Fractional order viscoplastic modeling of anisotropically overconsolidated clays with modified isotach viscosity

Wei Cheng, Zhen Yu Yin

Research output: Journal article publicationJournal articleAcademic researchpeer-review

3 Citations (Scopus)


Current overstress typed elastic viscoplastic models fall short in describing some time-dependent mechanical behaviors of anisotropically overconsolidated clays comprehensively. This paper presents a rigorous fractional order anisotropic elastic viscoplastic two-surface model for such clays, based on the principles of fractional consistency viscoplasticity and bounding or subloading surface theory. First, a three-dimensional formulation of isotach viscosity is proposed and integrated into two rate-dependent surfaces, i.e., the loading surface and yield surface. Then, by incorporating the stress-fractional operator of the rate-dependent loading surface into isotropic, progressive, and rotational hardening rules, the incremental form of stress-strain-time model with a fractional order viscoplastic flow rule is developed by meeting the consistency condition on the loading surface. Accordingly, the proposed model cannot only maintain the predictive capabilities of a classic bounding surface model but also describe the general features of the time-dependent behavior under various stress conditions. Validation and versatility of the proposed fractional order elastic viscoplastic model are successfully evaluated against constant strain-rate and stress relaxation tests on anisotropically overconsolidated resedimented Boston Blue clay.

Original languageEnglish
Article number103858
JournalInternational Journal of Plasticity
Publication statusPublished - Jan 2024


  • Anisotropy
  • Fractional derivative
  • Isotach
  • Overconsolidated clay
  • Two-surface model
  • Viscoplasticity

ASJC Scopus subject areas

  • General Materials Science
  • Mechanics of Materials
  • Mechanical Engineering


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