LRRPF52 Wrote:If I were you, I would consider just cutting a piece of Grendel brass in half longitudinally, taking a picture of it, and making your CAD file that way.

What would be very helpful to the forum would be if you compared Lapua, Hornady, Wolf PPU, 7.62x39 Federal, Lapua, Winchester, IMI, etc. necked-down to Grendel. The members here could provide you with samples of everything you don't have brass-wise.

You would also want to do a hardness analysis on all the samples, as they aren't the same. Lapua brass has the best longevity.

dmsims21 Wrote:I could model the brass in SolidWorks. I would need someone to supply external and internal dimensions. Meaning full results will be tricky as the material properties are different at the head and neck do to annealing. It would be interesting to check if case stress would be different in max and min chambers due to varying deformation. Simulating the "belted magnum" affect due to early extraction would be cool too.
Sorry to ramble and pull big words out of the air. It has been a long time since I took an FEA class. Good luck.

JASmith Wrote:Excellent project!! You will learn a lot.

I have a QuickDesign rendering of the Grendel based on a SAAMI - compliant drawing. I used it to design the .20 Grendel cartridge. The volume and resulting Quickload velocities turned out rather close to the measured numbers. PM me with an email address if you can use it.

If you are truly serious about modeling the Grendel, then you should contact VarmintAl. He has a rather interesting background, but suffice it to say he knows FEA rather well. He used LSDYNA for calculations like the one you are contemplating. He would be very pleased to offer advice and reference links. I can go into the differences between codes, but you will want to check to see if the one your class uses is capable of modeling at least static and preferably dynamic plasticity (implicit versus explicit time steps). Absent that feature, you will be able to get an idea of when the brass starts to get overstressed, but most codes start to crash when the elastic limits are exceeded.

I have some appreciation of the challenges of getting started in finite element analysis. Don't give up if the code you are obliged to use is limited to elastic behavior. It won't model the case behavior as the pressures get high enough to abuse the case. Other interesting analyses can be done where the system response is fully elastic. One is the response of the bolt head. Another is the chamber region. Fatigue in these areas are partly why Bill Alexander established the 50,000 PSI operating pressure rather than the 10-20% higher pressures the case can handle.

I used his results in working of a possible method of determining when pressures get too high. The method is probably useful only when the brass starts to move enough that inreases in pressures give one loose primers or worse. Those pressures are significantly higher than the nominal 50,000 psi one gets with SAAMI-compliant loads for the Grendel.

Look at his analysis of the .243 Winchester cartridge in the chamber and then contact him. If your email doesn't get answered in a few days, then it probably got snagged by his spam checker. PM me and I'll make sure the connection gets made.

PS I ran codes like these from the mid-80s through the late '90s so. I also know that VarmintAL was one of the most highly respected engineering analysts where I worked. He will be able to help even if he hasn't, like me, recently run a calculation.

Trooper Wrote:Out of curiousity, could one make the cases out of plastic? Steel would work, of course.

The military is starting to realize that it is very wasteful to leave brass in a combat zone. Plastic makes more sense (weight) but steel would do for military purposes.

cory Wrote:I do seriously doubt a nonmetallic material could withstand the heat, without failing and/or melting to the barrel. However, it would be interesting to see the outcome of a stress/thermal FEA on a non metallic material.

JASmith Wrote:...The military challenge is keeping them from melting or otherwise misbehaving when the barrel and chamber start to glow from extended rapid or full-auto fire.

Bill Alexander Wrote:The operating pressure and shape for the Grendel was partially derived with one eye on the use of a polymer casing. It has several attributes where it is similar to a steel case in behavior. While such a move would preclude the move towards a hotter loading as discussed in the military section of this forum it is quite possible with the current set up.

The challenges facing the use of polymers in a case are now primarily bullet retention and a clean release. Obturation is fine but some work is required as pressures rise above 24,000 psi.The interaction of the case with a hot chamber has been addressed successfully if one cares to dig enough but this seems to evade the current efforts except one.

Reloading is not possible.

In the examination of an FEA model I think you will find that the construction of the support structure and the constraints thereof are the biggest challenges. The system should all exist in the elastic regime except the case which does exhibit plastic behavior so your model should be able to account for both. For those interested the simple version is to examine the relative hoop expansion of the dissimilar materials as a compound thick cylinder problem. Very crude but enlightening.

JASmith Wrote:What would the market consequences be if Law-Enforcement went completely to plastic cases and the military to steel cases? The recent multi-billion round order would have been filled without impacting the brass market.

But, would manufacturers find enough remaining business in the civilian market to justify continuing brass cases? How would that impact reloaders?

JASmith Wrote:What would the market consequences be if Law-Enforcement went completely to plastic cases and the military to steel cases? The recent multi-billion round order would have been filled without impacting the brass market.

But, would manufacturers find enough remaining business in the civilian market to justify continuing brass cases? How would that impact reloaders?

Trooper Wrote:China is basically buying up all of the copper mines worldwide. Afghanistan has the second largest copper deposits in the world. China is ready to take that over once we are out of there.