Concept AE â 2015 Litecar Challenge Summary Concept AE ...
Concept AE – 2015 Litecar Challenge
Summary Concept AE combines multiple weight and safety innovations facilitated by three key technological innovations: • • •
Algorithmically controlled progressive additive manufacture Next-generation graphene nanotube weave Electroactive polymer and non-Newtonian crash components Aims and objectives
Local Motors Concept AE is an ultra lightweight concept developed by an interdisciplinary design and engineering graduate team. Our goal was to re-engineer the passenger car achieving two key aims: significant weight reduction and increased safety. Beyond that our team deliverable was an unrestricted view on what shapes, forms and materials could be used. At the start of the project it was rapidly agreed that passenger cars today are alarmingly similar in appearance to those of fifty years ago, and that an exciting demonstration vehicle ought to be developed to showcase the technical and procedural innovations. Concept AE is intended to inspire the engineering research necessary to overcome current hurdles to real world commercial lightweight vehicle development. Weight Reduction Overview There are two aspects to the weight reductions developed for concept AE; the innovations developed [in abstract] and then as applied to the demonstration vehicle. Weight Reduction Abstract: The key weight saving innovations for concept AE are in the primary chassis structure. It is a lightweight composite fabrication inspired by advances in biomedical 3D orthopaedic scanning1 The key innovation in concept AE is to utilise this data in the development of an additive manufacturing algorithm. (REF.1 Algorithmically Enhanced Additive Structural Manufacture). Two key functions – a swarm algorithm controlling structural geometry and a compound additive algorithm controlling material composition – offer the development of a previously impossible level of structure optimisation. The innovative use of algorithmic control in concept AE then facilitates further weight saving techniques currently in development. Structural batteries2 and
Concept AE – 2015 Litecar Challenge suspension components3 offer further opportunities for weight reduction through consolidation into the primary structure. Alongside algorithmic structural innovations, concept AE utilises future nanotechnology to reduce non-structural bodywork weight where possible. Practical Demonstrator: Having determined the conceptual innovations in design and manufacture necessary to significantly lightweight the car, attention was turned to a practical demonstration model. Utilising Algorithmically Enhanced additive manufacture, a double skin eggshell chassis – optimised natural form for strength – was determined. The use of Algorithmic Enhancement (REF.1) ensures the strength to weight ratio of the additive honeycomb between the CFRP skins is optimised to a currently impossible degree. AE also allows for optimised crumple zones and crash structures to be built into the single composite structure, a further component and weight reduction. CFRP has already been demonstrated as a structural material whilst simultaneously acting as the lithium intercalculating electrode of a lithium battery2. The development of algorithmic additive manufacture enables this facility in the honeycomb layer as well, radically expanding the surface area available to hold charge at minimal weight penalty. Further component consolidation comes from integrating the road isolation suspension systems into the main body through AE enabled smart composite construction3. All side bodywork is mitigated through use of a graphene net which provides the protection needed from wind, rain and debris, while weighing less than a hundredth of the equivalent section in pressed metal4 The graphene net is pulled tight via a sliding aluminium lead rail and electroactive seams (REF.2: Electro-Active Materials) threaded through the material. The traditional glazed laminate screen and roof are replaced by a single iridium coated polycarbonate sheet. Currently utilised in military aircraft and powerboat manufacture, it is an ultra-light glazing material ensuring high strength, low weight and optimal anti-glare and anti-scratch characteristics.
