Journal of Stress Analysis
https://jrstan.basu.ac.ir/
Journal of Stress Analysisendaily1Mon, 26 Jun 2023 00:00:00 +0330Mon, 26 Jun 2023 00:00:00 +0330Experimental and Theoretical Investigation of Mechanical Properties of Functionally Graded Epoxy/Graphene Nanocomposite
https://jrstan.basu.ac.ir/article_5210.html
In this paper, the experimental and theoretical investigation of mechanical properties of functionally graded (FG) epoxy/graphene nanocomposites is presented. Samples were organized for uniform distribution (UD) through weight percentage of graphene nanoparticles (0, 0.5% w/w, 1% w/w, and 1.5% w/w) as well as for FG distribution. Four samples with different weight percentages of nano-graphene (pure, 0.5% w/w, 1% w/w, and 1.5% w/w) were used to make FG samples. The distribution of nanoparticles was studied through a scanning electron microscopy (SEM). This study showed that no signs of agglomerated particles were observed in the SEM image in uniform distribution. Also, SEM imaging was performed for the FG sample, which showed that the boundaries of the layers were completely interconnected and that the distribution of nanoparticles was uniform and continuous from one surface to another. Then, the samples were subjected to tensile tests. The results of the tensile tests showed that the tensile modulus began to increase from 0 to 0.5 wt.% of nanographene and then decreased. For FG samples, the tensile modulus is commonly greater than the related values for the UD of graphene nanoparticles. The theoretical predictions of the elastic modulus for nanocomposites were made by three methods (Einstein, Mori-Tanaka, and Guth-Gold), then the experimental results were compared with the theory. In addition, for FG distribution, the samples were loaded transversely and the experimental deflection was obtained and the theoretical values calculated for the elastic modulus were compared with experimental ones. Also, the comparison between UD and FG samples show that the FG sample has the lowest deflection compared to the samples with uniform distribution of nanoparticles.&nbsp;The Effect of the Constrained Groove Pressing Process on Mechanical Properties of Thin Pure Copper Sheets
https://jrstan.basu.ac.ir/article_5213.html
Thin copper sheets with micro-dimensional thickness are increasingly used in forming processes. Copper is widely used in electronic industries and in many cases, it is required in the form of thin sheets with a thickness of less than 1 mm. However, decreasing the thickness of the sheet and extending its order to grain size leads to some problems such as dispersion of laboratory results and reduced material strength. In this study, an attempt has been made to improve the mechanical properties of copper sheets by applying the cold working method of Constrained Groove Pressing (CGP). By applying the accumulated plastic strains, the grain size decreased and the ratio of the sheet thickness to the grain size increased, thereby the mechanical properties of the sheet were improved. The results show that the application of the CGP process increases the ultimate strength up to 25% and the yield stress up to 114%. Moreover, it reduces the maximum strain up to 77% and increases the hardness up to 100%. The cross-sectional images taken by an optical microscope show changes in grain density and size under this CGP process. A finite element (FE) simulation has been performed to investigate the effect of the CGP process on the micro deep drawing process. The obtained results show a decrease in the Limiting Drawing Ratio (LDR) from 1.96 for as-received material to 1.7 for one pass and two passes and to 1.34 for three passes CGPed blank. Furthermore, a uniformity in shell thickness (STH) was observed along the cross-section of the blank.&nbsp;Parametric Investigation of Carbon Nanotube-Based Nanomechanical Mass Sensors Using Structural Mechanics and an Artificial Neural Network Approach
https://jrstan.basu.ac.ir/article_5211.html
The use of single-walled carbon nanotubes (CNTs) as mechanical sensors to detect tiny objects has dramatically expanded in the last decade. In this article, the parameters affecting the efficiency of sensors, including the diameter of single-walled carbon nanotubes (SWCNTs), the length of SWCNTs, SWCNT chirality, applied strain, and added mass, were investigated. At first, the effects of the desired parameters were investigated using structural mechanics. Then, an artificial neural network (ANN) was trained to predict the sensor behavior in other design points. After the training phase, the ANN-based model provided an accurate macro-model of a sensor. The results showed that the nanotube-based sensor could detect a mass of even 10 zeptograms (1zg=10&minus;21g) and that the applied axial strain significantly increased the efficiency of the sensor. According to the results, the ANN-based model can model the dynamic behavior of this type of sensor with significant accuracy. Moreover, the ANN-based model is 104 orders of magnitude faster than the existing models in structural mechanics.Experimental Analysis of the Effects of Plasma Cutting Parameters on Residual Stress Distribution by the Contour Method on St37 Sheets
