SHEAR ENERGY
arpa-e
“Shear Energy”
LITECAR Challenge
SHEAR ENERGY
Executive Summary
In an accident, impact safety is all about energy absorption and direction. Impact Kinetic Energy In = Energy Dissipation + Energy Storage + Kinetic Energy Out The energy has to go somewhere. Thus, the ultimate goal is to protect people by minimizing the kinetic energy transferred to vehicle occupants and pedestrians. My idea is to replace crash structures, such as a plastic bumper with its metal bumper beam, with an invention that has: A durable membrane outside layer containing shear thickening fluid that is compliant to pedestrians, but thickens on hard impact. This outside layer spreads the force an inner layer. An inner membrane layer, contains both shearthinning fluid and compressible objects. The shear thinning fluid, upon impact, spreads equal pressure compressing fullyenclosed balls of memory foam containing a light compressible gas such as Helium. The compressible balls absorb most of the energy. The shear-thinning fluid behaves like a solid normally (not sloshing around) and absorbs energy through shear viscous dampening as it squeezes through gaps between the balls like a damper. A compliant lightweight frame made of carbon fiber reinforced plastic, much like a tent frame, would help control the shape.
1
Kevin Lo “Reload”
arpa-e
“Shear Energy”
Shear Thinning Fluid
LITECAR Challenge
Memory Foam Spheres
Ballistic Nylon Membranes
Shear Thickening Fluid
Weight Reduction Methodology Most current vehicles have plastic bumper fascia, lined with foam, covering steel or aluminum bumper bars. These bumper bars are heavy consisting of several millimeter thick extruded, folded or hydro-formed tubing. My proposed idea replaces the inner air volume of the bumper bar with shear thinning fluid and lighter than air gas-filled enclosed memory foam balls. I expect the lighter than air gas to offset the additional weight of the memory foam and shear thinning fluid. The outer membranes and shear thickening fluid would also still be far lighter than the dense metal solids. While memory foam exists today, a more futuristic option is the use of metal and ceramic nanostructures being invented by Julia Greer at Caltech. These tiny 0.01mm lattice structures can be compressed and rebound essentially acting as nanostructure metallic memory foam. They are super lightweight and enable high compression. Could they be used for a car frame? Sure, but scaling them to car frame components is a 100,000x scaling. If they were manufactured today in their existing size, they could be placed inside the memory foam balls with no scaling innovation required.
2
Kevin Lo “Reload”
arpa-e
“Shear Energy”
LITECAR Challenge
Innovation The key innovative aspects of this entry are that it attempts to convert more kinetic energy from the current permanent plastic-deformation energy dissipation model of bumpers and metal bumper bars to elastic energy storage and non-plastic energy dissipation. Part of the hope is also that low impact events will produce less damage, less vehicle repair, and thus less waste. That is primarily done through the conversion of solid materials to fluids. Other key innovations of this entry are the structural use of both shear thickening and shear thinning fluids to distribute and dampen impact. Current plastic bumpers are inefficient at distributing force at low impact or high impact. Likewise, internal steel and aluminum bumper beams poorly distribute force and absorb energy primarily through plastic-deformation. My idea is to spread the energy across more of the materials, and absorb it through elastic-deformation and shear fluid-damping. Emerging breakthroughs in nanostructures add credence to this idea. Bill of Materials Conventional Bumper Assembly PC/ABS Bumper Foam Support Steel/Aluminum Bumper Bar My Invention Durable Membrane – Ballistic Nylon possibly with Kevlar or Spectra fiber reinforcement Shear thickening and thinning fluids Memory foam filled with lighter than air gas Material Shear Thickening Fluid Shear Thinning Fluid Durable membrane - Kevlar, Spectra fiber, Ballistic Nylon Existing Memory foam Helium or some other lighter than air gas (others include Nitrogen, Methane, Amonnia) Carbon Fiber Reinforced Plastic Frame
Quantity (lb)
Cost ($/lb) ?? ?? $15-$50 per yard length (5’ width) $5/lb guess
$10-$20/lb
Required Manufacturing Processes One unique manufacturing process that might be required is manufacturing the hollow foam balls in an environment where the interior gas is used to create the foamed shape. For instance, the interior gas may need to be initially a liquid with the conversion to gas well-controlled.
3
Kevin Lo “Reload”
arpa-e
“Shear Energy”
LITECAR Challenge
Because memory foam is typically made through a chemical gas release, it may be difficult to produce the lighter than air gas as the foaming byproduct. Also, innovations may have to be made in terms of building the membranes with the interior fluids and spheres. The interior materials may need to be frozen into a form, such that the membrane can be laid on top of the form much like how carbon fiber strips are sometimes laid on a shape.
