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Fracture surface in cases of proportional and non proportional stresses

Fracture surface in cases of proportional and non proportional stresses

Fracture surface in cases of proportional and non proportional stresses

(OP)
Hi all

Does anyone know whether the fracture surface changes if the stresses applied in the cycles change from proportional (desired) to non proportional ?

RE: Fracture surface in cases of proportional and non proportional stresses

Quote:

from proportional (desired) to non proportional ?

If you want a response you need to better define your question. Non-proportional to me is variable amplitude loads but this could be different to what you intended.

RE: Fracture surface in cases of proportional and non proportional stresses

(OP)
You are right , sorry, I meant, when we apply a certain displacement, but in a way that might cause the resulting stresses in the component get non proportional

RE: Fracture surface in cases of proportional and non proportional stresses

SFTmech
The fracture surface would change only if the nature of the fracture changes, i.e. ductile to brittle or vice versa. If the original stresses were producing fatigue leading to a ductile fracture, a change over to non-proportional stresses may well produce a fatigue leading to a brittle fracture!

RE: Fracture surface in cases of proportional and non proportional stresses

Yes,when the load was suddenly increased, the fracture structure COULD change from ductile to brittle. e.g. from spherical dimples to cleavage planes (transgranular or intergranular fracture).

RE: Fracture surface in cases of proportional and non proportional stresses

SFTMech.... in addition to others comments...

Flaw initiation/detection/characterization can be affected/driven by many complicated factors... but 'where-you-start' affects total crack-growth and fracture toughness.

For the X-material in question: Characterize the unique crack-growth [KI], critical crack length [fracture toughness, KIc] and stress corrosion cracking [SCC] parameters... bare minimum... using standard ASTM tests.

Geometry VS loading SS crack(s) orientations can affects crack growth dramatically.

The surface of the part can grossly affect fracture: rough/smooth [see ASME B46.1], porous [cast, pitted/corroded, scratched/scored/gouged], brittle [hard anodized, abusively plated, abusively machined, etc], shot-peened [properly or poorly], etc...

Service environment affects crack growth: Corrosives, chemical exposures, extreme heat, extreme cold

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

RE: Fracture surface in cases of proportional and non proportional stresses

I see many fracture modes mentioned here and possible being conflated, but I still have no clear idea about the question being asked.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

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