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The effect of the presence of a passivation layer on a metal rough surface during contact loading is investigated by means of dislocation dynamics simulations. The metal body is modeled as an FCC single crystal with a self-affine rough surface that is either bare, or covered by a thin coating, impenetrable to dislocations. This analysis permits to isolate the effect of surface roughening driven by dislocation motion: when the surface is bare the dislocations can glide out, leaving crystallographic steps at the surface that modify the local roughness; when the surface is passivated, dislocations are stopped by the interface. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 681813).

Viscoelasticity and roughness are among the possible causes of the adhesive hysteresis displayed by soft contacts. Viscoelasticity causes an increased effective work of adhesion due to stiffening of the contact, while roughness is responsible for elastic instabilities. Herein, we explore the interplay between viscoelasticity and roughness by simulating in two dimensions the retraction of a rigid cylinder, with wavy surface profile, from a viscoelastic half-space. The wave amplitude and length are varied to induce instabilities in the load–to–area response, while the retraction velocity is increased to promote viscoelasticity. Results show that, in the regime where viscoelasticity is confined to the edges of the wavy contact, the contributions of viscoelasticity and waviness to adhesive hysteresis are nearly independent and additive. At low retraction rates, the instabilities in the load-area curve typical of rough elastic contacts are suppressed by viscoelasticity: the contact stiffens to promote a stable decrease of the contact area with load. This occurs with a minimal change in work of adhesion. However, when the instantaneous limit is met at high retraction rates, mechanical instabilities appear. LN acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 681813).

Two-scale models are an effective tool to study mechanical problems in which features in a wide span of length scales must be considered. In the context of contact mechanics, however, this cannot be directly used due to a lack of scale separation, which results in a lack of representativeness of the local-scale results. In this work, a model is proposed that circumvents this issue by incorporating stochastically the variability of the local scale results into the global-scale problem. Several test cases are performed to show the performance of the model. Work funded in part by the Spanish Ministry of Science and Innovation through grant PID2021-126614OB-I00.

A seamless 2D dual-scale computational scheme is developed to study contact problems. The model consists of an atomistic domain close to the contact, coupled with an elastic continuum domain away from the contact. The atomistic formulation provides a description of the contact interaction through interatomic potentials and permits to capture atomic wear and defect formation in the contact region. The fields in the continuum domain are calculated by an efficient FFT-based Green’s function method. The novel scheme is validated against full atomistic simulations and applied to study the effect of adhesion on the scratching of a rough copper surface by a rigid smooth spherical tip.

