Influence Of Plastic Strain Research Articles

Simulation of Shear and Tensile Fractures Using Ductile Phase Field Modelling with the Calibration of P Wave Velocity Measurement and Moment Tensor Inversion

The appropriate understanding and formulation of rock discontinuities via FEM is still challenging for rock engineering, as continuous algorithms cannot handle the discontinuities in rock mass. Also, different failure modes of rock samples, containing tensile and shear failure, need to be computed separately. In this study, a novel double-phase field damage model was introduced with two independent phase field damage variables. The construction of the proposed model follows the thermodynamics framework from the overall Helmholtz free energy, with elastic, plastic and surface damage components. The proposed model is calibrated via traditional damage variables, based on ultrasonic wave velocity measurement and acoustic emission monitoring, and both show great consistency between simulation results and laboratory observations. Then the double-phase field damage model is applied to COMSOL software to simulate microcrack propagation in a pre-fractured rock sample. Both lateral and wing cracks are observed in this study, manifested as shear- and tensile-dominated cracks. We also observed different microcracking mechanisms in the proposed numerical models, such as tensile and shear cracking, the influence of plastic strain and the percolation between tensile and shear microcracks. Overall, this study provides valuable insights into the mechanics of microcracking in rocks, and the proposed model shows promising results in simulating crack propagation.

Influence of Plastic Strain on Heat Capacity of L485ME Pipe Steel Grade

The aim of this work is an experimental evaluation of a specific heat capacity as a function of plastic strain for thermo-mechanically rolled pipe material, with application of an infrared thermographic camera. The tensile load tests of samples prepared of L485ME (X70M) steel grade were performed with the use of a strength machine. Based on other known material thermophysical properties, the determination of heat source parameters was conducted with the use of an infrared thermography and with an optimization task solution. A linear regression equation describing the specific heat capacity as a function of plastic percentage elongation for L485ME steel grade was determined. The experimental results of the present study showed a linear increase in the specific heat capacity in the range of the analyzed tensile deformation up to 16%. The presented methodology is suitable for assessment of the material specific heat capacity as a function of strain up to the occurrence of the sample narrowing in a direction perpendicular to the tensile force.

The Influence of Plastic Strain and Microstructure on the Electrochemical Noise Response of AA 7004 in 0.6 M NaCl

The Influence of Plastic Strain and Microstructure on the Electrochemical Noise Response of AA 7004 in 0.6 M NaCl

Micromechanical aspects of the effect of temperature and local plastic strain magnitude on the fracture toughness of ferrite steels

The paper shows that the influence of plastic strain and temperature on the rate of crack nuclei (CN) formation is a crucial factor controlling the shape of the temperature dependence of fracture toughness and its scatter limits. Within the framework of the microscopic model described, it is explained that the dependence of the incompatibility of microplastic deformation at grain boundaries or interfaces on the value of plastic strain and temperature is the reason for the effect of these factors on the rate of CN formation. The dependencies of the CN bulk density on temperature and plastic strain are given. In the latter case, a non-monotonic change in CN density is observed. The maximum intensity of CN formation is observed when the critical value of plastic strain is reached. For ferritic structural steels, this strain is about 2%. Using reactor pressure vessel steel and cast manganese steel as examples, it is shown that not taking these effects into account in the local fracture approach leads to considerable errors in the prediction of the temperature dependence of the fracture toughness and its scatter limits.

Modeling of Superelastic–plastic Behavior of Porous Shape Memory Alloys Incorporating Void Shape Effects

A new constitutive model for describing the superelastic–plastic behavior of porous shape memory alloys (SMAs) is proposed. The model incorporates the influences of void shape and hydrostatic pressure as well as the elastic modulus mismatch between austenite and martensite. In addition, the interactions between plastic strain and transformation strain are considered via the plastic back stress. The porous SMAs are considered as two-phase composites with the dense SMA matrix and the second phase representing ellipsoidal voids. Based on Gurson’s formulation, the transformation and plastic flow potentials accounting for the transformation–plasticity coupling are developed. The numerical results present good agreement with available experimental data for various levels of porosity, which proves that the model is capable of capturing stress-induced phase transformation and plastic deformation of porous SMAs. Using the proposed model, the influence of plastic strain on reverse transformation and the effects of porosity and void shape on the pseudoelastic and plastic behavior of porous SMAs are investigated.

