APALIS Anthony Kim Sheetanshu Tyagi
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APALIS Anthony Kim Sheetanshu Tyagi
Executive summary
To successfully develop a light weight road vehicle, we have targeted the following avenues for weight
reduction:
1. Chassis and sub frames
2. Powertrain and wheel assemblies
3. Energy source (Batteries or engine)
Instead of just targeting one of these, a complete redesign of various components used in each sub system is
proposed which thus results in a much lighter vehicle. A systems approach primarily focused on weight saving
without compromise of functionality and strength is the primary objective. The following solutions are proposed
for achieving the desired solution:
1. A chassis decomposed into parts:
a. The proposed safety cell which will be manufactured using Solid free form fabrication. Cellulose
nano crystals (CNC), one of the strongest materials developed till date will be used for the same.
b. The sub frames proposed to be fabricated by the same process, will be made out of a new composite
composed of Dyneema fibers and polyurethane.
2. An electric power train consisting of hub motors will be used on all four wheels. Additionally, in wheel
suspension will be used thus eliminating all the linkages, compliance members etc. reducing the number
of components and weight.
3. Instead of Li-ion batteries, Graphene super capacitors will be used. Additionally an energy efficient
Photo Voltaic (PV) panel will be used instead of a roof.
The cumulative effect of these changes will result in a design which will be over 45% lighter than conventional
designs.
Weight reduction methodology
The combined effect of using innovative materials (described below in points 3, 4, 5) and a unique design
and manufacturing processes (explained in 1, 2), can bring down the overall weight by around 45%.
1. Manufacturing and design: Weight is saved in the chassis by using solid free form manufacturing (focus
is on Fused Deposition Modeling but will be referred to as SFF due to slight differences in suggested
process which is explained later in the report) which allows the printing of complex 3D geometries. SFF
gives the design and fabrication freedom to build complex shapes thus resulting in variable cross
sectional areas and hollow internals which can be printed to thus have material only where required. [3]
When SFF is coupled with a Computer aided optimization technique such as the soft kill option (SKO) to
design the chassis, extremely material efficient designs can be made. SKO uses inspiration from nature
and optimizes designs such that uniform stress is obtained in all scenarios thus eliminating extra weight.
The optimization process produces structures which mimic the way bones, tree branches, spider webs
etc. are designed. Variable cross sections and complex contours can be designed which can then be
printed using SFF thus yielding combined weight reductions of around 5% when compared to current
manufacturing and design techniques. [9] [23]2. Chassis material: The safety cell of the chassis will be fabricated by using a bio composite of cellulose
nano crystal fibers (CNC). The bulk density of this material is less than 2 g/cm3 (compared to 7.8 g/cm3
for steel) and the strength is twice as much as that of carbon fiber thus making the strength to weight
ratio of CNC five times that of high strength steel. The combined effect of strength and weight will yield
a 30% reduction in weight for the same value of strength. [8]
3. Sub frames material: The sub frames (front and rear crumple zones) will be designed out of a composite
of Dyneema and polyurethane, where polyurethane will be used as the base and Dyneema will be the
reinforcement. Dyneema has a density of below 1 g/cm3 and is 15 times stronger than steel on a weight-
for-weight basis, twice as strong as Aramid fiber. However the combined strength of the PU-Dyneema
composite should still be around 5 times that of steel thus making its specific strength around 8 times
that of steel. The combined density of the material will be under 1.2 g/cm3 compared to around 7.75
g/cm3 for steel. [7] Thus a weight reduction of around 30% should be realized.
Apart from the above, additional weight saving techniques such as the ones listed below will be adopted:
1. Using photo voltaic panels at various parts such as the roof. This will require lesser batteries, thus further
reducing weight. PV panels will be a viable solution only once the efficiency of affordable panels reaches
around 40-50%. Also the use of super capacitors made out of Graphene instead of lithium ion batteries
once the research matures can be considered. [12] These can also be embedded into the body itself thus
making it a multi-functional material (research for the same is underway). The same can be bonded to
the composite panel by using an advanced phenolic resin. [4] [15]
3. Using an active wheel system which has the suspension and drive integrated into the wheel thus
drastically reducing sprung mass. Michelin produces active wheel systems which after factoring in the
battery weight is around 200 pounds lighter than conventional gasoline power trains. [5] Our proposed
system (combined effect of wheel and batteries) will be around 40% lighter than electric vehicle
architectures as it does not use conventional Li-ion batteries but uses Graphene super capacitors instead.
