Plastic Deformation Characteristics Research Articles

Deformation and strength characteristics of Laves phases in titanium alloys

The superior reinforcement nature of Laves phases make them suitable for high-strength applications. Therefore, investigations on the deformation and strength characteristics of Laves phases are useful in development of an improved Laves phase-reinforced alloy. In this work, the Vickers micro-indentation method is used to evaluate and compare the deformation and strength characteristics of a hexagonal close-packed Laves phase (C14-type) in Ti-35Zr-5Fe-6Mn (wt%) and a face-centered cubic Laves phase (C15-type) in Ti-33Zr-7Fe-4Cr (wt%), considering the same volume fraction of Laves phase (~7.0%) in these alloys. Moreover, the effects of higher volume fraction of Laves phase (19.4%) on indentation-based deformation features are evaluated in Ti-35Zr-5Fe-8Mn (wt%). Remarkably, dislocation activity and plastic deformation features are evident in the C15-type Laves phase, whereas the C14-type Laves phase strongly blocks dislocation motion. Therefore, the C15-type Laves phase improves plastic deformability, whereas the C14-type Laves phase improves strength characteristics of Laves phase-reinforced alloys.

Wear Behavior and Mechanism of CoCrMo Alloy Fabricated by Powder Metallurgy Route

This research is devoted to study the wear behavior and mechanism of CoCrMo alloy due to the uitilization of the alloy in application mainly exposed to wear. Samples fabricated by powder metallurgy route compacted under (1000MPa) and sintered at (1200ºC) in the argon atmosphere. Wear test type pin-on-disc was performed under dry sliding condition over steel counterface disc. For the first group of wear tests four vertically loads (10,15,20 and 25) N were applied at fixed sliding speed (1.476) m.s−1, time (15 min) and sliding distance (1329m). The second group of tests were conducted at fixed applied load (25) N for (60 min) interrupted to four equal intervals and at the same above sliding speed. The worn surface of the tested samples and formed wear debris particles were investigated and analyzed with aid of SEM and SEM-Mapping facilities. The results showed that the wear rate increased by increasing the applied load and a transition from mild wear to severe wear was occurred at (20 N) for fixed sliding time (15min). The maximum measured wear rate was (39.72×10−7) mm3.mm−1 at the highest applied load. While for the second group the wear rate was decreased when the sliding time exceeded 30 min. The main wear mechanism was adhesive type detected by material transfer, with lower abrasive type which is revealed from the existence of fine grooves. Oxidation and plastic deformation features are also observed.

Effect of Cyclic Load Amplitude on the Evolving Characteristics of Accumulative Deformation in Subgrade Bed

To investigate the evolving characteristics of plastic deformation for the angular gravels that are used to construct subgrade bed, a laboratory model test is performed with cyclic load applying. Vertical deformation is measured in real time by displacement transducers and further modified to analyze the plastic behavior of model fillings. It can be found that vertical plastic deformation shows quite different developing patterns under the effect of different cyclic amplitudes for a given model. A power function is adopted to describe the relationship between deformation rate and loading times. By analyzing the value of the power exponent and the corresponding developing features of plastic deformation rate, model filling status can be classified into four different zones, i.e., rapid stabilization, tardy stabilization, tardy failure, and rapid failure. Such a classification reveals different developing patterns of plastic deformation and satisfies the design of subgrade bed for ballasted and unballasted railway.

Wear mechanisms in polyoxymethylene spur gears

The interaction of a polymer-steel spur gear pair is naturally prone to cause wear of the softer polymer material. Experimental equipment was therefore designed and constructed to run a polymer-steel spur gear pair with sufficiently accurate instrumentation such that the load and speed could be measured under a range of operating conditions. Plastic deformation features on the polymer teeth surface were observed through scanning electron microscopy and these are considered to be the primary sources of polymer gear wear during service. The wear mechanism is discussed and models are presented to describe the process by which it is created. This is due to the sliding/rolling under conforming contact conditions that are intrinsic to the involute spur gear pair. An iterative model based on the nonlinear properties of the polymer is presented, which shows how the material is deformed permanently and progressively under each load cycle. A second model also shows how the wear deformation features are created. Worn gear teeth were inspected and the quantity of material worn correlates well with the predicted wear volume.

