Striation Observation

2 Morphological Aspects of Fatigue Crack Formation and Growth 

These cracks develop after the main crack has passed and are due to local stress states. Sometimes they open on a plane perpendicular to that of propagation. 

Another characteristic feature that may be observed on each single striation, as in Fig. 2.35, is the presence of smaller closely spaced striations. The origin of these closely spaced striations may be explained by the striation mechanism proposed by Gross and schematized in Fig. 2.36. In this mechanism, basically similar to that of Fig. 2.25 and based on two stages process of blunting and closure re-sharpening of the crack tip, compressive closure stress. Fig. 2.36b, may activate a series of slip lines ahead of the crack tip that leave a trace on the main striation. 

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Figure 7.12 Fatigue striations observed on the fracture surface...

Figure 7. Fine and shallow fatigue striations observed in the region of early crack growth in...

Fig. 2.28 a Ductile, b brittle striations observed by Forsyth on 7.5 % Zn-2.5 % Mg aluminum alloy [15]. c plastic enclaves observed on a free surface associated with brittle striations [15]... 

Fig. 2.30 Striations observed by Milella on FeSlO carbon steel in the fatigue threshold zone. Striations width is about 0.1-0.2 j.m, but the real growth rate is significantly lower, about two orders of magnitude...

Fig. 2.35 Cracks between striations observed by MUella jnoduced after the crack has passed...

Fig. 16.27 Ductile fatigue striations observed on A 533 GrB Cll steel in water at 288 °C [33]...

Hulbrnt and Crew observed what seemed to be the same spectnun in the first striation of a discharge tube at 1 mm. of mercury. Bramley has found that at 1 mm. pressure the electrons in the striation nearest the cathode have velocities of about 10 or 15 volts and Horton and Davies give 12.6 volts as the lowest value of the electron velocities necessary to give this spectrum and find that a slight increase in voltage causes the blue... 

On crystal faces bounding a polyhedral crystal, step patterns resembling the contour lines on a topographic map or striations in one direction are observable depending on the nature of the face. These show the process of crystal growth or dissolution at an atomic level, and are referred to as the surface morphology or surface microtopography. 

The prismatic faces of natural rock-crystal are characterized by the development of striations parallel to the edges between m, r, and z faces (perpendicular to the c-axis). Natural rock-crystal showing no distinct striations is almost exceptional. In industrially mass-produced synthetic quartz using NaOH or KOH as mineralizers, no striations are observable on 1010 faces. As shown in Fig. 10.5(a), five-sided growth spiral hillocks are generally observed. However, if quartz crystals are synthesized in hydrothermal solution with NaCl as the mineralizer, the prismatic faces exhibit similar striations to those observed on natural crystals [5]. 

Figure 10.5. (a) Polygonal spiral growth hillocks universally observed on 1010 faces of synthetic quartz. (The arrows indicate the summits of the growth hillocks.) (b) Striation patterns commonly seen on the 1010 faces of natural and synthetic quartz grown in NaCl aqueous solution. 

OkkI. These are minus rhombohedral faces (-R), and in most cases they appear as 0112 faces with nail-head Habitus. Growth step patterns are not observed on these faces, which are characterized by the development of striations parallel to the edges with 1011. ... 

Among these prism faces, 1120 appears as an extreme of dog-tooth Habitus, and is characterized similarly to [hkil] by striations parallel to the edge with 1011. No reliable observations have so far been... 

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