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In this paper, to predict flow stress of Austenitic Stainless Steel (ASS) 304 at elevated temperatures the extended Rusinek–Klepaczko (RK) model has been modified using an exponential strain dependent term for dynamic strain aging (DSA) region. Isothermal tensile tests are conducted on ASS 304 for a temperature range of 323–923 K with an interval o...
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... material used in this investigation is ASS 304 and its chemical composition is given in Table 1. Flat tensile spec- imens of the dimensions as shown in Fig. 1 in accordance with sub-sized ASTM: E8/E8M-11 standards are used to con- duct the experiments. The samples are machined from a raw sheet material by wire-cutting electro-discharge machining process. A computerized UTM (refer [13]) with a maximum load capacity of 100 kN is used to conduct isothermal ten- sile tests. The machine is ...
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... These processes are primarily governed by local atomic diffusion. As a function of temperature, this significantly lowers the flow stresses, which eventually tend to saturate at values [13][14][15]. ...
One of the most common characteristics of metallic alloys is work hardening, which is most beneficial as it is the primary reason for the alloys’ tenacity to withstand loading even in the presence of internal flaws or geometrical errors. Thus, the work hardening coefficient gives the maximum amount of homogeneous plastic deformation in tensile straining. Thus, complex-forming operations are facilitated by a high coefficient without experiencing premature failure. Naturally, work hardening has a significant impact on the mechanical energy required to shape a material by plastic deformation, such as rolling, forming, etc. The quantity of energy that the material stores during plastic deformation is also managed by work hardening. As a result, it significantly influences how the metal behaves when it is subsequently softened during annealing. Finally, the hardening capacity and durability of the work hardened state are significant practical challenges because many high-volume stretch formed components are directly used. Typically, the current study begins, at homologous temperatures above 0.4 times melting point, with a description of work hardening at 700, 800, and 900°C temperatures in three different orientations with respect to rolling direction R 0, R 45, and R 90 and 10⁻¹−10⁻³ s⁻¹ strain rates, where thermally triggered processes exhibit a prominent role in work hardening. Three stages of behavior were identified by analyzing the tensile work hardening of ASS 304 steel. Dynamic strain aging is the cause of the anomalous fluctuation in the work hardening rate that is seen in hot working temperatures. X-ray diffraction examination is conducted to introspect any phase changes occurring in hot working regions improving plasticity of ASS 304.
... As summarizing in table 1, thick copper films (thickness: ∼250 μm) were electrodeposited on a dumbbellshaped metallic titanium electrode using a sulfuric acid bath (bath composition: CuSO 4 ·5H 2 O (1 M), H 3 BO 3 (0.4 M), PEG (Mw: 3,000) (0, 0.01, 0.03, 0.05 g L −1 ) and pH1) with a temperature of 80°C. In the present work, the dumbbell-shaped samples for an uniaxial tensile test were prepared refering to ASTM E08/E8M-11 standard [24,25]. Here, the sample size was reduced from the ASTM standard to immerse it completely in a small amount (300 mL) of electrolytic solution [26]. ...
Nanocrystalline thick copper films with the thickness of ~250 µm were electrochemically synthesized from an acidic aqueous solution containing polyethylene glycol (PEG) with the average molecular weight of 3,000 to investigate the preferential crystal orientation and mechanical properties such as microhardness and tensile strength. By addition of PEG to the electrolytic bath, the cathode potential was shifted to a less noble direction during the electrodeposition and the average crystallite size of electrodeposited copper thick films was decreased. The copper thick films electrodeposited from the solution without PEG exhibited a preferentially orientation in (220) texture while that obtained from the solution containing PEG was composed of nanocrystals with random crystal orientation that containing (111) and (200) textures. The micro-Vickers hardness, tensile strength, and elongation of the electrodeposited copper thick films reached up to 133 HV, 234 MPa, and 13.1%, respectively. These improvements in mechanical properties can be explained by the grain refinement effect and the random crystal orientation effect.
... Ni-Co alloy sheets (thickness ≈100 μm) were synthesized using an electroforming process in an acidic aqueous bath (40°C, pH show the shape and dimensions of the dumbbell-shaped titanium electrode. In the present work, the original specimens for tensile test were prepared refering to ASTM E08/E8M-11 standard [36,37]. Here, the dimensions were adjusted in order to electrodeposit small specimens in the electrolytic bath (300 ml). ...
