مجله مهندسی مکانیک امیرکبیر
سال پنجاه و پنجم شماره 4 (تیر 1402)

Nowadays, a new generation of electric vehicles with in-wheel motor technology has been introduced and is being developed. Increasing system efficiency, eliminating mechanical intermediaries, and achieving regenerative braking torque with better performance are the motivations to seek to improve this technology. In the present study, a half-car model with five degrees of freedom has been developed by considering a vehicle equipped with two in-wheel motors on the rear axle as a sample vehicle. Then, the braking strategy has been designed using a two-stage nonlinear predictive controller. The appropriate pressure for the brake fluid lines will be reached in the first stage. In the second stage, the proper amount of electric regenerative torque is obtained using the electronic braking force distribution (EBD) function. The amount of regenerative torque is calculated nonlinear prediction control method. Finally, the designed strategy is examined from the perspective of vehicle mileage capability. The results show that optimal braking can be achieved by utilizing the designed controller and the proposed model. Also, the amount of regenerated energy to the battery can be increased more than 24% during braking by using the proposed braking strategy and the designed control system in compared with the relevant studies.

Tool angles have a great impact on cutting mechanics and main machining parameters such as surface quality, tool life, specific energy and dynamic stability of the cutting process. One of the research topics is the development of mechanisms that can be used to create more control on the machining process, such as the tool angles, simultaneously in process. In this research, a new 2DOF tooling mechanism has been presented for turning machine, which provides the ability to adjust the normal rake and clearance angles of the tool during the process. This mechanism is used to develop a new active control method for chatter suppression and increasing the dynamic stability of the turning process. In this method, the controller detects the chatter through the vibration sensor then reduces the clearance angle of the tool by using the mechanism. This increases the process damping and by increasing the overall damping, it suppresses the vibrations. To design the active controller, the simulation was done in the MATLAB-Simulink and then according to the simulation results, an on/off controller was designed and implemented. Then, experimental tests were performed to evaluate the performance of the chatter suppression control system. Results showed that the proposed method can have a good effect in reducing chatter vibrations in the turning process and leads to a significant increase in the stability of the tuning process.

The use of additive manufacturing provides the opportunity to create complex geometries at a low cost. This paper introduces a novel nature-inspired additive manufactured graded lattice structure based on an elliptic unit cell. Altering the unit cells' dimensions by the dimension ratios in each repetition results in a graded layer. Linear tessellated layers provide a highly porous, graded structure whose specific properties can be customized at any spatial location. Geometric features were calculated with high accuracy using analytical analysis. Abaqus simulations were utilized to determine the mechanical properties of unit cells, layers, and lattices. A compression test was conducted on a polymer specimen made by the DLP technique to validate the results. For a conformal model, the elastic modulus along the latitude axis is five times bigger than the value along the longitude axis. An 8.8-fold increase in the elastic modulus is achievable by decreasing the longitude ratio from 1 to 0.75. A reduction of 0.3% in porosity by setting the longitude ratio to 0.75 and a decrease of 2% in porosity by lessening the latitude ratio to 0.75 results in increases of 2.6 and 2.77 folds in the elastic modulus along two directions, respectively. It is possible to tailor geometrical and mechanical properties to meet any design preference by selecting the proper dimension ratios, which can be utilized for medical implant design.

A three-dimensional analytical micromechanical model based on the unit cell is extended to extract the elastic properties of GNP-reinforced polymer nanocomposites. GNP/matrix interphase region changing gradually and is considered elastic with isotropic behavior. In order to simulate the random distribution of GNPs, the geometry of the representative volume element of the nanocomposite is divided into a three-dimensional cubic with N_α×N_β×N_γ subcells. First, the obtained results are compared with the available researches. Then, the effect of parameters such as the volume fraction and aspect ratio of GNPs, the effect of agglomeration as well as the random distribution of GNPs in the epoxy resin, and the thickness of the interphase on the response of the nanocomposite are investigated. It is shown that the agglomeration of GNP depends on its volume fraction. The results show that the elastic properties obtained from the present micromechanical model with taking into account the random distribution and the agglomeration of nanoparticles and also interphase are close to the experimental data. According to the obtained results, adding even a small volume fraction of GNPs has a significant effect on improving the properties of the nanocomposite. In addition, the modeling of the interphase region also has a great impact on the properties of the nanocomposite. Therefore, in order to realistically predict the behavior of nanocomposites, it is important considering to the interphase.

Nowadays, the practical applications of shell elements such as beams having thin-wall cross-sections are increasing greatly in various fields of engineering including aerospace, nuclear, marine, and automotive industries. This is due to their ability to optimally use structural materials and simultaneously reduce the total weight of the structure. Fiber polymer composites also have different conspicuous properties such as high stiffness-to-weight and strength-to-weight ratios, corrosion resistance, and high strength. Therefore, laminated composite C-section beam elements simultaneously possess both the beneficial features of fiber-reinforced composite materials and thin-walled cross-sections at the same time. Motivated by these facts, in this research, the flexural-torsional stability of multi-layer fibrous composite tapered beam-columns with channel-section subjected to axial and bending loads is investigated. For this purpose, the total potential energy governing the problem is extracted based on Vlasov’s model for small non-uniform torsion along with the classical laminated plate theory. Then, using Ritz’s methodology as an analytical solution technique, the endurable buckling load is calculated. After presenting the accuracy of the adopted method against the results obtained using Ansys finite element software, the effect of important parameters such as stacking sequences, fiber composite materials, boundary conditions, axial load eccentricity, web and flange tapering parameters, axial preloading on the linear buckling capacity of double-tapered multi-layer composite beam-column with channel-section under axial load and end moment is investigated.

Fatigue Crack Growth is an important physical phenomenon and one of the damage mechanisms in engineering materials. This damage mechanism is intensified in the presence of tensile residual stresses. In contrast, compressive residual stresses delay the fatigue crack growth process. In this study, The effects of tensile residual stresses are studied on fatigue crack growth in the titanium alloy Ti-6Al-4V specimens. Mechanical residual stresses are induced in the samples using the 4-point bending method and measured using the hole drilling technique. Fatigue crack growth tests are conducted on SEN(b) specimens according to the ASTM-E647 standard, using samples with and without residual stresses. The commercial finite element software ABAQUS was used to study the distribution of residual stresses, the plastic zone sizes at the crack front and fracture mechanics parameters. The finite element results were in good agreement with the experimental results. The results reveal that the presence of tensile residual stress may accelerate the fatigue crack growth rate in the specimens. This increase in fatigue crack growth rate can reduce the fatigue life of samples up to 50%.