Sharif Digital Repository

In this paper, the effects of the multi-walled carbon nanotubes (MWCNTs) and nanographene (GP) on the mechanical performance of the cementitious mortars were investigated in different environments. Six mix designs were fabricated by considering the previous studies and exposed to potable water, acidic, and alkaline environments. The GP and MWCNTs partially replaced the cement with 0.25 %, 0.5 %, and 1 % of its weight. The standard mechanical tests, X-ray diffraction (XRD), and scanning electron microscope (SEM) analysis were performed on the specimens. The results indicated that including the MWCNTs and GP increases the compressive strength by 10 % and 20 % and similarly improves the tensile... 

In Mg–Si alloys, both primary and eutectic Mg2Si particles normally appear with sharp edges, which can lead to weak mechanical properties as the result of stress concentration at the sharp corners of these brittle particles. Thus, it would be of great importance to modify the morphology of these particles. In this study, microstructure modification mechanisms after 0.5 wt% Y addition and heat treatment (HT) at 420 °C for 24 h are comprehensively studied in hypo-eutectic Mg–1Si and hyper-eutectic Mg–2Si alloys. Microstructural observations were performed using optical and scanning electron microscopy equipped with electron disperse spectroscopy, while phase analysis was done by X-ray... 

Porosity and permeability alteration due to the thermo-poro-elastic stress field disturbance from the cold fluid injection is a deciding factor for longer, more economic, and safer heat extraction from an enhanced geothermal system (EGS). In the Soultz-sous-Forêts geothermal system, faulted zones are the main flow paths, and the resulting porosity–permeability development over time due to stress reorientation is more sensitive in comparison with the regions without faulted zones. Available operational and field data are combined through a validated numerical simulation model to examine the mechanical impact on the pressure and temperature evolution. Results shows that near the injection... 

This paper deals with an experimental investigation into the mechanical performance and microstructure characteristics of the cementitious mortars containing recycled waste materials subjected to acidic, neutral and alkaline environments. The recycled waste materials include glass, eggshell, iron and rubber powder in various amounts, namely 7, 14 and 21% by volume, as the replacement for ordinary Portland cement (OPC). In this respect, to examine the mechanical performance of the specimens, the compressive, tensile and bending strength tests as well as water absorption test were carried out at the ages of 7, 28 and 90 days. Moreover, to study the microstructure of the specimens, the scanning... 

In this research, we investigate the effects of various microstructural features on the behavior of spherical steel sheets, using the crystal plasticity finite element method. The cementite phase ratio, the grain sizes of ferrite and cementite, and the percentage of residual pearlite in the steel structure due to incomplete annealing are the major microstructural parameters studied in this work. A grain generator software has been developed to generate hexagonal ferrite grains as well as circular cementite particles distributed in the ferrite matrix. We use a hard coating with special properties as an intermediate layer around the cementite grains to simulate the contact between ferrite... 

Encoders and resolvers are the most common position sensors in controlling electrical machines. However, due to their ability to work under harsh conditions, resolvers are more preferred. In linear position detection, the transversal edge effects and the longitudinal end-effects adversely affect the accuracy of conventional linear resolvers. On the contrary, due to the cylindrical symmetry of tubular machines, they are not subject to the edge effects. With this idea, this article presents a novel linear VR resolver with a tubular structure to achieve higher accuracy than the existing linear resolvers. A magnetic equivalent circuit model is then developed to prove the correct performance of... 

The global COVID-19 pandemic has affected the world’s population by causing changes in behavior, such as social distancing, masking, restricting people’s movement, and evaluating existing medication as potential therapies. Many pre-existing medications such as tocilizumab, ivermectin, colchicine, interferon, and steroids have been evaluated for being repurposed to use for the treatment of COVID-19. None of these agents have been effective except for steroids and, to a lesser degree, tocilizumab. Ivermectin has been one of the suggested repurposed medications which exhibit an in vitro inhibitory activity on SARS-CoV-2 replication. The most recommended dose of ivermectin for the treatment of... 

The probability of failure estimation of composite structures under applied loads is an inevitable requirement given the uncertainties related to the material properties, loads, and boundary conditions. The properties of composite materials have more scatter due to non-homogeneity and anisotropic characteristics, and manufacturing defects. In this paper, the reliability of S2-Glass/Epoxy laminate composite materials containing a central circular hole under static tensile load is presented. Failure in fiber-reinforced plastic structures, since individual faults in each ply cannot be traced, is a random process due to the scatter caused by the behavior of the material. According to the... 

