Session: MF-02-05 Materials for Hydrogen Service (Joint with CS-02 and HT-07) - Specimen Size and Rate Effects

Paper Number: 105971

105971 - Fracture Toughness Evaluation for an Ultra-High Strength Steel in High-Pressure Hydrogen Environment Ii: Effect of Specimen Thickness on Fracture Toughness 

To improve the environmental performance of automobiles for minimizing CO2 emission, the use of ultra-high-strength steel sheets is an effective way to reduce the weight of automobile bodies. It is well known that, in metallic materials, fracture toughness is dependent on the plate thickness, but the thickness effect in high strength steel has yet to be clarified in sufficient detail. Moreover, the fracture toughness of high-strength steel is significantly reduced by hydrogen. Therefore, it is essential to consider both the effects of thickness and hydrogen in the strength design in order to accelerate the implementation of thinner, higher-strength steel sheets. In this study, fracture toughness tests of a 1.7 GPa class steel were carried out in air and 90 MPa hydrogen gas using a 1.6 mm-thick, middle-crack tension (MT) specimen and 6-10 mm-thick, compact tension (CT) specimens. The hydrogen gas environment significantly degraded the fracture toughness as compared to air, in both of which the value measured with 1.6 mm-thick specimen was higher than those measured with the thicker specimens. Based on the experimental results in conjugation with the fractographic observation and elasto-plastic finite element analysis for the mechanical state ahead of crack front, the thickness effect under the influence of hydrogen is studied.

Presenting Author: Hisao Matsunaga Kyushu University

Presenting Author Biography: Work experience
• Professor, Department of Mechanical Engineering, Kyushu University, 2017-present.
• Associate Professor, Department of Mechanical Engineering, Kyushu University, 2012-2017.
• Visiting Scholar, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 2010-2011.
• Associate Professor, Department of Mechanical Engineering, Fukuoka University, 2005-2012.
• Lecturer, Department of Mechanical Engineering, Kyushu University, 2002-2005.
• JSPS Research Fellowship for Young Scientists, 1999-2002.

Main fields of competence
• Fracture Mechanics, Metal Fatigue, Hydrogen Embrittlement, Multiaxial Fatigue, Rolling Contact Fatigue.
• Reviews of domestic regulations and international standards for metallic materials used in high-pressure hydrogen gas environment.
• Experience within teaching and supervision on BSc, MSc and PhD level at Kyushu University and Fukuoka University.

Authors:

Yuya Tanaka Fukuoka University
Naoki Hirakawa Graduate School of Kyushu University
Hisao Matsunaga Kyushu University
Kaneaki Tsuzaki National Institute for Materials Science (NIMS)
Akinobu Shibata National Institute for Materials Science (NIMS)