Value Of Plastic Strain Research Articles

Influence of different wrought processes on the microstructure and texture evolution in AZ31 magnesium alloy

AZ31 magnesium alloys were deformed by five wrought processes (forging, rolling, extrusion, equal-channel-angular-extrusion (ECAE), and caliber rolling) under the condition of an introduced equivalent plastic strain of approximately 1.5 at 573 K. The strain components induced by these wrought processes were computed using the finite element method (FEM). By combining the calculation results with the microstructure observations, the texture and microstructure evolution were discussed from the viewpoint of the strain state. The FEM showed that approximately the same equivalent strain was induced at the center of the alloys where observations were performed. Therefore, as the values of the equivalent plastic strain were fixed in all wrought processes, the effect of the strain component could be compared. The forged and rolled alloys had an intensive basal texture perpendicular to the compression and normal directions, respectively. In the others, a basal fiber texture parallel to the material flow direction was observed. These basal textures were oriented perpendicular to the compressive strain, and their intensities strengthened with an increase in the strain component. The microstructure became more refined and homogenized as the magnitude of the minimum principal strain decreased. This decrease corresponds to the transition of the deformation mode from the uniaxial compression mode to the multidirectional deformation mode as long as the same equivalent strain is induced. This result demonstrates that the microstructure obtained through dynamic recrystallization depends on the deformation mode, separately from the effect of the conventionally reported equivalent plastic strain.

The Influence of the Parameters of the Skew Rolling Process for Bimetallic Elements on the Mechanical Properties and Structure of Materials.

This paper presents selected results of theoretical and experimental research into the manufacture of axisymmetric bimetallic components using three-tool skew rolling technology. In the tests, it was assumed that the outer layer would be a material intended for heat treatment. However, low-carbon steel was used for the core. Experimental investigations were carried out in an innovative CNC skew rolling mill. Tests were carried out at different technological parameters of the process. In addition, the geometric parameters of the billet and the way it was heated were analyzed in relation to the quality of the resulting weld between the two materials. The quality of the weld was assessed based on metallographic observation and on strength tests (shear method). On the other hand, theoretical studies were based on numerical modeling (FEM). The numerical analysis made it possible to determine the distribution of temperature, deformation and stress in the rolling bimetallic component. The results obtained indicated that it is possible to produce bimetallic materials from the proposed steel grades. In addition, a significant effect of the method of heating the billet in the chamber furnace on the microstructure in the joining zone and the shear strength was found. There was an increase in Rc strength of about 35% when using oxidation protection. The results indicated better strength when the billet is rolling with a smaller outer layer thickness (about 50 MPa). This was confirmed by the results obtained from the FEM analysis, which indicated higher values of plastic strain and the occurrence of higher compressive stresses in the near-surface zones of the rolled bimetallic forging, both of which facilitate the welding process. From the temperature distribution (in the range of (600-1200) °C) obtained during the rolling of the bimetal forging, it can be seen that contact with cold tools does not affect the temperature in the welding zone.

Modeling local deformation, damage distribution, and phase transformation in zirconia particle-reinforced TRIP steel composites

This study investigates tensile deformation, damage analysis, and the effect of microtexture on a 10 % vol. zirconia particle-reinforced TRIP steel composite. In situ tensile tests and simulations were conducted, with sequential SEM images captured during tensile loading tests and electron backscatter diffraction (EBSD) providing initial crystal orientation data. SEM images were utilized in digital image correlation (DIC) analysis to calculate the local plastic strain distribution using VEDDAC software. Initial micrographs and EBSD data were transformed into geometry files for simulations, employing crystal plasticity with a dislocation density-based model and a newly proposed phase field approach-based ductile-brittle damage criterion for both austenite and ceramic particles. MATLAB's image processing functions were used to compare and validate experimentally observed damage instances with simulation predictions. The effect of microtexture combined with various physical quantities was explored using MTEX. The results show that the simulations accurately predict strain concentration around ceramic particles, with a higher strain observed in the middle region compared to the DIC observations. The simulated strain in the austenitic matrix is found to be 1.4 times higher than the DIC measurements. Quantitative analysis of damage pixels reveals that the proposed critical plastic strain value aligns closely with experimental results, showing an error of - 0.25 % compared to 1.121 % for a smaller strain case. This comprehensive analysis provides insight into the effect of microstructural attributes on material performance and behavior under tensile deformation, leading to a validated microstructural-informed damage-inclusive crystal plasticity model.

