Investigation of Cracking Problem in ABS Bumpers
June 21st, 1982
Report for Richard Grant Accessories Ltd.
S F Bush
Summary
A large proportion, in the order of 90%, of front bumpers made from one lot (about 15 tons) of ABS sheet supplied by Telcon, have been found to fail by cracking in a particular region of the bumper. The vast majority (95%+) of the failed bumpers were found to have failed after they were installed on the vehicles, but before they entered service (i.e. at the pre-delivery checks). The ABS sheets supplied by Telcon were made in turn from Montsanto Lustran QE 1110, and were thermoformed into bumpers by Richard Grant during May and June 1980. This particular batch was the second in a sequence of three using Telcon sheet, the first batch being made in late 1979. Reported failures from batches one and three were very few and generally arose for a variety of reasons not connected with the cracking problem.
The investigation reported below is one of several commissioned by the interested parties to identify reasons for the cracking. Fundamentally the issue is to decide between the ABS granules supplied by Montsanto, the ABS sheet as delivered by Telcon, the processing into bumpers by Richard Grant, the installation by Skoda, and a combination of two or more of those. In arriving at a decision on this it is important to recognise that a fault in one area can show up as a fault in another. Thus processing can significantly alter the microstructure of the ABS material; conversely subtle unperceived changes in the ABS can cause difficulties in the processing.
Taken with the earlier investigations made by others, the new results reported below represent about as comprehensive a range of tests as can now be done, two years after the event. It is believed that the results obtained by all investigators are fundamentally consistent. The broad conclusion of this report is that the ABS material in the batch in question was significantly more crack-prone than that in the first batch.