بهنام آخوندی

With the emergence and expansion of additive manufacturing processes, especially the fused deposition modeling process, extensive research has been conducted on these processes. One important research area is strengthening the printed parts by the fused deposition modeling method. One of the main areas of research is related to the strengthening of printed parts by the fused deposition modeling method. This process enables the production of complex structures and the customization of parts. On the other hand, polylactic acid material is one of the main materials used in this process, which has been noticed over other materials due to its biocompatibility and biodegradability properties. In this research, the effect of annealing heat treatment on the compressive strength and modulus of porous samples has been investigated with the approach of using them in tissue engineering as a scaffold for bone tissue. The samples are 3D printed with wiggle, grid, and honeycomb patterns and with filling percentages of 40, 70, and maximum. In addition, the effect of two parameters, the extrusion width, and the layer height, has also been investigated. To create porous structures with interconnected porosities, the pattern of filling in each layer is rotated to a certain extent, and this causes the introduction of new porous structures that can have wide applications such as being used as scaffolds in tissue engineering. After evaluating the compressive mechanical properties of the samples, the same samples were heat treated, and then their compressive mechanical properties were also evaluated. The obtained results show that the maximum compressive strength and modulus occur in the sample with an extrusion width of 0.6 mm, layer height of 0.25 mm, wiggle filling pattern, and maximum filling percentage. The values ​​of compressive strength and modulus for the non-heat-treated sample are equal to 84.51 MPa and 2.28 GPa respectively and for the heat-treated sample, it is equal to 105.44 MPa and 2.29 GPa respectively.

Increasing the depth of microchannels on metallic bipolar plates (BPPs) in PEM fuel cells leads to an increase in the efficiency. In this research, the stamping process has been applied for manufacturing of the BPPs made of commercially pure titanium with a direct parallel flow field. The effect of process parameters including die clearance, forming speed, and sheet/die friction coefficient on the filling rate and thinning of the BPPs was investigated. The required tests were designed via the response surface method (RSM), implemented by a validated finite elements (FE) model, and the desired outputs were extracted. Then, a quadratic equation was presented for predicting the filling rate based on the input parameters using the regression method. In the following, using the artificial bee colony algorithm, the coefficients of the mentioned equation were enhanced and its error was decreased almost by 53%. Finally, an artificial neural network (ANN) was used to predict the filling rate. The results demonstrated that the proposed ANN model is very effective and approximates the filling rate of the microchannel with high accuracy.

Improving the mechanical properties of the 3D printed parts by a 3D printer based on fused filament fabrication by continuous fibers (carbon, glass, and aramid) has been the focus of many researchers. Due to the nature of additive manufacturing processes that produce the parts layer by layer, in most of the research, continuous fibers are layered on a 2D surface. Robots with high degrees of freedom have been used in cases where fibers are placed on curved surfaces. In this research, a method for deposition of the continuous glass fibers on a curved surface is presented. This method is implemented on a simple and cheap 3D printer. The presented method is based on modifying the G-code, creating a rotating axis for the nozzle, and applying and using computer-aided design and manufacturing techniques. Finally, by 3D scanning of the printed sample and comparing it with the 3D model, the amount of deviation and tolerance of the surface form is determined. The obtained experimental results indicate the effectiveness of the presented method for the deposition of continuous fibers on curved surfaces. With the presented system, continuous fibers are deposited on a curved surface that consists of paths with different degrees of curvature, by simultaneous impregnation of fiber and polymer. Comparing the scanned sample with the printed sample shows that the maximum deviation is 0.1 mm. This error is acceptable due to the nature of shrinkage and distortion of thermoplastic polymer materials in forming processes according to the DIN 16901 standard.

In this research, by using an artificial bee colony optimization algorithm, the mechanical properties of chromium nanobeams have been identified in such a way that the error of the mathematical model in the interpretation of the experimental results be minimized. Since conventional continuous medium theories cannot correctly simulate the behavior of structures in the nanoscale, also, large deflections in nano dimensions are not far from expected, therefore, the mathematical modeling of the large deflections of the beam based on surface effects is considered to predict the behavior of chromium nanobeams. The mechanical properties of chromium nanobeam have been considered the value of elastic modulus, the value of residual surface stress and the values of support properties, that is, the value of initial slope of the beam at the support and the value of bending spring coefficient of the support. In this research, the effects of mechanical properties have been investigated separately and simultaneously on the behavior of nanobeams. It has been determined that all four parameters must be considered to simulate the exact behavior of the nanobeam. In addition, among the investigated mechanical properties, removing the support properties in the prediction of experimental deflections causes the most errors, and removing the surface effects causes the least errors. Furthermore, the error has been reduced by far compared to previous works.

