help!!!! very important?

Question

who can give me 3 example of how cracks arise in a component. it is very important, please.

Answer 1

1. pre-existing flaws
2. temperature or pressure differences between the component
3. rust corrosion (Metals)
4. High hardness and low ductility of a component under stress or shear

Actually, its a combination of either of these, not merely by themself.

Cyclic stresses, such as bending something back and forth are fatigue failures, though, not cracks.

Answer 2

For electronic components:

1. Excess heat from soldering can crack the part.
2. Larger surface mount parts (2225 size and above) with different thermal coefficient of expansion than the PC material, can crack on the PC board, when the board is heated and cooled to extreme temperatures.
3. Excess PC board heat, poorly dissipated, can rupture (crack) aluminum electrolytic capacitors and some wet tantalum caps (this happens all the time in audio power amplifiers).
4. I have even seen some uncoated surface mount resistors crack from the light mechanical pressure of installing the part on the PC board by hand! (poor design of the component IMO).

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Answer 3

Not sure what you mean by component...
1) stress from repetative bending, think fatigue cracks
2) impact, think rock hitting windshield
3) rapid temperature changes, think warm water over ice cubes