فهرست مطالب

Journal of Stress Analysis
Volume:3 Issue: 2, Autumn-Winter 2018-19

  • تاریخ انتشار: 1397/12/10
  • تعداد عناوین: 11
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  • S. Etehadi, M. Botshekanan Dehkordi * Pages 1-14
    In this article, a vibrational behavior of sandwich beams with stiff and flexible cores and face sheets reinforced with carbon nanotubes is investigated. Carbon nanotubes are used as materials with properties varying along the thickness. In order to model the behavior of faces, the Timoshenko beam’s theory is employed and also for modeling the behavior of the core, three-dimensional elasticity is used. The axial stresses of the core are considered in this model and therefore it is suitable for modelling two types of stiff and flexible cores. The equations of motion are derived using the variations of energy, and the Navier method is used to solve the equations of motion. Results are presented for different volumes of carbon nanotubes with different distributions along the thickness of the faces. In the case of stiff core, results show that the FG-V distribution has the highest natural frequency and the FG-Λ distribution has the lowest natural frequency in all cases. For flexible core, the FG-X distribution leads to the highest natural frequency and also the FG-O distribution has the  lowest natural frequency. Furthermore, results indicate that an extended high-order sandwich panel theory is a suitable model for analysis of stiff and flexible core sandwich panels. It must be mentioned for the cores made of stiff materials, the normal stress along the length of the core must be considered. It is due to the fact that the obtained results show that ignoring the normal stress along the length of the core leads to the large difference in the natural frequency of the system. In this article, due to the high order displacement field of the core, the flexibility of the core can be seen in the modeling. Additionally, since the term σc xx of the core is considered in the strain energy, a stiff core can be modeled. In many works the axial stresses of the core is removed from equations, therefore according to the results of sandwich beam with stiff core, lots of errors will be observed. Therefore, a proposed theory in this research can easily model a sandwich beam with two types of stiff and flexible cores. Since the Timoshenko beam theory is also implemented for modeling faces, different pattern of CNTs can be investigated accurately.
    Keywords: Vibration analysis, Sandwich beam, Stiff, flexible core, FG carbon nanotubes, Extended higher order theory
  • M.A. Moazam, M. Honarpisheh * Pages 15-28
    The aim of this paper is to compare incremental and integral techniques in non-uniform residual stress measurement by the ring-core method and to present a procedure to determine the calibration coefficients of the integral technique. The mathematical basis of the integral technique for use in the ring-core method is explained. To determine the calibration coefficients of the integral technique a 3D FE model was introduced and the calibration coefficients are also presented in separate tables. The FE analysis of the pure bending and ring-core method were used to show the effectiveness of the presented coefficients and compare the integral and incremental techniques. The results indicated that the calculated non-uniform residual stresses by the integral technique were closer to the real values in comparison with the incremental method. Moreover, it was observed that the accuracy of the results decreased by increasing the depth of the groove.
    Keywords: Residual stress, Non-uniform, Ring-core, Calibration coefficient, Integral, Incremental
  • H. Mazaheri *, A. Ghasemkhani Pages 29-35
    In this article, analytical and numerical methods were employed to study swelling behavior of a cylindrical shell made of a functionally graded temperature sensitive hydrogel. The hydrogel shell has gradient property in radial direction. The shell cross-linking density is a linear function of the radial coordinate of the FGM shell. The analytical model was first developed for the hydrogel shell and a second order differential equation was derived which can be solved by numerical methods. Then, finite element solution of the under-study functionally graded hydrogel shell was performed by implementing the material model in ABAQUS software and by writing a user-defined subroutine. In this regard, the functionally graded hydrogel shell was modeled as multi-layered shell with discrete material properties. A good agreement between the analytical results and numerical simulation was observed and validity of analytical solution was confirmed. Thereafter, analytical model was employed to study the swelling behavior of functionally graded shell for different thickness ratios of the shell.
