Fatigue exists. It really does.

Hello everyone, long time no read.

I’d like to share with you a story on my fatigue tests. As you know, fatigue of R-UHPFC beams is the main topic of my research (if you don’t remember what this abbreviation stands for, check my previous posts!)

Do you remember that I was doing some tests in cooperation with Antoine? The first beam instrumented with his Fibre Optics we've tested back in December under quasi-static loading. This was done mostly to calibrate the future fatigue load levels.

Then, the fatigue test followed. We have started it just before Christmas (in fact, we started to run it a day before Antoine left for his holidays, and two days before I have left for mine). The plan was to run it for some three to four weeks continuously. Thanks to internet, we were controlling everything in the lab in Lausanne, while he was in Lebanon and me in Poland. That’s the real globalisation!

But, on December 27^th, the localized crack under the force application point has passed through one of the fibres in the upper flange. We've become ‘blind’ from this section on. Thus, we have had to temporarily stop the test. In mid-January, when both of us were back in Lausanne, we have re-connected and re-calibrated the fibre. The test continued.

In the beginning of February, strange thing happened. The jack could not produce anymore the force we wanted. Thus, we had to remove it without touching the sensors, not to de-calibrate them. That was like a surgery on an open heart, but our technicians are experts.

The jack was sent to the company for check-up. The reason of failure was… fatigue of one of the elements inside of the piston! After reparation, which took some 3 weeks, and re-installation on the testing rig (another week of work), in the beginning of March we have picked up the test. But, after just 2 days, the jack failed again! Unfortunately, during reparation, they have made a small mistake in the assembly. This meant another month of delay for me…

Finally, in the first days of April, the jack was installed again and the test continued. After another 2 weeks, on the 15^th of April, circa 8AM, the beam failed! And so, after almost 4 months and 6.5 million of cycles, we have finished the test. It took some 3 months longer than planned!

I am writing this to show that the research is not only a success story. There are many things that can go wrong. Some of them depend on us; on some we don’t have any influence. Of course, it’s us who decide how to deal with the problems… and how to manage the time not to waste it! And, trust me, during these 4 months I’ve had plenty of other topics to work on ;).

Back in 2017, when I was starting my research, one of the experts has told me: ‘the fatigue experiments are very… fatiguing’. Believe me, he was right.