Elastic-plastic Deformation Research Articles

The effect of the multiplicity of frictional action on the micromechanical properties of NiCrBSi-coatings

The paper investigates the effect of the number of passes (1 or 2) of an indenter made of fine cubic boron nitride during friction treatment of PG-SR2 and PG-10N-01 NiCrBSi-coatings on the micromechanical properties of their surface layers. The friction treatment of the coating surface under all the process conditions studied, in comparison with the initial polished state, increases the strength characteristics of the coating surface layer and the parameters indicating the resistance of the material surface to elastic-plastic deformation. The effect of the number of indenter passes during surface friction treatment on the strength characteristics is found to be more significant for the softer and more ductile PG-SR2 coating than for the PG-10N-01 coating. This is attributed to the higher strain hardenability of the former.

Elastoplastic analysis of AA7075-O aluminum sheet by hybrid micro-scale representative volume element modeling with really-distributed particles and in-situ SEM experimental testing

• Presents a novel computationally-efficient reconstruction of 3D RVE model of second-phase particle-strengthened AA7075-O sheet with real distribution of particles based on FIB-SEM techniques. • Three types of second-phase particles (i.e., irregularly-shaped iron-rich particle Al 3 Fe, elliptically-shaped particle MgZn 2 , and needle-like particle CuAl 2 ) are determined using SEM-based EDS and EBSD techniques. • Presents a systematic study of the overall elastic-plastic response by developing and applying a hybrid experimental analysis and computational modeling framework. • Good agreement is observed in the comparison of RVE results with that of in-situ SEM tensile tests, indicating that the real 3D microstructure-based RVE models can accurately predict the plastic deformation and interfacial failure evolution in AA7075-O sheet. This paper addresses the challenge of reconstructing randomly distributed second-phase particle-strengthened microstructure of AA7075-O aluminum sheet material for computational analysis. The particle characteristics in 3D space were obtained from focused ion beam and scanning electron microscopy (FIB-SEM) and SEM-based Electron Backscatter Diffraction/Energy Dispersive X-ray Spectrometry (EBSD/EDS) techniques. A theoretical framework for analysis of elastic-plastic deformation of such 3D microstructures is developed. Slip-induced shear band formation, void initiation, growth and linkage at large plastic strains during uniaxial tensile loading were investigated based on reconstructed 3D representative volume element (RVE) models with real-distribution of particles and the results compared with experimental observations. In-situ SEM interrupted tension tests along transverse direction (TD) and rolling direction (RD), employing microscopic-digital image correlation (μ-DIC) technique, were carried out to investigate slip bands, micro-voids formation and obtain microstructural strain maps. The resulting local strain maps were analyzed in relation to the experimentally observed plastic flow localization, failure modes and local stress maps from simulations of RVE models. The influences of particle size, shape, orientation, volume fraction as well as matrix-particle interface properties on local plastic deformation, global stress-strain/strain-hardening curves and interfacial failure mechanisms were studied based on 3D RVE models. When possible, the model results were compared with in-situ tensile test data. In general, good agreement was observed, indicating that the real 3D microstructure-based RVE models can accurately predict the plastic deformation and interfacial failure evolution in AA7075-O aluminum sheet.

Comparative numerical study of rate-dependent continuum-based plasticity models for high-velocity impacts of copper particles against a substrate

The problem of high-rate elastic-plastic deformation of micro-sized copper particles impacting against a copper substrate was investigated by applying the continuum-based formulation and finite element thermomechanical analysis. Comparative study of selected plasticity models was performed. The aim of the paper was to study strain rate-dependant plasticity for a wide range of strain rates. The strain-rate-dependant Johnson-Cook and Cowper-Symonds models were studied by comparing displacements, velocities, strains, strain rates, stresses, contact forces, and temperatures and their contribution to material yield stress. The study shows the importance of the high-strain rate yielding model and its adequacy for experimental data. Both models complement each other and may be regarded as soft and hard bounds of the solution. A new, combined, two-function model, containing two independent functions for each of the two ranges, is suggested. The proposed model describes a low strain rate sensitivity range using the Johnson-Cook expression, while allows fitting of the model for experimental results in a high strain rate sensitivity range, using a modified Cowper-Symonds expression. This combination is capable of describing both low and high strain rate regimes, giving the minimum deviation from experimental results.

