Roughness determines many functional properties of surfaces, such as adhesion, friction, and (thermal electrical) contact conductance. Recent analytical models simulations enable quantitative prediction these from knowledge the power spectral density (PSD) surface topography. The utility PSD is that it contains statistical information unbiased by particular scan size pixel resolution chosen researcher. In this article, we first review mathematical definition PSD, including one-...

Amontons' law defines the friction coefficient as ratio between force and normal force, assumes that both these forces depend linearly on real contact area two sliding surfaces. However, experimental testing of frictional models has proven difficult, because few in situ experiments are able to resolve this area. Here, we present a detection method with molecular-level sensitivity. We find while is proportional area, does not increase force. Contact simulations show due elastic interactions...

The 6000 series Al alloys, which include a few percent of Mg and Si, are important in automotive aviation industries because their low weight, as compared to steels, the fact strength can be greatly improved through engineered precipitation. To enable atomistic-level simulations both processing performance this alloy system, neural network (NN) potential for ternary Al-Mg-Si has been created. Training NN uses an extensive database properties computed using first-principles density functional...

Most natural and man-made surfaces appear to be rough on many length scales. There is presently no unifying theory of the origin roughness or self-affine nature surface topography. One likely contributor formation deformation, which underlies processes that shape such as machining, fracture, wear. Using molecular dynamics, we simulate bi-axial compression single-crystal Au, high-entropy alloy Ni$_{36.67}$Co$_{30}$Fe$_{16.67}$Ti$_{16.67}$, amorphous Cu$_{50}$Zr$_{50}$, show even homogeneous...

Physically motivated and mathematically robust atom-centered representations of molecular structures are key to the success modern atomistic machine learning. They lie at foundation a wide range methods predict properties both materials molecules explore visualize their chemical compositions. Recently, it has become clear that many most effective share fundamental formal connection. can all be expressed as discretization n-body correlation functions local atom density, suggesting opportunity...

The optimization of surface finish to improve performance occurs largely through trial and error, despite significant advancements in the relevant science. There are three central challenges that account for this disconnect: (1) challenge integration many different types measurement same capture multi-scale nature roughness; (2) technical complexity implementing spectral analysis methods, applying mechanical or numerical models describe performance; (3) a lack consistency between researchers...

Abstract Background We present a robust method to obtain the displacement field of dislocation core, which is one building blocks for development direct multiscale coupling an atomistic domain discrete dynamics engine in 3D (e.g. CADD3D). Methods The core structure achieved by modeling straight with arbitrary mixed angle using simulation. In order validate obtained structures, variational Peierls-Nabarro extended include characters. Results Both methods show comparable structures all studied...

Micromechanical homogenization is often carried out with Fourier-accelerated methods that are prone to ringing artifacts. We here generalize the compatibility projection introduced by Vondřejc et al. (2014) [24] beyond Fourier basis. In particular, we formulate for linear finite elements while maintaining Fourier-acceleration and fast convergence properties of original method. demonstrate this eliminates artifacts yields an efficient computational scheme equivalent canonical finite-element...

Atomistic models for friction su_er from the severe length- and time-scale restrictions of molecular dynamics. Even when they yield good qualitative results, it is di_cult to draw meaningful quantitative conclusions them. In this paper, a novel approach quantify scratching work energy associated with creation plastic zones presented. The combined statistical criterion determine significance simulation box size sliding rate e_ects on coe_cient. These two methods are applied large parametric...

Random alloys are multicomponent systems where the atomic type on each lattice site is independent of atom types any other site. The fluctuations in local configurations inherent to random alloy prevents accurate application standard force-based atomistic/continuum (a/c) coupling. Errors arise because two transitions, from atomistic continuum and random-to-homogeneous, occur at same location. Here, methods for a/c coupling that mitigate errors arising method proposed, studied, validated. In...

The problem of mechanical contact is a truly multiscale one. Atomistic effects that violate continuum theory dominate the deformations contacting asperities, while interactions between distant asperities occur through long-range elasticity. This thesis concentrates on numerical modelling nanoscale frictional crystalline metals by using both single-scale atomistic methods and improving concurrent methods. A novel approach to quantify work energy associated with plastic activity in \md...

We propose a matrix-free finite element (FE) homogenization scheme that is considerably more efficient than generic FE implementations. The efficiency of our follows from preconditioned well-scaled reformulation allowing for the use conjugate gradient or similar iterative solvers. geometrically-optimal preconditioner -- discretized Green's function periodic homogeneous reference problem has block-diagonal structure in Fourier space which permits its inversion using fast transform (FFT)...

The adjoint method allows efficient calculation of the gradient with respect to design variables a topology optimization problem. This is almost exclusively used in combination traditional Finite-Element-Analysis, whereas Fourier-based solvers have recently shown large efficiency gains for homogenization problems. In this paper, we derive discrete that employ compatibility projection. We demonstrate on composite materials and auxetic metamaterials, where void regions are modelled zero stiffness.