Plane Strain Compression Research Articles

Deformation Mechanisms of Magnesium Alloys with Rare-Earth and Zinc Additions under Plane Strain Compression.

The introduction of rare-earth (RE) elements into magnesium (Mg) alloys can significantly improve their ductility, thereby extending the applications of Mg products. However, the impacts of their chemical composition, temperature and processing methods on the mechanical properties of Mg products are highly debatable. In this work, we systematically investigate the deformation behaviors of Mg-Nd and Mg-Zn-Nd alloys using electron backscattered diffraction (EBSD) characterization. The samples were deformed to different stress levels to study the microstructure and texture development during channel die compression. The results reveal that the room temperature formability of the Mg-Nd alloy can be enhanced with the addition of Zn. This is attributed to the higher activities of prismatic slip and tensile twinning in the Mg-Zn-Nd alloy as compared to the binary counterpart, facilitating strain accommodation. When the strain increases, the growing and merging of the same twin variant rapidly consumes the parent grain, which is responsible for the texture modification from the transverse to the basal direction. At elevated temperatures, the twinning is suppressed in both alloys due to the decreased critical resolved shear stress of the non-basal slip systems. Additionally, an obvious sigmoidal yielding phenomenon is observed due to the multiple activation of the different deformation modes. These findings offer valuable insights into the evolution of the microstructure and texture during plane strain compression, elucidating the connections between material chemical composition, processing and mechanical properties, which are important for the advancement of Mg alloy application.

Study of plane strain compression of composite sheets

In the plane strain compression of multi-layers metal, each layer of metal shows a different degree of deformation due to the differences in material properties. Also, the deformation in different positions of a metal layer is always inhomogeneous. In this study, the effects of material ratios, friction between the metal layers and the amount of compression on the deformation behaviors of a bi-layer metal strip under plane strain compression are investigated. 2D plane strain finite element simulation models of AISI-1008/AL6061-T6 bi-layer metal strips are used. The results indicate that the strips show different deformation behaviors under different conditions, and non-smooth interfaces caused by the inhomogeneous material flow during the deformation process are detected in most cases.

Texture weakening and grain refinement behavior of the extruded Mg-6.03Zn-0.55Zr alloy during hot plane strain compression

A series of hot plane strain compression (PSC) experiments of the extruded Mg-6.03Zn-0.55Zr alloy were conducted on the Gleeble-3500 machine with strain rates of 0.01 s−1 to 10 s−1 and temperatures ranging from 300 °C to 500 °C to reveal the microstructure evolution during the secondary process. The effects of grain refinement and texture modification which were easily affected by the deformation mechanism and dynamic recrystallization (DRX) were systematically studied. Experimental results showed that the main deformation mechanism during PSC was basal <a> slip (74.3 %–94.9 %) and assisted by prismatic <a> slip (4.8 %–21.1 %) and pyramidal <c+a> slip (0.3 %–4.6 %). Since the pyramidal <c+a> slip and prismatic <a> slip were more preferred to activate owing to the significant decrease of critical resolved shear stress (CRSS) at a higher temperature, the activation of non-basal slip promoted the c-axes of the grains deviated from compression direction which weakened the basal fiber texture. Moreover, the activation of non-basal slip could promote DRX behavior to some extent. Further analysis of the DRX mechanism showed that the continuous DRX (CDRX) by continuous rotation of low angle grain boundaries was dominant at lower temperatures and higher strain rates, while discontinuous DRX (DDRX) which nucleated at the grain boundaries played a more and more important role as the temperature increased and strain rate decreased. After characterizing the orientations of the DRXed grains, the CDRXed grains owned a similar grain orientation with the deformed grain while the DDRXed grains exhibited a fairly dispersed distribution, indicating that the weakening effect of the basal texture was greater with a higher DDRX fraction.

