Effective Plastic Strain Research Articles

A novel single pass severe plastic deformation method using combination of planar twist extrusion and conventional extrusion

Forward shear normal extrusion (FSNE) as a new single pass severe plastic deformation (SPD) method was based on conventional extrusion combined with planar twist extrusion. The proposed method was studied by finite element analysis to investigate the effect of FSNE die geometrical parameters, i.e. deformation zone Length (LDZ) and distortion angle (α), on uniform stress-strain distribution during deformation. Consequently, the optimum condition was considered in design and the process was experimentally performed on aluminum alloy (0.27% Fe, 0.08% Si and balance Al (wt. %). It was found that L = 15 mm and α = 40° are the optimum die parameters that can result in higher effective plastic strain with a more uniform distribution. Microstructural evolution was also studied to demonstrate the capability of this technique in grain refinement and microstructure observations revealed the presence of ultra-fine grains after FSNE. Tensile testing results indicated that yield (YS) and ultimate (UTS) strengths increase 2.7 and 2 times for the processed sample compared to the annealed sample. Hardness results showed increase in hardness level from 25HV0.3/10 for non-processed to 53 HV0.3/10 for the processed state. The uniform distribution of hardness values in both transverse and longitudinal directions was achieved due to the uniform distribution of effective strain resulting from the optimum die design. Compared to other SPD methods, the present technique resulted in high accumulated plastic strain and hardness with uniform distribution and significant grain refinement after one pass.

Damage Evolution Due to Extremely Low-Cycle Fatigue for Inconel 718 Alloy

This paper evaluates the damage evolution process under extremely low-cycle fatigue (ELCF). The study explores the damage behavior under different stress states. The influence of the multiaxial state of stress on the metal’s life is determined. Two different stress states were examined: (a) axisymmetric and (b) plane-strain. The study is based on the modified Mohr–Coulomb (MMC) ductile fracture criterion that was extended to cover the ELCF regime in a previous research study. Four distinctive geometries are designed to study the effect of different stress states on ELCF life and damage evolution. The damage model is calibrated for life prediction to agree with the ELCF experimental results. The investigation of the damage evolution behavior is dependent on equivalent plastic strain, stress triaxiality, Lode angle, and cyclic loading effect. The damage evolution is extracted from Abaqus finite element simulations and plotted versus the equivalent plastic strain. The damage accumulation shows nonlinear evolution behavior under cyclic loading conditions. SEM images were taken to further study the microscopic failure mechanisms of ELCF.

Finite element analysis of plasticity behaviour of aluminium alloys in high-pressure torsion compressive loading stage

Purpose The purpose of this paper is to examine the plasticity behaviour of aluminium alloys in high-pressure torsion (HPT) compressive loading stage. It is a part of the strengthen lightweight material development through severe plastic deformation. Design/methodology/approach A finite element simulation of HPT compression stage by displacement control incremental loading was proposed by taking into account an unconstraint HPT configuration. The quasi-static condition was utilised, by embedding strain hardening plasticity constitutive model and considering frictional effects, to assess the plasticity behaviour of aluminium alloys, particularly AA2024 and AA6082. Findings The present investigation clearly indicates that the deviation of material flow as a result of sticking condition of µ⩾0.5, was found to be negligible. An inhomogeneous material flow along the sample radial and thickness direction was evident, producing a stress concentration at the edge of the loaded surface, indicating the anticipated region of failure. The effective plastic strain in the compression stage was also found to be significant. Based on the effective strain response, plasticity behaviour of the compressed sample was predicted. Originality/value This paper demonstrates the plasticity behaviour of the analysed aluminium alloys. Since the mechanical properties produced by the deformed material are closely related to the exerted plastic deformation, understanding the phenomenon associated with the plastic strain development is essential. The outcome of this research will assist in seizing the opportunities of improving both material properties and the HPT procedures.

