Methods and apparatus for testing rupture strength of tubular parts

A method of testing the rupture strength of a tubular part comprising a molded plastic cylindrical tube having a weld line extending radially across the wall of the tube at one point along the circumference thereof and extending the length of the tube, the tube being subject to radial expansion with respect to the longitudinal bore of the tube and having a tendency to rupture along the weld line when the tube is subsequently assembled with an insert member that is force fit into the bore of the tube, which method comprises:

• (a) placing an expansible tubular collet in the bore;
• (b) forcing an expanding member a predetermined distance into the collet so that the member expands the collet and the collet expands the walls of the part radially outward by a predetermined amount;
• and
• (c) measuring the peak force required to so expand the collet to provide an indication of the rupture strength of the tube, the peak force reading providing an indication of the weld strength of the tube and, where the weld does not rupture during the forcing step, an indication of the liklihood that the tube will fail prematurely in the field after subsequent assembly of the tube with the insert member.