Bend testing equipment

A. A typical requirement is "The test specimen shall be bent 180° over a mandrel of diameter 4 times the thickness (0.4 inch minimum) of the specimen."

Since 4 x 0.04" = 0.16" < 0.4", the preferred mandrel is 0.4" diameter (larger diameters lessen the rigor & value of the test).

Two mandrel devices are shown in ASTM D522, 'Standard Test Methods for Mandrel Bend Test of Attached Organic Coatings.' One is a rather standard hand-operated sheet metal bender in which one specimen end is clamped and then a pivoting plate (with handle for leverage) bends the extending specimen over the mandrel. In this device, a tapered mandrel of diameter 1/8" to 1.5" is used. The mandrel ends are clamped in place, so a straight rod of desired diameter could be substituted.

Also shown in ASTM D522 is a cylindrical mandrel test apparatus which requires bending solely by hand (fingers). Consists of 2 pentagon shaped plates, with a mandrel of a different diameter (3/8" to 1") held between at each corner. Both devices are available from Paul N. Gardner Company.

Perhaps the most suitable device would be a brake press for sheet metal of the type known as an airbrake. The specimen is placed across 2 spaced rollers between which the rounded die or mandrel is brought down. I haven't seen any small enough for lab use; perhaps someone can suggest a supplier.