This thesis is addressed to the understanding of the mechanisms at the origin of the contact wave fields at frictional interfaces and its relationship with the local characteristics of the surfaces in contact, as well as with the global dynamics and macroscopic frictional behaviour of the system. The aim of this work is to provide insights on the generation and propagation of the waves through the contact both to avoid instabilities and to control their effect on friction. The work is organized in two main parts. The first part presents the development of a non-linear finite element analysis in large transformations of the dynamic rupture at the interface with contact friction separating two bodies (isotropic and elastic) without relative motion. A rupture is considered when an initially sticking zone shifts in sliding state. The properties of the obtained ruptures are analyzed for a flat interface between dissimilar materials in function of the nucleation energy; then the effect of the interface roughness is analyzed. The differentiated rupture inside the asperities and the conditions for coupling and uncoupling between the waves radiating in the two bodies have been also investigated. In the second part, the analysis deals with the sliding onset between two bodies in contact. The sliding between two bodies made of different isotropic elastic materials and separated by a frictional interface is simulated. The evolution along the time of the global normal and tangential forces is analyzed, relating it to the local phenomena occurring at the interface. This part tries to investigate how micro-slips at the interface, acting as distributed ruptures, trigger the macro-slips between the two bodies. The interaction between local and global dynamics is also studied. Finally a numerical parameter space study is carried out, as a function of several system parameters (contact law, friction coefficient, material damping, normal load, translational velocity and regularization time). The results show the key role of the micro-slips and precursors (detectable wave propagations that occur at tangential global force well below the critical value expected by the friction law) in triggering the macro-slip between the two bodies. Depending on their distribution and magnitude the evolution of the contact forces passes from stick-slip-like behaviour to continuous sliding. The local dynamics at the contact (wave and rupture propagation) is linked to the global behaviour of the system (stick-slip, continuous sliding, induced vibrations); the effect of the contact and system parameters on the transfer of vibrational energy between the sliding contact and the system is investigated. The numerical results obtained by the two parts of the work show a good agreement with experimental results in literature.

Title: Development of effective code for earthquake dynamic source simulations Author: Bc. Jan Premus Department: Department of Geophysics Supervisor: doc. RNDr. František Gallovič, Ph.D, Department of Geophysics Abstract: Dynamic rupture modeling coupled with strong motion data fitting offers an insight into physical mechanisms behind earthquake sources [Gallovic et al., 2019]. Running a large number of dynamic model simulations is required due to the nonlinearity of the inverse problem. The goal of this Thesis is a development of an efficient forward solver for the dynamic inversions. The fi- nite difference staggered grid code FD3D by Madariaga and Olsen [1998] served as a basis for the development, offering sufficient speed, but rather low accu- racy. Traction at split node implementation of the fault boundary condition and perfectly matched layers as the absorbing boundary condition were required to obtain desirable accuracy. In addition to the slip weakening friction law, fast ve- locity weakening friction law has been implemented, increasing the applicability of the code. We test the new code FD3D TSN using USGS/SCEC benchmarks TPV5 (slip-weakening friction) and TPV104 (fast rate weakening friction) [Harris et al., 2018], showing very good agreement with results calculated by advanced numerical...

