タービン翼溝嵌合部の高温低サイクル疲労における微小き裂成長挙動と破損寿命

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Low cycle fatigue tests at the temperature of 600°C were carried out using a component specimen of 12%-Cr steel, which simulates the blade root and disc joint for turbines. Micro-cracks growth behavior at the joint region of the specimens was investigated to clarify the damage mechanism of the blade-root joints used in high temperature environments and to improve life assessment methods using a finite element analysis for them. Micro-cracks growth behavior similar to the smooth bar specimens was observed in the specimens tested under the conditions of relatively high total strain range. Micro-cracks initiation was observed at the notch region of the specimens in the early stage of life. The crack growth rate increased with surface crack length. Life of the component specimens under this condition was similar to the smooth bar specimens. While, the component specimens tested under the conditions of relatively low total strain range showed a different micro-cracks growth behavior. No cracks were observed at the notch region and some micro-cracks were initiated at the edge of the contact region of the specimens in the early stage of life. Almost no increase of the crack growth rate was observed. Life of the component specimens under this condition was shorter than the smooth bar specimens. This might be attributed to the fretting fatigue at the contact edge and a mean stresses. Life prediction using a normalized crack growth rate (da/dN/ae) was effective for the component specimens over a wide range of the strain range.

タービン翼溝嵌合部の高温低サイクル疲労における微小き裂成長挙動と破損寿命

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