In Russia found guilty of shortening the life of aircraft parts

Scientists of Perm National Research Polytechnic University (PNRPU) have found out how seriously dents from bird strikes shorten the service life of aircraft parts. They claim that, in particular, the service life of fiberglass aircraft parts after such incidents is reduced by 14 times — from about 14 years to 1 year.

"Fiberglass is widely used in aviation — it is lightweight, inexpensive and does not rust. But when stones, hail or birds hit it, dents and scratches appear on it. Existing control methods fix the defect, but cannot predict how long the damaged part will last. Designers lay inflated safety margins, which makes airplanes heavier, spend more fuel and pollute the air more, and flights become more expensive. For the first time, Perm Polytechnic scientists have comprehensively studied how scratches and dents affect the strength and durability of fiberglass. The results will help to more accurately determine when a part needs to be changed and when it can be operated further, saving resources without loss of safety," the Ministry of Education and Science of the Russian Federation told TASS.

During the tests of parts with scratches and dents on real loads arising in aviation, it turned out that scratches have almost no effect on strength: the scratch sample broke under the same load as the whole one. And the dents from the blows of stones, hail or birds turned out to be much more dangerous: a weak dent reduced the strength by 17%, medium — by 25%, strong — by 30%.

"This means that if the whole part was designed for a load of 100 kg, then with a strong dent it will withstand only 70 kg. At the same time, scratches and dents did not reduce the rigidity of the material: the damaged sample resisted bending in the same way as the whole. This is an important and disturbing conclusion: if you check the part for elasticity (for example, trying to bend it), you will not notice that it is damaged. The part may seem to be in good working order, but in fact its resource has already been reduced," said Anastasia Lykova, senior researcher at the Center for Experimental Mechanics of PNRPU, Candidate of Technical Sciences.

Also, when the samples were repeatedly loaded and unloaded, simulating takeoffs and landings, the whole sample withstood more than 5,000 cycles. The scratch reduced the resource by almost half — to 2800 cycles. And the sample with a strong dent withstood only 368 cycles, which is 93% less than the whole. So, according to the researchers, a part with a strong dent serves 14 times less.

"If the whole part works for 14 years, this one will break in a year," the university explained.

And a weak dent is most harmful during long quiet work, when there are a lot of loads, but they are small, like a passenger plane that flies every day. In this mode, a part with a weak dent can withstand four times fewer cycles than a whole one. A strong dent, on the contrary, is more dangerous with sudden overloads, when there are few loads, but each one is very strong, like a military fighter. Here, a part with a strong dent can withstand 50 times fewer cycles than a weak one.

The Ministry of Education and Science of the Russian Federation noted that the results of these studies will allow engineers to more accurately determine the permissible limits of damage. They can rely on quantitative estimates: how many cycles a part with a specific defect will withstand under a specific operating mode. This makes it possible to reduce the weight of aircraft, which means fuel consumption and emissions, as well as extend the actual life of parts.