Seismic Performance Evaluation of a High-Rise Building with Structural Irregularities

In this study, the seismic performances of a 14-storey office building in Nanjing, China, due to its plan and vertical irregularities in the structural system, were evaluated using the response spectrum method, elastic time history analysis and elastic–plastic time history analysis. In combination of these three methods, the storey drifts and elastic–plastic states of typical structural members under three levels of earthquakes were determined to verify the robustness of the structural design program. The damage states of typical structural members at some sensitive positions were estimated and evaluated under rare earthquakes. Consequently, all structural members were within the scope of elastic performances under the actions of frequent earthquakes. The maximum displacements and storey drifts satisfied the requirements of the design codes within the scope of elastic or elastic–plastic deformations. The induced damages could reach “moderate damage” states, satisfying the requirements for the expected performances by the codes. The consequences indicated that the design scheme and critical parameters for the building structure satisfied the requirements of seismic performances from the codes.

Validity Analysis of Elastic-Plastic Deformation Mechanics Problems Considering the Growth of Pores in the Material Via the Rice–Tracey–Huang Models. Part 3. Generalized Rice–Tracy–Huang Equation

Validity Analysis of Elastic-Plastic Deformation Mechanics Problems Considering the Growth of Pores in the Material Via the Rice–Tracey–Huang Models. Part 3. Generalized Rice–Tracy–Huang Equation

Deformation and seepage properties of raw coal during the simultaneous loading and unloading of axial stress and confining pressure

The mining of coal resources causes the stress on the front and both sides of the working face to be in a complex loading and unloading process, and the gas contained in the coal body migrates, which can cause gasdynamic disasters in severe cases. Therefore, this study designed a three-dimensional stress path based on the in situ stress distribution characteristics of the No. 2461 working face and conducted the experiment on the deformation and seepage characteristics of raw coal under simultaneous unloading (loading) axial stress and loading (unloading) confining pressure. It is considered that in the process of loading axial stress, the volumetric strain increases gradually with the increase in effective stress, and the permeability decreases exponentially with the increase in effective stress. In the process of simultaneous unloading axial stress and loading confining pressure, the volumetric strain of coal sample increases with the increase in effective stress, and the permeability decreases exponentially with the increase in effective stress. However, the processes of simultaneous loading axial stress and unloading confining pressure are opposite, and the variation curves of the two do not overlap, indicating that the coal sample undergoes elastic-plastic deformation after cyclic loading, the permeability cannot be restored to the initial state, and the volumetric strain further expands. The permeability damage rate and maximum permeability damage rate are used to evaluate the recovery degree and reduction range of coal samples' permeability. The volume expansion rate and maximum volume expansion rate are used to evaluate the expansion degree and increase range of coal samples' volume.

Establishment of scratching force model for micro-removal of SiCp/Al composites by ultrasonic vibration

In the process of micro-removal machining SiCp/Al, the real-time prediction of cutting force is of great significance to ensure the surface quality of the workpiece and safe production. Based on the two major sources of cutting forces: the elastic-plastic deformation resistance of the machined material and the friction between the tool and the material, this paper established an ultrasonic vibration-assisted scratching force model by considering four aspects: chip formation force, SiC particle breaking force, tool and Al matrix friction force and rolling friction force. The model was experimentally validated by a self-built ultrasonic scratching device, and the effects of scratching speed, SiC particle volume fraction, and ultrasonic amplitude on the scratching force were investigated. The results showed that the scratching force is minimum when the scratching speed is 400 mm/min for both ordinary scratching (OS) and ultrasonic vibration-assisted scratching (UVAS). As the volume fraction of SiC particles increases, the scratching force gradually increases. Under the same experimental conditions, the force of UVAS is much smaller than OS. The maximum error between the experimental value and the predicted value of the model is 33% and gradually decreases with the increase of scratching speed and SiC volume fraction. The overall trend of the two is consistent, which proves the feasibility of the scratching force model. This study can provide some theoretical guidance for the force control when machining SiCp/Al. The ultrasonic vibration-assisted scratching force model was established by considering the chip formation force, SiC particle breaking force, tool matrix friction force, rolling friction force and ultrasonic vibration applied. And the model was verified by experiments. • A new machining process of ultrasonic vibration-assisted scratching was proposed. • An ultrasonic vibration-assisted scratching force model was established. • The experimental values were in good agreement with the model predicted value, which verified the feasibility of the established model.