Chemical short-range order dependence of micromechanical behavior in CoCrNi medium-entropy alloy studied by atomic simulations

Chemical short-range order (CSRO) is a typical microstructural characteristic commonly found in multi-principal element alloys (MPEAs). For MPEAs with the face-centered cubic (FCC) structure, the presence of CSRO has been verified and characterized meticulously by using electron microscope. However, it is still challenging to reveal the effect of CSRO structure on the deformation microstructure and micromechanical behavior of those alloys. By applying atomic scale simulations, this study explores the micromechanical behavior of an equiatomic CoCrNi medium entropy alloy with random solid solution and three different degrees of CSRO under plane strain compression, respectively. The results show that CSRO can effectively promote planar slip of dislocations in the FCC matrix and elevate flow stress of the alloy. The planar slip and stacking of partial dislocations then lead to the formation of hexagonal-close-packed (HCP) structure lamellae. CSRO also modulates the morphology of dislocations. When dislocations cut through CSRO, it hinders the movement of dislocations while being destroyed by atomic plastic flow, causing CSRO and atomic clusters at the interface of the matrix to embed each other and generate antiphase boundaries which can significantly enhance the bulk yield strength. These findings provide fundamental insights into the interaction between CSRO and dislocations in CoCrNi MEA, guiding the design of MPEAs with superior combinations of strength and ductility.

An automatic thermo-mechanical testing apparatus for metal forming applications

Dynamic testing of materials is necessary to model high-speed forming processes (e.g. hammer forging, blanking, forming, etc.) and crash/impact behaviour of structures, amongst others. The most common machines to perform medium to high-speed tests are the servo-hydraulic high-speed tensile and compression machines and the Hopkinson bars. The paper analyses the use of a newly-developed laboratory testing facility, named the Automatic Thermo-Mechanical Tester (ATMT). This testing machine is equipped with a pneumatically accelerated Direct Impact Drop Hammer (DIDH), a furnace and automatised robotic arm, capable of characterising materials at intermediate strain rates, ranging from 100 to 300 s−1 in combination with temperatures up to 1350 °C. The hammer has been designed and constructed to conduct a variety of material characterisation tests, such as, upsetting or plane strain compression tests as well as component tests for validation purposes. The DIDH allows testing standard compression specimens at average strain rates in the order of 100 s−1 that decrease progressively until the it is fully stopped. It is, in combination with universal testing machines and Hopkinson bar systems, particularly suitable for experimental validation of loading-rate dependant material models. Compression tests were conducted with different hammer impact velocities generating a variety of strain rates at varying temperatures on S235JR structural steel, OFHC copper and wrought Inconel 625 nickel-based superalloy to assess the potential of the novel apparatus. A detailed finite element numerical study of the system was performed to assess several aspects such as the effect of the specimen geometry or its capability as an intermediate testing device, simulating a simplified system and the full Direct Impact Drop Hammer apparatus.

Tailoring a high-strength Al–4Cu alloy through processing of powders by up to 100 turns of high-pressure torsion

Processing by high-pressure torsion (HPT) was applied to a cold-pressed mixture of Al and Cu (4%wt) powders to successfully synthesise a high-strength nanocomposite. The powder consolidation and redistribution of second phases involved the stretching and fragmentation of the Cu domains into shorter strips and submicrometre particles. After 1 turn, the Al+4 wt%Cu alloy was not fully consolidated and exhibited numerous microvoids at the disc centre. For this reason, the material displayed comparatively low microhardness at this location which triggered early metal cracking during testing through plane strain compression. An adequate consolidation was achieved after 30 HPT revolutions as the composite exhibited a homogenous distribution of Cu fragments without any visible microcavities. This is consistent with the high flow stresses achieved during plane strain compression without incipient metal cracking. At this processing stage, there is evidence of partial dissolution of Cu into the Al–Cu solid solution followed by dynamic precipitation of Al2Cu nanoprecipitates. Additional straining up to 100 turns promoted further hardening up to 270 Hv and grain refinement down to ∼48 nm. However, this occurs concurrently with the coalescence and loss of coherency of the Al2Cu precipitates with the Al matrix.

