2 ms·

Interestingly that has kind of moved upstream to a design phase consideration in modern times due to the incredible depth of understanding we have about materia

Interestingly that has kind of moved upstream to a design phase consideration in modern times due to the incredible depth of understanding we have about materials. Structures can be designed such that their expected loading will not stress fasteners beyond their ‘yield strength’, which is well characterized. Fatigue complicates the analysis, but we understand that too nowadays, although that is an understanding forged by many unfortunate consequences, such as: https://en.m.wikipedia.org/wiki/Aloha_Airlines_Flight_243 https://en.m.wikipedia.org/wiki/Aloha_Airlines_Flight_243

mc32 5y ago
Maybe the following has been designed out; however, I've on occasion seen the following wear pattern which compromises the initial strength of a fastener (usually due to friction over time): _ _ _______| | _| |__/ | | ______ | |_ ____/ |_| |_|
- blamazon 5y ago
  First, I love the plain text diagram! (Edit: not fatigue) This failure should be predictable during the design phase and that fastener is either wrongly specified or should have a recommended number of cycles after which it should be inspected and replaced if found to be out of specification. Of course, many items in our built world do not receive the same level of design scrutiny as I would wish, nor the maintenance regime…
  - auxym 5y ago
    Unless I'm misunderstanding the diagram, it does not look like fatigue at all but rather yielding from shear loading. The definition of fatigue is a small crack (in fact microscopic in the beginning) that grows through the application of cyclical loading (typically about 10k cycles is the lower bound for high cycle fatigue, which does not involve macro yielding). Thus a fatigue failure would look like a fully ruptured part , usually with two distinct zones of the fracture face: one smooth zone from crack growth ( sometimes with characteristic "beach marks") and the final sudden rupture which is usually rough. https://en.m.wikipedia.org/wiki/Fatigue_(material) https://en.m.wikipedia.org/wiki/Fatigue_(material)
    - blamazon 5y ago
      You are correct, I had a brain fart.
    - mc32 5y ago
      What I was trying to convey, which I didn’t do well in the diagram, was you have a bolt holding two plates together or a splice, and you have wear on the bolt shank -not necessarily shearing.

mc32 5y ago

Maybe the following has been designed out; however, I've on occasion seen the following wear pattern which compromises the initial strength of a fastener (usually due to friction over time): _ _ _______| | _| |__/ | | ______ | |_ ____/ |_| |_|

blamazon 5y ago
First, I love the plain text diagram! (Edit: not fatigue) This failure should be predictable during the design phase and that fastener is either wrongly specified or should have a recommended number of cycles after which it should be inspected and replaced if found to be out of specification. Of course, many items in our built world do not receive the same level of design scrutiny as I would wish, nor the maintenance regime…
- auxym 5y ago
  Unless I'm misunderstanding the diagram, it does not look like fatigue at all but rather yielding from shear loading. The definition of fatigue is a small crack (in fact microscopic in the beginning) that grows through the application of cyclical loading (typically about 10k cycles is the lower bound for high cycle fatigue, which does not involve macro yielding). Thus a fatigue failure would look like a fully ruptured part , usually with two distinct zones of the fracture face: one smooth zone from crack growth ( sometimes with characteristic "beach marks") and the final sudden rupture which is usually rough. https://en.m.wikipedia.org/wiki/Fatigue_(material) https://en.m.wikipedia.org/wiki/Fatigue_(material)
  - blamazon 5y ago
    You are correct, I had a brain fart.
  - mc32 5y ago
    What I was trying to convey, which I didn’t do well in the diagram, was you have a bolt holding two plates together or a splice, and you have wear on the bolt shank -not necessarily shearing.