How gap tests of ductile and quasibrittle fracture limit applicability of phase-field, XFEM, cohesive, nonlocal and crack-band models?

• Published in: Computational Modelling of Concrete and Concrete Structures pp. 409 - 413
• Main Authors: Bažant, Z.P., Dönmez, A.A., Nguyen, H.T.
• Format: Book Chapter
• Language: English
• Published: CRC Press 2022
• Edition: 1
• Subjects: Quasibrittle Materials; Crack Band Model; Size Effect Law; Damage Constitutive Model; Energy Balance; FPZ; Polycrystalline Metals; YZ; Energy Release Rate; Fracture Parameters; LEFM; Gap Tests; Fracture Energy; Small Scale Yielding; Transitional Range; General Scaling Laws; Size Effect Curves; Ductile Fracture; Plastic Hardening; Cohesive Crack Models; Size Effect Method; Fracture Front; Energy Conservation; Sel; Crack Tip
• ISBN: 9781032328454; 9781032327242; 1032328452; 1032327243
• DOI: 10.1201/9781003316404-48

The recently developed gap test exploits the size effect method to determine the effect of crackparallel compression σxx on the material fracture energy, Gf , as well as the characteristic size cf of the fracture process zone (FPZ). The previous gap tests demonstrated that the Gf of concrete can get doubled or reduced to almost zero according to the T-stress (crack-parallel stress) level. A subsequent study of aluminum fracture (Nguyen, Dönmez and Bažant, 2021) concluded that a similar effect exists in ductile fracture of polycrystalline plastic-hardening metals. This paper strengthens this conclusion by presenting and interpreting further gap tests of aluminum. Together with the results of the recent gap tests of crack-parallel stress effect in quasibrittle materials, the experimental evidence shows that the linear elastic fracture mechanics (LEFM), its computational versions XFEM and Phase-Field, and the cohesive crack models are inapplicable in the presence of significant crackparallel stress-not only for concrete and other quasibrittle materials but also for plastic-hardening polycrystalline metals. On the other hand, the applicability of the crack band model with a realistic tensorial damage law is not limited.