Sharif Digital Repository

A time domain approach is used to study the cutting conditions in reaming process that leads the system to regenerative chatter vibrations. The dynamic analysis of the system includes inertia of the tool, centripetal and Coriolis terms, damping and the first mode bending of reamer. A model of cutting forces proportional to chip cross sectional area and process damping proportional to cutting speed is considered. Numerical simulation based on the Euler integration scheme is carried out to obtain time domain solution of the equation. Despite linearization in force modelling, the model is nonlinear due to the change in the tool engagement area. Another nonlinearity included in the model jumping... 

A time domain approach is used to study the cutting conditions in reaming process that leads the system to regenerative chatter vibrations. The dynamic analysis of the system includes inertia of the tool, centripetal and Coriolis terms, damping and the first mode bending of reamer. A model of cutting forces proportional to chip cross sectional area and process damping proportional to cutting speed is considered. Numerical simulation based on the Euler integration scheme is carried out to obtain time domain solution of the equation. Despite linearization in force modelling, the model is nonlinear due to the change in the tool engagement area. Another nonlinearity included in the model jumping... 

We first propose a quantitative approach to detect high risk outbreaks of independent and coinfective SIR dynamics on three empirical networks: A school, a conference and a hospital contact network. This measurement is based on the k-means clustering method and identifies proper samples for calculating the mean outbreak size and the outbreak probability. Then we systematically study the impact of different temporal correlations on high risk outbreaks over the original and differently shuffled counterparts of each network. We observe that, on the one hand, in the coinfection process, randomization of the sequence of the events increases the mean outbreak size of high-risk cases. On the other... 

The Ni-based superalloy GTD-111 is employed in high power stationary gas turbines because of its high temperature strength and oxidation resistance. The temperature dependence of the tensile behaviour of GTD-111 has been studied by tensile tests with a constant strain rate of 10-4s-1 over the temperature range of 25-900°C. The results showed an abnormal variation in tensile properties with increasing temperature. The yield strength decreased slightly with temperatures up to about 650°C and then increased between 650 and 750°C. Above 750°C, a rapid decrease in the yield strength was found. The tensile strength showed a similar behaviour except for its maximum, which occurred at 650°C.... 

In this study, we investigate the limitations and influence of various factors on the performance of trolling mode atomic force microscopy (TR-AFM). For this purpose, at first, based on the governing equations of motion and using a conventional control method, a simulation tool capable of correctly simulating the imaging procedure in TR-AFM is developed. Then based on the developed simulation tool, imaging of different surfaces is performed, and the effect of different factors on the image quality is analyzed. The flexibility of nanoneedle in TR-AFM has unpredictable effects on dynamics of system as well as imaging performance. One problem in imaging is due to coexistence of two stable... 

In the present study, a novel strategy based on particle motion mode is introduced to control the manipulation process of a bio-particle using trolling mode atomic force microscope. To achieve this goal, the reduced governing partial differential equations and the standard form of the system are used as a model for the system dynamic behavior. The governing equations take 6 degrees of freedom into account including extension, torsion, and two lateral bendings of the microcantilever as well as two lateral bendings of the nanoneedle. Manipulation process of the 500 nm radius particle on the substrate includes two phases named sticking and sliding. Sticking of the particle to the substrate... 

The Ni-base superalloy GTD-111 is employed in high-power stationary gas turbines because of its high temperature strength and oxidation resistance. The temperature dependence of the tensile behavior of GTD-111 has been studied by tensile tests in the temperature range of 25-900°C with a constant strain rate of 10-4s-1. The results showed an abnormal tensile property variation with increasing temperature. The yield strength decreased slightly with temperature up to about 650°C and then increased between 650 and 750°C. Above 750°C, a rapid decrease in the yield strength was found. The tensile strength showed a similar behavior except for its maximum that occurred at 650°C. The elongation... 

