Variables affecting dome test results

Abstract

The limiting dome height (LDH) test has been proposed as a simulative test to evaluate the stretch formability of sheet metals which shows good correlation with field forming performance. The present study investigates how deviations from the LDH test procedure and test geometry given in the literature affects the dome test results for aluminum body sheet alloys. The results should be helpful in explaining between-lab variability and helpful to laboratories which cannot perform the LDH test according to specification, because of equipment limitations, in interpreting their data.

Two dome test procedures, both of which are currently being used in R& D departments in the automotive and basic metals industries, were evaluated using four aluminum body sheet alloys. It was found that the procedures gave different numerical results and that the relative formability ratings varied with the procedure used.

The effects of sample thickness and lubrication on dome test results were also studied. A purely geometrical effect of thickness was found, with increasing thickness resulting in higher dome heights at failure. Well-lubricated samples resulted in different formability ratings for the four ABS alloys than do solvent-cleaned samples, accenting the need for dome tests to be performed dry since the ratings from the lubricated tests do not agree with production experience.

It is concluded that before a “best” procedure for performing dome tests can be selected, a correlation study similar to that of Ayres, Brazier, and Sajewski must be performed using both procedures. Cooperative efforts are under way to select and standardize a procedure for dome testing for both the automotive and basic metals industries.