선박용 엔진 Crank Throw 부품의 기계적 특성 및 피로한도에 관한 연구

Abstract

The crank throw is the most critical component of marine diesel engine with regard to the lifetime of the vessel. Because of the severe service environment, The mechanical properties including the reliability of fatigue limit must be satisfied. The crank throw was manufactured using free forging method. The material of crank throw is S34MnV for MAN B&W used at crankshaft widely. This paper is aimed at estimating both mechanical properties and fatigue limits. To obtain specimens for this dissertation, the crank throw was fully destroyed as several parts. The mechanical properties consist of Tensile strength, Impact Test, Microstructure and Sulphur print. To sum up, the crank throw's comprehensive test results are as follows. The microstructure of crank throw is composed of pearlite and ferrite with grain size No.9 in accordance with ASTM E114 after Normalized and Tempered Heat Treatment. When it comes to the mechanical properties, The overall results were approximately 700Mpa for Tensile Strength , 190~210HB for Surface Hardness, 25J for Charpy 2v Notch impact on Room Temperature respectively. To estimate the fatigue limit, the staircase method proposed by Dixon and Mood formulas was carried out. The condition of fatigue testing was axially loaded with push/pull load, namely R=-1 stress ratio. With the result of staircase method Testing, the determined mean strength and standard deviation were 296.3 MPa and 10.6 MPa, respectively. ii