Dynamic Fracture Mechanics
Covering a wide variety of topics in dynamic fracture mechanics, this volume presents state-of-the-art experimental techniques and theoretical analysis on dynamic fracture in standard and exotic materials.
TABLE OF CONTENTS Dynamic Fracture Mechanics
4: Dynamical crack tip instabilities
4 Dynamical crack tip instabilities
Cracks moving at low speeds create atomically flat mirror-like surfaces, whereas cracks at higher speeds leave misty and hackly fracture surfaces. This change in fracture surface morphology is a universal phenomenon found in a wide range of different brittle materials. The underlying physical reason of this instability has been debated over an extensive period of time.
Most existing theories of fracture assume a linear elastic stress-strain law. However, from a hypcrelastic point of view, the relation of stress and strain in real solids is strongly nonlinear near a moving crack tip. Using massively parallel large-scale atomistic simulations, we show that hypeielasticity also plays an important role in dynamical crack tip instabilities. We find that the dynamical instability of cracks can be regarded as a competition between different instability mechanisms controlled by local energy flow and local stress field near the crack tip. We hope the simulation results can help explain controversial experimental and computational results.
4.1 Introduction
Here we focus on the instability dynamics of rapidly moving cracks. In several experimental [25, 64, 74, 75] and computational [20, 22, 26, 76, 77] studies, it was established that the crack face morphology changes as the crack speed increases, a phenomenon which has been referred to as the dynamical instability of cracks. Up to a critical speed, newly created crack surfaces are mirror flat (atomistically flat in MD simulations), whereas at higher speeds, the crack surfaces start to roughen (mist regime) and eventually becomes very rough (hackle...
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