Mechanical Behavior Of Metals Research Articles

Significant mechanical softening of copper under coupled electric and magnetic stimuli

The mechanical reliability of metallic components is vital for the stable operation of electrical equipment, especially for those used in ultra-high voltage transmission and electromagnetic launching, where metallic materials inevitably suffer from high-density current and strong magnetic field. However, little has been known about the mechanical behavior of metals under the electric-magnetic coupling stimuli. Here, by performing quantitative electromechanical tests under the built-in magnetic field inside transmission electron microscope, we found that copper, one of most commonly used conductive metals, can be significantly softened by the coupled electrical-magnetic stimuli, manifested as notable yield strength drop by five-times and obvious creep deformation at room temperature. A plausible mechanism behind the unusual softening, local-Lorentz-force-assisted dislocations depinning, has been proposed. Our results shed new light on understanding the deformation-induced failure of metals served in electromagnetic environments, and also inspire a new mechanical processing way for reshaping metals at much lower loads and temperatures.

Сочетание криогенной деформации и электроимпульсной обработки как способ получения ультрамелкозернистых металлов

The data of a comparative analysis of the structure and hardness of pure metals with a face-centered cubic lattice – aluminum, nickel and copper, subjected to complex thermomechanical treatment (TMT), including isothermal cryogenic rolling at liquid nitrogen temperature and subsequent high-density electropulse treatment (EPT) were presented. The main stages, features and advantages of TMT, which first ensure strong work hardening of the processed material due to deformation at low temperatures and then its ultra-fast contact electropulse heating up to a specified temperature, were considered. A multi-level analysis of the metals structure evolution due to TMT was carried out using modern methods of scanning electron microscopy and X-ray diffractometry, recording a wide range of its linear and angular parameters. The kinetics and nature of the processes of the metals structure evolution under cryogenic rolling and EPT, their driving forces and controlling factors, as well as general patterns and temperature intervals of activation of the deformation structure recovery and recrystallization influenced by an electric pulse are identified and discussed. Based on the results of the analysis of the structural and mechanical behaviour of metals, it was concluded that the combination of severe plastic cryogenic deformation and a single-step treatment with ultrashort alternating current pulses is an effective way to obtain semi-finished products with controlled parameters of their structure and properties, including high-strength ultrafine-grain rolled products. At that the phenomenology and nature of the strengthening/softening of metals during cryogenic rolling and subsequent electropulsing are similar to those observed under cold rolling and furnace annealing.

Hexagonal close-packed (hcp) alloys under dynamic impacts

Predictions on the mechanical behavior of metals and alloys with a hexagonal close-packed (HCP) lattice under dynamic influences in a wide range of temperatures are in demand for solving a wide range of applied problems. This article presents new results of numerical simulation showing the general similarity of the mechanical behavior of HCP titanium, zirconium, hafnium, and beryllium alloys under dynamic loadings in a wide range of temperatures. These alloys belong to the important isomechanical subgroup of HCP alloys. A model for numerical simulation of mechanical behavior of HCP alloys under dynamic loadings in a wide temperature range was proposed. The model takes into account the change in contributions to the flow stress from the mechanisms of twinning and dislocation slip in the considered subgroup of HCP alloys. A kinetic damage model was adopted to describe the damage evolution under complex stress conditions and under dynamic loading. Thus, it was possible to increase the accuracy of predicting the dynamic fracture under tensile loads including the spall fracture.

Mechanical properties of metal and polymeric viscoelastic materials and their applications

Nowadays, With the wide application of metals and polymeric materials, how to describe the property of Viscoelastic material and how to apply them in engineering has become more and more critical. Due to the lack of insight into the mechanical properties of viscoelastic materials, many scholars have done a lot of experiments in studying the behavior of viscoelastic materials. Axial tensile tests were conducted on specimens to derive different mechanical behaviors of metals, polymers, and other materials at different temperatures and loading rates. Metal can generally be divided into elastic and plastic parts, while polymeric materials have the phases of the linear elastic region, drawing region, and oriented molecular strength region. This paper also shows a test conducted by Argon, Ali S., and M. I. Bessonov of four different kinds of polymers at different circumstances of temperature. After that, the paper shows the application of viscoelastic materials as CLD in damping and some engineering problems caused by the mechanical properties of viscoelastic materials. Currently, research on viscoelasticity should mainly focus on the application of Finite Element Methods and the acquisition of more experimental data to establish a complete theoretical system.

