Damage Tolerance Assessment of a Paper Pulp Refiner Disk

As long as materials continue to have imperfections in their structure, failure by cracking will continue to be a consideration in design. Cracks may be the result of material in homogeneity, service loading and may also be introduced during the manufacturing of either, the material itself or the structure in which the material is used. In the presence of a crack, a structure is more prone to fail at stress levels lower than those based on standard yield criteria. Components such as rotating machinery store large amounts of energy during operation and a fracture resulting from cracks in the rotating parts can be especially dangerous. Thus it is necessary to consider the failure mode of fracture when designing the disk and this requires a knowledge of the stress intensity factor of the crack in the disk and the fracture toughness of the disk material. In the present work the Boundary Element Method combined with Subtraction of Bueckner Singular Fields is used to obtain weight functions for an internal radial crack in an annular disk. A previously developed, general representation, of the weight function leads to integrals that can be evaluated analytically to obtain the stress intensity factor. Stress intensity factors are determined for the disk, containing a radial crack in a typical pulp refiner and the minimum level of fracture.