Particle-matrix debonding with Strength-Differential effects

In this work the onset of failure caused by particle-matrix debonding in aluminum alloy 2090-T3 and magnesium alloy AZ31 under either overall uniaxial plane strain tension or compression load is studied numerically using a unit cell model. Especially for magnesium AZ31, experiments show a significant difference in the tensile-compressive yield stresses, the so-called Strength-Differential-effect (SD-effect). This SD-effect cannot be captured by any isotropic yield function and only by recent anisotropic yield functions. To accurately model AA 2090-T3 and magnesium AZ31 the general yield function by Yoon et al. (2014) is adopted in addition to the isotropic von Mises plasticity yield function and the anisotropic yield function of Hill (1948). The numerically predicted strain at which void nucleation initiates is generally found to be larger for magnesium AZ31 than for AA 2090-T3. However, depending on the orientation of the principal axes of plastic anisotropy this void nucleation strain varies significantly. This holds true for both materials, but the void nucleation strain of AA 2090-T3 in compression is numerically predicted to be practically identical whether or not isotropic or anisotropic plasticity is considered. In tension the void nucleation strain of AA 2090-T3 based on anisotropic plasticity is found to be more than double the strain obtained by von Mises plasticity. The numerically predicted void nucleation strain of magnesium AZ31 is significantly affected by the yield function adopted. For the von Mises yield function the value of the void nucleation strain is in between the predictions based on the anisotropic yield functions. For both tension and compression, the yield function of Yoon et al. (2014) results in the largest void nucleation strain, whereas the yield function of Hill results in the smallest strain value. This holds true for all five orientations of the principal axes of plastic anisotropy investigated.

Estimation of peak stress of AM30 magnesium alloy during hot plane strain compression

This paper presents the results of an analysis of the hot deformation flow behaviour of magnesium alloy AM30. The true stress–strain curve's experimental results are used to plot the hardening curve. The critical strain value and maximum softening strain value are calculated using the hardening curve. The estimation of peak stress is done by employing the constitutive Arrhenius hyperbolic equation. Material constants are determined using exponential and power equations.The estimated peak stress compared with the experimental peak stress and good agreement between both the stress value is found.

Hydraulic fracturing process in rocks – small-scale simulations with a novel fully coupled DEM/CFD-based thermo-hydro-mechanical approach

In the paper, a two-dimensional (2D) numerical simulation of a small-scale hydraulic fracturing process in rock specimens possessing a single injection slot was conducted. A unique DEM/CFD-based pore-scale thermal-hydro-mechanical (THM) model was used to simulate two-phase laminar fluid flow (water and gas) with heat transfer in non-saturated porous materials with low porosity. Using a DEM fully coupled with CFD (based on a fluid flow network composed of channels in a continuous domain between discrete elements) and heat transfer at the mesoscale, a series of numerical calculations for small cohesive granular specimens of simplified spherical mesostructure with one injection slot were carried out. Plane strain compression conditions were assumed. Both the fluid (diffusion and advection) and bonded particles (conduction) were involved in heat transfer. The impacts of the fluid's dynamic viscosity, gas phase content, and temperature difference between the rock matrix and the fluid injection on the process of hydraulic fracture initiation and propagation were all examined in-depth. It was discovered that those effects were all of great significance to the behaviour of a single hydraulic fracture.

Understanding the mechanisms behind the development of cube orientation in the non-cube grains during plane strain compression of medium to high stacking-fault energy FCC metals

Medium to high stacking-fault energy FCC metals develop a pronounced cube texture during static recrystallization. Previous studies reported that the recrystallized grains can nucleate from the cube-oriented regions developed in the non-cube grains during plane strain compression. However, the mechanisms behind the development of cube orientation in the non-cube grains are still unknown. In this work, we used an elasto-viscoplastic fast Fourier transform (EVP-FFT) based crystal plasticity model to study the lattice rotation of non-cube orientations under plane strain compression. Firstly, we focus on a non-cube grain which developed the cube orientation in previous experimental work. The non-cube orientation does not rotate towards the cube orientation during single material point deformation under ideal plane strain compression. In contrast, the same non-cube orientation develops cube-oriented fragments during the polycrystalline deformation. Analysis of the micro-mechanical fields reveal that the local deviation of the RD-ND shear component leads to a remarkable change in the slip system activity which promotes the lattice rotation towards the cube orientation. Although the mechanism remains unchanged, the location and volume fraction of the cube orientation developed in the non-cube grain vary significantly in different grain neighborhoods. For the general case of a polycrystalline microstructure, deviation of the RD-ND shear component shows the highest correlation with the development of the cube orientation in the non-cube grains. The deviation is larger for the non-cube grains with higher Taylor factor. These findings have significant implications for the cube texture control during the practical rolling operation and recrystallization.

