Mounted on flat spring 3 are masses m₂, shaft 1 with unbalanced mass m₁ and mass m₃. Masses m₁, m₂ and m₃ are selected so that when shaft 1 rotates, the two overhanging ends of spring 3 vibrate in phase and with the same amplitude. This applies an alternating load to test-piece 2 along axis x-x. The magnitude of the load is regulated by means of spring 4.
$2138$EL,M$