Moving cracks in viscoelastic materials: temperature and energy-release-rate measurements

A novel set up is proposed to measure the energy release rate versus crack propagation speed in viscoelastic materials. The new test is referred to as the square sample tear test. In comparison to other techniques as the pure shear specimen and the pure tensile specimen tests, the square sample geometry guarantees at the same time: (i) a constant flux of elastic energy at the crack tip, (ii) the full development of the annular dissipative region around the crack tip, where the material is in the transion region of the viscoelastic response spectrum. Both conditions allow to precisely control the crack propagation speed and to test the predictions of existing theories. By employing the new set-up we measure the energy release rate as a function of the crack propagation speed. We also measure with a high precision infrared camera the increase of temperature at the crack tip, showing that, notwithstanding the low speed regime considered during the experiments, the viscoelastic dissipation at the crack tip leads to a measurable temperature increase of about 1◦C