Concept AE – 2015 Litecar Challenge With power-storage weight reduced through structural batteries, sintered aluminium hubs form the outer casing for compact digital drive motors at the rear of the car. This radically lowers powertrain weight, running through a single pinion gear into the drive hub. Durable, tackier rubber reduces tyre size and weight, while graphene cables are woven together to provide the structural support for the wheel5. Inspired by the lightweight design of vintage wire spoke wheels and skinned with a protective polymer coating the unsprung weight of the wheel unit is massively reduced, offsetting the implications of drive hubs on ride and handling. Smart materials fill the gaps. Bio-chemical compounds derived from cellulose polymers are utilised in the 3D printing of ultra light seating sections. A shared seat bracket incorporated to the B-pillar reduces internal component weight whilst increasing rear passenger safety. Paper-thin OLED displays6 provide the necessary functionality at lowest possible weight penalty. Finally electroactive materials remove the requirement for extensive airbag safety systems, with an innovative approach to front passenger safety developed from the procon-10 research in the mid 1980s. Innovation Many of the concepts applied in concept AE use cutting edge technology but are not original. Concepts such as structural carbon fibre batteries7 and complex geometric structures made from Additive Manufacture8 are available today, and either facilitated or advanced in Concept AE. Furthermore, the development potential of graphene has been carefully mapped, with commercialisation constraints the current barriers to progress. This section will focus instead on identifying the original future concepts that we envisioned for the car: Algorithmic Structural Enhancement, Electroactive Materials and Reactive Non Newtonian Crash Structures. With the safety and manufacturing implications of AE extensively covered earlier in the paper the relevant areas for Electroactive and non-Newtonian materials are included herein. REF.1: Algorithmically Enhanced Additive Structural Manufacture. Material composition alters three main variables: Strength, Toughness and Weight. Through advanced loading simulations the structural requirements and composition of the chassis body can be modelled. The sim data gathered facilitates two algorithms. The first algorithmic function determines the optimum material geometry at any point in the structure to minimise weight while meeting the strength/toughness requirements.
Concept AE – 2015 Litecar Challenge The second algorithmic function will then enable the material composition to be continuously varied to match the optimal material geometry calculated for every point in the structure. These algorithms represent a form of licensed IP – one which would enable self funding of AE research through development of high performance licensable component algorithms. Combined with next generation additive printing hardware, Algorithmically Enhanced Additive Manufacture creates the optimum balance of weight to impact resistance possible, significantly reducing concept weight.
Toughness = T, Strength = S, Density = D Material = M = {T, D, S} Advanced loading simulation produces required T and S values at each point in the structure. These fixed T-S relations can then be used to compute the desired material mixture to produce the minimum weight.
With a and b fixed, the optimum material variables (w, x, y, z) can be found to create a minimum c value. (Material values represent the percentage of each material present in a mixture) (i): algebraic abstract example algorithmic component
Table 1 Strength-toughness relationship of different metals 9
Concept AE – 2015 Litecar Challenge
REF.2: Electroactive Materials Concept AE makes significant weight reductions through replacement of actuators, hinges, and motors with electro-active materials – complex polymers that are able to produce large strains when an electric current is applied across the material10. The future concept is of a material that can significantly change its material properties and/or dimensions by the application of an electric current across it. For example a material can be used as a structural member when a current is being applied, however then can become elastic or significantly decrease in size when the current is removed. Safety Electroactive materials also represent significant safety innovation in Concept AE, with multi-use materials that can act as both impact protection and functional parts (steering wheel, dashboard) simultaneously. Manufacture Currently Polyvinylidene fluoride, (PVDF) shows the greatest levels of electro-active response11. The current tests with PVDF show that the electroactive properties can be changed depending on how the material is formed. Using different pressures, temperatures and forming processes to create the PVDF crystal, the structure and hence the response characteristics of the material can be altered. This variability shows great promise for potential future development of such materials, yet with current materials showing maximum electro-active strains of 300%12 there is further research development required.
Material
Density (g/cm )
Yield Stress (Mpa)
Youngs Modulus (Mpa)
Impact Strength (J/m)
Tensile Strength (Mpa)
PVDF
1.79
50
8.3
100-200
50
General purpose Polystyrene
0.96-1.04
40
3-3.5
37-59
34.5-48.3
3
Table 2. Comparison of material properties of electroactive PVDF and general purpose polystyrene13,14 Comparison of the properties of current electro-active materials (PVDF) against polystyrene gives closest outlook for the potential of electro-active materials developments. They display properties that are similar to or better than those of general purpose polystyrene – validation for further research into the properties of electroactive materials.