This paper investigates the deflection of chromium nanobeams using the design of experiments method. Using the full factorial method, a number of 100 experiments were designed in which the length and the force on the nanobeam were considered input variables at 25 and 4 levels, respectively and the deflection of the nanobeam was considered output. First, all 4 force levels (8, 9.5, 11, and 12.5 nN) were used for the analysis, and closed-form equations were obtained to estimate the deflection of the nanobeam. The results showed that the effect of the length is more than the force, by increasing the length so that the deflection changes with third degree. The third-order regression model predicts the deflection with high accuracy, and its error value is lower than the first and second-order regression models. Afterward, two levels of force (8 and 11 nN) were used for analysis, and new equations were obtained to estimate the deflection of the nanobeam. The new equations were used for interpolation and extrapolation of the nanobeam's deflection in forces of 9.5 and 12.5 nN, respectively. The results demonstrated that the regression model using two force levels accurately predicts the deflections of nanobeams as well. The results of this research demonstrated that it is possible to estimate the nanobeam's deflection without the need to perform more experiments and spend cost, perform complex calculations, and solve differential equations; the nanobeam's deflection can be accurately estimated with algebraic formulas.

Haptic devices are used to simulate virtual objects for users. Accurate simulation of objects in the virtual environment improves the user's relationship with the virtual environment. In most simulations of virtual objects, objects are simulated as springs and dampers. However, if virtual mass is also taken into account alongside virtual spring and damper elements, the utilization of h devices in simulating objects will lead to increased diversity, enhancing the realism of the objects. In this article, to simulate the virtual object, in addition to the virtual spring and damper, the virtual mass is also considered and its effect on the stability of the haptic device is investigated. In fact, closed-form equations have been obtained for determining the stability boundary by considering the virtual object in the form of mass, spring and damper, which have been validated in different time delays using simulation and experimental results.

The optimal forming of the metallic parts with the lowest required forming force has always been the focus of researchers. In this paper, effective parameters in hydrodynamic deep drawing assisted by radial pressure of cylindrical cups with a flat head with minimum required forming force have been investigated. At first, the necessary experiments were designed using the fractional factorial design of experiment. In this design, maximum fluid pressure, punch velocity, punch nose radius, friction coefficient between punch and sheet, friction coefficient between die and sheet, and die entrance radius were considered input variables. An experimentally validated finite element model was used for performing the designed experiments and extracting the maximum punch force for each experiment. Finally, by using analysis of variance, the main and the interaction effects of the parameters on the maximum punch force were determined. Results showed that the maximum fluid pressure and punch nose radius have the highest influence on the maximum punch force. Decreasing the maximum fluid pressure from 39 to 15 MPa, leads to a decrease of 55% in the maximum punch force. Also, by reducing the punch nose radius from 10 to 2 mm, the maximum punch force decreases by 55%.

Haptic Devices (HDs) are used to simulate virtual objects for the user. The dynamics of the HD and the opertator’s hand have a great effect on the stability and performance of the HD. In this research, the dynamic identification of the user's hand and HD has been done using methods of Artificial Bee Colony Optimization (ABCO), Crow Search Algorithm (CSA), and Genetic Algorithm (GA), during experiments in two cases. In the first case, only the dynamics of the HD has been identified, then in the second case, the mentioned methods have been generalized for the simultaneous recognition of the dynamics of the user's hand and the HD. For this purpose, first, in each case, the theoretical stability boundary is obtained as a function of the available dynamic parameters. Then, by performing experiments on the KUKA Light Weight 4 robot in two cases of presence and absence of the operator’s hand, the experimental stability boundary has been obtained. Afterwards, by using ABCO, CSA, and GA in each case the desired dynamic parameters are obtained in such a way that the difference between the theoretical and experimental stability boundary is minimized. Studies show that while all three methods have been able to identify the parameters well, the GA method produces less error and has a better performance in this field.