Prediction of Plastic Damage Index for Assessing Rib Pillar Stability in Underground Metal Mine Using Multi-variate Regression and Artificial Neural Network Techniques

Large diameter blasthole stoping method has been selected to mine a copper orebody from underground below an open pit mine. The damage induced in the rib pillars as a result of large-scale production is one of the major challenging issues. Three-dimensional numerical modelling techniques with the parametric variation of material of ore and waste, stoping sequence and crown pillar thickness is applied to analyze the stability of stopes at various levels. A total of 138 finite element models are analyzed. In this study, the concept of plastic damage index (η), defined as the ratio of effective plastic strain to effective total strain, is introduced along with strength reduction ratio (κ). The parameter κ is determined during post-yielding phase of rocks tested under uniaxial compression. An analytical equation is derived to relate these two parameters and five damage classes are also developed for predicting the rib pillar stability. Results of the numerical analysis are assessed in terms of the proposed plastic damage index; and, predictive models of η are developed using multi-variate regression and artificial neural network. These models suggest that stoping sequence is the most crucial parameter for rib pillar stability followed by depth of working, rock material type and crown pillar thickness.

Influence of milling direction in the machinability of Inconel 718 with submicron grain cemented carbide tools

The nickel-based alloys have a growing demand in many fields due to their outstanding properties at high temperatures. These properties lead to relatively low machinability, one of the main obstacles to its more extensive use. Improvements in cutting tool quality are one of the key points to overcome the challenges. The decrease to a submicron scale of the grains of cemented carbide tools is one of the alternatives to improve the machinability of the nickel-based superalloys. In this paper, two different grades of submicron grains of uncoated cemented carbide tools, TMG30 (10% Co, S30-40) and CTS18D (9% Co, S20-40), were evaluated in the end milling process of Inconel 718, through a 24 factorial design of experiments having as parameters the cutting speed, feed rate, machining direction (up and down milling), and tool grade. The tool life, machining power, and surface roughness were used as machinability evaluators. It was found that the machining direction, cutting speed, and feed rate had a significant influence on the machinability output variables, with the machining direction being the most significant one. The differences in the two tool grades were too small to be statistically significant. Simulations using the finite element method of the effective plastic strain, validated by the measurement of experimental machining power, showed that the up milling presented around 14% more plastic deformation than the down milling, which combined with the work-hardenability of the Inconel 718 explains the shorter tool life of this condition.

Experimental and numerical study on the influence of process parameters in electromagnetic compression of AA6061 tube

ABSTRACTHigh velocity forming (HVF) technique is a forming process that deforms tubes and sheets with added advantages like less springback, wrinkling, improved strain distribution, better surface finish, and improved product quality. Electromagnetic forming is one of the HVF processes that work on the principle of electromagnetic induction and Lorentz force. In the present study, electromagnetic compression of AA6061 tube has been studied experimentally and analytically using finite element method simulation. Aluminum alloy AA6061 tubes of 56 mm outer diameter (OD) and 1 mm thickness were compressed using a four-turn bitter coil with the help of 40 kJ capacitor bank. A range of energy generated from a single and/or double capacitor banks was applied and gap between coil inner diameter and tube OD was varied to study their effect on deformation. Resultant velocity, magnetic field, effective plastic strain, displacement, and current density were calculated numerically and their effect on compression is compared. A regression equation has been developed using a factorial design of experiment method to calculate the rib depth at various energy and gap. A correlation was established between discharge energy and gap with deformation of tube, and variation of various numerically calculated parameters was analyzed.

