Preconditioning of hard rocks by microwave energy has recently been considered a potentially effective technology in mechanical rock breakage for civil and mining engineering. To obtain the amount of mechanical damage that a single-mode microwave treatment produces in rocks, it is necessary to analyze and evaluate the thermal cracking process by microwave heating at different power levels, exposure times, and distances from the antenna. The current study employs the scanning electron microscopy imaging technique to capture images from surfaces of irradiated rock specimens and to compare them with a nontreated specimen. To evaluate and quantify the amount of cracking (i.e. crack density, crack size, etc.) in a rock specimen after microwave irradiation with different microwave input operating parameters, the following steps were evaluated. First, several experiments of single-mode microwave treatments with different operating parameters were performed on rectangular specimens of basalt. Then, cylindrical core samples with a dimension of r = 0.5 cm, h = 2cm, were drilled from the center of the irradiated specimens and prepared for image processing. The results of the present study show that there are significant differences between the number of microcracks present in samples irradiated at different power levels and distances from the antenna. Also, longer exposure times result in more severe cracks.
KEYWORDSAbstract. In this paper, we study static bending and free vibration behaviors of Bernoulli-Euler microbeams with a single delamination using the modi ed couple stress theory. The delaminated beam is modeled by four interconnected sub-beams using the delamination zone as their boundaries. The free and constrained mode theories are utilized to model the interaction of delamination surfaces in the damaged area. The continuity as well as compatibility conditions are satis ed between the neighboring sub-beams. After veri cation of the results for some case studies with available solutions, the e ects of various parameters, such as spanwise and thicknesswise locations of the delamination, material length-scale parameter, and boundary conditions, on the static bending and free vibration characteristics of the size-dependent microbeam, have been investigated in detail.
The brain is encased in the skull and suspended and supported by a series of three fibrous tissue layers: Dura mater, Arachnoid and Pia matter, known as the Meninges. Arachnoid trabeculae are strands of collagen tissues located in a space between the arachnoid and the pia matter known as the subarachnoid space (SAS). The SAS trabeculae play an important role in damping and reducing the relative movement of the brain with respect to the skull. The SAS is filled with cerebrospinal fluid (CSF), which is a colorless fluid that surrounds all over the brain inside the subarachnoid spaces. This fluid stabilizes the shape and position of the brain during head movements. To address normal and pathological SAS functions, under conditions where an electrical stimulation is applied, this study proposes a novel fully-coupled electro-Fluid-Structure Interaction (eFSI) modeling approach to investigate the response of the system of SAS-CSF under the applied electric current, which is provided by the transcranial Direct Current Stimulation (tDCS) technique according to the following steps. First, a two-dimensional channel model of the brain SAS with several trabecular morphologies is numerically simulated using the finite element (FE) method. The channel model is then subjected to a specific electric field intensity by applying a 1∼2mA direct current. COMSOL Multiphysics v. 5.3a software is used to perform the coupled eFSI numerical simulation in order to investigate the effects of the applied electric field on the flow of the CSF, thereby showing the deflection of the trabeculae inside the channel model. The results of this study demonstrate that the induced electric field causes less deflection of the trabeculae by exacerbating the velocity profile of the cerebrospinal fluid flow and decreasing the flow pressure applied on each trabecula inside the trabecular SAS channel. This electro-mechanostructural modeling approach is significant because of the applied current on the channel walls that can directly affect the CSF flow. In fact, the results of this study can open up a new horizon for future research on disorders like hydrocephalus, which involves an unusual production rate of the CSF inside the brain. This disorder may be controlled by applying an electric current in the brain, using one of the available brain stimulation techniques, i.e. tDCS. By using an electrical stimulation technique, one might control the dynamics of brain function and, therefore, regulate dysfunctionality through the first eFSI multiphysics modeling approach proposed in this study. Briefly, the brain SAS may be considered as a novel region for electrotherapeutic and electromechanical neuromodulation.
Ceramic coated fabrics have been employed for heat resistant clothing such as fire-fighters gears, fire-proof insulators, and heating and cooling insulators. Thus, transient heat conduction and thermal properties of such fabrics are needed for the design of the clothing. The goal of this study is to measure the transient heat conduction and the coefficient of thermal expansion of ceramic coated fabrics with different woven morphologies. This has been accomplished through an experimental setup consists of a hotplate assembly, applying a uniform temperature, with the accuracy of +/− 1 °C in less than 500 msec, a ceramic coated fabric and an infra-red thermometer assembly. This set up has been validated by using a known material such as aluminum and copper for the coefficient of thermal expansion measurement. The hot plate temperature was varied between 30 to 400°C within 300 seconds. The transient heat conduction and the thermal coefficient of the woven ceramic coated fabrics were compared with ceramic nonwoven fabrics materials. Finally, upon comparing different samples and measuring the coefficients of thermal expansion, K’s, the level of delay in heat transfer with respect to time has been determined.
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