https://jrstan.basu.ac.ir/article_5212.html
Today, due to the advancement of technology and continuous improvement of manufacturing products and greater economic efficiency, new energies are used in production processes. One of these methods for cutting metals is the arc or plasma cutting process. Identifying residual stress is important for any process in terms of its amount and type (tensile or compressive). Considering the importance of evaluating residual stresses after the plasma cutting process and given the fact that residual stresses related to the plasma cutting process have yet to be investigated, this issue was investigated in this paper. The effects of parameters of cutting current intensity, i.e., cutting voltage and cutting speed, which are defined in a plasma machine, were investigated in St37 sheets with thicknesses of 5, 8, and 10mm. For this purpose, following the plasma cutting process in stress-relieved samples, the amount and type of residual stresses along the length and depth of the samples were measured by the contour method. Results showed that in the direction of the sample&rsquo;s length and in the area around plasma cutting, tensile residual stresses, and in the center of the part in the same direction, compressive residual stresses had their highest value. Also, in the direction of the sample&rsquo;s depth, the type of residual stresses was compressive. The highest value of compressive residual stress in the depth direction was obtained for samples with a thickness of 5mm and a current intensity of 200 A.&nbsp;Investigation of the Effect of Cracks on Vibrational Properties of Composite Cylindrical Shells
https://jrstan.basu.ac.ir/article_5214.html
Composite structures are prone to reduced performance due to defects occurring over time during the manufacturing and loading process. In this study, the effect of longitudinal and circumferential cracks alone as well as their combined (longitudinal and circumferential together) effect on vibrational properties of composite cylindrical shells was investigated simultaneously using experimental and numerical modal testing. Also, the effect of crack length and depth in longitudinal and circumferential directions on the natural frequencies of composite cylindrical shells was investigated. Initially, in order to validate the finite element (FE) model, an intact shell and a defective shell were modeled and analyzed, and the results were compared with the reference. After validating the FE model, first, modeling and frequency analysis were carried out for a composite cylindrical shell consisting of four layers of woven glass fibers (300 g/m2) impregnated with an epoxy resin with a 0.73-mm thickness for each layer. Then, the defects (cracks) in both longitudinal and circumferential directions in different dimensions and sizes were modeled and after analyzing all samples (intact and defective), natural frequencies and shape modes were obtained. To perform the experimental modal testing (EMT), several shell samples, similar to the simulated samples, were made and the natural frequencies were extracted for all samples. The natural frequencies obtained from the two methods were compared and the estimates show that the results of both methods are in a good agreement. The results also show that longitudinal cracks affect the natural frequencies and the mode shape more than circumferential cracks do.&nbsp;Experimental Investigation of Curvature Uniformity in the Laser Bending Process
https://jrstan.basu.ac.ir/article_5215.html
The laser bending process (LBP) is a powerful tool for the fabrication of precise bending angles as a die-less manufacturing process. The curvature uniformity of bent sheets is an important and controversial object of study. In the current article, the effect of the process variables on the bending angle and curvature uniformity of the laser bending of sheets was studied. The process parameters included the laser power, scanning speed, and the number of irradiations. The effect of the input process variables on bending angle and curvature uniformity was investigated by conducting a set of 15 experiments designed by the response surface methodology (RSM) algorithm. The statistical analysis showed that the bending angle decreased by decreasing the number of irradiation passes and the laser power, while the bending angle increased by decreasing the scanning speed. Furthermore, the curvature uniformity of the lateral edge of the sheet decreased by decreasing the number of irradiation passes and the laser power. The curvature uniformity increased first and then decreased by decreasing the scanning speed of the irradiated beam. The interaction of the number of irradiation and the scanning speed created a local maximum point at a high number of irradiation passes and a low scanning speed. The effect of the number of irradiation variations became negligible by increasing the scanning speed up to 8mm/s.&nbsp;Fatigue Endurance Optimization of a Steam Turbine Blade Curved Fir-Tree Root
