TWI used its large resonance testing rigs to develop a new methodology for SCR and pipeline fatigue testing. The development of the testing procedures involved the following steps:
Establishing RPM and strain range relation.
In resonance fatigue tests, the target strain (stress) range is achieved by controlling the speed of the motor, expressed in terms of revolutions per minute (RPM).
Dividing each block into several sub-blocks.
The fatigue data, representing annual fatigue damage, are divided into several sub-blocks to represent variations in sea states.
Establishing the relation between RPM and time for each sub-block.
TWI then determined the number of cycles at each stress range for each sub-block
Finally, data recording and processing.
Controlling the resolutions of the motor using programmed software allowed precise control over the variation of the stress amplitudes. An example of stress–time signal achieved in full-scale VA test trials is shown in Figure 2.