**Published:** Jan 1977

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**Source: **STP627-EB

The strain energy released per unit of axisymmetric crack surface created statically can be expressed in terms of a J-integral related quantity. However, as soon as the crack starts to move only part of this energy will actually flow to the dissipative regions close to the crack tip and the rest will be distributed as kinetic and potential energy in the structure.

An energy balance at the crack tip requires that the flow of energy to the tip must be equal to the fracture energy, which for a given material is supposed to be a specific function of the crack-tip velocity. The energy flow is assumed to be expressible as the static strain energy release rate, times a dynamic screening function, which depends on the instantaneous crack-tip velocity only.

By using numerically calculated values for the strain energy release rate, an analytic expression for the dynamic screening function, and experimentally found data for the velocity dependence of the fracture energy, it has been possible to predict the motion of a penny-shaped crack in a bar of polymethylmethacrylate under uniaxial tension. The agreement with a small series of simple experiments is good.

**Keywords:**

axisymmetric, crack propagation, nonuniform velocity, penny shaped, polymethylmethacrylate, J-integral, quasi-dynamics, dynamics, fracture properties

**Author Information:**

Bergkvist, H *Senior staff scientist, Institut CERAC S.A., Centre Europeen de Recherches, Atlas Copco, Ecublens,*

**Committee/Subcommittee:** E08.03

**DOI:** 10.1520/STP27396S