A state-of-the-art review on all constitutive models in simulating mechanical behaviour of metals and alloys

A state-of-the-art review on all constitutive models in simulating mechanical behaviour of metals and alloys

A state-of-the-art review on all constitutive models in simulating mechanical behaviour of metals and alloys

A state-of-the-art review on all constitutive models in simulating mechanical behaviour of metals and alloys

Pseudoelasticity in twinned α-Fe nanowires under bending

The pre-existing twin boundaries play an important role in the mechanical behaviors of metals. In the present work, we studied the bending deformation of [100]-oriented α-Fe nanowires seeded with 〈111〉/{112} twin boundaries using atomistic simulations. Bending behaviors along two different orientations were investigated. The initially flat twin boundaries become curved with a high density of 1/6 〈111〉/{112} partial dislocations under bending when the neutral plane intersects with twin plane along [01-1] direction, whereas could transform to the nonconventional {110} interfaces under bending when the neutral plane intersects with twin plane along [111] direction. The bent α-Fe nanowires could recover to the original state upon unloading, leading to a unique pseudoelasticity. The driving force for shape recovery primarily arises from the high interfacial energy, i.e. curved {112} twin boundaries or the transformed {110} interfaces. We further characterized the recoverability by the ratio η of the nanowire size (external length scale) to twin boundary spacing (internal length scale). This η-dependent recoverability matches well with the experimental data at large length scale. The present work may help understand the unique mechanical properties associated with twin boundaries in metals.

Effect of scanning strategies on the microstructure and mechanical behavior of 316L stainless steel fabricated by selective laser melting

Five scanning strategies were applied for relating the microstructural and crystallographic morphology to the mechanical properties of 316L stainless steel fabricated by selective laser melting (SLM). The results indicate that scanning strategies have a significant effect on the microstructure, grain growth, grain size and therefore mechanical properties of SLM-built 316L stainless steel. Applying the scanning strategy with the rotation angle between successive layers breaks the columnar growth of grains and fine equiaxial grains are formed, leading to an improvement of tensile strength and good ductility of SLM-built samples. Moreover, the microhardness is improved by applying the scanning strategy with a rectangular pattern. This work demonstrates the scanning strategy during SLM process acts as an essential factor affecting energy input, and therefore tailors the meso-/micro-scale structure and mechanical behavior of metals.

Influence of Thermal Treatment on SCC and HE Susceptibility of Supermartensitic Stainless Steel 16Cr5NiMo.

A 16Cr5NiMo supermartensitic stainless steel was subjected to different tempering treatments and analyzed by means of permeation tests and slow strain rate tests to investigate the effect of different amounts of retained austenite on its hydrogen embrittlement susceptibility. The 16Cr5NiMo steel class is characterized by a very low carbon content. It is the new variant of 13Cr4Ni. These steels are used in many applications, for example, compressors for sour environments, offshore piping, naval propellers, aircraft components and subsea applications. The typical microstructure is a soft-tempered martensite very close to a body-centered cubic, with a retained austenite fraction and limited δ ferrite phase. Supermartensitic stainless steels have high mechanical properties, together with good weldability and corrosion resistance. The amount of retained austenite is useful to increase low temperature toughness and stress corrosion cracking resistance. Experimental techniques allowed us to evaluate diffusion coefficients and the mechanical behaviour of metals in stress corrosion cracking (SCC) conditions.

Quasicontinuum Simulation of the Effect of Lotus-Type Nanocavity on the Onset Plasticity of Single Crystal Al during Nanoindentation.