Concept AE – 2015 Litecar Challenge
Non-Newtonian Reactant Crash Structures Non-Newtonian materials are quite widely known. Viscoelastic materials are an example of a non-newtonian material which is able to increase its resistance to deformation when under a large impact force15. This initial promise inspired the team to make innovative use of viscoelastic material properties as low weight impact attenuating crash structures. Safety A non-Newtonian crash structure would alter its energy absorption properties dependant on the speed and nature of the collision occurring. This reduces the volume of material necessary to oppose the impact forces, therefore reducing the weight of the required crash structure. Even the most advanced crash structures used today are limited by their fixed energy absorbing properties. The energy absorbed by the structure in a crash is dependant on the volume of material that is involved in the crash. This means over engineering is required to ensure that the vehicle passengers will be protected in a range of crash situations16 Manufacture Carbon fibre currently provides the optimal energy absorbing properties for use in impact attenuation devices17. In a study comparing plain fibre weave against a fibre-viscoelastic combination, it was found that impact energy absorbed was increased by a factor of 2018. As such, a form of composite viscoelastic honeycomb, as used in Concept AE, is a likely route to commercialisation. This is the final major innovation enabled by the complex structural manufacturing potential of Algorithmically Enhanced Manufacture. It allows full utilisation of the energy absorbing properties of the IDM by producing a minimal crash structure that still provides sufficient coverage over the entire vehicle, saving weight and saving lives. Bill of Key Materials All figures c.2015 where available.
Concept AE – 2015 Litecar Challenge
Innovative Component The consensus over the course of the project has been that while Algorithmic Enhancement is a hugely exciting facilitator of lightweight innovation, it is not the most exciting original development demonstrated on Concept AE. That title goes to non-Newtonian viscoelastic crash structures. It is an innovation that presents potentially radical improvements in both crash structure weight and the overall crash resistance of the vehicle. With the first research into viscoelastic ballistic resistance showing great promise, it is an innovation with massive potential socio-economic value. Saving weight and saving lives – it has a ring to it! Potential Challenges The various future concepts in Concept AE do not represent structures or materials that are available today. However, through research and engineering conceptualisation we have tried to retain a degree of realism and proximity to current day technology to make research into these innovations both exciting and worthwhile. As such, the properties proposed are generally extrapolations of those currently available from materials available today. Certain areas clearly represent a greater developmental challenge than others – graphene weave and electroactive materials most evidently so. In response to these concerns, particularly futuristic materials have only been specified where a more feasible alternative could provide near-equivalent real world performance. As the very inspiration behind the electroactive safety wheel – Audi’s procon-10 – demonstrates, there is more than one route to a viable solution. Bibliography 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Parthasarathy, Jayanthi, Binil Starly, and Shivakumar Raman. "A design for the additive manufacture of functionally graded porous structures with tailored mechanical properties for biomedical applications." Journal of Manufacturing Processes 13.2 (2011): 160-170. Hagberg, Johan. "Electrochemical Performance of Commercial Carbon Fibers Towards Usage As Electrodes in Structural Li-Ion Batteries." 227th ECS Meeting (May 24-28, 2015). Ecs, 2015. Yu, W. J., and Ho-Chul Kim. "Double tapered FRP beam for automotive suspension leaf spring." Composite structures 9.4 (1988): 279-300. Hu, Kesong, et al. "Graphene-polymer nanocomposites for structural and functional applications." Progress in Polymer Science 39.11 (2014): 19341972. Zhong, Xiaohua, et al. "Carbon nanotube and graphene multiple-thread yarns."Nanoscale 5.3 (2013): 1183-1187. Kido, Junji, Masato Kimura, and Katsutoshi Nagai. "Multilayer white light-emitting organic electroluminescent device." Science 267.5202 (1995): 13321334. Jacques, Eric. "Lithium-intercalated Carbon Fibres: Towards the Realisation of Multifunctional Composite Energy Storage Materials." (2014). Murr, L. E., et al. "Next-generation biomedical implants using additive manufacturing of complex, cellular and functional mesh arrays." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368.1917 (2010): 1999-2032. http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-toughness/basic.html Carpi, Federico, et al., eds. Dielectric elastomers as electromechanical transducers: Fundamentals, materials, devices, models and applications of an emerging electroactive polymer technology. Elsevier, 2011. Martins, P., A. C. Lopes, and S. Lanceros-Mendez. "Electroactive phases of poly (vinylidene fluoride): Determination, processing and applications." Progress in polymer science 39.4 (2014): 683-706. Bar-Cohen, Yoseph, and Qiming Zhang. "Electroactive polymer actuators and sensors." MRS bulletin 33.03 (2008): 173-181. http://www.sbioinformatics.com/design_thesis/Polystyrene/polystyrene_Properties&uses.pdf http://www.aftonplastics.com/materials/kynar_pvdf.pdf Yin, H. J., et al. "Flow characteristics of viscoelastic polymer solution in micro-pores." SPE EOR Conference at Oil and Gas West Asia. Society of Petroleum Engineers, 2012. Thornton, P. H., and R. A. Jeryan. "Crash energy management in composite automotive structures." International Journal of Impact Engineering 7.2 (1988): 167-180. Thornton, P. H. "Energy absorption in composite structures." Journal of Composite Materials 13.3 (1979): 247-262. Song, Young Seok, et al. "Viscoelastic and thermal behavior of woven hemp fiber reinforced poly (lactic acid) composites." Composites Part B: Engineering43.3 (2012): 856-860. Khajavi, Siavash H., Jouni Partanen, and Jan Holmström. "Additive manufacturing in the spare parts supply chain." Computers in Industry 65.1 (2014): 50-63.
Summary Concept AE combines multiple weight and safety innovations facilitated by three key technological innovations: • • •
Algorithmically controlled progressive additive manufacture Next-generation graphene nanotube weave Electroactive polymer and non-Newtonian crash components Aims and objectives
Local Motors Concept AE is an ultra lightweight concept developed by an interdisciplinary design and engineering graduate team. Our goal was to re-engineer the passenger car achieving two key aims: significant weight reduction and increased safety. Beyond that our team deliverable was an unrestricted view on what shapes, forms and materials could be used. At the start of the project it was rapidly agreed that passenger cars today are alarmingly similar in appearance to those of fifty years ago, and that an exciting demonstration vehicle ought to be developed to showcase the technical and procedural innovations. Concept AE is intended to inspire the engineering research necessary to overcome current hurdles to real world commercial lightweight vehicle development. Weight Reduction Overview There are two aspects to the weight reductions developed for concept AE; the innovations developed [in abstract] and then as applied to the demonstration vehicle. Weight Reduction Abstract: The key weight saving innovations for concept AE are in the primary chassis structure. It is a lightweight composite fabrication inspired by advances in biomedical 3D orthopaedic scanning1 The key innovation in concept AE is to utilise this data in the development of an additive manufacturing algorithm. (REF.1 Algorithmically Enhanced Additive Structural Manufacture). Two key functions – a swarm algorithm controlling structural geometry and a compound additive algorithm controlling material composition – offer the development of a previously impossible level of structure optimisation. The innovative use of algorithmic control in concept AE then facilitates further weight saving techniques currently in development. Structural batteries2 and
Concept AE – 2015 Litecar Challenge suspension components3 offer further opportunities for weight reduction through consolidation into the primary structure. Alongside algorithmic structural innovations, concept AE utilises future nanotechnology to reduce non-structural bodywork weight where possible. Practical Demonstrator: Having determined the conceptual innovations in design and manufacture necessary to significantly lightweight the car, attention was turned to a practical demonstration model. Utilising Algorithmically Enhanced additive manufacture, a double skin eggshell chassis – optimised natural form for strength – was determined. The use of Algorithmic Enhancement (REF.1) ensures the strength to weight ratio of