A theory of biological composites undergoing plastic deformations

Natural biological composites such as bone, dentin, nacre and enamel exhibit anisotropic microstructures, giving rise to orientation-dependent mechanical properties. Although the mechanical properties of these materials have been studied extensively, there is limited progress on modeling the common features associated with the orientation-dependent plastic deformation of biological composites. In this study, we develop a continuum theory for elastic-viscoplastic deformations of anisotropic biological composites. The pressure-sensitive and plastically dilatant plastic flow is incorporated into the theory, and the plastic spin related to the kinematics of the underlying substructure during macroscopic plastic deformation is explicitly taken into account. A special set of constitutive equations are implemented in a finite element program. Furthermore, the material parameters have been calibrated and numerical simulations of elastic-plastic deformation in bone are performed. It is found that the theory can capture the major features of plastic deformation of biological composites. The numerical simulations are in good agreement with experiments, demonstrating that the model is capable of predicting the complex plastic deformation of bone.

Investigation of Grain Anisotropy on Surface Area between Carbon Steel Wire and Die at Drawing

Drawing is characterized by non-uniform character of plastic deformation, which is transferred from the die to the processed wire. Such impact causes specific change of wire microstructure. In the surface area the thin layer with highly deformed grains is observed. It is important to measure the thickness of this thin layer. For this purpose it is proposed in this paper to use the value of coefficient of anisotropy, which is calculated as the ratio of mean quantity of phase particles, crossed by secant line perpendicular to deformation axis on the unit of secant line length to the mean quantity of phase particles, crossed by secant line parallel to deformation axis on the unit of secant line length. Distribution of coefficient of anisotropy, both for low and high carbon steel wire after drawing, was obtained by Thixomet PRO software. It made it possible to calculate the thickness of highly deformed area automatically taking into consideration the difference of steels microstructure.

Characteristics of plastic deformation associated with hydrogen-induced delayed crack propagation in a sheet of single-crystal Fe-Si alloy

Characteristics of plastic deformation associated with hydrogen-induced delayed crack propagation in a sheet of single-crystal Fe-Si alloy

The effect of strain rate under multiple forging on the mechanical and microstructural properties

The flow stress of aluminum alloy 6082M under cyclic, non-monotonic plastic deformation has been determined by multiaxial forging experiments, using the MaxStrain system on a Gleeble 3800 thermo-physical simulator. The simulations were done at ambient temperature with different strain rates of 0.1, 1.0 and 10 1/s. The plastic strain amplitude per forging pass was 0.4. The accumulated equivalent strain was around 4 in each forging simulation.For the mechanical modeling of the cyclic, non-monotonic plastic deformation characteristic of the forming process, a control program and measurement arrangements have been developed. These controlled the equivalent logarithmic strain and the equivalent strain rate implemented in each forming step. It was also suitable for measuring the dimensions of the deformed material volume between the tools. These parameters and the measured force data were applied in the mechanical model, based on the principle of virtual velocities.In parallel with the cyclic experiments, monotonic plane-strain Watts-Ford compression tests were also performed. Strain rate influence for material properties has been investigated. Monotonous and cyclic flow curves were compared, and significant differences were found. Contrary to the monotonous flow curve, the cyclic flow stress showed the Bauschinger effect, occurring when the load direction was changed. Concerning the effect of strain rate it can be concluded that the applied strain rate influences the strain hardening, the resultant hardness and the characteristic properties of the generated ultrafine-grained microstructure.

Cyclic mean stress relaxation behaviour of P91 steel: Experiments and constitutive modeling

In the present study effect of mean strain on cyclic plastic deformation characteristics of P91 steel is experimentally evaluated and compared with results of finite element simulation considering cyclic plasticity models. P91 steels being used in various components in fossil fired and nuclear power plants are subjected to cyclic loading with mean strains/stresses. Symmetrical and asymmetrical strain controlled tests of P91 steel conducted at room temperature revealed cyclic softening nature during the fatigue cycling process. The influence of mean strain imposed showed strong dependence on stress relaxation behavior and fatigue life of P91 steel. Tensile mean stress was found to relax steeply in initial cycles followed by stabilization during the asymmetric strain cycling. A reduction in fatigue life is observed with increase in mean strain for particular strain amplitude. An attempt has also been made to simulate asymmetric strain controlled behavior of P91 steel through cyclic plastic modeling in the framework of rate independent plasticity theory. Ohno-Wang material model is employed to predict the influence of mean strain on stress relaxation behavior of the investigated steel. The simulated results depicted that Ohno-Wang model captures the cyclic plastic deformation behavior of P91 steel reasonably well.