Yield locus and texture evolution of AA7475-T761 aluminum alloy under planar biaxial loading: An experimental and analytical study

AA7475 aluminum alloy is used as a structural material in aerospace and automobile applications where complex loading conditions are applicable. The material properties under multi-axial loading are recommended for efficient component design. Hence, the mechanical behaviour of AA7475-T761 aluminium alloy was investigated through planar biaxial tensile tests. The yield locus evolution and plastic strain direction were measured at higher plastic strain values (up to 7 %) at various load ratios. The yield loci were constructed and compared with existing yield criteria. Yld2000–2d yield criterion demonstrated accurate predictions with a deviation of approximately 1 %, highlighting its effectiveness in capturing the yield behavior of AA7475. Microstructure analysis using Electron Backscatter Diffraction (EBSD) was conducted to understand the misorientation evolution under the multi-axial loading. Bulk-texture analysis was performed using X-ray diffraction method. Texture analysis revealed that uniaxial deformation favoured the development of Cube and Inverse-Copper textures, while biaxial deformation yielded split Inverse-Goss texture formation. Fractography study shows very different fracture surfaces of biaxial samples compared to uniaxial samples. Overall, this study contributes to a comprehensive understanding of the yield behavior, microstructure, and texture evolution of AA7475-T761 aluminium alloy under different loading conditions at very large strains.

Forming limit and failure characterization of as-received and bi-axial prestrained Cu-Cr-Zr-Ti alloy sheets in the context of multistage forming

The characterization of forming limit utilizing Cu-Cr-Zr-Ti alloy sheets during the multistage forming process is imperative for successfully fabricating thrust chamber liners used in satellite launch vehicles. Therefore, the present work studies the effect of prestrain on the forming limit and failure behaviour of this alloy under different deformation paths. A stretch-forming setup was utilized to induce 8% equi-biaxial prestrain (EBP), and subsequently, these prestrained specimens were deformed till the onset of failure using the same setup. After prestraining, a shift in the failure strains was observed in the principal strain space, whereas it was found to be absent in the polar effective plastic strain, principal stress and effective plastic strain-stress triaxiality loci. The cup height along different deformation paths was marginally decreased in the prestrained specimens because of the reduction in failure strains, and the fracture occurred in the prestrained region. Further, failure analysis revealed intergranular cracks in the specimens deformed along plane strain and uniaxial deformation paths due to the presence of micron-size Cr-rich precipitates along grain boundaries. However, intergranular and transgranular cracks were present in the prestrained specimens, which were deformed equi-biaxially similar to the as-received specimens. The presence of nano-size Cr-rich precipitates inside the grains acted as nucleation sites for voids during equi-biaxial stretching, leading to transgranular cracks. It was also observed that failure in the prestrained and as-received specimens occurred at a similar effective plastic strain value due to the combined effect of void density and void size. Based on experimental observations, it was inferred that the forming limit of Cu-Cr-Zr-Ti sheets under a two-stage forming process was primarily affected by the presence of micro and nano-size Cr-rich precipitates.

The experimental and numerical investigation of fracture behaviour in PMMA notched specimens under biaxial loading conditions – Tension with torsion

This paper presents the results of experimental fracture test of flat PMMA specimens under biaxial loading condition tension with torsion (proportional). The specimens were made in two thicknesses: 5 and 15 mm and were weakened with V-type edge notches with different root radii: 0.5; 2 and 10 mm. Thanks to the ARAMIS 3D 4 M non-contact vision system, measurement of the elongation and twist angle were recorded. During experimental part all of the deformation processes were observed using PHANTOM cameras. Obtained records made it possible to precisely indicate the moment of crack initiation (tensile force and torsional moment values). Using the microscopic observations the location of crack initiations were determined. Results obtained for biaxial loading were compared with those obtained for uniaxial tension and torsion. Based on experimental data the numerical calculation with FEM were carried out. The principal stress and plastic strain distribution under critical load, were obtained. The points of occurrence of stress maxima and plastic strain were indicated, which were taken as potential crack initiation sites. On the basis of the stress and plastic strain values measured at the critical points, a stress–strain fracture criterion was formulated, which was then positively verified. Additionally, new form of stress–strain fracture criterion was proposed. The bilinear form of the fracture criterion can be successfully used to predict fracture in PMMA flat specimens, regardless of the notch root radius, type of load or element thickness.

