Page 187 - Failure Analysis Case Studies II

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Fig. 4. Macrograph of brittle crack, running along stress concentration of buttress corner, and ending at points shown
by closed arrows.

Fig. 5. Macrograph of brittle crack on inner surface, with ends shown by closed arrows. Weld line at left (open arrow)
co-linear with crack, and surrounded by extensive flow line pattern.

upright position when in use on the car. The crack was brittle in nature, and extending ca 6.3 cm
internally and almost the same distance externally (Figs 4 and 5).
The external surface was clear of any other major defects, and no defects were at first apparent
on the inner surface owing to a superficial deposit from the cooling water system. On gentle
rubbing, however, very clear traces of flow line patterns could be seen over much of the inner
surface. Such patterns were revealed because the ends of the glass fibre reinforcement tend to
roughen the otherwise smooth surface, and they also tend to be aligned with the melt flow, so will
collect particles and show any major changes in fibre or melt orientation. Figure 5 in particular,