Investigation of accurate forming of a semi-ellipsoidal shell part by an electromagnetic forming method

Forming a sheet into a predesigned die cavity is an effective way to improve the dimensional accuracy of deformed parts. However, it is difficult to obtain good die-fitting quality for workpiece deformed at high speed during the one-time discharge electromagnetic forming (EMF) process. To address this challenge, a numerical simulation model was established to help optimize the forming process that affects the die-fitting quality in the formation of a semi-ellipsoid shell part. Then, experiments were conducted according to the optimized forming process. Finally, the dynamic deformation behavior of the workpiece was revealed. The results showed that the drawing deformation mode can effectively improve the die-fitting quality as well as the effective plastic strain distribution of the shell part compared with the bulging deformation mode. Moreover, reducing the initial blank diameter is a more effective way to improve draw-in compared with adjusting the blank holder force. Furthermore, a semi-ellipsoid shell part was manufactured with a maximum die-fitting gap of no more than 1.4 mm at a one-time discharge voltage of 11.5 kV. The deviation was only 1.45% of the maximum forming height. The results provide a foundation for forming a large semi-ellipsoidal shell part by the one-time discharge EMF method.

Effect of Strain-Rate and Temperature on Mechanical Response of Pure Tungsten

This paper presents the results obtained from the investigation of the mechanical behaviour of two different batches of pure tungsten specimens. The interest in pure tungsten is due to its special properties, which has led to it finding applications in several fields, including nuclear physics. At this moment, it is used as a core material for fixed particle producing targets in several accelerator facilities around the world and it is a candidate for future ones. In these facilities, tungsten directly interacts with high energy proton beams and, consequently, is subjected to considerable deformation at high strain-rates and temperatures. From these considerations, there comes the need to properly investigate the material response under these extreme conditions. For this purpose, an ad-hoc testing campaign was performed on small dog-bone specimens in tension. The results will be applicable to the ongoing design of CERN’s AD-target as well as to other future tungsten targets operating at high power and dynamically loaded in multiple accelerator facilities. Due to tungsten’s high Ductile-to-Brittle Transition temperature, it was not possible to test it at temperatures less than 250 °C. Tests were performed at two different strain-rates (nominal value of 1 s−1 and 103 s−1) reaching a maximum temperature of 1000 °C. The dynamic tests were performed by using a Hopkinson Bar setup in the direct impact configuration. Both at low and high strain-rates, heating of the specimen was achieved using an induction coil system. A numerical inverse procedure was applied to analyse the experimental data with the aim to obtain the equivalent stress versus effective plastic strain at the different loading conditions to be used for calibration of the strength model and for the evaluation of strain-rate and thermal softening sensitivities of the material.

Phase transformations, vacancy formation and variations of optical and photocatalytic properties in TiO2-ZnO composites by high-pressure torsion

TiO2 and ZnO, two semiconductors with promising optical properties, are considered as potential candidates for solar and photocatalytic applications. Although chemical methods have been primarily used to enhance the optical properties of these oxides, the current authors recently reported enhanced photocatalytic performance of pure TiO2 and ZnO by plastic straining due to the generation of high-pressure phases and oxygen vacancies. In this study, to improve the optical properties further, large fractions of ZnO/TiO2 interphase boundaries are also introduced by application of high-pressure torsion (HPT) straining to a mixture of anatase-TiO2 and wurtzite-ZnO powders. It was found that the amounts of oxygen vacancies and nanograined high-pressure TiO2-II and rocksalt-ZnO phases increase with increasing plastic strain. Moreover, due to the plastic strain effect, the rutile-TiO2 phase is formed at room temperature, which is at least 600 K below the reported anatase-to-rutile transition temperature. These structural features, together with the formation of large fraction of interphase boundaries, lead to electron spin resonance, optical bandgap narrowing, diminishing of the band-to-band photoluminescence and thus, improvement of photocatalytic hydrogen generation. Despite improvements in the photocatalytic activity of TiO2-ZnO composites after large straining, photocatalytic activity becomes poor by processing at ultra-large strains due to the significant reduction in crystallinity.

