Shear Zone Model Research Articles

Parameter identification of Johnson–Cook constitutive model based on genetic algorithm and simulation analysis for 304 stainless steel

Addressing the significant discrepancy between actual experimental cutting force and its predicted values derived from traditional constitutive model parameter identification methods, a reverse identification research of the Johnson–Cook (J-C) constitutive model for 304 stainless steel was conducted via genetic algorithm. Considering actual cutting zone and the influence of feed motion on the rake (flank) angle, an unequal division shear zone model was established to implement the theoretical calculation for shear zone stress. Through cutting experiments, the spindle speed was negatively correlated with the cutting force at first, and then became positively correlated; The empirical formula (EXP model) for turning force was corrected, revealing that the EXP model was unable to provide optimal predicted values for cutting force. The influence of the J-C constitutive parameter C on the cutting morphology was firstly investigated through simulation analysis, and determined an appropriate value for C, then obtained the precise values for the other four constitutive parameters by genetic algorithm. Moreover, the simulated values of cutting force in JC1 model (obtained from the Split Hopkinson Pressure Bar test) and JCM model (the improved model using genetic algorithm) were obtained by three-dimensional (3-D) simulation via FEM software. The results indicated that, the maximum error between actual experimental cutting force and its simulated values (by JCM model) was 14.8%, with an average error of 6.38%. These results outperformed the JC1 and EXP models, suggesting that the JCM model identified via genetic algorithm was more reliable.

Paleogene mid-crustal intrusions in the Ruby Mountains–East Humboldt Range metamorphic core complex, northeastern Nevada, USA

Abstract Middle Eocene to early Oligocene intrusions, widespread in the Ruby Mountains–East Humboldt Range metamorphic core complex, Nevada, USA, provide insights into a major Paleogene magmatic episode and its relation to tectonism in the northeastern Great Basin. These intrusions, well-exposed in upper Lamoille Canyon, range in composition from gabbro to leucomonzogranite. They form small plutons, sheets, and dikes that intrude the metamorphic and granitic infrastructure of the core complex. Two types of Paleogene monzogranite were recognized. The first is exemplified by two of the larger intrusive bodies, the Snow Lake Peak and Castle Lake intrusions, which occur as sheet-like bodies near and at the structural base of metamorphosed Neoproterozoic and Cambrian Prospect Mountain Quartzite where it is inverted above Cambrian and Ordovician marble of Verdi Peak in the Lamoille Canyon nappe. Swarms of dikes are associated with these intrusions. U-Pb (zircon) ages range ca. 40–33 Ma and typically display relatively simple and minor inheritance. The rocks have the lowest εHf (zircon) and εNd (whole rock) of any of the middle Cenozoic granites. The second type of monzogranite, Overlook type, typically occurs as thin, isolated dikes and leucosome-like bodies in Late Cretaceous granites of the infrastructure, with no obvious relationship to the large monzogranite bodies. Overlook-type monzogranite displays complex zircon inheritance, yields igneous ages ca. 37–32 Ma, and has εHf (zircon) and εNd (whole rock) identical to those of Late Cretaceous granites in the core complex. These isotopic and field data indicate that Overlook-type monzogranite formed in situ through anatexis of host Cretaceous granites. A pervasive thermal event was required to stimulate this crustal melting. Gabbros from Lamoille Canyon and quartz diorite dated from 32 km away signal mantle-derived magmatism ca. 39–37 Ma (U-Pb, zircon) was a driver of crustal melting and hybridization. Eocene 40Ar/39Ar apparent ages on hornblende and biotite are consistent with syn- to post-magmatic extensional exhumation and decompression. Thus, the core complex provides a window into trans-crustal magmatism and insight into how such magmatism affected the Nevadaplano orogenic plateau. This Paleogene thermal pulse, which may relate to removal of the Farallon slab by delamination of mantle lithosphere, involved partial melting of the upper mantle and transfer of magma and heat to the Nevadaplano crust. Lower-crustal melting of Archean(?) to Paleoproterozoic rocks resulted in Snow Lake Peak–type magmas, and middle-crustal melting of granite in the infrastructure yielded Overlook-type magmas. This crustal magmatism, as exemplified by the intrusions in the core complex, likely played a role in destabilizing the Nevadaplano and its later collapse during middle Miocene extension. The Paleogene intrusions and associated structural features also provide insight into the evolution of the core complex through either the buoyant upwelling of a melt-rich diapir (gneiss-dome model) or buoyant upwelling of the melt-rich middle crust synchronous with a west-rooted mylonitic shear zone (extensional shear-zone model). We favor a hybrid that incorporates both models.

