Thanks. Maybe more than my high school chemistry can deal with.
Originally Posted by the Schwartz
Thanks. Maybe more than my high school chemistry can deal with.
As I was digging through some of the research material that I have amassed throughout the years, I came across this one (see attached)― Non-Newtonian Behavior of Ballistic Gelatin at High Shear Rates, Experimental Mechanics (2012) 52:551–560. I thought that you might like to see it.
Non-Newtonian Behavior of Ballistic Gelatin at High Shear Rates, Experimental Mechanics (2012) 5.pdf
In the attached paper there is a simple power law that allows for the adjustment of dynamic viscosity at high shear rates which is really useful for calculating Reynolds Numbers (Re = ρVD/μ) for high-velocity penetration events in the 10-4 seconds range. The coefficients for the power law were fitted against the empirical data using the 'least squares' method.
The equation is:
μ = αγ(n-1)
where μ = dynamic viscosity in centipoise (cp) for 10% gelatin
γ = shear strain rate in s-1
α = 4.5 x 10-3 kg∙s(n-2)
n = 2.22
As stated in the paper above, when the dynamic viscosity for a projectile is calculated for shear strains of 2,000s-1 and 8,000s-1, dynamic viscosity increases about 5 times as shown below:
4.5 x 10-3 kg∙s(2.22-2) x 2,000s-1(2.22-1) = μ = 3,243 cp
4.5 x 10-3 kg∙s(2.22-2) x 8,000s-1(2.22-1) = μ = 17,598 cp
Of course, the Q-model can be used to compute such time frames.
For the latest test that I conducted here: https://pistol-forum.com/showthread....slug-(P152XT1) ―
―the computed duration for that test was on the order of 4.858 milliseconds, so dynamic viscosity would have been on the order of―
4.5 x 10-3 kg∙s(2.22-2) x 2,058s-1(2.22-1) = μ = 3,716 cp
―which means that the average Reynolds Number (Re = ρVD/μ) for this event would be Re = 29.211 indicating that turbulence would be very low since Re < 2,000.
ETA: This paper might also add some valuable insight:
Laminar, Turbulent, and Inertial Shear-Thickening Regimes in Channel Flow, PRL 113, 254502 (2014.pdf
Last edited by the Schwartz; 04-16-2019 at 03:54 PM.
''Politics is for the present, but an equation is for eternity.'' ―Albert Einstein
Full disclosure per the Pistol-Forum CoC: I am the author of Quantitative Ammunition Selection.
This:
should have read:
Missed correct placement of the decimal in the computed Re. That's what I get for typing so fast.
''Politics is for the present, but an equation is for eternity.'' ―Albert Einstein
Full disclosure per the Pistol-Forum CoC: I am the author of Quantitative Ammunition Selection.
Good video.
I attended a ballistics workshop with Johann way back when. Good dude.
"It's surprising how often you start wondering just how featureless a desert some people's inner landscapes must be."
-Maple Syrup Actual
I definitely think that there are a few obvious points regarding the RCB stuff:
- There's no way to compare a bullet's performance in clear gel to anything other than its performance in clear gel. Trying to come up with some sort of conversion for ordnace gelatin or tissue or water-filled ziploc baggies or whatever is pointless.
- It goes completely wonky at higher velocities. Shooting it with rifles may be fun, but that's about it.
- The amount of tea-leaf reading people do over yaw cycles and "temporary cavities" in clear gel is silly, since it has no real correlation to what happens in tissue.
That Being Said™, however, I'll note that the pistol bullets I have usually seen that expanded well through 4LD and were found in the denim on the far side of a 16" block of clear gel were projectiles like the 124gr +P or 147gr HST and GDHP. So I guess they work well in that stuff, too.
Last edited by Tamara; 04-20-2019 at 09:51 PM.
In the past I was very obsessive and opinionated re: self defense ammunition and caliber selection. When I started working in the ER in my 1st year of medical school and realized how much of a non-factor the bullet was in GSW patient outcomes I quickly got off my soap box.
I am still choosy enough to only buy Speer/Federal products because I think they represent the highest quality product on the market, but I don't give really any of this stuff thought anymore. I really don't think it matters.
When it comes to pistol bullets, at least, "Shot placement is king, adequate penetration is queen, and everything else is angels dancing on pinheads."
Hence my comment about Ralpie’s brother and the denim....
You asked about the denim, which everybody and their brother uses and is the accepted standard. You didn't ask what jello Ralphie's brother was made of. Wrong retort.
Reply With Quote