Nanocrystalline nickel–cobalt (Ni–Co) binary alloy sheets were fabricated through electroforming in an acidic aqueous bath using exfoliation from a metallic titanium cathode. Cobalt content in Ni–Co alloy sheets ranged from 28.8 at% to 72.0 at% depending on experimental parameters, such as cathodic overpotential and bath composition. The surface roughness (Ra) of the electroformed alloy sheets significantly decreased down to 1.5 μm as saccharin sodium dihydrate was added as an additive to the acidic aqueous solution bath. X-ray diffraction profiles and transmission electron microscopy images indicated that the electroformed Ni–Co alloy sheets have a nanocrystalline structure (grain size ≈ 30 nm). The lattice constant of the electroformed Ni–Co alloy sheets increased with an increase in cobalt content (i.e. solute atom concentration). The mechanical properties were significantly improved because of the synergistic effects of crystal grain refinement and solid solution strengthening. The microhardness and tensile strength of the electroformed Ni–Co alloy sheets reached 609 kgf/mm2 and 1757 MPa (XCo = 49.9 at%), respectively. The tensile strength of the electroformed Ni–Co alloy sheets in this study significantly exceeded that of solidified Ni–Co alloys (approximately 370 MPa). Therefore, this study offers a technique to enhance the mechanical properties of electroformed Ni–Co alloy sheets.
... The behaviour of materials subjected to loading over a wide range of strain rates and temperatures is described using different phenomenological and physical models, e.g. power law [9], Zerilli-Armstrong [10], Rusinek-Klepaczko [11][12][13], Nemat-Nasser [14], Follansbee-Kocks [15,16], Johnson-Cook [17][18][19][20], Miller [21], Bodner [22], Walker [23], Kocks [24] and Krempl [25]. These models include the hardening effects and static or dynamic recovery in different way. ...
Numerical simulations of the extrusion process assisted by die cyclic oscillations (KOBO extrusion) is presented in this paper. This is highly non-linear coupled thermo-mechanical problem. The elastic-viscoplastic Bodner–Partom-Partom material model, assuming plastic and viscoplastic effects in a wide range of strain rates and temperatures, has been applied. In order to perform simulations, the user material procedure for B–P material has been written and implemented in the commercial FEM software. The coupled Eulerian–Lagrangian method has been used in numerical computations. In CEL method, explicit integration of the constitutive equations is required and remeshing is not necessary even for large displacements and large strains analyses. The results of numerical simulations show the heterogeneous distribution of stress and strain inside container and the non-uniform distribution of strain in the extruded material. The increase of material temperature has been noted. The results obtained (stress, temperature, location of plastic zones) qualitatively confirm the results of experimental investigations. The application of the user material procedure allows accessing all material state variables (current yield stress, hardening parameters, etc.), and therefore it gives detailed information about phenomena occurring in extruded material inside recipient. This information is useful for a proper selection of parameters of the KOBO extrusion process e.g. synchronization of the punch displacement with the die oscillations frequency to avoid the saturation of material isotropic hardening, which blocks the progress of extrusion.
... The accurateness of the numerical methods chiefly influenced by how accurately the constitutive equation represents the deformation behaviour of the material. In this context, numerous literature has reported on flow stress prediction for different automotive and aerospace grades of sheets using different constitutive models [30][31][32][33][34]. Different phenomenological models such as Khan-Huang (KH) model, Cowper-Symonds (CS), Johnson-Cook (JC), Arrhenius type equations (m-Arr) etc., envisage the deformation behaviour of the material based on empirical findings. ...
... σ ¼ σ a þ ðs i σ i þ s e σ e Þ μðp; TÞ μ o (11) Figure 6. Graph of (a) ln σ À A in Equation (11) is generally characterised as a function of Young's modulus as denoted in Equation (12) [33]. ...
... The optimisation technique using a genetic algorithm was utilised in order to obtain these values taking into consideration the sensitiveness of the final prediction to the initial assumptions. The values were determined using MATLAB equipped with a genetic algorithm toolbox, and the extensive details regarding the optimisation process have been reported elsewhere [33,59]. Further, Equation (18) was utilised to obtain the value of the saturation stress component (σ es ). ...