Improvement of the Unequal Division Shear Zone Model Based on Sensitivity Analysis and Classification of Uncertain Parameters

Improvement of the Unequal Division Shear Zone Model Based on Sensitivity Analysis and Classification of Uncertain Parameters

Identification of the Constitutive Parameters of Viscosity and the Prediction of the Cutting Force of S32760 Duplex Stainless Steel under a High Strain Rate

The mechanical properties of S32760 duplex stainless steel under dynamic loading conditions at high strain rates are significantly different from those under quasi-static conditions. As a result of large strain, high strain rate, and high temperature, the analysis of the cutting process needs to factor in the influence of the viscous behavior of the material on the plastic deformation process. Based on the viscous effect of the two phases and the mixing rule, a mechanical threshold stress (MTS) constitutive model of S32760 duplex stainless steel considering the viscous effect is established to analyze the effect of strain rate on flow stress. An inverse identification method of the constitutive parameters based on Oxley's theory is proposed. The constitutive parameters of S32760 duplex stainless steel were reversely modified using an equal shear zone model and an orthogonal cutting experiment. The results show that the viscosity of the austenite phase was greater than that of the ferrite phase, and the strain rate had the greatest influence on the viscosity effect in the constitutive model. The prediction error of the constitutive model constructed in this manuscript was less than 4%, which had high accuracy.

Numerical Simulations Reproduce Field Observations Showing Transient Weakening During Shear Zone Formation by Diffusional Hydrogen Influx and H2O Inflow

AbstractExposures on Holsnøy island (Bergen Arcs, Norway) indicate fluid infiltration through fractures into a dry, metastable granulite, which triggered a kinetically delayed eclogitization, a transient weakening during fluid‐rock interaction, and formation of shear zones that widened during shearing. It remains unclear whether the effects of grain boundary‐assisted aqueous fluid inflow on the duration of granulite hydration were influenced by a diffusional hydrogen influx accompanying the fluid inflow. To better estimate the fluid infiltration efficiencies and the parameter interdependencies, a 1D numerical model of a viscous shear zone is utilized and validated using measured mineral phase abundance distributions and H2O‐contents in nominally anhydrous minerals of the original granulite assemblage to constrain the hydration by aqueous fluid inflow and diffusional hydrogen influx, respectively. Both hydrations are described with a diffusion equation and affect the effective viscosity. Shear zone kinematics are constrained by the observed shear strain and thickness. The model fits the phase abundance and H2O‐content profiles if the effective hydrogen diffusivity is approximately one order of magnitude higher than the diffusivity for aqueous fluid inflow. The observed shear zone thickness is reproduced if the viscosity ratio between dry granulite and deforming, reequilibrating eclogite is ∼104 and that between dry granulite and hydrated granulite is ∼102. The results suggest shear velocities <10−2 cm/a, hydrogen diffusivities of ∼10−13±1 m2/s, and a shearing duration of <10 years. This study successfully links and validates field data to a shear zone model and highlights the importance of hydrogen diffusion for shear zone widening and eclogitization.