Numerical Simulation on Borehole Instability Based on Disturbance State Concept

This paper carries out a study on the numerical simulation of borehole instability based on the disturbance state concept. By introducing the disturbance damage factor into the classical Mohr–Coulomb yield criterio, we establish a finite element hydro-mechanical coupling model of borehole instability and program the relevant field variable by considering elastic–plastic deformation in borehole instability, the distribution of the damage disturbance area, the variation of porosity and permeability with the disturbance damage factor, etc. Numerical simulation shows that the borehole stability is related to the action time of drilling fluid on the wellbore, stress anisotropy, the internal friction angle of rock, and borehole pressure. A higher horizontal stress difference helps suppress shear instability, and a higher rock internal friction angle enhances shear failure around the borehole along the maximum horizontal principal stress. When considering the effect of the internal friction angle of rock, the rock permeability, disturbance damage factor, and equivalent plastic strain show fluctuation characteristics. Under the high internal friction angle of rock, a strong equivalent plastic strain area and disturbance damage area occur in the direction of the maximum horizontal principal stress. Their cloud picture shows the mantis shape, where the bifurcation corresponds to the whiskers of the shear failure area in borehole instability. This study provides a theoretical basis for solving the problem of borehole instability during drilling engineering.

Mechanical properties and deformation mechanisms of (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C high‐entropy ceramics characterized by nanoindentation and scratch tests

High-entropy carbides ceramics (HECCs) have attracted extensive attention for their broad application prospects in harsh environments, due to the excellent properties. In this work, the (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C HECCs were prepared using spark plasma sintering at 1800 °C. Then, mechanical properties of HECCs were tested by nanoindentation and scratch tests under different loading conditions. Finally, the mechanical properties and deformation mechanisms were discussed in detail. The density of sintered HECCs reached 8.98 g/cm3, with a relative density of 95.63%. The HECCs demonstrated a single-phase with rocksalt microstructures. The elastic modulus of HECCs was almost a constant under different strain rates, while the hardness obviously increased as the indentation strain rate increasing. In addition, a simple fitted formula was developed to establish the function of hardness and strain rate. Under a relative low scratch load, the HECCs exhibited complete elastic–plastic deformation, and the material removal mechanism was plastic deformation. With increasing scratch load, the material removal mechanism of HECCs transformed into the combined action of plastic deformation and brittle fracture. Furthermore, the deformation mechanisms of HECCs were also influenced by the scratch velocity. At a higher scratch velocity, more local fractures at the micro-scale occurred, and the numbers and sizes of chips and debris also increased.

Theoretical prediction of cross-sectional deformation of circular thin-walled tube in large elastic–plastic deformation stage under lateral compression

The present paper focusing on the most important energy absorbing system of the circular thin-walled tubes or shells under lateral compression between two rigid plates, which is also a basic mechanical issue, studies the cross-sectional deformation in terms of the compressive force applying to the tube in the large elastic–plastic deformation stage during the lateral compressive process by both theoretical as well as finite element analysis (FEA) methods. Firstly a FEA simulation for the thin-walled tube’s lateral compressive process between two parallel plates is carried out to analyze the mechanical response and deformation characteristics, and then it is validated by tube’s lateral compressive experiment using digital image processing technology. Following the simulation results, some assumptions are proposed for theoretical derivation. Secondly focusing on the large elastic–plastic deformation stage (Stage II, in this paper), the compressive deformation of thin-walled tubes is divided into elastic and plastic regions according to the von Mises yield criterion. In elastic region the linear strain–displacement relations of shell theory and Hooke’s stress–strain relations are employed, and in plastic region the nonlinear large strain–displacement relations of doubly-curved shell theory and the power hardening rule are employed. Then considering both geometric and material nonlinearities, the equilibrium equation, which is a complicate integral equation with the variable upper limit, is derived using the principle of virtual work. It is solved by expanding the integrand as a set of polynomials power series. Then the predicted cross-sectional deformation in terms of the compressive force can be obtained by the iterative method. Finally some lateral compressive simulations involving various tubes with different geometric parameters are carried out, and the theoretical model is validated by comparison of the cross-sectional profiles predicted by theoretical model with those obtained by the simulations as well as other methods. At the same time, the applicable conditions of this model are discussed. This paper will play a positive role in studying the cross-sectional deformation for various shells under lateral compression in different application areas.