2次均質化法を用いた多結晶材料の圧縮変形における寸法依存性と加工条件の関係評価

In a hot steel rolling process, the rolling force and the strain distribution in a rolled material is strongly affected by the friction coefficient between the work roll and the rolled material and the rolling shape factor which is the ratio of the contact length between the work roll and the material to the material thickness. In this respect, many numerical attempts have been made to reveal their relationship. These simulations often suppose the homogeneity of the material because of simplicity. However, the recent researchers have suggested that the heterogeneity in microstructure can cause size effect on deformation behavior of polycrystalline material. In order to clarify the size effect in the rolling process, this study investigates the size effect on the deformation force and the strain distribution in the plane strain compression which is simple and similar to the flat rolling in effects of the friction coefficient and the shape factor, using the second-order homogenization-based finite element (2nd HMFE) simulations. Simulations are performed by two-dimensional 2nd HMFE with different friction coefficients, shape factors, work hardening parameters and size ratios between micro and macrostructures, which are related to strain heterogeneity in a deformed material. As a result, in case of the small friction coefficient, relatively uniform deformation tends to occur in the material, which results in small effects of the size ratio on deformation behavior. In contrast, in case of the large friction coefficient, size effects on the compression force and the strain distribution appears to be large when the shape factor of a deformed material approaches 1. It is considered to be because high strain gradient tends to reduce the plastic work in the microstructure and a deformation band in which the strain gradient is higher is formed in the material in such a case.

A physically-based constitutive model for amorphous glassy polymers in large deformations

A physically-based constitutive model for predicting the mechanical response of amorphous glassy polymers at room temperature and low strain rates was established within the frame of thermodynamics and kinematics. In our previous work (Lan et al., 2022b), the concepts of permanent entanglement (PE) and dynamic entanglement (DE) were utilized to reproduce the complicated behavior of amorphous glassy polymers from quasi-static to dynamic loading at temperatures from below to near the glass transition temperature. PE formed by the coiling of macromolecular chains is relatively stable and contributes to the yield and unloading behavior. DE formed by the weak interaction between monomers of adjacent segments is unstable and contributes to the macroscopic yield peak and strain hardening. However, due to including many parameters, the model is not easy to apply in practice. In this work, by ignoring the influence of temperature, the previous model (Lan et al., 2022b) was simplified. Taking polycarbonate (PC) and polystyrene (PS) as examples, the simplified model focused on the macroscopic mechanical behavior under simple compression and cyclic simple compression, analyzed the effects of mesh and specimen size on the evolution of shear bands under plane strain compression, and compared the obvious differences in localized deformation of these two types of amorphous polymers under plane strain compression. In addition, the forging process of PC at room temperature was simulated. By comparing the predictions with the experiments, it is demonstrated that the simplified model can reproduce the macroscopic mechanical response of amorphous polymers under simple compression, cyclic simple compression, plane strain compression and forging.

Coupled hydromechanical analysis of sparsely fractured crystalline rocks

This paper addresses the issue of evolution and coalescence of localized damage zones in sparsely fractured crystalline rocks. The approach incorporates a constitutive law with embedded discontinuity, which is phrased in terms of both the hydraulic and mechanical response. The formulation takes into account the hydromechanical interaction in regions intercepted by discontinuities. An internal length scale parameter is employed in the definition of equivalent hydraulic conductivity and the tangential stiffness operators, and the onset of newly developed macrocracks is detected by the bifurcation analysis. An enhanced mixed u-p finite element formulation is derived which considers the effect of progressive evolution of the fracture aperture in the weak statements of balance equations. Fully implicit temporal discretization is employed, and the finite element formulation is stabilized by invoking the Polynomial-Pressure-Projection (PPP) technique. A coupled FE analysis is conducted examining the response of Luc du Bonnet granite, with pre-existing fracture network, subjected to plane strain compression that triggers the crack propagation and coalescence. The approach is first verified on some benchmark problems that involve the presence of a dominant fracture. The results of simulations are compared with those obtained using a very fine mesh incorporating interface elements. Later, a series of coupled analyses are carried out examining the hydromechanical response in the presence of multiple fractures.