https://jrstan.basu.ac.ir/article_5429.html
In this paper, the guide curve of a fir-tree root is parametrically modeled for the optimization of a newly designed free-standing low-pressure last-stage blade airfoil of a steam turbine. These geometrical parameters include the location of the center point of the curve root centerline and the radius of the root curvature, while the axial length and the pitch are kept fixed. The mechanical safety factor is computed at the upper section of a predefined root profile for each considered design parameter in a commercial finite element software. For high cycle fatigue failure analyses, the maximum alternating stresses are calculated from harmonic responses under the dynamic fluid loading obtained from computational fluid dynamics (CFD) simulation at the maximum continuous rating condition. Preliminary modal analysis is performed to estimate the natural frequencies for the principal modes near the low engine order excitation. On this basis, dynamic stresses are calculated at corresponding frequencies prone to low order engine modes of excitement. Moreover, harmonic response is obtained at nozzle passing frequency for each set of design parameters. In addition, the total strain is computed at the upper section of the root from elastic-plastic analysis under centrifugal loading resulting from 110% of nominal operating speed. Therefore, a multi-objective optimization genetic algorithm is used to optimize the root design parameters with objectives of maximizing safety factors obtained from both strain-based low cycle fatigue and stress-based high cycle fatigue analyses.Numerical analysis and microstructure analysis and mechanical properties of non-homogeneous laser welding process for 304L stainless steel and St37 low carbon steel by the design of experiments method
https://jrstan.basu.ac.ir/article_5430.html
One of the most suitable and up-to-date bonding technologies is laser welding, due to its low local energy, complete laser beam penetration, heat-affected area, perfectly uniform fusion with minimal distortion, and ultimately residual stresses, Less is created. The use of the laser welding process, due to its high-speed performance and weight loss made by the structure, is now expanding in the industry. This study investigated the ability of a 304L stainless steel laser and st37 low carbon steel to use laser welding with a maximum power of 1000 watts. The effect of process parameters on welding penetration, microscopic structure, heat affected area (HAZ), mechanical properties, and microstructure of laser-affected area were studied and compared with TIG welding. In this research, the mechanical properties and microscopic structure of laser welding in two non-homogeneous sheets of 304 L stainless steel and low-carbon st37 were studied. In this study, with the help of laser energy, an experimental-statistical model based on the DOE method and adjustment of laser parameters was prepared for two non-homogeneous plates with a 2 mm thickness of 304 stainless steel and low carbon steel with the lip-to-lip connection. Then microstructural tests were performed and analyzed by optical microscopy (OM). DOE analyzed the results of microstructures and mechanical properties with the RSM method and optimal settings and results were presented. The above results were performed by laboratory method and re-laser testing was performed and the most ideal parameters and results were obtained.Nonlinear Free Vibrations of a Carbon Nanobeam Carrying an Elastically Mounted Concentrated Mass
https://jrstan.basu.ac.ir/article_5490.html
In the present study, the interaction of nonlocal parameters with linear mode shapes and nonlinear forced frequency response of Rayleigh nanobeam system connected to a suspended mass-spring-damper is examined. For this purpose, the dimensionless vibration equations governing the system based on the theory of displacement elasticity are extracted using the power series and the Green function concept considering the Kelvin-Voigt viscoelastic damping. Also, the method of multiple scales is considered to derive the equations of motion. Then, the forced response of the system under the extensive uniform harmonic external force is analyzed around the first natural frequency and the occurrence of the initial resonance. In order to examine the frequency response, nonlocal parameter, and system parameters, a degree of freedom is considered. Thus, the modal interaction occurs through the initial resonance. To validate the results of this study, the natural frequencies of the system with the results of the previous research &nbsp;are also compared with a beam without a mass-spring-damper and based on the same assumptions. Accordingly, it is revealed that increasing the mass-spring-damper leads to changing the amplitude in the nanobeam oscillation. The novelty of the paper lies in the combination of a continuous system with a discontinuous system by nanomaterials in the form of free and forced vibrations. A detalied look at the literature reveals that the analysis of free and forced vibrations using nonlocal theories is presented for the first time here.Nonlinear Quasi-static Analysis of SMA Curved Beams