Monazite as a monitor of shear strain in orogenic crust

The Ramsay-Graham heterogeneous simple shear zone model revolutionized our understanding of finite strain variation in orogenic belts. Many deeply exhumed (>20 km depths) shear zones in orogenic continental crust are a consequence of sub-simple shear strain accumulation during contraction and displacement at high temperature. Here we explore the micro-scale record of this process using syn-kinematic monazite in two shear zones in a >20,000 km2 terrane of exhumed lower continental crust. Field observations combined with high-spatial resolution X-ray mapping, Th–U-Pb electron microprobe petrochronology, and electron backscatter diffraction analysis demonstrate that monazite grains can provide an important textural and temporal record of shear strain in mylonite and ultramylonite gneisses. Monazite grains exhibit aspect ratios of 1.7–4.6 parallel to the stretching lineation and parallel or oblique (<30°) to the penetrative foliation. Monazite EBSD data for grain orientation spread, i.e., average misorientation relative to the mean, are consistent with no significant dislocation-accommodated internal deformation. We conclude that dissolution precipitation creep of monazite produced compositionally-defined geometries compatible with the dextral sense of shear observed in outcrop and thin section. Syn-kinematic rims on monazite grains that develop in low strain domains during accumulation of shear strain can provide absolute ages for μm-to km-scale kinematics in continental orogens.

Evolutional model and syn-kinematic emplacement of a continental-scale strike-slip shear zone: an example of southwestern Nigeria

Evolutional model and syn-kinematic emplacement of a continental-scale strike-slip shear zone: an example of southwestern Nigeria

An analytical cutting force model of quasi-intermittent vibration assisted swing cutting based on predictive machining theory

Quasi-intermittent vibration assisted swing (QVASC) method was aimed to improve the cutting machinability of difficult-to-machine materials. Inherited the intermittent cutting characteristics of the elliptical vibration cutting (EVC) technology, this method reduces the impact of residual height on the machined surface quality. But there is still a lack of in-depth research on cutting force modeling of QVASC. Based on the conventional cutting force model, a cutting force prediction model in QVASC processing, which considers the time-variable characteristics of QVASC, adopts the non-equidistant shear zone model and regards the workpiece material properties, tool geometry, and cutting conditions as the input data are proposed in this paper. Using the micro-element method, the proposed model decomposed the cutting edge to calculate the cutting force and the cutting force value by superimposing them. It finally predicts the chip flow angle. Experimental results show that when the cutting velocity increases, the average cutting force and the Z -direction increases by 20%, the average cutting force and the Y direction decreases by 17%. The average cutting force along X direction remains unchanged; the depth of cutting became larger. Besides, the average cutting force X decreased by 18%, Y decreased 21%, and Z increased by 13%. As the feed rate increases, the X direction is increased by 26%, and the Z direction is reduced by 22%, while the cutting force in the Y direction is unchanged. After comparing and verifying the measured value and the predicted value, the minimum error of the prediction model reaches 4.01%, which validates the force model of QVACS.

Slide‐Hold‐Slide Protocols and Frictional Healing in Discrete Element Method (DEM) Simulations of Granular Fault Gouge

AbstractThe empirical constitutive modeling framework of rate‐ and state‐dependent friction (RSF) is commonly used to describe the time‐dependent frictional response of fault gouge to perturbations from steady sliding. In a previous study (Ferdowsi &amp; Rubin, 2020), we found that a granular‐physics‐based model of a fault shear zone, with time‐independent properties at the contact scale, reproduces the phenomenology of laboratory rock and gouge friction experiments in velocity‐step and slide‐hold (SH) protocols. A few slide‐hold‐slide (SHS) simulations further suggested that the granular model might outperform current empirical RSF laws in describing laboratory data. Here, we explore the behavior of the same Discrete Element Method (DEM) model in SH and SHS protocols over a wide range of sliding velocities, hold durations, and system stiffnesses, and provide additional support for this view. We find that, similar to laboratory data, the rate of stress decay during SH simulations is in general agreement with the “Slip law” version of the RSF equations, using parameter values determined independently from velocity step tests. During reslides following long hold times, the model, similar to lab data, produces a nearly constant rate of frictional healing with log hold time, with that rate being in the range of ∼0.5 to 1 times the RSF “state evolution” parameterb. We also find that, as in laboratory experiments, the granular layer undergoes log‐time compaction during holds. This is consistent with the traditional understanding of state evolution under the Aging law, even though the associated stress decay is similar to that predicted by the Slip and not the Aging law.