Passenger Safety As described previously, key safety aspects of this entry are its overall potential for elastic energy storage and energy dissipation in a less-destructive manner. The technology is limited by potential material constraints. Since the system should be lighter, there is also potentially margin to require more volume within the automobile. Calculation Example. For example, for an enclosure measuring 1.5m wide by 0.15m x 0.15m. If the membranes and spheres permit a pressure of 20 atmospheres, then the potential energy storage is as follows:
= 2.0 MPa × 0.03375 m3 × ln(0.1 MPa/2.0 MPa) = -200 kJ The kinetic energy of a car with mass of 1000 kg at speed 70 km/h can be expressed as E = 1/2 mv2 = ½ * (1000 kg) * ((70 km/h) (1000 m/km) / (3600 s/h))2 = 189 kJ
It seems reasonable to assume that a reasonable amount of energy storage is available through this system. The potential challenge then becomes the rate of dissipation of that stored energy. Innovative/Safety Component The inner membrane component consisting of the sheer thinning fluid acting to compress the memory foam balls is the innovative safety component that absorbs and dissipates energy. The movement of the ball surfaces within the fluid creates viscous damping. And the compression of the balls stores large amounts of energy as described above.
4
Kevin Lo “Reload”
arpa-e
“Shear Energy”
LITECAR Challenge
Potential Challenges Roadblocks include:
5
The performance of this innovation is highly dependent upon the maximum pressure that the membrane can contain o What materials are available for energy storage besides compressed gas and memory urethane foams? Metal and ceramic nanostructures are one futuristic option as they are extremely lightweight, highly compressible, and exhibit memory behavior. o Also, a hybrid design that uses a smaller bumper bar behind this proposed solution could be done while the capability of this innovation is iteratively improved. Manufacturing membrane enclosures that do not leak and can handle high pressures from impact may be difficult o Secondary sealing processes may be required o Initial iterations may carry more development risk The amount of structure required to support and maintain the shape of the bumper may be higher weight of add to development time; more difficult to change o Could be applied in commercial and industrial settings were design changeover is less frequent This idea may add both weight and improve safety. One will have to balance how much safety versus how much weight savings. o A hybrid design that still uses a plastic bumper in front and possibly a smaller bumper bar behind this proposed solution would probably be done while the capability of this innovation is developed o Balance of internal pressure; Memory foam cannot handle high pressures versus internal pressure of membrane o Increase rigidity of sphere housing
Kevin Lo “Reload”
“Shear Energy”
LITECAR Challenge
SHEAR ENERGY
Executive Summary
In an accident, impact safety is all about energy absorption and direction. Impact Kinetic Energy In = Energy Dissipation + Energy Storage + Kinetic Energy Out The energy has to go somewhere. Thus, the ultimate goal is to protect people by minimizing the kinetic energy transferred to vehicle occupants and pedestrians. My idea is to replace crash structures, such as a plastic bumper with its metal bumper beam, with an invention that has: A durable membrane outside layer containing shear thickening fluid that is compliant to pedestrians, but thickens on hard impact. This outside layer spreads the force an inner layer. An inner membrane layer, contains both shearthinning fluid and compressible objects. The shear thinning fluid, upon impact, spreads equal pressure compressing fullyenclosed balls of memory foam containing a light compressible gas such as Helium. The compressible balls absorb most of the energy. The shear-thinning fluid behaves like a solid normally (not sloshing around) and absorbs energy through shear viscous dampening as it squeezes through gaps between the balls like a damper. A compliant lightweight frame made of carbon fiber reinforced plastic, much like a tent frame, would help control the shape.
1
Kevin Lo “Reload”
arpa-e
“Shear Energy”
Shear Thinning Fluid
LITECAR Challenge
Memory Foam Spheres
Ballistic Nylon Membranes
Shear Thickening Fluid
Weight Reduction Methodology Most current vehicles have plastic bumper fascia, lined with foam, covering steel or aluminum bumper bars. These bumper bars are heavy consisting of several millimeter thick extruded, folded or hydro-formed tubing. My proposed idea replaces the inner air volume of the bumper bar with shear thinning fluid and lighter than air gas-filled enclosed memory foam balls. I expect the lighter than air gas to offset the additional weight of the memory foam and shear thinning fluid. The outer membranes and shear thickening fluid would also still be far lighter than the dense metal solids. While memory foam exists today, a more futuristic option is the use of metal and ceramic nanostructures being invented by Julia Greer at Caltech. These tiny 0.01mm lattice structures can be compressed and rebound essentially acting as nanostructure metallic memory foam. They are super lightweight and enable high compression. Could they be used for a car frame? Sure, but scaling them to car frame components is a 100,000x scaling. If they were manufactured today in their existing size, they could be placed inside the memory foam balls with no scaling innovation required.