Cavern spacing of CAES cavern group in hard rock based on plastic zone and deformation analysis

Existing research on layout parameters of compressed air energy storage (CAES) cavern groups in hard rock has indicated that the key influential factors for group stability include buried depth, diameter, and cavern spacing. Among these, in contrasting to other factors, the research on cavern spacing is limited. This paper focuses on the issue of safe spacing and proposes a numerical method to determine it. By establishing a series of finite element models, the stress state of surrounding rock, changes in shape, equivalent plastic strain of plastic zone, and cavern wall deformation under different spacing have been studied. When a group of air storage caverns in rows is subjected to high internal pressure, for a small spacing, the plastic zone of the surrounding rock between two caverns is connected. Here, the size of the plastic zone, equivalent plastic strain value, and deformation of the cavern wall are relatively large, making the surrounding rock highly susceptible to damage. As the spacing increases, the horizontal width of the plastic zone, the maximum equivalent plastic strain value, the displacement changes of the cavern wall remain stable. This spacing is virtually the same as that when the plastic zone of the surrounding rock is no longer connected and can be selected as a safe spacing. This study explores the design of cavern safe spacing of underground CAES cavern groups and discusses several influencing factors, which can provide references for follow-up energy storage engineering and research.

Assessment of phenomenological models for Indentation Size Effect (ISE) through physically based dislocation density evolution

The depth dependent hardness, referred to as indentation size effect (ISE) has gained considerable attention. ISE is attributed to the strain gradient caused by the inhomogeneous strain distribution beneath the indenter tip. The depth dependence of hardness is phenomenologically accounted using an appropriate length scale parameter. The Unified model is one such model that is built on Nix–Gao’s model and focuses on integrating various length scale parameters resulting from both microstructural and geometrical effects. One aspect of the current work is to assess the applicability of the Unified model to a material like bulk Nickel with a history of cold work. Also, the physics of ISE in metals can be related to the dislocation mean free path influenced by strengthening mechanisms. Past attempts are scarce to quantify the ISE through the microstructure variables. In the present work, an attempt has been made to simulate the nanoindentation test using a dislocation density based constitutive model. The objective of this study is to establish a correlation between the equivalent plastic strain resulting from deep depth indentation (which does not exhibit a size effect) and an equivalent dislocation density. The dislocation density here serves as a state variable that describes the microstructure-dependent mechanical behaviour. The modified KME, a dislocation density-based model, is incorporated as a user subroutine in a commercial finite element solver. It has been proven to accurately predict the indentation behaviour at substantially large depths, which aligns well with the predictions of the Unified model or experimental observations. The good correlation between the value of effective dislocation density and equivalent plastic strain in the plastic zone underneath the indenter assures to extend the use of dislocation density as a state variable to predict ISE.

A new approach to evaluate Ramberg-Osgood parameters for SS316LN using different types of specimens

A novel methodology is proposed for evaluating the stress-strain curve and determining the Ramberg-Osgood parameters (n, α) of SS316LN material. This involves utilizing load-displacement data from various specimen types, including both smooth and notched tensile specimens with different notch radii, in conjunction with finite element analysis. An error minimization method was used for evaluating the material parameters. The proposed approach for the evaluation of unique Ramberg-Osgood parameters provides a better result than that of the material stress-strain data of smooth specimen test. Ramberg-Osgood parameters were evaluated at two temperatures, i.e., 25°C and 650°C and compared with RCC-MRx code. Stress-strain equation as provided in the RCC-MR, can’t be used in FE analysis if the plastic strain exceeds 1.5% at certain regions of structure containing discontinuity, e.g., regions like shell-nozzle junction, vessel head, T-junction etc. The approach developed in this work shall help to obtain the material stress-strain curve over a wide range of plastic strain values. Ramberg-Osgood parameters were evaluated for the whole temperature range of 25°C and 650°C, which can be used for structural integrity analysis of reactor components made of stainless steel grade SS316LN. The range of applicability of data for RCC-MR code was extended beyond 1.5% of plastic strain in this work. The equations derived in this work shall be useful for structural integrity analysis and life assessment of structural components of nuclear reactors.

