DEVELOPMENT OF HIGH ENERGY DISSIPATION COMPOSITE SYSTEM UTILIZING SHEAR THICKENING MATERIALS PHYO KHANT A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2011 Acknowledgements I would like to express my deep and sincere gratitude to my supervisors, Professor Liew Jat Yuen Richard and Associate Professor Tan Beng Chye Vincent, for their valuable guidance and support throughout the course of this project Special thanks goes to Dr Davy Cheong for his kind guidance as well as his constructive advice and encouragement from beginning to end of my research work I gratefully acknowledge to Ang Kah Yee (National Junior College), Wong Ting Chong and Sai Murugan Pandit (FYP students from Mechanical Engineering,NUS) for their valuable assistance and contributions to my research work I would like to express my gratitude to the lab officers of NUS Impact Lab, Mr Alvin Goh and Mr Joe Low for their help and timely advice I especially want to thank my wife for her understanding, support and motivation i Table of Contents Table of Contents Acknowledgements…………………………………………………………………….i Table of Contents… …………………………………………………………………ii Summary……… ……………………………………………………………………vi List of Figures ………………………………………………………………….… viii List of Tables …………………………………………………………………… xii Introduction…… ………………………………………………………………… ….…1 1.1 Objectives… ……………………………………………………… ………… ….3 1.2 Scope ……………………………………………………………………… ………4 Literature Review …………………………………………………………………….…5 2.1 Soft body armor………………………………………………………… ……….…5 2.2 Behind armor blunt trauma …………………………………………………………6 2.3 Shear thickening fluids…… ……………………………………………… ………8 2.3.1 Mechanism of shear thickening ………………………………… ……… 10 2.3.2 Order-disorder theory………………………………………………… …… 10 2.3.3 Hydrocluster theory………………………………………………… ………11 2.3.4 Applications of shear thickening fluids ….…………………………….… …12 Drop Impact response of shear thickening fluids………………………………… …….13 3.1 Introduction……………………………………………………………… …….….13 3.2 Experiment………………………………………………………… …………… 14 3.2.1 Materials 14 3.2.2 Experimental set-up and test method 15 3.3 Results and discussion 16 3.4 Conclusion 20 Reducing blunt trauma with shear thickening fluids…………………………… ………21 4.1 Introduction…………………………… ………………………………………….21 ii Table of Contents 4.2 Experimental set-up…………………………………… ………… ………………22 4.2.1 Test materials…………………………………………… ………………… 23 4.2.1.1 Shear thickening fluids……………………………………… …………23 4.2.1.2 Ballistic fabric ………………………………… ……………… 23 4.2.1.3 Clay backing……………………………………………….…………….25 4.2.2 Experimental method………………………………………… ……….…… 25 4.3 Ballistic limit for the Twaron CT717 fabric ………….……………………… 26 4.4 Blunt trauma tests on STF packages with different concentration …… ………… 27 4.5 Development of STF-fabric composite pad ………………………….……… 29 4.5.1 Effectiveness of different combination of composite systems for blunt trauma reduction……………………………………………………29 4.5.2 The effectiveness of STF at impact velocity of 145 m/s……………… …….31 4.5.3 The effectiveness of epoxy treated Twaron fabric in STF packages……………………………………………………………… 32 4.5.4 The effectiveness of STF-fabric composite system… ……………… …… 34 4.6 Development of STF-fabric blunt trauma pad …………………………… …… 36 4.7 Energy dissipation mechanism of STF-fabric composite pad… ………………… 38 4.8 Conclusion………………………………………………………………………… 41 Reducing blunt trauma with shear thickening polymers……………………………… 43 5.1 Introduction…………………………………………… ………………………….43 5.2 Experimental set-up and method of testing………………………… …………… 44 5.3 Effectiveness of shear thickening polymer (STP)-fabric composite pad…………46 5.4 Performance comparison of STP and STF composite pad… ………….………… 49 5.5 Ballistic impact tests with varying thickness of STP composite pad……………53 5.6 Mechanism for DOP reduction due to interaction between STP and Twaron fabric…………………….…………………….………………….54 5.7 Conclusion………………………………………………………………………….56 Improving ballistic limit with shear thickening polymers ……………………… …… 57 iii Table of Contents 6.1 Introduction…………………………………………………………………………57 6.2 Experimental set-up and test materials……… …………………………….………58 6.2.1 Experimental set-up……………………….………………………………… 58 6.2.2 Test materials…………………… ……………………………………………59 6.2.2.1 Ballistic fabric.……………………………………………………… …59 6.2.2.2 Shear thickening polymer (STP) pad………… …………………… …59 6.3 Results and discussion………………………………………….…………….