Sharif Digital Repository

If one folds a thin viscoelastic sheet under an applied force, a line of plastic deformation is formed that shapes the sheet into an angle. This study determines parameters that define this angle and shows that, no matter how much load one applies, it is impossible to make angles less than a certain minimum angle in a definite time. Moreover, it is shown that regardless of whether the sheet is released freely afterward or kept under load, a logarithmic relaxation process follows the first deformation. The slope of this logarithm is the same in both conditions and depends neither on the applied force nor on the thickness of the sheet, which indicates that it is directly a probe of the... 

We have studied the mechanical properties of a few-layer graphene cantilever (FLGC) using atomic force microscopy (AFM). The mechanical properties of the suspended FLGC over an open hole have been derived from the AFM data. Force displacement curves using the Derjaguin–Müller–Toporov (DMT) and the massless cantilever beam models yield a Young modulus of Ec ~ 37, Ea ~ 0.7 TPa and a Hamakar constant of ~ 3 × 10 − 18 J. The threshold force to shear the FLGC was determined from a breaking force and modeling. In addition, we studied a graphene nanoribbon (GNR), which is a system similar to the FLGC; using density functional theory (DFT). The in-plane Young's modulus for the GNRs were calculated... 

The objective of this paper is designing, modeling and wrench feasible workspace analysis of a 3D cable suspended robot as IRPM (Incompletely Restrained Positioning Mechanism). This type of robots supports a load platform in space by less than or equal to six spatially arranged cables. We use the model of 6 cables spanned in the same manner as a Stewart parallel mechanism. This mechanism is suitable for the accurate positioning of heavy loads. Concentrating on the operations of heavy loads handling, studying the workspace and ways of increasing it is of high importance. Several workspaces exist amongst which the constant and total orientation statically reachable combined and wrench feasible... 

This paper presents the background of low back problem caused by repetitive fatigue loading. We emphasize on mechanism of Intervertebral Disc (IVD) and conditions for which the disc does not recover its original status under repetitive work and cause low back pain. The objective of this study is to identify structural changes in system parameters for fatigue loaded intervertebral disc. Principal component analysis (PCA) is used for studying the behavioral change of spine against cyclic loading as a function of time. Percentage difference and similarity factor was calculated for the analysis. Specimens were applied with impulse testing to measure the stiffness and acceleration after fracture,... 

A new method for image registration has been previously proposed by the authors, which the registration is based on physical forces. The registration parameters are translation and rotation. This method assumes images like charged materials that attract each other. In this case, one of the images moves in the same direction as the applied force while the other one is still. The movement of the image continues until the resultant force becomes zero. This approach estimates the registration parameters simultaneously and leading to a better optimized set of registration parameters. The registration error for this method is 1 to 3 pixels. In this paper we aim to develop this method for the... 

Laparoscopic surgery is a Minimally Invasive Surgery (MIS) procedure which is performed in the abdominal cavity. In this paper, the spleen tissue and a laparoscopic surgical grasper were modeled using ABAQUS software to investigate the tool-tissue interaction, considering large deformations for the spleen tissue. The spleen tissue was modeled as a hyper-elastic material. The laparoscopic grasper includes three gripping jaws that always remain parallel. The sliding can occur between the gripping jaws and the spleen tissue. It was found that the relationship between the pinch forces and push forces keeps its linearity in different values of friction coefficient (0-0.3). The pushing force... 

The Poiseuille flow through slit-like nanochannels is investigated using the nonequilibrium molecular dynamics simulations. To drive a dense flow through the channel, we use two self-adjusting vertical plates strategy. These plates force the liquid to flow through the nanochannel under adjustable inlet and outlet boundary conditions. Comparing with the dual-control-volume grand-canonical molecular dynamics method, the current strategy provides many advantages. The current strategy does not need particle insertion and deletion, therefore, the system dynamics would not be affected at all. Moreover, the number of particles in the simulation system is fixed due to inserting the two... 

This paper addresses the effect of different optimization criteria for the control purpose of vehicle suspension. In the present study, active vibration control system for a 5 degree-of-freedom (DoF) pitch-plane suspension model with bounce and pitch motions is investigated. In the proposed vehicle model, the impact of the wheel-axle-brake assemblies' masses is also considered. The developed model is controlled using a fuzzy logic controller (FLC) to minimize the vibration of the driver's seat. The controller is designed to control the applied force to the seat. Furthermore, in order to determine the optimal value of fuzzy system parameters, genetic algorithm (GA) optimization search is used... 

We have studied the mechanical properties of a few-layer graphene cantilever (FLGC) using atomic force microscopy (AFM). The mechanical properties of the suspended FLGC over an open hole have been derived from the AFM data. Force displacement curves using the Derjaguin-Müller-Toporov (DMT) and the massless cantilever beam models yield a Young modulus of Ec ∼ 37, Ea ∼ 0.7TPa and a Hamakar constant of ∼ 3 × 10 -18J. The threshold force to shear the FLGC was determined from a breaking force and modeling. In addition, we studied a graphene nanoribbon (GNR), which is a system similar to the FLGC; using density functional theory (DFT). The in-plane Young's modulus for the GNRs were calculated from... 

This paper addresses the effect of different optimization criteria for the control purpose of vehicle suspension. In the present study, active vibration control system for a 5 degree-of-freedom (DoF) pitch-plane suspension model with bounce and pitch motions is investigated. In the proposed vehicle model, the impact of the wheel-axle-brake assemblies' masses is also considered. The developed model is controlled using a fuzzy logic controller (FLC) to minimize the vibration of the driver's seat. The controller is designed to control the applied force to the seat. Furthermore, in order to determine the optimal value of fuzzy system parameters, genetic algorithm (GA) optimization search is used... 

Resistance spot welding of dissimilar materials especially in different thickness is generally more challenging than that of similar materials due to differences in the physical, chemical and mechanical properties of the base metals. And also when the part is under static and dynamic forces the health of spot-welds is crucial. Hence, the influence of welding parameters such as current, time, applied force and hold time on the shear-tensile load has been investigated in this study. Moreover, in this research the case study is one of the most important body parts of the vehicle which is front wheel house, and effect of above-mentioned parameter on the strength of spot-welds has been...