In addition to the need for lightweight properties, the metallic bipolar plates in the PEM fuel cells should work in a humid and acidic environment. Due to its low density and excellent corrosion resistance, titanium is a proper candidate for manufacturing bipolar plates. In this paper, the manufacturing of bipolar plates made of commercially pure titanium with an initial thickness of 0.1 mm was investigated using the stamping process. A four-channel die with a parallel flow field was used in the experiments. To estimate the formability of microchannels of the bipolar plates, the response surface method, genetic algorithm, and adaptive neural fuzzy inference system were employed. Die clearance, stamping speed, and friction coefficient between the sheet and die were considered input variables, whereas the die filling rate was as output. The designed experiments using the response surface method were used to train the meta-heuristic techniques. The results showed that the regression model obtained from the response surface method predicts the die filling rate with acceptable accuracy. Furthermore, the coefficients of the equation obtained from the regression have been improved using the genetic algorithm and the error rate has been reduced by about 53%. Finally, an adaptive neural fuzzy inference system was used to predict the die filling. The results showed that the proposed system is very feasible and approximates the maximum filling rate with high accuracy.

Thin-walled tube bending is one of the important processes for manufacturing parts in the automotive and aerospace industries. This paper investigates the effect of heat treatment on the bendability of thin-walled tubes made of AA6063 alloy. With the hydro rotary draw bending process, the cross-section ovality of the as-received, annealed, and artificial aged tubes has been examined at different fluid pressures. In the experiments, the tube diameter to tube thickness ratio was 13.88. Also, the critical bending ratio was 1.6, and the bending angle was 90 degrees. By examining the results, it has been found that heat treatment and fluid pressure had an important effect on the quality of the bent tubes. By increasing the fluid pressure to 3.6 MPa, critical cross-section ovality has decreased in all specimens. The maximum decrease of cross-section ovality is obtained in the annealed sample by 49%. Also, in the artificially aged specimens, the critical cross-section ovality decreases by about 45%. It has also been observed that at a pressure of 3.6 MPa, the critical cross-section ovality of the annealed sample has improved by 19% compared to the artificially aged specimens.

Achieving the minimum thinning and required forming force is one of the main purposes in the manufacturing of sheet products using the hydroforming process. This paper investigates forming of the copper sheet using the hydrodynamic deep drawing assisted by radial pressure via the design of experiment method and finite element (FE) analysis. Firstly, the necessary experiments have been designed using the Taguchi design of experiment method. In this design, maximum fluid pressure, punch velocity, the friction coefficient between punch and sheet, the friction coefficient between die and sheet, the gap between blankholder and die, punch nose radius, die entrance radius, and prebulge pressure were considered as input variables and thinning ratio and punch force considered as response functions. Then, designed experiments were performed using an experimental verified FE model and the desired results were obtained. Finally, the optimum levels of input variables were obtained using the Taguchi optimization method and the confirmation experiments were performed using the FE simulation. Results show that the punch nose radius and die entrance radius are the essential parameters on the thinning ratio. Also, the maximum fluid pressure is the most effective parameter on the punch force.

Thickness distribution is one of the important parameters in the sheet metal forming processes. This paper investigates the forming of flat cylindrical cups made of steel using the hydrodynamic deep drawing process via experiment and simulation. At first, the process was simulated using the ABAQUS finite element software. Afterward, the results of the finite element simulation are compared with results of the experiments. Comparing the results showed that the thickness distribution and punch force have an acceptable agreement in the experiment and numerical methods. Then, using the validated finite element model, the effect of the process parameters including the friction coefficient between the punch and the sheet, the friction coefficient between the blank holder and the sheet, the corner radius of the punch and the die, as well as the gap between the blank holder and the die on the maximum thinning of the steel cups have been investigated. Finally, the obtained results revealed that the corner radius zone of the punch is the critical forming zone since the maximum thinning occurs in this region. Also, by increasing the friction coefficient between the sheet and the punch, the maximum thinning decreases by 10% at the corner radius zone of the punch. In addition, by increasing the friction coefficient between the sheet and the blank holder, the maximum thinning increases by 20%. Likewise, by increasing the corner radius of the punch and the die, the maximum thinning decreases by 25%, and also, by increasing the gap between the die and the blank holder, the maximum thinning decreases by 10%.

