فهرست مطالب

Stress Analysis - Volume:3 Issue: 1, Spring-Summer 2018
  • Volume:3 Issue: 1, Spring-Summer 2018
  • 122 صفحه،
  • تاریخ انتشار: 1397/07/15
  • تعداد عناوین: 11
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  • S. Abdolazimzadeh, S. Mazdak *, E. Sharifi, M.R. Sheykholeslami Pages 1-10
    Tailor welded blanks (TWBs) include welded metal sheets, for the purpose of obtaining the desired structure of materials, decreasing product weight and increasing process flexibility and efficiency. Weld-line movement in TWBs during process is always considered as a challenging problem. Weld line movement is one of the influencing parameters, having effect on sheets formability. The subject of this study is presenting numerical model for predicting weld line movement and thickness distribution in TWBs sheet during deep drawing process. In this paper, by applying the finite element approach, ABAQUS software, a method has been developed for predicting weld line movement in TWBs. Design of experimental method (DOE) was done based on sheet thickness, radius of die, and experimental design matrix parameters has been used for obtaining weld line movement prediction model. Experimental tests were done to confirm the correctness of the simulations. Finally, the effect of punch and die radius, weld-line situation and thickness rate, on weld line movement and thickness distribution in square TWBs have been reported.
    Keywords: Deep drawing, Weld line movement, Tailor welded blanks, Finite element approach
  • A. Madadi, H. Eskandari, Naddaf *, M. Nemati Nejad Pages 11-19
    The present study analyzes the bond stress in steel reinforcements embedded in concrete containing polymer fibers, micro- and nano-silica particles. For this purpose, 36 cylindrical (with a diameter of 10cm and height of 15cm) and 36 cubic (10 × 10 × 10cm) specimens containing different contents of additives and three types of cement strength grade (i.e. 32.5, 42.5 and 52.5MPa) were constructed and subjected to pull-out and compressive strength tests, respectively. The experimental observations were then compared to previously proposed models available in the literature. The results indicated that microand nano-silica particles, compared to fibers, had more impacts on improving the reinforcement-concrete bond strength. Moreover, the highest bond strength was observed for the specimen containing equal content of microand nano-silica particles. An acceptable agreement was also obtained between the results of current study and previous models, highlighting the capability of the proposed models in prediction of the actual behavior of such specimens.
    Keywords: Reinforcement-concrete bond, Pull-out test, Polymer fibers, Micro-silica, Nano-silica, Cement strength grade
  • K. Reza Kashyzadeh, G.H. Farrahi *, M. Shariyat, M.T. Ahmadian Pages 21-33
    The present paper investigates the effect of changes in wheel primary angles such as Camber and Toe angles on the fatigue life of vehicle steering knuckle under multi-input random non-proportional 3D stress components. In order to develop real loading conditions for the steering knuckle, the localizing equivalent road as a combination of some rough roads (ISO road classification B-F for highway out of town, urban highway, urban asphalt, soil road, and flagstone, respectively) based on statistical data collected from different cities by utilizing a general questionnaire including road type and vehicle velocity was considered. Then, the various actual load histories obtained through multi-body dynamics analysis of a full vehicle model were applied on several points of the component. The fatigue life of steering knuckle was predicted by using some prominent multi-axial fatigue criteria for non-proportional loading, rain-flow cycle counting algorithm, and Palmgren-Miner damage accumulation rule. Finally, the effect of different values of wheel angles on the fatigue life of the steering knuckle was examined. The results showed that the highest and lowest fatigue life of steering knuckle are related to the values of 2 positive and negative degrees of camber angle, respectively. The stress level is reduced in the various equivalent load histories by changing the toe angle to 0.2 negative, resulting in an increase in the fatigue life of steering knuckle.