Assessing the fracture and fatigue resistance of nanostructured thin films

Fatigue failure through sustained loading of ductile materials manifests in irreversible motion of dislocations, followed by crack initiation and growth. This contrasts with the mechanisms associated with brittle ceramics, such as nanostructured physical vapor deposited thin films, where inhibited dislocation mobility typically leads to interface-controlled damage. Hence, understanding the fatigue response of thin films from a fundamental viewpoint – including altered atomic bonds, crystal structures, and deformation mechanisms – holds the key to improved durability of coated engineering components. Here, a novel method utilizing quasi-static and cyclic-bending of pre-notched, unstrained microcantilever beams coupled with in situ synchrotron X-ray diffraction is presented to study the fracture toughness and fatigue properties of thin films under various loading conditions. Investigating a model system of sputter-deposited Cr and Cr-based ceramic compounds (CrN, CrB2, and Cr2O3) demonstrates that the fatigue resistance of such thin films is limited by the inherent fracture toughness. In fact, cantilever cycling close to the critical stress intensity is sustained up to 107 load cycles on all materials, without inducing noticeable material damage, structural or stress-state changes. The observed variation in fracture toughness is put into context with linear-elastic fracture theory and complementary micro-pillar compression, thereby elucidating the wide range of values from as low as 1.6±0.2 MPa√m for Cr1.79O3 up to 4.3±0.3 MPa√m for Cr1.03B2, respectively. Moreover, possible mechanisms governing the elastic-plastic deformation response of all coatings, both in quasi-static and cyclic-loading conditions, are discussed. Our findings contribute key-insights into the underlying mechanisms dictating the damage tolerance of PVD coated components by relating fatigue strength limits to fundamental material properties.

Criteria for ultimate aseismic capacity of high rockfill dam

<p indent="0mm">The ultimate aseismic capacity is important to evaluate the seismic safety of a rockfill dam. However, no specification in China explicitly stipulates the criteria for the ultimate aseismic capacity of a rockfill dam. Existing evaluation factors and their indices to represent earthquake-induced damage to rockfill dams are not unified, and there is a problem with the safety degrees obtained by the indexes of different evaluation factors not being coordinated. In this study, a large number of systematic analyses of overall elastic-plastic deformation and slip deformation of high rockfill dams (height &gt; <sc>200 m)</sc> under earthquake are performed in addition to a comparative study of measured engineering analysis. Based on the above studies, four basic principles for determining the criteria for the ultimate aseismic capacity of a high rockfill dam are proposed: strictly following the mapping relationship between the relative settlement ratio of dam crest and the damage degree of dams under earthquake, ensuring that the dam can not be a collapse in extreme earthquakes, taking the relative settlement ratio of dam crest as the key control evaluation factor, and ensuring the coordination of different evaluation factors such as the relative settlement ratio of dam crest and the slip deformation of dam slope. Finally, the criteria for the ultimate aseismic capacity of a high concrete face rockfill dam and a core-wall rockfill dam under earthquake conditions are proposed. The findings of the study could provide an important standard basis for determining the ultimate aseismic capacity of a high rockfill dam.

