COMPLAS 2023

Accelerated Fatigue Crack Growth Analysis Based on Phase Field Modeling

  • Kristensen, Philip (Technical University of Denmark)
  • Golahmar, Alireza (Technical University of Denmark)
  • Martínez-Pañeda, Emilio (Imperial College London)
  • Niordson, Christian (Technical University of Denmark)

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Phase field modelling of fracture presents a versatile method for analysing complex crack problems where predictions of crack paths naturally result from numerical analyses. The method has been applied to a variety of fundamental problems across many scales from the micromechanical to the structural scale. While initially formulated for brittle failure based on Griffith’s energy principle, phase field methods have been extended to a variety of physical problems including ductile failure, environmental assisted cracking and fatigue. Based on a cyclic degradation framework, the phase field model is often based on a cycle by cycle approach modelling a number of load increments through each load cycle. This has been shown to allow modelling of different SN curves and Paris-law behaviours. In high-cycle fatigue accelerated solutions strategies are needed in order to model a technologically relevant number of load cycles. This has been approached by cycle jump methods where the local damage variable is extrapolated for a number of cycles. In this work two novel methods for accelerating fatigue crack growth calculations are proposed. The first is a Modified Newton Method, which is useful when only small changes to the physical system take place for each load cycle – a condition usually valid for high-cycle fatigue. The second method proposed is to accelerate the numerical analysis by using just a single load step per cycle based on a novel fatigue accumulation strategy. Each of these acceleration strategies speed fatigue calculations significantly, and they may even be used in conjunction. The methods proposed are discussed in relation to analyses of a single edge notched tension specimen, an asymemetric three point bending specimen containing three circular holes, and a three dimensional beam problem with a tilted edge crack. It is demonstrated how the acceleration scheme allows for modelling hundreds of thousands of load cycles without significant loss of model accuracy.