New developments carried out by crankshaft manufacturers in order to fulfill more strict material strength requirements set by engine builders is causing new challenges in crankshaft quality control. Higher stress amplitudes in engine operation and the fact that higher strength materials tend to have smaller allowable flaw size against metal fatigue call for more efficient non-destructive evaluation (NDE) of the crankshafts. Wärtsilä has together with its partners carried out a development work with the intention in implementing new hardware and detection guide-lines to safeguard the high-level reliability of the crankshaft material. Introducing of ultra-clean steels already has a very high contribution in crankshaft safety, but in parallel with that new NDE methods are needed with improved accuracy and detection level. The most essential applied stresses in the shaft from the reliability point of view are highly concentrated in a relatively small material volume in the vicinity of the crank fillets. Finite element and fracture mechanical analyses give essential information about the critical defect sizes in function of applied stresses and location, and further, information about the needed accuracy of the used NDE system. As a result of analyses carried out it is possible to guide the ultrasonic NDE in different phases. High performance, but more time consuming techniques, will be applied in critical areas, and, conventional techniques in other parts of the shaft. Based on the required accuracy, i.e. minimum detectable imperfection size, the phased array techniques has been used in the project as a highest accuracy evaluation method. This paper reports the results of the stress and strength analyses made and material tests determining the fracture-mechanical data of modern crankshaft steels, and, finally reports benefits of the phased array NDE method over to conventional non-destructive ultrasonic methods when applied in either as forged pre-machined or in finish-ground shafts, including visualization of detectable imperfections. Practical experience of NDE is also discussed including selection of probes; especially for difficult geometries, accuracy and reliability of the methods, option for automated detection, inspection data handling and relative costs.
Modern ultrasonic quality evaluation of large crankshafts
Moderne Qualitätsbewertung großer Kurbelwellen mittels Ultraschall
2010
8 Seiten, 19 Bilder, 2 Quellen
Conference paper
Storage medium
English
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