The Effects of Strain on Stability of Passivation in Austenitic Stainless Steels: Comparison with Heat Treatment

The passive film mainly consists of oxides and hydroxide and is a key for corrosion protection of metallic materials. It increases the durability and performance of engineering components by spontaneous formation of effective, adherent barrier between the corrosive environment and a substrate. Herein, influence of plastic strain and after heat treatment on austenitic stainless steels was compared with the focus on stability of the passive film. The following materials were used in this study: Sanicro 28™, AISI 316 L, and AISI 304 L. These specimens were subjected to a true strain of 0.58. The conventional three-electrode cell was used to record the anodic potentiodynamic polarization curves. The grain size and other misorientation parameters were extracted using electron backscattered diffraction (EBSD). Fourier transform infrared spectroscopy (FTIR)-imaging was used for capturing chromium oxide (Cr2O3) peaks for all specimens. The average area of Cr2O3 peaks was compared with deformed and after heat treatment of 700 °C 30 min specimens. It was found that heat-treated specimens exhibited slightly higher average area of Cr2O3 than deformed.

Influence of plastic strain on fatigue damage assessment for seismic load (Proposal K<sub>s</sub> factor as an alternative to K<sub>e</sub> factor)

Influence of plastic strain on fatigue damage assessment for seismic load (Proposal K<sub>s</sub> factor as an alternative to K<sub>e</sub> factor)

Plastic Effect Analysis of High Strength Steel Frame Structure

High strength steel structure is more and more widely used in the field of building structure because of its advantages in mechanical properties. The design of high-strength steel frame often refers to steel structure. For the high-strength steel with no yield platform of stress-strain curve, the influence of plastic strain before the nominal yield strength of its material on the results of the frame remains to be studied. In order to study the influence of plastic effect on high-strength steel frame, the second-order elastic-plastic analysis of typical frame is carried out and compared with the simplified design method of steel structure design standard. The results show that the plastic effect has no significant effect on the bending moment and lateral displacement of high-strength steel frame in most cases. Base on the analysis results, the design suggestions of high-strength steel frame structure are put forward.

Fracability evaluation of lacustrine shale by integrating brittleness and fracture toughness

Rock brittleness and fracture toughness are important parameters for evaluating rock fracability. The stress-strain curves indicate that the lacustrine shale is strongly brittle. Brittle failure occurs rapidly when the stress of the lacustrine shale reaches its peak value. In addition, the lacustrine shale has different plastic strains before and after peak stress; this can relax the stress concentration of the crack tips. Therefore, the plastic strain that occurs before and after the peak stress can cause decreasing brittleness, which can be used to distinguish the brittleness and fracability in the formation of the lacustrine shale clearly. Moreover, this further enlarges the difference in the brittleness index. Based on the influence of plastic strain on brittleness, we have developed a new brittleness evaluation method that uses the ratio of linear elastic strain energy to the total strain energy before complete rock failure, which can indicate the difference of the lacustrine shale clearly. Fracture toughness is another important parameter that impacts the fracture extension and influences fracability. Based on the impact of brittleness and fracture toughness on the fracability, we have developed a new fracability evaluation method. The brittleness index increases with increases in the quartz content, and it decreases with increases in the albite feldspar and calcite contents. The fracture toughness decreases with increases in the quartz and clay contents, and it increases with increases in the siderite content. In addition, we established an empirical formula that can evaluate the brittleness index and the fracture toughness using mineral contents obtained from elemental logging. Using the new fracability evaluation method to optimize the fracturing stage, the preliminary field test indicates that the new approach was effective in the lacustrine shale formation.

Macroscopic consequences of Piobert–Lüders and Portevin–Le Chatelier bands during tensile deformation in Al-Mg alloys

Lüders bands and the Portevin–Le Chatelier effect are both due to plastic flow instabilities that affect a wide variety of metallic materials. The present study focuses on understanding these behaviors. Field kinematic measurements combined with the comparison of two specimen sizes are used here to characterize the Al–Mg alloy AA5086, by investigating the kinetics of individual localization bands. A unifying point of view is proposed for the classification of these bands together with the identification of a constitutive relation linking strain increments and nucleation stress, as well as evidence of the factors determining the development of serration behaviors. This leads to a novel interpretation of the spatiotemporal behavior of the bands as being the result of a competition between the influence of plastic strain and its gradient.

Elastoplastic State of an Elliptical Cylindrical Shell with a Circular Hole

Static problems for an elastoplastic elliptical cylindrical shell with a circular hole are formulated and a numerical method for solving it is developed. The basic equations are derived using the Kirchhoff–Love theory of deep shells and the theory of small elastoplastic strains. The method employs the method of additional stresses and the finite-element method. The influence of plastic strains and geometrical parameters of the shell subject to internal pressure on the distributions of stresses, strains, and displacements in the zone of their concentration is studied.

