International Journal of Advanced Design and Manufacturing Technology
Volume:12 Issue: 4, Dec 2019

High demands of quality development in the industry especially automotive, necessitates multi-objective optimization of the manufacturing processes. Fuel cells are one of the most important sources of renewable energies that Bipolar Plates (BPPs) are their main components. Metallic BPPs are known as a suitable replacement of the graphite plates due to their lower weight and cost. Accordingly, this study employs Multi-Criteria Decision Making (MCDM) methods to determine the best forming condition in the stamping of titanium BPP. In the first step, the process is analyzed using the Finite Element (FE) simulation. Afterward, validation of the FE model is confirmed by performing the experiments using titanium ultra-thin sheet with a thickness of 0.1 mm. Subsequently, a set of tests with 15 experiments are assumed to be as alternatives. In addition, filling ratio, thinning ratio and forming load are considered as different criteria. In order to select the optimum condition considering three mentioned responses simultaneously, TOPSIS and VIKOR methods are applied. In addition, a weighting procedure combining AHP and Entropy approaches is used. Based on the weighting results, the highest and lowest weights were obtained for filling ratio (0.5398) and forming load (0.1632), respectively. Likewise, a Spearman’s rank equal to 0.9357 was obtained that demonstrates high compatibility between TOPSIS and VIKOR methods. Overall, the best (optimum) forming condition has obtained an experiment with a clearance of 0.2 mm, the speed of 3.5 mm/s, and friction coefficient as 0.2.

In this research, the multi-pass friction stir processing on AZ91 alloy has been simulated with the three-dimensional numerical modeling based on the ABAQUS/ Explicit. This simulation involves the Johnson-Cook models for defining the material behavior during this intense plastic deformation and investing the fracture criterion. Friction stir processing is a complex process that includes several issues such as high strain rate deformation, microstructure evolution, the asymmetric flow of material, and heat. Therefore, the modeling of this process is challenging. This model simulates the tool plunging and stirring phases in the two-pass process. In this paper, to prevent too much damage in the elements during processing, the Arbitrary Lagrangian-Eulerian technique for automatically remeshing of distorted elements has been used. This work shows that the numerical modeling can be an efficient method to study the effect of process parameters on the thermal evolution and the stress distribution. The thermal model was calibrated using the experimental results from the previous works. This model can predict the transient temperature distribution and residual stress field during FSP on AZ91. The results show that the maximum temperature in the advancing side is more than that in the retreating side. In addition, numerical results show that at the end-position of the process, the tool during the lift-up leaves the keyhole region in a compressive stress state.

The main target of this paper is to obtain an optimum wedge angle for best static and dynamic performance of a V-shaped clamp band separation mechanism. For this purpose, by using the finite element method, the proper 3D model for V-clamp band mechanism has been modelled and analysed in Abaqus/Explicit solver. In order to study the effect of wedge angle on bending and axial stiffness of V-clamp joint, many quasi-static analyses with different wedge angles were accomplished so the relation between wedge angle and axial stiffness of V-clamp joint under symmetric bending loading is extracted. In the next step, dynamic analyses were accomplished so the relation between wedge angle and separation time (duration between trigging moment and the time of disconnecting between flanges and wedged clamps) is extracted. For verification, this project results have been compared with the results of other researches and good agreement is observed. The results show that the optimal wedge angle for obtaining maximum stiffness together with minimum spring back disconnection time for the V-clamp band mechanism is 20˚.

A molecular dynamics simulation study is employed to investigate the elastic and basic thermal properties of thermoset polymer based nanocomposite sample reinforced by CNT. The COMPASS force filed was used to construct the simulation box. The simulation box contains the cured epoxy resin molecules obtained from cross linking process of DGEBA and DETA which were located around the CNT (10,10). NVT and NPT ensembles were performed to equilibrate the system and convergence of temperature, energy and density have been checked. The elastic constants of molecular sample of nanocomposite were determined based on stiffness matrix and compared with the molecular results of pure resin. The results show that the Young's modulus in the transverse direction of nanocomposite model is less than that in longitudinal direction indicating the transversely isotropic behaviour at atomic scale.  Glass transition temperature (Tg) and coefficient of thermal expansion (CTE) were calculated through the linear fitting of density-temperature diagram for the CNT-reinforced nanocomposite model. Atomistic simulation results showed decrease in Tg and CTE comparing to the pure epoxy. Moreover, the simulation results were compared with the measured values and good agreements are observed.

