선박용 디젤 주기관 스터드볼트의 피로파괴 안전성에 관한 연구

Abstract

Bolting is widely spreaded for its reliability, productivity, cost and easy-dismantling process for repair and exchange. Cylinder cover is fastened with cylinder block by the stud bolts placed at the upper part of cylinder liner.

Stud bolt for cylinder cover is repeatedly given axial forces from the initial fastening torque and explosion pressure as variable load from the combustion chamber. Because variable stress conditions cause stress concentration on the screw threads, factors such as allowable stress and limitation of the stress concentration should be decided at the stage of design for minimizing fatigue failure caused by stress concentration and for selecting proper bolt materials and sizes.

From the research, presumed the number of cycles for variable stress generated on stud bolt for the expecting design life by modeling MAN B&W 12K98MC-C engine. And collected and analyzed other fatigue test results of stud material, High Tensile Alloy Steel(SNCM439).

The statistical analysis of research results presents (10% failure probability)fatigue strength equation which can explain effects of what influence stress concentration factor and stress ratio have on fatigue strength.

Furthermore, theoretical calculation of FEM modeling program makes it possible to obtain each values of stress concentration.

The cumulative damage factor based on Miner-Palmgren hypothesis is used for the practical procedure of fatigue life prediction. Also, the quantitative safety analysis of fatigue failure of the stud bolt for cylinder cover can be done, and then results are reflected for the design optimization.