the additive honeycomb between the CFRP skins is optimised to a currently impossible degree. AE also allows for optimised crumple zones and crash structures to be built into the single composite structure, a further component and weight reduction. CFRP has already been demonstrated as a structural material whilst simultaneously acting as the lithium intercalculating electrode of a lithium battery2. The development of algorithmic additive manufacture enables this facility in the honeycomb layer as well, radically expanding the surface area available to hold charge at minimal weight penalty. Further component consolidation comes from integrating the road isolation suspension systems into the main body through AE enabled smart composite construction3. All side bodywork is mitigated through use of a graphene net which provides the protection needed from wind, rain and debris, while weighing less than a hundredth of the equivalent section in pressed metal4 The graphene net is pulled tight via a sliding aluminium lead rail and electroactive seams (REF.2: Electro-Active Materials) threaded through the material. The traditional glazed laminate screen and roof are replaced by a single iridium coated polycarbonate sheet. Currently utilised in military aircraft and powerboat manufacture, it is an ultra-light glazing material ensuring high strength, low weight and optimal anti-glare and anti-scratch characteristics.
Concept AE – 2015 Litecar Challenge With power-storage weight reduced through structural batteries, sintered aluminium hubs form the outer casing for compact digital drive motors at the rear of the car. This radically lowers powertrain weight, running through a single pinion gear into the drive hub. Durable, tackier rubber reduces tyre size and weight, while graphene cables are woven together to provide the structural support for the wheel5. Inspired by the lightweight design of vintage wire spoke wheels and skinned with a protective polymer coating the unsprung weight of the wheel unit is massively reduced, offsetting the implications of drive hubs on ride and handling. Smart materials fill the gaps. Bio-chemical compounds derived from cellulose polymers are utilised in the 3D printing of ultra light seating sections. A shared seat bracket incorporated to the B-pillar reduces internal component weight whilst increasing rear passenger safety. Paper-thin OLED displays6 provide the necessary functionality at lowest possible weight penalty. Finally electroactive materials remove the requirement for extensive airbag safety systems, with an innovative approach to front passenger safety developed from the procon-10 research in the mid 1980s. Innovation Many of the concepts applied in concept AE use cutting edge technology but are not original. Concepts such as structural carbon fibre batteries7 and complex geometric structures made from Additive Manufacture8 are available today, and either facilitated or advanced in Concept AE. Furthermore, the development potential of graphene has been carefully mapped, with commercialisation constraints the current barriers to progress. This section will focus instead on identifying the original future concepts that we envisioned for the car: Algorithmic Structural Enhancement, Electroactive Materials and Reactive Non Newtonian Crash Structures. With the safety and manufacturing implications of AE extensively covered earlier in the paper the relevant areas for Electroactive and non-Newtonian materials are included herein. REF.1: Algorithmically Enhanced Additive Structural Manufacture. Material composition alters three main variables: Strength, Toughness and Weight. Through advanced loading simulations the structural requirements and composition of the chassis body can be modelled. The sim data gathered facilitates two algorithms. The first algorithmic function determines the optimum material geometry at any point in the structure to minimise weight while meeting the strength/toughness requirements.
Concept AE – 2015 Litecar Challenge The second algorithmic function will then enable the material composition to be continuously varied to match the optimal material geometry calculated for every point in the structure. These algorithms represent a form of licensed IP – one which would enable self funding of AE research through development of high performance licensable component algorithms. Combined with next generation additive printing hardware, Algorithmically Enhanced Additive Manufacture creates the optimum balance of weight to impact resistance possible, significantly reducing concept weight.
