Micro Tensile Test comments requested 1

[bvasa]

Hello, all.

I'd like your comments on micro tensile testing.
-Are the results consistent and valid?
-Are there factors that can influence and/or nullify the results (surface finish, heat induced when cutting samples, etc.)?
-Are they directly comparable to tests run with the standard samples?
-Is there another method that is more appropriate for determining the strength of material with a thin cross-section?

I do a lot of cold metal forming, usually in 1010-1020 steel or aluminum. The workpieces are cylindrical, with finished wall thicknesses ranging from 1.2mm to 3mm. Material thickness reduction is up to 85%. The big question I need to answer is what material properties are exhibited in the part after forming. I need a good method of evaluating these properties in order to answer it.

Any direction will be appreciated.

Thanks!
bvasa

 

[Goahead]

Hi,
ASTM E-8 covers tensile testing even for substandard specimens, provided the proportions are maintained. Other than that I do not know of any approved micro tensile method.

Results are consistent and valid (and comparable) provided you remain within the specimen forms and dimensions of ASTM E-8.
All the factors you mention have influence an all tensile specimens, even regular ones.
Another method for determining properties is obviously Vickers hardness testing, except that this will not give you any indication as to the ductility of your material: comparison of hardness to strength is empiric, based on databases of recorded results, not deriving from basic principles.

With a reduction of upto 85% you obviously reduce ductility very much, unless you restore it through heat treatment after cold forming.

Could you load test your items or even test them to destruction?

http://www.welding-advisers.com/

 

[bvasa]

I guess a more general approach to my question would be:
Is there a good reference book or a test methodology that would allow me to predict the strength of a cold-formed part, knowing the raw material (focusing on low-carbon steel for now), initial heat treat condition, finished dimensions and percent reduction?

I'm hoping that there is some standard reference material that will have at least some of the specific data points I need.

The answer I was hoping to NOT hear was that I would need to do a variety of destructive tests to develop my own empirical database. I provide design feedback for a number of my customers, and having to test all the various part configurations would be time-consuming and expensive. However, that may be the BEST answer.

Thanks for the feedback, Goahead.
Best regards,
bvasa