https://jrstan.basu.ac.ir/article_5488.html
Considering many applications of Shape Memory Alloys (SMAs) in order to make structures smarter, a quasi-static analysis of curved beams made of SMA has yet to be investigated. Therefore, a quasi-static analysis of curved beams made of SMA under constant transverse force was investigated in this research. Hence, the 3D Hernandez-Lagoudas model was used to express the nonlinear properties of an SMA curved beam. For the mathematical modeling of the SMA curved beam, the Timoshenko beam theory was applied considering the nonlinear strains. Then, the governing equations were extracted using Hamilton&rsquo;s principle. The kinematic equations of SMAs were coupled with the governing equations of the beam, which made the analysis more complex. Differential quadrature method (DQM) in conjunction with the Newton&ndash;Raphson method was utilized to solve the nonlinear governing equations. DQM is a new numerical method based on the transformation of differential governing equations into algebra using weighting coefficients. The main objective of this paper is to obtain the martensite volume fraction, stress, and strain for all points of the beam. To validate this paper, results of static bending of a straight beam made of SMA using DQM were confirmed with other researchers&rsquo; works. Numerical results showed that with the increase in the curvature radius of the curved beam, the area of the hysteresis loop was increased, indicating a decrease in the strength of the structure and, consequently, an increase in thestatic deflection. In addition, some new outcomes were studied for various boundary conditions. In the case of a clamped-clamped curved beam, it was concluded that at the beam&rsquo;s ends, the martensite volume fraction had the highest value and as it approached the center of the beam, this value decreased.&nbsp;Analytical Methods for the Plane Problem in Piezoelectric Plate Containing a Polygonal Hole
https://jrstan.basu.ac.ir/article_5489.html
In the engineering design of perforated piezoelectric plates, understanding the effect of geometrical and significant parameters on stress concentration is of vital importance. In this paper, the effect of the hole shape on the stresses induced in perforated piezoelectric plates under mechanical loading was studied. The stress concentration was investigated using an analytical method based on the two-dimensional elastic theory, the Lekhnitskii method and conformal mapping by PZT-4 material and the load angle, the bluntness, and the rotation angle of the 3- to 6-sided polygonal holes. It was found out that the desirable hole angular position for which the minimum stress concentration was obtained was dependent on the order of the polygonal hole. To validate the precision of the reported solution, its results were evaluated by numerical methods achieved from finite element method (FEM) in ABAQUS software. The analytical results were in a reasonable correlation with the finite element (FE) results.Analysis of Influences of Parameters on Hydrostatic Compressive Stress in Cyclic Extrusion Compression Angular Pressing for CP-Ti
https://jrstan.basu.ac.ir/article_5492.html
Cyclic extrusion compression angular pressing (CECAP) is a new severe plastic deformation method used to improve mechanical and metallurgical properties of metals. In this process, hydrostatic compressive stress has a considerable effect on the quality of the fabricated sample, where, as it rises, the probability of the appearance of the crack initiation on the sample is reduced. In this research, the effects of the process parameters of CECAP on magnitude and distribution of the hydrostatic compressive stress were investigated using finite element analysis (FEA) and response surface method (RSM). Temperature ( ), input extrusion diameter (D), exit extrusion angle ( ), frictional coefficient , and longitudinal distance of input extrusion to extrusion compression angular pressing (ECAP) region (L) were selected as input parameters, and hydrostatic compressive stress ( ) was considered as response variable. Analysis of Variance (ANOVA) was extracted to evaluate the accuracy of the developed mathematical model and determine the significant factors. Results revealed that parameters of temperature and exit extrusion angle influence the hydrostatic compressive stress ( ) considerably. Also, the effect of interaction between the parameters is significant. The optical microstructure on the CECAPed section revealed that, for point C (center of section), the grain size is larger, reaching 3 &mu;m, while for point A (near to outer surface), the grain size reaches 1.5 &mu;m, showing that as it becomes near to the section, the grain size tends to be smaller. In order to verify the accuracy of the study, the hardness distribution behavior was compared by the strain distribution behavior obtained from finite element method (FEM). Moreover, the hydrostatic compressive stress of the current CECAP process was compared with other investigations and a significant improvement was observed. All experimental tests and the results of other investigations showed a good agreement with FEM results.An Efficient Optimal Analysis Approach to Reliability-Based Design Optimization of Symmetric Skeletal Structures