Malauradament tothom coneix la COVID-19, i és un fet que s’ha expandit una pandèmia a nivell mundial afectant així a la salut, la economia i als estils de vida que si bé ja no són com ho eren prèviament, és possible que mai ho tornin a ser. Noves circumstàncies i problemes impliquen noves solucions. Amb l’objectiu principal de facilitar les situacions més quotidianes del dia a dia, s’ha elaborat aquest projecte a fi de dissenyar un producte capaç de resoldre aquests nous conflictes. L’idea inicial del projecte era la de lidiar amb situacions d’un ciutadà qualsevol com ara obrir i tancar portes, prémer botons o bé subjectar-se en el transport públic sense haver de desinfectar-se constantment les mans o buscant algun element alternatiu per a no crear contacte directe. La solució a aquest conflicte implica així un nínxol de mercat que contempla pràcticament a tota la població mundial, però les característiques que es buscaven en el producte encaixaven perfectament amb la feina a realitzar d’un repartidor (Obrir/tancar portes, prémer el timbre i transportar paquets). Així doncs, sense desestimar mai un usuari quotidià, el públic més fiable del producte seria el d’un treballador com a repartidor. Els objectius han estat marcats en complir les funcions bàsiques esmentades; aportant sempre seguretat, robustesa, comoditat i facilitat d’ús. Per tal de reproduir les exigències fixades, s’ha elaborat un element retràctil incorporat al avantbraç, capaç d’accionar-se amb una sola mà per tal d’evitar el contacte directe amb les superfícies potencialment infectades, contempla també un dipòsit el qual anirà emplenat de gel desinfectant amb una capacitat de uns 30 usos per tal de garantir la seguretat del usuari i de la resta de persones que puguin interactuar amb les mateixes superfícies. Tant els materials emprats com el dimensionat de les peces ha estat estudiat i calculat mitjançant suposicions empíriques i comprovacions de simulació i càlcul per tal d’aconseguir un producte robust, pràctic, segur i ergonòmic. Un cop finalitzat el projecte s’observa que l’enfoc al sector dels repartidors és un nínxol de mercat molt apte per el producte ja que satisfà les seves necessitats i és un sector en plena expansió, així com que no només es crea un producte pioner i/o innovador, sinó que s’incorpora un nou concepte basat en un mecanisme retràctil incorporat aplicable a altres sectors i situacions com ara a mode de “guant” protector en les manipulacions perilloses a l’industria. La COVID-19 ha modificado los estilos de vida de todas las personas a nivel mundial. Por eso se ha iniciado este proyecto, para facilitar y solucionar algunos aspectos que han cambiado los hábitos habituales de las personas. Se ha diseñado un aparato el cual va incorporado al antebrazo con el fin de evitar el contacto directo con superficies potencialmente infectadas por la COVID-19. El aparato es activado y desactivado con un sencillo golpe de muñeca el cual acciona un mecanismo retráctil ofreciendo una superficie adaptable a la palma de la mano a modo de guante protector. El dispositivo consta de un depósito rellenado de gel desinfectante con una cuantía de más de 30 usos para garantizar la seguridad del usuario y el resto de personas. Unfortunately, everyone knows about COVID-19, and it is a fact that a pandemic has spread worldwide affecting health, the economy and lifestyles, which are not as they were before and may, never be again. New circumstances and problems imply new solutions. With the main goal of facilitating the most everyday situations, this project was developed in order to design a product capable of resolving these new conflicts. The initial idea of the project was to deal with situations of any citizen such as opening and closing doors, pressing buttons or holding on to public transport without having to constantly disinfect your hands or looking for an alternative element to do not create direct contact. The solution to this conflict thus involves a niche market that covers virtually the entire world population, but the characteristics sought in the product fit perfectly with the work of a distributor (Open/close doors, ring the bell and transport packages). So, without ever dismissing an everyday user, the most reliable audience for the product would be a worker like a distributor. The objectives have been set in fulfilling the basic functions mentioned; always providing security, robustness, comfort and ease of use. In order to reproduce the set requirements, a retractable element has been developed incorporated in the forearm, capable of being operated with one hand in order to avoid direct contact with potentially infected surfaces, it also includes a tank which will go filled with sanitizer with a capacity of about 30 uses to ensure the safety of the user and other people who may interact with the same surfaces. Both the materials used and the dimensions of the parts were studied and calculated using empirical assumptions and simulation and calculation tests in order to achieve a robust, practical, safe and ergonomic product. Once the project is completed, it is observed that the focus on the distributors sector is a niche market that is very suitable for the product because it meets their needs and it is a sector in full expansion, as well as not only creating a pioneering product and/or innovative, but incorporates a new concept based on a built-in retractable mechanism applicable to other sectors and situations such as a protective “glove” in hazardous handling in the industry.

Continua a l'article "A contact domain method for large deformation frictional contact problems. Part 2: Numerical aspects" publicat a la revista "Computer methods in applied mechanics and engineering", 2009, vol. 198, p. 2607-2631. In the first part of this work, the theoretical basis of a frictional contact domain method for two-dimensional large deformation problems is presented. Most of the existing contact formulations impose the contact constraints on the boundary of one of the contacting bodies, which necessitates the projection of certain quantities from one contacting surface onto the other. In this work, the contact constraints are formulated on a so-called contact domain, which has the same dimension as the contacting bodies. This contact domain can be interpreted as a fictive intermediate region connecting the potential contact surfaces of the deformable bodies. The introduced contact domain is subdivided into a non-overlapping set of patches and is endowed with a displacement field, interpolated from the displacements at the contact surfaces. This leads to a contact formulation that is based on dimensionless, strain-like measures for the normal and tangential gaps and that exactly passes the contact patch test. In addition, the contact constraints are enforced using a stabilized Lagrange multiplier formulation based on an interior penalty method (Nitsche method). This allows the condensation of the introduced Lagrange multipliers and leads to a purely displacement driven problem. An active set strategy, based on the concept of effective gaps as entities suitable for smooth extrapolation, is used for determining the active normal stick and slip patches of the contact domain.

