6.5 Grendel CAD - FEA

[cory]

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.

PM sent. Than You!

VarmintAl I'm assuming he's a member of the horde, I'll be in contact with him in the near future.

I'll be using an academic version of Patran. Unfortunately I know it limits the use of several advance functions. I'll be surprised if it's not limited to elastic behavior, but I'll check on that and let you know.

At this point in my experience, all of my challenges in FEA's has been with a finicky software. I'd be shocked if Patran was the FEA software of choice for anyone.

I actually have been expecting the brass to remain structurally sound beyond the 50 ksi limit, demonstrating the bolt to be the likely weak link. I'm hoping this would at the very least contribute to the discussion on improving the Grendel, started by Guardsman26.

I would like to continue this project to eventually include the bolt in a dynamic analysis, to demonstrate where the bolt could be improved. However, that may remain outside the scope of my abilities. It certainly does at the moment. haha