Air Force Institute of Technology Topology Optimization of Additively Manufactured Penetrating Warheads Hayden Richards Masters Student Department of Aeronautics and Astronautics David Liu AFIT Assistant Professor Department of Aeronautics and Astronautics 4 Mar 15
Overview • Problem Overview • Motivations / Goals • Research Methodology • Optimization Strategies • Design Process • Results & Discussion • Preliminary Warhead(s) • Optimizations & Analysis • Design, Printing, and Testing Details • Summary / Conclusions 2
Problem Statement • Problem: Traditionally manufactured penetrator warhead cases have undesirable fragmentation properties because of their thick walls. • Question: Can a warhead be designed to maintain penetrative performance while 3
Motivation • Additive Manufacturing ‘3D Printing’ • Lattice Structures • Topology Optimization http://www.manufacturingthefuture.co.uk/research/ http://www.shining3dscanner.com/en-us/Direct_metal_laser_sintering.html http://patapsco.nist.gov/imagegallery/details.cfm?imageid=1328 Sigmund, O. ‘A 99 line topology optimization code written in Matlab’ 4
Goals • Primary Goals • Explore the viability of additive manufacturing as a method for penetrating warhead production • Reduce wall thickness for better fragmentation performance while maintaining penetration capability • Fabricate and test printed warheads • Supporting Capabilities • Introduce lattice structures as possible to reduce mass • Use topology optimization to influence design decisions 5
Research Methodology 1) Fabricate standard design using AM methods 2) Define test parameter loading conditions 3) Produce optimized warhead solution through topology optimization process 4) Translate solution into actual optimized warhead design 5) Fabricate optimized design using AM methods 6) Perform further analysis and live-fire testing 6
Standard Design • Unitary warhead case • Mat’l = 15-5 Stainless • Length = 7.50 in • Diameter = 1.00 in • Walls < 0.120 in thick • CRH as specified • To be closed using traditionally manufactured end cap • Designed using Solidworks 2013 • Printed using DMLS on EOS M270-M280 series 7 What is the standard design, explain Explain three iterations, evolution
Model Generation • HyperWorks was used for all FEA and optimization work • Motivation for loading conditions: 8 Talk about problem: how do we take the standard case and change its performance? What process was used for this Have drawing of problem impact
Optimization Generation • Derivation of optimization parameters: • Size, shape, C.G., and total mass were conserved • Design space was inner 50% of the wall thickness and entire interior area / volume • Internal volume fraction was used to control mass • Compliance was used for optimization objective • Displacement was used as the measure of merit 9
Test Parameter Loading = Applied forces = Constraints 10
Warhead Optimization • Optimization parameters: • Decision variable: 2D design property • Responses: comp = total compliance, volfrac = design property volume fraction • Constraint: volfrac = (0.20-0.30) • Objective: minimize comp • Loadstep: C2-F2 (body, angle), min/max member size 0.5-1.0 11
Solution-Design Translation 1) Import solution to Solidworks, identify desired solid regions (consider printability limitations): 2) Revolve regions to form solid, cut longitudinal channels, generate outer case wall separately: 12 Once we have solution, how do we transform into 3D body?
Solution-Design Translation 3) Develop ideal lattice structure (ensure printability) and shape to desired volume to fill moderate-density spaces: 4) Combine these two pieces together to generate internal structure (solid and lattice): 13
Solution-Design Translation • Combine to form entire warhead with case wall in printing configuration and additional machined end cap: • Optimized has ~30-40% thinner walls than standard 14
Optimized Design Fabrication • EOS M280 in PH1 / 15-5 stainless steel Optimized design (3) Standard Design (2) 15
Fabrication Overview • Preliminary Warhead • Laying down orientation • Out-of-round, outside tolerance • Standard Warhead #1 (S1-1, S1-2) • Standing up, rough stock removed • C.G. location unsatisfactory for test • Standard Warhead #2 (S2-1, S2-2) • Standing up, printed to size • Mass, C.G. matched • Optimized Warhead #1 (O1-1, O1-2) • Standing up, printed to size • Requires further post-processing • Mass, C.G. matched 16
Live-Fire Testing • Goals are: • Have both AM warheads survive penetration event • Measure penetration • Have AM optimized design penetrate deeper than AM standard design in both obliquity conditions 17
Live-Fire Testing • Test Data: • Instrumented: • Flight attitude information • Penetration depth and character • Warhead recovery 18
Flight Attitude HSDCs • Side: • Top: • Target: 19
HSDC flight videos • Side, O1-1 • Overhead, S2-1 20 (FH, S7) (FO, S4)
Penetration Performance • Penetration Data: 21
Penetration HSDC videos • O1-2: • S2-2: 22 T S5 T S6
Warhead Recovery • First Standard Warhead Designs: • S1-1: • S1-2: 23
Warhead Recovery • 0º Oblique Warhead Designs: • S2-1: • O1-2: 24
Warhead Recovery • 20º Oblique Warhead Designs: • S2-2: • O1-1: 25
Summary • Problem Overview • Motivations / Goals • Research Methodology • Optimization Strategies • Design Process • Results & Discussion • Preliminary Warhead(s) • Optimizations & Analysis • Design, Printing, and Testing Details • Summary / Conclusions 26
Lessons Learned • Specific lessons learned during design processes: • Regarding topology optimization: • Consider and recognize all assumptions and simplifications used to generate models and perform analyses / optimizations • Trust the optimization routine to generate a valid result, but only provided the input parameters are valid and appropriate • Regarding design for additive manufacturing: • Design for 3D printing requires many iterations • Design to printer capabilities and accept complications • Take advantage of machine capabilities 27
Project Conclusions • Additive manufacturing is the only suitable method for the production of complex geometries such as those used in this research • However, there are still limitations due to specific additive manufacturing techniques which resulted in design compromises • Cost can rely heavily on design • Additive manufacturing can produce parts generated by topology optimization techniques • Empirical testing is the best method of confirming analytical results, especially given the dynamic nature of this problem 28
Sponsors • This research was sponsored by: • Damage Mechanisms, Munitions Directorate, Air Force Research Laboratory, and • Joint Aircraft Survivability Program Office. 29
Questions? 30
Abstract Research at the Air Force Institute of Technology explored the viability of producing penetrating warheads using 3D printing. Three different warhead designs were developed in this research, all with constant outer diameter, length, mass, and center of gravity location. Two of the designs, referred to as the “standard designs,” were unitary with a constant-thickness case wall representing typical penetrating warhead designs. The third warhead design, referred to as the “optimized design,” was developed based on topology optimization solutions under loading conditions reflective of penetration events. The optimized warhead design, to improve fragmentation characteristics, reduced case wall thickness by 40% by relocating the mass removed from the unitary walls to internal structures within the warhead. Lattice structures occupied moderate-density regions within the topology optimization solution. Based on Finite Element Analysis (FEA) calculations, the optimization solution guiding the optimized warhead design reduced total warhead compliance by 90.1% compared to the two unitary models. Two warheads were produced for each of the three different designs. The finished warheads were live- fire tested at Eglin Air Force Base, Florida and tested against 5 ksi semi-infinite contained concrete targets at 0º and 20º angles of obliquity (AoO). For 0º AoO tests, the standard warheads demonstrated the effectiveness of 3-D printed steels by penetrating similarly to equivalent wrought steels. For 20º AoO tests, significant “tail slap” was observed and caused significant structural damage to both warheads. The results of this test helped to support AFRL/RW research on the use 3D printing for future Air Force munitions. 31 200word abstract V3
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