Characterization of Hydrogen-Induced Contact Fracture in High-Strength Steel

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Akio Yonezu ◽  
Michihiro Niwa ◽  
Xi Chen
Keyword(s):  
Crack Propagation ◽  
Hydrogen Content ◽  
High Strength Steel ◽  
Cohesive Zone Model ◽  
High Strength ◽  
Zone Model ◽  
Cracking Behavior ◽  
Stress Criterion ◽  
Contact Fracture ◽  
Fracture Damage

This study investigated the hydrogen embrittlement (HE) cracking behavior produced by local contact loading of high-strength steel. When a spherical impression was applied to a hydrogen-absorbed high-strength steel, HE induces contact fracture, where radial cracks are initiated and propagated from the indentation impression. The length of the radial crack was found to be dependent on the hydrogen content in the steel as well as the applied contact force. A combined experimental/computational investigation was conducted in order to clarify the mechanism of hydrogen-induced contact fracture. In the computation, crack propagation was simulated using a cohesive zone model (CZM) in finite element method (FEM), in order to elucidate stress criterion of the present HE crack. It was found that the normal tensile stress was developed around impression, and it initiated and propagated the HE crack. It was also revealed that the hydrogen content enhanced contact fracture damage, especially the resistance of crack propagation (i.e., threshold stress intensity factor, Kth). The findings may be useful for countermeasure of contact fracture coupled with hydrogen in high-strength steel. Such phenomenon is potentially experienced in various contact components in hydrogen environment.

Effect of defect length on rolling contact fatigue crack propagation in high strength steel

2015 ◽  
Author(s):  
T. Makino ◽  
Y. Neishi ◽  
D. Shiozawa ◽  
Y. Neishi ◽  
D. Shiozawa ◽  
...  
Keyword(s):  
Crack Propagation ◽  
High Strength Steel ◽  
Rolling Contact Fatigue ◽  
Contact Fatigue ◽  
High Strength ◽  
Rolling Contact ◽  
Micro Ct ◽  
Middle Line ◽  
Micro Computed Tomography ◽  
Depth Direction

 The objective of the present paper is to clarify the effect of defect length in depth direction on rolling contact fatigue (RCF) crack propagation in high strength steel. RCF test and synchrotron radiation micro computed tomography (SR micro CT) imaging were conducted. In the case of the defect with the 15 ?m diameter, flaking life decreased with increasing defect length. In a comparison of the CT image and the SEM view, the shapes of defects and the locations of the horizontal cracks were almost the same respectively. The mechanism of RCF crack propagation was discussed by finite element (FE) analysis. Defects led to higher tensile residual stress than that without defects in the region where the defect exists. The shear stress range at 0.1 mm in depth on the middle line of the defect and the range of mode II stress intensity factor at the bottom of a vertical crack increased with increasing defect length.

Modeling of Crack Growth in Thin Sheet Aluminum

1999 ◽  
Author(s):  
T. Siegmund ◽  
W. Brocks ◽  
J. Heerens ◽  
G. Tempus ◽  
W. Zink
Keyword(s):  
Crack Growth ◽  
Cohesive Energy ◽  
Cohesive Zone Model ◽  
Plastic Material ◽  
Thin Sheet ◽  
High Strength ◽  
Cohesive Strength ◽  
Zone Model ◽  
Additional Material ◽  
Center Crack

Abstract The present study reports on the application of a cohesive zone model to the analyses of crack growth in thin sheet specimen of a high strength aluminum alloy. In addition to the elastic-plastic material properties, the two parameters cohesive strength and cohesive energy describe material separation. For the sheet specimen under investigation the cohesive energy is determined via a numerical-experimental approach using tests on notched tensile specimens as well as a damage indicator. The cohesive energy is found to be close to the corresponding value of plane strain fracture toughness. The cohesive strength is approximately twice the yield strength. With these two additional material parameters being determined crack growth experiments in center crack panels are analyzed. Good agreement with experimental records is found. Finally the applicability of the model to study complex crack configurations as in multi-site damaged specimens is demonstrated.

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