Crack Definition
Crack Definition
(OP)
Good day guys,
Do you know if there is a std definition of crack?
I have heard that in NDT there is a crack when the length of the defect is three times more than its width. Unfortunately I have not found any document stating that.
Thanks,
D.
Do you know if there is a std definition of crack?
I have heard that in NDT there is a crack when the length of the defect is three times more than its width. Unfortunately I have not found any document stating that.
Thanks,
D.





RE: Crack Definition
SAE AMS2647
Discontinuity - Any interruption in the normal physical structure or configuration of a part, such as cracks, laps, seams, inclusions, or porosity. A discontinuity may or may not be a relevant defect.
ISO 6157, ASTM A788, etc.
Crack — A crack is a clean (crystalline) fracture passing through or across the grain boundaries and may possibly follow inclusions of foreign elements. Cracks are normally caused by overstressing the metal during forging or other forming operations, or during heat treatment. Where parts are subjected to significant reheating, cracks usually are discolored by scale.
ASTM E1316
defect, n — one or more flaws whose aggregate size, shape, orientation, location, or properties do not meet specified acceptance criteria and are rejectable.
discontinuity, n — a lack of continuity or cohesion; an intentional or unintentional interruption in the physical structure or configuration of a material or component.
flaw, n — an imperfection or discontinuity that may be detectable by nondestructive testing and is not necessarily rejectable.
RE: Crack Definition
RE: Crack Definition
RE: Crack Definition
RE: Crack Definition
RE: Crack Definition
Ruag - why do you need a definition? what materials are you dealing with? in what context do you need to do an inspection and need a definition? many aircraft SRM's have definitions for different defect / damage types.
RE: Crack Definition
It's interesting someone would need a definition of a crack.
It would in my mind would be for metals.
& it is not allowed for aerospace/aviation critical applications regardless of it's size.
It's probably taken for granted by most what a crack is.
There's welding cracks, heat treat cracks, grinding cracks, straightening cracks, bending cracks & on.
but it's possible for other non metallic materials.
or like plastics, stones or what ever.
see attached Mil-std-1907 definitions
Mfgenggear
RE: Crack Definition
Mfgenggear
RE: Crack Definition
Whatever you call it, crack, flaw, or discontinuity, the result is the same: things are no longer held together. Which depending on the loading and remaining residual strength, could result in a problem (and does not matter if metal, CFRP, or stone). Safety is at risk if the flaw/crack cannot be detected before failure.
The back story must be very interesting. Please divulge if you can.
RE: Crack Definition
RE: Crack Definition
Yes thats true I should add more to my comment.
My statement is in regard to the mfg details, sub assembly.
& final assembly, with very very critical applications.
My experience doe not extend to all ready flying aircraft.
to my knowledge no cracks where ever permitted.
there is always exception to the rules. especially for non stress parts or Assemblies. I normally worked with flight articles.
I am surprised that a flying aircraft allows for cracks regardless if it still passes stress calc's.
Thanks
Mfgenggear
RE: Crack Definition
RE: Crack Definition
Thanks a lot for your support.
Actually I am dealing with a component that is made of magnesium-casting and afterwards milled to the final geometry.
The production procedure requires dye penetrant inspection after the milling, but this procedure is not very clear in defining the acceptable size of defects.
As you know casting parts are prone to pores and applying the mentioned NDT I get several indications. Then my question: how to distinguish between pores and cracks? Is there a std. definition of crack that can help me to solve my doubt?
Thanks.
RE: Crack Definition
2) maybe talk to a casting manufacturer ?
3) maybe take pix to show inclusion/pore (acceptable) or crack (unacceptable) ? part of this may be "it's a surface detect, that'll be removed in final dressing" ?
4) don't stand under/near old military a/c (particularly Canadian C130, and Ozzie SH3s, and Canadian SH3s ... and a long list of others !!)
RE: Crack Definition
Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations
RE: Crack Definition
SAE AMS 2175 Castings, Classification and Inspection Of
http://standards.sae.org/ams2175/