Investigation of Crack Problems in Steering Column Knob Assembly II
November 12th, 1981
Report to Lucas Electrical Systems Ltd.
S F Bush
Summary and Conclusions
- The strain guage responses to loading the knob case were markedly different in character for the two candidate ABS resins, Ronfaling MH86 (DSM) and Teluran 877T (BASF).
- The principal observed difference was the much higher initial recorded strain followed by relaxation in the Ronfalin case.
- Given the relatively small standard test differences between the two materials, the experimental method has show itself likely to be a sensitive indicator of differences in the as-moulded conditions – which was the purpose of the investigation to discover.
- A simplified analysis (a) shows that the more compliant material (Teluran 877T) is, in this particular moulding, likely to have less tendency to crack at the weld line (as reported verbally to Mr R D C Bone on October 13th); (b) indicates a relationship between cooling time in the mould and limiting applied stress which should apply more generally.