Dynamic fracture of a discrete media under moving load

Most of the research concerting crack propagation in discrete media is concerned with specific types of external loading: displacements on the boundaries, or constant energy fluxes or feeding waves originating from infinity. In this paper the action of a moving load is analysed on the simplest lattice model: a thin strip, where the fault propagating in its middle portion as the result of the moving force acting on the destroyed part of the structure. We study both analytically and numerically how the load amplitude and its velocity influence the possible solution, and specifically the way the fracture process reaches its steady-state regime. We present the relation between the possible steady-state crack speed and the loading parameters, as well as the energy release rate. In particular, we show that there exists a class of loading regime corresponding to each point on the energy-speed diagram (and thus determine the same limiting steady-state regime). The phenomenon of the forbidden regimes is discussed in detail, from both the points of view of force and energy. For a sufficiently anisotropic structure, we find a stable steady-state propagation corresponding to the slow crack. Numerical simulations reveal various ways by which the process approaches - or fails to approach - the steady-state regime. The results extend our understanding of fracture processes in discrete structures, and reveal some new questions that should be addressed

Universality classes of transition fronts in the FPU model

Steady transition fronts in nonlinear lattices are among the most important dynamic coherent structures. We use the Fermi-Pasta-Ulam model with piecewise linear nonlinearity to show that there are exactly three distinct classes of such fronts which differ fundamentally in how (and whether) they produce and transport oscillations. To make this Hamiltonian problem analytically transparent, we construct a quasicontinuum approximation generating all three types of fronts and then show that the interconnection between different classes of fronts in the original discrete model is the same as in the quasicontinuum model. The proposed framework unifies previous attempts to classify the transition fronts as radiative, dispersive, topological or compressive and categorizes them instead as different types of dynamic defects

Influence of fracture criteria on dynamic fracture propagation in a discrete chain

The extent to which time-dependent fracture criteria affect the dynamic behavior of fracture in a discrete structure is discussed in this work. The simplest case of a semi-infinite isotropic chain of oscillators has been studied. Two history-dependent criteria are compared to the classical one of threshold elongation for linear bonds. The results show that steady-state regimes can be reached in the low subsonic crack speed range where it is impossible according to the classical criterion. Repercussions in terms of load and crack opening versus velocity are explained in detail. A strong qualitative influence of history-dependent criteria is observed at low subsonic crack velocities, especially in relation to achievable steady-state propagation regimes

Analysis of dynamic failure of the discrete chain structure with non-local interactions

In the present work the steady-state crack propagation in a chain of oscillators with non-local interactions is considered. The interactions are modeled as linear springs while the crack is presented by the absence of extra springs. The problem is reduced to the Wiener-Hopf type and solution is presented in terms of inverse Fourier transform. It is shown that the non-local interactions may change the structure of the problem solution well-known from the classical local interactions formulation. In particular, it may change the range of the region of stable crack motion. The conclusions of the analysis are supported by numerical results. Namely, the observed phenomenon is partially clarified by evaluation of the structure profiles on the crack line ahead