نشریه مهندسی مکانیک مدرس
سال بیست و دوم شماره 1 (دی 1400)

The aim of this research is to develop a semi-active secondary suspension system equipped with magnetorheological dampers to reduce the amplitude of vibrations and shocks to sensitive payloads in the cargo section of road truck. First, a double-ended magnetorheological damper was modeled, designed and built for use in a secondary suspension system of light trucks. Next, a pallet with a secondary suspension system consisting of four magnetoreheological dampers was constructed to be installed on the load side of the light truck. Then, the behavior of the system was examined by testing it by passing the vehicle on the speed-bump profile. By performing dynamic tests with harmonic excitation on the damper, the results showed that the maximum damping force with the electric current of 2 Amp is increased 11.6 times compared to 0 Amp. Furthermore by using the forces obtained from the Spencer model in predicting the dynamic behavior of the damper with an average relative error of %1.49 compared to the force obtained from the experimental test and implementing the two-dimensional model of the half-truck, the performance of the system in passing the speed-bump profile was investigated.The results of simulations and experimental tests showed that with increasing electric current intensity from 0 to 2 Amp, the maximum amplitudes of the sensitive payload decreased in passing the speed-bump %43.6 and %32.4 in simulations and experimental tests comparing to the situation without the secondary suspension system respectively.

The importance of environmental issues has increased the use of biodegradable polymers which nowadays have become among main components in medical and biological applications. In the present study, a new combined method of fused filament fabrication (FFF) and batch foaming was introduced to improve the properties of poly lactic acid. For this purpose, FFF samples were produced with infill percentages of 100, 80 and 60 and then, foamed in batch process. Due to the importance and effect of the void fraction on structural and mechanical performance as well as the biodegradability of materials with porous structure, especially for medical purposes, void fraction and impact strength were evaluated. The results showed that the void fractions of FFF samples were 3%, 13% and 25% in infill percentages of 100, 80 and 60, respectively while after the foaming they reached to 14%, 19% and 30%. The findings revealed that the impact strength of FFF foamed samples was improved compared to FFF solid samples. For samples with 100 infill percentage, the impact strength improved from 207 to 506 J/m2 due to the foaming procedure with nano-sized cells created by the batch foaming.

Forming limit diagrams (FLDs) are very important in predicting the behavior of the sheet. Therefore, predicting and drawing these diagrams by theoretical and experimental methods has been one of the main objectives of this paper. In this paper, the formability behavior of 5083 aluminum sheet was investigated by considering the strain hardening behavior. Tensile tests has performed in seven directions 0°, 15°, 30°, 45°, 60°, 75° and 90° from the rolling direction due to identify and calibrate coefficients of BBC2008 advanced yield criteria. The yield stresses was defined in the plane strain mode, also the anisotropy coefficients and the appropriate error function were extracted; Then the relationships of the plane strain yield stress were added to the error function. The error function was optimized using Genetic Algorithm and limit strains were calculated using yield coefficients. The results showed that if the strain hardening exponent increases by 0.1, the limit strains increase by 30 to 40%. Also the results showed that the initial imperfection factor ( ) has a great effect on determining the FLD and with a very small change, it has a great effect on the FLD; So that by increasing this factor to about 0.016, the values of the limit strains are almost doubled. Using the results of this paper and having sheet properties such as yield strengths and anisotropy coefficients and proper selection of yield criteria, the FLD of different sheets to be theoretically determined with acceptable accuracy.

Mutations in DNA and the development of mutated genes that are inherited or acquired during a personchr(chr('39')39chr('39'))s lifetime can cause cancer. This type of disease causes the loss of normal control of cell growth and proliferation. Breast cancer, with its prevalence in both men and women and the higher incidence of women in the female population, is one of the most important cancers in the medical community. Appearance changes in the breast, the presence of a lump, and discharge and bleeding from the nipple are signs of breast cancer. Targeted treatment of this disease reduces the complications of treatment methods. Also, recognizing the mechanical properties of the cell, such as the Youngchr(chr('39')39chr('39'))s modulus, and examining the changes caused by cancer in these properties will make treatment more efficient and help the pharmaceutical sciences. For this purpose, in this paper, the MCF-10 breast cell has been studied using atomic force microscopy and nanomanipulation method. Atomic force microscope is one of the efficient tools in the structural studies of biological particles with the possibility of producing images of soft tissues under different environmental conditions and in a non-destructive manner. Chung, chen and brake contact are the models used in the simulation. Finally, with the simulations performed, the Young modulus of 1200 Pa is considered for this cell. Also, considering the comparisons made with experimental work, the chen contact model has been introduced as the optimal model for extracting cellular properties.

In this paper, using finite element simulations and experimental results, the changes in deformation length and longitudinal strain in flexible roll forming are investigated and the relationship between them is determined. Flexible roll forming is a novel manufacturing process for producing profiles with variable cross-section. One of the important parameters of this process is the distance from the starting point of the deformation before the forming station to the central cross-section of the rolls at that station, which is called the deformation length. This parameter plays a key role in determining the distance between the forming stations and the deformation behavior of the sheet. The effect of roll diameter and mechanical properties of the sheet on the deformation length is also determined. The results showed that the maximum deformation length occurs when forming the stretching zone of the channel profile with variable cross-section, which is due to the additional tension applied to the edge due to the concave geometry of the flange in this zone. The results also showed that with increasing roll diameter and yield stress, the deformation length in all four of the stretching and compression zones and the slim and wide areas of the channel profile with variable cross-section increases, while with increasing sheet thickness, the deformation length in these zones decreases.

The ECAP-Conform is one of the newest and less known processes that improve mechanical properties. In the present study, the effective parameters of the ECAP-Conform process for AA7075 have been investigated. Influence of parameters such as roller radius, bending angle, die channel angles, rod/roll friction coefficient, rod/die friction coefficient, and the aspect ratio of the die groove on the torque, the applied force on the die, the stress, and the effective plastic strain, the output rod curvature, and the strain distribution uniformity have been investigated. The design of experiments was carried out based on the response surface method by the Minitab software, and simulations were performed using the ABAQUS software. To validate the FEM, the ECAP-Conform process of AA7075 rod was performed and the comparison of experimental and numerical results have acceptable compliance (7.5% error). It was found that the die channel angles and the rod/die friction coefficient have a more significant effect on all responses. Moreover, to maximize the imposed strain and strength, and to minimize the process torque and curvature, as well as achieving a uniform distribution of strain, the optimal output parameters have been obtained.