Stress concentration around nanosized defects such as cavities always leads to plastic deformation and failure of solids. We investigate the effects of depth, size, and shape of a lotus-type nanocavity on onset plasticity of single crystal Al during nanoindentation on a (001) surface using a quasicontinuum method. The results show that the presence of a nanocavity can greatly affect the contact stiffness (Sc) and yield stress (σy) of the matrix during nanoindentation. For a circular cavity, the Sc and σy gradually increase with the cavity depth. A critical depth can be identified, over which the Sc and σy are insensitive to the cavity depth and it is firstly observed that the nucleated dislocations extend into the matrix and form a y-shaped structure. Moreover, the critical depth varies approximately linearly with the indenter size, regarding the same cavity. The Sc almost linearly decreases with the cavity diameter, while the σy is slightly affected. For an ellipsoidal cavity, the Sc and σy increase with the aspect ratio (AR), while they are less affected when the AR is over 1. Our results shed light in the mechanical behavior of metals with cavities and could also be helpful in designing porous materials and structures.

The Application of Phase Field Method in Microstructure Evolution Simulation

The physical properties and mechanical behaviour of metals are determined by their microstructure frequently. The microstructure is referred to the size, shape and spatial arrangement of phases, grains, etc. These microstructure features have the mesoscopic length scale. How to obtain the desired microstructure is one main task of metal alloy design. However, it is difficult because the microstructure evolution is influenced by the chemical driving force during phase transformation, the composition of the alloy, etc. With the development of computing power and computer modelling, the computational material science is playing an important role in the microstructure design. Especially the kinetic phase field method is a powerful tool which is fast developed and widely used in these years. The phase field method is a phenomenological approach based on classical thermodynamic and kinetic theories. It describes a microstructure by using field variables. In this paper, the basic principle and application of this method are presented.

Temperature analysis during the drawing of an aluminum cylindrical cup

Both the plastic deformation and the friction forces generate heat in sheet metal forming processes. This yields a temperature rise on the blank and tools, which is mainly dictated by the blank properties and the press speed. Although modest values of temperature rise yield negligible changes in the mechanical behavior of metals, the lubricant properties are rather influenced by the temperature. Thus, the deep drawing of an aluminum cylindrical cup was selected to evaluate, experimentally and numerically, the temperature variation of the forming tools and blank at room temperature. Different values of punch speed are compared to evaluate the impact of the heat losses to the environment. The experimental results show that the temperature rise on the die surface is higher than 9°C when the punch speed is 10 mm/s. The temperature is underestimated by the finite element model due to the isothermal conditions imposed on the forming tools.

Improving ductility by increasing fraction of interfacial zone in low C steel/304 SS laminates

Interfaces have been found to play an important role in mechanical behaviors of metals and alloys with heterogeneous microstructures. In present study, low C steel/304 stainless steel (SS) laminates with varying fractions of interfacial zone were fabricated by hot-rolled bonding, annealing and pickling, then cold rolling, subsequent annealing followed immediately by water quenching to study the effect of fraction of interfacial zone on the tensile properties. Heterogeneous distributions in chemical composition, grain size, phase and hardness were observed in the interfacial zone. The yield strength was observed to be constant with varying fractions of interfacial zone, while the ultimate strength and the uniform elongation were found to increase with increasing fraction of interfacial zone. High density of geometrically necessary dislocations (GNDs) were found to distribute in the interfacial zone and show a peak at the interface due to the mechanical incompatibility across the interface. Moreover, the density of GNDs was found to increase with increasing tensile strain in the interfacial zone. Back stress hardening was found to play an important role in the laminates, especially at the elasto-plastic transition stage. Higher fraction of interfacial zone can induce stronger back stress hardening and higher density of GNDs in the samples, thus resulting in better tensile ductility.

