نشریه مهندسی مکانیک مدرس
سال بیست و سوم شماره 7 (تیر 1402)

In this research, the drawing force was evaluated in the cold drawing process of 410 stainless steel tubes. By FEM simulation, upper limit solving methods, slab analysis, and the experimental process of drawing force and optimal angle of the die was obtained. The practical drawing was done with an industrial drawing device using a fixed plug method. Abaqus software was used to simulate the process. Determining the required drawing force and predicting it was calculated using the methods of horizontal analysis and the upper limit of its range. According to the results, the lowest value of the coefficient of friction was 0.15 and the lowest drawing force was obtained at the die angle of 32 degrees. In addition, by simulating the process in Abaqus, the force was calculated and the validation of the results was done to predict the required force. After conducting the practical tests, the difference between the experimental and simulation predicted force was determined to be less than 7%.

Today, various military, aerospace, automotive, etc. industries need materials with a high strength-to-weight ratio. The use of metal-based composite materials, especially aluminum-based composites, has increased greatly. Machining is needed to achieve high dimensional accuracy in products made with aluminum-based composites. Due to the presence of reinforcing material such as silicon carbide, machining of this type of material is difficult. Therefore, it is important to study the parameters affecting the machining of aluminum-based composites. In this study, the effect of spindle speed, feed rate, depth of cut and percentage of reinforcing particles were discussed using experimental and statistical test methods. The responses of surface roughness and material removal rate were investigated. The behavior of the input parameters on the responses of the process has been carefully investigated quantitatively and qualitatively. Answers have also been optimized. According to the obtained results, the spindle speed has the greatest effect on the surface roughness. Also, feed rate 33%, spindle speed 28%, depth of cut 26% and the percentage of reinforcing particles 13% have an effect on the chipping rate.

In this study, variations in the residual stresses distribution were studied in different hole-making strategies including; conventional, multi-step drilling and helical milling. Residual stresses were measured for 12 perforated samples made of 4340AISI steel, using nanoindentation method. The results showed the highest near-surface compressive residual stress in the multi-step drilling (up to 373.5 MPa). Also, due to the phase transformation on the surface, the effect of plastic work was eliminated and tensile residual stresses up to a maximum of 114.7 MPa were measured in the drilling process. On the other hand, decreasing the cutting speed and increasing the feed rate raised the compressive stresses up. The trend exception was formation of the white layer in the drilling process. Comparison of the stresses measured on the reference sample also showed a difference of about 28.6% between the two methods of XRD and nanoindentation, which shows an acceptable repeatability of the measurement using nanoindentation method.

The aim of the current research was to investigate the hot tensile behavior and fracture morphology of 410 steel in the temperature range of 950-1100°C and two strain rates of 0.05 s-1 and 0.5 s-1. The results showed that the peak stress and yield stress decreased with increasing temperature, which confirmed the decrease of strength against deformation with increasing process temperature. In strain rate of 0.05 s-1 with increasing temperature, the peak strain decreased continuously, while in strain rate of 0.5 s-1 was observed an increment trend after initial decrease due to competition between work hardening and softening mechanism such as dynamic recovery and dynamic recrystallization. The fracture morphology results showed that they were in good agreement with the mechanical results when at 950 °C the brittle fracture mechanism had a high contribution and the soft fracture surface morphology (increasing dimples and decreasing cleavage planes) was dominant with increasing process temperature. At strain rate of 0.05 s-1, the size of the voids and cracks formed during process was much larger than the cracks created at strain rate of 0.5 s-1, which indicated considerable tearing and decrease in fracture strain (elongation) of the samples in during hot tensile testing at low strain rate.

In this paper, a finite-time fault tolerant controller based on sliding mode algorithm, as a robust control method, is presented to control the attitude stabilization of the quadrotor system in the presence of actuator fault and uncertainty. The controller is designed based on the nonlinear model of a quadrotor and its stability analysis is performed according to the Lyapunov stability theorem. Also, regarding some weaknesses of MEMS sensors such as partly high noise and bias error, an extended Kalman filter is designed and implemented in order to merge sensors data and reduce the noise effect on the outputs. To validate the controller performance, the experimental tests is implemented on a full-scale quadrotor in real-time. The evaluation of the designed strategy is carried out in different scenarios, no fault in the actuators and a partial loss of effectiveness of an actuator as well as uncertainty in the quadrotor parameters. The experimental results reveal the superiority of the sliding mode tolerant strategy over feedback linearization in the presence of various faults and uncertainty effects.

In the first part of this study, the mechanical properties of the uniform auxetic unit cell (negative Poisson’s ratio) have been investigated for application in the hip implant. We used auxetic cells to increase the contact surface between implant and bone under tensile loads. The elastic modulus of the uniform auxetic structure have been obtained by numerical, analytical and experimental methods in y direction. Comparing the elastic modulus in y direction of the analytical and numerical simulation with experimental tests showed there are a good agreement between the results. In the second part, the gradient structure has been used in order to reduce the stress shielding on the contact surface of the bone and implant, increase the efficiency of implant replacement and reduce infection. In the gradient structure, the elastic modulus in the contact surfaces is considered close to the elastic modulus of the bone, and gradually increases in the next layers. The elastic modulus of the gradient structure was calculated by two numerical and analytical methods. In the numerical method, the elastic modulus was obtained from Abaqus software and coding on MATLAB. The difference of the elastic modulus in these two methods was 4.8%, which shows that there is an acceptable agreement between the results.