A Bipotential Method Coupling Contact, Friction and Adhesion

International audience– The paper is related to the analysis and the modeling of structural interface behaviors when unilateral contact, friction and adhesion interact. Among the contact models in literature, the model developed by Raous, Cangémi, Cocou and Monerie (RCCM model) is retained. It consists to include strict unilateral contact to avoid interpenetration, initial adhesion progressively decreases when the load increases, and Coulomb's friction which is progressively activated when adhesion decreases. Because of its implicit character, the Coulomb friction law with adhesion is non-associated, and the notion of superpotential with normality rule cannot be used anymore. In the present work, to overcome this non-associated character, a specific potential adapted to coupling unilateral contact, friction and adhesion is build and named bipotential. A numerical model is proposed and improved to solve the boundaries values problem. The algorithm is implemented in the finite element code SYMEF which has been developed at the University of Bechar (Algeria). A comparative study is made between the bipotential model and the previously developed RCCM model. The numerical results show that, this approach is robust and efficient in terms of numerical stability, precision convergence and CPU time compared to the RCCM model

Combined sticking: a new approach for finite-amplitude Coulomb frictional contact

Engineering-level accuracy of discretization methods for frictional contact originates from precise representation of discontinuous frictional and normal interaction laws and precise discrete contact techniques. In terms of discontinuous behavior in the quasi-static case, two themes are of concern: the normal interaction (i.e. impact) and the jumps in tangential directions arising from high frictional values. In terms of normal behavior, we use a smoothed complementarity relation. For the tangential behavior, we propose a simple and effective algorithm, which is based a stick predictor followed by corrections to the tangential velocity. This allows problems with impact and stick-slip behavior to be solved with an implicit code based on Newton–Raphson iterations. Three worked examples are shown with comparisons with published results. An extension to node-to-face form in 3D is also presented

Contamination, risk, and source apportionment of potentially toxic microelements in river sediments and soil after extreme flooding in the Kolubara River catchment in Western Serbia

Climate change is contributing to an increase in extreme weather events. This results in a higher river flooding risk, causing a series of environmental disturbances, including potential contamination of agricultural soil. In Serbia, the catastrophic floods of 2014 affected six river basins, including the Kolubara River Basin, as one of the larger sub-catchments of the large regional Sava River Basin, which is characterized by large areas under agricultural cultures, various geological substrates, and different types of industrial pollution. The main aim of this study was to establish the sources of potentially toxic elements in soil and flood sediments and the effect of the flood on their concentrations. Field sampling was performed immediately after water had receded from the flooded area in May 2014. In total, 36 soil samples and 28 flood sediment samples were collected. After acid digestion (HNO3), concentrations of the most frequent potentially toxic elements (PTE) in agricultural production (As, Cd, Cr, Cu, Ni, Pb, Zn) and Co which are closely related to the geological characteristics of river catchments, were analyzed. The origin, source, and interrelations of microelements, as well as BACKGROUND: values of the PTE of the river catchment, the pollution index (Pi), enrichment factor (Ef), and geological index (Igeo), were determined, using statistical methods such as Pearson correlations, principal component analysis (PCA), and multiple linear regression (MLRA). The content of the hot acid-extractable forms of the elements, PCA, and MLRA revealed a heavy geological influence on microelement content, especially on Ni, Cr, and Co, while an anthropogenic influence was observed for Cu, Zn, and Cd content. This mixed impact was primarily related to mines and their impact on As and Pb content. The pseudo-total concentrations of all the analyzed elements did not prove to be a danger in the catchment area, except for Cu in some samples, indicating point-source pollution, and Ni, whose pseudo-total content could be a limiting factor in agricultural production. For the Ef, the Ni content in 59% soil and 68% flood sediment samples is classified into influence classes. The similar pseudo-total contents of the elements studied in soil samples and flood sediment and their origin indicate that the long-term soil formation process is subject to periodic flooding in the Kolubara River Basin without any significant changes taking place. This implies that floods are not an endangering factor in terms of the contamination of soil by potentially toxic elements in the explored area

On two variational inequalities arising from a periodic viscoelastic unilateral problem

International audienc

CISM-IUTAM Summer School on Friction and Instabilities

The book addresses instability and bifurcation phenomena in frictional contact problems. The treatment of this subject has its roots in previous studies of instability and bifurcation in elastic, thermoelastic or elastic-plastic bodies, and in previous mathematical, mechanical and computational studies of unilateral problems. The salient feature of this book is to put together and develop concepts and tools for stability and bifurcation studies in mechanics, taking into account the inherent non-smoothness and non-associativity (non-symmetry) of unilateral frictional contact laws. The mechanical foundations, the mathematical theory and the computational algorithms for such studies are developed along six chapters written by the lecturers of a CISM course. Those concepts and tools are illustrated not only with enlightening academic examples but also with some demanding industrial applications, related, namely, to the automotive industry

Gradient of Damage Enhancement for Cohesive Interface Laws

Gradient enhancements have become increasingly popular in the last decades for dealing with problems in mechanics suffering from spurious mesh sensitivity induced by strain softening. Many proposals exist in this sense and various techniques and formulations have been presented and successfully applied to study localization and fracture. Numerical results will be presented to show the superior performances of the damage enhanced model with reference to typical fracture propagation tests, where the gradient model is expected to provide meaningful answers quite independently from the mesh size. This improvement is neither marginal nor negligible mainly in view of identification of material parameters of the interface relationship via an inverse approach. Actually, even in the simplest deterministic case, the inverse procedure may require hundreds of forward analyses using a FE mesh that should be able to resolve the cohesive zone for a sufficiently wide range of material parameters