Influence Of Microgeometry Research Articles

Modelling laser modified secondary electron yield response of surfaces

Electron clouds hinder the operation of particle accelerators. In the Large Hadron Collider (LHC), the copper beam screens are located within close proximity to the beam path, resulting in beam-induced electron multipacting, which is the main source of electron cloud formation. Conditions for multipacting are encountered when such surfaces have a secondary electron yield (SEY) greater than unity. Roughening the surface through laser processing offers an effective solution for reducing secondary electrons. Laser ablation leaves behind a complex rough, multi-scale geometrical surface with an altered chemical composition. Current models often over-simplify the geometry, do not have sufficient experimental data to derive input parameters, and exclude SEY-reducing mechanisms such as the surface chemistry. Leading to electron-matter interactions which do not resemble that of a real surface. Here, this complex surface is studied on copper used in the LHC, and the influence of microgeometry, inhomogeneous nanostructure and complex surface chemistry on the SEY is investigated. A novel, improved model is proposed that characterises these sophisticated structures, enabling the efficient design of surfaces to reduce SEY. To validate the model, samples were made using a variety of laser parameters. Modelling insights revealed that secondary electron suppression is not only caused by the microgeometry but also the nanostructure and chemical modification play a role. Contrary to the conventional theory, high aspect ratio structures are not necessarily required for effective SEY reduction. Currently, the model is applicable to a variety of surface morphologies and could be employed for other materials.

Influence of microgeometry in the point contact zone of rest friction on fatigue life for friction bearing units

A comprehensive methodology has been developed to assess the maximum contact stresses and deformations in the point contact zone and the maximum tangential stresses, including their position in the subsurface zone in depth and in the rolling direction when the microgeometry of the rest contact.

Adhesive Interaction of Elastic Bodies with Regular Surface Relief

This paper focuses on adhesive interaction between an axisymmetric indenter and an elastic half-space taking into account the surface microrelief in the form of regularly located identical asperities covering the indenter. The microlevel contact between the asperities system and the elastic half-space is considered discrete. The solution to the problem at the macrolevel is constructed using the dependence of the effective specific adhesion force on the value of the nominal gap obtained by solving the problem at the microlevel. The constructed solution makes it possible to model the influence of microgeometry and adhesion parameters on the contact interaction of elastic bodies at the macrolevel.

Effective longitudinal shear moduli of periodic fibre-reinforced composites with functionally-graded fibre coatings

This paper presents a homogenization method for unidirectional periodic composite materials reinforced by circular fibres with functionally graded coating layers. The asymptotic homogenization method is adopted, and the relevant cell problem is addressed. Periodicity is enforced by resorting to the theory of Weierstrass elliptic functions. The equilibrium equation in the coating domain is solved in closed form by applying the theory of hypergeometric functions, for different choices of grading profiles. The effectiveness of the present analytical procedure is proved by convergence analysis and comparison with finite element solutions. The influence of microgeometry and grading parameters on the shear stress concentration at the coating/matrix interface is addressed, aimed at the composite optimization in regards to fatigue and debonding phenomena.

Influence of microgeometry on membrane potential of shaly sands : Sen, P N GeophysicsV54, N12, Dec 1989, P1543–1553

Influence of microgeometry on membrane potential of shaly sands : Sen, P N GeophysicsV54, N12, Dec 1989, P1543–1553

Influence of Microgeometry on Membrane Potential of Shaly Sands

ABSTRACTThe microgeometry of the pore space influences the membrane potential Em. and theDC electrical conductivity σ of a shaly sand in a similar manner, independent of the details of the geometry: Em and σ being related via the conductivities of cations and σanions;σ=σcation + σ onion, and Em α σ cation/(σcation + σanion). This explicit relationship is used to investigate the role of the geometrical factors which influence both Em and σ in a related manner. The dependence of σ on the water conductivity σw can be well approximated with four geometrical parameters which can be obtained from the slopes and the interceptsof σ vs. σw curve at high and low salinities. We show that these geometrical factors appear in the expression for Em a well. These geometrical parameters (one of them is the formation factor) vary from rock to rock, and any trend in these parameters depend on the local geology.

Influence of microgeometry on membrane potential of shaly sands

The microgeometry of the pore space influences the membrane potential [Formula: see text] and the dc electrical conductivity σ of a shaly sand in a similar manner, independent of the details of the geometry. [Formula: see text] and σ are related via the conductivities of cations and anions [Formula: see text] and [Formula: see text], and [Formula: see text]. This explicit relationship is used to investigate the role of the geometrical factors that influence both [Formula: see text] and σ in a related manner. The dependence of σ on water conductivity [Formula: see text] can be well approximated with four geometrical parameters, which can be obtained from the slopes and the intercepts of curves of σ versus [Formula: see text] at high and low salinities. I show how these geometrical factors appear in the expression for [Formula: see text] as well. The geometrical parameters, one of them being the formation factor, vary from rock to rock; and any trend in the parameters depends on the local geology. For the data on a group of 140 different cores, the geometrical factors could be well approximated by functions of porosity, cementation exponent, and charge density, to give a simple conductivity formula analogous to the empirical formulas that are most widely used in formation evaluation. These empirical factors are used to obtain an approximate formula for [Formula: see text].