https://jrstan.basu.ac.ir/article_5491.html
The properties of symmetrical structures can cause the optimal analysis of these types of structures to have greater ease, speed, and accuracy. It also saves space for storing large-scale matrices. Reducing these computational costs is very useful in structural problems that require frequent analysis of the specific structure. One of the problems that need repeated structural analysis is reliability-based design optimization (RBDO) of structures utilizing meta-heuristic algorithms. This study presents an efficient approach to the optimal analysis of symmetric skeletal structures. With a systematic and programmable procedure, this approach extracts the submatrices whose dimensions are half or less than half of the main structure's stiffness matrix. Then, the inverse of the stiffness matrix can be determined by calculating the inverse of submatrices whose dimensions are half or less than half the dimensions of the main structure's stiffness matrix. Two symmetric benchmark structures with general loading were investigated to assess the proposed approach to solving the RBDO problem. The proposed approach reduces the dimensions of matrices that must be inverted, and the computational time for solving the RBDO problem using enhanced vibrating particle system (EVPS) algorithms, compared to the direct method.Thermo-mechanical Buckling Analysis of Non-homogeneous Open Circular Cylindrical Shells Reinforced with Single-walled Carbon Nanotubes
https://jrstan.basu.ac.ir/article_4398.html
&nbsp;In this paper, the thermo-mechanical buckling analysis of a non-homogeneous open cylindrical shell reinforced with single-walled carbon nanotubes with a uniform/non-uniform distribution on an elastic foundation under thermal andmechanical loads has been addressed. Using the minimum energy principle, the governing differential equations of this system are derived and in order to determine the properties of the reinforced composite shell, the modified mixtures law has been used. It is assumed that the properties of single-walled carbon nanotubes are acquired from molecular dynamics simulation. It is also assumed that the material properties of the reinforced carbon nanotube composites are linear in the thickness and are defined based on mixture law via a micro-mechanical model in which the nanotube performance parameter is considered. After solving these equations, the effects of geometric characteristics of the shell and material properties on the critical load and critical temperature of shell buckling are investigated.&nbsp;Resistance Spot Welding Process of AISI 304 Steel: Application of Sensitivity Analysis and ANFIS-GWO Methods
https://jrstan.basu.ac.ir/article_4648.html
&nbsp;For the Resistance Spot Welding (RSW) process, the effects of Welding Current (WC), Electrode Force (EF), Welding Cycle (WCY), and Cooling Cycle (CCY) on the Tensile-Shear Strength (TSS) of the joints have been experimentally investigated. An Adaptive Neural-Fuzzy Inference System (ANFIS) based on data taken from the test results were developed for modelling and predicting of TSS of welds. Optimal parameters of ANFIS system were extracted by Gray Wolf Optimization (GWO) algorithm. The results show that ANFIS network can successfully predict the TSS of RSW welded joints. It can be concluded that the coefficient of determination and mean absolute percentage error for the test section data is 0.97 and 2.45% respectively, which indicates the high accuracy of the final model in approximating the desired outputs of the process. After modeling with ANFIS-GWO, the effect of each input parameter on TSS of the joints was quantitatively measured using Sobol sensitivity analysis method. The results show that increasing in WC, WCY, EF, and CCY leads to an increase in TSS of joints. &nbsp;Sensitivity Analysis for Stress, Heat-Treating, and Rare-Earth Elements on Fatigue Lifetime of AZ91 Magnesium Alloy
https://jrstan.basu.ac.ir/article_4649.html
