Resonance fatigue of tubular steel goods has become a relatively common method of testing fatigue life of full circumference welded joints. EWI has maintained a system for such tests for many years and has conducted several standard qualification programs of steel riser welds for offshore applications. However, we have also employed the resonance fatigue system to test materials that have lower moduli of elasticity which causes them to deflect significantly more than steel to reach a similar level of stress. This is not a common application of resonance fatigue testing equipment.
The materials that EWI has the most experience testing using the resonance method are high strength aluminum and titanium. Currently, EWI is running a resonance fatigue program on aluminum pipe. The difficulties of testing material that will displace almost three times that of steel for a similar stress are maintaining strain gages and associated wiring on the test piece during the test. In addition, the vibration from the pipe must be isolated from the support equipment.
During recent testing I was able to video the testing and slow it down to see the motion of the pipe during the test. The displacement that occurs is quite impressive as can be seen in this movie.