A Smoothed Particle Hydrodynamics (SPH) procedure for simulating cold spray process - A study using particles

Cold spray process has been of great interest in coating and additive manufacturing because it does not need heat supply during impact. Cold spray generally uses particles of diameters 10 μm to 50 μm traveling at velocities of 300 m/s to 1200 m/s, and it takes place at very small time and length scales. Thus, it becomes difficult to observe the detailed process experimentally. The primary objective of this study is to use SPH and highlight its capability for modeling cold-spray process. A novel way of establishing boundary conditions using Monaghan type 2 particles is adopted in this study. Additionally,our SPH model includes failure modeling for copper particle impacts. Particles of different sizes and at different angles are studied to reveal the effects of impact which includes recording effective plastic strain, deformation and temperature. It was found that larger particles had greater ability to adhere to the surface of the substrate and an impact angle between 80° and 90° has higher chances of adherence to the substrate. An increase in maximum effective plastic strain is seen which causes thermal softening leading to plastic flow of material. This fluid-like flow causes adherence of the particle on the substrate. Finally, the in-house SPH procedure is extended to simulate three-dimensional cold spray problems with multiple particles.

Measuring flow curve and failure conditions for a MEMS-scale electrodeposited nickel alloy**Contribution of the U.S. Department of Commerce, National Institute of Standards and Technology. Not subject to copyright in the USA.,††Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the analytical procedure adequately. Such identification is not intended to imply recommendation or endorsement by

Implementation of advanced electroplated Ni alloy materials in MEMS-scale mechanisms requires performance predictions that are based on actual, rather than idealized, material properties. Accurate characterization of material properties is necessary to the formulation of material models used in finite element analysis (FEA) simulations that can be relied upon for critical design applications. Quantitative material models, and specifically those implemented in FEA codes, require the use of the true stress-true strain material flow curve as input. Simulations of failure conditions require that a failure criterion be known, such as the failure strain. The subject of this paper is a method for obtaining such characterization of MEMS-scale electroplated materials; it addresses the challenges associated with measurement of stress and, particularly, strain that arise from geometric constraints on MEMS-scale specimens and instrumentation. These include thicknesses a few tenths of a millimeter and below, component dimensions 1 mm and less and planar geometries. A method for refining the material quasi-static flow properties, by inverse-modeling of data from quasi-static tests, is reported. Tests were performed on an electrodeposited nickel alloy by use of a small-scale conventional loading apparatus, with digital imaging to measure specimen displacements. Simulations were carried out using two general purpose, commercially available FEA codes. Inverse modeling was applied to the data to obtain true stress-true strain flow curves. The FEA simulations of the local displacements converged to the experimental results for both commercial codes. Forward-modeling was then used to determine the maximum equivalent true plastic strain in the specimen neck; the calculated values converged to significantly different values in the two codes. This result suggests a need for caution in the use of reported values for maximum effective plastic strain as a failure criterion in FEA simulations.

Stability analysis of the Xinlu Village landslide (Chongqing, China) and the influence of rainfall

On June 28, 2016, a landslide occurred in Xinlu Village, Qijiang District, Chongqing, China. The landslide volume was 854,200 m3. Exposed to continuous rainfall, the rocky part of the trailing edge slipped first, and then the soil part of the leading edge was pushed downward. Numerical simulations were used to analyze the formation characteristics of the landslide and to predict the stability of the landslide after the slip. In order to ensure the accuracy and rationality of numerical calculation, we used field surveys, laboratory tests, and back-calculation to restore the typical sections, determine the relevant mechanical parameters, and control boundary conditions. The displacement, stress, effective plastic strain distribution, and safety factor, obtained by numerical calculation, were compared to examine the action of rainfall. According to the evaluation of landslide stability and numerical calculation results, the Xinlu Village landslide remained in a peristaltic stage after the initial overall sliding, and additional sliding could occur under storm conditions.