In-situ investigation of deformation behavior and fracture mechanism of laminated Al/Ti composites fabricated by hot rolling

In this work, laminated Al/Ti composites were fabricated by hot rolling at three different temperatures (400 °C, 450 °C and 500 °C). The deformation behavior and fracture mechanism of composites were studied by the in-situ tensile test. The results indicated that the ductile shear fracture (for 400 °C and 450 °C rolled specimens) and ductile delamination fracture (for 500 °C rolled specimen) were the main fracture failure modes of Al/Ti multilayers. Results shown that the tensile load and displacement of the 500 °C prepared Al/Ti were better than other samples due to the higher rolling temperature. The changes of slip lines and plastic bands were the main plastic deformation characteristics for the Al layer and Ti layer metals, respectively. The investigation found that the major crack nucleation type in Ti layer was fold belt cracking. The slip bands cracking, cross-slip cracking, particle interface cracking and grain boundary slide cracking were the primary crack nucleation patterns for the Al layer.

Experimental and Mechanism Study of a Polymer Foaming Grouting Material for Reinforcing Broken Coal Mass

To study the mechanism of grouting reinforcement of broken coal mass, simulation experiments on grout reinforcing of broken coal mass were performed by using traditional materials, namely, Superfine Cement (SC) and Aluminate Cement (CA), and selfdeveloped Polymer Foaming (PF) grouting material. The macromechanical test results of the different grouting reinforced specimens showed that the residual strength of broken coal increased by different degrees after grouting, and the reinforcement effect was improved most notably by the PF material, which caused obvious plastic deformation characteristics of the coal mass that highly adapted to the deformation of the surrounding rocks, moreover, the long-term reinforcement effect was beneficial. Scanning Electronic Microscopy (SEM) showed that the grout-coal interfaces of the SC and CA materials were relatively loose and mainly affected by the types, quantities, and existence forms of cement hydration products, but had little relation to the properties of the injected medium. However, SEM showed a close combination at the interface with the PF material, which presented acceptable molecular compatibility. Moreover, FTIR indicated that some chemical grafting reactions occurred between the PF and coal mass, thereby leading to a firm polymer coating on the coal surface; thus, the grouting reinforcement effect of the broken coal mass was improved.

Equivalent and effective strains during severe plastic deformation (SPD)

ABSTRACTThis paper considers the characteristics of severe plastic deformation (SPD) to estimate its efficacy and to compare different processing techniques. In contrast to effective strains by von Mises and Hencky, the rotation component of the strain rate is included in the analysis as a mode of deformation, which ranges from simple shear to pure shear. Distortions of material elements during a uniform plane plastic flow are calculated using a kinematic approach. For the fixed deformation mode, the current state is defined by the accumulated shears that are identical to the von Mises effective shear strains. In specific cases of pure shear and simple shear, the accumulated shears match the specific distortions of round or square elements prescribed by Hencky or von Mises approach, respectively. The mode of deformation is important to the structural effects of SPD. In general, two separated characteristics, accumulated shear and the coefficient of deformation mode, are necessary to describe strains during SPD.

High mechanical strengths and ductility of stainless steel 304L fabricated using selective laser melting

Achieving not only high mechanical strengths but also high ductility is recently established using an additive manufacturing technique called selective laser melting. In the present study, stainless steel 304L fully dense samples were successfully printed using the 3D systems – ProX 300 printing machine. The ductility and tensile yield strength were almost two and three times higher compared to those of ASTM cast’s alloy. Honey comb like nano-cellular structure with different orientation was observed in the fine grains (∼4 μm) due to fast cooling rate. In addition, the formation of martensite phase in random grains is also a contributor to the strengths. Furthermore, negative residual stresses in the build and horizontal directions were detected and assisted further increase in the tensile strength. Fractography revealed the ductile feature of plastic deformation and the crack openings at unmelted particles or pores.