    Keywords: Temperature sensitive hydrogel, Analytical solution, Finite element method, Micro-valve, Functionally graded hydrogel
  • E. Selahi * Pages 37-46
    In this paper by employing ANSYS Workbench software and three-dimensional finite element simulation, failure analysis of hybrid bonded and bolted single and double lap joints with laminated composite adherends subjected to axial, shear and bending loads were performed. In order to select an appropriate and optimized element number, the convergence behavior of single and double lap joints were investigated. Then the failure study of each single and double lap hybrid composite joints for the three time dependent loading cases were performed. To demonstrate the validity and precision of the presented simulations, the obtained results were compared with the results presented in the available literatures. The results of this research indicated that, in the single lap joint subjected to axial load, the replacement of hybrid bonded bolted joint instead of adhesive joint leads to significant increase of 56% in the load bearing capacity of the joint.
    Keywords: Failure, Composite, Hybrid joint, Adherend, Adhesive, Bolt
  • M.R. Karafi *, S.A. Mirshabani Pages 47-58
    The purpose of this paper is to develop a design procedure for Langevin ultrasonic transducers with lateral dimensions larger than a quarter of the longitudinal wave length. In this case, the assumption of the one-dimensional design is not valid, and this method cannot predict the experimental resonance frequency. Some researchers have considered radial and longitudinal normal stresses by means of the apparent elasticity method and reduced the error between the design and experimental resonance frequency. In this research, 3D normal stresses of a transducer’s components i.e. longitudinal, radial and circumferential were considered in the design procedure. The apparent elasticity method was used to modify the elastic modulus and the wave numbers of the transducer‘s components. Resonance lengths of the components were then calculated using the modified values. The design resonance frequency of the transducer was 20kHz. The experimental resonance frequency was measured as 19810Hz. The error of 0.95% between analytical and experimental results showed that the new design procedure can fairly estimate the resonance frequency of the transducer.
    Keywords: Langevin ultrasonic transducer, 3D vibrations, Piezoelectric, Resonance frequency, Apparent elasticity method
  • M.J. Khoshgoftar *, M. Shaban Pages 59-68
    In this paper, a mixed modeling approach for orthotropic laminated plates is developed. By adopting Hellinger-Reissner functional and dimension reduction method along the thickness, the governing equations were derived. By considering other theories i.e. classical plate theory, first order shear deformation theory and elasticity theory, the advantages of the current work are illustrated with some numerical results. Excellent agreements were observed by comparing the obtained results with three-dimensional elasticity theory for laminated thick plates. In the presented method, shear correction factor was not required for considering shear strain components. Furthermore, finite element simulation was implemented in Abaqus software by using two-dimensional shell elements and compared with obtained results. It is seen that although finite element model predicts good results for displacement field but it cannot provide any suitable results in thickness direction.
    Keywords: Mixed variational formulation, Hellinger-Reissner principal, Linear elastic, Laminated plate, Elastic analysis
  • E. Ghazizadeh, A.H. Jabbari Mostahsan, M. Sedighi * Pages 69-73
    Magnesium alloys are a unique choicefor orthopedic implants due to their biocompatibility and biodegradability properties. In this article, the impact of hot-extrusion process is investigated on microhardness, microstructure, and corrosion behavior of magnesium/2.5wt% hydroxyapatite (HA) rods as a bio-composite. Hot extrusion process was implemented on the as-cast samples in two different steps resulting two various total extrusion ratios of 5:1 and 20:1. The corrosion susceptibility of the extruded composites was studied by polarization test in simulated body fluid (SBF) as a corrosive environment. According to the results, adding hydroxyapatite reinforcing particles and applying higher extrusion ratios caused grain refinement in the matrix comparing to the pure magnesium. Moreover, while the hardness of the pure magnesium sample decreased slightly after the second extrusion pass, it was enhanced in the composite specimens. Besides, both extrusion ratio and reinforcing particles had direct effects on the corrosion behavior, so that with the presence of HA particles and applying the higher extrusion ratio, the corrosion resistance of the samples was improved.