Experimental and Numerical Modeling on Fatigue Damage in FRP and PM Confinement Tilt’s Fulcrum RC Segments under Humid and Constant Amplitude Loading

It is a stringent challenge to swiftly rehabilitate and strengthen the concrete segments on the metro tunnel that are under the humid environment and vibration fatigue by the locomotives. By means of fatigue experiments under the constant amplitude loading, the repair materials (fiber reinforced polymer (FRP) and polymer matrix (PM)) which can be moisture proof and resist the cyclic load are introduced. Hereafter, a fatigue model of tilt’s fulcrum reinforced concrete (RC) segments under constant amplitude loading are proposed by the calibration of S-N curves through these fatigue test. The fatigue model explains for the (a) scope of pre-damage, (b) mechanical properties of the repaired concrete segments, such as the specific rupture times of cycle and stress-crack opening relation, and (c) effective plastic strain behavior of the RC segments. The results show that the purely PM is an excellent candidate for repairing the fatigue loaded damaged RC segment. It (L-4-2) had an average mechanical behavior for cyclic load bearing compared with the remaining specimens. On the other hand, the numerical model predictions had an approximately 96.00% of agreement with the corresponding test results.

Simulation of failure processes of as-cast Ti-5Al-5Nb-1Mo-1V-1Fe titanium alloy subjected to quasi-static uniaxial tensile testing

A three-dimensional (3D) microscopic structural finite element model reflecting the realistic pore distribution of as-cast Ti-5Al-5Nb-1Mo-1V-1Fe titanium alloy was built through micro-computed tomography (micro-CT). The model was then introduced into ANSYS LS-DYNA software to investigate the 3D spatial evolution process of damage and failure under quasi-static uniaxial tension. To validate the simulation results, we tested the uniaxial tensile responses of Ti-5Al-5Nb-1Mo-1V-1Fe and quantitatively characterized the tensile fracture morphology with a 3D profilometer. To reveal the underlying mechanism of damage and failure, we took the triaxiality of Rσ into consideration. Local principal stress concentration was found to exist around two micro-pores at the initial stage, thus inducing two crack sources; as the load increased, more crack sources were generated and steadily propagated through void growth and coalescence under the influence of multiaxial principal stress concentration, thus leading to the local tensile failure of the model. When cracks reached a critical size, the shear stress concentration became the dominant factor affecting failure, thus inducing severe effective plastic strain between cracks. The cracks rapidly connected through plastic slip and cleavage, thereby resulting in the final shear failure of the model. The simulation results were in good agreement with the observed experimental results.

Analytical Modeling of White Layer Formation in Orthogonal Cutting of AerMet100 Steel Based on Phase Transformation Mechanism

The white layer formed in machining has significant impacts on the friction property, fatigue resistance, and service life of products. This paper presents an analytical model for white layer prediction in orthogonal cutting based on phase transformation mechanism. The effects of stress, elastic, and plastic strain on phase transformation temperature are taken into consideration. A function related to cutting temperature and phase transformation temperature is defined to determine the white layer thickness. The theoretical model is validated by machining AerMet100 steel under different cutting conditions. Optical microscope and X-ray diffraction (XRD) are employed to analyze the microstructures of the white layer. A phase transformation is detected in the white layer region, and the predicted white layer thicknesses are in good agreement with the measured values. In addition, the plastic strain is found to be the major factor that causes a reduction in phase transformation temperature. This work can be further applied to optimize cutting conditions to improve machined surface integrity.

Finite Element Analysis of Single Point Incremental Forming (SPIF) of Aluminum 7075 Using Different Types of Toolpath

To make large number of parts in automotive, aerospace, and appliances industries, sheet conventional metal forming processes, such as stamping, are used. However, for small number of productions, novel flexible manufacturing processes, such as incremental sheet forming (ISF) must be utilized to decrease the production costs. Studying the process parameters in ISF process such as, the toolpath, step size, tool size, feed rate, lubrication, and wall angle is essential as they are affecting the formability and deformation behavior of this process. The purpose of this study was to investigate the effect different types of toolpath, such as z-level (profile) and helical (spiral) to form a truncated-conical geometry in simulation of the single point incremental forming (SPIF) of AA7075-O. A detailed comparison of these tool paths' predictions was made with respect to the effective plastic strain distribution, part thickness, tool force and moment.