Mechanical Behavior of Metal under Hydrostatic Pressure and Low Temperature

The current work describes the behavior of metal under hydrostatic pressure and low temperature using finite element concept. This study was carried out in three stages: modelling, analysis and post processing. Structural steel and aluminum are tested at 600 bar pressure and 4°C temperature. Solid model of cylindrical shape having internal diameter 420 mm and thickness 25 mm was created and same was investigated for stress analysis using ANSYS 17.2 APDL emphasizing on hydrostatic behavior. Failure criterion is based on maximum stress to determine the onset of damage in material. In post processing phase, the material was checked for deformation and equivalent Von-Mises stresses developed around the material. The objective of this present paper is of two fold. Firstly the investigation of metal under high pressure through stress analysis is carried out followed by metallographic studies. The stress analysis results suggest that metals like steel which has BCC structure shows the remarkable decrease in ductility over the range of temperature. The maximum Von Mises stresses that the material can with stand were 65.14 MPa and 56.38 MPa for structural steel and aluminum respectively and revealed having high factor of safety for desired applications. It can be said that aluminum having FCC crystal structure are stiff and ductile even at low subzero temperature. The theoretical calculations are done and they are in agreement with the experimental results. It can be anticipated that influence of high pressure and low temperature can be criticized by two factors in terms of flow strength and fracture strength of metal. Ductile to Brittle Transition Temperature (DBTT) plays a vital role and can be considered as a measure of behavior of metal under high pressure and low temperature. So, it revels that the crystal structures of metals is the major factor which affects the behavior of metal which eventually affect the ductility and toughness of metal when subjected to high pressure and low temperature operations. However, in thick material the question of structural discontinuity and stress concentration is still regarded as open for further scope of study.

How Does Hydrogen Affect the Mechanical Behavior of Metals and Alloys?

How Does Hydrogen Affect the Mechanical Behavior of Metals and Alloys?

Evaluation of Structural Stability of Materials through Mechanical Spectroscopy: Four Case Studies

Microstructural stability is one of the utmost important requirements for metallic materials in engineering applications, particularly at high temperatures. The paper shows how Mechanical Spectroscopy (MS) (i.e., damping and dynamic modulus measurements) permits the monitoring of the evolution of lattice defects, porosity, and cracks which strongly affect the mechanical behavior of metals and sometimes lead to permanent damage. For this purpose, some applications of the technique to different metals and alloys (AISI 304 stainless steel, PWA 1483 single crystal superalloy, nanostructured FeMo prepared via SPS sintering and tungsten) of engineering interest are presented. These experiments have been carried out in lab conditions using bar-shaped samples at constant or increasing temperatures. The results can be used to orient the interpretation of frequency and damping changes observed through other instruments in components of complex shape during their in-service life.

The Role of Hydrogen and Other Interstitials in the Mechanical Behavior of Metals

This is the Thirty-fourth Edward De Mille Campbell Memorial Lecture, presented by Alexander R. Troiano, Chairman, Department of Metallurgical Engineering, Case Institute of Technology, Cleveland. The lecture was presented November 4, 1959 during the Forty-first Annual Convention of the American Society for Metals, held in Chicago. This text is reproduced without change from the Campbell Memorial Lecture as delivered before the American Society for Metals.

Modelling the coupling between hydrogen diffusion and the mechanical behaviour of metals

It is well known that hydrogen can have a detrimental effect on the mechanical properties of metals. The aim here is to provide a fully coupled model of the HELP (Hydrogen Enhanced Local Plasticity) mechanism with hydrogen transport. Using the similarities between the heat and mass diffusion equations, a coupled temperature–displacement procedure has been adopted to allow the coupling between hydrogen diffusion and the mechanical behaviour of the material to be simulated. The diffusion equation takes into account the fact that hydrogen atoms reside in interstitial sites and in trapping sites such as dislocations. In the simulations presented here it is assumed that concentration of hydrogen at the dislocations is in equilibrium with the concentration in the matrix interstitial sites. The mechanical behaviour of the material is represented by an isotropic hardening law in which the flow stress decreases with increasing hydrogen content in the matrix which is evaluated by solving the fully coupled mechanical diffusion equations. We use the model to analyse the response of a plane strain component which contains deep and sharp doubled-edged notches. For highly constrained components of this type the hydrostatic component of stress scales with the local yield strength of the material. A high local hydrostatic stress would result in a high hydrogen concentration, but a high hydrogen concentration results in softening, i.e. a low yield strength, and therefore a low hydrostatic stress. These conflicting relationships result in a balance being achieved between hydrostatic stress, hydrogen concentration and yield strength, i.e. the response does not become unstable. Also there is a high degree of kinematic determinacy in the way which the component deforms, i.e. the strain pattern in the presence of hydrogen is very similar to that when there is no hydrogen. A consequence of these two effects is that softening of the constitutive response due to the presence of hydrogen, does not lead to localization of strain and a macroscopic brittle response. Softening must be combined with other degradation process for the material to embrittle.

