Microstructure,Texture Evolution,and Strain Hardening Behaviour of As-extruded Mg-Zn and Mg-Y Alloys under Compression

Microstructure,texture evolution and strain hardening behaviour of the Mg-1Y and Mg-1Zn(wt%)alloys were investigated under room temperature compression.Microstructural characterization was performed by optical microscopy,scanning electron microscopy,electron back scattered diffraction and transmission electron microscopy.The experimental results show that Mg-1Zn alloy exhibits conventional three-stage strain hardening curves,while Mg-1Y alloy exhibits novel six-stage strain hardening curves.For Mg-1Y alloy,rare earth texture leads to weak tensile twinning activity in compression and consequently results in a moderate evolution to<0001>texture.Moreover,inefficient tensile twinning activity and weak slip-twinning interaction give rise to excellent ductility and high hardening capacity but low strain hardening rate.For Mg-1Zn alloy,basal texture leads to pronounced tensile twinning activity in compression and consequently results in rapid evolution to<0001>texture.The intense tensile twinning activity and strong slip-twinning interaction lead to high strain hardening rate but poor ductility and low hardening capacity.

Modeling of strain hardening and dynamic recrystallization of ZK60 magnesium alloy during hot deformation

The flow stress behavior of ZK60 alloy at elevated temperature was investigated. The strain hardening and dynamic recrystallization of the alloy were modeled by Kocks-Meching model and Avrami equation, respectively. A new constitutive equation during hot deformation was constructed to predict the flow stress considering the dynamic recrystallization. The results show that the flow stress curves predicted by the proposed equation have high correlation coefficients with the experimental data, which confirms that the developed model is accurate and effective to establish the flow stress equation of ZK60 magnesium alloy during hot deformation. Microstructure observation shows that dynamic recovery occurs in the initial stage of hot deformation. However, the microstructure turns to recrvstallization structure as the strain increases.

Effect of strain rate and deformation temperature on strain hardening and softening behavior of pure copper

The effects of the deformation temperature and the strain rate on the hot deformation behavior of pure copper were investigated based on compression tests. The expressions of strain hardening rate, dynamic recrystallization critical stress, saturated stress, dynamic recovery volume fraction and dynamic recrystallization volume fraction were determined. According to the processing map, the instability regions occur in regions of 400?450 °C, 0.001?0.05 s?1 and 450?750 °C, 0.05?1 s?1. The deformation mechanism in the stability region is dynamic recrystallization. The flow stress was predicted. The results also show that the true stress–true strain curves predicted by the extracted model are in good agreement with the experimental results.

Analysis of plane strain bending of a strain hardening curved beam based on unified yield criterion

The analysis of plane strain elastic-plastic bending of a linear strain hardening curved beam with a narrow rectangular cross section subjected to couples at its end is conducted based on a unified yield criterion. The solutions for the mechanical properties of plane strain bending are derived, which are adapted for various kinds of non-strength differential materials and can be degenerated to those based on the Tresca, von Mises, and twin-shear yield criteria. The dependences of the two critical bending moments, the radii of the interfaces between the elastic and plastic regions and the radial displacements of the points at the symmetrical plane on different yield criteria and Poisson’s ratios are discussed. The results show that the influences of different yield criteria and Poisson’s ratio on the two critical bending moments, the radii of the interfaces between the elastic and plastic regions and the radial displacements of the points at the symmetrical plane of the curved beam are significant. Once the value of bis obtained by experiments, the yield criterion and the corresponding solution for the materials of interest are then determined.

Characterization of Tensile Strain Hardening Behaviors for 32Mn-7Cr-1Mo-0.3N Cryogenic Austenitic Steel

The strain hardening behaviors of 32Mn-TCr-1Mo-0.3N austenitic steel were characterized by a simple and effective method. The results show that Hollomon relationship is not applicable during total uniform deformation stage. The flow equation was proposed, Inσ=αexp（lnε/b）＋c. The variation rates of strain hardening exponents with true strain at 77 K are obviously higher than that at other temperatures and the value of d^2σ/dε^2 becomes positive during high strain stage. The characters of this variation are principal reasons for increasing elongation at 77 K. The forming of mechanical twin as well as ε-martensite leads to a high elongation at 77 K.

