) decreased. The higher oxygen content of weld metal was useful for the formation of inclusions, which promoted the nucleation of acicular ferrite and dimples, contributing to the growth of plasticity and toughness of weld metal.

Assessment of the drinker type on water intake and toy type on behaviour of nursery piglets

This study was conducted to assess the effect of two types of drinkers on water intake (WI) and two types of toys on behavioural observations of piglets in the nursery phase. A total of 72 crossbred entire male piglets (Landrace × Large White, Agroceres♂ and DanBred♀), weaned at 21 days of age, with an average initial body weight (AIBW) of 6.75 ± 0.19 kg were used. Two statistical models were fitted for WI. In model I, animals were distributed in a completely randomized design (CRD) with a split-plot in time, composed of six treatments (2 types of drinkers × 3 experimental phases), eight replications (days of sampling), and 36 animals/experimental unit (EU), without using AIBW as a covariate. In model II, animals were distributed in a CRD with two treatments (fixed or pendular nipple drinkers), eight replications (days of sampling) and 36 animals/EU, with use of AIBW as a covariate. For assessment of behavioural observations, the model was adjusted in a randomized block design, consisting of four treatments [two types of toys (metal chain and plastic bottle) × two daytime periods (morning and afternoon)], nine replications and three blocks constituted in time (days), totalling four pigs/EU. The results indicated an effect on animal daily WI in the starter phase in model I (p &lt; 0.000) and II (p = 0.006). There was an effect (p ≤ 0.05) of toy type for behavioural observations, in which pigs showed a greater proportion of fighting and belly nosing when they had the bottle toy. However, animals spent more time (p ≤ 0.05) eating, drinking water, overlapping, and playing with the toy when they had access to the chain toy. There was an increase (p ≤ 0.05) in sleeping behaviour in the morning period, as well as greater (p ≤ 0.05) behavioural activity in the afternoon period. In conclusion, WI of nursery piglets was positively influenced by growth phase, and the fixed drinker stimulated greater WI in piglets in the starter phase. In addition, the metal chain, as an environmental enrichment, promoted improvements in feeding behaviour and WI, reducing fighting events, and the afternoon period had increased behavioural observations overall.

Molecular dynamics studies of 〈a〉 -type screw dislocation core structure polymorphism in titanium

The atomic scale computation of dislocation core structures has become an essential tool in the development of models for the plasticity of metals. Competing dislocation core structures are often analyzed at $T=0$ K (with $T$ the temperature), and the dislocation core structure with the lowest energy is assumed to be the structure dictating the dynamics of the individual dislocation at finite temperatures. It is shown here that, for some hexagonal-close-packed (HCP) metals, this approach may be too simplistic. As a prototypical example, $\ensuremath{\langle}a\ensuremath{\rangle}$-type screw dislocations within HCP Ti modeled using an empirical interatomic potential are considered. It is shown using molecular dynamics simulations that, at room temperature and above, the core structure of the dislocation is remarkably complex and variable. The implications of this complexity for the dynamics of the dislocations are discussed.

Sweep-tracing algorithm: in silico slip crystallography and tension-compression asymmetry in BCC metals

Direct Molecular Dynamics (MD) simulations are being increasingly employed to model dislocation-mediated crystal plasticity with atomic resolution. Thanks to the dislocation extraction algorithm (DXA), dislocation lines can be now accurately detected and positioned in space and their Burgers vector unambiguously identified in silico, while the simulation is being performed. However, DXA extracts static snapshots of dislocation configurations that by themselves present no information on dislocation motion. Referred to as a sweep-tracing algorithm (STA), here we introduce a practical computational method to observe dislocation motion and to accurately quantify its important characteristics such as preferential slip planes (slip crystallography). STA reconnects pairs of successive snapshots extracted by DXA and computes elementary slip facets thus precisely tracing the motion of dislocation segments from one snapshot to the next. As a testbed for our new method, we apply STA to the analysis of dislocation motion in large-scale MD simulations of single crystal plasticity in BCC metals. We observe that, when the crystal is subjected to uniaxial deformation along its [001] axis, dislocation slip predominantly occurs on the {112} maximum resolved shear stress plane under tension, while in compression slip is non-crystallographic (pencil) resulting in asymmetric mechanical response. The marked contrast in the observed slip crystallography is attributed to the twinning/anti-twinning asymmetry of shears in the {112} planes relatively favoring dislocation motion in the twinning sense while hindering dislocations from moving in the anti-twinning directions.