&nbsp;In this article, the changes in High-Cycle Fatigue (HCF) lifetimes of the AZ91 magnesium alloy are investigated under the influences of the different heat treatments and also the Rare-Earth (RE) element addition. For this purpose, some different heat treatments, including a common solution treatment, with different ageing treatments and RE elements were performed. Then, the sensitivity analysis was done using the regression analysis by the DESIGN EXPERT software on the experimental data. At a similar fatigue lifetime, the RE element increased the strength or the stress level by at least 30%, and also, the RE element with heat-treating enhanced the material strength by at least 50%. The results of sensitivity analysis on the experimental data illustrated that the stress level, the heat treatment, and the RE element (RE) were the most effective parameters on the fatigue lifetime, respectively. Besides, the fatigue lifetime was sensitive to the interaction of the heat treatment and the RE element. In addition, the fracture surface analysis demonstrated that allsamples had three different zones for the crack initiation, the crack growth, and the sudden final fracture. &nbsp;Numerical Study on the Effect of Biaxial Surface Stresses on the Measurement Accuracy of Mechanical Properties in A516 Using Indentation
https://jrstan.basu.ac.ir/article_4650.html
&nbsp;Accuracy in determination of mechanical properties in industrial parts is a major issue in engineering. Various methods have been introduced to estimate the mechanical properties of the industrial parts, and each has its own features and limitations. The present research investigates the accuracy of Instrumented Indentation Technique (IIT) with Kim&rsquo;s model in determining mechanical properties, including elastic modulus, yield stress, and work hardening of the A516 steel samples having surface stresses. To this end, some 3D simulations, using IIT on the steel sample with different surface stress state, were performed, and the method&rsquo;s error in comparison to the initial assumed values were obtained. The results show that the surface stresses significantly affect the error in determining the materials&rsquo; properties, and the error in samples with tensile surface stress is more than that of samples with compressive one. To validate the results, some experimental samples with specified initial stress were prepared, which measured mechanical properties by the IIT and then were compared with the tensile test results. &nbsp;Experimental Investigation of Textured Surfaces in Line and Point Mixed Lubrication Contact
https://jrstan.basu.ac.ir/article_4651.html
&nbsp;Finding a way to reduce the wear resulted from aperities interactions in mixed lubrication regime is an interesting area. One of the inspiring solution is surface texturing. Using a convenient laser, a textured surface with arbitrary micro cavity shape and size was prepared accurately. In this study, the effect of laser surface texture on the wear and friction behavior of discs in line and point contact in mixed lubrication regime was investigated. The effect of texturing area, linear velocity, and vertical load were examined. The friction coefficient variation reaches a narrow margin after an adequate distance. The results showed that wear decreases with increasing speed and decreasing the applied force. Comparing the results between plane and textured discs, it was found that the coefficient of friction was reduced between 12 and 19% and theamount of wear was reduced by almost more than 40%. &nbsp;Investigation of Elastic Leak in Rectangular Hydrogel Seals
https://jrstan.basu.ac.ir/article_4652.html
Eliminating the need for external manipulation due to the ability of hydrogels to sense the environmental stimuli and swelling, makes it suitable for sealing applications. As the matter of fact, many researchers from both academia andindustry have investigated hydrogel seals experimentally and numerically. In this work, by using constitutive models available in the literature, the sealing properties of rectangular hydrogel seals are numerically investigated. To investigate elastic leakage of hydrogel seals subjected to fluid pressure, leakage models of elastomeric ones are implemented. The methods are validated by comparing the result of the model with available experiments in the literature. Afterward, the mechanism of leakage of hydrogel seal is presented, and then, parameter studies are carried out. It has been found that increasing the cross-link density, hydrogel length, and the ratio of hydrogel thickness to the gap it seals increases the value of fluid pressure associated with leakage. &nbsp;Design and Simulation of a Laser Measurement Technique in Split Hopkinson Pressure Bar Test
https://jrstan.basu.ac.ir/article_4814.html
