The Use of Fractography in Design Development

In the fabrication of prototypes of this assembly, cracks were discovered in the ferrite part after welding and additional cracking was observed after the grinding 

The conclusion from examination of these features is that the fracture originated at the top of the micrograph and ran initially as indicated by the two curved arrows. It then stopped at the semicircular arc about 1.5 mm from the origin. In the next stage of fracture, the crack ran to the approximate center of the part and again 

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 

Understanding how failures are produced also requires knowledge of the true state of stress at the flaw. In a bend specimen, for example, where was the flaw located relative to the neutral plane Was there any prestressing of the flaw because of residual thermal stresses or because of anisotropy of the material system  

These are the kinds of questions that can be answered through ffactographic analyis. Not only does the analysis permit the location of the critical flaw, but it permits a description of the severity of the flaw in terms of a penny-shaped flaw of equivalent size. Furthermore, as noted above, an examination of the shape of the 

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