Plastic Deformation Characteristics Research Articles

Regularities of steel wear under the impact of discrete water-droplet stream, Part I: Initial stage of droplet-impingement erosion

Key features of plastic deformation and erosive wear craters that develop in the surface layer of austenitic and sorbite structure steels during the incubation period of the droplet-impingement erosion have been studied. Using electron microscopy, nanoindentation, and simulation, it has been shown that the degradation of the surface at the initial erosion stages is caused by fatigue processes that develop under hydrodynamic cavitation. Based on Goodman’s fatigue model, the conditions for the safe operation of the material under the impact of droplet impingements are defined.

2505 Fundamental study on crystalline structure for development of functional surface

In this paper, functional surface development by controlling crystalline structure on surfaces of materials is suggested. In order to reveal the mechanism of crystalline structure change by Nano Plastic Forming method, plastic deformation characteristics of single crystal pure iron are examined experimentally by means of shearing tests. Stress-strain curves are measured and Critical Resolved Shear Stresses of activating slip systems are calculated based on crystal plasticity theory. Besides shearing tested specimens are annealed and crystalline structure are analyzed by EBSD for study of effects of microscopic plastic deformation and annealing on recrystallization.

軽金属板材の塑性変形特性—測定とモデル化の手法—

軽金属板材の塑性変形特性—測定とモデル化の手法—

Simulation of LCF Characteristic of AA6063 Al Alloy Under Different Aging Conditions

Cyclic plastic deformation characteristics in the low cycle fatigue (LCF) regime of AA6063 Al-alloy subjected to three widely different aging conditions, namely: highly under aged (HUA), peak aged (PA) and highly over aged (HOA), have been simulated by finite element method considering Chaboche as well as Ohno-Wang phenomenological cyclic plasticity models. Results of LCF tests under the investigated strain ranges (0.4-1.0%) reveal that HUA state demonstrates significant cyclic hardening and better fatigue life compared to PA and HOA states. Simulation of stabilized hysteresis loops considering kinematic hardening formulation by Ohno-Wang model exhibits better correlation over Chaboche model.

영구동토 급속안정화를 위한 롤타입강재매트의 모델링과 해석(II) - 변수해석 -

Using the finite element analysis model presented in accompanying paper, parametric study was performed in this paper. Various parameters were considered such as the width of wheel loads-induced permanent plastic deformation, backfill, equivalent thickness and orthogonal characteristic of steel mats. The effects of these parameters were analyzed for vertical and rotational displacements, maximum moment and tensile stress. From the parametric studies, it is found that great vertical deflection and tensile stress above allowable flexural tensile strength are developed in steel mats by the wheel loads-induced permanent plastic deformation. Backfill or increasing the thickness of steel mats is a feasible solution on this problem.

A constitutive model for anisotropic tubes incorporating the variation of contractile strain ratio with deformation

The contractile strain ratio (CSR) is an important index measuring the anisotropy of tubes. The values of CSR vary non-linearly with the amount of plastic deformation. However, up to now, there are no constitutive models which are able to take this variation into account. In order to obtain the actual deformation characteristics and improve the prediction capability for plastic deformation processes of anisotropic tubes, this study developed an elasto-plastic constitutive model based on Hill׳s 48 anisotropic yield function. In this constitutive model, the variation in CSR with plastic deformation was considered. A user material subroutine VUMAT incorporating the constitutive model was developed based on ABAQUS/Explicit platform. The comparisons between the finite element (FE) simulations and experiments for uniaxial tension, uniaxial compression and numerical control (NC) bending process of Ti–3Al–2.5V titanium alloy anisotropic tube, show that this constitutive model is reliable. The simulation accuracy was improved and the plastic deformation characteristics could be better described for the anisotropic tubes by using this constitutive model.

Plastic deformation characteristics of Cu/X (X[dbnd]Cu[sbnd]Zr, Zr) nanolayered materials

Nanolayered materials exhibit unique plastic deformation behavior, i.e., a bulk-like to small-scale plasticity transition and a scaling behavior of extremely small activation volume (V*<10b3) with intrinsic size. This unusual plastic transition phenomenon likely stems from the dislocations respectively emit from interfaces and Frank–Read-type bulk sources below and above a critical intrinsic size ∼20nm. We quantitatively capture the scaling relationship between strain rate sensitivity and intrinsic size by a phenomenological model based on the Orowan–Frank–Read process.