[6]
Total weight saving when compared to properties/characteristics of 4000 lb sedans:
The values are approximate as exact analysis of the structure will require FEA analysis of parts based on material
properties and fabrication methods. The values are conservative and with proper design, much greater weight
savings can be made:
CONTRIBUTOR APPROXIMATE WEIGHT SAVING (IN LBS)
1 SKO and SFF 75
2 Cellulose nano crystals 400
3 Dyneema composite 400
4 Graphene/PV Panel 500
5 Active wheel 200
This thus results in a 1775 lb weight saving which is around 45% the weight of the car.Innovation
A new vehicle design is suggested which makes use of novel materials and manufacturing/design techniques.
The proposed innovations are:
1. Dyneema- Polyurethane composite for crumple zones
This innovative composite material is proposed to be used for the front and rear sub frames and also for
the doors on the sides. The use of a foamy composite like Dyneema-PU will result in extremely tough
and safe vehicles due to the higher energy absorption capabilities. It has toughness 3 times and on a
weight for weight basis is the strongest fiber on the market with the greatest specific strength. Basic
research has been done on the impact absorption properties of this composite and has also been used
in armored vehicles and bullet proof vests for impact resistance. [7][19]
2. Cellulose nano crystal composite for safety cell
Cellulose nano crystals (CNCs) can be produced with minimal impact on the environment and is more
than two times stronger than the steel or carbon fiber currently being used. It can be produced using
cost and energy effective methods and is
3. Solid free form manufacturing and Soft kill approach optimization
The fabrication technique has not yet been proposed for automobiles but has promise due to its wide
scope and interesting results. This coupled with computer aided optimization technique can change the
way cars are designed and will result in structures which will have material deposited only where
required. It results in complex designs which resemble the structure of natural structures such as bones,
spider webs and trees with no excess material unlike current optimization which is limited due to the
forming and welding operations currently used.
4. Composite fabrication technique: Proportioning and deposition system
A new machine which is capable of fabricating the composites mentioned is proposed and explained in
detail later in the report. This makes it possible for automated composite manufacturing in a fast and
efficient manner.
Bill of materials
Since most of the materials proposed are still in research stage, approximate or targeted costs has been
mentioned based on the data obtained from various references. [19] [20] [21] [22]
MATERIAL COST (per kg) DENSITY (g/cm3) TENSILE STRENGTH (MPa)
1 Polyurethane $4 1.2 30
2 Cellulose nano crystals $10 1.53 7500
3 Dyneema fibers $35 0.97 4000
4 Graphene sheet $450 ~2 130000Required manufacturing processes
1. Solid Freeform fabrication
The manufacturing technique adopted for the chassis and sub frames will be solid free form
manufacturing (SFF). The form of SSF proposed is analogous to fused deposition modeling and uses a
heated semi-solid slurry form of the material and deposits it in successive layers on one another. SFF is
a manufacturing approach based on creating three-dimensional bodies by the addition of material layer
by layer, without molds or machining. [17] SFF is still in its nascent stages and currently relies on a
manufacturing technique in which the raw material is fed into a carrier where it melts to the right
temperature and gets deposited on to a moving bed (picture in ref. 17 and 18). It has been successfully
tried to form bio composite materials too and therefore can in theory be used for CNC. [16]
To implement the same to fabricate a large scale chassis, a big Computer numerically controlled
nozzle controlled by a robotic arm which can move along all five axes can be used to deposit material
layer by layer. The points can be programmed into the machine and the speed and volume of material
can be adjusted so as to provide variable thicknesses and stiffness. The volume and speed can be
adjusted to change the volume rate and thus adjust adhesion levels, alignment of particles, density and
strength too. A proposed design for the same is also mentioned later in the report.