In this work, uniaxial tensile tests of Inconel-718 (IN718) sheets were performed at elevated temperature domain of 773-1023K and a deformation rate between 0.001-1s-1. A substantial reduction in maximum stress was observed at 923K indicating a decrease in peak load by approximately 75.6% and 8.5% in contrast to room temperature (303K) and 773K respectively. Further, different con-stitutive models, namely Cowper-Symonds (CS), Mechanical Threshold Stress (MTS), and Johnson-Cook (JC), were established to envisage the stress-strain behaviour. The CS model predicted flow stress response better with the correlation coefficient, average absolute error, and standard deviation of 0.98, 4.09% and 6.14% respectively. Also, formability experiments were performed at higher temperatures of 773K and 923K using stretch forming test facility. The highest dome height was noted at 923K signifying an improvement in limiting dome height (LDH) by 32% with respect to 303K. Further, thermo-mechanical numerical simulations of the process were successfully carried out, integrating established con-stitutive models independently. The predicted formability parameters , such as maximum attained load and surface strain distribution, were validated with the experimental data. The CS constitutive equation predicted the deformation behaviour close to the experimental results and, therefore, was considered as the appropriate model.
... The combined effect of strain, temperature, and strain rate over flow stress, for a variety of materials has also analyzed in detail by many researchers using various physically and phenomenologically based constitutive models (Ref [18][19][20]. Among these models, the Sellar hyperbolic sine equation based upon the activation energy concept is popularly used (Ref 21 Based on a detailed literature survey, it has been observed that extensive work has been reported for strain hardening and constitutive model development of traditional structural alloys, such as steel and aluminum. ...
In present study, flow stress behavior and material properties of Dual phase (DP) 590 steel has been investigated for different process parameters such as temperature (Room Temperature (RT) to 400oC), strain rate (0.0001-0.01s-1) and three different sheet orientations viz., Rolling (RD), Transverse (TD) and Normal direction (ND). Flow stress increases with increase in temperature and strain rate. The yield and ultimate stress also decreased by approximately 13.85% and 13.45% respectively with increase in temperature from RT to 400oC but no particular trend is observed for elongation. Subsequently, microstructural and fractography studies were conducted using scanning electron microscope. The volume fraction of martensitic phase seems to decrease with increase in temperature. In addition, an increase in ratio of high angle grain boundaries was observed from the electron back scatter diffraction studies with increase in grain size of material. The ductile type of failure was observed at all testing conditions. Furthermore, an investigation of strain hardening behavior using Swift and Voce model have been carried out for DP590 steel. Three stages of hardening is observed in case of both the applied strain hardening models. Predicted flow stress with Voce model displayed good relation with experimental data. The combined effect of temperature and strain rate are considered by formulating Arrhenius based Sellar model for flow stress prediction. Sellar model displayed good flow stress prediction capability as the average absolute error is 4.561%, standard deviation is 2.637% and correlation coefficient is 0.962.
... The JC model has been used to describe the behaviour of various metals such as iron [18,20], copper [18,20], steels [18,[20][21][22][23] or lightweight alloys [24][25][26]. In practice, if neglecting thermal softening, the identification of JC constitutive parameters includes two steps which rely on statically determinate approaches. ...
Rate-dependent behaviour characterization of metals at high strain rate remains challenging mainly because of the strong hypotheses when tests are processed with statically determinate approaches. As a non-standard methodology, Image-Based Inertial Impact (IBII) test has been proposed to take advantage of the dynamic Virtual Fields Method (VFM) which enables the identification of constitutive parameters with strain and acceleration fields. However, most of the test parameters (e.g. projectile velocity, specimen geometry) are not constrained. Therefore, an FE-based approach is addressed to optimize the identification over a wide range of strain and strain-rate, according to two design criteria: (1) the characterized viscoplastic spectra, (2) the identifiability of the parameters. Whereas the first criterion is assessed by processing the FEA simulations, the second is rated extracting material parameters using synthetic images to input the VFM. Finally, uncertainties regarding the identification of material constants are quantified for each IBII test configuration and different camera performances.
... The JC model has been used to describe the behaviour of various metals such as iron [36,38], copper [36,38], steels [36,[38][39][40][41] or lightweight alloys [42][43][44]. In practice, if neglecting thermal softening, the identification of JC constitutive parameters includes two steps which rely on statically determinate approaches. ...