Ductile fracture of high-strength bolts under combined actions at elevated temperatures

Steel bolted connections are critical structural components that can initiate progressive collapse at ambient and elevated temperatures. High-strength bolts are highly vulnerable members due to rapid strength degradation at high temperatures. This paper presents a numerical study on the ductile fracture of the frequently used Grade 8.8 and 10.9 structural bolts under tension, shear, and combined forces at 20–700 °C. True stress–strain curves have been defined up to fracture for both grades. The fracture parameters have been calibrated by a total of four experiments: two tensile and shear tests for each grade. The ductile fracture models with proposed fracture parameters have been further validated by pretensioned shear tests at elevated temperatures. The relationship between equivalent strain and triaxiality was investigated based on the numerical results. In general, equivalent plastic strain values become larger with increasing temperature. The fracture analysis with given ductile fracture parameters estimates the test results with reasonable accuracy under all failure modes. The fracture model can be used in numerical analysis to investigate the ductile failure of the high-strength bolted connections at ambient and elevated temperatures. Furthermore, the influence of displacement at fracture values on the results was investigated by a three-bolted inclined shear test.

Damage evolution and fracture of aluminum alloy based on a modified Lemaitre model

Ensuring that metal materials do not fail during the forming process is a concern; forming is a complex process with development of a large amount of macroscopic and mesoscopic damage inside the metal. In this study, the damage evolution of 5052 aluminum alloy during the plastic forming process was studied using a modified Lemaitre damage model. First, a combination of theoretical derivation, experimental analysis, and fracture scanning was used to study the material damage evolution law at different strain rates. Subsequently, a more accurate nonlinear relationship between plastic strain and damage value was proposed, and an assumption regarding the Lemaitre damage model was revised. A VUMAT user material subroutine based on the Lemaitre damage model was developed; the reliability of the modified Lemaitre damage model was verified by numerically simulating the tensile process of 5052 aluminum alloy at different strain rates. The relative error between the fracture failure location of the specimen obtained from the numerical simulation of the modified Lemaitre model and that in the experiment was 3%.

An experimental and computational study of through-depth strain distribution during frictional treatment of a metastable austenitic steel

Frictional treatment, as a method of surface plastic deformation, forms a gradient hardened layer. In the case of metastable steels, this hardening is due, among other things, to the formation of strain-induced α'-martensite. The most reliable information about the thickness of this hardened layer can be obtained by measuring the hardness on transverse sections. This paper compares strain distribution through the depth of the hardened layer, obtained from layer-by-layer phase analysis and finite element modeling, with the data of durametric studies for the AISI 321 metastable steel subjected to frictional treatment under various loads on the indenter. A satisfactory coincidence of the distributions of the α'-phase concentration and hardness through the depth is observed only for the specimen subjected to frictional treatment at a maximum load of 400 N on the indenter. At the other loads on the indenter, the thickness of the layer containing α'-martensite is lower than the thickness of the hardened layer estimated from the durametric studies. In contrast, it is shown that, for all the loads applied to the indenter during frictional treatment, the through-depth distributions of the calculated values of equivalent plastic strain obtained from finite element modeling agree satisfactorily with the experimental hardness values.