In orthopedic surgery, the drilling process is used to internally fix the fracture zone. During bone drilling, if the temperature exceeds the limit of 47 °C, it results in altered bone alkaline phosphatase nature, occurrence of thermal necrosis, non-fixation and inadequate bone fusion In order to investigate the effective parameters of the drilling process, after three-dimensional modeling of the femur bone in Mimics software and determination of bone coefficients based on the Johnson-Cook model, numerical simulation of the cortical and trabecular bone oblique drilling process have been performed. The drilling process was performed in both normal and high speed modes based on reverse heat transfer theory using DEFORM-3D software. The results of numerical simulation after validation with experimental results showed that this theory is capable of estimating the temperature and heat flux in this process and the occurrence of necrosis in both processes (normal and high speed) is imminent. The temperature in the drilling area of the trabecular bone is higher than the cortical bone at all speeds and feed rates and the axial force of the trabecular bone is less than the cortical bone at all speeds and feed rates. The optimum point leading to the minimum temperature in normal drilling of trabecular and cortical bone is the feed rate of 150 mm/min and the rotational speed of 2000 rpm. This optimum point is obtained in the high-speed drilling of trabecular and cortical bone at the feed rate of 150 mm/min and rotational speed of 4,000 rpm and 7,000 rpm.

Structural health monitoring based on electromechanical impedance is one of the methods for real-time monitoring and detection of structural damage using the coupling properties of piezoelectric materials. When a structure is exposed to corrosion, an electrochemical process is initiated and defects occur over the surface of the structure. In corrosion-prone structures, although a slight decrease in the mass is produced, it results in a significant decrease in its mechanical strength, integrity and fatigue life span. Therefore, the precise monitoring of structural health is important for detecting corrosion-induced surface defects and predicting the effect of corrosion on the mechanical properties and integrity of a structure. In this paper, the electromechanical impedance method is used to investigate the corrosion defect in the health monitoring of a cantilever beam and to identify and determine the factors affecting the damage index of corrosion. Experiments carried out to measure the impedance spectra on an aluminum beam, and a controlled acid corrosion has been imposed on the beam. The scalar damage index was used to quantify the defect. Empirical results obtained from experiments on cantilever beam show that factors like damage intensity, support positions and damage distance to the support location are effective on damage index caused by corrosion. The results show that there is a relationship between the support location and the damage location with the damage index. Also, it is observed that applied damage index as root-mean-square deviation of impedance has a direct relationship with the intensity of corrosion damage.

Corrosion is a type of irreversible destruction of a metal by chemical or electrochemical reaction with ambient. The loss of materials caused by corrosion in metallic structures is a widespread and urgent problem in various industries including petroleum, gas, aerospace, construction, mining, and manufacturing. Pipes used in the oil and gas industry as well as aluminum pipes used for heat transfer in cooling systems are subject to corrosion. Therefore, the evaluation and detection of corrosion, progressive damage, is of particular importance both qualitatively and quantitatively. In this study, a new electromechanical impedance measurement method was used to detect corrosion inside an aluminum tube. Defects or changes in the structure integrity cause changes in the mechanical impedance of the structure which shown as the alteration in the piezoelectric electrical impedance, due to the piezoelectric coupling characteristics. For this study, a circular corrosion cross-section with insulation of the surrounding environment on the inner wall of the tube was created by the corrosive acid solution in a period of 180 minutes until the tube was pierced. Measurement of impedance spectrum in the range of 10-20 kHz was performed to monitor changes in impedance shape as a result of corrosion progress in steps of 20 minutes. Comparing the impedance spectrum at each step with healthy state, changes in amplitude and resonance frequencies revealed and extracted quantitatively. Experimental results from the scalar damage criteria increased linearly with increasing corrosion depth, indicating the effectiveness of this method in real-time detection of corrosion damage in the pipe.

This paper presents an experimental study on the effects of printing parameters on the tensile strength of the polymer-metal composites printed via Fused Deposition Modeling (FDM) technique .In the recent years, 3D printer systems have been widely employed in various industries. FDM is one of the most widely used 3D printer systems worldwide due to its simplicity and lower cost. Although extensive research works have been carried out in the area of 3D printing, less efforts have been reported in developing new materials and their use in FDM process. The materials utilized in this study consisted of Cu particles in ABS polymeric matrix with a constant 25 wt.% of metal powder. The filament production line was implemented to accustom with the manufacturing process. The printing variables were selected as nozzle (orifice) diameter, layer height, fill pattern and nozzle temperature that were examined in three levels. Taguchi method was employed to find the optimal FDM process parameters. The main effect, signal-to- noise ratio and analysis of variance were employed to analyze the process parameters in order to achieve optimum tensile strength of the composite material specimens. Finally, the specimens were produce at the optimized parameters to confirm the tests and method.