Gap Test of Crack-Parallel Stress Effect on Quasibrittle Fracture and Its Consequences

Hoang Thai Nguyen, Madura Pathirage, Gianluca Cusatis, Zdenek P. Bazant*

*Corresponding author for this work

Research output: Contribution to journalArticle

1 Scopus citations

Abstract

In the standard fracture test specimens, the crack-parallel normal stress is negligible. However, its effect can be strong, as revealed by a new type of experiment, briefly named the gap test. It consists of a simple modification of the standard three-point-bend test whose main idea is to use plastic pads with a near-perfect yield plateau to generate a constant crack-parallel compression and install the end supports with a gap that closes only when the pads yield. This way, the test beam transits from one statically determinate loading configuration to another, making evaluation unambiguous. For concrete, the gap test showed that moderate crack-parallel compressive stress can increase up to 1.8 times the Mode I (opening) fracture energy of concrete, and reduce it to almost zero on approach to the compressive stress limit. To model it, the fracture process zone must be characterized tensorially. We use computer simulations with crack-band microplane model, considering both in-plane and out-of-plane crack-parallel stresses for plain and fiber-reinforced concretes, and anisotropic shale. The results have broad implications for all quasibrittle materials, including shale, fiber composites, coarse ceramics, sea ice, foams, and fone. Except for negligible crack-parallel stress, the line crack models are shown to be inapplicable. Nevertheless, as an approximation ignoring stress tensor history, the crack-parallel stress effect may be introduced parametrically, by a formula. Finally we show that the standard tensorial strength models such as Drucker-Prager cannot reproduce these effects realistically.

Original languageEnglish (US)
Article number071012
JournalJournal of Applied Mechanics, Transactions ASME
Volume87
Issue number7
DOIs
StatePublished - Jul 1 2020

Keywords

  • computational mechanics
  • concrete
  • fiber-reinforced materials
  • finite element analysis
  • fracture mechanics
  • fracture properties
  • fracture testing
  • mixed mode fracture

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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