Deformation of Al–Zn–Mg–Cu composite samples under nonstationary thermomechanical conditions

The paper studies the technology of deformation and heat treatment of an aluminum-matrix composite material under nonstationary conditions, which is upsetting with gradual heating to near-solidus temperatures under mild loading conditions. The composite material is based on the V95 aluminum alloy discretely reinforced with 10% of SiC particles. The purpose of the study is to compare the deformation behavior of the samples and analyze their microstructure under different conditions of thermal deformation processing. The structure of the material is studied by optical and electron scanning microscopies. The paper discloses the behavior of the rate of relative strain as dependent on temperature, as well as the features of structure formation in an aluminum-matrix composite depending on the heating conditions. The most pronounced differences are found in the central part of the samples closer to the deforming tool (flat dies). On the symmetry axis in the central region of the samples there are differences in the crystallographic orientations of the material textures. Microhardness values and their distribution on the section are obtained. For the sample with slow heating, there is no tendency for the increase of the microhardness values in the regions with high values of plastic strain, this being indicative of a more complete recrystallization process and lower dislocation density.

The elasto-plastic numerical study of crack initiation in notched PMMA specimens under uniaxial loading conditions – Tension and torsion

This paper presents the results of FEM numerical calculations aimed at describing the plastic strain and stress fields under critical loading conditions: tensile force or torsional moment. The calculations were carried out with reference to the results of experimental tensile and torsional tests of flat PMMA specimens weakened with V-notches of different root radii: 0.5, 2 and 10 mm. The procedure for conducting nonlinear numerical analyses is described, including the determination of the actual hardening curve by the hybrid method. A high level of consistency between the results of the experimental and numerical calculations was obtained through description of PMMA with the elastic–plastic material model. The points of occurrence of stress maxima and plastic strain were indicated, which were taken as potential crack initiation sites. On the basis of the stress and plastic strain values measured at the critical points, a stress–strain fracture criterion was formulated, which was then positively verified.

Voids effect on micromechanical response of elastoplastic fiber-reinforced polymer composites using 1D higher-order theories

This work investigates the effect of voids within the matrix of composite materials. Effects on local stress and plastic strain values are evaluated by conducting a micromechanical analysis. The microscale Representative Volume Element (RVE) is modeled through refined 1D elements based on the Carrera Unified Formulation (CUF). Using 1D models for the RVE leads to a significant reduction in computational costs compared to standard 3D elements. Fibers are modeled as orthotropic, and the matrix has an elastoplastic behavior. Random distributions of voids are considered, and statistical analyses are carried out. Furthermore, the influence of the depth of the RVE is investigated. The results show significant mean and peak stress values increases as the void volume fraction grows. Also, the use of deeper RVE leads to higher stress values.

Effect of plastic strain and specimen geometry on plastic strain ratio values for various materials

The aim of this paper is to show influence of two elements on plastic strain ratio value, or "r" value. The first element is value of plastic strain, and second is specimen geometry. Extensive experiment was conducted according to appropriate tensile test procedure with 3 materials and 5 different specimen geometries. Steel sheet S235JR, austenitic stainless-steel sheet X5CrNi18-10 and Al alloy sheet AlSi0.9MgMn (i.e. ENAW 6081) were used during the experiments. Nominal thickness for all three sheets was 1 mm. Three out of five specimen geometries had 20 mm width and gage length of 60, 120 and 160 mm while the rest of specimens had width of 15 mm and gage length of 50, 100 mm. All the specimens were laser cut in rolling direction. In preparation part of the experiment, behind material characterization (obtaining base mechanical properties) identification of homogenous deformation field was performed, i.e. plastic strain at the beginning of localization, for each specimen. Related to that strain value 6 degrees of deformation were realized: 75%, 80%, 85%, 90%, 95% and 100%. Results showed expected and significant difference in "r" value for used materials, but influence of specimen geometry and realized plastic strains were low.

Effect of plastic strain and specimen geometry on plastic strain ratio values for various materials

The aim of this paper is to show influence of two elements on plastic strain ratio value, or "r" value. The first element is value of plastic strain, and second is specimen geometry. Extensive experiment was conducted according to appropriate tensile test procedure with 3 materials and 5 different specimen geometries. Steel sheet S235JR, austenitic stainless-steel sheet X5CrNi18-10 and Al alloy sheet AlSi0.9MgMn (i.e. ENAW 6081) were used during the experiments. Nominal thickness for all three sheets was 1 mm. Three out of five specimen geometries had 20 mm width and gage length of 60, 120 and 160 mm while the rest of specimens had width of 15 mm and gage length of 50, 100 mm. All the specimens were laser cut in rolling direction. In preparation part of the experiment, behind material characterization (obtaining base mechanical properties) identification of homogenous deformation field was performed, i.e. plastic strain at the beginning of localization, for each specimen. Related to that strain value 6 degrees of deformation were realized: 75%, 80%, 85%, 90%, 95% and 100%. Results showed expected and significant difference in "r" value for used materials, but influence of specimen geometry and realized plastic strains were low.