The Split Hopkinson Pressure Bar (SHPB) is a commonly used technique to measure the stress-strain behavior of materials at high strain rates. Using Utilizing the strain records signals recorded in the input and output bars, the average stress, -strain and strain rate in the sample can be calculatedis determined by the one-dimensional wave propagation equations of SHPB formulas based on the one-dimensional wave propagation theory. The accuracy of a SHPB test is based on this assumption as well as dynamic equilibrium. In this paperarticlework, the possibility feasibility of using a laser measuring system to obtain the dynamic properties of a wide range ofvarious materials using split Hopkinson pressure bar without strain gages is studied. In this method which is a non-contact one, the displacements of bar/sample interfaces are measured directly using a laser extensometer technique. After designing a proper set of optical elements, the operation of the method is evaluated using numerical simulation in ABAQUS/Explicit. Cast iron, aluminum and polypropylene samples, which represent the properties of hard to soft, respectively, were studied to evaluate the proposed measurement method for different materials. The comparison with other strain gage methods shows good agreement and lower fluctuation in stress-strain curves. Moreover, since the one-dimensional wave propagation is not used in this method, we show by numerical simulation that the proposed method can be used even with shorter pressure bars which can reduce the cost of manufacturing and maintaining the SHPB apparatus.&nbsp;Effects of the Geometric Profile of Twist Channel Angular Pressing (TCAP) on the Deformation Behaviors and Microstructure Evolution of AL7050 Alloy
https://jrstan.basu.ac.ir/article_4815.html
&nbsp;Severe plastic deformation processes are used as a method to increase the mechanical strength of metals. One of the new deformation methods is twist channel angular pressing (TCAP). TCAP has been developed based on a combination of twist extrusion processes (TE) and Equal Channel Angular Pressing (ECAP) process. In this paper, the effect of TCAP die geometry on the grain size distribution and plasticity properties using simulation in DEFORM software is investigated. For this reason, dies with internal angles of 90◦, 100◦ and 110◦, external (corner) angles of 0◦, 10◦ and 20◦ and twist angles of 30◦, 45◦, 60◦ are used. In addition, the location of the twist channel is examined before and after the ECAP location. The distribution of plastic strain, grain size distribution, and the required punch force for the TCAP process on Aluminum alloy 7050 are extracted in all conditions. The results showed that locating the twist section after ECAP location led to a better microstructure in the billet. Also, die with a twist angle of 45◦, an internal angle of 110◦, and a corner angle of 0◦ created the best results; therefore, the grain size decreased from 100&micro;m to 3.67&micro;m.&nbsp;Optimization of Superimposed Residual Stress Components to Improve Fatigue Life of Work Roll in Hot Rolling Process Using Artificial Neural Network and Genetic Algorithm
https://jrstan.basu.ac.ir/article_4816.html
&nbsp;In this paper, a semi-analytical model was proposed to superimpose the initial residual stress components on the work roll surface and subsurface to minimize the maximum value of Von-Mises Stresses (MVMS) during the hot rolling process to reduce the possibility of roll wear and increase the fatigue life. A Finite Element Model (FEM) was proposed to assess the temperature and thermomechanical stress in work roll during hot rolling. An analytical method was developed to implement the three initial residual stress components designed by the full factorial analysis of variance (ANOVA) method in the obtained FEM thermomechanical stress results. An Artificial Neural Network (ANN) was used to establish an objective function to relate the initial residual stress components to the MVMS. Subsequently, the single and multi-objective Genetic Algorithm (GA) optimization were used to find the optimal value of initial residual stress components to minimize the MVMS on the surface and subsurface of the work roll. The results showed a significant reduction of boththe value and amplitude of the MVMS on surface and subsurface of a work roll during the hot rolling process.&nbsp;An Analytical Approach for Modeling Fluid-structure Interaction Problems in Axisymmetric Domains
https://jrstan.basu.ac.ir/article_4817.html
&nbsp;Few analytical approaches have been proposed so far for solving FluidStructure Interaction (FSI) problems in the literature. In fact, FSI is generally so complicated that its analytical solution remains almost unavailable. Inspired by this fact, here an analytical methodology is presented for modeling steady-state fluid-structure interaction problems in axisymmetric domains. For this purpose, the Navier-Stokes equations for the flow of the incompressible viscous fluid, and the linear elasticity equations for the deformation of the solid structure are expressed in axisymmetric coordinates. Appropriate boundary conditions are also employed that are capable of coupling the fluid and solid domains by imposing kinematic and dynamic constraints on the fluid-structure interaction interface. The set of fluid and structure equations are solved by MATLAB symbolic toolbox. The accuracy of the presented analytical approach is verified in two different ways. First, by specializing the results for the simple case of a thick cylindrical pressure vessel, second, by comparing the analytical results for flow through a nozzle with numerical results obtained by ANSYS/CFX simulation. Variation of the stress components is obtained in the nozzle wall. The results of the analytical approach are in good agreement with those of the numerical modeling. The proposed methodology can be used for fast yet efficient solution of fluid-structure interaction problems in axisymmetric configuration. &nbsp;Laser Treatment of Pure Titanium Surface in Various Irradiated Media: Investigating Hardness Properties of Ablated Ti Surface
