Search

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.

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)