Toughness = T, Strength = S, Density = D Material = M = {T, D, S} Advanced loading simulation produces required T and S values at each point in the structure. These fixed T-S relations can then be used to compute the desired material mixture to produce the minimum weight.
With a and b fixed, the optimum material variables (w, x, y, z) can be found to create a minimum c value. (Material values represent the percentage of each material present in a mixture) (i): algebraic abstract example algorithmic component
Table 1 Strength-toughness relationship of different metals 9
Concept AE – 2015 Litecar Challenge
REF.2: Electroactive Materials Concept AE makes significant weight reductions through replacement of actuators, hinges, and motors with electro-active materials – complex polymers that are able to produce large strains when an electric current is applied across the material10. The future concept is of a material that can significantly change its material properties and/or dimensions by the application of an electric current across it. For example a material can be used as a structural member when a current is being applied, however then can become elastic or significantly decrease in size when the current is removed. Safety Electroactive materials also represent significant safety innovation in Concept AE, with multi-use materials that can act as both impact protection and functional parts (steering wheel, dashboard) simultaneously. Manufacture Currently Polyvinylidene fluoride, (PVDF) shows the greatest levels of electro-active response11. The current tests with PVDF show that the electroactive properties can be changed depending on how the material is formed. Using different pressures, temperatures and forming processes to create the PVDF crystal, the structure and hence the response characteristics of the material can be altered. This variability shows great promise for potential future development of such materials, yet with current materials showing maximum electro-active strains of 300%12 there is further research development required.
Material
Density (g/cm )
Yield Stress (Mpa)
Youngs Modulus (Mpa)
Impact Strength (J/m)
Tensile Strength (Mpa)
PVDF
1.79
50
8.3
100-200
50
General purpose Polystyrene
0.96-1.04
40
3-3.5
37-59
34.5-48.3
3
Table 2. Comparison of material properties of electroactive PVDF and general purpose polystyrene13,14 Comparison of the properties of current electro-active materials (PVDF) against polystyrene gives closest outlook for the potential of electro-active materials developments. They display properties that are similar to or better than those of general purpose polystyrene – validation for further research into the properties of electroactive materials.
Concept AE – 2015 Litecar Challenge
Non-Newtonian Reactant Crash Structures Non-Newtonian materials are quite widely known. Viscoelastic materials are an example of a non-newtonian material which is able to increase its resistance to deformation when under a large impact force15. This initial promise inspired the team to make innovative use of viscoelastic material properties as low weight impact attenuating crash structures. Safety A non-Newtonian crash structure would alter its energy absorption properties dependant on the speed and nature of the collision occurring. This reduces the volume of material necessary to oppose the impact forces, therefore reducing the weight of the required crash structure. Even the most advanced crash structures used today are limited by their fixed energy absorbing properties. The energy absorbed by the structure in a crash is dependant on the volume of material that is involved in the crash. This means over engineering is required to ensure that the vehicle passengers will be protected in a range of crash situations16 Manufacture Carbon fibre currently provides the optimal energy absorbing properties for use in impact attenuation devices17. In a study comparing plain fibre weave against a fibre-viscoelastic combination, it was found that impact energy absorbed was increased by a factor of 2018. As such, a form of composite viscoelastic honeycomb, as used in Concept AE, is a likely route to commercialisation. This is the final major innovation enabled by the complex structural manufacturing potential of Algorithmically Enhanced Manufacture. It allows full utilisation of the energy absorbing properties of the IDM by producing a minimal crash structure that still provides sufficient coverage over the entire vehicle, saving weight and saving lives. Bill of Key Materials All figures c.2015 where available.
