Hydrogen and Notch Effects on Torsional Fatigue of Stainless Steel

This work investigates the axial-torsional fatigue and cyclic deformation behaviour of 304L stainless steel at room temperature. Four fully reversed strain-controlled loading paths (axial, torsional, proportional axial-torsional, and 90º out-of-phase axial-torsional) and a fully-reversed shear strain-controlled with static axial stress loading were investigated. For axial, torsional, torsional with static stress and few proportional experiments, an initial cyclic softening was followed by secondary hardening related to martensitic transformation. Secondary hardening was not observed for non-proportional loading nor for some proportional experiments. The influence of the non-stabilized cyclic deformation behaviour on the fatigue life estimates of two multiaxial critical plane fatigue models (Smith–Watson–Topper and Fatemi–Socie) was investigated. Life estimates based on the stress-strain hysteresis loops corresponding to the maximum softening and to the half-life were similar for the two models.

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Results of in-phase axial-torsional fatigue experiments on 304 stainless steel. (Report)Bonacuse, P.J. and Kalluri, S. NASA Tech. Memo TM-101464 1989, 19 pp

International Journal of Fatigue ◽

10.1016/0142-1123(89)90175-8 ◽

1989 ◽

Vol 11 (5) ◽

pp. 374-374

Keyword(s):

Stainless Steel ◽

304 Stainless Steel ◽

Torsional Fatigue ◽

Nasa Tech

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Failure analysis of eleven Gates Glidden drills that fractured intraorally during post space preparation. A retrieval analysis study

Biomedical Engineering / Biomedizinische Technik ◽

10.1515/bmt-2016-0245 ◽

2018 ◽

Vol 63 (4) ◽

pp. 407-412

Author(s):

Youssef S. Al Jabbari ◽

Raymond Fournelle ◽

Sara M. Al Taweel ◽

Spiros Zinelis

Keyword(s):

Stainless Steel ◽

Root Canal ◽

Fatigue Cracks ◽

Microstructural Analysis ◽

Acrylic Resin ◽

Sem Analysis ◽

Root Canal Preparation ◽

Torsional Fatigue ◽

Hand Piece ◽

Macroscopic Observation

Abstract The purpose of this study was to determine the failure mechanism of clinically failed Gates Glidden (GG) drills. Eleven retrieved GG drills (sizes #1 to #3) which fractured during root canal preparation were collected and the fracture location was recorded based on macroscopic observation. All fracture surfaces were investigated by a SEM. Then the fractured parts were embedded in acrylic resin and after metallographic preparation, the microstructure and elemental composition was evaluated by SEM and EDS. The Vickers hardness (HV) of all specimens was also determined. Macroscopic examination and SEM analysis showed that the drills failed near the hand piece end by torsional fatigue with fatigue cracks initiating at several locations around the circumference and propagating toward the center. Final fracture followed by a tensile overloading at the central region of cross section. Microstructural analysis, hardness measurements and EDS show that the drills are made of a martensitic stainless steel like AISI 440C. Based on the findings of this study, clinicians should expect fatigue fracture of GG drills that have small size during root canal preparation. Selection of a more fatigue resistant stainless steel alloy and enhancing the instrument design might reduce the incidence of quasi-cleavage fracture on GG drills.

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