design and modeling of a thermoplastic composite tail …...design and modeling of a thermoplastic...

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Design and Modeling of a Thermoplastic Composite Tail Cone for a Kinetic Energy Penetrator

Design and Modeling of a Thermoplastic Composite Tail Cone for a Kinetic Energy PenetratorJuan Serrano, Uday Vaidya, Adolfo Villalobos, and George HusmanSchool of EngineeringUniversity of Alabama at Birmingham

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INTRODUCTION

Kinetic Energy PenetratorM1A1 tanks have a 120mm smooth bore gun that fires several types of ammunition.

ProjectileTailcone Primer

Sabot Cartridge Case Propellant

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DETAIL OF TRAINING ROUND PROJECTILE COMPONENTS

Projectile (Body)

Tailcone

Threaded Section

Tracer

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TAILCONE XM 1002 PROJECTILECURRENT DESIGN

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ROLE OF TAIL CONE IN KINETIC ENERGY PENETRATORS

Two kinds of rounds: Practicerounds and Combat rounds

• In combat rounds, the projectile does not have a tailcone, but it is fin-stabilized

• Purpose of a tailcone is to provide stability and limit the range of the projectile

Fin Stabilized

Tail ConeStabilized

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MOTIVATION

•Conventional tail cone made of 7075 T6 aluminum adequate properties but expensive (machining)• Explore lower cost materials and processing options that yield similar performance•Finite Element Analysis is the only efficient way to design such a component

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LONG FIBER THERMOPLASTICS

• Fiber aspect ratio ~ 600-2400• Superior mechanical

properties than unreinforced TP

• Higher impact strength• Reduced tendency to creep• Damping • Corrosion resistance• High volume processability• Ability to fill complex

geometries

20 mm

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BACKGROUND INFO ON THE JOURNEY OF THE TAIL CONE

Source: Army Research Laboratory

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BEFORE DETONATION

05000

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Acceleration (g) Pressure (MPa)

Time (ms)

ProjectilePrimer

Sabot

Cartridge Case

PropellantTailcone is the only component that sits inside the chamber

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MAXIMUM PRESSURE AND ACCELERATION (IN BORE)

Maximum acceleration of 44,300 g at 1.95 ms

Maximum pressure of 406 MPa at 1.95 ms

Average temperature of 1980 K

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Acceleration (g) Pressure (MPa)

Time (ms)

You cannot replicate these conditions in the lab, therefore FEA is the most efficient route to address this problem

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OUT OF BORE

05000

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Acceleration (g) Pressure (MPa)

Time (ms)

Projectile takes 6.15 ms to reach the end of the chamber

• The stresses are various orders of magnitude smaller when compared to the in-bore case

• Frictional heat when in contact with air

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FINITE ELEMENT ANALYSIS, DESIGN AND VERIFICATION

Source: Army Research Laboratory

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Two (2) dimensional axisymmetric mesh of the tailcone was generated to optimize computational time for solution convergenceThe use of an expandable 2d model allows for the use of a highly refined finite element mesh Quads were used in the analysis

MESHING DETAILS

Structural Analysis: PLANE 42

Thermal Analysis: PLANE 55

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MESHING DETAILS (2)

• PLANE 42 was used as the element type for the pressure and gravitational simulations.

• Used for 2-D structural modeling of solid structures. It has capabilities to be used either as a plane element (plane stress or plane strain) or as an axisymmetric element.

• The element is defined by four nodes having two degrees of freedom at each node: translations in the nodal x and y directions. The element has plasticity, creep, swelling, stress stiffening, large deflection, and large strain capabilities.

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MESHING DETAILS (3)

• PLANE 55 was used for thermal analysis of the tail cones.

• PLANE 55 can be used as a plane element or as an axisymmetric ring element with a 2-D thermal conduction capability.

• The element has four nodes with a single degree of freedom, temperature, at each node.

• The element is applicable for steady-state or transientthermal analysis.

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DETAILED MESH

Simplifying problem allowed for fine meshing.

Computational time was very short.

Not more than 2 minutes using a Pentium 4 - 2.4Ghz 1 GB RAM2d model Axisymmetric expansion

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ALUMINUM TAIL CONE ANALYSIS

• Thermal analysis for in-bore and out-of-bore conditions

• Structural analysis in-bore

100805Melting T (solidus) (K)

500960Specific Heat (J/kg*K)

50130Thermal Conductivity (W/m*K)

0.270.33Poisson's Ratio

20071.7Modulus (GPa)

N/A503Tensile Strength (MPa)

78002810Density (kg/m3)SteelAluminumProperty

From: www.matweb.com

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THERMAL ANALYSIS (ALUMINUM)TRANSIENT SOLUTION IN BORE

Steel

Aluminum

Initial Temp - 300 K

Applied Temp1980 K

Unknown temperature surfaces

Temperature in K

0.84 mm of molten material

Steel

AluminumIn-bore condition thermal analysis at 6 ms for 7075 aluminum and steel

0.40 mm affected steel

Boundary conditions Post processing

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Transient condition thermal analysis 5 s for 7075 aluminum and steel

