Journal of Stress Analysis
Volume:6 Issue: 1, Spring-Summer 2021

Considering the importance of composite connections, this study evaluated two experimental and numerical methods for bolted joints of epoxy-glass composite plates. Then, using an artificial neural network, a model was defined between experimental and numerical results. The results of this study showed that the maximum force tolerated by bolted joints was various at several distances and its maximum value was tolerated by the connection at 4cm equal to 5332 and 7093N, for two specimens. Comparison of numerical and experimental results of Von-Mises stress for distances of 2, 3, and 4cm was done. The Von-Mises stress for these distances was 313.59, 217.57, and 177.71MPa, respectively. In this research, the connection of epoxy-glass plates using M6-bolt was studied, and by increasing the coverage of two composite plates, the Von-Mises stress in the connection was raised. Concerning the determination of the stress measuring path, from the internal edge of the critical notch to the end of the defined range with a smaller mesh, the Von-Mises stress was extracted, which in distance equal to 3cm with the vertical arrangement, maximum stress was equal to 513MPa. The minimum stored energy of the numerical method in the connection was related to the bolted joint with a two-bolt in the vertical position.

Design procedure of pressure vessels is very important due to their vast applications in many industries. This procedure is mainly based on determining the stress and strain distribution, which is resulted from the internal pressure. In this paper a thin-walled pressure vessel of circular-arc cross-section is analytically studied. The vessel is a surface of revolution generated by rotating a circular arc about an axis that neither intersects the arc nor necessarily passes through the arc center. Both convex and concave vessels with open- and closed-end conditions are considered. The equilibrium equations for a proper element of the vessel surface are derived and solved analytically. Assuming small deformation and elastic behavior for the vessel, the integral constant is determined based on the end boundary conditions of the vessel. Since this type of pressure vessel was not studied in the previous literature, the results of present model are compared with similar ABAQUS Finite Element (FE) simulation. A very close agreement was observed. This evidently implies the validity of the presented model.

Incremental forming process, as one of the methods used for forming complex parts in rapid prototyping, has various applications in the automotive and aerospace industries. The incremental forming process can be used to flange a metal sheet that, compared to conventional flanging, not only increases the formability but also does not require expensive dedicated dies. The deformation and damage mechanisms in the incremental forming process are completely different from conventional forming processes and need exact and thorough investigation. The present study is aimed at evaluating the damage and deformation mechanics in the hole-flanging process by single-stage and multistage incremental forming on AA6061-T6 sheets, considering several parameters affecting damage and fracture, including equivalent plastic strain, stress triaxiality, and lode angle parameter. These important parameters can reveal the stress and strain states as well as the deformation mechanism, which have been less addressed in the hole-flanging by incremental forming. The results indicated that the stress and strain states varied in different regions of the flange wall, such that the strain state was as plane strain at the bottom of the wall in contact with the unformed part of the sheet, biaxial tensile state at the middle of the wall, and uniaxial tensile state at the top of the wall on flange edge. The highest damage was observed at the flange edges, and the fracture occurred at low values of stress triaxiality in this area, indicating the shear fracture in the hole-flanging of AA6061-T6 sheets during the incremental forming. Finally, a slight increase was observed in the forming limit by forming with a multistage strategy instead of the single-stage one, although the equivalent plastic strain increased significantly.

This paper analyzes the effects of yield stress and nanoparticles transport on the natural convection of viscoplastic Casson nanofluids. The non-linear coupled partial differential equations are solved numerically using Buongiorno’s mathematical model. The governing parameters for the problem are the Rayleigh number (Ra), yield number (Y), and thermophoresis and Brownianmotion parameters (N t&Nb). The effects of these parameters on the fluid flow, heat and mass transfer, and the shape of yielded and unyielded regions are examined and discussed in detail. The results demonstrate that the heat and mass transfer rates increase as the Rayleigh number increases, while the opposite behaviors are observed with increasing the yield number. The fluid is difficultly yielded at low Rayleigh number. The heat and mass transfer are primarily due to conduction at the high values of the yield number. The main effect of thermophoresis and Brownian motion parameters is on temperature and concentration distribution in the cavity. These parameters also show significant impacts on critical heat and mass transfer.