The sub frames and main frame will be done separately and bolted on which will also save time.
The process though slower than the current production methods used for steel and aluminum, will
produce a more homogeneous structure free of welds and joints. It will be a single process in which the
entire structure is printed in one go with no need for additional mounts, brackets etc. as they will be
embedded into the structure’s design itself. Surface finish can be done separately after.
2. Production of Cellulose nano crystals
CNC can be produced from any kind of synthetic or natural elements such as agricultural or pulp
waste but we have chosen the most energy efficient and environment friendly process to produce them
which is to produce CNCs synthetically using genetically engineered blue-green algae (a cyanobacteria
sourced from vinegar bacterium). [13] The research for the same has already been carried out and has
proven successful in fabricating high strength cellulose nano crystals using a cost effective process.
3. Production of Dyneema
An electro-spinning method called Force Spinning will be employed to fabricate ultrafine nano
fibers of Dyneema. [25] This is a cost effective process which lowers the cost of the fiber as mentioned
above by 50%. This is a relatively new process and research is still being done to improve the process to
the point it can be used for mass production of any nano fiber. It uses high speed centrifugal force to
break down a compound to produce crystalline nano fiber. The details of the process are provided and
using it Dyneema nano fibers can be readily obtained. [34]
4. Fabrication of the PU-Dyneema and CNC-Epoxy composites: Proportioning and Deposition system
Composites consisting of PU-Dyneema and CNC-Epoxy have not been manufactured before and
therefore a solution which can fabricate the composite in the right ratio and deposit it using SFF will have
to be developed. A solution for the same does not exist which is why we have come up with a composite
fabrication technique suited for SFF. A rough sketch of the same is attached too.
Both materials are kept in separate containers where they are first heated up to a specified
temperature at which it forms a semi solid slurry (temperature will have to be tested for). Then the two
materials are passed into a proportioning system to adequately mix the two. A small centrifugal rotatorwhich rotates at high speeds will be used to obtain an adequate mix between the nano fibers and epoxy
(both being mixable due to their hydrophilic semi solid form). After this it will pass through a regulation
system where the percentage and variation in nano fiber will be checked for. If the mix is inadequate,
the regulator will shut the output valve and redeposit the material into the mixing chamber. If mixed to
the satisfied amount, the material will be passed through multiple micron sized extrusion nozzles where
the fiber will be aligned in the right direction. Once the two materials have been adequately
proportioned and mixed, they pass through a heated nozzle where they are reheated to a required
temperature and then deposited on to a bed. The nozzle is connected to a robotic arm which is capable
of moving along 5 axes. A closed loop system which constantly monitors the position and point of
application of material feeds data back into the proportioning system and nozzle. Both systems adjust
the amount of fiber being mixed and amount of material being deposited accordingly. This is a machine
which can fabricate composites and deposit the material, thus combining processing and fabrication.
Passenger safety
Frontal and rear impacts accounted for 55 percent of passenger vehicle occupant deaths in 2013.[11] One
of the issues with current crumple zones is that aluminum and steel are not tough enough to absorb the energy
in the case of impact and are also stiff which thus lowers deformation. An ideal material for the crumple zone
would be one which is extremely tough, thus absorbing most of the energy in impact. Therefore the front and
rear crumple zone are fabricated from a new composite composed of Polyurethane foam and Dyneema nano
fibers [10] which can absorb twice as much energy as Kevlar. Moreover the passengers are cocooned using a stiff
CNC chassis, which is twice as stiff as carbon fiber. [8] Thus the amount of deformations in the passenger cabin
is limited which makes it safer for the passengers seated. The energy absorption in the crumple zones on all
sides is also improved by around three times.