Temperature in K

Steel

Aluminum

Applied Temp 550 K

Steel

Aluminum

Initial Temperature from in-bore analysis

Frictional heat when in contact with air

THERMAL ANALYSIS (ALUMINUM)TRANSIENT SOLUTION OUT OF BORE

Boundary conditions Post processing

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STRUCTURAL ANALYSIS (ALUMINUM)LINEAR ELASTIC IN BORE

Pressure

Displacement constrains in X and Y

x

y

Stresses in Pa

In-bore condition von Mises analysis for 7075 Aluminum

Boundary conditions Post processing

G’s

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DESIGN CONCEPT

• The tail cone is formed by a long fiber thermoplastic molded portion with a metal insert

• Geometry replicates that of the aluminum tail cone (hollow back)

Metal Insert

LFT Tail cone

25 mm

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LFT COMPOSITE TAIL CONE ANALYSYS

• Thermal analysis for in-bore and out-of-bore conditions

• Structural analysis in-bore

271Melting T (K)

2200Specific Heat (J/kgK)

0.52Thermal Conduction (W/mK)

0.4Poisson's Ratio

13.79Modulus (GPa)

221Tensile Strength (MPa)

1460Density (kg/m3)

PA 66 – 40% GFProperty

From: www.rtpcompany.com

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In-bore thermal analysis at 6 ms for PA 66 – 40% GF, 6061 Aluminum and Steel

Temperature in K

Aluminum

Steel

LFT

0.065 mm of molten material

THERMAL ANALYSIS LFT TRANSIENT IN BORE

Steel

Aluminum

Initial Temp = 300 K

Applied Temp 1980 K

PA 66 -40%GF

Boundary conditions Post processing

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THERMAL ANALYSIS LFT DESIGNTRANSIENT OUT OF BORE

Steel

Aluminum

Initial temp from in-bore analysis

PA 66 - 40%GF

Out-of-bore thermal analysis at 5 s for PA 66 -40%GF, Aluminum 6061 and Steel

Steel

LFT

Aluminum

The LFT has a small heat affected region, when compared to aluminum

Temperature in K

Applied Temp 550 K

Boundary conditions Post processing

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STRUCTURAL ANALYSIS LFT DESIGNLINEAR ELASTIC IN BORE

Pressure

Gravity

Fully Constrained

Normal Constraints

Normal Constraints

In-bore condition Tsai-Wu ratio analysis for threaded geometry PA 66 - 40% GFDetail

Failure Criteria

Boundary conditions Post processing

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INITIAL FIRING TRIALS

Observed failure path

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TRANSITION REGION

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Acceleration (g)

Time (ms)

Acceleration

Pressure

Pressure (MPa)

P0

P0

High pressure gas escapes from chamber

Pi

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• Pressure is 1/7th of the pressure in-bore

• Difference in pressure cause higher stresses

• Moment caused by the force F at a distance L

TRANSITION REGION

P2

P0

M

F

L

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STRUCTURAL ANALYSIS (ALUMINUM)LINEAR ELASTIC TRANSITION

Pressure

Constraints in X and Y

x

y

Stresses in Pa

Transition condition von Mises analysis for 7075 Aluminum (without gravitational acceleration)Detail

Failure Region

Boundary conditions Post processing

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Failure Criteria

Transition condition Tsai Wu ratio analysis for threaded geometry PA 66 - 40% GF(Detail)

Failure Path

STRUCTURAL ANALYSIS LFT DESIGNLINEAR ELASTIC TRANSITION

Post processing

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ANOTHER LOOK AT THE FIRING TRIALS

Observed failure path

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REVISED DESIGN CONCEPT:FILLED BACK TAIL CONE

• The filled back LFT tailcone advantages:

– Smaller moment arm– Larger area subjected

to P2– Thicker moment arm

F

M

L

P0

P2

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STRUCTURAL ANALYSIS LFT DESIGNLINEAR ELASTIC TRANSITION

Transition condition Tsai-Wu ratio analysis PA 66 - 40% GF(Detail)

Failure Criteria

3 of the 22 threads are failing

Probable failure path

Post processing

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x-displacement plot of the stressed tailcone relative to its original position

Region of maximum displacement of the interface (average of 0.09 mm)

Displacement (m)

STRUCTURAL ANALYSIS LFT DESIGNLINEAR ELASTIC TRANSITION

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SECOND SET OF FIRING TRIALSFILLED BACK LFT COMPOSITE

Three part sabot

LFT tailcone

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SUMMARY

• Design and FEA model developed while simple showed to be accurate enough to represent the complicated loading scenario.

• A successful full-cycle FEA design of a XM1002 training round utilizing LFT composite was demonstrated.

• The transition region was found to be the most critical condition during firing.

• The filled-back LFT tail cone was successful in meeting all the loading conditions

• LFT material has extremely low thermal conductivity. this makes the LFT polymer less prone to failure from temperature.

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SUMMARY (CONT)

• The LFT tail cone is projected to cost 20% that of the aluminum version.

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ACKNOWLEDGEMENTS

• Army Research Laboratory Co-operative agreement W911NF-04-2-0018

• James Sands, James Garner and Pete Dehmer, Army Research Laboratory