In the present investigation, to fabricate Nano-composites made of wrought aluminum alloy 7075 and multi-walled carbon nanotubes, carbon nanotubes and the alloy powders were initially dispersed in ethanol using an ultrasonicshaker to form a primary mixture. The milled powder mixture was converted into the final specimens by Spark-Plasma Sintering. To achieve a uniform distribution of carbon nanotubes in the matrix alloy, ethanol or stearic acid can be used as a Processing Control Agent (PCA). For each of the seven specimens, a series of tests were performed to study the effects of the reinforcement phase on the base alloy. As shown, the reinforced specimens were harder compared to the pure Al7075 and the sample reinforced with 1wt% of multi-walled carbon nanotubes has both the highest hardness and flexural strength among all the specimens. Additionally, when the weight fraction reached 2%, there was a noticeable drop in the mechanical properties. This novel alloy produced by powder metalurgy can be very helpul for industrial application where the increase in strength and hardness is deireable.

This paper studies the mechanical behavior of a polymeric degradable vessel subjected to internal pulsatile pressure, external pressure, and axial elongation. Two deformation-induced evolution laws are selected to investigate time-position-dependent material properties of the polymeric vessel. The vessel is subjected to the neo-Hookean constitutive model and an axisymmetric condition. To simulate finite deformation in the degradable vessel, FlexPDE commercial software is invoked in which the governing equations are solved by Standard Galerkin Finite Element Method (SGFEM). Results show that stresses pulsationally increase during degradation. Deformation response of the degradable vessel against time reveals the creep-like behavior of degradable polymers. Degradation rate begins from an initial peak value and decreases over time. The impact of degradation on invariants of the deformation tensor versus time and the vessel radius is discussed. Degradation evolution is higher in the outer radius of the vessel because of higher deformation in this region.

This paper investigates the weldability of super-duplex steel hollow pipes, which are welded by Gas Tungsten Arc Welding (GTAW) process, using destructive and non-destructive tests. Non-destructive inspections were performed by visual inspection and radiography, which indicate the proper quality of the performed welds. Material analysis, metallographic, tensile and hardness tests have been performed for different welding positions. The effects of the welding position on the microstructure and mechanical properties of the welded specimens were investigated. The results of the metallographic test reveal the good balance between austenite-ferrite phases in the weld zone. According to materials analysis, chromium to nickel weight percent is higher at the 12 o’clock position. The hardness test results show that the average hardness is the same in different welding positions. The presented results indicate the good weldability of the super-duplex steel pipes fabricated by the GTAW process. The weldability assessment of the GTAW super-duplex steel hollow pipes using both destructive and non-destructive tests, at different welding positions, is an innovative research.

The Distribution of displacements and stresses in a finite length hollow cylinder made of Functionally Graded Material (FGM) subjected to coupled hygrothermal loading was investigated. The simply supported cylinder was under a transient coupled hygrothermal loading. Furthermore, the internal pressure and viscoelastic foundation can be considered for the cylinder. The coupled equations of heat and moisture transfer and motion equations of the cylinder were solved employing the Fourier series expansion method, the Differential Quadrature Method (DQM), and the Newmark method along the longitudinal direction, the radial direction, and the time domain, respectively. Finally, the distribution of temperature, humidity, deformations, and stresses was obtained. The effects of coupled and uncoupled hygrothermal loading, grading index, hygrothermal boundary condition, and viscoelastic foundation are illustrated in the numerical examples. The results show that the FGM cylinder touches the temperature balance before using the uncoupled model rather than the coupled model. Moreover, by serving the time, the radial displacement, and maximum hoop stress increase, and longitudinal displacement decreases to reach steady-state condition.

