The basic working principle of FatigPro is very simple. You can do the following simple experiment to see how it works.
Take a paper clip. Actually, take three of them.
Straighten the paper clip. Bend the paper clip from the same spot several times. You will see that it will break after 8-10 bends.
Repeat the same with the third paper clip. Only this time put the notch deeper. You will see that it will break much faster.
Now do the same to the next paper clip. But this time put a notch in the middle using a file.
You will see that the one with the notch will break sooner.
FatigPro is the engineered version of this concept. We make the sensor from the same material as the structural member and put 3D notches on the fingers. The notches are engineered in such a way that they break at specified milestones (fatigue lives) with +/- 3% accuracy.
What is meant by “milestones” is exactly like the road mileage signs when you are driving. The sensor tells you how much “distance” is left until the final failure point. In this example, the sensor tells you when 10, 50, 70, 80, 90% of fatigue life is left.
FatigPro is applied to the critical part of the structure which is flexing under fatigue cycles.
FatigPro flexes and goes through the same fatigue cycle as the main structure. Adhesion of the sensor to the structure is engineered to ensure that.
As the fingers inside the sensor go through the fatigue cycles, engineered notches take effect and fingers start breaking prematurely.
First finger breaks at 10% of the fatigue life of the structural member. Second at 50%, third 70% and so on. These indicate true fatigue life since the sensor goes through the same disturbances as the main structural components.
A very nice thing about FatigPro is that this process requires no electrical power. So FatigPro can work for a long time. FatigPro uses power only for communication purposes. So a small battery may last for 40 years. (yes, there are batteries with 40-year shelf life) RFID or all other IoT communication technologies can be used for communication.
FatigPro is applied to the critical parts of the structure. Application is done similar to strain gauge application. FatigPro is similar in size to the strain gauge, but the similarity ends there. FatigPro works without a battery and you don’t need to log data continuously. FatigPro “pushes” messages when the fatigue level reaches predetermined levels.
The cycle numbers given in the figure indicate the true number of SHM (fatigue) cycles.
Please see how FatigPro would inform the user about the progress of fatigue in this case.
