Brittle/quasi-brittle transition in dynamic fracture: An energetic signature

TL;DR

This study investigates the energetic and fractographic signatures of a brittle/quasi-brittle transition in dynamic fracture of PMMA, revealing a critical velocity where fracture energy increases sharply and microcracking patterns emerge.

Contribution

It introduces a simple model linking energetic and fractographic data, highlighting a brittle/quasi-brittle transition in amorphous materials during dynamic fracture.

Findings

Fracture energy increases threefold at a critical velocity.

Conic patterns on fracture surfaces indicate damage spreading.

Transition occurs below the micro-branching instability velocity.

Abstract

Dynamic fracture experiments were performed in PMMA over a wide range of velocities and reveal that the fracture energy exhibits an abrupt 3-folds increase from its value at crack initiation at a well-defined critical velocity, below the one associated to the onset of micro-branching instability. This transition is associated with the appearance of conics patterns on fracture surfaces that, in many materials, are the signature of damage spreading through the nucleation and growth of microcracks. A simple model allows to relate both the energetic and fractographic measurements. These results suggest that dynamic fracture at low velocities in amorphous materials is controlled by the brittle/quasi-brittle transition studied here.