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In this study failure analysis of a mini van diesel engine intake valve is analyzed in detail. Failure occurred at the groove of the valve. First mechanical and chemical properties of the valve are determined. After visual investigation of the fracture surface it is concluded that fracture occurred due to fatigue. Damaged valve, valve seat, cylinder block and piston surface is investigated and construed. Failure constituted 300 kilometers after the rectification of the engine. Therefore rectification and assembly steps of valve and engine parts are analyzed in detail. Considering assembly, design and working conditions of the engine, stresses occurring at the failure surface are calculated. Endurance limit and fatigue safety factor is determined. Because of high fatigue safety factor, reasons for failure are investigated and effects causing stress increase at groove of the valve are established. These effects are faulty assembly of the valve and valve seat causing a high impact effect. In conclusion effect of impact ratio on stress increase is explained.

In this paper corrosion-fatigue failure of a roller in a cardboard production plant has been analyzed. The failure occurred at the bearing neck of the roller. Mechanical and chemical properties of the roller are determined and the fracture surface is investigated. Forces applied on the roller is examined, stress calculations are carried out and fatigue safety factor is calculated. Stress analysis is also applied to roller and bearing neck by using Finite Element Method (FEM) and the results are compared with the calculated values. Because of very high safety factor, reasons for failure are investigated and effects of fatigue failure are determined. These effects are corrosion-fatigue, working conditions and notch effect. In conclusion precautions which have to be taken to prevent a similar failure is explained by using FEM.

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