Service induced fcc→hcp martensitic transformation in a Co-based superalloy

Co-based superalloy, ECY768, applied on gas turbine vanes, shows the presence of cracks after service. EBSD studies revealed hcp transformation in the base material near cracked regions. This phase arises from a martensitic transformation of fcc matrix and bestows high fragility. The phase transformation is related to temperature and loading distribution that characterises components in service. However, at the service temperatures, the hcp transformation is not expected for ECY768. An in-house thermodynamic database was developed using the Calphad approach and thermodynamic calculations were applied to the complicated alloy composition for phase stability range evaluation. Moreover, a testing campaign was planned to artificially create this martensitic transformation and to comprehend the influence of plastic strain on fcc-hcp transformation. The transformation mechanisms were understood and some methods were developed for hcp-phase removal through refurbishment heat treatment.This paper is part of a thematic issue on the 9th International Charles Parsons Turbine and Generator Conference. All papers have been revised and extended before publication in Materials Science and Technology.

On the Uniqueness Conditions and Bifurcation Criteria in Coupled Thermo-Elasto-Plasticity

The global and local conditions of uniqueness and the criteria excluding a possibility of bifurcation of the equilibrium state for small strains are derived. The conditions and criteria are derived analyzing the problem of uniqueness of solution of the basic incremental boundary problem of coupled generalized thermo-elasto-plasticity. This paper is a continuation of some previous works by the author, but contains new derivation of the global and local criteria excluding a possibility of bifurcation of the equilibrium state for a comparison body dependent on statically admissible fields of stress velocity. All the thermal elastoplastic coupling effects, non-associated laws of plastic flow and influence of plastic strains on thermoplastic properties of a body were taken into account in this work. Thus, the mathematical problem considered here is not a self-conjugated problem. The paper contains four Appendices A, B, C and D where the local necessery and sufficient conditions of uniqueness have been derived.

Influence of Plastic Strain on Mechanical Properties of Metallic Films by Sharp Indentation

Influence of Plastic Strain on Mechanical Properties of Metallic Films by Sharp Indentation

Stochastic damage hysteretic model for concrete based on micromechanical approach

In the present paper, a kind of stochastic damage hysteretic model is proposed to describe the damage and hysteretic behaviors of concrete material. According to the model, a parallel system made up of micro-elements, which are developed based on the micro-tensile and shear damage mechanism respectively, is adopted to obtain the overall responses of concrete. The influence of plastic strain and hysteretic energy dissipation of the material are also considered in the model. To reflect the stochastic properties of concrete, the fracture strain of the micro-element is set as a random variable. Then the monotonic, loading and unloading curves of the parallel system are derived analytically by averaging the stochastic micro-elements and two hysteretic rules are combined to the proposed model to account for complicated loading conditions. Furthermore, a nonlocal process is introduced to the model to overcome the mesh dependence issues of softening materials. Finally, several numerical examples are conducted, demonstrating that the proposed model can provide reliable results reflecting the damage, plasticity and hysteretic behaviors of concrete material.

Experimental Waviness Evolution of Interstitial Free - IF Steel Sheet under Biaxial Stretching

The purpose of present study is to present experimental results and a mathematical model for the evolution of surface waviness parameters with plastic strain of Interstitial Free - IF steel sheet under uniaxial and biaxial stretching tests. Roughness and waviness are very important quality parameters to be evaluated in sheet metal forming. Various waviness profile parameters such as the arithmetic average waviness Wa, the total height peak-valley waviness Wt, maximum peak height Pp and maximum valley depth Pv were measured during uniaxial and biaxial tests. Tensile test specimens at 0º, 45º and 90º to the direction of rolling and Nakazima type specimens of IF steel were fabricated. After preparing the test specimens, incremental simple tensile and Nakazima biaxial tests with flat punch were performed to characterize the negative and positive quadrant of the Map of Principal Surface Limit Strains, MPLS, of IF steel sheet. Measurements of waviness parameters of the specimen surface at incremental plastic strain stages were performed at the same surface site. Also, during the uniaxial and biaxial tests, the following plastic strains were calculated from printed circular mesh at each incremental step: ε1 longitudinal major strain and ε2 transverse minor strain. From these data, curves of waviness parameters versus equivalent strain were plotted to obtain a phenomenological equation of 4th or 3rd degree polynomial type. Furthermore, the growth rates of Wa and Wt parameters with the equivalent plastic strain were assessed. From the growth rate curves, it was possible to verify how the sheet thickness imperfections evolves during straining, being possible to predict the influence of plastic strain on the waviness values of IF steel sheets. From the analysis of Wa and Wt growth rates during straining, it was possible to proposed a criteria for the onset of local necking or limit strains in the MPLS. The waviness parameters Wt is the best for characterizing the onset of local necking in sheet metal forming.