In the present work Image-Based Inertial Impact (IBII) tests are performed on Ti6Al4V material. The IBII test uses an impact on the edge of the specimen to generate a short pulse that loads the specimen. Three specimen geometries have been tested: a classic rectangular specimen, and two specimen geometries with stress concentrating geometries (i.e. a hole and notches) to enhance high levels of plastic strain. Full-field measurement of the acceleration and strain are successfully used in combination with the Virtual Fields Method (VFM) to identify the strain rate sensitivity parameter of the Johnson-Cook model. The strain/strain rate spectra covered by each specimen are analysed. Finally, the influence of the virtual field used in the identification process is discussed as well as the simultaneous identification of the Johnson-Cook model strain rate sensitivity parameter and the strain rate threshold parameter.
... Austenitic stainless steels are extensively used in many fields of manufacturing because of their superior mechanical and functional properties such as high ductility, high strength, acceptable weldability and superb resistance against corrosion [1][2][3][4][5][6][7][8]. Additionally, they have an exceptional toughness and a high heat resistance, wherefore they can successfully be used from cryogenic to red-hot temperatures [9]. ...
The present study describes the process characteristics of the Cold-Metal-Transfer (CMT) Pin-Welding by welding structures on austenitic stainless steel (AISI 304) and characterizes the corresponding mechanical properties. Pin-Welding technology enables the possibility of welding small-scaled structures out of the welding wire. The mechanical properties and microstructures of the welded structures were investigated on different pin formations. Experimental samples extracted from the welded structure were subjected to tensile and hardness tests and microstructural examinations. Tensile test results were obtained lower than the welding wire owing to the process heat input, but both presented similar proportional results. The structures hardness formed out of wire diameter of 0.8 mm and 1.2 mm was obtained in an interval between 200-250 HV. Because the base metal has nearly similar hardness values, the whole structure exhibits a stable hardness distribution after the welding process. K e y w o r d s : welding, joining, austenitic steels, stainless steels, mechanical properties
... In RK model, 57 the flow stress (σ) is expressed as equation (37): ...
... It has been reported in the literature that the material shows viscoplastic behavior in the strain-rate range of 10 −5 to 10 7 s −1 . 57 The terms B 0 and E 2 are the material constants, and ν and n 0 are the temperature sensitivity and strain-hardening exponent at T = 0 K, respectively. The thermal activation component (σ * ) in equation (37) is usually represented as a function of strain rate and temperature, as mentioned in equation (40): (40) where σ 0 is the effective stress at T = 0 K, and E 1 and m * are the material constants. ...
... Step 1: At reference temperature (773 K) and lower strain rate (0.001 s −1 ) condition, the contribution of the thermal activation (σ * ) was assumed to be negligible, as per the literature. 57 At σ * ≈ 0, equation (40) was reduced to equation (41): ...
The fabrication of Inconel 718 (IN718) sheet metal components often requires larger deformation loads at room temperature. In this regard, deformation of the material at elevated temperature is a promising approach for reducing the forming load and enhancing the formability. Hence, the flow-stress behavior of IN718 sheets at elevated temperatures within the range of 773–973 K over wide ranges of strain rate (from 0.001 to 1 s−1) was studied by uniaxial tensile testing. The peak load reduced significantly by 75.6 and 8.5 % at 923 K and 0.001s−1 compared with room temperature and 773 K, respectively. Also, the total elongation improved by 65.4 and 16.5 % at 923 K with respect to room temperature and 773 K, respectively. In addition, a substantial improvement in the total elongation was observed with decrease in strain rate at higher temperatures. Seven different constitutive models, viz., Johnson-Cook (JC), modified-JC (m-JC), modified-Arrhenius equation (m-ARR), mechanical threshold stress (MTS), Rusinek-Klepaczko (RK), modified Zerilli-Armstrong (m-ZA), and the artificial neural network (ANN) were developed to describe the deformation behavior of IN718 sheet material at elevated temperatures and varying strain rates. Furthermore, suitability of these developed models was determined by comparing three standard statistical parameters, namely correlation coefficient (R), average absolute error (Δ), and standard deviation (SDA). The results showed that m-JC and m-ZA models predicted the flow stress very well in accordance with the experimental data. However, the trained ANN model could predict the flow-stress behavior more accurately throughout the entire testing condition. Though the ANN model was the best among all seven models, it was strongly dependent on an extremely good set of experimental data. Hence, the physical-based m-ZA model was considered to be the suitable model that could precisely predict the flow-stress behavior of IN718 sheet material.
