Energy Release Rate for a Crack in a Tilted Block

Abstract

Abstract Approximate relations were obtained previously for the tilting stiffness of a rubber block bonded between two rigid plates, assuming linear elastic behavior.1 They take into account restrictions placed on the deformation by the bonded surfaces, a feature that becomes extremely important for thin blocks of an incompressible material. Results are reviewed here for two special cases: an infinitely wide or a relatively narrow block. In both cases the length and width are assumed to be large compared to the block thickness. Approximate values are then derived for the energy release rate G for a relatively deep crack running into the block on the tension side, parallel to the bonded surface. Values for tilting stiffness and energy release rate have also been calculated by finite element analysis (FEA) for slightly compressible rubber blocks, with Poisson's ratio in the range: 0.49 to 0.5, and for blocks of various thicknesses. Good agreement is obtained with the approximate theory for deep cracks, when the assumptions on which the theory is based are more likely to be valid. Application of repeated tilting deformations to a bonded rubber block appears to be a simple way of measuring crack growth rates under mechanical fatigue. Moreover, a wide range of energy release rates can be employed using a single specimen.