…… 60 6.3.1 Ballistic limit (BL) for STP composite pad……………… ………………….60 6.3.2 Energy absorption capacity of STP pad… ………………………………… 63 6.4 Conclusion………………………………………………………………………… 65 Incorporation of epoxy treated Twaron fabric for impact protection…………….………66 7.1 Introduction…………………………………………………………………………66 7.2 Test materials and methods……………………………………………………… 67 7.3 Ballistic performance of stacking sequence of neat and epoxy treated fabric plies………… ……………………………………………….69 7.4 Mode of deformation and energy absorption mechanisms… …………………….75 7.5 Ballistic impact tests on epoxy treated Twaron fabric with STP – fabric composite blunt trauma pad … 76 7.6 Conclusion…………………………………… ………………………………… 77 Application of shear thickening polymers in hip protectors…………………………… 79 8.1 Introduction………………………………… …………………………………….79 8.2 Materials and testing method………… ……… ……………………………… 80 8.3 Results and discussion…………….……………………………………………… 82 8.4 Conclusion………………………………………………………………………… 85 Conclusion………………………………….…………………………………………….86 10 References……………………………………………………………………………… 89 Appendix A Compression of clay backing……………………………………… 96 iv Table of Contents Appendix B Measurement of DOP in clay backing……………………………….97 Appendix C Fibrous surfaces used for ballistic impact test on STP packages… 98 Appendix D Dimensions of metal box containing clay backing……………… 99 Appendix E Dimensions of wooden box containing clay backing……………….100 Appendix F Detailed results for ballistic tests on STP packages……………… 101 Appendix G Detailed results for ballistic impact (blunt trauma) tests on STP packages………………………………………………… 102 Appendix H Detailed results for ballistic impact test for epoxy treated Twaron fabric systems………………………………………….… 104 v Summary Summary In this research, novel impact energy dissipation composite systems which utilize shear thickening materials is developed and explored With the aim of reduction nonperforating behind armor injuries, flexible impact energy dissipation systems using cornstarch-water suspension as the shear thickening fluids (STF) were fabricated and tested Firstly low velocity impact response of the shear thickening fluid with different concentration was performed The performance of impact resistance was investigated in terms of penetration depths in clay witness placed behind the STF The concentration of 58.82wt% of cornstarch showed the best performance in resisting impact forces A new composite system comprising woven Twaron ballistic fabric impregnated with shear thickening fluid is introduced next The ballistic impact response of the system was studied Impact tests suggest that the combination of the fabric layers and shear thickening fluids resulted in greater impact energy dissipation It was also shown that developed STF-fabric pad is effective in reducing blunt trauma Thereafter, a new shear thickening material was introduced and a shear thickening polymer (STP)-fabric composite pad was developed The effectiveness of the STP with different composite layers was studied The STP pad containing plies (2 x 2) of epoxy treated Twaron gave the lowest depth of penetration in clay witness Results showed that the STP is most effective in reducing blunt trauma when used in conjunction with armor fabric due to the interaction between both materials This interaction results in greater energy absorption and dissipation possibly due to vi Summary increased stiffness, viscous dissipation and increased inter-yarn friction caused by shear thickening of the STP during impact The mm thick STP-fabric composite pad was found to reduce blunt trauma by 25% when placed behind flexible body armor The study also investigated the effects of adding epoxy treated layers in fabric systems Results showed that the addition of epoxy treated layers was effective in reducing blunt trauma and this is attributed to increased stiffness, inter-yarn friction and fabric projectile friction Additionally, the placement of neat layers in front of treated layers in fabric systems was found to be most effective in reducing blunt trauma This suggests that the stacking sequences of neat and epoxy treated fabric plies are found to be important in improving protective performance, which affected not only the back face signature (BFS) but also the ballistic limit vii List of Figures List of Figures Figure 2.1 Wave propagation in soft body armour due to projectile impact…… …5 Figure 2.2 Classification of fluids based on the stress versus rate of strain relationship…………………………… ………………………… Figure 2.3 Shear thickening behavior (viscosity vs shear rate) of 57 and 62 volume % colloidal silica dispersed in ethylene glycol for steady shear flow….