Influence of Deep Cryogenic Treatment on Microstructures and Mechanical Properties of an Ultrafine-Grained WC-12Co Cemented Carbide

Effect of deep cryogenic treatment (DCT) on the microstructures and mechanical behavior of ultrafine-grained WC-12Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co and binder phase Co in cemented carbide were analyzed in detail to correlate the strengthening mechanism with its α → ε phase transition. The results show that DCT resulted in a slight increase in hardness and bending strength of ultrafine-grained WC-12Co cemented carbide. For the ultrafine-grained cemented carbide after DCT, there is no significant change in the microstructure and the elemental distribution of the cemented carbides, but the fractured morphology shows a feature of plastic deformation. In the cases of pure Co and the binder phase Co in WC-12Co cemented carbide, they exhibit different features of phase transformation. The improvement of mechanical property of cemented carbide can be attributed to the increased amount of ε-Co in WC-12Co composites after DCT.

Plastic Deformation Modes in Mono- and Bimodal-Type Ultrafine-Grained Austenitic Stainless Steel

An attempt was made to track plastic tensile deformation modes operating in bulk ultrafine-grained austenitic stainless steel with mono- (maximum at ~0.6 μm) and bimodal-type (minimum at ~0.5 μm and maximum at ~1.65 μm) grain size distributions produced by cyclic thermal processing. Post tensile deformation electron backscatter diffraction studies were conducted to analyse the impact of grain size distribution on plastic deformation characteristics. The study revealed extensive strain localisation in the monomodal-type grain size distribution, leading to poor strain-hardening behaviour. On the other hand, the bimodal-type distribution disclosed a conventional dislocation-mediated deformation mechanism operating in the coarse grains, while it was restricted to initial small strains in ultrafine austenite grains. The subsequent deformation process in these ultrafine austenite grains was dictated by nucleation and autocatalytic growth of strain-induced α′-martensite. The observed martensitic transformation of ultrafine austenite grains in preference to coarse grains was attributed to activation of local ‘grain to grain’ interactions.

Multi-scale modeling of dislocation boundaries: Understanding interaction and effect of rotation angle

The formation and evolution of dislocation boundaries during plastic deformation is one of the primary basis for understanding material strength, shaping, texture, re-crystallization properties, and plastic deformation itself. Better understanding of plastic deformation characteristics will provide for enormous benefits in manipulation of manufacturing processes. Although several analytical and numerical studies have been conducted on 2D analysis of simplified configurations of dislocation boundaries, more complex dislocation boundaries have not received much attention. The present paper presents a 3D numerical analysis of a geometrically necessary dislocation boundary using a multi-scale simulation technique: the multi-scale discrete dislocation plasticity (MDDP). The characteristics and internal structure of the dislocation boundary are extracted from experimental measurements. Effect of dislocation boundary rotation angle on the generated self-stress field and behavior of multiple dislocation boundaries is investigated.

An upper bound solution for twist extrusion process

Twist extrusion, a promising severe plastic deformation technique for grain refinement down to ultrafine/nanocrystalline microstructures, was introduced as an attempt to provide large plastic deformation conditions similar to those in high pressure torsion while allowing large workpiece dimensions for industrial applications. As a relatively new severe plastic deformation technique, twist extrusion requires in-depth investigation of its plastic deformation characteristics. In this study, the twist extrusion process with a square shape die cavity has been analyzed using an upper bound solution to estimate the required power, deformation pattern, and optimum process condition. The analysis has been performed based on two kinematically admissible velocity fields while the effects of friction condition, die geometry, and mean equivalent strain have been considered. The results indicate that the die geometry and process parameters can dramatically change the deformation pattern and extrusion power.

Development of new cyclic plasticity model for 304LN stainless steel through simulation and experimental investigation

Cyclic plastic deformation characteristics of 304LN stainless steel material have been studied with two proposed cyclic plasticity models. Model MM-I has been proposed to improve the simulation of ratcheting phenomenon and model MM-II has the capability to simulate both cyclic hardening and softening characteristics of the material at various strain ranges. In the present paper, strain controlled simulations are performed with constant, increasing and decreasing strain amplitudes to verify the influences of loading schemes on cyclic plasticity behaviors through simulations and experiments. It is observed that the material 304LN exhibits non Masing characteristics under cyclic plastic deformation. The measured deviation from Masing is well established from the simulation as well as from experiment. Simulation result shows that the assumption of only isotropic hardening is unable to explain the hardening or softening characteristics of the material in low cycle fatigue test. The introduction of memory stress based cyclic hardening coefficient and an exponentially varying ratcheting parameter in the recall term of kinematic hardening rule, have resulted in exceptional improvement in the ratcheting simulation with the proposed model, MM-II. Plastic energy, shape and size of the hysteresis loops are additionally used to verify the nature of cyclic plasticity deformations. Ratcheting test and simulation have been performed to estimate the accumulated plastic strain with different mean and amplitude stresses. In the proposed model MM-I, a new proposition is incorporated for yield stress variation based on the memory stress of loading history along with the evolution of ratcheting parameter with an exponential function of plastic strain. These formulations lead to better realization of ratcheting rate in the transient cycles for all loading schemes. Effect of mean stress on the plastic energy is examined by the simulation model, MM-I. Finally, the micro structural investigation from transmission electronic microscopy is used to correlate the macroscopic and microscopic non Masing behavior of the material.

