Failure origins

Fracture markings can be used to locate the failure origin, which is the discontinuity or flaw that caused the appHed stress to be amplified locally. Once the failure origin has been located, the failure stress can be estimated using the flaw size and equation 6, or the distances to the boundaries of the mirror, mist, and hackle (whichever is most evident) and the foUowing relation (63)... 

Fig. 10. Photograph of fracture surface of H-451 graphite bend specimen illustrating failure originating at natural flaws at the tensile surface.

In the case of BPA-PC, the thin film investigation of deformation micromechanisms (Sect. 4.2) shows that CDCs occur around 60 °C. So, it is unlikely that the craze at the crack tip occurring at - 20 °C, or above, could be a CDC. The observed MW dependence of failure originates from the above described mechanism with CSCs. 

Don t be hypercritical of research results. An inventor s opinion of the success of a project as evidenced by his writings made at the time is very important. He can t state failure originally and then attempt to claim success at a later time when confronted by overlapping work of an adversary. 

There has been a conspicuous number of in-service failures of pressure vessels built of certain steels having h her strengths obtained by quenching and tempering. Most of these failures originated in geometric details that had been used for decades w ith conventional steels without similar difficulties. 

Plate/electrode alloy Lot serial number Specimen number Maximum stresst Cycles Failure origin... 

Figurel.il Failure origin in a zirconia-toughened alumina, caused by the presence of a zirconia aggregate in the starting powder. (Reproduced courtesy of CRC Press, Boca Raton, FL.)...

Figure 8.75 Fracture surfaces in brittle materials generally show a smooth region that surrounds the failure origin (mirror region) but the surface increases in roughness as the crack accelerates (mist region) until crack branching occurs. The branched region contains ridges known as hackle. (Optical micrograph courtesy of Matt Chou.)...

Figure 8.79 Scanning electron micrographs showing failure origins in singlecrystal alumina (sapphire) fibers a) internal pore b) surface flaw. (Courtesy of Paul Heydt.)...

Figure 8.81 Impact failure origin in glaze coating from a space shuttle tile scanning electron micrograph. (Reproduced courtesy of The American Ceramic Society, Westerville, OH.)...

V Poisson s ratio and h the specimen thickness at the failure origin. 

Figure 14.8 Defects at failure origin of ceramic materials, (a) Surface grinding defect in silicon (from O. Borerro-Lopez, unpublished results) (b) Internal pore in polycrystalline alumina ...

Fig. 7.11 Stereomicroscope views (32x and 57x magnification) of two broken halves of a Lava (3 M Espe) fatigue-failed zirconia specimen, a The mirrors (smooth surfaces) and b the radiating hackle lines surround the failure origin located on the tensile surface of this specimen [26], With kind permission of Elsevier...

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