Papers by Keyword: Charpy Absorbed Energy

Abstract: Charpy impact toughness values show large statistical scatter, particularly in the ductile-to-brittle transition temperature (DBTT) range. Although the statistical distribution of Charpy absorbed energy has not been clarified, critical values of the stress intensity factor, J-integral and crack-tip opening displacement (CTOD) at brittle fracture generally show the Weibull distribution with two or three parameters. This study proposes a brittle fracture model, based on the weakest link theory, for evaluating the scatter in Charpy absorbed energy KV. The numerical results show that the amplitude of the opening stress fields ahead of the V-notch at varying amounts of KV are uniquely characterized as the square of the applied load. With these numerical results, the Weibull shape parameter of the statistical distribution of KV is almost equal to 2. The proposed statistical model is verified through experimental results. It is found that the statistical distribution of KV is characterized by a two-parameter Weibull distribution with the shape parameter of 2 under the condition of pure brittle fracture.

Abstract: Recently, the weld fractures of column-diaphragm joints were reported to disrupt the cyclic loading tests on steel welded beam-to-column connections in Taiwan. This paper analyzes the root cause leading to the weld fractures. To confirm the effects of electro slag welding (ESW), the hardness, toughness and microstructure are investigated for a SN490B steel column-diaphragm joint. The result shows that the ESW process may give the weld a relatively low hardness. In addition, the heat affected zone (HAZ) can absorb much less energy than the parent material. In detail, the 30-mm thick parent material absorbs energy more than 105J, satisfying the code requirement of 27J at 0oC in the Charpy impact tests. However, the welding heat causes the microstructure of HAZ to be notably coarse, reducing the Charpy value to 21 J. To prevent the weld fractures, it is recommended to refine the grain sizes of HAZ, improving the toughness. It is also suggested to develop and use the compatible welding materials.