Concept AE – 2015 Litecar Challenge
Innovative Component The consensus over the course of the project has been that while Algorithmic Enhancement is a hugely exciting facilitator of lightweight innovation, it is not the most exciting original development demonstrated on Concept AE. That title goes to non-Newtonian viscoelastic crash structures. It is an innovation that presents potentially radical improvements in both crash structure weight and the overall crash resistance of the vehicle. With the first research into viscoelastic ballistic resistance showing great promise, it is an innovation with massive potential socio-economic value. Saving weight and saving lives – it has a ring to it! Potential Challenges The various future concepts in Concept AE do not represent structures or materials that are available today. However, through research and engineering conceptualisation we have tried to retain a degree of realism and proximity to current day technology to make research into these innovations both exciting and worthwhile. As such, the properties proposed are generally extrapolations of those currently available from materials available today. Certain areas clearly represent a greater developmental challenge than others – graphene weave and electroactive materials most evidently so. In response to these concerns, particularly futuristic materials have only been specified where a more feasible alternative could provide near-equivalent real world performance. As the very inspiration behind the electroactive safety wheel – Audi’s procon-10 – demonstrates, there is more than one route to a viable solution. Bibliography 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Parthasarathy, Jayanthi, Binil Starly, and Shivakumar Raman. "A design for the additive manufacture of functionally graded porous structures with tailored mechanical properties for biomedical applications." Journal of Manufacturing Processes 13.2 (2011): 160-170. Hagberg, Johan. "Electrochemical Performance of Commercial Carbon Fibers Towards Usage As Electrodes in Structural Li-Ion Batteries." 227th ECS Meeting (May 24-28, 2015). Ecs, 2015. Yu, W. J., and Ho-Chul Kim. "Double tapered FRP beam for automotive suspension leaf spring." Composite structures 9.4 (1988): 279-300. Hu, Kesong, et al. "Graphene-polymer nanocomposites for structural and functional applications." Progress in Polymer Science 39.11 (2014): 19341972. Zhong, Xiaohua, et al. "Carbon nanotube and graphene multiple-thread yarns."Nanoscale 5.3 (2013): 1183-1187. Kido, Junji, Masato Kimura, and Katsutoshi Nagai. "Multilayer white light-emitting organic electroluminescent device." Science 267.5202 (1995): 13321334. Jacques, Eric. "Lithium-intercalated Carbon Fibres: Towards the Realisation of Multifunctional Composite Energy Storage Materials." (2014). Murr, L. E., et al. "Next-generation biomedical implants using additive manufacturing of complex, cellular and functional mesh arrays." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368.1917 (2010): 1999-2032. http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-toughness/basic.html Carpi, Federico, et al., eds. Dielectric elastomers as electromechanical transducers: Fundamentals, materials, devices, models and applications of an emerging electroactive polymer technology. Elsevier, 2011. Martins, P., A. C. Lopes, and S. Lanceros-Mendez. "Electroactive phases of poly (vinylidene fluoride): Determination, processing and applications." Progress in polymer science 39.4 (2014): 683-706. Bar-Cohen, Yoseph, and Qiming Zhang. "Electroactive polymer actuators and sensors." MRS bulletin 33.03 (2008): 173-181. http://www.sbioinformatics.com/design_thesis/Polystyrene/polystyrene_Properties&uses.pdf http://www.aftonplastics.com/materials/kynar_pvdf.pdf Yin, H. J., et al. "Flow characteristics of viscoelastic polymer solution in micro-pores." SPE EOR Conference at Oil and Gas West Asia. Society of Petroleum Engineers, 2012. Thornton, P. H., and R. A. Jeryan. "Crash energy management in composite automotive structures." International Journal of Impact Engineering 7.2 (1988): 167-180. Thornton, P. H. "Energy absorption in composite structures." Journal of Composite Materials 13.3 (1979): 247-262. Song, Young Seok, et al. "Viscoelastic and thermal behavior of woven hemp fiber reinforced poly (lactic acid) composites." Composites Part B: Engineering43.3 (2012): 856-860. Khajavi, Siavash H., Jouni Partanen, and Jan Holmström. "Additive manufacturing in the spare parts supply chain." Computers in Industry 65.1 (2014): 50-63.
