Beach marks

New York. The second symposium in Miami Beach marked an effort to draw attention to the rapidly growing accumulation of information in this field. 

Figure 2.18 Fatigue fracture surface appearance of a failed crankshaft, showing beach marks on the lower part. The origin of the primary fracture is indicated by the arrow. (Reprinted with permission from ASM International. All rights reserved www.asminternational.org)...

The presence of beach marks shows that fatigue is a major factor in the failure. Relatively small areas of crack propagation zone indicate short service life. 

Metallographic examination showed the cracks initiated at the first thread immediately adjacent to the nut. Beach marks were present indicating the presence of fatigue. 

Usually, CF under free corrosion gives beach marks too, but sometimes they may be less visible because of corrosion products. Corrosion fatigue fractures are normally transgranular, and contrary to dry fatigue often branched. 

It is interesting to observe the curved slip lines on the fractured surface of the nanocrystalhne 3Y-TZP ceramic, where the role played by the dislocations in the plastic deformation is evident. Also note the appearance of the curved slip lines that resemble the microstructures observed in metals (the beach markings see, for example, Polakowski and Ripling). These lines represent hiatuses between working and rest periods during fatigue in metals (see Fig. 7.44). 

Fig. 10.5. Examples of fatigue fracture. The smooth regions of the surfaces, containing beach marks, are caused by fatigue the rough regions are the surfaces of final fracture. These regions wiU be explained in the following sections...

Even with the naked eye, so-called beach marks (sometimes also called arrest lines) can frequently be discerned on the fracture surface (see figure 10.5 on page 337). They are due to changes in the load during component service... 

Beach marks indicative of the cyclic progress of a car door coating failure. 

Crack surface appearance Cleavagelike Beach marks and/or striations Cleavagelike... 

Fig. 1.4 View, from both sides (a) and (b), of the morphology of the spindle failure. The origin of the fatigue crack can be seen by following the beach marks opposite to the overload fracture area...

Fig. 2.14 Beach marks in the form of circumferential rings visible at naked eye on the head of a rail failed by fatigue [19]. The initial crack is the dark circle at upper left...

Service fracture of 4130 steel shaft with sharp circumferential notch subjected to unidirectional bending fatigue. Fig. 2.19a [22]. Fatigue initiated on the lower part where metal fibers were in traction. Beach marks, due to oxidation when... 

High temperature fatigue failure under axial loads of a valve stem of 21-2 valve steel (21 % Cr, 2 % Ni, 8 % Mn, 0.5 % C, 0.3 N) in solution-treated and aged condition and faced with stellite 12 alloy (30 % Cr, 8 % V, 1.35 % C, rem Co), Fig. 2.20 [24]. Note the ratchet marks around the circumference that denote the presence of multiple initiation sites (indicated by arrows). The wavy shape of beach marks is indicative of oflF-axis load that has introduced a bending component. 

In the last paragraph we have been showing how beach marks evidence packages of cycles. Now we will discuss of any single cycles that may leave a mark on fatigue fracture surface. At variance with beach marks that can be seen at naked... 

Often features of a fatigue fracture are visible, such as beach marks or clamshell marks and stria-tions. Beach marks or clamshell marks may be seen in fatigue failures of materials that are not in continuous use. They may be used for a period of time, allowed to rest, and then used again. Striations are thought to be steps in crack propagation. Thousands of striations may be found within each beach mark. 

A fatigue fracture feature, often observed in electron micrographs, that indicates the position of the crack front after each succeeding cycle of stress. The distance between striations indicates the advance of the crack front across that crystal during one stress cycle, and a hne normal to the striation indicates the direction of local crack propagation. See also beach marks. 

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