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| THE HYDROGEN-INDUCED DELAYED FRACTURE OF TYPE Ⅲ CRACK SPECIMENS |
| Chu Wuyang Ju Shuryahn Hsiao Chimei and Wang Cheng (Beijing University of Iron and Steel Technology) |
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Abstract The effect of the stress state on the apparent yield stress, which is the external stress required to cause the local macroscopic plastic deformaton, is investigated with combined type(Ⅰ+Ⅲ)specimen. The possibility of hydrogen embrittlement, i. e. hydrogen induced cracking of the type Ⅲ specimen is investigated. The results show that the apparent torsional yield stress of the severely charged type Ⅲ specimens does not decrease, and then the hydrogen induced delayed crackingand fracture cannot occur on the original crack plane. For combined type (Ⅰ+Ⅲ)specimen, the apparent torsional yield stress can be decreased only when K_1 is so large that hydrogen induced delayed plastic deformation can occur under the action of K_1 itself. For the charged type Ⅲ crack or notch specimen, the hydrogen induced delayed cracking can occur on the plane inclined at an angle of 135°(or -45°) to the original crack plane when a large enough torque is sustained for a long time. This delayed failure is a typical intergranular fracture. The plane shear fracture can be obtained on the original crack if the charged type Ⅲ specimen is twisted to fracture immediately. For uncharged or outgassing type Ⅲ specimen, no delayed cracking and failure occurs even if a maximum torque is sustained for a long time. The interactive energy between the stress field of type Ⅲ crack and the strain field of hydrogen atom is calculated. The result shows that the interactive energy has a minimum value on the plane inclined at an angle of 135° (or-45°) to the original crack plane. Therefore, atomic hydrogen will diffuse to and enrich into these planes. The hydrogen induced delayed cracking and fracture will occur on the plane inclined at an angle of 135° to the original crack plane when the hydrogen concentration on the plane reaches a critical value.
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Received: 25 June 1982
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