Non-destructive evaluation of metal plasticity using a single impact microindentation

We present a non-destructive method for determination the metal plasticity using dynamic microindentation with a spherical indenter. Based on the impact loading curve, expressions for its quantitative characterization are derived. Theoretical results are supported by multiple experiments with 10 metals and alloys. The values of the plasticity parameter calculated from the depths of the indenter penetration are close to the values obtained from the energy parameters of the indentation. We have analyzed the influence of the strain and the strain rate on the value of the plasticity parameter as well as the dependence of the dynamic plasticity on the change of the initial impact velocity. Obtained results are important for the express analysis of the plastic properties of metals in out-of-lab conditions.

Analysis of operational factors affecting the serviceability of seaport hoisting and transporting equipment

Metal structures of seaport equipment are operated under high-cycle loading, and this peculiarity is primarily taken into account in well-known approaches to their service life assessment. These approaches consider the as-received state of metal and regulate its mechanical properties. However, such procedures are unsuitable for substantiating the safe excessive operation of steel structures, since they don’t take into account the degradation of the mechanical properties of metal during its long-term operation under intense cyclic loading. Two crucial factors in the serviceability loss of hoisting and transport equipment during their long-term operation have been analysed. The former is intensive cyclic loading which promotes the development of fatigue damage and initiates the growth of fatigue cracks. Another one lies in the detrimental effect of the marine environment in the operational degradation of port metal structures since the marine atmosphere could be not only corrosive but also has hydrogenating capabilities. Hydrogenation, in turn, contributes to the in-service loss in metal plasticity and, from the other side, accelerates fracture by the hydrogen embrittlement mechanism.

Simulation of Crystal Plasticity in Irradiated Metals: A Case Study on Zircaloy-4

Simulation of Crystal Plasticity in Irradiated Metals: A Case Study on Zircaloy-4

3D printed planetary gearbox for robotic arm joints

3D printing technology has become very popular in last several years as a cheap way how to make different parts. 3D printing is as a perfect tool for prototyping of various, mostly difficult, structures which is the reason why it is more and more use in mechanical design. This article is focused on assessment if 3D printing technology can be used for creating light, durable and cheap variation of classic metal or moulded plastic gearboxes for electric motors which can be used for low cost robotic arms. For this purpose was in CAD software designed a small two-stage planetary gearbox with identical stages. All parts of gearbox were printed by FDM 3D printer with most common printing material PLA. The gearbox has been tested on noise, durability, resistance and maximum load on lever to find out where can be potential of 3D printed gearboxes.

Investigation into movable dislocation evolution feature and strengthening effect for metal twin Al from atomic perspective

It is an universal phenomenon that the dislocations are produced in metal plastic deformation, which will has a potential value in fundamental research field for metal strengthening and toughening if its evolution characteristics and laws are investigated. Therefore, this behavior of movable dislocation for metal Al is studied by atomic simulation, and the microscopic mechanism of metal strengthening and toughening are also revealed through studying the interaction between movable dislocation induced by nano-indentation and twin boundary. Furthermore, the movable dislocation features, and dislocation density, and hardness, and adhesive effect are analyzed, and the comparison between the single boundary height and the multilayer twin boundary height is conducted. It is found that the plastic deformation of aluminum mental can be dominant by coordinating the amorphous generation and hexagonal close-packed structure under high speed deformation. In the nano-indentation process, the twin boundary has two obvious effects on movable dislocation of moving changes: one is to hinder the dislocation from migrating, the other is to induce dislocation to produce a cell, which result in the dislocation entanglement and generation of cross slip, it is also the main reason why the metal has excellent mechanical properties of strengthening and toughening features. These results demonstrate that the local non-contact region on the surface of Al substrate can induce atomic mismatch spots to appear during loading, and when the distance between the twin boundary and the upper surface of the substrate decreases, the effects of dislocation winding and dislocation slip become more obvious, and the anti-adhesion effect also decreases. In addition, the twin boundary is treated as the propagation of plastic ring source in the dislocation emission process when substrate is continuously loaded. These results provide an important theoretical source for improving metal strengthening and toughening effect.

Experimental Study on the Erosion of Pipelines under Different Load Conditions

The influence of the material stress state induced by internal and external forces on the erosion rate of pipelines has rarely been investigated in the literature. In order to fill this gap, using a tensile tester machine, a two–phase gas–solid particles jet erosion test was carried out considering a 316L stainless steel under different tensile stresses and different erosion angles. The results show that: 1) In the elastic range, with the increase of stress, the erosion rate manifests a rising trend; 2) In the metal plastic range, the increase of stress leads to a decrease of the erosion rate; 3) The erosion rate at a small erosion angle is more sensitive to the increment of stress. The present research demonstrates that the combined effect of erosion and material internal stress can contribute to determine the effective resistance of the vulnerable parts of piping systems (such as elbows or similar components).

