1. Medium Caliber Multipurpose Ammunition Technology Study – Uses of Modeling and Simulation
A. Atwood
Naval Air Warfare Center Weapons Division, China Lake
E. Friis, M. Stromgard
Nordic Ammunition Company, Raufoss, Norway
B. Richards
Naval Surface Warfare Center, Crane
April 14, 2004
NDIA Gun & Ammunition Conference

2. Purpose
Demonstrate application of modeling and simulation tools developed in the Multipurpose Program

3. Why Modeling and Simulation?
Used to save time and reduce operation costs
Decrease the number of live fire tests
Reduce development time
Examine effects of manufacturing changes
Optimum product to the war fighter

4. MP-Ammunition Technology Program
RMATS has validated models for manufacturing, ballistics, trajectory, and target function of the MP ammunition.
Impact & Penetration
Ignition & Burning
Effect within target

5. Press loaded energetic powders are major constituents of the MP-Ammunition
Pyrotechnic charge
Powder:
Zirconium
Powder:
Tracer
Powder:
Pyrotechnic charge
Powder:
High explosive
Powder:
Self-destruct device

6. Key Technology Areas - Manufacture and Launch
Development of powder models
Evaluation of press loading techniques
Quasi-Static Compaction
Field testing of nose tips with various fill techniques
Cat Scan
Compaction Apparatus

7. Numerical Simulations
Material models •
metal parts
incendiary & HE
target
Interactions
Material geometry
Loading forces
&
initial velocities
Numerical parameters
OUTPUT
press-filling operation
launching effects
flight effects
initial condition
(prior to impact)
impact & penetration
(course of events)
ignition stimuli
burning
fragmentation
Numerical code

8. Model Applications Improved 20 mm MP LD Development of penetrator
Evaluation of yaw
Effects of manufacturing
PGU28/B

9. Background
Out bore unintended ignition of the 20 mm MP LD round

11. Task – Product Improvement
Requirements
No ignition when hit by particles
Ignition when hitting the target
No ignition in drop test
Procedure
Used knowledge and tools developed in the RMATS program to suggest a new nose cap design
Use numerical simulations to study the behavior of different nose cap designs
Firing experiments with different (selected) nose cap designs

12. Original and chosen robust nose cap
Original design
0.9mm
Robust design
5mm

13. Task – Penetrator Development
Developed an analytical penetration model which unites the Walker-Anderson model and cavity theory
Simulation of penetration of tungsten carbide penetrator, to study when and why it penetrates and when and why it brakes up
Used the powder model as material model for the penetrator
The grid of the target and
projectile after 20 microseconds

14. Task - Yaw
Have studied the connection between propellant gas flow by the muzzle and yaw
The results from
the simulation
were used as input
into a mathematical
model in
Mathematica,
to calculate the
yaw angle.

15. Task – Effect of Manufacture
PGU28/B
In-bores/prematures
Most probable causes

16. PGU 28/B, PGU-28A/B and M70LD Design
Press fitted nose cap
M70LD
PGU-28A/B
Threaded nose cap

17. Damage with 20 mm PGU 28/B
Cobra

18. Causes of Prematures? Early in the investigation:
It was believed that normal function of the round could not cause the observed damage
Possible ignition mechanisms investigated:
Plugged bore resulting in 2 rounds firing simultaneously
A single MP round exhibiting abnormal behavior
Detonation instead of deflagration

19. Model of barrel damage
Establish the material data for the M61 A1 gun barrel and the 20 mm PGU 28/B shell body:
Tensile tests
Expanding ring tests
Study of fragmentation pattern
of 20 mm PGU 28/B (outside barrel)
Simulation of these experiments to establish/calibrate material data
Firing tests in barrel
Static
Dynamic
Simulation of these experiments to be able to study the nature of the prematures

20. Example of Results: Simulation: Experiment:
Simulations where PGU 28/B is set off while the round is moving (dynamic situation).
Burning regime was as a normal
functioning round, i.e. convective burning.
Round functioned in the thin region of the barrel.
Barrel damage as a result of the experiment
of a dynamic function of the PGU 28/B round
in the thin region of the barrel.

21. Nature of the Observed Prematures:
Normal initiation of the round in the barrel will give a barrel rupture as observed for the incidents of investigation
A single round is sufficient
Initiation of a round passing an area previously damaged
This means:
The mechanism is deflagration and not detonation
Plug bores disregarded
Barrel damage from one round may cause the ignition of subsequently fired rounds

22. Possible Causes for the Observed Prematures
One of the energetic materials must be brought to a situation where it meets the ignition criterion to ignite the round
Possible causes:
Pinching of nose tip incendiary between the nose cap and the shell body
Friction between nose tip incendiary and the closure nozzle
Nose tip incendiary particles impacting projectile incendiary during set-back
Rapid compaction of a low density area in the nose cap specific to the PGU 28/B

23. Pinching of Loose Incendiary Between the Nose Cap and the Shell Body
The tolerance extremes show that the fit of the nose cap may vary significantly
A loose fit may result in:
Loose incendiary migration between the different parts
Possibility for relative movement between nose cap and shell body during launch

24. Possibile Pinching in PGU 28/B
Incendiary pressed into the gap during the assembly process
PGU-28/B
Incendiary
Shell body
This is a potential
ignition phenomenon specific to a press fitted nose cap design
Nose cap
Closure nozzle
Loose incendiary from assembly process

25. Loose Incendiary from the PGU28/B Assembly Process
Simulations of compaction:
Last press increment results in loosely compacted RS41
During assembly process closure nozzle acts like a loading punch with a center hole
Loose incendiary
Loose powder found in opened rounds

26. Friction Between Incendiary and Closure Nozzle
Powder may be “shed” due to the set-back forces, causing friction as it slides down the closure nozzle:
Incendiary
Closure nozzle
Nose cap
Shell body
Risk of reaching the
ignition temperature due to
friction between powder and the closure nozzle is higher for PGU 28/B
Steel closure nozzle versus aluminum in other versions

27. Nose incendiary impacting projectile incendiary during setbackv
Incenidary 2
incendiary1 K
The hot-spot and bulk temperature as a function of time.
Hot spot temperature calculated in Mathematica.
NIKE2D simulation of nose incendiary hitting projectile incendiary at 240 m/s.
- shows the grid after the initial hit
This is a probable ignition cause for the 20 mm PGU 28/B with low compaction of last increment and press fitted closure nozzle

28. Hot-Spots Due to Compaction of Low Density Areas
Simulated set-back during launching
Performed hot spot calculation
This is below the ignition criterion, but it is a significant temperature increase. Rapid compaction of this low density area can not be ruled out as a possible ignition mechanism.
Thot-spot = 130 K
Low density in the nose tip will NOT cause ignition
Thot-spot = 10 K

29. Conclusions
Validated modeling and simulation tools developed in the RMATS program are being used
Product improvement and development
Improved 20 mm nose tip
Penetrator development
Calculations of yaw
Explain complex phenomena
In-bore PGU28/B prematures
Most likely that a combination weaknesses unique to the design and manufacture
Press fitted nose cap/closure nozzle
Low-density area of incendiary in the middle of the nose tip
Fine particle size distribution of the nose tip incendiary
Weaknesses are not found in other MP ammunition
20 mm PGU 28A/B will “fix” the problem