Analytical Model of Hole Diameter and Self-Guiding Machining Mechanism of BTA Deep Hole Drilling

The goal of this study was to explore the self-guided machining mechanism of boring and trepanning association (BTA) deep hole drilling and realize precise control of the machining quality. The motion analysis method was used to analyze the center motion trajectory of the drill during the entrance, and the self-guiding mechanism and hole-forming mechanism of BTA deep hole drilling were revealed. Considering the bending deformation of the drilling tube and the tool structure parameters, according to the elastic-plastic deformation theory and Hertzian contact theory, a novel analytical model of the extrusion contact between the guide pads and the hole wall of the BTA deep hole drilling was established for the theoretical prediction of the extrusion deformation and the machining hole diameter. Combined with the finite element method (FEM) simulation model, the variation law of the contact inclination angle, contact stress, and extrusion deformation of the guide pads and the hole wall with the drilling conditions were studied. The total extrusion deformation between the guide pad and the hole wall was between 10 and 50 μm. The maximum error between the FEM simulation results and the test results was 18.1%, and the maximum error between the analytical model results and the test results was 23.6%. The simulation and experimental results showed that the established extrusion contact model could accurately predict the extrusion deformation of the hole wall and the machining hole diameter.

Experimental facility for studying the physical properties of materials in a plane stress state

An original experimental facility for studying the physical properties of materials during elastic-plastic deformation along two axes has been created. The facility has no ferromagnetic parts in the working area, thus enabling us to make more accurate magnetic measurements. Biaxial deformation is simulated by the finite element method in order to optimize the geometry of the specimen and to determine the stress state in the central zone of the specimen. Test experiments on the effect of biaxial tension on the coercive force of the 12G2S are performed.

Elastic-plastic deformation of surrounding rocks under graded yielding support of tunnel

Elastic-plastic deformation of surrounding rocks under graded yielding support of tunnel

Experimental Study on Dynamic Mechanical Properties of Sandstone Corroded by Strong Alkali

In order to analyze the effect of different corrosion times on the dynamic compression mechanical properties of sandstone, the coal mine sandstone specimens are subjected to corrosion in NaOH solution with pH 11 for 0 d, 1 d, 3 d, 7 d, 14 d, and 28 d, and then, the impact compression tests and Brazilian splitting test are conducted using a split Hopkinson pressure bar apparatus. The study results show that sandstone specimen mass and the average density growth rate increases, with the corrosion time first rapidly increasing and then tending to level off the trend. The impact of the compression specimens on the dynamic stress–strain curve change law is basically the same, but the time gradient curve shape is different, and the line elastic deformation stage and plastic deformation stage curve difference gradually decreases. The specimen dynamic compressive strength and the dynamic elastic modulus with corrosion time are quadratic, and the exponential function declines the relationship. After corrosion of 28 d sandstone specimens, the dynamic compressive strength and dynamic elastic modulus are much lower than the uncorroded specimens. The average strain rate and the dynamic peak strain with the corrosion time extension are a quadratic function of the increasing relationship after the corrosion effect of the sandstone dynamic peak strain, and the average strain rate is significantly greater than the uncorroded specimens. With the corrosion time extension of sandstone specimens by the impact of damage degree being increased, the 14 d and 28 d specimen ruptures’ degree is much greater than other time gradients. The dynamic tensile strength of the split specimens decreases with increasing corrosion time; the dynamic peak strain increases quadratically; and the transmitted energy also decreases with increasing corrosion time.

Numerical Simulation on Hydraulic Fracture Height Growth across Layered Elastic–Plastic Shale Oil Reservoirs

Shale oil reservoirs are characterized by having various types of vertical sublayers, a large contrast in rock mechanical properties, well-developed bedding, and high clay content, which are likely to cause rock elastic–plastic deformation. In numerical simulations of hydraulic fracture (HF) propagation in the shale oil reservoirs, the effects of rock elastic–plastic deformation and complex bedding structure on the layer-crossing behavior of HF are not considered. To understand the mechanism of HF height growth in shale oil reservoirs, we used the cohesive zone method to establish an elastic–plastic finite element model of HF propagation by considering the effects of shell limestone interlayers, the Mohr–Coulomb yield criterion for shear–plastic failure, the cross-mechanical interaction between bedding and shale oil reservoir, and the complex situations such as the HF height across high-electrical resistivity bedding and high-conductivity fractures. The effects of internal friction angle, cohesion, layer stress contrast, fracture toughness, bedding bond strength, injection rate, elastic modulus, and bedding shear strength on HF height growth in shale oil reservoirs are studied, and the characteristics of HF width profile, injection pressure, failure mode, and maximum HF width are compared. Compared with the layer stress contrast, cohesion, internal friction angle, and fracture toughness, the injection rate, elastic modulus, and bedding shear strength and bond strength have a larger effect on the vertical HF width. Increment of the injection rate, decrease of the elastic modulus, and increment of the bedding shear strength and bond strength are favorable for HF height growth in the shale oil reservoir. As rock cohesion and internal friction angle increase, the HF width decreases. At the initial stage of fracturing fluid injection, the maximum HF height and injection pressure fluctuate. Lower cohesion and internal friction angle promote rock shear failure in HF height growth. Our study provides guidance for the stimulation of fracture crossing layers in the shale oil reservoirs.

