Sprecher
Beschreibung
In nickel-based superalloy components operating at high temperatures, such as rotor disks in aero engines, intergranular cracking can be a critical failure mode. The accelerated crack propagation along grain boundaries is driven by the combined effects of fatigue and oxygen diffusion and is described as dynamic embrittlement. The damage mechanism is highly depending on the characterisitics of grain boundarys and limits the application of polycrystalline high-temperature superalloys. Hence, a reliable computational method for the assessment of integranular cracking in polycrystalline alloys is required.
It is the aim of this work to employ cohesive zone models for the description of intergranular fracture and to derive a scaling law that ensures finite-element mesh independent cyclic traction-separation laws (TSL) under fatigue loading. This enables a detailed assessment of intergranular fatigue behavior within the framework of digital material twins. A mechanic cohesive zone model is developed that describes damage initiation and evolution depending on the grain boundary type. The cohesive properties of grain boundaries are derived from atomistic calculations under monotonic loading, and a scaling approach is evaluated to bridge the TSL from the atomistic to the macroscopic scale. The scaling approach of Möller et al. (2018) for bilinear TSL is generalized from simple atom pairs to specific grain boundary types under monotonic loading. To model fatigue crack growth, the TSL is extended to describe damage under fatigue loading using the exponential Xu-Needleman-TSL. The concepts of bilinear and the Xu-Needleman-TSL are analyzed in terms of their scaling behavior.
