Service Load Fatigue Strength of a Crank Shaft Steel Material

Abstract

The strength design of crank shafts is generally based on fatigue test data obtained by subjecting specimens to testing under a constant stress amplitude which is different from actual stress patterns, so it is necessary to confirm the effects of this service load (stress) oil the fatigue strength of crank shaft steel materials.
Actual bending stress patterns on crankpin fillets of all crankthrows were measured by FM telemeters during the shop trial of a six cylinder 4-cycle diesel engine, and then the selected stress patterns based on the wave analyses were used as the inputs to the push-pull fatigue testing machine of a servo-hydraulic type to carry out fatigue tests with plane carbon steel specimens.
This results of the service load fatigue tests were compared with those of the rotating bending fatigue tests and the push-pull fatigue tests whose stress patterns are a constant stress amplitude to examine the influential factors such as wave areas of a tensile side, maximum tensile stresses, minor stress waves, mean stresses and stress amplitudes of primary waves, synthetic wave effects etc.