L’objectif de cette thèse est d’approfondir la connaissance sur la génération et la propagation des ondes à travers l’interface de contact afin de contrôler leurs effets sur le frottement, contrôler les instabilités et réduire les phénomènes d'usure. Le travail est organisé en deux parties principales. La première partie est axée sur une analyse non-linéaire par éléments finis en grandes transformations; la rupture dynamique à l’interface de contact avec frottement, qui sépare deux corps (isotropes et élastiques) en condition de pré-charge statique, est simulée. On définit comme étant une rupture une zone, initialement en adhérence, qui change son état en devenant glissante. Les propriétés des ruptures sont analysées pour une surface plane entre deux matériaux différents en fonction de l’énergie de nucléation; l’effet de la rugosité de surface est ensuite analysée. En outre, la rupture "cumulatives" dans les aspérités et les conditions pour le couplage ou le non-couplage entre les ondes qui se propagent dans les deux corps sont étudiées. Dans la deuxième partie, l'amorçage du glissement entre deux corps en contact constitués de matériaux différents et séparés par une interface avec frottement, est simulée. L’évolution, en fonction du temps, des forces globales (normale et tangentielle) a été mise en relation avec les phénomènes locaux qui se déroulent à l’interface. L'analyse montre comment les micro-slips à l'interface, en agissant comme ruptures localisées, déclenchent les macro-slips entre les deux corps. L'interaction entre les dynamiques locale du contact et globale du système a été aussi étudiée. Enfin, une analyse paramétrique est menée en fonction de plusieurs paramètres (loi de contact, coefficient de frottement, amortissement matériau, charge normale, etc.). Les résultats mettent en avant le rôle-clé des micro-slips et des précurseurs (propagations d'ondes détectables qui ont lieu pour des valeurs de la force tangentielle globale inférieures à la valeur prévue par la loi de frottement) dans l'amorçage du macro-slip entre les deux corps. En fonction de leur distribution et de leur intensité, l'évolution des forces de contact change en passant d'un comportement de type stick-slip à un glissement continu. La dynamique locale au contact (propagation des ondes et ruptures) a été reliée au comportement global du système (stick-slip, glissement continu, vibrations induites); l'effet des paramètres du contact et du système sur le transfert d'énergie vibrationnelle entre le contact glissant et le système a également été examinée: en fonction de leurs valeurs, on peut avoir différentes modalités d'excitation du système (par une distribution de micro-slips ou par des macro-slips) et différentes processus de propagation et dissipation d'énergie. Les résultats numériques obtenus dans les deux parties de la thèse sont cohérents avec les résultats expérimentaux de la littérature. / This thesis is addressed to the understanding of the mechanisms at the origin of the contact wave fields at frictional interfaces and its relationship with the local characteristics of the surfaces in contact, as well as with the global dynamics and macroscopic frictional behaviour of the system. The aim of this work is to provide insights on the generation and propagation of the waves through the contact both to avoid instabilities and to control their effect on friction. The work is organized in two main parts. The first part presents the development of a non-linear finite element analysis in large transformations of the dynamic rupture at the interface with contact friction separating two bodies (isotropic and elastic) without relative motion. A rupture is considered when an initially sticking zone shifts in sliding state. The properties of the obtained ruptures are analyzed for a flat interface between dissimilar materials in function of the nucleation energy; then the effect of the interface roughness is analyzed. The differentiated rupture inside the asperities and the conditions for coupling and uncoupling between the waves radiating in the two bodies have been also investigated. In the second part, the analysis deals with the sliding onset between two bodies in contact. The sliding between two bodies made of different isotropic elastic materials and separated by a frictional interface is simulated. The evolution along the time of the global normal and tangential forces is analyzed, relating it to the local phenomena occurring at the interface. This part tries to investigate how micro-slips at the interface, acting as distributed ruptures, trigger the macro-slips between the two bodies. The interaction between local and global dynamics is also studied. Finally a numerical parameter space study is carried out, as a function of several system parameters (contact law, friction coefficient, material damping, normal load, translational velocity and regularization time). The results show the key role of the micro-slips and precursors (detectable wave propagations that occur at tangential global force well below the critical value expected by the friction law) in triggering the macro-slip between the two bodies. Depending on their distribution and magnitude the evolution of the contact forces passes from stick-slip-like behaviour to continuous sliding. The local dynamics at the contact (wave and rupture propagation) is linked to the global behaviour of the system (stick-slip, continuous sliding, induced vibrations); the effect of the contact and system parameters on the transfer of vibrational energy between the sliding contact and the system is investigated. The numerical results obtained by the two parts of the work show a good agreement with experimental results in literature.