Fatigue and Stress | Metal Fatigue Flashcards
Ultimate stress is where the metal will ___ after applying a ___
fracture, single load
Repeated loads well below the level of ultimate stress will eventually have a similar effect, called metal ___
fatigue
___ ___ is the initiation and propagation of microscopic cracks, due to the slippage of atomic planes within a metal component
Metal fatigue
An applied load only needs to be around __% of the ultimate load or stress for a fatigue crack to occur.
30
Fatigue cycles are ___ and ___ ____
cumulative non reversible
The most significant factors are:
- Type of operation
- Magnitude and frequency of loads
- Quality of material
Composite materials, fatigue is not a consideration at stress cycle around __% of the ultimate stress, because the individual elements tend to fail rather than the structure itself
80
Compared to metal, composite structures weaken ___
gradually
The local stress at any round hole in a sheet of metal under tension is _ times the average
3
Fatigue cracks have 3 stages, which are:
- Initiation
- Growth
- Final Fracture
Corrosion helps a crack grow ___
faster
Stop drilling is __
drilling a small hole at the end of the crack to stop it spreading.
Weak points can be reduced by using ____ instead of rivets and bolts and by casting wing skins in large panels
adhesives
Airworthiness can be extended if 4 golden rules are followed:
- Accurate records
- Stay with limitations of flight manual
- Do not use wrong parts
- Report exceedances
Corrosion can occur when dissimilar metals are used together and one of them breaks down into various compounds, either by ___ or ___ action
chemical or electrolytic
Corrosion worsens with ___ temperature and ___ humidity
increased increased
When steel is mixed with aluminium, you will get ___ corrosion after moisture acts as an electrolyte.
galvanic
Corrosion can be prevented with ___ based, or by ___ ___ the panels
zinc, electrically isolating
Steel terminals should be ___ plated if you want to use them with copper cabling
cadmium
Copper and cadmium are relatively ___ in terms of electrical potential
close
Aluminium and magnesium will corrode ___ because they ___ in terms of electrical potential
easily far
Oxidation is the loss of at least ___ electron(s) when two or more substances interact, which may or may not include oxygen
one
Oxygen is very caustic with ___
iron
With copper, a ___ ___ of copper oxide will form
greenish layer
Destructive oxidation cannot occur if the oxygen cannot penetrate a surface to reach the ___ ___ it craves
free radicals
Stress Corrosion Cracking is the unexpected failure of normally ductile metals subjected to ___ __ in a corrosive environment, especially at ___ temperatures
tensile stress, higher
SSC is caused by ___
chemicals
The chemicals that can cause SSC will make the metal look ___ ____ ____
bright and shiny
SSC progresses ___
rapidly
SSC is more common among ___ than pure metals
alloys