Measurement of plastic strain and plastic strain rate during orthogonal cutting for Ti-6Al-4V

Finite Element Modelling used to predict machining outcomes needs to be supplied with the appropriate material thermomechanical properties which are obtained by specific testing devices and methodologies. However, these tests are usually not representative of the extreme conditions achieved in machining processes and the obtained material law may not be suitable enough. Inverse identification could address this problem by obtaining material thermomechanical properties directly from machining outcomes such as cutting forces, temperatures, strain or strain rates. Nevertheless, this technique needs to be supplied with accurate machining outcomes. However, some of them such as strain or strain rate are difficult to be properly measured. The aim of this paper is to present a methodology to measure plastic strain and strain rate during orthogonal machining under plane strain conditions. The main idea is to create a physical microgrid in a workpiece and to analyze the distortion suffered by this grid. The novelty of the method consists on its capability of measuring strain and strain rate fields in a very localized area (primary shear zone) using a single image. The methodology was applied in orthogonal cutting of Ti-6Al-4V under cutting conditions that are representative of the broaching process. Experimental results were compared with DIC measurements, analytical results based on unequal division shear zone model, literature results and with numerical fields obtained from an AdvantEdge-2D model.

Is complex fault zone behaviour a reflection of rheological heterogeneity?

Fault slip speeds range from steady plate boundary creep through to earthquake slip. Geological descriptions of faults range from localized displacement on one or more discrete planes, through to distributed shearing flow in tabular zones of finite thickness, indicating a large range of possible strain rates in natural faults. We review geological observations and analyse numerical models of two-phase shear zones to discuss the degree and distribution of fault zone heterogeneity and effects on active fault slip style. There must be certain conditions that produce earthquakes, creep and slip at intermediate velocities. Because intermediate slip styles occur over large ranges in temperature, the controlling conditions must be effects of fault properties and/or other dynamic variables. We suggest that the ratio of bulk driving stress to frictional yield strength, and viscosity contrasts within the fault zone, are critical factors. While earthquake nucleation requires the frictional yield to be reached, steady viscous flow requires conditions far from the frictional yield. Intermediate slip speeds may arise when driving stress is sufficient to nucleate local frictional failure by stress amplification, or local frictional yield is lowered by fluid pressure, but such failure is spatially limited by surrounding shear zone stress heterogeneity.This article is part of a discussion meeting issue ‘Understanding earthquakes using the geological record’.

Friction behavior in metal cutting: Modeling and simulation

This work presents a simplified constitutive modeling approach to describe the operating friction mechanisms during metal cutting. The modeling approach is based on an advanced experimental set-up with high speed filming of the orthogonal cutting process as well as the classical Oxley’s parallel shear zone model. Finite element cutting simulations on carbon steel AISI 1045 with different uncut chip thicknesses and cutting speeds were conducted to validate the developed friction modeling approach. A realistic numerical prediction of cutting process reactions could be achieved.

A hybrid model for force prediction in orthogonal cutting with chamfered tools considering size and edge effect

Researches on the modeling of machining difficult-to-cut metals are important for optimization of the processing parameters, in which the force modeling is essential due to its significant influence on the performance of tools and the quality of parts. A semi-analytical method for force prediction in orthogonal cutting with chamfered tools considering both edge and size effect is proposed in this paper. The plastic deformation in the shear band was investigated using a parallel shear zone model and unequal division shear zone model. The influence of size effect on cutting force was discussed and a simplified expression of improvement factor is introduced to describe the sharp increase of shear stress under the condition of low feed rate. Simulations of orthogonal cutting with different chamfer lengths are conducted to analyze the variation of cutting force with respect to chamfer length, which reveals that the influence of chamfer length on cutting force is determined by the ratio of chamfer length to uncut chip thickness. A modified function considering the trend of material flow condition is proposed, which treats the total cutting force as a combination of cutting forces caused by chamfered edge and rake face. The calibration of constants in the proposed method is achieved using particle swarm optimization (PSO), a meta-heuristic algorithm for complicated non-linear models. The experiments show that the method works well on both fitting and predicting modules in orthogonal cutting of AISI 304 using cemented carbide tools with 15° chamfer angle or 25° chamfer angle.