How large is the area of real contact when two solids are brought into contact? This fundamental question has interested scientists since the pioneering work of Hertz published 1882. The problem is of tremendous practical importance, since the area of real contact influence a large number of physical properties such as the contact resistivity, heat transfer, adhesion, friction and the wear between solids in stationary or sliding contact. The focus of this thesis is the study the rough contact on micro scale between a rubber and steel surfaces. These surfaces are referred to a radial lip seal working on a rotational metal shaft. In this thesis this contact is studied using the Finite Element commercial software ABAQUS to study the elastic contact of reduced flat surface that represents the whole model of a radial lip seal in contact with a metal shaft. The other main goal of the thesis is to propose different methodologies to generate rough surfaces on a micro scale. These models for rough surfaces are generated using the SOLIDWORKS software. The simulation results are compared with the existing main theories that study this contact in order to achieve a better understanding of the micro scale surface contact mechanics. Outgoing

This work focuses on the assessment of the relative performance of the so-called contact domain method, using either the Lagrange multiplier or the penalty strategies. The mathematical formulation of the contact domain method and the imposition of the contact constraints using a stabilized Lagrange multiplier method are taken from the seminal work (as cited later), whereas the penalty based implementation is firstly described here. Although both methods result into equivalent formulations, except for the difference in the constraint imposition strategy, in the Lagrange multiplier method the constraints are enforced using a stabilized formulation based on an interior penalty method, which results into a different estimation of the contact forces compared to the penalty method. Several numerical examples are solved to assess certain numerical intricacies of the two implementations. The results show that both methods perform similarly as one increases the value of the penalty parameter or decreases the value of the stabilization factor (in case of the Lagrange multiplier method). However there seems to exist a clear advantage in using the Lagrange multiplier based strategy in a few critical situations, where the penalty method fails to produce convincing results due to excessive penetration. The Spanish Ministry of Science and Innovation and the Catalan Government Research Department are gratefully acknowledged for their financial support under Grants BIA2008-00411 and 2009 SGR 1510, respectively.

Initially, cross country skis were used to move from place to place through the snow in winter. Now mainly it is performed in recreational and competition environments. Its intuitive basic technique, the direct contact with nature and the health characteristics makes this sport a very attractive activity for a lot of people from a large range of ages.In competition, technique is brought to the extreme and it is conditioned by many characteristics. In this case equipment is very important for good performance and skiers look for the optimum ski. Here is where special test benches and tools are used to evaluate mechanic behaviors and match up the skier with the equipment.Methods to evaluate skis already exist, some of them old but yet reliable. However, in the last 20 years test methods have improved a lot with new devices and new data is obtained, which is decisive in the ski market and competition. This project focuses on different techniques to obtain mechanical properties of the cross country ski. The methods should allow the interested to evaluate the performance of the ski as well as match it up with the best skier. Validerat; 20120620 (anonymous)

Continuació de l'article "A contact domain method for large deformation frictional contact problems. Part 1: Theoretical basis" publicat a la revista Computer Methods in Applied Mechanics and Engineering, Vol. 198, #33-36, July 2009, p. 2591-2606 This second part of the work describes the numerical aspects of the developed contact domain method for large deformation frictional contact problems. The theoretical basis of this contact method is detailed in the first part of this work. Starting from this, the present contribution focuses on describing important algorithmic details that go along with the finite element implementation for two-dimensional problems. Important aspects are the construction of the contact domain mesh, via a constraint Delaunay triangulation, the linearization of the discretized contact contributions and some important technical aspects about the extrapolation procedure used for the predictive active set strategy. Finally a set of numerical examples is presented to demonstrate the performance of the developed contact strategy. Demanding static and dynamic contact problems in the context of large deformations, including frictional effects as well as self contact, show the wide applicability and the robustness of the proposed method.

Durante del trabajo final de master se realizará la optimización de la simulación del contacto mecánico dentro de un código de elementos finitos de aplicación industrial. Las tareas incluyen búsqueda bibliográfica y estudio de los algoritmos de contacto clásicos, con especial énfasis en el "Contact Domain Method"; el cual se implementará y validará con casos industriales con el objetivo de conseguir mayor rapidez y robustez en la solución, comparando con el método que actualmente se está empleando en el código