Hydrogen embrittlement behavior of Inconel 718 alloy at room temperature

Hydrogen embrittlement of Inconel 718 alloy was investigated. Multi-scale observation technique were employed, comprising slow strain rate tensile tests, scanning electron microscopy and transmission electron microscopy analysis. The results demonstrate that hydrogen charging deteriorates mechanical properties of the alloy. Inconel 718 alloy shows partial Portevin-Le Chatelier (PLC) effect at room temperature when hydrogen charging current density is 220 mA cm−2 and 590 mA cm−2. Moreover, plastic deformation features with dislocation cells are detected in hydrogen-induced brittle zone. Thus, it is concluded that dragging effect of hydrogen atoms on dislocations contributes to PLC effect.

Analysis of the Plastic Strain Distribution and Damage Accumulation During T-Shaped Equal Channel Angular Pressing

T-ECAP process is a reversion of equal channel angular pressing which employs T shaped die instead of L shaped die. In the present study, 2D finite element method was employed to evaluate the plastic deformation characteristics of Al6061 alloy during T-ECAP processing. Deformation homogeneity was analyzed in term of plastic strain distribution and compared with conventional ECAP process. In addition, strain rate distributions in deformation zone, damage accumulation in sample and pressing force required for T-ECAP process were analyzed. Results showed that the plastic strain distribution in sample after T-ECAP processing is not affected significantly with the variation of friction coefficient which is in contrast with conventional ECAP where the plastic strain is increased at the bottom side of sample by increasing friction between sample and die. Also in the case of T-ECAP process, it was observed that the maximum damage factor is decreased with increasing friction coefficient. The V shaped deformation zone has been detected in T-ECAP process and the pressing force has been found to increase with increasing friction.

Effect of Strain Heterogeneities on Microstructure, Texture, Hardness, and H-Activation of High-Pressure Torsion Mg Consolidated from Different Powders.

Severe plastic deformation techniques, such as high-pressure torsion (HPT), have been increasingly applied on powder materials to consolidate bulk nanostructured materials. In this context, the aim of the present study is to compare the plastic deformation characteristics during HPT of two distinct Mg-based powder precursors: (i) atomized micro-sized powder and (ii) condensed and passivated nanopowder. Dynamic recrystallization could take place during HPT consolidation of the atomized powder particles while the oxide pinning of the grain boundaries restricted it for the condensed powder. Consequently, there have been substantial differences in the development of the microstructure, texture, local strain heterogeneities, and hardness in the two types of consolidated products. Different types of local strain heterogeneities were also revealed in the consolidated products. The associated diversity in microstructure within the same consolidated product has been demonstrated to have an effect on the hydrogen activation kinetics to form hydrides for these Mg-based materials that could be suitable for solid state H-storage applications.

An experimental study of deformation and fracture characteristics of shale with pore-water pressure and under triaxial cyclic loading

The deformation and fracture characteristics of shale in the Changning-Xingwen region were experimentally studied under triaxial cyclic loading with a controlled pore-water pressure. An RLW-2000M microcomputer-controlled coal-rock rheometer was used in the State key Laboratory of coal mine disaster dynamics and control in Chongqing University. These experimental results have indicated the following. (i) The shale softened after being saturated with water, while its failure strength decreased with the increase of axial strain. (ii) A complete cyclic loading–unloading process can be divided into four stages under the coupling action of axial cyclic loading and pore-water pressure; namely the slow or accelerated increasing of strain in the loading stage, and the slow or accelerated decreasing of strain in the unloading stage. (iii) The axial plastic deformation characteristics were similar when pore-water pressures were set to 2, 6 and 10 MPa. Nevertheless, the shale softened ostensibly and fatigue damage occurred during the circulation process when the pore-water pressure was set to 14 MPa. (iv) It has been observed that the mean strain and strain amplitude under axial cyclic are positively correlated with pore-water pressure, while the elastic modulus is negatively correlated with pore-water pressure. As the cycle progresses, the trends in these parameters vary, which indicates that the deformation and elastic characteristics of shale are controlled by pore-water pressure and cyclic loading conditions. (v) Evidenced via triaxial compression tests, it was predominantly shear failure that occurred in the shale specimens. In addition, axial cyclic loading caused the shale to generate complex secondary fractures, resulting in the specimens cracking along the bedding plane due to the effect of pore-water pressure. This study provides valuable insight into the understanding of the deformation and failure mechanisms of shale under complicated stress conditions.

