فهرست مطالب

  • Volume:13 Issue: 1, 2020
  • تاریخ انتشار: 1399/02/17
  • تعداد عناوین: 8
|
  • Hami Tourajizadeh *, Oveas Gholami Pages 1-15
    In this paper, a new optimal method for modelling of a 3PRS robot is proposed according to NOC algorithm. An optimal method of selecting the generalized coordinate is presented and a new algorithm of extracting the null space of over and under constrained robots is proposed through which a lower amount of mathematical calculations is required. In this method, using the principal of derivatives of implicit functions, the null space of constraint matrix will be extracted. Afterwards the null space matrix is calculated with orthogonal columns. The proposed method is implemented on a 3PRS robot which is an under constrained robot. This robot is a kind of parallel spatial robot with 6 DOFs which can be controlled using 3 active prismatic joints and 3 passive rotary ones. This robot similar to other parallel robots has heavy, complicated and nonlinear model which needs heavy and time consuming mathematical calculations. The proposed strategy of extracting the null space of the robot, extremely and heavily decreases the volume of required mathematical calculations for modelling the robot and consequently decreases the inevitable consumed time of processing and numerical errors and increases the accuracy of simulations.
    Keywords: Constrained Robot, Modeling, NOC, Null Space Matrix, 3PRS Parallel Robot
  • Tohid Mirzababaie Mostofi, Mostafa Sayah Badkhor, Hashem Babaei * Pages 17-29
    In this paper, a large-scale experimental study has been conducted in order to evaluate the high-velocity compaction of aluminum powder using Gas Detonation Forming (GDF) processing technique. In this series of experiments, the effect of the distribution of grain particle size, initial powder mass, and loading conditions on green density and strength of compacted products were thoroughly studied. The maximum relative green density and green strength of 97.6% and 17.9% were achieved. Group Method of Data Handling (GMDH)-type neural network in conjunction with Singular Value Decomposition (SVD) method was exerted to model the high-velocity compaction process of aluminum powder. The main objective of this idea is to demonstrate how two characteristics of the high-velocity compaction, namely, the relative green density and strength of products vary with the changing of significant parameters, involved in GDF processing technique.
    Keywords: Aluminum Powder, GDF, High-Velocity Compaction, Neural network
  • Mahdi Karami Khorramabadi * Pages 31-37
    In this paper, the theoretical predictions of mechanical properties of functionally graded and uniform distributions Epoxy/clay nanocomposites are presented. The specimens were prepared for uniformly distribution of nanoclay with different nano particles weight percent (pure, 3 wt%, 5 wt% and 7 wt%) and functionally graded distribution. The distribution of nanoparticles has been investigated by Field Emission Scanning Electron Microscopy (FESEM). For uniformly distribution of nanoclay, it is shown that there is no sign of the agglomerates found via FESEM imaging which can address well the distribution of nanoclay particles in epoxy. In addition, for functionally graded distributions, it is found that dispersion of nanoclays vary smoothly and continuously from one surface to the other one. The mechanical properties have been determined by simple extension tests. The results of extension tests show that elastic modulus begins to increase up to 5 wt% of nanoclay and then decreases. So, for functionally graded distribution, the elastic modulus is generally larger than the corresponding values for uniform distribution of nanoclay. The theoretical predictions of Young’s modulus for functionally graded and uniform distributions nanocomposites are calculated using a genetic algorithm procedure. The formulation for Young modulus includes the effect of nanoparticles weight fractions and it is modified for functionally graded distribution. To investigate the accuracy of the present theoretical predictions, a comparison is carried out with the experimental results. It is found that the results obtained from the theoretical predictions of genetic algorithm procedure are in good agreement with the experimental ones.
    Keywords: Epoxy, clay, Functionally graded, Genetic Algorithm Theory, nanoparticles
  • Amin Al Taha, Mohamadmehdi Keshtkar * Pages 39-49
    Radiative heat transfer has an important role in many industrial equipment; i.e. furnaces, boilers and high temperature heat exchangers. In this paper, combination of Weighted Sum of Gray Gas Method (WSSGM) and Discrete Ordinate Method (DOM) are used together in order to numerically study the radiative heat transfer behavior in a non-gray participating medium. Moreover, the concept of Blocked-off region for irregular geometries is used to simulate the T-shaped furnace. The effect of different radiative parameters, i.e. scattering coefficient and wall emissivity on thermal behavior and wall heat fluxes is investigated and compared for both gray and non-gray media. The results show thatwhen scattering coefficient increases, more radiation is scattered in the medium and therefore less heat flux reaches the walls such that by increasing scattering coefficient from 1.0 to 5.0, the incident radiative heat flux decreases up to 15% in some parts of bottom wall. It is seen that by increasing wall emissivity from 0.5 to 1.0, wall heat flux increases more than 60%. Moreover, results show that, by increasing the temperature, the maximum error strongly increases which indicates that in many engineering problems, the gray medium assumption leads to great error in results.
    Keywords: Blocked-Off, Discrete Ordinate Method, Non-Gray Media, Radiative Heat Transfer, Weighted Sum of Gray Gas Method
  • Sayed Alireza Hashemi, Saeid Esmaeili, Mazyar Ghadirinejad, Saeed Saber Samandari, Erfan Sheikhbahaei, Alireza Kordjamshidi, Amirsalar Khandan * Pages 51-58