Interfacial investigations on the microstructure evolution and thermomechanical behavior of explosive welded CLAM/316L composite

In this paper, a comprehensive study combined multiple characterizations and SPH numerical simulation was conducted to investigate the microstructure evolution, extreme thermomechanical behavior and consequences of the explosive welded CLAM/316L interface. The interfaces of the two welding materials underwent remarkable temperature rise and rapid cooling under high-speed collision conditions, forming a tight bond that presents a wavy structure with vortices. The SPH simulation adequately reproduced the heating and cooling process of the interface during explosive welding, revealing the high heterogeneity of the thermodynamic behavior during the impact process. Furthermore, the EBSD analyses showed the perplexing evolution of crystal structure at the bonding interface with vortex, including ultra-fine grains, columnar grains, equiaxed grains, deformed grains and serious lattice distortion. By correlating the temperature histories and grain characteristics at different positions of the interface, the formation mechanism of diverse grains was revealed, referring to crystallization from liquid, recrystallization from the solid and plastic deformation. The recrystallization at the interface was closely related to the material properties, and the significant variations in dislocation density and plastic strain values at the interface, as well as the thermal softening of the material, could be explained by different degrees of dynamic recovery and recrystallization.

Investigating mechanical characteristics of novel precast segmental lining using experimental and numerical methods

In recent years, precast segmental lining (PSL) has attracted much attention in tunnel engineering. In practice, the segmentation method is an essential consideration for PSL. This study proposes a novel PSL with a specific steel space truss. It uses physical and numerical modeling and considers three different segmentation principles in the experiments. In addition, this research develops an accurate three-dimensional finite element model, enabling a detailed analysis of the novel PSL. It also investigates the influence of joint thickness and stiffener on the novel PSL. The experimental results indicated changes in the lining's displacement, internal force, and failure mode. They revealed that cracks initially appear at the block joints. Considering the force and deformation of the lining, the method based on the maximum moment position principle is optimal because it can achieve the lowest deformation and bending moments. The numerical results showed that increasing the joint thickness or welding stiffeners raises the bending stiffness, reduces the joint opening, and decreases the plastic zone and strain value, thereby improving the joints' reliability. The findings are advantageous for the tunnel PSL design and can serve as a reference for joint optimization.

Improving concrete fatigue resistance with COVID-19 rubber gloves: An innovative sustainable approach

Since the COVID-19 outbreak in late 2019, a surprisingly large amount of personal protective equipment, such as medical rubber gloves, have been frequently used, and this medical waste can cause very major environmental problems. A multidisciplinary collaborative approach is needed to combat the pandemic and lessen the environmental risks associated with the disposal of medical waste. This study developed an innovative approach by incorporating shredded rubber glove fibers (RGF) into aggregates to enhance the fatigue resistance of concrete. In this study, different volume contents (0.5%, 1.0%, 1.5%, 2.0%) of RGF were added to the aggregate for the first time. The effects of different RGF contents on the fatigue characteristics of concrete were examined through repeated loading tests and SEM analysis. The results show that the width and number of cracks produced by rubber glove fiber concrete (RGFC) after repeated loading are significantly reduced compared with normal concrete (NC). Following repeated loading, RGFC exhibited higher total, plastic, and elastic strain values than NC, demonstrating greater deformability and elasticity. However, the maximum total strain growth rate and the total strain growth range of the RGFC group were only 2.26 × 10−3/time and 14.0%, which were significantly smaller than the 3.8 × 10−3/time and 31.7% of the NC group, showing better stability, corresponding to enhance the fatigue resistance of concrete. The interfacial transition zone (ITZ) was abnormally smooth with a thin thickness and no visible gaps were discovered, based on the results of SEM test performed on the RGFC. The findings obtained in this study may provide new ideas for the resource utilization of medical waste.