An improved technique for characterizing the fracture toughness via scratch test experiments

Micro-to-macro transitions for continua with surface structure at the microscale

This paper provides a damage mechanism on single crystal silicon wafers by a scratch test. Relationship between normal indent load and scratch force was measured on the major planes of single crystal silicon using scratch test at room temperature. Scratching tracks of the surface of single crystal silicon after the scratching tests under very small loading forces were observed. It appears that relationship between normal indent load and scratch force correlates the critical load of damages of silicon.

Cement paste degradation under external sulfate attack: An experimental and numerical research

Summary URTeC 1618856 Predicting the effective gas permeability of gas shale, at scales from a few centimeters to hundreds of meters or even larger, is a requirement for assessing the productivity of shale gas plays, for developing appropriate production and stimulation plans, and, perhaps more importantly, for quantifying associated uncertainties. Like other fine-grained sediments, gas shales are heterogeneous at every scale, from nanometers to kilometers, but these rocks are also rich in organic matter. At microscopic scales, gas shales contain mostly sub-nano to sub-micron sized, intra-/inter-inorganic pores and fissures, as well as intra-kerogen pores that are probably due to gas generation. Gas transport takes place through these small void spaces in a pressure and temperature or simply state dependent non-Darcy manner, with gas sorption being a key feature in intra-kerogen pores. A multi-scale upscaling is necessary for predicting effective transport properties at useful scales. The upscaling must account for these two important aspects of gas shale flow arising from the sub-micron scales. We consider here the extension of a multi-scale upscaling framework that was developed for predicting a wide range of properties of organic-lean shales/mudstones (Aplin et al., 2012; Ma et al., 2013), applying it for predicting the effective gas permeability of organic-rich gas shales. Unlike for organic-lean shales, no empirical relationship has been established between effective gas permeability and the lithological and/or physico-chemical properties for organic-rich shales, although a relationship of that form is a critical aspect of the framework. Directly modeling gas shale at micron scales and calculating the effective gas permeability is a possibility for overcoming the lack of robust measured data. However, despite advances in image-based gas shale characterization down to even sub-micron, this approach can only be applied to samples of tens of microns in dimension, and it is known not to provide sufficient information alone for constructing representative grain/pore models for predicting effective gas permeability. Noting the similarities between organic-lean and organic-rich shales, we propose to employ the approach for constructing pore-space models for organic-lean shales, and apply these methods, with extension, to gas shales. Specifically, the sample-scale properties of the organic-lean shales are adopted as constraints for constructing representative pore-space models using image-based, local gas shale characterizations at micron scales. On such models, effective gas permeability is estimated and is used to populate models of layered shale systems via the correlation of total organic contents (TOC) and the degree of pore formation in kerogens. This paper illustrates the extensions we propose for the existing framework, with justifications, and outlines the necessary techniques.

Dynamic properties of polymer surfaces affect their ability to withstand abrasive actions. Kinetic conditions, like velocity, penetration depth and shape of the abrasive particles, change the abrasion mechanisms and the morphology of the abraded surface. Using the scratch technique, along with profilometry measurement across the scratches, we have been able to completely characterize the residual scratch morphology. Pile-up deformation and visco-plastic relaxation are key phenomena that characterize the importance of ductility in the scratch resistance of polymer surfaces. Cross profilometry aids in studying the relaxation of the scratch morphology for different time and temperature history after the scratch is made. The effect of scratch velocity, penetration depth and indenter geometry on the contact pressure and friction coefficient estimated during a scratch test can also be analyzed. Following Eyring's law, a good correlation, was found between normal indentation and scratch testing in the evolution of the contact pressure with the applied strain rate. This work results in a better understanding of the stresses and the strains applied by an abrasive particle, and especially relates the dynamic mechanical properties of viscous materials, like stress exponent, to their scratch behavior. The method presented can provide for the measurement of dynamic properties of polymer surfaces or thin films under a very large range of strain rates.

