The entire Comet fleet was grounded whilst a board of enquiry met.
MIT News Office
Before the recovered wreckage was fully analysed the board concluded that the aircraft had been brought down by a turbine blade in one of the engines shattering and so causing an explosion in the fuel tanks. On April 8th a second Comet crashed killing all onboard. It had made only flights.
The entire fleet was grounded a second time. In the meantime tests were being carried out on a Comet airframe. It was filled with water then pressurised and depressurised to simulate the change in external air pressure an aircraft experiences each time it completes a high altitude flight. After three thousand simulated flights cracks were found around a window in the roof of the cockpit. In the other aircraft metal fatigue would have caused this crack to grow until the fuselage suddenly ripped open. The square design of the windows had produced unexpectedly high stresses on the metal skin of the aircraft also the panels had been punch riveted, which increased the permanent stresses on the skin, rather than drill riveted and glued as per the design specification.
A combination of poor design and a bad manufacturing lead to the deaths of fifty six passengers and crew.
The initial failure had been caused by a faulty weld that attached a metal plate to a hole cut in the support. The support was repeatedly stressed each time the platform was hit by a wave. A crack formed in the weld which grew due to metal fatigue, this spread into the support itself which failed. With the support gone additional stresses were placed on the remaining five supports.
These failed due to mechanical overload. The root causes of the failure were widespread.
Introduction to Metal Fatigue | Technical Report Mechanical Engineering
Bad design meant that the platform would fail if a single support were lost, bad construction meant that the support was weakened by unplanned additions to the design and poor maintenance meant that a 70 mm long crack had not been noticed in a critical component of the platform. In all of the crew lost their lives.
- Metal Fatigue?
- Cultural Sociology An Introduction.
- Fatigue Demonstration;
- Metal fatigue;
- Our Kind of People: Inside Americas Black Upper Class.
- Metal Fatigue Failure Theory and Design Considerations!
As you might expect, the larger the stress on a component the fewer stress cycles are needed to lead to failure. Different materials respond differently too. A typical fatigue response is shown here. Notice that the cycles scale is logarithmic:. As the number of cycles increases so the tolerable stress for aluminium decreases. As an example, an aluminium component that is regularly subjected to a stress of MPa can be expected to fail after about 1,, cycles. If the component is part of an aircraft fuselage that is only stressed once each flight then even if it made ten flights a day every day of the year then the component would last for over years, far greater than the life of the aircraft.
If however it were part of the undercarriage wheel that was stressed each time the wheel rotated it might be cycled several thousand times each flight and so would be likely to fail after a few hundred flights. The latter case would clearly be unacceptable. The steel sample shows a different pattern. The peak cyclic stress continues to drop until it reaches MPa.
After this it remains constant. This means that so long as the stress that a component made of this material was subjected to was kept below MPa then it would never fail due to fatigue. Each alloy will however have its own distinctive fatigue curve and so the graph presented here should not be used to determine the life of real world components. Take two metal bars, one aluminium, the other mild steel.
They should be as thin as is practical. Cut a notch in each to half the width of the bar. Bolt an electric motor with an eccentric cam to the end of each bar and then mount both bars vertically with the notch at the top. Turn on both motors to the same speed. Make sure that no damage will be done when one of the bars breaks off. Place padding on the floor so that the motor is not damaged. You could try to construct a cut off so that when the bar finally fails the power will automatically disconnect. Two strips of copper sheet are tapped together and a third sheet is sandwiched between the two.
Crocodile clips make the connections to either end of the cut off. When the broken end of the bar falls it pulls out the central strip disconnecting the power. The duration of the demonstration will depend many factors specific to your set up such as the thickness of the metal and the mass, position and speed of the eccentric cam, however each time the motor rotates microscopic damage will be done to the aluminium at the tip of the notch.
A crack will form and gradually grow with each cycle.
- Buy Metal Fatigue.
- BOAC flight 781!
- Metal Fatigue?
- Cracking the Personality Code.
- Vocabulary and Spelling Success in 20 Minutes a Day (Skill Builders in 20 Minutes).
- Metal Fatigue!
Eventually the crack will reach a critical length and it will grow rapidly across the remaining metal. The aluminium bar will then snap. Whether the steel bar survives will also depend on too many factors specific to your set up to make a prediction here. However even if it does fail then, all other things being equal, it will do so after the aluminium has failed. Examine the fracture surface of the aluminium. The section away from the notch will be rough, where the bar fractured suddenly due to ductile tearing. There are in fact two distinct areas of fatigue; they are called high and low cycle fatigue.
High cycle fatigue typically leads to failure after between 10 3 and 10 8 cycles. It involves relatively small stresses, always within the elastic limit of the material in question. This is the type of fatigue failure that has been discussed up to this point. With low cycle fatigue the component is likely to fail before it reaches cycles, the amount of distortion involved in each cycle will be so large as to produce plastic deformation of the material.
You can investigate low cycle fatigue for yourself very easily. Securely clamp a thin metal sheet or wire between two thicker plates. Place two more plates above these but leave a small gap between the two sets.
This ensures that all the flexing occurs at a single well defined location. Set this against a card so that the angle of deflection can be measured easily. It should spring back slightly but not all the way to the zero position; this confirms that the material has exceeded its elastic limit. This is one complete cycle. In subsequent cycles you need not allow the sample to spring back neither do you need to stop at the zero mark.
Develop your base and command your forces carefully - the enemy can appear from any direction, including above and below! Choose from three warring factions - The Milagro, Neuropa or Rimtech are competing CorpoNations, each with their own technologies and research capabilities. Capitalize on their individual strengths and weaknesses for the optimum strategic advantage! Follow the story of three estranged brothers, as they scavenge high technology from the ancient alien Hedoth to fight a war against their very own bloodline.
Includes both cooperative and death match modes. Force your enemy to surrender! Launch and airborne assault using hover jets! Destroy the menacing threat from above! Overwhelm your enemy with combined arms! Recommended: OS: Windows 10 Processor: 1. See all.
View all. Click here to see them. Customer reviews.
Overall Reviews:. Recent Reviews:. Review Type. Date Range. To view reviews within a date range, please click and drag a selection on a graph above or click on a specific bar. Show graph. Brought to you by Steam Labs. Filter reviews by the user's playtime when the review was written:. No minimum to No maximum. Off-topic Review Activity. When enabled, off-topic review activity will be filtered out. This defaults to your Review Score Setting. Read more about it in the blog post.
Related Metal Fatigue
Copyright 2019 - All Right Reserved