Ultrasonic Assisted Deep Drawing (UADD) is a state of the art Conventional Deep Drawing (CDD) process that results in improved formability and decrease in forming force. In this novel technology, the forming tool fluctuates under low amplitude and high frequency which is supplied by an ultrasonic package including generator and transducer. The main objective of this research is study of various parameters affecting the deformation behavior of the formed thin cylindrical-parts by UADD process, based on experimental tests and numerical methods followed by statistical approach. In this regard, a sophisticated Finite Element Model (FEM) including surface effect and stress superposition is developed. Nevertheless, a robust technological equipment is designed and fabricated in which the special die as a main vibratory tool can be longitudinally stimulated by enforced vibrations with frequency very close to the 20kHz. Consequently, experiments are performed to determine the effectiveness of the ultrasonic vibration, as well as, calibrate the established FE model. The simulation outputs and the relevant experimental tests are compared based on the forming force and drawing depth results, and an acceptable agreement is achieved. Based on the validated numerical model, Design of Experiment (DOE) by Response Surface Methodology (RSM) is utilized to run multiple simulations. Moreover, the effect of six parameters in the UADD process on the maximum forming force and the minimum thickness of the formed cup is statistically evaluated and high-reliability regression models based on the analysis of variance (ANOVA) with 90 simulations are generated to estimate these two output parameters. As a result, ultrasonic vibration amplitude, punch nose radius, and blank diameter with 37.22, 21.68, and 19.03% of contribution, respectively, were the most effective parameters on the required forming load. Furthermore, the results illustrated that ultrasonic vibration amplitude was the most important parameter on thickness reduction of sheet with 69.92% contribution.

Strain rate is an effective parameter in characterization of ductile materials. In this work, the influence of strain rate on damage evolution in copper is investigated through analytical approach, experiment, and numerical simulation. In the analytical approach, a modified damage model is proposed to take account of the effect of strain rate on damage parameter based on Continuum Damage Mechanics (CDM). A new technique is used for evaluation of damage evolution in tensile dog bone specimens using a Split Hopkinson Tensile Bar (SHTB). The results of high strain rate tests are used to validate the modified damage model. The proposed model is based on Bonora ductile damage model in which the effect of strain rate is incorporated. The numerical simulations are performed by implementing the proposed model in the finite element commercial code, ABAQUS/Explicit using VUSDFLD subroutines. A reasonable agreement was observed between the experimental data and the proposed damage model.

In this paper, the low-velocity impact response of laminated composite cylindrical shells subjected to the combined pre-loads is investigated. The pre-load is applied as the mechanical pre-load (axial force and radial pressure) and the thermal pre-load. The boundary conditions are considered as simply supported and the behavior of the material is linear-elastic. The equations are based on the first-order shear deformation theory and the Fourier series method is used to solve the analytical equations. The impactor studied as a large mass and therefore the impact response is considered to be quasi-static. The results show that regardless of the type of the axial pre-load (tensile or compressive), changes in contact parameters during the impact are linearly related to the temperature changes. Furthermore, these variations with respect to the radial pressure is almost linear for the tensile axial pre-load, but it is nonlinear for the compressive axial pre-load.

In this paper, an analytical solution and a numerical simulation of the pH-sensitive hydrogel micro-valves exposed to pH variation are proposed. Case studies consist of micro-valve with homogeneous single-layer and FG hydrogel as the active part. The results of both methods are in good agreement indicating the validity of both methods. In addition, The numerical and analytical solutions were compared between two ranges of cross-linking densities of hydrogels. In order to reach a convergent solution for the finite element model of the micro-valve, the hydrogel layer is considered to have a number of different layers, and an appropriate number of layers are considered. In the next step, parameters affecting the micro-valve behavior are studied, which are the dimensionless thickness ratio, the number of acidic groups in the network, and the salt molarity of the external solution. The findings show that as the thickness ratio, number of acidic groups, and salt concentration in the external solution result increases, the hydrogel part of the micro-valve experiences a higher degree of swelling and deformation, which should be considered when designing these devices.