https://jrstan.basu.ac.ir/article_4818.html
&nbsp;Titanium (Ti) has poor tribological and mechanical properties such as low hardness and wear resistance. In this study, we considerably improve Ti&rsquo;s hardness by laser ablation method. Ambient air, N2 gas chamber and N2/liquid water environments were separately selected as irradiation environments and their effect was comparatively studied on Ti treatment surfaces. The fabrication of titanium nitride (TiN) structure was successfully confirmed by XRD analysis in N2 gas and N2/liquid water as irradiation media. Accordingly, there was good adhesion between TiN structure and Ti&rsquo;s surface. Vickers hardness test indicated the laser treatment and TiN structure significantly improved Ti&rsquo;s hardness. The formed TiN structure in N2/liquid water environment had the highest hardness value of 530Hv comparing to hardness of ablated Ti in N2 gas (370Hv) and air (340Hv). The escalation of Ti hardness and generation of TiN structure with lasertreatment in N2/liquid water environment is a favorable aspect of this method.&nbsp;Experimental and Numerical Crushing Behavior of Sandwich Structures with Two-layered Bi-directional Corrugated Core and Single-layered Bi-directional Interconnected Corrugated Core
https://jrstan.basu.ac.ir/article_4819.html
This paper investigates the quasi-static compressive strength of two sandwich structure designs in which cores consist of trapezoidal corrugated panels. In one design, the core consists of a steel cross-corrugated two-layered structure, while in the other design, the core consists of a single layer of bidirectional interconnected corrugated core made of ST37 steel sheets. To investigate the energy absorption capacity of these sandwich structures quasi-static compression is performed numerically and experimentally. First, from each design, a test specimen is constructed and tested under quasi-staticcompressive load. Following that, the finite element models of the designs are constructed and their crushing process is simulated and the FEM method results were compared with the test results and the FE model is verified. After verification of the numerical model, for each design, three different trapezoidal wave profiles are modeled and, the mechanical behavior of the other bidirectional interconnected corrugated cores is evaluated numerically. The results showed that the maximum force and energy absorption capacity of the sandwich structures with the single-layered bi-directional interconnected corrugated core is higher than the strength and energy absorption capacity of their counterparts with the same weight in the two-layered bi-directional corrugated core group with the same weight. It was also found that, inthe single-layered bi-directional interconnected corrugated core group, the failure mode is plasticity near the welding joints, while for the single-layered bi-directional interconnected corrugated core, the failure mode is plastic buckling of the corrugated core under compressive load and some local plastic deformation in the connection of the layers.&nbsp;Investigation of the Effect of Nano-Al2O3 Addition on the Tensile and Flexural Strengths of Friction Stir Processed Polycarbonate
https://jrstan.basu.ac.ir/article_5598.html
In this paper, the effects of two factors named plunge depth and translational speed on tensile strength, flexural strength, and hardness of polycarbonate reinforced with Al2O3 nanoparticles by friction stir processing (FSP) was investigated. To study the effects of the mentioned variables, design of experiments (DOE) and statistical analysis were used. Each of the factors was considered at five levels. A total of 14 specimens were subjected to FSP. It was found that the effect of plunge depth on the values of tensile strength, flexural strength, and hardness of the FSP-ed samples was more than the translational speed. Increasing the plunge depth from 0 to 0.4 mm caused a 52.3% decrease in tensile strength and a 42.6% decrease in flexural strength. In addition, it was found that increasing the plunge depth had a stronger effect on the tensile strength and caused a more severe decrease in it. According to the statistical analysis, the optimal plunge depth and translational speed to create the highest tensile strength and flexural strength is 0 mm and 42&ndash;46 mm/min, respectively. The hardness of the processed sample was inversely proportional to the plunge depth and translational speed. By increasing the plunge depth from 0 to 0.4 mm and increasing the translational speed from 30 to 90 mm/min, the hardness of the processed zone decreased by 38.8% and 32.6%, respectively.