Effect of a graded interlayer on the stress intensity factor of cracks in a joint under thermal loading

In a bimaterial joint with and without a graded interlayer, the stress intensity factor of cracks perpendicular to the interface was calculated for a thermal loading by a homogeneous change in the temperature. In joints without an interlayer, the stress intensity factor increases to infinity as the crack approaches the interface for the case of the Young’s moduli E₁/E₂>1 (crack in material 1). Introducing a graded interlayer with a continuous transition in the material properties between the two joined materials leads to a continuous change in the stress intensity factor if the crack propagates from material 1 into material 2. Results are presented for different transition functions of the material properties and for different thickness ratios of the layers. The possible beneficial effect of a graded interlayer is discussed.