Evaluating the influence of deformation variables on dynamic recrystallization behavior using a crystal plasticity model

The present study is an attempt to model dynamic recrystallization (DRX) in a single phase metal using a mean field crystal plasticity (MFCP) based approach. A new empirical equation is proposed to model nucleation, in which the nucleation rate is a function of microstructure and plasticity descriptors that are known to affect DRX behavior, such as the temperature, strain rate, grain fineness and stored energy. Grains undergo nucleation when their dislocation density exceeds a threshold value. Subsequently, new grains grow based on the difference in stored deformation energy with respect to the average value over all grains. The MFCP-DRX model is able to correctly predict trends for the flow stress, dislocation density evolution, grain size evolution and kinetics across a range of temperatures and strain rates for uniaxial compression. Transition of the flow stress from single to multiple peaks is observed with increasing temperature and decreasing strain rate, thus comparing well against known DRX trends. The evolutions of crystallographic texture during DRX in uniaxial compression and plane strain compression are compared against experimental observations. A sensitivity analysis is conducted to understand the effect of variables on nucleation and growth. The competition between nucleation and growth dominated deformation in different strain regimes is analyzed in detail across various temperatures and strain rates.

Influence of plane-strain compression on the microstructure and tribological behavior of GUR 1050 UHMWPE

Ultra-high molecular weight polyethylene (UHMWPE) has been used as a bearing surface in orthopedic implants due to its outstanding physical and mechanical properties. Modifications in the structure of the polymer have a direct effect on its wear. In this work, plane-strain compression in a channel die was applied to induce microstructural changes in specimens of UHMWPE GUR 1050. These structural changes were characterized using a combined approach involving Raman spectroscopy and atomic force microscopy. These qualitative and quantitative characterization resulted in a valuable understanding of the changes in the material microstructure when subjected to plastic deformation. A molecular non-uniform alignment of the UHMWPE molecules, with fragmentation and kinking of polymer lamellae, was observed in the direction of material flow, perpendicular to the compressive load direction, following an inhomogeneous strain field generated by the mechanical compression. The microstructural analyses revealed an increased crystalline content and decreased intermediate phase while amorphous phase content remained unchanged, in all the regions of the deformed specimen. The tribological performance, evaluated by the scratch resistance force, decreased along the material flow direction and increased along the load direction in the deformed polymer compared to that of the uncompressed polymer. Plane-strain compression was able to modify the polymer microstructure, introducing directional anisotropy in its tribological behavior that can impact the wear performance of the material.

On the Plasticity and Deformation Mechanisms in Magnesium Crystals

This work presents an overview of the mechanical response and microstructure evolution of specifically oriented pure magnesium single crystals under plane strain compression at room temperature. Crystals of ‘hard’ orientations compressed along the c-axis exhibited limited room temperature ductility, although pyramidal ⟨c + a⟩ slip was readily activated, fracturing along crystallographic 112¯4 planes as a result of highly localized shear. Profuse 101¯2 extension twinning was the primary mode of incipient deformation in the case of orientations favorably aligned for c-axis extension. In both cases of compression along ⟨112¯0⟩ and ⟨101¯0⟩ directions, 101¯2 extension twins completely converted the starting orientations into twin orientations; the subsequent deformation behavior of the differently oriented crystals, however, was remarkably different. The formation of 101¯2 extension twins could not be prevented by the channel-die constraints when c-axis extension was confined. The presence of high angle grain boundaries and, in particular, 101¯2 twin boundaries was found to be a prerequisite for the activation of 101¯1 contraction twinning by providing nucleation sites for the latter. Prismatic slip was not found to operate at room temperature in the case of starting orientations most favorably aligned for prismatic slip; instead, cooperative 101¯2 extension and 101¯1 contraction twinning was activated. A two-stage work hardening behavior was observed in ‘soft’ Mg crystals aligned for single or coplanar basal slip. The higher work hardening in the second stage was attributed to changes in the microstructure rather than the interaction of primary dislocations with forest dislocations.

