by Fatigue is a fatal killer of all construction machinery.
The construction machinery mentioned here includes aircraft flying in the sky, trains, cars and tanks running on the ground, ships and submarines driving at sea, nuclear power plants, centrifuges, steam turbine blades, etc.
According to data statistics, 50% ~ 90% of the damage of mechanical parts (such as axle, crankshaft, connecting rod, gear, spring and bolt) are fatigue damage.
It is also reported that fatigue failure accounts for 49% of the damage of all components of aircraft jet engine.
In addition, pressure vessels, offshore oil platforms and a variety of welded structures (such as bridges, towers, etc.), even household appliances (including bicycles, hinges of wardrobe and faucet handles in kitchen, etc.) will suffer fatigue damage.
Shocking fatigue failure case 1 the tragic history of comet aircraft fatigue is the first killer of the aircraft.
The comet, the world’s first large jet, became a short-lived model due to fatigue failure.
The comet (see Figure 1) was designed by de Haviland in 1949 and officially put into test flight operation in 1952.
The new plane can carry 80 passengers and fly at an altitude of 10000 meters at a speed of 800 km / h.
At the same time, it is a sealed engine room; Passengers feel no discomfort at an altitude of 10000 meters.
Moreover, it flew smoothly.
It was considered to be the most advanced in terms of passenger capacity, flight speed and comfort at that time.
It was the world’s leading large jet at that time.
Figure 1 the de Havilland comet took off from Rome, Italy on January 10, 1954.
The destination of the flight was London, England.
Unfortunately, less than half an hour after taking off, the fuselage suddenly burst in the air, and then fell into the Mediterranean from an altitude of 9000 meters, killing all the passengers and crew on board.
The accident shocked the whole world.
Previously, people were not impressed by the understanding of the air crash.
British aviation experts set up a special investigation team to analyze the cause of the accident.
What is more shocking is that shortly after that, another “comet” plane also had the same accident and crashed in the Naples sea, Italy.
In less than a year from May 1953 to April 1954, three of the nine “comet” aircraft put into the route disintegrated in the air in exactly the same way.
A crack was found on a window in the wreckage of the plane.
At the same time, the researchers conducted strict tests on the grounded “comet” aircraft one by one.
They put the aircraft in a huge tank and repeatedly pressurized it with water to simulate the impact of various loads such as air friction, resistance, pressure and vibration when the aircraft flies at high speed in the air.
A total of more than 9000 hours before and after the experiment, cracks were found in the aircraft skin, similar to those on the wreckage of the crashed aircraft.
Conclusion: the disintegration accident of comet was caused by fatigue cracks in metal parts during flight.
History shows that if it were not for the comet accident, people’s understanding of fatigue might have been delayed for some time.
2 fatigue failure of engine of “Boeing 747” passenger plane on March 27, 1977, 15 minutes after taking off at San Francisco International Airport, a “Boeing 747” passenger plane vibrated violently and fell rapidly due to the failure of engine 4.
The exhaust hole of the faulty engine burst into sparks and caught fire, causing the engine shell to crack and drop debris.
Fortunately, the crew immediately shut down the faulty engine and returned home.
Finally, the plane landed safely at San Francisco International Airport.
According to Agence France Presse, on August 20, 2010, an Qantas Airways “Boeing 747” – 438 airliner flying from San Francisco to Sydney had an engine failure at an altitude of 25000 feet (about 7500 meters).
Later, the investigation report produced by the Australian Transport Safety Administration (ATSB) showed that the accident was also caused by the fracture of turbine blades caused by metal fatigue.
3.
The landing gear of the US “Boeing 737” passenger plane broke when it landed in New York on the evening of July 22, 2013 (early morning Beijing time) on a Korean East Asia Airlines “Boeing 737” passenger plane carrying about 150 people.
10 people were injured when the nose of the aircraft taxied to the ground.
Figure 2 is a picture of passengers taxiing out of the cabin from the slide.
Generally speaking, the aircraft landing gear is hit violently when landing, which is easy to cause fatigue fracture.
In order to prevent fatigue fracture of landing gear, aircraft design units usually carry out drop vibration fatigue test in the laboratory.
The drop test machine can simulate the impact load of the aircraft when landing, and test the impact resistance of the landing gear through multiple impacts.
Figure 2 passengers taxiing down from the tail exit of the passenger plane (Xinhua / Reuters) 4 German high-speed rail accident that shocked the world.
The German high-speed rail accident that shocked the world was mainly caused by friction and fatigue.
On June 3, 1998, when the German high-speed railway “ice884” train was approaching aishude road bridge, it suddenly derailed.
The third carriage hit the first beam column on the right side of aishude road bridge, and the road bridge collapsed.
Then the rear carriages collided one after another, killing 101 people and injuring more than 100 people.
The accident analysis pointed out that the initiator of the accident was the train wheel.
In order to reduce the vibration during driving and increase the comfort of passengers, the wheels of the train are made into a multi-layer composite structure.
As a result, the friction between the outer ring hub and the inner disc leads to the fatigue failure of the outer ring rim.
Figure 3 is a picture of the accident of “ice884” train on German high-speed railway.
(for details, please refer to “friction” in Xiao He’s words by Zhang Shuangyin, which is published in the “popular science garden” column of the popular science website of the Institute of Mechanics).
Figure 3 Photo 5 fatigue damage of subway escalator in Germany high speed railway accident on June 3, 1998.
In 2011, a serious accident caused casualties on a brand of escalator in Beijing.
After careful analysis by researchers, it was found that the accident was caused by the fatigue fracture of a connecting bolt between the escalator driving host and the front seat plate.
This fracture triggered a series of subsequent damage, which eventually led to disastrous consequences.
(for details, please refer to why escalator accident happened by Chen Guangnan and Wu Chenwu, Published in the “popular science garden” column of “mechanics garden” on the popular science website of the Institute of mechanics.
What is fatigue? Definition of fatigue: the increment of local and permanent damage at a certain point of material or structure under cyclic load (stress); After enough stress (or strain) cycles, damage accumulation can produce cracks in materials or structures, and further expand the cracks to complete fracture, which is called fatigue failure.
The term fatigue was put forward by Spencer in 1839.
From 1950s to 1960s, Waller first measured the S-N curve characterizing fatigue performance, and put forward the concept of fatigue limit, which laid the foundation of fatigue research.
Fatigue life refers to the cycle times of material failure under a given stress (or strain) level.
The theory of fatigue mechanics contains rich content.
As a popular science essay, only the most important basic concepts are introduced here: 1s-n curve 4 is a typical S-N curve.
Abscissa n represents cycle times; The ordinate s represents the stress level (average stress or stress amplitude)..