This article presents an important investigation of material removal mechanism in grinding utilizing single grit scratch tests. The investigation helps people to understand the abrasive cutting behaviour when the abrasive cutting edge shape alters during single grit grinding. The results provide fundamental knowledge of the grinding material removal process, which helps to improve grinding performance and quality. Cubic boron nitride grits of 40/50 mesh size were used to perform scratch tests on the alloy Inconel 718. The concepts of material pile-up ratio and actual material removal area were introduced to measure the material removal efficiency during grinding. It is found that pile-up ratio decreases and actual material removal area increases when the depth of cut increases, albeit the material removal mechanism is highly dependent on the abrasive grit cutting edge shape. The material removal mechanism along the scratch length shows different behaviours at the entrance and exit sides of the scratching passes. When a grit was moving along its scratch path, it pushed material forward resulting in high material accumulation at the exit side of the scratches. Consequently, cutting is more prominent at the entrance side of the scratch, whereas ploughing or pile-up is extremely high at the exit side of the scratches. The research finding provides crucial information for grinding process optimization.

Here we report quasi-isentropic dynamic compression and thermodynamic characterization of solid, precompressed deuterium over an ultra fast time scale (< 100 ps) and a microscopic length scale (< 1 ìm). We further report a fast transition in dynamically compressed solid deuterium that is consistent with the ramp to shock transition, with a time scale of less than 10 ps. These results suggest that high density dynamic compression of hydrogen may be possible on microscopic length scales.

Nanotechnology is a fast expanding field with several applications in science, engineering, healthcare, pharmaceutical, and other areas. Nanoparticles (NP) are frequently produced through a variety of physical and chemical methods. Recently, green synthesis technologies that are more simple, sustainable, and cost-effective have been developed. The environmentally friendly/sustainable synthesis of titanium dioxide nanoparticles (TiO2 NPs) has been in great demand in the previous quarter. Bioactive components found in organisms, such as plants, facilitate the processes of bio-reduction and restriction. This review described green synthesis of TiO2 NPs, the photocatalytical uses, and managing the larvicidal activity of disease-spreading mosquitoes. Various natural reducing agents including proteins, enzymes, phytochemicals, and others, are involved in the synthesis of TiO2 NPs. Current research findings and future concerns in a viable platform based on biologically meditated TiO2 nanostructures for industrial applications.

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various areas of technology and applied science, such as aerospace and communication engineering, sensing, metrology, nonlinear photonics, and quantum optics. In this article, we present the principal techniques used in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators. First detailed in this article is the protocol for resonator polishing, which is based on a grind-and-polish technique close to the ones used to polish optical components such as lenses or telescope mirrors. Then, a white light interferometric profilometer measures surface roughness, which is a key parameter to characterize the quality of the polishing. In order to launch light in the resonator, a tapered silica fiber with diameter in the micrometer range is used. To reach such small diameters, we adopt the "flame-brushing" technique, using simultaneously computer-controlled motors to pull the fiber apart, and a blowtorch to heat the fiber area to be tapered. The resonator and the tapered fiber are later approached to one another to visualize the resonance signal of the whispering gallery modes using a wavelength-scanning laser. By increasing the optical power in the resonator, nonlinear phenomena are triggered until the formation of a Kerr optical frequency comb is observed with a spectrum made of equidistant spectral lines. These Kerr comb spectra have exceptional characteristics that are suitable for several applications in science and technology. We consider the application related to ultra-stable microwave frequency synthesis and demonstrate the generation of a Kerr comb with GHz intermodal frequency.

Stochastic differential equations evolving in a Stiefel manifold occur in several applications in Science and Engineering. For ordinary differential equations evolving in Stiefel manifolds there is a solid literature on numerical implementation guaranteeing adherence to the manifold. But for stochastic differential equations, numerical methods are in their infancy. Indeed some existing schemes fail to satisfy the required geometric constraints. We develop a new and efficient scheme to simulate a stochastic differential equation evolving in a Stiefel manifold, based on the Cayley transform. In particular, we show how to construct drift and diffusion terms to obey geometric conditions, ensuring evolution in the Stiefel manifold. Comparative simulations illustrate the new scheme showing that it is geometry preserving over large numbers of time steps.

This thesis deals with the study of optimal control problems for the incompressible Magnetohydrodynamics (MHD) equations. Particular attention to these problems arises from several applications in science and engineering, such as fission nuclear reactors with liquid metal coolant and aluminum casting in metallurgy. In such applications it is of great interest to achieve the control on the fluid state variables through the action of the magnetic Lorentz force. In this thesis we investigate a class of boundary optimal control problems, in which the flow is controlled through the boundary conditions of the magnetic field. Due to their complexity, these problems present various challenges in the definition of an adequate solution approach, both from a theoretical and from a computational point of view. In this thesis we propose a new boundary control approach, based on lifting functions of the boundary conditions, which yields both theoretical and numerical advantages. With the introduction of lifting functions, boundary control problems can be formulated as extended distributed problems. We consider a systematic mathematical formulation of these problems in terms of the minimization of a cost functional constrained by the MHD equations. The existence of a solution to the flow equations and to the optimal control problem are shown. The Lagrange multiplier technique is used to derive an optimality system from which candidate solutions for the control problem can be obtained. In order to achieve the numerical solution of this system, a finite element approximation is considered for the discretization together with an appropriate gradient-type algorithm. A finite element object-oriented library has been developed to obtain a parallel and multigrid computational implementation of the optimality system based on a multiphysics approach. Numerical results of two- and three-dimensional computations show that a possible minimum for the control problem can be computed in a robust and accurate manner.

