Grade 8.8, 10.9, 12.9 mechanical properties

[inline6]

Hi, does anyone know what the typical uniaxial mechanical properties of these Metric grade bolts are.

I am aware of the proof/yield stress and UTS but NOT the elongation values which is what i am really after?

i want to know how much strain do the bolts undergoe before actual fracture? For example similar quench and tempered plate grade 700 has approx same yield and UTS and elongation is ~18% min.

I am not after and elongation data for preload purposes but failure seperation of the joint in the inelastic region.

thanks

 

[Metalguy]

It's not that simple. Depends on the design of the bolt. Look up "reduced diameter" bolts or such made by ARP or SPS.

They allow the uniform reduced section to stretch (elastically and plastically) before the threaded section. "Regular" bolts have a severe stress concentration at the thread roots which governs their plastic flow.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[inline6]

thread stripping failure is not one of the modes that is likely exist due to the type of loading. in any event these geometry effects could be accounted for in a FE Model

if one machined a standard unaxial test specimen from a bolt what would be the elongation %?

 

[inline6]

i should rework that last post it should be tensile failure at threads or shear failure of threads are not likely to exist

 

[Metalguy]

I think you can expect ~15% elongation for unthreaded 12.9 bolting material.

It depends on the diameter, perhaps a bit less for big stuff.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[inline6]

which the comes to how the 8.8 and 12.9 compare, will an 8.8 show markedly more ductile behaviour particulary when subjected to high strain rates?

i have to balance out that an 8.8 while not as strong may prevent seperation of a joint under dynamic load compare to a 12.9 which might be stronger but more likely to fracture

 

[Metalguy]

This is getting more involved. If you are aware of strain rate influence, you should be able to figure all this out yourself.

You can do a lot worse than have bolts made from HY80, or the latest improved version whose name/number escapes me right now.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[desertfox]

Hi inline6

I found this site which gives some idea of the stress/strain curves for bolt materials:-

http://www.fastenal.com/web/en/69/b...SnY0t1YMgXNRwQSpzj34jrLH2!840019863!188412597

desertfox

 

[desertfox]

Hi inline6

I'm interested in why you need the strain rates for the bolt materials,normally bolted joints are designed based on the proof stress, after a bolt exceeds its proof stress it would be deemed to have taken a permanent set and any further external load would allow the clamped components to seperate and the joint considered failed.

desertfox

 

[israelkk]

http://www.mdmetric.com/fastindx/t12u.pdf

 

[inline6]

i am wanting to know whether i should use 12.9 or 8.8 if maximising energy absorbtion before fracture is the goal. whether the 8.8 is overload at much lower force on joint may not be an issue if the extra ductility allows the bolts to be intact albeit considered failed by more traditional analysis.

 

[Metalguy]

What you apparently want is a "tough" steel. 8.8 would be expected to be tougher than 10.9 and 12.9.

If you don't need high strength, consider HY80, one of the toughest steels made.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[desertfox]

Hi inline6

As Metalguy said 8.8 would be tougher than the 10.9 or 12.9 however there are lots of other factors to consider which were not party to in relation to your application, so its hard for us to give any further recommendation unless you can tell us more about your situation.
Have you considered asking a fastener supplier for the information your seeking?

desertfox

 

[TVP]

inline6,

Standards like ISO 898-1 and SAE J429 have requirements for minimum elongation in a tensile test:

8.8 according to ISO 898-1 : 12% min
10.9: 9% min
12.9: 8% min

Grade 5 according to SAE J429 : 14% min
Grade 8 : 12% min

The Fastenal link provided by desertfox shows elongation in inches rather than %, but this appears to be for a standard 2 inch gage length, which means that the Grade 5 has ~ 25% elongation and the Grade 8 ~ 11.5% Since toughness is related to area under the stress-strain curve, you can see that a Grade 5 (~ PC 8.8) is much tougher than a Grade 8 (~ PC 10.9).