    In Osteoporosis, bone mechanical strength decreases and as a result, the risk of bone fracture increases. Osteoporosis is also referred as a "silent illness" since it usually develops asymptomatic until it breaks a long bone, like the femur. In recent years, porous scaffolds have been utilized to repair damaged bone tissue. For bone tissue engineering, synthetic scaffolds should have acceptable mechanical properties, in addition to the required biological properties. In this regard, the finite element simulation is used to predict the mechanical properties of porous bone scaffolds as one of the most common methods for reducing the experimental tests, because the acquisition of mechanical properties of such scaffolds is very time-consuming and expensive. Due to the widespread use of hydroxyapatite (HA) in the manufacture of bone scaffold composites, the mechanical properties of HA-wollastonite scaffold composites are obtained by laboratory tests and finite element methods. Comparison of the simulation of finite element analysis (FEA) and the experimental results indicate the success of the FEA simulation. In conclusion, new finding satisfied expectations as being suitable for mechanical and biomaterial aspect of a porous scaffold which is proven by laboratory tests and FEA simulations. Due to that fact, the result of this study can be employed to obtain scaffolds well-suited for bone implementations.

    Keywords: Bone Scaffold, Bio-Nanocomposites, Computational, Laboratory Analysis, Finite Element Analysis, hydroxyapatite
  • Hadi Hamidizadeh, Mahmoud Mousavi Mashhadi *, Younes Mohammadi Pages 59-68
    In this work, the pull in analysis of microbeam with geometric discontinuity for two different boundary conditions has been investigated. Boundary conditions are considered as Clamped-Free (CF) and Clamped-Clamped (CC). The governing equations are transformed into non-dimensional form and then solved using Differential Quadrature method (DQ). The conductive polymer length scale parameter was also obtained. The effects of different parameters and pull in voltage on microbeam are studied. Most of the microbeams analyzes were made of Gold, Nickel or Silicon, but we used variety of conductive polymers in this paper. The results show that conductive polymer microbeams can be a suitable substitute for expensive metals. The results can be used to design and improve the performance of Micro-Electromechanical System (MEMS) devices.
    Keywords: Conductive polymer, Differential quadrature method, Electrostatic, Strain gradient
  • Peyman Mashhadi Keshtiban * Pages 69-81
    Equal channel angular pressing (ECAP) is one of the most appealing severe plastic deformation (SPD) methods. The proposed equal channel multi angular pressing (ECMAP) process enhances the efficiency of traditional ECAP technique with decreasing the process time. In this study, a complete investigation was done by the design of experiment (DOE) by compound Taguchi-Grey technique. FEM was applied by ABAQUS software in order to achieve responses of proposed Taguchi tests. Die geometrical parameters together with an important process parameter were selected as input factors and strain characteristics and also, required process load were selected as responses. The relationships between responses and input factors were obtained by regression analysis. Then, an analysis of variance (ANOVA) was used to determine the influence of each input factor on responses. ANOVA analysis revealed that FC with contribution percentage of 87.21% has the most influential factor on RPL. Furthermore, it was inferred that among input factors, with contribution percentage of 94.57% has the most effect on the PEEQ. Finally, a multi objective optimization study was done by grey relational analysis. It was concluded that among all input factors, die channel angle, friction coefficient (FC), and die corner angle with contribution percentages of 42.30%, 26.08% and 14.84% are the first, second and third most influential factors on objectives, respectively.
    Keywords: ANOVA, Equal channel multi angular pressing, Optimization, Taguchi-Grey
  • Farshid Jafarian *, Emad Mohseni Pages 83-90
    AISI H13 die steel is widely used in different industries because of its especial properties. During the machining of hard materials, some of the mechanical properties of the material are changed due to the generation of intensive thermo-mechanical loads and plastic deformation into the workpiece. Controlling these intensive changes in machined surfaces is an important task and significantly affects the performance of the machined part. In addition, surface roughness is one of the aspects of surface texture and affects the fatigue life of the material. Since machining of hard materials is a difficult procedure and it is confronted with several limitations, new methods in machining processes are essential to be developed. One of these methods is using cryogenic coolant where the machining temperature may be considerably reduced by spraying liquid nitrogen on the cutting region. Based on this, at the present study, the variation of thermal loads and surface roughness at different machining parameters were evaluated under dry and cryogenic conditions. To do this, a thermal infrared camera and liquid nitrogen delivery system was used during the machining of hardened AISI H13 steel. Compared with dry condition, the effectiveness of the cryogenic coolant on surface roughness and thermal loads were analysed and discussed at different cutting speed, feed rate, and depth of cut. Finally, it was found that, applying cryogenic coolant in machining of AISI H13 die steel can be very effective to enhance performance and quality of the machined component in terms of surface roughness and thermal loads.
    Keywords: AISI H13, Cryogenic Machining, Surface Roughness, Thermal Loads