    Keywords: Magnesium, Hydroxyapatite, Bio-composites, Hot-extrusion, Microstructure, Microhardness, Corrosion properties
  • M. Omidi Bidgoli, A. Loghman *, M. Arefi Pages 75-82
    This paper presents two-dimensional stress and strain behavior of a FG rotating cylindrical shell subjected to internal-external pressure, surface shear stresses due to friction, an external torque, and constant temperature field. A power law distribution was considered for thermomechanical material properties. First order shear deformation theory (FSDT) was used to define the displacement and deformation field. Energy method and Euler equation were employed to derive constitutive differential equations of the rotating shell. Systems of Six differential equations were achieved. Eigenvalue and eigenvector methods were used to solve these equations. It was found that the material grading index has a significant effect on stresses and strains of a rotating functionally graded material cylindrical shell in radial and longitudinal directions.
    Keywords: Grading index, FG rotating cylinder, Stress, strain, Thermomechanical loading, Friction bed
  • S.M. Hosseinian *, F. Bahmani Pages 83-93
    For existing reinforced concrete structures exposed to freeze-thaw conditions, there is an increasing engineering concernover their remaining safety. This paper presents a novel experimental-theoretical stochastic model for evaluating the reliability of concrete structures subjected to freeze-thaw conditions based on stress limit reduction. Reliability theory and experimental works provide the basis for the model development. Water cement ratio, air content, and number of freeze-thaw cycles are considered as the model variables. Compressive stress limit reduction in freeze-thaw conditions was treated as a stochastic variable. The effectiveness of the proposed model was evaluated using an example concrete structure element. The paper demonstrates that after, for example, 10 years experiencing FT cycles in a cold city; the reliability of the example concrete beam reduces to 52.5 percent for −10◦C concrete freezing temperature. It was found that the results of the proposed method are accurate compared to the literature. It was also found that the results of the proposed method are in good agreement with those obtained based on concrete’s non-destructive tests.
    Keywords: Reliability, Freeze-thaw cycles, Stress limit, Concrete, Stochastic model, Compression
  • S.R. Hoseini Vaez *, N. Fallah, A. Mohammadzadeh Pages 95-107
    In this study, a two-stage damage identification approach based on modal flexibility differences and whale optimization algorithm (WOA) was applied to localize and quantify damages in large-scale double-layer truss structures. In first stage, damage locating vector (DLV) method using EDS (exponential decreased stress) was employed to find the real damaged elements of structure; then, WOA algorithm was used to determine the severity of suspected damaged elements obtained from the first stage. To evaluate the reliability of the proposed approach, two large-scale double-layer truss structures were studied. Furthermore, to assess the effect of noise on the accuracy of damage detection, the article compares the results of EDS with NCE. Calculation results demonstrate that the combination of DLV method using EDS and WOA algorithm provides an effective tool to carefully determine the location and the severity of structural damages in noisy condition directly. Moreover, the approach determines damages even though there are the low number of used mode shapes and a high number of structural elements.
    Keywords: Damage identification, Whale optimization algorithm, Damage locating vector, Large-scale double-layer trusses Two-stage approach, Exponential decreased stress
  • S. Karimi, J. Jafari Fesharaki * Pages 109-116
    This paper focuses on reducing stress concentration in a plate with a hole. For this purpose, a novel Reliever Topological Material Elimination (RTME) approach was introduced which uses the topology optimization technique to specify the best areas to remove material in order to refine flow of stress and reduce the Stress Concentration Factor (SCF), consequently. Using the Solid Isotropic Material with Penalization (SIMP) method, topology optimization was formulated. Three major elimination areas were determined from material elimination patterns observed in topology optimization. Two possible RTME cases were proposed numerically. To evaluate the efficiency of the method, finite element analyses were conducted for one previous technique and the results werediscussed. In addition, the results of finite element analysis were validated by some experimental tests. According to the final results, RTME approach gives up to 35.5% stress reduction, 44% SCF mitigation, and decrease about 28% of the initial volume. In comparison with the previous technique, using RTME is more effective in decreasing the SCF and weight of the plate, simultaneously.
    Keywords: Stress concentration factor, Topology optimization, SIMP method