Slow crack propagation

A short summary of this paper. Slow crack propagation in heterogeneous materials. Kierfeld1 and V. Using the generalized Griffith criterion we derive the equation of motion for the crack tip position accounting for dissipation, thermal noise, and the random forces arising from the defects.

We find that aggregations of defects generating long-range interaction forces e. We demonstrate that heterogeneous materials with frozen defects contain a large number of arrested microcracks and that their fracture toughness is enhanced to the experimentally accessible time scales. DOI: Mk, Np Fracture mechanisms and their relation to the material the elastic medium, and iii frozen dislocations interacting structure is a long-standing problem [1].

Ideal crystals are with the crack. The range of elastic interactions with the subject to fast brittle fracture —as was first explained by crack tip increases when going from the type i , to Griffith [2]—while homogeneously amorphous systems types ii and iii.

Real materials are neither heterogeneities inducing long-range elastic forces, i. Real crystals do contain defects; but even in frozen dislocations iii. We show that thermally activated the ultimately disordered substances the defects are not cracks exhibit anomalously slow dynamics with vanishing distributed homogeneously but form spatially inhomoge- mean velocity for all three types of disorder. It is intuitively plausible that defect propagation and derive experimentally observable charac- aggregates promote crack nucleation as the crack can settle teristic material properties such as the statistics of the at an energetically favorable nucleation site.

At the same critical stresses and the power-law distributions of crack time one can expect that random heterogeneities impede waiting times. This explains that in materials containing the subsequent crack propagation process as shown in long-range structural defects arrested microcracks are ex- Fig.

This poses the important question about the ultimate perimentally observable [7]. In a perfectly homogeneous elastic me- nucleation of critical cracks. The tigate fracture probabilities and the statistics of the fracture driving force for the crack tip advance is the release of the times.

We consider both zero- and finite-temperature crack dynamics, the latter being governed by thermal activation. In two dimensions a crack front is a point—the crack tip; thus the additional effects arising from crack front roughening are absent. Left: Sketch of an arrested crack solid ellipse in a tip. We include both dissipative and thermal forces, and the random array of frozen dislocations with cores represented by position-dependent random forces acting on the crack tip symbols?

We discuss three basic kinds crack nucleation. We adapt Gaussian distributed overdamped dynamics. It was shown in Ref. Bal- defects [8]. The approximation in Eq. For give rise to activated crack propagation. B Phys. C Phys. D Phys. E Phys. Research Phys. Beams Phys. ST Accel. Applied Phys. Fluids Phys. Materials Phys. ST Phys.

At high crack velocities the properties of the composite depend on the properties of the polymeric matrix, the filler, and the filler volume fraction, but at low velocities the interface is the controlling factor in the durability of these composites exposed to an aqueous environment. Abstract The double-torsion test technique was used to study slow crack propagation in a set of dental composite resins including two glass-filled and two microfilled materials.

Publication types Research Support, Non-U.