    Keywords: Fatigue damage, Steering knuckle, Wheel alignment, Camber angle, Toe angle
  • G.H. Majzoobi *, K. Rahmani , A. Atrian Pages 35-45
    The Mg-SiC nanocomposite specimens were produced at low strain rate of 8×10−3s−1 using a universal INSTRON testing machine, strain rate of about 8×102s−1 using a drop hammer and at strain rate of about 1.6×103s−1 employing a Split Hopkinson Pressure Bar (SHPB). Tribological behavior of the samples was investigated in this work. The compaction process was performed at the temperature of 723K. The results showed increase in the wear resistance as the nano reinforcement increased. The results also indicated that as the reinforcement content increased to 10 vol%, the weight loss reduced approximately by 63%, 58%, and 35% for the samples fabricated by SHPB, drop hammer, and quasi-static hot pressing, respectively. The results also suggested that the wear rate of samples fabricated by SHPB was nearly 40% lower than that for quasi-statically fabricated samples and non-reinforced samples.
    Keywords: SiC, Nanocomposite, Powder metallurgy, Dynamic compaction, Wear
  • M.H. Farshidi *, H. Doryo, M. Yuasa, H. Miyamoto Pages 47-51
    In this work, tendencies of pure Niobium, Fe-20Cr stainless steel, and Ti-36Nb-2Ta-3Zr to formation of micro shear bands inside their microstructures during severe plastic deformation are compared with their mechanical properties. For this purpose, strain hardening behavior and strain rate sensitivity of flow stress of these alloys were measured using tension tests and nano-indentation tests, respectively. Microstructures of the alloys were studied using electron backscattering diffraction method before and after imposition of severe plastic deformation. Results show that increase of the strain hardening exponent and/or strain rate sensitivity of flow stress causes decrease of tendency to formation of micro shear bands during deformation. Moreover, formation of micro shear bands can be approximately predicted using a parameter previously proposed for prediction of formation of macro shear bands.
    Keywords: Micro shear band, Severe plastic deformation, Strain hardening, Strain rate sensitivity of flow stress
  • M. Molaei, M. Safari *, H. Deilami Azodi, J. Shahbazi Karami Pages 53-60
    In hydromechanical deep drawing process, a space of liquid replaces the matrix and the final shape of part is established based on the form of stiff punch. The application of hydroforming process is forming complex parts with higher quality than traditional forming methods. The advantages of multi-layer sheets are using different material characteristics, achieve higher strength and consequently get better forming condition. Forming of poor formable light-weight metals like aluminum alloys is difficult, which can be made easy with using hydroforming process. Having suitable range of the effective parameters of the process is important and can help to form parts with higher quality. In this research, the hydromechanical deep drawing of the two-layer bimetallic Copper/Aluminum 3003 with conical shape was studied using the finite element method (FEM) and the effect of different parameters of the process such as final pressure, friction coefficient, pre-bulging pressure, and pre-bulging height on maximum thickness reduction and thickness distribution were inspected. The results showed that increasing of the friction between blank and die or blank and blank-holder increases the thinning ratio, while by increasing of the friction between blank and punch, the maximum ratio of thickness reduction declined. In addition, optimum range of the pre-bulging pressure and pre-bulging height of this case study was extracted by numerical simulations. A study was also carried out using experimental setup for verifying the FEM results. By comparison of experimental and numerical results, good reliability was seen between them.
    Keywords: Hydromechanical deep drawing, Bilayer conical cup, Experimental investigation, Numerical simulation
  • A.R. Shahani *, A. Farrahi Pages 61-68
    The effect of three different sheet thicknesses of friction stir spot welding on lap-shear specimens of Al 6061-T6 alloy was experimentally analyzed. Different fatigue life evaluation models were applied to estimate the fatigue behavior of the friction stir spot welding in different thicknesses. Experimental results show a clear correlation between static strength and fatigue behavior of different welding conditions. Results of tensile and fatigue tests demonstrated the sheets with 2mm indicated the optimum thickness which were studied in this research. At the same cycles, fatigue results of different thicknesses showed considerable differences in the low cycles in comparison with the higher ones. The evaluation models of Pook, Zhang and three-dimensional finite element models were investigated in the different sheet thicknesses. The three-dimensional finite element model evaluated fatigue behavior better than the other models at different sheet thicknesses.