Reversible Compaction in Sheared Granular Flows and Its Significance for Nonlocal Rheology

AbstractNaturally occurring granular flows like landslides often have a gas‐like rapidly moving layer immediately adjacent to a slower quasistatic layer. Determining the nature of coupling between these regimes is critical to capturing flow behavior. Using image analysis and a rheometer, we measure dilation, acoustic energy, and velocity profiles for quartz sand sheared in a geometry that imposes multiple flow regimes at once. We show that acoustic energy resulting from grain collisions in the fastest part of flow causes (a) weakening and compaction of the transitional regime layer between quasistatic and fast flow and (b) increasing slow flow via reduced friction. Thus, the volume of the entire shear zone is governed by competing effects of dilation near the boundary and compaction in the more distant transitional layer. This understanding of the partition of volume change across the shear layer can guide models of natural shear zones and interpretation of deposits.

Predicting cutting force with unequal division parallel-sided shear zone model for orthogonal cutting

Predicting cutting force with unequal division parallel-sided shear zone model for orthogonal cutting

A PSO-based semi-analytical force prediction model for chamfered carbide tools considering different material flow state caused by edge geometry

The prediction of force in metal cutting is essential when estimating tool wear, surface quality and energy consumption. As a significant characteristic in tool design, edge geometry results in more challenges in force modeling especially under the condition of cutting with chamfered insert. In this paper, a semi-analytical model is proposed to describe the effect of chamfered edge on cutting force considering multiple material flow state. In orthogonal cutting, shear effect is calculated based on the unequal division shear-zone model and Johnson-Cook's material constitutive law. Two kinds of chip-tool contact patterns are considered to discuss the effect of tool edge, chip flows on both chamfered edge and rake face when chamfer length is close to Uncut Chip Thickness (UCT), or chip flows only on chamfered edge when chamfer length is much larger than UCT. Edge force coefficients of chamfered edge are modeled as linear functions with respect to shear stress, chamfer length and chamfer angle. The variation of edge force with respect to edge geometry is studied through Finite Element Method (FEM) simulations. The modified force prediction model is established by introducing a factor S to describe the trend of edge effect with respect to the ratio of chamfer length to UCT. Finally, a modified force prediction model is presented and the constants in the model can be calibrated through a Particle Swarm Optimization (PSO)-based algorithm. Experiments of orthogonal cutting AISI304 with different chamfered carbide inserts are performed to validate the correctness and feasibility of the proposed model. The experimental results show that this model is effective in predicting the cutting force components under the condition of different edge preparations and cutting parameters.

Zippered Shear Zone Model for Interacting Shear Zones in the Borborema Province, Brazil, as Constrained by U‐Pb Dating

AbstractShear zones typically interact to form connected systems or networks to accommodate crustal deformation, but our knowledge of how this happens is fragmentary. Understanding branching and interacting shear zones requires knowledge of timing, deformation kinematics, and rheology. The Senador Pompeu, Tauá, and Cococi strike‐slip shear zones of the Borborema Province (NE Brazil) have a central role and location in the Neoproterozoic assembly of Gondwana and provide a means to understand shear zone interaction. We apply (i) U‐Pb in situ SHRIMP analysis of zircons from syntectonic plutons and dykes to constrain the timing of shearing and (ii) vorticity and strain analysis on pluton's megacrystic facies deformed in the magmatic state and during final stages of crystallization. Obtained ages show that the shear zone pair was active under high temperature at 583.5±4.6 Ma, while felsic dykes were emplaced in the brittle regime in the wall rocks. Average vorticity estimates of 0.70 indicate a strong component of pure shear in the shear zones. Despite the transpressional character, the dispersion in estimates of thinning and thickening for the Senador Pompeu shear zone highlights variations of offset rate for the interacting branches that leads to localized transtension. We conclude that the kinematic framework of the Senador Pompeu and Tauá conjugate pair involves the formation of a dextrally closing zipper structure involving the trailing Cococi shear zone to the southwest, which in turn caused the northeastward extrusion of the enclosed crustal wedge and possibly activation of the nappe system of the Ceará Central domain.