Effect of the cube orientation on formability for FCC materials: A detailed comparison between full-constraint and self-consistent predictions

A rate-dependent self-consistent (VPSC) polycrystal-plasticity model, in conjunction with the MK approach, has been used successfully to address and explain plastic deformation features and localization conditions that cannot be treated with the full-constraint (FC) Taylor scheme. Signorelli and Bertinetti [On the role of constitutive model in the forming limit of FCC sheet metal with cube orientations, International Journal of Mechanical Sciences, 51: 473–480, 2009] investigated FCC sheet-metal formability, focusing on how the cube texture affects localized necking. In the present work, we extent this research to include two types of textures experimentally observed in aluminum alloys: the {100} 〈001〉 Cube orientation rotated 45° with respect to the sheet normal direction; and the {100} 〈uvw〉 orientations. The effect of these orientations on the FLD is studied numerically, and a detailed comparison between MK-FC and MK-VPSC, derived from orientation stability and geometrical hardening, is made. The classical MK model, based on strain-rate imposed boundary conditions, was generalized in order to explicitly and correctly includes stress boundary conditions for materials with changes in anisotropy during deformation. In plane-strain stretching, the enhanced formability of the rotated 45° {100} 〈001〉 orientations has been correlated with texture evolution. In equi-biaxial stretching, the MK-FC approach predicted greater limit-strain values than did the MK-VPSC model. Qualitative differences in geometrical hardening/softening were also found.

A damage-based constitutive model for rock under impacting load

Using the Splitting Hopkinson Pressure Bar (SHPB) experimental system, investigations were made into the dynamic mechanical performances of underground soft rocks. The experiments proved that the measured stress–strain curves display the characteristics of plastic deformation. By making use of a revised overstress constitutive formula for the stress model and by taking into account that the strain rate and strain are a function of 1−E(t)/E0, a revised overstress constitutive formula for the stress model was simplified by applying dimensional analysis and consequently, a simplified overstress formula was obtained for the stress model. Then, by taking into consideration the effects of damage under a dynamic load on the dynamic loading strength of the rock, the continuous damage theory and the statistical strength theory were introduced into the development of the simplified overstress constitutive formula for the stress model. Hence, a damage-based constitutive formula for an overstress model, which can be appropriately applied to the analysis of full dynamic stress–strain curves, was developed. By using the simplified damage-based constitutive formula for an overstress model, the actually measured curves are fitted, indicating that the fitting curves and those actually measured are in good agreement.

Influence of confining pressure and impact loading on mechanical properties of amphibolite and sericite-quartz schist

In order to investigate the dynamic mechanical properties of amphibolite and sericite-quartz schist under confining pressure, two rocks are subjected to impact loadings with different strain rates and confining pressures by using split Hopkinson pressure bar equipment with a confining pressure device. Based on the experimental results, the stress-strain curves are analyzed and the effects of confining pressure and strain rates on the dynamic compressive strength, peak strain and failure mode are summarized. The results show that: (1) The characteristics of two rocks in the ascent stage of the stress-strain curve are basically the same, but in the descent stage, the rocks gradually show plastic deformation characteristics as the confining pressure increases. (2) The dynamic compressive strength and peak strain of two rocks increase as the strain rate increases and the confining pressure effects are obvious. (3) Due to the effect of confining pressure, the normal stress on the damage surface of the rock increases correspondingly, the bearing capacity of the crack friction exceeds the material cohesion and the slippage of the fractured rock is controlled, which all lead to the compression and shear failure mode of rock. The theoretical analysis and experimental methods to study the dynamic failure mode and other related characteristics of rock are useful in developing standards for engineering practice.

Sliding Wear of TiCN PVD Coated Prealloyed Chromium Sintered Steel

AbstractThe present paper deals with the sliding wear behaviour of prealloyed chromium sintered steel (Fe-1.5Cr-0.2Mo) with graphite powder added in the amount of 0.7%. The wear characteristics, such as profilograms, wear tracks morphology and wear curves of the as sintered specimens and TiCN coating were investigated through pin-on-disk tests. The specimens were sintered in pusher furnace at the temperature of 1453 K for 2400 s in a nitrogen-hydrogem atmosphere. Dominant bainitic microstructures with evident features of plastic deformation at the worn surface were detected. The coating of the investigated prealloyed steels increases the wear resistance in comparison with the as-sintered state according to the wear curves. Microstructural and EDX analyses confirmed that delamination and oxidation wear are the main wear mechanism in wear tests.

