Modelling short crack propagation in a single crystal nickel-based superalloy using crystal plasticity and XFEM

Abstract

Short cracks appearing under fatigue conditions are of major concern for safety-critical components. In this paper, a computational approach based on crystal plasticity and extended finite element method is developed to predict the slip-controlled short crack growth in a single crystal nickel-based superalloy. The onset of fracture is controlled by cumulative shear strain of individual slip system and the direction of crack growth follows crystallographic slip plane. Simulations are carried out for [111] orientation at 24 °C and 650 °C, and the results confirm the capability of this approach in predicting the tortuous crack path and irregular propagation rate.

Discrete crystal plasticity modelling of slip-controlled cyclic deformation and short crack growth under low cycle fatigue

“…By comparing collected CRSS data from existing experimental work (Fig. 2b) [37,47,[57][58][59], the following relationship is proposed…”

“…A total of 125280 eight-node brick element (C3D8) elements with an average size of ~0.5 μm were contained in this area. The rest of the domain was assigned the CP model calibrated in our previous work [37] and discretised into 5792 C3D8 elements and 1526 six-node linear triangular prism (C3D6) elements. A predefined crack of 12 μm was introduced to the centre of the notch to reflect the initiation of the crack observed experimentally (see the magnified section in Fig.…”

“…Each integration point of an element will have its own indicating value, and an element will be deleted when all integration points have zero indicating values. In this work, considering the slipcontrolled crack growth behaviour observed in the in-situ SEM experiments, the individual cumulative shear strain (ICSS) proposed by [37] was utilised as a damage criterion to reflect the contribution of each slip system, which is defined as…”

“…The CP parameters calibrated in Section 4.1 were used in these simulations. Here 175 °C temperature difference between the crack growth experiment (650 °C) and the LCF (825 °C) experiment used for CP model parameter calibration is not expected to significantly affect the macroscopic response or change the distribution of plastic deformation on each slip system [37]. Also, the aim of this work was to examine the capability of the discrete slip band model in simulating the slip-controlled short crack propagation which is mainly dependent on crystal orientation, therefore the difference caused by temperature was neglected in our current study.…”

“…This method can recover the alternating crack path and the variations in propagation rates in both single crystals and polycrystals. In another XFEMbased study [37], the cumulative shear strain of individual slip system was adopted as a criterion to predict the slip-controlled crack growth in a single-crystal nickel-based superalloy. The experimentally observed zig-zag crack paths were captured and analysed by tracking the activities of slip systems near the crack tip.…”