The core of polyurethane (PU) foams is enhanced by adding 20-30% of Dyneema. The low strength and
high toughness of foam is supplemented by the high toughness and high strength of Dyneema. Dyneema
composites are ideal for crumple zones because of three major advantages: 1) highest percentage of absorbed
energy versus total impact energy. 2) Small damage area and no brittle fracture behavior. 3) Highest absorbed
energy level as a function of areal density. Since the front and rear are also not supposed to house the power
train and are therefore spacious, the design of the crumple zones can be made with much higher freedom. So
not only will it deform much lesser than current structures do, it will also impart much lower energy into the
stiffer CNC safety cell thus leaving the passengers unaffected and causing lesser damage to the vehicle. [24]
The same material is also used to fabricate the structure of the doors and will therefore offer resistance
in side impact. So instead of forming the door out of multiple steel sheets which are spot welded together, the
door will be printed as one thick piece. The glass window and indoor controls can be installed in to the same
externally. The interiors will be unaffected. Additionally, A thin sheet of Graphene can be embedded to function
as super capacitors, which will also add strength and rigidity to the door.
Innovative/Safety component
The use of Dyneema-Polyurethane composite as a structural material to form the crumple zones in the
front and rear and also as a side impact attenuator. The use of this material has not been tried before but shows
promise due to the unique properties of both materials which are well suited to make a structure which issupposed to absorb energy. The use of the “Proportioning and Deposition System” machine suggested to do
has huge potential to automating the entire composite fabrication process thus cutting cost and time.
Potential challenges
1. Proving the large scale manufacturability of solid free form manufacturing
SFF is currently only capable of fabricating small parts with results which are extremely impressive. Large
scale 3D robotic printers exist and are being used to print plastics but the implementation of the same for
SFF and the composites proposed has yet to be tested. [26] The existence of patents has hindered the speed
of this research and now that they are expiring, more rapid research can be carried out. The properties
obtained are as stated but a system which can fabricate economically and quickly at large scales is still to be
designed. A basic design is proposed in the report but still requires a lot of work before it can even be
considered for actual implementation. Currently, the production of a chassis is done in multiple stages but
by using SFF, it is reduced to two stages which can counter the problem. The applicability of solid free form
fabrication has been tested and multiple nozzle designs and methods can be seen in the reference. [29]
2. Economic feasibility of the materials mentioned
Dyneema: The major issue with Dyneema is cost and fabrication techniques which limit the usability.
But by using the manufacturing method Force spinning proposed above, costs can be lowered. With further
research, affordable and large volume production modifications can be made to Force Spinning to the point
that it is economical to use.
CNC: The critical challenge is to achieve the transfer of the exceptional mechanical properties of the
nano crystalline composite to the macro scale properties of the bulk nano composites and maintain the
ability to obtain well-dispersed hydrophilic reinforcing nano cellulose crystals in hydrophobic polymer
matrices. Yet another specific challenge is to increase the stiffness of the nano composites without
decreasing their high extensibility. Current research is underway which is focusing on the microstructure
variation on application of high load. The cost can be kept low for cellulose as it is abundantly available but
the actual material has not been tested enough to the point where it can be used for large structures. Further
research and alterations in production techniques should push it to the point where is a viable solution.
3. Fabrication process of the nano-composites mentioned
The primary reasons composites are not as widely used as metals or plastics is the fact that it is very
expensive to do so. But if the entire composite fabrication process can be automated to a point where one
fabrication unit can take care of the fabrication and deposition, it becomes very easy and convenient (as
proposed). It saves space, labor and infrastructure costs. As of now, manufacturing composites is labor
intensive and time consuming which is why it’s costly and difficult to do so but with advances in material
science and manufacturing, a machine like the one suggested can be realized.
4. Economic and technical feasibility of SFF to be made a viable solution
Existing systems are still predominantly based on rapid prototyping machine architectures where a
different mentality exists for the requirements of the produced parts. Further research into various facets
such as modelling, process design and controls is required to take full advantage of the process.
The biggest issues with SFF are in validating the process for the materials suggested, the speed and time it takes
(without compromising tolerances and accuracy) and the cost involved.Potential ways of improvement:
1. A fundamental understanding of the basic science behind the SFF process. In particular, a better
understanding of the interaction between the various energy sources and materials is key. Material
properties at the large scale will have to be tested for. On a basic research level, there is also a much
greater need for understanding the physics of the interlayer bonding.