Inverse identification of modified Johnson–Cook model for cutting titanium alloy Ti6Al4V using firefly algorithm

The original Johnson–Cook equation fails to describe the significant thermal softening phenomenon of flow stress in cutting process of titanium alloy Ti6Al4V. Recently, some researchers developed some modified Johnson–Cook models of Ti6Al4V by introducing some additional parameters. But effective parameter identification method is unavailable in those research works. In this work, an inverse approach is developed to determine the additional parameters. A modified Johnson–Cook model with the hyperbolic tangent function is adopted, in which four unknown parameters need to be determined. The parameter assessment is taken as an optimization process based on the unequal division parallel-sided shear zone model. Along with the measured cutting force and chip thickness, the firefly algorithm is introduced to search for the parametric optimal solution. Those four parameters are determined when the difference between the predicted and experimental effective stress at shear plane reaches its minimum. The identified constitutive model is subsequently verified by finite element simulation of orthogonal cutting process, and compared with previous different material models. With the identified modified Johnson–Cook model, the serrated chip is observed in all the simulations. A good agreement between verification experiments and simulations is achieved. An acceptable prediction accuracy with an error of 10.28% on cutting force and an error of 18.12% on chip size is achieved.

A Model for Predicting Dynamic Cutting Forces in Sand Mould Milling with Orthogonal Cutting

Cutting force is one of the research hotspots in direct sand mould milling because the cutting force directly affects the machining quality and tool wear. Unlike metals, sand mould is a heterogeneous discrete deposition material. There is still a lack of theoretical research on the cutting force. In order to realize the prediction and control of the cutting force in the sand mould milling process, an analytical model of cutting force is proposed based on the unequal division shear zone model of orthogonal cutting. The deformation velocity relations of the chip within the orthogonal cutting shear zone are analyzed first. According to the flow behavior of granular, the unequal division shear zone model of sand mould is presented, in which the governing equations of shear strain rate, strain and velocity are established. The constitutive relationship of quasi-solid–liquid transition is introduced to build the 2D constitutive equation and deduce the cutting stress in the mould shear zone. According to the cutting geometric relations of up milling with straight cutting edge and the transformation relationship between cutting stress and cutting force, the dynamic cutting forces are predicted for different milling conditions. Compared with the experimental results, the predicted results show good agreement, indicating that the predictive model of cutting force in milling sand mould is validated. Therefore, the proposed model can provide the theoretical guidance for cutting force control in high efficiency milling sand mould.

The effect of pulsed current on the shear deformation behavior of Ti-6Al-4V alloy

Pulse current-assisted forming is a new technology to improve the plastic deformability of titanium alloy. In this work, Shearing tests of Ti-6Al-4V alloy were conducted using hat-shaped specimens under pulsed current (electroplastic shearing) and constant temperature (isothermal shearing). The actual deformation in shear zone of electroplastic shearing was larger than that of isothermal shearing. The shear load is also decreased by the pulsed current. Microstructure variation in the shear zone was investigated by scanning electron microscopy. An evident straight shear band was observed in the electroplastic shearing specimens. The deformation model of shear zone was established. Intracrystalline deformation was markedly easier for the grains with the pulsed current and induced larger deformation of the grains along the shear direction. Microcracks were observed in the shear zone of isothermal shearing, but none were found in the shear zone of electroplastic shearing. Evident crack healing was found in the crack tip of the shear zone of electroplastic shearing.