Numerical Analysis of Conventional and Modified Equal Channel Angular Pressing

While conventional equal channel angular pressing (ECAP) has been widely investigated as the prominent severe plastic deformation method, no detailed work has been carried out on the modified ECAP techniques. So, this work deals with the numerical characterization of 7075 aluminum billet processed by conventional and modified ECAP methods. It has been found that T-shaped ECAP is the best technique to choose from the effective plastic strain point of view. Also, the highest plastic strain distribution uniformity and concomitant least required pressing load belong to the cross-ECAP condition. Moreover, conventional ECAP process should be selected if the minimum temperature rise and damage have been considered. Eventually, shear plane mode of oblique, V-shape, and X-shape is attained for the conventional, T-shaped, and cross-ECAP conditions, respectively.

An equivalent von Mises stress and corresponding equivalent plastic strain for elastic–plastic ordinary peridynamics

Simple formulas for calculating equivalent von Mises stress and von Mises effective plastic strain in an elastic–plastic ordinary peridynamic analysis are proposed. The equivalent von Mises stress is calculated by equating the deviatoric part of strain energy obtained from classical continuum mechanics and peridynamics. The effective plastic strain is proposed so that it reduced to uniaxial plastic strain in uniaxial tension test. Two example problems of the plate with a hole and a central crack under tension are considered to verify the validity of the proposed formulas. The plots of von Mises stress, equivalent plastic strain, plastic zone area and horizontal and vertical displacements are extracted and compared with the results obtain from the finite element analysis. The results show the good accuracy of the peridynamics in predicting the above mentioned parameters as well as the validity of the suggested formulas in predicting von Mises stress and equivalent plastic strain.

Influence of residual plastic strain on the thermoelastic behavior of a titanium alloy

The thermoelastic effect that manifests as a change in temperature of a body undergoing adiabatic elastic deformation has been utilized for full-field stress analysis in solids using the infrared thermal imaging technique. This technique has been used for nondestructive evaluation of residual stresses in components. The present study endeavors to examine the effect of residual plastic strain, due to a previously imposed plastic deformation, on the thermoelastic behavior of solids. Near-α titanium alloy specimens have been plastically deformed, and after reaching a plastic strain level, the test has been interrupted. The thermoelastic response of the interrupted specimens has been examined. The infrared thermal imaging technique has been used to capture the spatiotemporal evolution of the surface temperature of the specimens. It has been observed that the thermoelastic coefficient of the alloy increases as a function of prior/residual plastic strain for small deformations. It has been shown that the theoretical framework used to explain the effect of residual stress on the thermoelastic coefficient assuming a perfect crystal lattice is not applicable to explain the effect of residual plastic strain on the thermoelastic coefficient. A modification of the existing theory has been proposed to explain the dependence of the thermoelastic coefficient on the residual plastic strain. A thermodynamic framework considering the local entropy and internal energy density has been developed to study the behavior. The microscopic aspects of the energetic of thermoelasticity have been discussed and based on this a continuum dislocation dynamic model has been proposed to explain the variation in the thermoelastic coefficient.

Mechanism of Crack Propagation for K9 Glass

In order to study the mechanism of crack propagation, the varied cutting-depth scratch experiment is carried out and smoothed particle hydrodynamics (SPH) simulation method is used to assistant the investigation. The SPH simulation results reveal that crack will propagate in the direction where stress concentration exceeds the fracture toughness of K9 glass. The initial crack length in critical transition depth is calculated by combining the critical stress of fracture and the fracture toughness of K9 glass. Based on the effective plastic strain, the relation between scratching depth and crack depth is obtained. The recovery of crack tip is found and explained from the relationship between cutting depth and crack depth. Using the energy balance theory of Griffith, the variation of material internal energy is revealed. Comparing the scratching forces obtained from experiment and simulation, the validity of simulation results is verified. The phenomenon of crack delayed propagation is found in both experiment and simulation. The explanation of mechanism is given.