Is it possible to convert from a Rockwell R scale to the Brinell scale?

I have no material engineering experience any sort of education in materials and am having a hard time finding an answer.

I want to know what a Rockwell R105 equivalency is on the Brinell scale.

Google is pretty cool!

http://www.engineersedge.com/hardness_conversion.htm

https://www.carbidedepot.com/formulas-hardness.htm

Google is cool!

I used it. Found no readily available information regarding the conversion from Rockwell R to Brinell, as you can see in those two charts you linked, and then came here to ask for some help.

This isn't my normal area of engineering, and I'm pulling from school memory, text books on my desk, and google.  That said...

It may be possible that there isn't really a meaningful equivalent of the two.  Brinell seems suited, much like Rockwell B and C, to harder materials.  

The Brinell test has a nice well defined equation (rather than typing it out from my textbook, here's a link contained in DasRonin's link http://www.engineersedge.com/manufacturing/brinell_hardness_test_equation_13173.htm).

However, my textbook gives the Equation for Rockwell hardness as:

R = C1 -C2*t

Where R is Rockwell harness, t is the depth of penetration, and C1 and C2 are constants that are defined based on the scale of Rockwell hardness that you are using (R in this case). However, I am unable to locate any information telling me just what these coefficients are for R, just that this scale is used for much softer materials such as polymers or soft metals.

I did note this from the University of Buffalo's Civil Engineering resources website (http://civil.eng.buffalo.edu/cie616/2-LECTURES/Lecture%204a%20-%20Material%20Testing/HARDNESS%20TEST.pdf)



Which furthers my theory that they (Rockwell R and Brinell) may not be compatible/relate-able scales.  It's worth noting that my textbook also goes into detail that their "conversion table" between Brinell and Rockwell C and B that is shown in the book is only valid for steels. Considering that the values are definable for one material but do not have corresponding values for another also lends credence to this.

I hope that helps, but I have a feeling it doesn't.

For morbid curiosity, what is the material and why is it needed to convert between the units?

Looking here http://www.buehler-asia.com/brochure/download-02_Hardness_Table_01.pdf, it can be surmised that the equation for Rockwell R can be derived from the table on page 10.

i.e. The Rockwell R hardness, HRR = 130 - 500t, where t is in millimeters.  So C1 is 130 and C2 is 500.

Captain_Morgan thanks for the links and the time to do some research.

I am conducting a forensic firearm and toolmark experiment as part of a masters program. My experiment is examining whether or not bullets fired from a fused filament fabrication 3D printed Defense Distributed Liberator pistol can be identified under the Association of Firearm and Tool Mark Examiner's (AFTE) conclusion guidelines.

The pistol is printed with Octave brand ABS thermoplastic and I have used .38spl. Federal LRN ammunition. I chose to use lead bullets rather than FMJ (gilding brass, commercial bronze, or cartridge brass) believing that the brass jacket material would be harder than the ABS barrel and therefore leave no marks.

The LRN bullets were a good choice; I was able to fire and recover bullets with varying levels of detail from the bore. Now I am trying to explain why I skipped FMJ entirely in the project and went straight to LRN. If I can say FMJ gilding brass is ___________BHN, Federal LRN bullets are 6 BHN, and Octave ABS is ___________ BHN. I will be able to better explain why FMJ was skipped altogether.

I have no scientific or engineering background and learning as I go as far as the hardness scales and properties of materials. The best answer that I have found is that there are some rough conversion tables available for some of the scales; such as Rockwell A, B, or C to Brinell, but not for every scale.

If there is not a direct conversion between the scales used to measure the hardness of plastic and those used to measure metal, is there any way to compare the relative strength of these three materials? Soft bullet lead (~6 BHN, not hard cast, ABS, and FMJ copper alloy).

The numbers I have found so far are:  ABS Rockwell R105-R110, Federal lead bullet ~6 BHN, and gilding brass/copper alloy C21000 ~90 BHN.

Thanks for the assistance!

ETA: I am going back to the forensic lab tomorrow and will be speaking with several very experienced firearm and toolmark examiners. I will see if they have an input. I don't know if I will have access to any hardness testing equipment but I will ask around. The hardness levels of the material is not a huge part of the project but it would help.

After reading your reply, Cytic, I would have typed out almost exactly what Chapman did.  Even if your school doesn't have an engineering department, there is likely a near-by lab or other university that does have the capability to test the hardness.  Just call around.  Especially since you're doing research for a master's program, some other grad student will probably have mercy on you.

It also comes unglued when the test tool is a different material, using a different load (impulse) etc.

It has little practical meaning.