chap 10

chap 10: Detection of surface and subsurface defects

*3 mthd:

1)Visual inspection
a)using naked eye
b)optical aids
-small lens , pen torch
c) industrial telescope
-tv camera
d) in sito metallography

2)Magnetic partical process
-use electromagnetic waves and particles
-magnetic lines of forces are predominattly inside the material
-with defects, field is distorted, local magnetic flux leakage field.
- fine ferromagnetic particles applied to the surfaces of the test piece will be attractred by the flux leakages field and accumulate at the defect site.
-build-up particles can be seen by naked eyes
-magnetic line are always at right angle to the direction of the current flowing in a conductor.-right hand rule!!

*sensitivity
-highly.able to detect as little as 0.001mm

*factors affecting sensitivity:
a)orientation of the defect
b)shape and chartic of the nagetic particles
c) sensitiviy increases eith the increasing field strength

*limitation:
a)material must be able to be strongly magnetized
b)onli surface, not internal defects.

3)liquid penetrant process
step1: surface preparation
step2: application od penetrant
step3: removal of excess
step4:development
step5:observation and inspection.
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