Potential Use of Strain Hardening ECC in Permanent Formwork with Small Scale Flexural Beams

Utilizing pre-cast ECC panels as participating permanent formwork of concrete members, and the validity of using ECC to disperse the single crack in concrete into multiple ones in ECC were studied. In the process, totally two kinds of ECC with different tensile properties, 7 series of flat panels with different top surface figures and 3 U-shape panels with different inner surface forms were investigated. To evaluate the performance of the permanent formworks, small ECC-concrete composite beams were cast and tested mechanically. The 4-point bending test results show that the use of pre-cast ECC panels as permanent formwork can significantly improve the load capacity and toughness of a concrete member, effectively dispersing single widely opened crack in concrete into multiple ones in ECC. Most permanent formworks show perfect bond with the concrete cast on them, while the ones with partially debonded zone achieve the best mechanical performance. The U-shape permanent formworks show better performances than the flat ones, achieving much betler improvements in both the load capacity and toughness, together with better crack width control.

Strain hardening behavior of Mg-Y alloys after extrusion process

The strain hardening is an effective mode of enhancing mechanical properties in alloys.In this work,the strain hardening behaviors of Mg-xY(x=1,2,and 3 wt%)after extrusion process was investigated using uniaxial tensile tests.Results suggest that the Mg-xY alloys are composed ofα-Mg with a little amount of Mg24Y5 phase.The average grain size reduces from 19.8μm to 12.2μm as the Y content adds from 1 wt%to 2 wt%.Nevertheless,when Y content reaches 3 wt%,the grain size reaches to 12.9μm,which is close to that of Mg-2Y.The strain hardening rate decreases from 883 MPa to 798 MPa at(σ-σ0.2)=40 MPa,and Mg-2Y and Mg-3Y have the similar strain hardening response.Moreover,Mg-1Y shows an obvious ascending stage after the steep decreasing stage,which is mainly caused by the activation of twinning.The strain hardening behavior of Mg-xY is explained based on understanding the roles of the deformation mechanisms via deformation microstructure analysis and Visco-Plastic Self Consistent(VPSC)model.The variation of strain hardening characteristics with increasing Y content is related to the effects of grain size and texture.

Damage evolution model of strain hardening cementitious composites under the uniaxial stress state

The deformation and damage behaviors of strain hardening cementitious composites （SHCC） under the uniaxial stress state were investigated in this paper. Two ductile failure-based constitutive models were introduced to describe the uniaxial tension and compression properties of SHCC only using a few parameters. The computation method of model parameters was developed to ease the simulation procedures. Damage evolution of the SHCC was simulated by the formulation of continuum damage mechanics subsequently. The results show that the proposed models fit the stress-strain curves reasonably well, and the damage variables show different growth rules under uniaxial tension and compression. It is concluded that the proposed method can not only simply simulate the constitutive behavior of SHCC with the reasonable accuracy but also capture the characteristic of material degradation.

EFFECT OF STRAIN RATE(?) ON STRAIN HARDENING EXPONENT n OF SOME METALLIC MATERIALS

Variable strain rate tension tests for 4 metallic materials show that as the strain rate in creases the strain hardening exponent n decreases. The trend follows a two stage linear relation between n and Ig (?). When (?) < (?)cp, i.e. under quasi-static loading, n can be considered as a constant, but when (?)>(?)cp, n decreases rapidly till an ideal plastic state. n = 0. The characterizations and mechanisms of softening induced by high (?) are discussed.

Effect of strain hardening and strain softening on welding distortion and residual stress of A7N01-T4 aluminum alloy by simulation analysis

The effect of strain hardening and strain softening behavior of flow stress changing with temperature on welding residual stress, plastic strain and welding distortion of ATN0 1-T4 aluminum alloy was studied by finite simulation method. The simulation results show that the weld seam undergoes strain hardening in the temperature range of 180-250 ℃, however, it exhibits strain softening at temperature above 250 ℃ during welding heating and cooling process. As a result, the strain hardening and strain softening effects counteract each other, introducing slightly influence on the welding residual stress, residual plastic strain and distortion. The welding longitudinal residual stress was determined by ultrasonic stress measurement method for the flat plates of A7N01-T4 aluminum alloy. The simulation results are well accordant with test ones.

Strain hardening behavior, strain rate sensitivity and hot deformation maps of AISI 321 austenitic stainless steel

Hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800–1200℃ and constant strain rates of 0.001,0.01,0.1,and 1 s^(−1).Hot flow curves were used to determine the strain hardening exponent and the strain rate sensitivity exponent,and to construct the processing maps.Variations of the strain hardening exponent with strain were used to predict the microstructural evolutions during the hot deformation.Four variations were distinguished reflecting the different microstructural changes.Based on the analysis of the strain hardening exponent versus strain curves,the microstructural evolutions were dynamic recovery,single and multiple peak dynamic recrystallization,and interactions between dynamic recrystallization and precipitation.The strain rate sensitivity variations at an applied strain of 0.8 and strain rate of 0.1 s^(−1) were compared with the microstructural evolutions.The results demonstrate the existence of a reliable correlation between the strain rate sensitivity values and evolved microstructures.Additionally,the power dissipation map at the applied strain of 0.8 was compared with the resultant microstructures at predetermined deformation conditions.The microstructural evolutions strongly correlated to the power dissipation ratio,and dynamic recrystallization occurred completely at lower power dissipation ratios.