……………………………………………….… …9 Figure 2.4 Hydrocluster theory for shear thickening suspension morphology… …11 Figure 3.1 Micrograph of cornstarch particles………………………………….… 14 Figure 3.2 Steady-state shear rheology of 55wt% cornstarch in water suspension 14 Figure 3.3 Drop tower set-up …………………………………………………… 15 Figure 3.4 Perspex acrylic container with clay witness for drop testing……………15 Figure 3.5 Photo of Twaron fabric with aluminum legs……… ………….……….15 Figure 3.6 Depth of penetration in clay backing for 0.5m drop tests onto 10 mm of STF …………………………………………………….…….17 Figure 3.7 Depth of penetration in clay backing for 0.5m drop tests onto 20 mm of STF …………………………………………………….…….18 Figure 3.8 Penetration depth versus drop impact energy from drop tests onto 20 mm STF at 58.82wt% concentration …………………………… 19 Figure 3.9 Shear thickening zones developed upon impact onto STF covered by Twaron fabric with aluminum legs…………… ………… 20 Figure 4.1 Thin rubber encapsulated cornstarch suspension for impact absorption ………………………………………………………….… 23 Figure 4.2 Clay witness………………………… …………………………….… 25 viii List of Figures Figure 4.3 Schematic diagram of high pressure gas gun set-up for ballistic tests…………………………………………………………………… 25 Figure 4.4 Depth of penetration in clay witness for systems of different concentration of STF covered with ply of Twaron for ballistic tests at 75 m/s…….………………………………………… …… …28 Figure 4.5 Depth of penetration in clay witness for different STF composite systems for ballistic test at 75 m/s………… ……………….30 Figure 4.6 Depth of penetration in clay witness for STF and water systems of same thickness of 20 mm for ballistic tests at 145 m/s…………… 31 Figure 4.7 Depth of penetration in clay witness for STF systems of same weight of 255g for ballistic tests at 145 m/s…………… .33 Figure 4.8 Depth of penetration in clay witness for systems without STF for ballistic tests at 145 m/s…………………………………………… … 34 Figure 4.9 Depth of penetration in clay witness for systems of same weight of 255g for ballistic tests at 145 m/s…………………… ………… …35 Figure 4.10 Depth of penetration in clay witness for systems of same thickness of 20 mm for ballistic tests at 350 m/s… ………… … 37 Figure 4.11 Front (Left) and back face (Right) of STF-fabric composite pad after 350 m/s impact…………… …………………… 38 Figure 4.12 Clay witness after projectile impact at 350 m/s for STF-fabric composite pad (Target D)………… ………………………………… 38 Figure 4.13 Impact sequence of STF-fabric composite pad……………… ……… 40 Figure 4.14 Damage in integrated plies after impact………………………… … 41 Figure 5.1 Target set-up for assessing blunt trauma in ballistic testing……… … 44 ix References 10 Hoffman, R.L., Discontinuous and dilatant viscosity behavior in concentrated suspension III Necessary conditions for their occurrence in viscometric flows Advances in colloid and interface science, 1982.17:161-184 11 Hoffman, R.L., Explanation 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Appendix Appendix A – Compression of clay backing Figure A: Compression of clay backing with machine(Top) and Flat clay surface before impact (Bottom) A metal block with a base of 93.6 x 101.7mm and height 25.3mm is placed on top of the clay during compression to ensure the compressive force is distributed evenly A force of 1962N is applied to the block of clay for 10 seconds to ensure a well compressed block free of voids Excess clay is removed after compression, using a hand saw 96 Appendix Appendix B – Measurement of DOP in clay backing Figure B: Indentation on clay backing (Left) and measurement of DOP (Right) Measurement of DOP is done with a digital height gauge with a pointer attached Before impact, the pointer is lowered to the flat surface of the clay backing, and the reading is calibrated to zero After impact, the pointer is lowered to the lowest point of the indentation and the DOP is read off the meter Calibration has to be done before impact as part of the clay surface will be raised after impact 97 Appendix Appendix C–Fibrous surfaces used for ballistic impact tests on STF packages ply epoxy treated Twaron with second layer roughened [image shows roughened layer] ply epoxy treated Twaron bonded with non-woven polyester fiber pad [image