A three-axial fixture rotates the item in a particular direction to obtain the vibration components to be present along the three orthogonal axes of the items.
When the test to be performed is of sinusoidal type and has to be repeated along the three axis, it is possible to apply the three vibrations at the same time.
The addition of the three vibration vectors together will lead to an higher vibration in one direction.
This allows the test to be executed on the three axis at the same time by increasing the vibration level and orienting the item along the resultant vector.
The use of a triaxial fixture speeds up the test reducing to 1/3 the total test time. With many items the vibration applied at the same time along different axis better highlights weakness of the item to vibration.