薄肉超小型試験片の単軸駆動式二軸引張試験方法の開発

We have established a biaxial tensile test method suitable for the measurement of the local plastic deformation characteristics of a hard aluminum alloy sheet 3104-H, which is a typical material for aluminum can bodies, as a representative of the low work hardening materials. The present method consists of the following: (1) a microminiature cruciform specimen, (2) a newly designed linkage mechanism mounted on a uniaxial tensile testing machine, and (3) the loading path diagram as an experimental method to measure the biaxial stress–strain curves accurately from the biaxial tensile tests with linear displacement paths of the chucking jigs. The following are drawn from the biaxial tensile tests for the thin test material: (i) using the proposed biaxial tensile testing apparatus, we measured a contours of plastic work, and it was in good agreement with that measured using the conventional linear stress path tests, (ii) we were successful to determine the real yield points for various biaxial tensile states using the loading path diagrams and to measure the contour of plastic work corresponding to the maximum equivalent plastic strain of 0.0012, and (iii) the contour of plastic work is well approximated using the Yld2000-2d yield function with an exponent of 7.78.

Surface integrity of nickel-based alloys subjected to severe plastic deformation by abusive drilling

Surface integrity of nickel-based superalloys after machining operations has become a topic of major interest in the aerospace sector. In the present work, the characteristics of nickel-based alloys (Alloy 718, Waspaloy, Alloy 720Li, and RR1000) subjected to abusive drilling conditions have been investigated using experimental methods such as FEG-SEM, EBSD, XRD, TEM and nano-indentation. The results indicated the presence of nano-sized grains typical of severe plastic deformation in the machined surface while the presence of plastic slip bands was observed in the sub-surface layers. Correlations between the thermo-mechanical properties of the nickel-based alloys and the severe plastic deformation features of the machined surfaces are presented.

A planar twist channel angular extrusion (PTCAE) as a novel severe plastic deformation method based on equal channel angular extrusion (ECAE) method

Planar twist channel angular extrusion (PTCAE) is a new severe plastic deformation method to produce bulk ultra-fine-grained materials which is based on conventional equal channel angular extrusion by applying additional planar twist strain in deformation zone of ECAP process and simultaneously imposing larger strain and increasing severe plastic deformation methods efficiency. Plastic deformation characteristics of PTCAE method were analyzed through finite element analysis using Deform 3D V.5 software, processing loads and values of effective strain in different directions of sample were studied for different planar twist angles (α) in comparison with the results of conventional ECAP with the same channel dimension and arc of curvature angles. Die and punch were assumed as rigid bodies, whereas the billet, with dimensions of 10 mm × 10 mm × 70 mm was considered to be deformable pure aluminum. The processing conditions such as friction coefficient, ram speed, mesh size and other factors were held constant to make comparison between the different processing conditions possible. The results indicated that more strain values with more uniform distribution may be achieved after PTCAE method in comparison with the conventional ECAP method. Also, it is observed that in α = 20, the equivalent strain distribution is homogenous approximately in both of vertical and horizontal directions of the cross-section of the sample. Therefore, PTCAE can be considered as a promising severe plastic deformation technique for future industrial applications which can be installed on any standard extrusion equipment without any additional required facilities that are essential in other new severe plastic deformation methods and can be used instead of ECAP process significantly and beneficially.

Emergence of external size effects in the bulk-scale polycrystal to small-scale single-crystal transition: A maximum in the strength and strain-rate sensitivity of multicrystalline Cu micropillars

Using microcompression methodology, various plastic deformation characteristics, namely the strength, strain-rate sensitivity (SRS) and activation volume, of 〈100〉-single-crystalline (SC) Cu micropillars and nanostructured multicrystalline (MC) Cu micropillars with several grains were systematically investigated at different strain rates for a wide range of external sample sizes ranging from 300 to 2000nm. The results revealed that the paradigm of “smaller is stronger” for small-scaled SC pillars holds true in nanostructured MC Cu micropillars above the strongest external size; however, below this size, a decrease in the external size triggers the reverse size effect, i.e. “smaller is weaker”. The appropriate introduction of grain boundaries into SC pillars can markedly improve the smoothness of their plastic flow and significantly enhance their SRS. Additionally, we demonstrated that the SRS of MC Cu pillars increases with decreasing size up to a certain limit and then decreases with a further decrease in the external sample size; thus, a maximum SRS emerges. A phenomenological model was proposed to rationalize the scaling behavior of the activation volume with the external sample size and to highlight the effect of the internal feature size on the rate-limiting behavior of conventional bulk nanostructured metals (Cu).