on Left shows polyester surface] Figure C: Fibrous surfaces used for System (Top) and System (Bottom) 98 Appendix Appendix D – Dimensions of metal box containing clay backing RIGHT FRONT ISOMETRIC PLAN Figure D: Dimensions of metal box containing clay backing 99 Appendix Appendix E - Dimensions of wooden box containing clay backing RIGHT FRONT ISOMETRIC PLAN Figure E: Dimensions of Plywood box [Central hole not present for ballistic impact test, hole was created for impact energy absorption test] 100 Appendix Appendix F - Detailed results for ballistic tests on STP packages Table F: Concentration tests ply front layer Twaron 58.8wt% 55 wt% 52.6 wt% Water(300ml) Empty package Test Velocity DOP (m/s) (mm) 74.10 8.62 77.10 10.95 75.50 9.57 72.60 10.24 73.00 12.90 Test Velocity DOP (m/s) (mm) 72.60 7.98 76.00 10.20 74.10 10.40 73.90 11.60 74.50 13.30 Test Velocity DOP (m/s) (mm) 71.80 7.40 72.00 8.60 71.00 10.30 72.30 9.90 73.00 11.90 Test Velocity DOP (m/s) (mm) 73.10 8.30 Test Velocity DOP (m/s) (mm) 73.10 9.40 Average Velocity DOP (m/s) (mm) 72.83 8.00 74.26 9.49 73.53 10.09 72.93 10.58 73.50 12.70 101 Appendix Appendix G - Detailed results for ballistic impact (blunt trauma) tests on STP packages Table G1: DOP results for ballistic impact test on packages with no STF or STP Test Test Test Average No STF System Thickness Mass Velocity D.O.P Velocity D.O.P Velocity D.O.P Velocity D.O.P (mm) (g) (m/s) (mm) (m/s) (mm) (m/s) (mm) (m/s) (mm) A 0 151.8 61.88 153.5 63.81 149.7 61.06 151.7 62.25 B 1.8 150.8 28.93 149.9 27.13 150.5 28.03 150.4 28.03 Table G2: DOP results for ballistic impact test on STP packages Shear Thickening Polymer System Thickness Mass (mm) (g) 15 60 15 58 15 58 15 57 15 57 15 45 Test Test Test Average Velocity D.O.P Velocity D.O.P Velocity D.O.P Velocity D.O.P (m/s) (mm) (m/s) (mm) (m/s) (mm) (m/s) (mm) 146.6 56.32 149.7 58.61 152.9 59.76 149.7 58.23 152.4 20.01 148.7 16.73 150.6 17.24 150.6 17.99 151.2 12.47 151.8 13.02 149.7 11.69 150.9 12.39 150.3 9.53 153.5 10.89 151.1 10.31 151.6 10.24 151.5 11.38 150.6 10.14 147.0 9.64 149.7 10.39 152.4 15.10 148.0 13.61 150.6 14.06 150.3 14.26 102 Appendix Table G3: DOP results for ballistic impact test on STF packages Test Test Test Test Average STF (58.8wt% Cornstarch) Thickness Mass Velocity D.O.P Velocity D.O.P Velocity D.O.P Velocity D.O.P Velocity D.O.P System (mm) (g) (m/s) (mm) (m/s) (mm) (m/s) (mm) (m/s) (mm) (m/s) (mm) 15 205 152.1 42.31 150.3 41.56 147.6 39.72 149.7 41.19 149.9 41.20 15 193 149.7 29.85 147.1 28.76 153.8 31.61 150.6 30.05 150.3 30.07 15 193 149.7 9.51 151.8 10.32 148.1 8.98 149.9 9.60 15 190 148.4 7.1 149.7 7.16 150.6 7.38 149.6 7.21 15 190 148.1 5.62 148.8 5.78 151.3 6.23 149.4 5.88 15 170 147.4 7.61 153.1 8.36 150.6 7.98 150.4 7.98 * Area of Targets: 100mm by 100mm 103 Appendix Appendix H - Detailed results for ballistic impact test for epoxy treated Twaron fabric systems Table H1: DOP results for ballistic impact test epoxy treated Twaron fabric systems Fabric Velocity (m/s) Mass (g) DOP (mm) Perforated Ply system Configuration Test Test Test Test Test Test Test Test Test 3 AVG Bending Test Test Test Angle (Deg) 30N 337.8 328.9 328.9 191 193 192 32.15 33.75 31.65 32.52 8 32.3 30E 335 328.9 328.9 209 210 209 28.11 26.85 26.19 27.05 13 11 10 4.2 15N + 15E 328.9 328.9 328.9 201 206 203 27.14 25.93 27.08 26.72 14 20N + 10E 328.9 324.5 324.5 195 198 201 27.72 30.32 29.71 29.25 10 22.2 10N + 10E + 10N 326.7 328.9 328.9 201 199 199 31.36 31.27 29.24 30.62 10 10 17.8 10N + 20E 326.7 328.9 328.9 205 203 205 26.68 26.33 26.15 26.39 10 11 12 15E + 15 N 328.9 328.9 328.9 202 201 201 32.36 31.94 32.74 32.35 12 10 12 14 20E + 10 N 328.9 328.9 328.9 205 207 201 28.71 26.71 29.57 28.33 10 10 10 12 * Area of each layer of Twaron : 150mm by 150mm 104 ... Response of Shear Thickening Fluids Drop Impact Response of Shear Thickening Fluids 3.1 Introduction The ballistic properties of Kevlar fabrics can be improved by the addition of shear thickening. .. Mitigation of these injuries can potentially benefit from the development of shear thickening fluid based composites as they require materials that have the potential of absorbing large amount of energies... the shear thickening characteristic of STF and strength of composite pads, penetration tests will be carried out at high velocity impact to investigate the efficiency of the selected composite system