    Keywords: Friction stir spot welding, Fatigue, Mechanical behavior, Sheet thickness
  • Y. Mohammad Hashemi, M. Kadkhodaei * Pages 69-79
    This paper presents an investigation into shape memory alloy (SMA) springs considering the effects of geometry changes under small as well as large deformations. Helical springs were fabricated by shape setting of NiTi wires through heat treatment. The products exhibited pseudoelasticity at the ambient temperature, and their force-displacement responses were examined by performing simple tension tests. A model was further proposed to study tension and compression of SMA springs, and it was shown that the consequences of geometrical changes in tension and compression of springs are different. The numerical results of large and small deformation models were verified by experimental tensile results. In order to design a spring with maximum dissipative performance, a designer has three geometric parameters to set: wire diameter, spring diameter, and the number of active coils. The influences of these parameters on dissipated energy were studied in both displacement- and force-control loadings, and a framework for designing SMA springs with the purpose of achieving maximum applicable dissipation was at last developed.
    Keywords: Shape memory alloy, SMA, Spring, Large deformation, Dissipated energy, Geometric parameters
  • M. Esmaeilnia Omran *, A. Hoseini Karani Pages 81-91
    Progressive and general collapse of structures are extremely able to cause great casualties and financial losses. Accordingly, evaluation the performance of structures after losing primary elements is of great importance to prevent the structural collapse. This paper presents the progressive collapse assessment of RC moment frames with concrete shear wall system according to different span lengths. First, story column was destroyed by removing its reaction in different scenarios. Then, performance of the structure was evaluated under this circumstance to assess the different span length effects in RC moment frames with concrete shear wall. The results indicated that the shear wall has a positive effect on preventing progressive collapse and reduces the maximum vertical displacement by 30%. It was also observed that maximum Dynamic Amplification Factor (DAF) in the building occurs with the shear wall and the minimum length of the span. However, the maximum Demand Capacity Ratio (DCR) in a critical element for a building was obtained with the longest span and without the shear wall. Therefore, it was concluded that the DCR ratio is more suitable for evaluation of the progressive collapse severity than the DAF parameter.
    Keywords: Progressive collapse, Span length, Concrete structures, Nonlinear dynamic analysis
  • M. Saadatfar * Pages 93-110
    In the present article, the influences of interlaminar bonding imperfection and constant magnetic field, as well as hygrothermal environmental conditions, on the stresses and displacements of a cylindrical shell with surface bounded sensor and actuator are investigated. The multiphysics analysis was carried out to explore the effects of moisture, temperature, electrical and mechanical loadings as well as magnetic field. The shell was simply supported and could be rested on an elastic foundation. The material properties of the shell and piezoelectric sensor and actuator were assumed to be functionally graded in the radial direction according to power-law function. Using the Fourier series expansion method through the longitudinal direction and the differential quadrature method (DQM) across the radial direction, governing differential equations were solved. The validity of the present work was verified by comparisons with other published works. Numerical results are presented to illuminate the effects of aspect ratio of shell and magnetic field on the responses of the hybrid shell.
    Keywords: Bonding imperfection, Hygrothermal, Magnetic field, Functionally graded hybrid shell
  • H. Rabiee, S.A. Galehdari * Pages 111-121
    Since rotor system of helicopters is responsible for producing lift forces and thrust, analyzing their vibrations is very essential. This research describes a method applied for developing a computer program to analyze coupled vibration of helicopter rotor. Natural frequency and rotor blade mode shapes were analyzed by MATLAB software. In-plane, out-of-plane coupled and torsion vibration were also considered in this analysis. First, Myklestad method, which is one of the most accurate ones to calculate vibration, was used to find governing equations of rotor vibrations. Based on governing equation, vibration code was developed by MATLAB software. After that for validating the program, the obtained results were compared with numerical results using PATRAN software, with maximum 4.264% error. In these problems, three beams in different geometric and material conditions with clamped end were defined. The innovation of this research is developing a MATLAB code to calculate the coupled natural frequencies and mode shapes of helicopter blade.
    Keywords: Coupled modal analysis, Helicopter, Blade, Matlab, Myklestad method