The strength of adhesive bonds depends greatly on the conditions under which the bonding process is carried out. Therefore, variations in this process lead to variations in the accuracy of the results acquired from strength tests of these bonds. It is the responsibility of the manufacturer to prepare samples in accordance with the ASTM standard.
The ASTM standard specifies that “the testing machine shall conform to the requirements of Practices E 4.” For this test, we used the 5569 electromechanical test frame, with a 50 kN load cell and 30 kN capacity mechanical wedge action grips with coarse serrated faces. The standard further specifies that “the long axis of the test specimen coincide with the direction of applied pull through the center line of the grip assembly.” In order to ensure that the load be applied in exactly the same direction as the center line, we inserted spacers into the grips. Ideally the spacers would be bonded to, or machined into, the specimen.
For more information visit the Definitive Guide to ASTM D1002 Lap Shear Testing of Adhesively Bonded Materials.