1. Fabrication of Functionally Graded Composite Energetic Materials Using Twin Screw Extrusion Processing Hugh A. Bruck Dept. of Mechanical Engineering University of Maryland Mitch Gallant NSWCIHDIV-Indian Head,MD & Dept. of Mechanical Engineering University of Maryland Continuous Mixer & Extruder Users’ Group Meeting Indian Head, MD 30 October 2002 This work was supported by the Office of Naval Research YIP: Dr. James Short, program manager

2. Motivation Composite Energetic Materials have been traditionally manufactured using batch processing New continuous manufacturing technology known as Twin Screw Extrusion (TSE) is being used to produce higher quality composite energetic materials with more flexibility and control Current manufacturing of composite energetic materials is focused on homogeneous formulations The continuous nature of the TSE process is ideally suited for the manufacture of functionally graded materials

3. Naval Grand Challenges NAVSEA –Missile Defense High & Controlled Lethality Warheads Green Warheads Long Range Enhanced Maneuver –Sixth Generation Energetic Systems On-the-fly Dial-a-yield Energetics –Assured Lethality/Effects & Scalable Combat Power Extended Range guided Munitions Green Energetics Increased Range/Standoff ONR –Materials by Design First principles for the effects of gradient microstructures on material performance Computational techniques for yielding the processing conditions to fabricate gradient architectures that optimize system performance

4. Technical Objective Tailor Burn Rate Performance in a Monolithic Rocket Motor Utilizing New Design and Control Schemes for Twin Screw Extrusion based on Functionally Graded Material (FGM) Architectures Propellant Continuously Extruding from Die of TSE FGM Architecture

5. Research Objectives 1)How do dynamic variations in process conditions and composition during TSE affect the evolution of functionally graded architectures? 2)Can the architectures be predicted by newly- developed residence distribution (RD) models? 3)Can the gradient architectures produced by dynamic processing conditions be characterized? Twin Screw Extrusion Process

6. Research Objectives (cont’d) 4)Can the burn rate performance of the gradient architectures be predicted? 5)How can the process and performance models be integrated with optimization methods to determine the appropriate TSE processing conditions to manufacture FGCEMs? Increasing Distance along Extrudate Cross-section of Extrudate Material Variation in TSE Extrudate

7. Functionally Graded Propellant Concept

8. Inverse Design Procedure Research Approach Research is being con- ducted at UMD/College Park and NAVSEA-IH through a collaborative research agreement (Center for Energetic Concepts Development) ComputationalToolsManufacturingScience Materials Characterization Inverse Design Procedure – synergistic integration of component design with fabrication processes for optimizing performance using FGMs

9. Dynamic Characterization of TSE Process Residence Time Distribution: RVD Model: Can predict gradient architecture using RVD convolution!

10. RTD Measurements Screw Design and Throughput Effects Screw Design and Temperature Effects 218 C, less retention 177 C, greater retention 10 lb/hr, less retention 5 lb/hr, greater retention Characterized Effects of Screw Design, Throughput, and Temperature on RTDs for 28 mm TSE

11. RTD Modeling Absorbance Probe Time (sec) Reasonable Unconstrained Fit to Gao RTD Model Gao RTD Model T d = 0 (a = 3.35 x 10 -2 /s) T d = 15.2 T m = 84.3 (a = 4.34 x 10 -2 /s)

12. RTD Modeling (cont’d) Modified Weisstein Model Absorbance Probe Time (sec) Better Unconstrained Fit to RTD Data!  = 47.5 s

13. Gradient Measurements Graded Polymer Composites 5 cm

14. Microstructural Characterization Average Individual Particle Size Average Particle Size for the Distribution of Particles Similar Treatment for Shape Factor Analysis Discrete Fast Fourier Transform Analysis of Frequency Variations in Particle Distribution Discrete 2D FFT Frequency variation in particle distribution

15. Statistically-based combustion model Combines Beckstead, Derr, and Price (BDP) model with Glick’s statistical formalism Models composite propellant as a random arrangement of polydispersed pseudopropellants Polydispersed pseudopropellants Petite Ensemble Model

16. Steady–state PEM calculations (w/o fuel) Use COE to determine T s,ox from adiabatic flame temperature calculations (PEP, NASA SP-273) Gradient effects? Burn rate variation w/ composition

17. 3-D FEA Modeling of Rocket Motor Performance Transfinite InterpolationPartial Differential Equation SPP 02 (3-D Euler CFD code) Graded elements?

18. Genetic Algorithms (GAs) Differential Evolution GA Optimization Methods  Robust  Employs evolutionary principles (mutation, crossover) Optimal Material Distribution Comparison of Computational Time

19. Inverse Design Procedure for FGCEMs

20. Conclusions A Twin Screw Extrusion (TSE) process is being used to manufacture Functionally Graded Composite Energetic Materials Using Residence Distribution (RD) Models, the transient effects of the TSE process on the evolution of functionally graded materials can be characterized by convolving the RD with the transient operating condition The modified Weisstein model provides a better fit to the RTD than the Gao model Gradient measurements correlated with RD convolution predictions A new inverse design procedure is being developed that integrates RD, PEM, and FEA models with GAs for TSE processing of functionally graded composite energetic materials using an inverse design procedure