Wearable robots are becoming increasingly practical to use to rehabilitate wounded parts of the body as the number of injuries to the hand, particularly fingers, has increased. Wearable robots are designed to help people save time and money. This exoskeleton is intended to rehabilitate the thumb such that it may do an opposing movement with one Degree Of Freedom (DOF) and a cable system. Two drums, one on the thumb and the other on the tip of the assistive finger place the cables, which feature a cable adjusting screw that can be adjusted for fingers of various lengths. To choose the assistive finger from 4 intact fingers, the two perspectives of the cable length changes and finger forces... 

In this research, friction stir joining of aluminum-polypropylene/talc composite was investigated due to the numerous applications of aluminum-polymer joints in automotive and aerospace industry. A novel tool design, including a rotary/stationary holder, was used to improve the appearance and mechanical performance of friction stir lap joints by preventing the mixed molten polymer and aluminum particles from exiting the stirred zone. Effect of tool transverse speed on the joint microstructure and strength was investigated. Using the rotary/stationary holder, tensile-shear strength of the joints increased (by ~ 45 to ~ 220% at various transverse speeds). Since during the tensile-shear test... 

Biodegradable magnesium (Mg) alloys exhibit great potential for use as temporary structures in tissue engineering applications. Such degradable implants require no secondary surgery for their removal. In addition, their comparable mechanical properties with the human bone, together with excellent biocompatibility, make them a suitable candidate for fracture treatments. Nevertheless, some challenges remain. Fast degradation of the Mg-based alloys in physiological environments leads to a loss of the mechanical support that is needed for complete tissue healing and also to the accumulation of hydrogen gas bubbles at the interface of the implant and tissue. Among different methods used to... 

Physics-informed neural networks (PINNs) have received significant attention as a unified framework for forward, inverse, and surrogate modeling of problems governed by partial differential equations (PDEs). Training PINNs for forward problems, however, pose significant challenges, mainly because of the complex non-convex and multi-objective loss function. In this work, we present a PINN approach to solving the equations of coupled flow and deformation in porous media for both single-phase and multiphase flow. To this end, we construct the solution space using multi-layer neural networks. Due to the dynamics of the problem, we find that incorporating multiple differential relations into the... 

Accelerometers that work based on intensity modulation of light are more sensitive, economically feasible, and have a simpler fabrication process compared to wavelength modulation. A micro-opto-electro-mechanical-system accelerometer based on intensity modulation of light is designed and fabricated. A movable shutter that is attached to the proof mass is designed to change the intensity of light. Moreover, the mechanical part is designed to improve the overall sensitivity and linear behavior in the measurement range. The designed accelerometer is fabricated by a deep-reactive-ion-etching (DRIE) process. The DRIE process used in this report is based on a Bosch-like process, which uses SF 6... 

Nowadays, the significance of sustainability has urged composite manufacturers to replace traditional synthetic fibers with eco-friendly natural alternatives due to their environmental and economic benefits. This work aims to fabricate hybrid polypropylene (PP) composites with short flax fibers, octene-ethylene copolymer (POE) rubber particles, and maleic anhydride-grafted polypropylene (MAPP) compatibilizer. The main goal is to gain an insight into the combined effect of toughening mechanisms induced by the short fibers and rubber particles at the crack tip and wake of composites, which is a crucial step in reaching a balance between toughness and rigidity. In this regard, a novel... 

Material properties and fracture characteristics are among the most prominent parameters that should be considered for a wide range of graphene applications. This article reviews recent advances in theoretical studies on the mechanical properties and fracture behaviors of graphene, focusing on the effect of various simulation models. Most studies investigated single-layer graphene sheets (SLGSs) under uniaxial tensile tests using different common interatomic potentials, particularly AIREBO. Although researchers have examined a similar problem, specifically for pristine graphene, the differences in the reported values are considerable. These discrepancies are most evident in fracture... 

Incorporating titanium dioxide (TiO2) nanoparticles into the polymeric matrix offers an opportunity to obtain nanocomposites with improved functionality. In this study, the commercial TiO2 nanoparticles (TNP) were surface treated by different concentrations of aminopropyl triethoxy silane (APTS) as a coupling agent and triethylamine (Et3N) as a surface grafting catalyst by an aqueous process to prepare a nanocomposite with superior properties. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were performed to confirm the successful surface modification of TNP. The prepared modified TiO2 nanoparticles (mTNP) with different weight fractions were used as... 

Mechanical characterization of fractures, i.e., identifying their characteristic parameters such as energy release rate, is crucial to assess the safety and stability of structural members. This is generally achieved using a combination of finite element analysis and optimization. Machine learning models are increasingly used to characterize engineering problems. While such models have shown impressive performance on smooth data, their performance diminishes significantly on data with discontinuities and sharp gradients. For fractures, this issue is more severe due to the singular solutions in the vicinity of the fracture tips. To resolve this difficulty, leveraging classical fracture...