A crystal plasticity based approach to establish role of grain size and crystallographic texture in the Tension–Compression yield asymmetry and strain hardening behavior of a Magnesium–Silver–Rare Earth alloy

Existence of tension–compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications.The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium–Silver–Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing.The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests.The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts.The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock–Mecking’s analysis.Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior.This was especially dominant with coarsening of grain size.Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations.The role of crystallographic texture for inducing the polarity to Tension–Compression yield asymmetry was corroborated.A critical grain size in Magnesium–Silver–Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.

Equivalent strain hardening exponent of anisotropic materials based on spherical indentation response

Uniaxial strain hardening exponent is not suitable for describing the strain hardening behaviors of the anisotropic materials, especially when material deforms in the multi-axial stress states. In this work, a novel method was proposed to estimate the equivalent strain hardening exponent of anisotropic materials based on an equivalent energy method. By performing extensive finite element (FE) simulations of the spherical indentation on anisotropic materials, dimensionless function was proposed to correlate the strain hardening exponent of anisotropic materials with the indentation imprint parameters. And then, a mathematic expression on the strain hardening exponent of anisotropic materials with the indentation imprint was established to estimate the equivalent strain hardening exponent of anisotropic materials by directly solving this dimensionless function. Additionally, Meyer equation was modified to determine the yield stress of anisotropic materials. The effectiveness and reliability of the new method were verified by the numerical examples and by its application on the TC1M engineering material.

Tensile Behavior of Strain Hardening Cementitious Composites (SHCC) Containing Reactive Recycled Powder from Various C&D Waste

This work investigates the feasibility of utilizing reactive recycled powder(RP)from construction and demolition(C&D)waste as supplementary cementitious material(SCM)to achieve a ductile strain hardening cementitious composites(SHCC).The recycled mortar powder(RMP)from mortar waste,recycled concrete powder(RCP)from concrete waste and recycled brick powder(RBP)from clay brick waste were first prepared,and the micro-properties and tensile behavior of SHCC containing various types and replacement ratios of RPs were determined.The incorporated RP promotes pozzolanic and filler effects,while the hydration products in cementitious materials decrease with RP incorporation;therefore,the incorporated RP decreases the compressive strength of SHCC.Attributed to the reduction in the matrix strength,the incorporated RP increases the crack-bridging extent and ductility of SHCC;the irregular micro-structure and high reactivity of RP also help the strain-hardening performance of the prepared SHCC.In addition,the strainhardening performance of SHCC containing RMP and RBP is surperior to that of SHCC with RCP and is slightly lower than that of SHCC with fly ash(FA);for instance,the ultimate strain of SHCC containing 54%FA,RMP,RCP and RBP is 3.67%,3.61%,2.52%and 3.53%,respectively.In addition,the strain-hardening behavior of an SHCC doubled mix with FA and RMP or RBP has a similar ultimate strain and a higher ultimate stress than SHCC containing only FA.

Evaluation of Strain Hardening Parameters

The plane-strain compression test for three kinds of materials was carried out in a temperature range between room temperature and 400℃.Theσ-εcurves and strain-hardening rate at different temperatures were simulated and a reasonable fit to the experimental data was obtained.A modified model created by data inference and computer simulation was developed to describe the strain hardening at a large deformation,and the predicted strain hardening are in a good agreement with that observed in a large range of stress.The influences of different parameters on strain hardening behaviour under large deformation were analysed.The temperature increase within the test temperatures for stainless steel 18/8 Ti results in dropping of flow stress and strain-hardening rate.For favourableγ-fibre texture to obtain high r,the cold rolling was applied at large reduction.In the experimental procedure,the X-ray diffraction test was carried out to compare the strain hardening and microstructure under large deformation for a bcc steel(low carbon steel SS-1142).The results indicate that the high strain-hardening rate possibly occurs when the primary slip plane{110}is parallel to the rolling plane and the strainhardening rate decreases when lots of{110}plane rotate out from the orientation{110}∥RP.

Ultimate Bending Capacity of Strain Hardening Steel Pipes

Based on Hencky＇s total strain theory of plasticity,ultimate bending capacity of steel pipes can be determined analytically assuming an elastic-linear strain hardening material,the simplified analytical solution is proposed as well.Good agreement is observed when ultimate bending capacities obtained from analytical solutions are compared with experimental results from full-size tests of steel pipes.Parametric study conducted as part of this paper indicates that the strain hardening effect has significant influence on the ultimate bending capacity of steel pipes.It is shown that pipe considering strain hardening yields higher bending capacity than that of pipe assumed as elastic-perfectly plastic material.Thus,the ignorance of strain hardening effect,as commonly assumed in current codes,may underestimate the ultimate bending capacity of steel pipes.The solutions proposed in this paper are applicable in the design of offshore/onshore steel pipes,supports of offshore platforms and other tubular structural steel members.