Mechanical Load-Induced Atomic-Scale Deformation Evolution and Mechanism of SiC Polytypes Using Molecular Dynamics Simulation.

Silicon carbide (SiC) is a promising semiconductor material for making high-performance power electronics with higher withstand voltage and lower loss. The development of cost-effective machining technology for fabricating SiC wafers requires a complete understanding of the deformation and removal mechanism. In this study, molecular dynamics (MD) simulations were carried out to investigate the origins of the differences in elastic–plastic deformation characteristics of the SiC polytypes, including 3C-SiC, 4H-SiC and 6H-SiC, during nanoindentation. The atomic structures, pair correlation function and dislocation distribution during nanoindentation were extracted and analyzed. The main factors that cause elastic–plastic deformation have been revealed. The simulation results show that the deformation mechanisms of SiC polytypes are all dominated by amorphous phase transformation and dislocation behaviors. Most of the amorphous atoms recovered after completed unload. Dislocation analysis shows that the dislocations of 3C-SiC are mainly perfect dislocations during loading, while the perfect dislocations in 4H-SiC and 6H-SiC are relatively few. In addition, 4H-SiC also formed two types of stacking faults.

Axial impact fracture and elastic–plastic deformation characteristics of the assembly of different numbers of spherical particles

Axial impact fracture and elastic–plastic deformation characteristics of the assembly of different numbers of spherical particles

Effect of Salt Solution on the Mechanical Behaviours of Geopolymer Concrete under Dry-Wet Cycles

Seawater splashing and frequent rainfall in the coastal area will often cause the concrete members to be affected by dry-wet cycles. In order to investigate the effect of salt solution on the mechanical behaviours of geopolymer concrete under dry-wet cycles, a series of tests on erosion of geopolymer concrete by three different salt solutions were carried out by using the mass loss rate, compressive strength, erosion resistance coefficient, and elastic modulus. The results show that, with the increase of dry-wet cycles, the mass of the specimen increases slightly at 20 dry-wet cycles and then decreases gradually. Then, the stress-strain curve of geopolymer concrete can be divided into three stages: linear growth stage, deceleration growth stage, and slow decline stage, which correspond to the elastic deformation stage, elastic-plastic deformation stage, and crushing stage, respectively. The overall trend of the stress-strain curve is similar under different dry-wet cycles, and the peak stress decreases with the increase of dry-cycle. The relationship between stress and strain of geopolymer concrete samples with different salt solutions is similar, while their strength characteristics have changed obviously. Furthermore, with the increase of dry-wet cycles, the compressive strength and the relative elastic modulus of geopolymer concrete gradually decrease, which reflects that sulfate erosion will lead to the strength loss of geopolymer concrete, causing its internal damage, thus having adverse effects on it. Different salt solutions have the great influence on the mass loss rate, compressive strength, erosion resistance coefficient, and elastic modulus of geopolymer concrete. In detail, the mixed salt solution erosion results in the greatest damage to geopolymer concrete and accelerates the damage. Chloride salt solution erosion causes middle damage to geopolymer concrete. Compared with the other two salt solutions, sulfate solution erosion leads to the least damage to geopolymer concrete and then sulfate has a certain inhibitory effect on the damage of geopolymer concrete. In addition, based on the test results, the constitutive model considering dry-wet cycles damage of salt solution is proposed, and the correctness is verified. This study has a good guiding value for geopolymer concrete engineering in coastal areas.