Local Microstructure and Texture Development during Friction Stir Spot of 5182 Aluminum Alloy

The local microstructure, texture gradient and mechanical properties through the shoulder dimension (10 mm) of upper and lower AA5182 aluminum sheets were investigated using electron backscatter diffraction (EBSD) and Vickers microhardness after friction stir spot welding (FSSW). Based on the microstructural features (mean grain size, grain boundary type and dynamic recrystallization (DRX)), the upper sheet was found to be mainly composed of the stir zone (SZ) and thermomechanically affected zone (TMAZ) due to the high deformation induced simultaneously by the tool rotation and the shoulder download force, while the SZ, TMAZ, heat-affected zone (HAZ) and base metal (BM) were detected in the lower sheet due to the limited effect of the shoulder on the lower sheet. The texture changes, due to the nature of the deformation, demonstrated a shear-type texture at the SZ to a plane strain compression deformation type texture at the TMAZ and then a recrystallization texture at the HAZ and BM. The microhardness gradually decreased with the increasing distance from the keyhole along the SZ, TMAZ and HAZ regions. Eventually, the microstructure and microhardness evolutions were correlated based on the Hall–Petch relationship.

Hot compression deformation behaviour and microstructure evolution of Ti-3.5Al-3.5V-0.5Fe-0.6Mo-0.5Cr alloy

Ti-3.5Al-3.5V-0.5Fe-0.6Mo-0.5Cr alloy is a new superplastic titanium alloy The alloy was deformed by plane strain compression at 820°C~880°C, 0.16 s−1~8 s−1, which can provide reference for obtaining homogeneous microstructure during the rolling process. The results show that the flow stress of the alloy has a negative correlation with the deformation temperature and a positive correlation with the strain rate. The flow softening behavior of alloy is greatly influenced by deformation temperature. The fraction and the length of α lamellar increase with the decrease of temperature, and the flow-softening phenomenon of the alloy is more obvious. The homogeneity of microstructure and the recrystallization ratio of α lamellae increase with the increase of deformation temperature and the decrease of strain rate. The alloy can obtain homogeneous microstructure at 850°C, 0.16 s−1, and 880°C, 0.16 s−1~1.6 s−1 deformation conditions.

Identification of Hosford’s Yield Criterion Using Compression Tests

The paper presents a simple and efficient method for identifying two-parametric isotropic pressure-independent yield criteria. The experimental procedure includes the upsetting of three types of specimens. The upsetting of cylinders and rings is used to evaluate the effect of friction. Together with the plane strain compression in a die, these tests provide two points of the yield locus on the π-plane. The experimental procedure is used in conjunction with the plasticity theory based on Hosford’s yield criterion. The plastic work is used to describe the hardening of the material. This hardening law can be reformulated in terms of the equivalent strain after the yield criterion is determined. The experimental/theoretical procedure above applies to steel C15E.

Effects of stress histories and drainage conditions on inception of strain localization in unsaturated soils

A diagnostic method to detect the inception of strain localization, which is based on the singularity of a total acoustic tensor, was developed for variably saturated soils. The effective stress approach was used to establish coupling between the multiphase fluid flow and deformation fields, while isotropic hardening/softening due to changes in suction and plastic volumetric strain were accounted for. To this end, several fundamental testing conditions were investigated, including Conventional Triaxial Compression (CTC) and Extension (CTE), Plane Strain Compression (PSC) and Extension (PSE) under drained, constant water content, and undrained loadings. It was found that, for the silty soil and stress histories considered, suction can completely prevent the onset of strain localization in undrained CTE tests and partially prevent the onset in constant water content and drained CTE tests. Furthermore, while suction can significantly affect the inception of strain localization in all PSC tests, it has almost no effect on the onset of strain localization in all PSE tests. Finally, suction affects more significantly the orientation and mode of shear bands at the inception of strain localization in extension tests than in compression tests.