Development of methodology and technical equipment for study of metal plastic flow in processing processes. Part 1. Design and manufacture of special bench-type milling CNc mashine for study of plastic flow of metal

Experimental evaluation of the metal plastic flow in the mechanical processing processes is an important task both to substantiate the correctness of the solutions obtained by finite element modeling, and to formulate reasonable recommendations for establishing modeling boundary and initial conditions. One of the effective methods for estimating of the material particles movement during various processes is the particle image velocimetry method (PIV). To implement this method for the processes of cutting and deep rolling, it is necessary to ensure high requirements for experimental equipment. Analysis of the existing CNC machines characteristics has shown the required characteristics are not fully provided. Therefore, a special CNC machine was developed and manufactured for experimental research, providing high drive power, rigidity, vibration resistance and accuracy.

Deformation behavior and microstructure in the low-frequency vibration upsetting of titanium alloy

Low-frequency vibration-assisted metal plastic forming is a novel promising technology, adopting a high-pressure-capability device compared to the ultrasonic vibration system. This work focuses on the low-frequency vibration assisted upsetting (LFVAU) process of Ti45Nb, to reduce the flow stress and crack initialization in the cold deformation of titanium alloy. The results show that the flow stress is significantly reduced by applying the vibration, and this stress reduction phenomenon becomes more obvious with larger frequency and amplitude. The vibration promotes the dislocation movement and grain rotation, resulting in dislocation annihilation in the shear band but dislocation concentration and low-angle grain boundary formation near the grain boundary in the large deformation zone. Therefore, more homogenous deformation occurred in LFVAU compared to the conventional quasi static upset (QUS) specimen, though the grain size is similar in the cylinders after QSU and LFVAU. Based on the above research results, the application of low-frequency vibration assisted processing technology in the field of aerospace will help to improve the plastic deformation quality, especially the riveting quality for Ti45Nb.

Plastic Structure Formation of the 1570R Alloy (System Al-Mg-Sc) using the Physical and Mathematical Theory of Metal Plasticity

Plastic Structure Formation of the 1570R Alloy (System Al-Mg-Sc) using the Physical and Mathematical Theory of Metal Plasticity

FTMP場の理論に基づく多結晶塑性の考え方

A critical feature of polycrystalline metal plasticity has been identified to be the growing “stress/strain fluctuations” that drive evolutionary aspects of the field in the scale, in contrast to the dislocation substructuring at intra-granular scale. The next step for us to examine would be how they are interacted and would further affect the system responses such as the Bauschinger behavior. The present article overviews the progress that the authors has promoted hitherto.

On use of interlocking structures in plastic metal working

An effective method to increase the rigidity and reliability of materials and structures by choosing a rational geometry of structural elements and conditions for their interaction with each other is proposed. This method, associated with interlocking structures, has found application in the creation of new technical solutions in metallurgy.

Some features of soil cultivation with a cutting wedge

Currently existing soil cutting models do not explain all available experimental results. When modeling the process of cutting soils, the models developed for cutting metals were taken as a basis. But the automatic transfer of the principles of cutting metals to the theory of cutting soil without sufficient grounds leads to contradictions and errors. Soil cutting has its own characteristics that do not occur when cutting metals and which must be taken into account when modeling the destruction process during cutting. When cutting brittle materials, as well as when cutting soils and soils, a number of phenomena are observed that are not present when cutting plastic materials, for example, the formation of advanced cracks in front of the cutting wedge. The purpose of the study is to establish the features of soil cultivation with a cutting wedge that are not typical for metal processing, but which take place during mechanical tillage and which must be taken into account when modeling the processes of cutting mechanics. On the basis of the comparative analysis, a significant difference between the geometry of the cutting part of the tillage wedge and the geometry of the wedge for processing plastic metal materials was revealed. The loading model of the cutting part of the tillage wedge is obtained. It is shown that during the operation of the tillage wedge the angle of action of the cutting force is positive. When modeling the processes of soil cutting mechanics, in order to obtain a correct model of the cutting process, it is necessary to take into account this fact: the angle of action of the cutting force is positive. Loading of the material being machined with a cutting wedge according to the scheme, when the angle of action of the cutting force is positive, is the most optimal in terms of the energy intensity of the cutting process compared to others.