Crack growth threshold testing with flat-bottom hole specimens and artifact evaluation of electrothermal crack tip marking

• Published in: Engineering fracture mechanics 2021-05, Vol.249, p.107737, Article 107737
• Main Author: Pettit, R.G.
• Format: Article
• Language: English
• Subjects: Amplitudes; Crack growth threshold; Crack initiation; Crack propagation; Crack tips; Electrothermal Crack-Tip Marking; Forging; Fracture surfaces; Marking; Nickel alloy; Titanium alloy
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2021.107737

•Sequel to submission submission EFM-D-20-00898.•Evaluates reduced diameter flat-bottom hole specimen configuration for threshold testing.•Includes K-solution.•Introduces electrothermal crack tip marking process and theoretical basis.•Quantifies artifact associated with electrothermal marking.•Titanium and nickel alloys tested. A prior study [1] benchmarks a relatively new axisymmetric Flat Bottom Hole (FBH) specimen concept for use in crack growth threshold testing, with reduced crack initiation loads achieved by applying by an electrical pulse around the notch tip prior to testing. In this study, an improved electrothermal pulsing technology is used with higher current capability, and more precisely timed pulses. Electrical pulses were applied at high amplitude to initiate the crack at further reduced loads, and also at a lower amplitude to locally heat tint the crack tip during the test to leave visible marks on the fracture surface for post-test evaluation. For specimen, one of the marks was applied at near-threshold conditions before the completion of the threshold test to evaluate whether the marking method introduces artifact into the results. A small, but quantifiable artifact was observed immediately following marking at near threshold conditions, vanishing after 0.001-0.003 in. of crack growth. Test results include data for Ti 6-4 forging and Inconel 718 forging.