The geometric stress concentration at the buttress corner 2.įragments of cold slug adjacent to the corner and 4.įrozen-in strain due to cold tool or cool melt conditions when moulded. It was possible to quantify the effect of the several weakening mechanisms at work in the failure. The bead would have formed during this phase of the failure. Judging by the several white stains observed on the buttress surface immediately above the lateral corner, it is likely that there were several very slow leaks before the final, catastrophic failure when the cracks propagated catastrophically. The latter are especially likely to form at or near a thickening of the tank wall (e.g. There were several types of defect seen in the fracture surface here, including a large weld line, cold slug fragments and voids.
#ALI INSPECTOR CRACK CRACK#
The critical crack probably resulted from the coalescence of several smaller cracks below the fan buttress. The exposed surfaces were covered with fine ‘crazy-paving’ cracks indicative of oxidative cracking, and there were also numerous weld lines in the moulding.Ī reasonably clear picture of the failure emerged as a result of detailed examination of the critical fracture surface, and comparison of the properties of new and unused tanks. The step then failed again at the other end to produce the final form. Close inspection of the fracture surfaces showed that the larger attached part had broken first, the critical crack growing from near the support in the upper part of the step ( Fig. 8.40).
#ALI INSPECTOR CRACK FREE#
The step appeared to have broken from two points near the supporting tubes to which it was fixed, so as to give a large free fragment and two parts which were still attached ( Fig. 8.39). The step had only been installed for 4 weeks from new, so the failure was unusual, especially since the rest of the steps were made from the same material (ABS) and had been there for several years. A 12-year-old girl suffered leg cuts when a plastic step suddenly broke while she was ascending the ladder in June 1995. But other safety-critical products can fail too, such as steps besides swimming pools to allow access to the water ( Fig. 8.38).
0 kommentar(er)