Multiscale Approaches to Hydrogen-Assisted Degradation of Metals

Hydrogen embrittlement (HE) is a serious and costly industrial problem that affects many commonly used structural metals. Given the wide range of service environments in which hydrogen may occur or be produced, this represents a very serious threat to the structural integrity of machinery and infrastructure in many industries. Despite having been studied for several decades, there is still little consensus regarding the underlying mechanisms for HE. Recently developed theoretical and experimental methods, which enable the evaluation of the influences of hydrogen on the mechanical behavior of metals at the nano-scale, are helping to elucidate new aspects of these mechanisms. However, an urgent need remains to develop tools for the prediction of the reliability and lifetime of materials and components affected by hydrogen. Critical to achieving this goal is the development of accurate descriptions of hydrogen–microstructure interactions under conditions relevant to those occurring in service. As these interactions occur at all length scales, this poses a true multiscale challenge (Fig. 1). The International Symposium on Multiscale Approaches to Hydrogen-Assisted Degradation of Metals at the TMS2014 Annual Meeting & Exhibition in San Diego, California organized with the aim of promoting the exchange of ideas and information regarding the application of cutting-edge theoretical and experimental methods to industrial problems involving hydrogen-assisted degradation of metals. A particular focus of the symposium was multiscale modeling (e.g., coupled atomistic, mesoscopic, and macroscopic descriptions of hydrogen transport and damage mechanisms) as well as integrated theoretical and experimental approaches to hydrogen– microstructure interactions (e.g., the application of experimental methods for model validation and determination of modeling parameters). The symposium brought together leading researchers in the field of HE, as well as representatives from a broad range of industries that provided vital insights into the impact of HE. A total of 32 presentations were given during the 4-day meeting. The following five articles are based on presentations that were selected to show the diversity of topics covered at the symposium. In the article ‘‘Hydrogen Embrittlement of PulsePlated Nickel,’’ Reese et al. provide an overview of an experimental program at Airbus Group, which is aimed at evaluating the susceptibility of pulse-plated (PP) Ni to HE. This material is used in the fabrication of the components for the ARIANE 5 launcher. Due to the nature of the PP process, some hydrogen may be incorporated into the material during deposition. Depending on the process parameters used, this hydrogen, in combination with residual stresses resulting from welding, may result in HE. Although this does not pose an immediate problem, there is a need to better understand the influences of microstructure and process parameters on the susceptibility of PP-Ni to HE. The study is part of a wider EU-funded program called ‘‘MultiHy’’ (Multiscale modelling of hydrogen embrittlement), which aims to develop advanced multiscale models to assist companies to better understand how HE occurs during manufacture and service. ‘‘Hydrogen Embrittlement of Ferritic Steels: Deformation and Failure Mechanisms and Challenges in the Oil and Gas Industry’’ by Srinivasan and Neeraj reviews recent and forthcoming publications in which the HE of two commonly used pipeline steels, X65 and X80, was investigated using advanced analytical techniques. Analysis of the deformation substructures under the fracture surfaces using transmission electron microscopy (TEM) and the observation of nanovoids on the fracture surfaces using high-resolution scanning electron microscopy (SEM) led the authors to propose that the mechanism for HE involves vacancy-induced nanovoid nucleation and growth. The results are JOM, Vol. 66, No. 8, 2014

Constitutive description of severely deformed metals based on dimensional analysis

A constitutive equation for description of mechanical behaviour of metals at large strains was proposed to relate the important process variables associated with severe plastic deformation. Dimensional analysis based on the so called π-theorem was used for this purpose; in which the obtained dimensionless groups were related and rewritten to achieve the constitutive equation. The validity of the proposed relationship was investigated using the flow stress data of an aluminium alloy processed by accumulative roll bonding (ARB), copper processed by equal channel angular pressing (ECAP) and low carbon steel processed by constrained groove pressing (CGP) technique. It was shown that the predictions of the proposed model agree well with the experimental observations over a wide range of strain for different materials. Moreover, this model was able to address both hardening and softening at high strains. These prove the applicability of the π-theorem as an alternative approach to derive the constitutive relationships of heavily deformed metals with emphasis on the microstructure evolution.