Effects of Temperature and Disperse Phase of Disordered γ on Strain Hardening Rate of Ni_3Al

Investigations have been made on the effects of temperature and fine disperse phase of disordered γ on strain hardening rate of Ni3Al based alloy. The result is found that there exists a peak temperature for the strain hardening rate of Ni3Al based alloy below the peak temperature of its yield strength. Analysis shows that the appearance of the peak temperature of strain hardening rate is caused by both the decreasing of the movability of <101> superdislocations on {111}slip plane and the increasing of the dynamic recovery in Ni3Al with increasing temperature. A Ni3Al based alloy hardened by disperse phase of disordered γ has been obtained by controlling chemical composition and treating processes. The peak temperature of strain hardening rate of this alloy is increased due to the fine disperse phase of disordered γ, which causes the reductions of the movability of the superdislocations and the dynamic recovery in Ni3Al

Influence of the Main Technological Variables of Cyclical Mechanic-Thermal Processing on the Strain Hardening of Steel Parts

The main objective of the present work was to determine the influence of the most important technological variables of CMTP （cyclical mechanic-thermal processing） on the strain hardening in the surface layers of steel parts. For this, it was designed a full factorial plan at two levels of five independent variables that include the whole processing in two and three cycles, the cold-forming degree and force during the plastic deformation （burnishing）, and the temperature and time at the given temperature during the aging. Each cycle is composed of plastic deformation at room temperature plus aging. As dependent variables, the degree and penetration depth of strain hardening were evaluated. Based on the appropriately used set of experimental data, it had been fitted an exponential model for each dependent variables and also a two-degree polynomial fitting of in-depth evolution of microhardness profile was obtained. The amount of cycles and the cold-forming degree are the technological variables of CMTP that influence the most on strain hardening, although other variables also are significant. The microhardness profile highlights that during the CMTP, the strain hardening decreases from the outer bound to the transition zone of the surface layers, where it disappears.

Impact of gradient microstructure on strain hardening via activation of multiple deformation mechanisms in CoCrNi medium entropy alloy

Face centered cubic(FCC)structural medium/high entropy alloys(MEAs),characterized by excellent strength and ductility,have attracted significant attention by the research community.The incorporation of gradient structures(GSs)further can enhance their mechanical properties.In the present research,we employ the rotation acceleration shot peening technique to introduce a GS within the CoCrNi FCC MEA to investigate underlying mechanisms governing the physical deformation processes during the generation of GSs through processing,which the primary goal is mitigating the intrinsic trade-off between strength and ductility.Through the microstructures analysis along the depth direction,both pre and post uniaxial tensile plastic deformation,we unveiled that the low stacking fault(SF)energy characteristic of the CoCrNi MEA triggered the emergence of diverse defects in the core region.The presence of nanoscale deformation twins,SFs,Lomer–Cottrell dislocation locks and phase transformation from FCC to hexagonal close-packed at twin boundaries synergistically enhanced the strain hardening capacity of the material.

Effects of Grain Size and Cryogenic Temperature on the Strain Hardening Behavior of VCoNi Medium‑Entropy Alloys

The mechanical behavior of VCoNi medium-entropy alloys with five different grain sizes at three different temperatures was investigated.The VCoNi alloys with different grain sizes exhibit a traditional strength–ductility trade-off at 77 K,194 K and 293 K.Both the yield strength and the uniform elongation of the VCoNi alloys with similar grain size increase with decreasing the deformation temperature from 293 to 77 K.Obvious strain hardening rate recovery characterized by an evident up-turn behavior at stage II is observed in VCoNi alloys with the grain size above 11.1μm.It is found that the extent of the strain hardening rate recovery increases with increasing grain size or decreasing deformation temperature.This may mainly result from the faster increase in the dislocation multiplication rate caused by the decrease in the dislocation mean free path,the decrease in the absorption of dislocations by grain boundaries and the dynamic recovery from the cross-slip with increasing grain size,as well as the suppressed dynamic recovery at cryogenic temperatures.The critical grain sizes for the occurrence of the recovery of strain hardening rate are determined to be around 9.5μm,8.3μm and 3μm for alloys deformed at 293 K,194 K and 77 K,respectively.The basic mechanism for the strain hardening behavior of the VCoNi alloys associated with grain size and deformation temperature is analyzed.