Phase Change Materials (PCMs) have been the subject of many researches in recent years due to the storage and release of energy at low temperature ranges. PCMs store or releasing a large amount of energy at a constant temperature range leads to saving energy. In this paper, the numerical modelling of a multilayer composite wall including PCM located on the southern side of a building is carried out using an implicit method. The data correspond the fifteenth day of each month in Tehran. The governing equations are discretized by the implicit Crank Nicolson method and solved by iteration method using MATLAB software. Finally, the location and volume fraction of PCM in the wall of the building are studied to achieve maximum efficiency. The results show that the effect of latent and sensible heat results in a reduction in the input heat flux and thermal load to the building. The optimum location for the PCM layer is the middle layer of the composite wall to reduce the heat transfer rate inside the building. In addition, it is found that the PCM volume fraction in gypsum does not have a significant effect on the thermal performance of the multi-layer composite wall. Hence, low volume fraction reduces the costs without affecting the thermal performance of the building.

Two main problems exist with friction stir spot welded joints; remaining of a keyhole after welding and low strength of joints. In this paper, a novel method is proposed to address both problems in a simple and cost-effective way. This process is named “Reinforced Friction Stir Spot Welding” or “RFSSW” which is based on recently introduced “TFSSW” process. SiC powder was added to the friction stir spot joints of polyethylene sheets with a thickness of 3 mm. First, the sheets were welded using conventional friction stir spot welding tool with a cylindrical pin. Then, the keyhole was filled with SiC powder. In the second stage, for stirring of SiC particles in the nugget and refilling the keyhole as well, a pinless tool was utilized. A homogenized distribution of reinforcing powder was obtained in the nugget. The effect of welding parameters including refilling tool shoulder diameter, refilling dwell time, and refilling tool rotational speed were evaluated in both TFSSW and RFSSW. In both processes, the refilling tool shoulder diameter was the most effective parameter. The strength was increased by 40% applying TFSSW and a further increase by 20% was obtained by reinforcing. Optimized parameter levels are refilling tool shoulder diameter of 24 mm, refilling tool rotational speed of 800 rpm, and refilling dwell time of 50s which result in shear strength of 1079 N.

Hydro screw is an axial micro hydro turbine of Archimedean origin. Due to ever-increasing need for clean fuel based and environmentally clean electric power, a research project was undertaken at IROST. In this study, the effect of spiral variable pitch on hydro screw turbine has been studied numerically. Based on the results, it was found that the turbine had the best efficiency with a spiral pitch of 1.5. Accordingly, the small model of this turbine was made and tested in the laboratory. The results indicate that the numerical results of the calculations are in good agreement with experimental result, and therefore they can be used safely in the course of subsequent turbine studies. In summary, the results indicate that the maximum turbine output is between 62% and 68% which is about 30% higher than the constant pitch blade turbine.

In this research, the effect of different structural parameters on the dynamic behaviour of a thick plate with a smart attached mass, which is a mass embedded with the Shape Memory Alloy (SMA) fibers were investigated. The results showed that the inherent stiffness of the smart attached mass and the localized stiffness due to the effect of SMA fibers both play a significant role in the dynamic behaviour of the plate, and ignoring either of these parameters results in a considerable change in the system responses. The size and position of the smart attached mass were also found to be of particular importance, since the effect of the weight of SMA and attached mass and the forces induced by SMA transformation all have significant and sometimes conflicting effects on the system vibrations. The results also showed that the changes in the system parameters, and particularly the characteristics of the SMA fibers such as activation temperature, pre-strain, and volume fraction, result in the appearance of dynamic responses that cannot be neglected.

Manufacturing of complicated industrial components is one of the main challenges for mechanical engineers in sheet metal forming processes. Incremental sheet metal forming (ISMF) is used widely for forming complicated shapes by a single rotating tool. This paper examines the experimental investigation of two-point incremental forming of a complicated specimen made of AA3105 aluminum alloy. The part shape consists of positive and negative cavities and the shape complexity limits the manufacturing process to two-point incremental forming process (TPIF). In addition, the effects of selected process parameters such as forming depth in each increment of process, tool rotational speed and various forming patterns on thickness distribution and thinning percentage of specimen are investigated. The forming pattern includes the sequence of forming the cavities (Internal/External pattern and External/Internal pattern). The main finding of the study can be expressed that the thinning ratio of manufactured specimen is increased with an increase in the forming depth in each increment of TPIF. Also, the higher rotational speed leads to a reduction in the thinning of the fabricated specimen. The results prove that the use of Internal/External forming pattern leads to reduction in the thinning of the manufactured specimen.