In this article, we make a detailed study of some mathematical aspects associated with a generalized Lévy process using fractional diffusion equation with Mittag–Leffler kernel in the context of Atangana–Baleanu operator. The Lévy process has several applications in science, with a particular emphasis on statistical physics and biological systems. Using the continuous time random walk, we constructed a fractional diffusion equation that includes two fractional operators, the Riesz operator to Laplacian term and the Atangana–Baleanu in time derivative, i.e., a A B D t α ρ ( x , t ) = K α , μ ∂ x μ ρ ( x , t ) . We present the exact solution to model and discuss how the Mittag–Leffler kernel brings a new point of view to Lévy process. Moreover, we discuss a series of scenarios where the present model can be useful in the description of real systems.

In this paper, we carry out a systematic study to discover the properties of a subclass of meromorphic starlike functions defined using the Mittag–Leffler three-parameter function. Differential operators involving special functions have been very useful in extracting information about the various properties of functions belonging to geometrically defined function classes. Here, we choose the Prabhakar function (or a three parameter Mittag–Leffler function) for our study, since it has several applications in science and engineering problems. To provide our study with more versatility, we define our class by employing a certain pseudo-starlike type analytic characterization quasi-subordinate to a more general function. We provide the conditions to obtain sufficient conditions for meromorphic starlikeness involving quasi-subordination. Our other main results include the solution to the Fekete–Szegő problem and inclusion relationships for functions belonging to the defined function classes. Several consequences of our main results are pointed out.

In several applications in science and engineering, different types of matrix problems emerge from the discretization of partial differential equations. This thesis is devoted to the development of new algorithms to solve this kind of problems. In particular, when the matrices involved are sparse and non-symmetric. The new algorithms are based on the Induced Dimension Reduction method [IDR(s)]. IDR(s) is a Krylov subspace method originally proposed in 2008 to solve systems of linear equations. IDR(s) has received considerable attention due to its stable and fast convergence. It is, therefore, natural to ask if it is possible to extend IDR(s) to solve other matrix problems, and if so, to compare those extensions with other well-established methods. This work aims to answer these questions. The main matrix problems considered in this dissertation are: the standard eigenvalue problem, the quadratic eigenvalue problem, the solution of systems of linear equations, the solution of sequences of systems of linear equations, and linear matrix equations. We focus on examples that arise from the discretization of partial differential equations.

In this work delamination behavior <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1,6\ \mu\mathrm{m}$</tex> thin AF4 coatings on silicon (Si) and glass (SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) substrates were tested by scratch testing. The coatings were deposited by vapor deposition polymerization (VDP) technique on untreated and polished 8-inch Si and SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> wafers, with root mean square (RMS) roughness of 4 and 2 nm, respectively. Scratch tests were performed in displacement and load controlled mode, where scratch depths were varied from 1 to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1,6\ \mu\mathrm{m}$</tex> . The indentation loads and subsequently depths, were varied to observe different delamination features over the penetration depth at the substrate-coating interface. Additionally, the scratches were observed in-situ with scanning electron microscopy (SEM) to better understand the changes in lateral force during the test. The results showed that cohesive failure in AF4 happens before adhesive failure at indentation depths down to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1,4\ \mu\mathrm{m}$</tex> , At <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1,4\ \mu\mathrm{m}$</tex> depth we can observe first adhesive failure features on the AF4 coating - SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> substrate interface. This shows that the AF4 coating on the SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> substrate has a slightly lower adhesion than on the Si substrate. The adhesion failures on both samples start to occur at scratches near the AF4-substrate interface, without chipping on the sides. The results also showed that if the scratch depth is not near the AF4-substrate, only the cohesive failure in AF4 can be seen, which indicates very good adhesion for both samples.