Issue 23

F. Felli et alii, Frattura ed Integrità Strutturale, 23 (2013) 127-135; DOI: 10.3221/IGF-ESIS.23.13

Figure 9 : SEM micrograph of a circular impression found in the central part of the piston (sample 1).

Figure 10 : SEM micrograph of a longitudinal wear groove found in the central part of the piston (sample 1).

Figure 11 : SEM micrograph of a longitudinal wear groove found in the central part of the piston (sample 1).

Figure 12 : SEM micrograph of the scored area found in the central part of the piston (sample 1).

All these observations allow to conclude that the superficial defects observed came from a wear process generated by the relative sliding on the EN3358 steel surfaces of an harder spherical components which can be easily identified in the hypereutectoidic steel spheres employed in the locking system. These spheres remain always pressed on the piston surface as testified by the circular impressions observed in the central part of the pistons. During the opening phase they drag

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