![]() #Crack atelier scientifique crackThe knowledge on the crack macro mechanisms could also improve the process of hydraulic fracturing. The understanding of this phenomenon could lead to the design of energy-absorbing materials due to a correlation between the fracture toughness and the number of branches. The macro crack branching in brittle materials is an unstable dynamic phenomenon which occurs when a single crack achieves a critical speed. Modeling of macro crack branching with continuum damage model ![]() On the other hand, macroscopic models can be useful to provide to the discrete modeling more precise loading conditions, since the real loading (impact for instance) and the global structural mechanisms (global bending, shear cone) can be reproduced. Discrete models allow to reproduce these different phenomena, while they are considered phenomenologically in a continuum damage model. In quasi-static, the breakdown usually comes from the propagation of a unique macro-crack. Indeed, if the strain rate increases, materials exhibit a higher strength in tension, which is generally assumed to be the consequence of the coalescence of multiple cracks. In particular, the damage evolution law parameters can be fitted, and especially the strain rate effects. Modeling explicitly the cracks enables to understand the local mechanisms of failure and calibrate the macroscopic damage models. In that case, we rather use continuum models, such as damage models, where the cracks are not reproduced but considered through a variable that describe the degradation of the elastic properties.įigure 1 : Representation of a discrete crack by a continuous field ![]() For computational cost reasons, it is not possible then to lead a computation at the scale of a structure. The disadvantage of these methods, especially when high strain rates are considered, is that a fine spatial discretization is needed to reproduce the complex cracks patterns obtained (including merging, branching and instabilities). Discrete models are used in this case, or finite elements coupled with the cohesive elements approach. At the fine scale, we want to describe explicitly the cracks, from their initiation to their propagation and coalescence. Two levels of prediction are then necessary. For a reinforced concrete structure, the consequences are in general the development of a crack network, which can possibly lead to the ruin of the structure, but also for example to the loss of impermeability of confinement wall. At LSMS, a strong focus is on dynamic loadings, such as impacts or explosions. For safety reasons, for instance in civil engineering, it is important to be able to predict the damage encountered by a structure after an accidental event. ![]()
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