Towards validation of crack nucleation criteria from V-notches in quasi-brittle metallic alloys: Energetics or strength?

Tianchen Hu, John E. Dolbow, Zohar Yosibash

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


We discuss crack nucleation observations from a series of experiments that have proven to be particularly challenging for model validation. In particular, we focus attention on crack nucleation from a series of V-notched specimens of an AISI 4340 steel alloy subjected to four-point bending. Details of the specimen geometry, loading, and experimentally-measured forces are provided for V-notches with opening angles of 30, 60, and 90 degrees. Despite the relatively simple geometry and loading, and the fact that the specimens exhibit small scale yielding, model-based simulations that can accurately reproduce the critical forces at crack nucleation across the full set of specimens have proven to be elusive. Along these lines, we present model-based simulation results from finite-element discretizations of phase-field models for fracture. We provide results using both a well-established phase-field model for brittle materials as well as a recently-developed phase-field model for ductile materials. Importantly, both models tie crack nucleation to critical values of energy, and both are shown to be lacking in their accuracy to varying degrees. We also use standard finite-element calculations of a calibrated plasticity model to demonstrate that much greater accuracy in the calculated critical forces can be obtained with the use of a particular strength envelope.

Original languageEnglish
Article number115419
JournalComputer Methods in Applied Mechanics and Engineering
StatePublished - 1 Dec 2022
Externally publishedYes


  • Crack nucleation
  • Phase-field for fracture
  • Quasi-brittle materials
  • Strength envelope
  • V-notches

ASJC Scopus subject areas

  • Computational Mechanics
  • Mechanics of Materials
  • Mechanical Engineering
  • General Physics and Astronomy
  • Computer Science Applications


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