Fatigue Strength of Nodular Iron Crankshafts 2001-01-3412

Within motor and vehicle industry, there is a permanent trend to improve existing materials in respect of their properties and economic fabrication, or to replace the same by new materials that meet adequate requirements to a greater extent than the existing ones. One of such materials that is gaining wide usage is nodular iron which belongs to a group of available low cost materials. As a structural material it is highly competitive with other structural materials, steel in particular. Nowadays nodular iron is used for making vital machine and engine components such as, for example, crankshafts, camshafts, gears.

The paper offers results obtained in the process of testing high speed diesel engine nodular iron crankshaft fatigue strength. To get a complete assessment of fatigue strength experimental test results and their proper use, scatter of such test results has been considered separately. Actually the scatter of test results represents one of the greatest problems in experimental tests. By introducing and analyzing the destruction probability the authors got the sound basis for determination of engine crankshaft safety and reliability. Thus the dilemma of how to use results obtained by testing fatigue strength of notnitrided and nitrided nodular iron crankshafts is eliminated. The destruction probability both in the zone of limited durability and endurance limit has been analyzed by means of Weibull distribution.

Also the paper offers analysis of factors that affect nodular iron Nl.80 crankshaft endurance. It has been found out that the porosity, slag, flake graphite and carbides in structure represent the most influential factors affecting the nodular iron crankshaft endurance.