2. To take full advantage of the characteristics of SFF, new design and analysis software which prioritize
optimization techniques such as the SKO approach need to be developed for use in the automotive
industry. This will help in lowering the amount of material, therefore speeding up the process. A
remarkable cost reduction can be obtained if the component shape is modified to exploit SFF
potentialities. [17]
3. The cost of machines, materials, and maintenance is seen as an obstacle to wider adoption of SFF. Using
new technology to create advanced instrumentation and robotic arms which keep the entire
implementation cost comparable to the current system is key to the feasibility of the process. The
number of fabrication and machining steps involved in making a large size chassis can be reduced from
rolling, cutting, forming, welding, drilling etc. to just formation of compound, printing and surface finish.
If implemented correctly, that can be a huge contributor in bringing down costs and time.
In a paper by Atzeni, a complete detailed cost analysis of High pressure die casting was made against a form
of SFF (Selective laser sintering) in which the design was modified to suit SLS too. The cost for medium volume
was in greater favor for SLS (and this was in 2012), so with the advance of better tooling and more knowledge
of the micro structure, etc. more cost effective machines can be built which can thus drive down the overall
costs significantly. [27]
5. Solid free form fabrication of advanced nano crystalline composite materials
The reasons why SFF techniques such as fused deposition modeling don’t currently work for nano-
composites are: [31]
1. The strength of the final structure is low due to weak understanding of the micro structure. With further
research and understanding, this problem can be alleviated.
2. Continuous nano fibers (~100-200 nm in dia) are needed as the nozzle gets clogged. Various dimensions
of nano fiber can be tested against various precise nozzle shapes to find the right point. New
instrumentation will have to be developed which has not happened yet due to the use of rapid
prototyping equipment.
3. Very expensive due to set up/ infrastructure cost. This will change with time as the setup becomes more
commercialized. Like everything else, volumes can drive down costs too. Moreover standardized process
parameters and synthesis parameters do not exist.
Therefore to successfully implement SFF for nano composites, the above problems will have to be solved.
Currently the DOE in collaboration with Oakridge National Laboratory are researching into producing materials
and machines which are capable of printing nano crystalline composites. FDM of polymers and a Bi-Component
extrusion system are being tested, thus validating our claim for the fabrication method (SFF) and proposed
manufacturing technique. [33] The first carbon fiber 3D printer is already in production and another printer that
prints composites SLS is in production. [34] As more companies look into the above mentioned problems, the
solution will become more feasible.REFERENCES [1] Roadmap for Additive Manufacturing Identifying the Future of Freeform Processing Edited by David L. Bourell, Ming C. Leu , David W. Rosen [2] Solid Freeform Fabrication Using Semi-Solid Processing by Christopher S. Rice [3] Lightweight metal cellular structures via indirect 3d printing and casting Nicholas A. Meisel, Christopher B. Williams, Alan Druschitz [4] A new way to make sheets of graphene: http://newsoffice.mit.edu/2014/new-way-make-sheets-graphene- 0523 [5] Michelin Unveils Active Wheel in Affordable Electric Car: http://www.treehugger.com/cars/michelin- unveils-active-wheel-in-affordable-electric-car.html [6] Graphene Supercapacitors Ready for Electric Vehicle Energy Storage: http://www.technologyreview.com/view/521651/graphene-supercapacitors-ready-for-electric-vehicle- energy-storage-say-korean-engineers/ [7] Bi-stable structures for energy absorption Composite structures under tension Zachary Whitman and Valeria la