2
Kevin Lo “Reload”
arpa-e
“Shear Energy”
LITECAR Challenge
Innovation The key innovative aspects of this entry are that it attempts to convert more kinetic energy from the current permanent plastic-deformation energy dissipation model of bumpers and metal bumper bars to elastic energy storage and non-plastic energy dissipation. Part of the hope is also that low impact events will produce less damage, less vehicle repair, and thus less waste. That is primarily done through the conversion of solid materials to fluids. Other key innovations of this entry are the structural use of both shear thickening and shear thinning fluids to distribute and dampen impact. Current plastic bumpers are inefficient at distributing force at low impact or high impact. Likewise, internal steel and aluminum bumper beams poorly distribute force and absorb energy primarily through plastic-deformation. My idea is to spread the energy across more of the materials, and absorb it through elastic-deformation and shear fluid-damping. Emerging breakthroughs in nanostructures add credence to this idea. Bill of Materials Conventional Bumper Assembly PC/ABS Bumper Foam Support Steel/Aluminum Bumper Bar My Invention Durable Membrane – Ballistic Nylon possibly with Kevlar or Spectra fiber reinforcement Shear thickening and thinning fluids Memory foam filled with lighter than air gas Material Shear Thickening Fluid Shear Thinning Fluid Durable membrane - Kevlar, Spectra fiber, Ballistic Nylon Existing Memory foam Helium or some other lighter than air gas (others include Nitrogen, Methane, Amonnia) Carbon Fiber Reinforced Plastic Frame
Quantity (lb)
Cost ($/lb) ?? ?? $15-$50 per yard length (5’ width) $5/lb guess
$10-$20/lb
Required Manufacturing Processes One unique manufacturing process that might be required is manufacturing the hollow foam balls in an environment where the interior gas is used to create the foamed shape. For instance, the interior gas may need to be initially a liquid with the conversion to gas well-controlled.
3
Kevin Lo “Reload”
arpa-e
“Shear Energy”
LITECAR Challenge
Because memory foam is typically made through a chemical gas release, it may be difficult to produce the lighter than air gas as the foaming byproduct. Also, innovations may have to be made in terms of building the membranes with the interior fluids and spheres. The interior materials may need to be frozen into a form, such that the membrane can be laid on top of the form much like how carbon fiber strips are sometimes laid on a shape.
Passenger Safety As described previously, key safety aspects of this entry are its overall potential for elastic energy storage and energy dissipation in a less-destructive manner. The technology is limited by potential material constraints. Since the system should be lighter, there is also potentially margin to require more volume within the automobile. Calculation Example. For example, for an enclosure measuring 1.5m wide by 0.15m x 0.15m. If the membranes and spheres permit a pressure of 20 atmospheres, then the potential energy storage is as follows:
= 2.0 MPa × 0.03375 m3 × ln(0.1 MPa/2.0 MPa) = -200 kJ The kinetic energy of a car with mass of 1000 kg at speed 70 km/h can be expressed as E = 1/2 mv2 = ½ * (1000 kg) * ((70 km/h) (1000 m/km) / (3600 s/h))2 = 189 kJ
It seems reasonable to assume that a reasonable amount of energy storage is available through this system. The potential challenge then becomes the rate of dissipation of that stored energy. Innovative/Safety Component The inner membrane component consisting of the sheer thinning fluid acting to compress the memory foam balls is the innovative safety component that absorbs and dissipates energy. The movement of the ball surfaces within the fluid creates viscous damping. And the compression of the balls stores large amounts of energy as described above.
4
Kevin Lo “Reload”
arpa-e
“Shear Energy”
LITECAR Challenge
Potential Challenges Roadblocks include:
5
The performance of this innovation is highly dependent upon the maximum pressure that the membrane can contain o What materials are available for energy storage besides compressed gas and memory urethane foams? Metal and ceramic nanostructures are one futuristic option as they are extremely lightweight, highly compressible, and exhibit memory behavior. o Also, a hybrid design that uses a smaller bumper bar behind this proposed solution could be done while the capability of this innovation is iteratively improved. Manufacturing membrane enclosures that do not leak and can handle high pressures from impact may be difficult o Secondary sealing processes may be required o Initial iterations may carry more development risk The amount of structure required to support and maintain the shape of the bumper may be higher weight of add to development time; more difficult to change o Could be applied in commercial and industrial settings were design changeover is less frequent This idea may add both weight and improve safety. One will have to balance how much safety versus how much weight savings. o A hybrid design that still uses a plastic bumper in front and possibly a smaller bumper bar behind this proposed solution would probably be done while the capability of this innovation is developed o Balance of internal pressure; Memory foam cannot handle high pressures versus internal pressure of membrane o Increase rigidity of sphere housing
Kevin Lo “Reload”
