Session: MF-15-01 Fatigue and Fracture of Welds and Heat Affected Zones

Paper Number: 106317

106317 - Investigation on a Method of Counting Low-Cycle Fatigue in Steel Under Crack Closure and Random Variable Amplitude Loading 

Low-cycle fatigue (LCF) plays an important role in the evaluation of steel structures subjected to earthquakes, such as line pipes, power plants, and buildings. In LCF, fracture is caused by the propagation of cracks generated by large deformations. Therefore, it is important to predict how the cracks will grow. LCF approaches allow obtaining the relationship between the amplitude and the number of cycles of fracture. However, the conventional method for predicting the number of cycles of fracture in LCF is incomplete because of two reasons. First, the amplitude is random in a real environment. Second, the conventional counting method of the number of cycles of fracture cannot be applied to the vibration after crack initiation because crack closure occurs. This means that the conventional method also includes invalid cycles which do not contribute to crack extension due to the crack closure phenomenon. In other words, a mechanism for predicting the number in a random amplitude situation is required. Thus, methods for predicting have been proposed by many researchers.

The authors have developed a quantitative and predictive method to assess the material subjected to random pre-strain cycle patterns, considering a method to quantify material damage and the Bauschinger effect. In the present study, the authors use the back stress tensor to elaborate a model to assess LCF cases from specimens notched on both sides. In addition, the relationship between vibration history at a constant amplitude and the number of cycles of fracture were obtained and an investigation was conducted to quantify the effect of crack closure on crack growth.

Presenting Author: Jo Watanuki The University of Tokyo

Presenting Author Biography: Jo Watanuki is a student in a master's course at the graduate school of the University of Tokyo, supervised by Professor Tomoya Kawabata, who is a Fracture Mechanics specialist. He graduated from Hyogo Prefectural Kakogawa Higashi High School in 2018 and the faculty of engineering at Chiba University in 2022. He then entered Department of Systems Innovation, School of Engineering, The University of Tokyo, in 2022 and is currently a first-year student in a master's course. He focuses specifically on low-cycle fatigue and its impact on steel structures. Makuhari beach is his favorite place to study watching a spectacular sunset.

Authors:

Jo Watanuki The University of Tokyo
Tomoya Kawabata The University of Tokyo
Shunsuke Takagi Tokyo Electric Power Company Holdings, Inc.