Influence of plastic strain on the hydrogen evolution reaction on nickel (100) single crystal surfaces to improve hydrogen embrittlement

Hydrogen-induced embrittlement can be accountable for premature failure of structure in relation with physical and/or chemical processes occurring on material's surface or in the bulk of the material. Hydrogen Evolution Reaction (HER) corresponding to the early step of hydrogen ingress in the material is explored in present study in relation with plastic strain. HER on nickel (100) single crystal in sulphuric acid medium can be related by a Volmer–Heyrovsky mechanism. The corresponding elementary kinetic parameters as symmetry coefficients, activation enthalpies, and number of active sites have been identified via a thermokinetic model using experimental data. These parameters can be affected by defects associated with plastic strain. Irreversible plastic strain modifies the density and the distribution of storage dislocations affecting the surface roughness at atomic scale and generating additional active adsorption sites. Furthermore, surface emergence of mobile dislocations induces the formation of slip bands, which modify the surface roughness and the electronic state of the surface and increases the (111) surface density. The consequence of plastic strain on HER is explored and discussed in relation with both processes.

Estimation model for magnetic properties of stamped electrical steel sheet

AbstractLess deterioration in the magnetic properties of electrical steel sheets in the process of stamping out the iron core is necessary in order to maintain performance. First, the influence of plastic strain and stress on the magnetic properties is studied using test pieces, in which plastic strain is added uniformly and residual stress is not induced. Because the influence of plastic strain is expressed using the equivalent plastic strain, at each equivalent plastic strain state the influence of the load stress is investigated. Second, the elastic limit is determined to be about 60% of the macroscopic yield point (MYP), and this agrees with the stress limit inducing irreversible deterioration in the magnetic properties. Therefore, simulation models, in which excess elastic limit plastic deformation begins and the magnetic properties deteriorate sharply, are proposed. Additional points taken into consideration in the deformation analysis are the strain rate sensitivity of flow stress, the anisotropy under deformation, and the influence of stress triaxiality on fracture. Finally, the proposed models are shown to be valid because the magnetic properties of rectangular sheets 5 mm wide stamped out from a nonoriented electrical steel sheet (35A250 JIS grade) can be estimated with good accuracy. It is concluded that the elastic limit must be taken into account in both the stamping process simulation and magnetic field calculation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(2): 1–11, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22269

Evolution of Roughness on Straining of Interstitial Free – IF Steel Sheet

This study aims to assess the evolution of surface roughness and waviness parameters with plastic strain in Interstitial Free – IF steel sheet. For the achievement of this study, it was considered various roughness and waviness profile parameters such as: arithmetic average roughness (Ra), maximum distance peak-valley (Rt), average waviness (Wa) and waviness of the total height peak-valley (Wt). Tensile test specimens of IF steel at 0º, 45º and 90º to the direction of rolling were fabricated. After preparing the sheet proof specimens, it was performed simple tensile tests and measurements of roughness and waviness of the specimen surface at various strain stages resulting in a large quantity of data. During the tensile test, it has been measured the following plastic strain to indicate the incremental step: (e1) longitudinal strain and (e2) transverse strain. From these data, it was possible to obtain points needed to plot the curves of roughness and waviness parameters versus strain and to determine the material behavior using equations of the equivalent strain. From the curves drawn it was possible to see how the material roughness and waviness behaves during the straining in the uniaxial tensile state, with the possibility to predict the influence of plastic strain on roughness and waviness parameters and the onset of local necking of IF steel sheet. The waviness parameters Wt is the best for characterizing the onset of local necking.

電磁鋼板の打抜き加工による磁気特性劣化量の推定技術の開発

Less deterioration in the magnetic properties of electrical steel sheets in the process of stamping out the iron core is necessary in order to maintain performance. First, the influence of plastic strain and stress on the magnetic properties is studied using test pieces, in which plastic strain is added uniformly and residual stress is not induced. Because the influence of plastic strain is expressed using the equivalent plastic strain, at each equivalent plastic strain state the influence of the load stress is investigated. Second, the elastic limit is determined to be about 60% of the macroscopic yield point (MYP), and this agrees with the stress limit inducing irreversible deterioration in the magnetic properties. Therefore, simulation models, in which excess elastic limit plastic deformation begins and the magnetic properties deteriorate sharply, are proposed. Additional points taken into consideration in the deformation analysis are the strain rate sensitivity of flow stress, the anisotropy under deformation, and the influence of stress triaxiality on fracture. Finally, the proposed models are shown to be valid because the magnetic properties of rectangular sheets 5 mm wide stamped out from a nonoriented electrical steel sheet (35A250 JIS grade) can be estimated with good accuracy. It is concluded that the elastic limit must be taken into account in both the stamping process simulation and magnetic field calculation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(2): 1–11, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22269