Arrest line

Arrester line tiischorge Nom i fj a / dis c h a rg e c urrent Rated voltage Typical energy capahUity of... 

The length of installed pipe between the ignition source and the flame arrester is critical to the proper performance of end-of-line and in-line deflagration flame arresters. Line lengths greater than those used in the test allow higher flame speeds and pressure to... 

Nail involvement presents as pitting, discoloration ("oil spots"), crumbling, splinter hemorrhages, growth arrest lines, or tissue build-up around the nails. 

Macroscopic Appearance of Fracture Surfaces. The most striking observations (Table III) of fracture surface topography are the occurrences of stress-whitening and extensive plastic deformation at the higher water contents, and the occurrence of arrest lines at high values of AK. 

In addition (see Figure 6), the samples containing 2.2 wt % water showed large crack arrest lines at high values of AK (AK > 3.7 MPa/n). These arrest lines, which were associated with the periodic interruption of the FCP test to read the crack-tip position, imply the occurrence of creep. (If creep is closely confined to the crack-tip, it may well be associated with crack blunting.) Some finer lines were observed as well (for discussion see the following section). 

Figure 6. Coarse and fine crack arrest lines found on the fatigue fracture surface of nylon 66 equilibrated to contain 5.7 wt % water. Arrow shows direction of fatigue crack growth.

Failure investigations usually involve a detailed examination of fracture surfaces. The crack front geometry, at various stages of the fracture process, can usually be deduced, providing information about the type of loads that were acting. The basic principle is that the crack plane is perpendicular to the most tensile principal stress. Markings on the fracture surface can indicate the direction of crack growth and the approximate crack velocity, while crack arrest lines can show the sequence of crack front positions. 

Fig. 9.52 Hydrogen blistering and microcracks in the specimen precharged with /=50mA/cm for 30 h (a) unbroken blisterings (b) broken blistering with cracking, AFD and BEC are the fracture surface of the blistering cracks and (c) arrest lines EF, GH, and IJ on the fracture surface of the blistering crack [188].

Figure 17. Case Cl. Images of the interior surface. The fracture origin is an internal crack (large arrows) that started entirely in the outer veneer and then propagated into both porcelain layers in steps creating concentric arrest lines.

Glearly, it is important to use appropriate radiological investigations to not only identify the type of fracture in terms of Salter-Harris classification but also its severity in terms of magnitude of displacement, both before and after reduction. For this GT scans are invaluable. During follow-up close observance of growth arrest lines may provide an early indication of PPG. 

During the dynamic crack growth, local heat generation takes place at the crack tip. If the temperature is high enough, a plastic zone is formed at the tip (Fig. 3) and its traces are the so-called "arrest lines" which appear on the fracture surface after... 

Optical microscopy is a simple and inexpensive method to obtain the overall view of the fractme smface. By applsring the reflected light mode information on the origin of the fractme, the crack propagation direction, location of arrest lines can be gained. Also, in the transmission mode, it is... 

In some instances, a crack will stop growing and will then be restarted under a different stress system. The result is an abrupt change in direction of crack growth that produces a feature like the Wallner fine. This feature is termed an arrest line. 

When the two fracture surfaces are compared, it becomes apparent that the arrest line running horizontally across the center of Figure 9. 0d crossed the fracture surface in Figure 9.10c at the point at which the circular arrest line meets the diagonal edge. The two cracks started at opposite sides of the part in nearly orthogonal planes and stopped when they intersected. 

The development of the fracture surface can be understood in terms of the processing sequence that the ferrite part saw. The scenario that was developed begins with an initial down-shock in which the hot ferrite was dropped into a cold liquid. Probably, the crack in the diametral plane extended only to the first arrest line in that down-shock, but the crack in the orthogonal plane may have run all the way to the circular arrest line. The next step in the growth of the cracks may... 

Arrest Line. A rtb mark (q.v) defining the crack front shape of an arrested crack, before the crack is spread again by a new stress. 

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... 

The CNB test specimen does not require crack length measurement, thereby providing some convenience to the user. However the SEPB and SCF test methods require quality measurements if accurate fracture toughness estimates are expected. For the SEPB test specimen, the precrack front is very difficult to delineate unless it leaves a crack arrest line. An arrest line is easily detected if the crack tip turns out of plane or is hooked, thereby making the precrack and fast fracture plane non-coplanar, as shown in Figure 7. In one study, some cracks were so planar that the front could not be detected with conventional optical microscopy [12]. In such cases, the use of dye penetrants have been successful as shown in Figure 8, however, in some cases penetrants tend to bleed on the fracture surface and the measurements must be made immediately. Dye penetrants must be used with caution as they may cause environmentally assisted crack growth. 

---