Effect of He-irradiation fluence on the size-dependent hardening and deformation of nanostructured Mo/Zr multilayers

Previous studies demonstrated that the He ion irradiation damage tolerance of nanostructured metallic multilayers (NMMs) was closely dependent on the layer thickness (h): smaller h led to lower irradiation hardening. Here in Mo/Zr NMMs, we uncovered that the h-dependent irradiation hardening and corresponding plastic deformation characteristics are also sensitive to the He+ irradiation fluences. At a low irradiation fluence of 1.0 × 1016 He+·cm−2, the irradiation hardening decreased monotonically with reducing h. While at a high irradiation fluence of 1.0 × 1017 He+·cm−2, a non-monotonic h-dependence was unexpectedly displayed with the minimum irradiation hardening at h of ∼25 nm. The irradiation fluence also affects the strain rate sensitivity (m) remarkably. Irradiation of 1.0 × 1016 He+·cm−2 induced a transition in SRS m from positive in the as-deposited Mo/Zr NMMs to negative SRS in their irradiated counterparts. This transition was rationalized in terms of dynamic strain aging that considered dislocation-bubble interactions. Irradiation of 1.0 × 1017 He+·cm−2, however, resulted in a non-monotonic h-dependence of m, with the bottom located at a turning point of h ∼50 nm. Coupling effect of the layer thickness and the applied fluence on irradiation hardening and plastic deformation characteristics was quantitatively elucidated by employing a strengthening model and a thermally activated model, respectively, where parameters of the characteristic microstructural features, i.e., the layer thickness and irradiation (He) defects, were both included.

Effect of distortional hardening behaviour on material responses of pure titanium sheets during hydraulic bulge test

Plastic deformation characteristics of pure titanium sheets are identified by conducting several tensile tests and hydraulic bulge test. Distortional hardening behaviour of the tested material is examined experimentally by comparing the uniaxial tensile results of three specimens taken from different orientations. This study verifies the effect of the distortional hardening behaviour on the material responses for pure titanium sheet by conducting a finite element analysis for the bulge test. For this purpose, a material model is calibrated based on the experimentally measured data. In this model, both yield surface and potential surface were well described by the Yld2000-2d function under the theory of associated flow rule. To match with experimental observation, all parameters of the yield function are implied as functions of the equivalent plastic work during plastic deformation. Additionally, a modified Voce hardening function was applied to reproduce the hardening behaviour for the examined material over large strains. Based on simulation results, it is concluded that the distortional hardening behaviour strongly affects the evaluation of the apex height during the bugle test.

Effect of Tungsten Inert Gas Remelting on Microstructure, Interface, and Wear Resistance of Fe-Based Coating

Tungsten inert gas arc (TIG) process was employed to remelt Fe-based coating deposited by plasma spraying. Subsequently, the microstructure, interface, and the wear resistance of the coatings before and after remelting were studied. The results showed that the lamellar structure, pores, and inclusions of Fe-based coating were eliminated and the porosity significantly decreased from 4% to 0.4%. The as-sprayed coating contained microcrystalline region, nanocrystalline region, and transition region, while single crystal region and rod-shaped (Fe,Cr)23C6 were observed in the remelted coating. There was no element diffusion and dissolution phenomenon at the interface; thus, the bonding form between the as-sprayed coating and substrate mainly was mechanical bonding. On the contrary, the diffusion transfer belt (DTB) emerged at the interface of the remelted coating and substrate, the remelted coating was bonded with the substrate metallurgically. Additionally, the average microhardness and elastic modulus of the remelted coating increased by 33.4% and 53.2%, respectively, compared with the as-sprayed coating. During wear process, the as-sprayed coating exhibited obvious brittle fracture characteristics, while the remelted coating appeared typical plastic deformation characteristics and its weight loss reduced by 39.5%. Therefore, TIG remelting process significantly improved the microstructure, mechanical properties, and wear resistance of Fe-based coating.