Saponara; http://www.toyobo-global.com/seihin/dn/dyneema/seihin/tokutyou.htm [8] Cellulose extract stronger than carbon fiber or Kevlar: http://www.gizmag.com/cellulose-nanocrystals- stronger-carbon-fiber-kevlar/23959/ [9] Design in Nature: Learning from Trees by Claus Mattheck [10] Impact Performance of Dyneema PE/Epoxy Composites in Comparison with other Commercial Fibers by K. F. M. G. J. Scholle [11] Crash data: http://www.iihs.org/iihs/topics/t/general-statistics/fatalityfacts/passenger-vehicles#Crash- types [12] Graphene super capacitor: http://www.21stcentech.com/transportation-update-volvo-e-car-concept- runs-super-capacitor/; http://www.iflscience.com/technology/graphene-based-supercapacitors-could- eliminate-batteries-electric-cars-within-5-years; [13] Engineering Algae to make the ‘Wonder Material’ Nanocellulose for Biofuels and More: http://www.newswise.com/articles/engineering-algae-to-make-the-wonder-material-nanocellulose-for- biofuels-and-more [14] Graphene-based supercapacitor with carbon nanotube film as highly efficient current collector - Marco Notarianni, Jinzhang Liu, Francesca Mirri, Matteo Pasquali and Nunzio Motta [15] Indirect solid free form fabrication of local and global porous, biomimetic and composite 3D polymer- ceramic scaffolds by Taboas JM, Maddox RD, Krebsbach PH, Hollister SJ. [16] Solid Freeform Fabrication of Composite-Material Objects Parts specified by CAD data files could be fabricated as needed. Lyndon B. Johnson Space Center, Houston, Texas [17] Semi-Solid fabrication: https://www.google.com/patents/US5887640
[18] Predicting the material properties of a polyurethane matrix (a composite within a composite) by J. P. Foreman, D. Porter, D. Pope, F. R. Jones [19] CNC Properties: Cellulose Nanocrystals (CNC) Background and Processing by Liyan Zhao and Frank J. Tosto ; Bio-based nanocomposites: based nanocomposites: challenges and opportunities challenges and opportunities by John Simonsen [20] Graphene properties: http://cheaptubes.com/carbon-nanotubes-prices.htm; Graphene Nanoplatelets: A Multi‐functional Nanomaterial Additive for Polymers and Composites by Lawrence T. Drzal [21] Polyurethane properties: http://ocw.mit.edu/courses/materials-science-and-engineering/3-11- mechanics-of-materials-fall-1999/modules/props.pdf [22] Dyneema properties: http://www.toyobo-global.com/seihin/dn/dyneema/seihin/tokutyou.htm [23] SKO (soft kill option): the biological way to find an optimum structure topology by A Baumgartner [24] High Performance Dyneema Fibers in Composites by J L J van Dingenen [25] Electrospinning of Ultrahigh-Molecular-Weight Polyethylene Nanofibers by d. m. rein, l. shavit-hadar, r. l. khalfin, y. Cohen, k. shuster, e. zussman [26] Large scale 3D printers: http://www.hizook.com/blog/2013/11/13/large-scale-rapid-prototyping-robots- industrial-robot-arm-extruders-and-building-sca [27] Economics of additive manufacturing for end-usable metal parts by Eleonora Atzeni & Alessandro Salmi [28] Additive manufacturing: technology, applications and research needs by Nannan GUO, Ming C. LEU [29] Polymer composite additive manufacturing to simultaneously build hierarchical materials and net-shape structures by Dr. Ben Farmer [30] Additive manufacturing (AM) and nanotechnology: promises and challenges by Christopher Williams, Olga Ivanova and Thomas Campbell [31] Critical factors on manufacturing processes of natural fibre composites by Mei-po Ho a , Hao Wang a , Joong-Hee Lee b , Chun-kit Ho c , Kin-tak Lau a,d,⇑ , Jinsong Leng e , David Hui [32] Carbon Fiber Reinforced Polymer Additive Manufacturing by Chad Duty [33] World’s first Carbon fiber printer: http://www.extremetech.com/extreme/175518-worlds-first-carbon- fiber-3d-printer-demonstrated-could-change-the-face-of-additive-manufacturing-forever [34] Force spinning: http://fiberiotech.com/technology/forcespinning/ ; Electrospinning to ForcespinningTM by Kamal Sarkar, Carlos Gomez, Steve Zambrano, Michael Ramirez, Eugenio de Hoyos, Horacio Vasquez, Karen Lozano
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