Trolling mode atomic force microscopy (TR-AFM) has resolved many imaging problems by a considerable reduction of the liquid-resonator interaction forces in liquid environments. The present study develops a nonlinear model of the meniscus force exerted to the nanoneedle of TR-AFM and presents an analytical solution to the distributed-parameter model of TR-AFM resonator utilizing multiple time scales (MTS) method. Based on the developed analytical solution, the frequency-response curves of the resonator operation in air and liquid (for different penetration length of the nanoneedle) are obtained. The closed-form analytical solution and the frequency-response curves are validated by the... 

Trolling mode atomic force microscopy (TR-AFM) has overcome many imaging problems in liquid environments by considerably reducing the liquid-resonator interaction forces. The finite element model of the TR-AFM resonator considering the effects of fluid and nanoneedle flexibility is presented in this research, for the first time. The model is verified by ABAQUS software. The effect of installation angle of the microbeam relative to the horizon and the effect of fluid on the system behavior are investigated. Using the finite element model, frequency response curve of the system is obtained and validated around the frequency of the operating mode by the available experimental results, in air... 

The original article contained a mistake in Equation 1. The corrected Equation 1 is shown below: MX+Cx+Kx=f.The original article has been updated © Springer Nature B.V. 2022  

In this study, a nonlinear observer for high-speed estimation of the sample surface topography in a small duration of the probe transient motion utilizing a 2DOF model of TR-AFM is proposed. Since the time duration to reach the steady-state periodic motion of the oscillating probe in conventional imaging methods is relatively high, the proposed nonlinear observer in this research is able to address this limitation and estimate the surface topography throughout transient oscillation of the microcantilever. With this aim, topography estimation process utilizing a Thau observer without any linearization of the system dynamics is designed and coupled with the system dynamics to achieve sample... 

In this study, a nonlinear observer for high-speed estimation of the sample surface topography in a small duration of the probe transient motion utilizing a 2DOF model of TR-AFM is proposed. Since the time duration to reach the steady-state periodic motion of the oscillating probe in conventional imaging methods is relatively high, the proposed nonlinear observer in this research is able to address this limitation and estimate the surface topography throughout transient oscillation of the microcantilever. With this aim, topography estimation process utilizing a Thau observer without any linearization of the system dynamics is designed and coupled with the system dynamics to achieve sample... 

Transformation-induced plasticity (TRIP) steel resistance spot welds are delicate to low-energy interfacial failure via crack propagation through martensitic fusion zone during cross-tension (CT) loading. This paper addresses the effect of three different types of in situ postweld heat treatment (PWHT) on the mechanical properties of TRIP steel resistance spot welds. Depending on the post weld second pulse current level, three different strengthening mechanisms were found including (i) martensite tempering with reduced hardness, (ii) refining of martensite packets with improved toughness and (iii) nugget re-melting/enlargement combined with possible reduction of grain boundary impurity... 

A simple equation of state (EoS) has recently been introduced (J. Phys. Chem. B2009, 113, 11977-11987) as (Z - 1)v2 = e + f/ρ + gρ2, where Z ≡ pv/RT is the compressibility factor, v = 1/ρ is molar volume, and e, f, and g are temperature dependent parameters. This EoS has been found to be accurate for all types of nano and bulk solids and bulk fluids, in the entire temperature and pressure ranges for which experimental data are reported, except for the isotherms within 1 ≤ T r = T/Tc ≤ 1.1 for the spherical and near spherical species and for a wider temperature range for the cylindrical molecules. The aim of this work is to investigate the validity of a three-term expression similar to the... 

Nonpharmaceutical measures such as social distancing can play an important role in controlling the spread of an epidemic. In this paper, we use a mathematical model combining human mobility and disease spreading. For the mobility dynamics, we design an agent-based model consisting of pedestrian dynamics with a novel type of force to resemble social distancing in crowded sites. For the spreading dynamics, we consider the compartmental susceptible-exposed-infective (SEI) dynamics plus an indirect transmission with the footprints of the infectious pedestrians being the contagion factor. We show that the increase in the intensity of social distancing has a significant effect on the exposure...