抄録
The present study investigates mesoscopic fatigue deformation behavior of a nodular cast iron via the in-situ observation of mesoscopic structures such as spheroidal graphite inclusions, grain boundaries and multiple small cracks. For this purpose, the in-situ observation system has been constructed by the use of an advanced CCD camera system. The camera system can zoom in on the fatigue-damaged specimen surface at a magnification of up to ×800. The observation reveals that most of the cracks observed starts at the separations of the matrix/graphite interfaces. Incipient cracks grow along gain boundaries; nevertheless, when become larger than, say, 500μm, they begin to grow in the direction perpendicular to the applied strain axis. Coalescence of multiple small cracks often causes the sudden fracture of the specimens. The mesoscopic strain distributions within the observation area were calculated from the change of arbitrary positions of observation on the specimen surface by using the multi-dimensional spline interpolation technique. The result reveals that even under strain-controlled fatigue condition, local strain varies considerably, reflecting damage the material has suffered from mesoscopic defects such as spheroidal graphite, grain boundaries and small cracks.
