Stress Concentration Factors of Cast Surfaces 1

[izax1]

What is the SCF of a normal Sand Cast Alu surface? How would you apply that SCF to your calculated (from FEA) stresses?? This is a fatigue loading, and SCF will have a significant impact on Fatigue Life.

Thanks

Bernt

 

[ecampos]

I dont think that you can use Stress concentration factors for a cast aluminum part. You probably should not be using a aluminum casting for a fatigue application. MIL-HNDK-5 does not show any fatigue curves for cast aluminum, but it does give some for wrought aluminum, leading me to beleive that the fatigue theories do not apply.


Edson Campos
edsoncampos@earthlink.net

 

[brad]

While I don't have my books handy to prove my contention, I would strongly dispute the above statement by ecampos.

While I don't have an answer for SCF, I do know that aluminum is frequently used in fatigue calculations (though not as much as steel, as it has not historically been studied as much for fatigue properties).

Just because one cannot find something in a particular book does not delegitimize it. There are sources for this type of information.

Bernt, I'm incommunicado for two weeks, so I won't be able to give you any specific answers. However, I would encourage some searches in the literature, and a talk with an aluminum manufacturer's rep, if you know any.
Also, look into some of the fatigue software companies--Safe Technologies, MSC/Fatigue, LMS. They may be able to provide you with some material properties and details that are included in their products. That may give you a good start.

They should be able to help you.
Good Luck

 

[ecampos]

Dear Bradh,
If you read my posting a little more closely, you will note that I make a distinction between "CAST" and "Wrought" Aluminum. Of course Aluminum can be used for fatigue apps., but a Cast aluminum structure is probably not a good idea for a fatigue app. I merely informed "Bernt" that there are no S/N curves for cast aluminum in MIL-HNDBK-5 which usually lists all these properties for materials that have a history of being used for that type of application.


Edson Campos
edsoncampos@earthlink.net

 

[butelja]

Just my 2 cents worth. I would think that the stress concentration factor for a casting would vary with the part size. If a sand casting has a certain surface finish, the average "defect" size on the surface will remain constant, while the reference dimension of the part will vary with part size. Stress concentration factors are usually a function of r/H, r/D, etc., all of which are the ratio of the geometry defect or discontinuity to the reference dimension.

 

[GregLocock]

Cast aluminium is definitely used for components where fatigue is an issue.

Look under the bonnet (hood) of most cars and start counting the applications.

Cheers

Greg Locock

 

I appreciate all your answers and involvement in this case. I agree that cast Al. parts is used in many fatigue applications. In fact I am involved in one, and that is the very reason for my question. I would really be interested in som ballpark numbers for SCF on Cast Alu surf (or any cast surf for that matter)

Regards
Bernt