Arrest marks

A steel coal-conveyor drive shaft failed in service due to the occurrence of a transverse crack that passed through the right keyway near the centre of the keyway as shown in Figure 7.50. The shaft was cut so that the crack could be opened to expose the corroded mating fracture surfaces. After cleaning with hydrochloric acid, examination of the fracture surfaces showed them to be relatively smooth textured, flat and perpendicular to the axis of the shaft and the keyway. Two sets of crack arrest marks was concentric to... 

Figure 7.51 The fracture surfaces were relatively smooth-textured and flat two sets of concentric crack arrest marks were visible on the fracture surface. (Reprinted with the permission of M. Zamanzadeh, ATCO Associates, Pittsburgh, USA)...

Fig 11. Fracture surfaces of PE specimens showing the variation of shear lip size, crack tip crazing and crack arrest marks as a function of impact velocity. 

This model can also be used to explain the crack arrest markings and cleavagelike facets on the fracture surface, as well as the discontinuous nature of crack propagation [32, 33], although more research into surface films and brittle fracture is required before this model can be thoroughly evaluated [34],... 

Fig. 7.52 Representative scanning electron micrographs of the nominally identical fracture-surface morphologies obtained in Mg-PSZ (MS grade) for a overload fracture under monotonic loads at AK 11.5 MPa and (b) fatigue fracture under cyclic loads at AK 6 MPa m. Note, in contrast to metals, the absence of striations or crack-arrest markings on the fatigue fracture surface. Arrow indicates general direction of crack growth [6]. With kind permission of John Wiley and Sons...

Figure 3. An SEM image of an opened crack from a seat comer. The arrow on the left points toward the crack initiation site on the top siuface of the seat. The elliptical crack arrest marks are typical of slow crack growth with intermittent loading. The smooth smface of the crack is typical of ESC in amorphous materials. The arrow on the right shows the freshly generated stress-whitened area that was produced when the crack was opened up.

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