A review of the proposed KIsi offset-secant method for size-insensitive linear-elastic fracture toughness evaluation

Douglas N. Wells, Mark A. James, Phillip A. Allen, Kim R.W. Wallin

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Recently proposed modifications to ASTM E399, Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic Materials, would provide a new size-insensitive approach to analyzing the force-displacement test record. The proposed size-insensitive linear-elastic fracture toughness, KIsi, targets a consistent 0.5-mm crack extension for all specimen sizes by using an offset secant that is a function of the specimen ligament length. With intent to increase flexibility in the test method, the KIsi evaluation method removes the Pmax/PQ criterion, which can penalize materials with rising tearing resistance curves, and increases the limits on specimen deformation, which allows more plasticity at the crack tip at the onset of crack extension. The primary motivation for this investigation is to confirm the validity of this new interpretation of the force-displacement test record in regard to the increase in acceptable specimen deformation. This article summarizes a finite element study of the effects of increased crack tip plasticity on the KIsi evaluation method, with two primary points of investigation: the continued validity of linear-elastic fracture mechanics (LEFM) to describe the crack front conditions and the effect of crack tip plasticity on compliance change in the force-displacement record. The analytical study illustrates that LEFM assumptions remain valid at the increased deformation limit; however, the influence of plasticity on the compliance change in the test record is problematic. A proposed revision to the validity criteria for the KIsi test method is described.

Original languageEnglish
JournalMaterials Performance and Characterization
Volume7
Issue number2
DOIs
Publication statusPublished - 31 Jul 2018
MoE publication typeNot Eligible

Fingerprint

Plasticity
Fracture toughness
Crack tips
Cracks
Fracture mechanics
Ligaments
Compliance

Keywords

  • Fracture toughness
  • Linear-elastic
  • Offset secant
  • Size-insensitive

Cite this

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abstract = "Recently proposed modifications to ASTM E399, Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic Materials, would provide a new size-insensitive approach to analyzing the force-displacement test record. The proposed size-insensitive linear-elastic fracture toughness, KIsi, targets a consistent 0.5-mm crack extension for all specimen sizes by using an offset secant that is a function of the specimen ligament length. With intent to increase flexibility in the test method, the KIsi evaluation method removes the Pmax/PQ criterion, which can penalize materials with rising tearing resistance curves, and increases the limits on specimen deformation, which allows more plasticity at the crack tip at the onset of crack extension. The primary motivation for this investigation is to confirm the validity of this new interpretation of the force-displacement test record in regard to the increase in acceptable specimen deformation. This article summarizes a finite element study of the effects of increased crack tip plasticity on the KIsi evaluation method, with two primary points of investigation: the continued validity of linear-elastic fracture mechanics (LEFM) to describe the crack front conditions and the effect of crack tip plasticity on compliance change in the force-displacement record. The analytical study illustrates that LEFM assumptions remain valid at the increased deformation limit; however, the influence of plasticity on the compliance change in the test record is problematic. A proposed revision to the validity criteria for the KIsi test method is described.",
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A review of the proposed KIsi offset-secant method for size-insensitive linear-elastic fracture toughness evaluation. / Wells, Douglas N.; James, Mark A.; Allen, Phillip A.; Wallin, Kim R.W.

In: Materials Performance and Characterization, Vol. 7, No. 2, 31.07.2018.

Research output: Contribution to journalArticleScientificpeer-review

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