Pull-Out and Push-Out Tests for Rubber-to Metal Adhesion

Abstract

Abstract A study has been carried out of adhesive failure forces for a steel rod embedded in and bonded to a rubber block. Emphasis has been placed on comparing tension (pull-out) and compression (push-out) forces. A fractional contribution to the pull-out force appeared to be significant for rods having a diameter greater than about 0.5 mm in the present experiments. Indeed, it became a large fraction of the total force when the rod diameter was 1 mm or more. On the other hand, it was negligibly small in push-out experiments. They would therefore be preferred on this basis for measuring the strength of adhesion. But experimental difficulties in carrying out compression tests are considerable. Tall blocks become unstable under large compressive loads, and short ones are markedly stiffer than long ones, due to restraints on their lateral expansion, which are difficult to specify and control. Thus, although measurements of push-out force for a wide variety of samples have been shown to be in good accord with a simple theoretical treatment of debonding, ignoring friction, it is recommended that pull-out tests be retained for assessing the strength of adhesive bonds. Caution is necessary to minimize the effect of friction. The theoretical treatment indicates that the product aL of the rod radius a and the embedded length L should be held smaller than the cross-sectional area of the block in which the rod is embedded.