Maximum Allowable Stresses

[mattaroccia01]

Dear All,
my name is Gianluca and I am new to this wonderful forum.
I have a question for all the structural engineers which doesn't let me sleep very well.
It is about the maximun allowable stresses (static and fatigue analysis) of steels. I know there are a lot of international codes on which I can find this numbers, but the problem I have is when the steel I am using in not on common standards so I only know the UTM and the Yield Strenght. Due to the complexity of the geometry it is very hard to apply the laws of the fatigue analysis we all studied. The component I am referring to is a shovel bucket for an hydraulic excavator. As you understand it is very hard to evaluate all the redution coefficiets due to the dimensional effect and the stress concentration coefficient. There are very good codes (like the German DIN 15018) which gives the maximun static and fatigue allowable stresses for certen types of steel. Other than those is a complete darkness. How would you procede? Is there an International Standard where I can find the numbers I need? Does anybody knows the following steels (commercial names)
Creusabro 4800
Dillidur 400
XAR 400 e XAR 500?

Thanks for all of you who will be willing to share some knoledge and guides on a very important issue.

Hope to hear from you soon.

 

[Ron]

Gianluca...welcome to the forum. I hope you enjoy it.

As for allowable stresses, I use the percentages that apply to stated limits such as 0.66Fy for extreme fiber bending stress and 0.6Fy for general tension, and 0.4Fy for shear. In the absence of any other guidance these should be fine.

For fatigue it is better to have an S-N curve for each material. Anything else is guessing. As an example, if you have two materials with the same yield strength, but significantly different elongation percentages, they will react differently to fatigue, with the less ductile material being more susceptible to strain hardening and having a potentially lower fatigue resistance.

I'm not familiar with the steels that you noted...perhaps someone else here can provide some guidance on that.

Ron

 

[ishvaaag]

http://www.matweb.com/search/datasheettext.aspx?matguid=2fe94d5bf4914b5183b9affb2f43dfc8

http://steel.keytometals.com/default.aspx?ID=CheckArticle&NM=163

http://www.1stdirectory.com/Companies/107609_A_J_Marshall_Special_Steels_Ltd.htm

google...

 

[JStephen]

Ideally, you'd use your corporate experience in designing and fabricating with similar steels and similar buckets.

The third one listed, I assume is an abrasion resistant material, which could be quite a bit different from standard structural steels.

 

[hokie66]

Agree with JStephen. The way excavator buckets and similar digging appliances are made depends on experience. The designs evolve as field experience exposes weaknesses. The major manufacturers protect their information rigorously.