|The winning design: “WaterBone”. Click to enlarge.|
Local Motors, in partnership with the Advanced Research Projects Agency-Energy (ARPA-E), announced the winner of the LIghtweighting Technologies Enabling Comprehensive Automotive Redesign (LITECAR) Challenge. The design challenge served to accelerate innovative ideas by using novel material technologies, structural designs, energy absorbing materials and unique methods of manufacturing to reduce vehicle curb weight while maintaining current US automotive safety standards. 254 conceptual designs were submitted. (Earlier post.)
The winning design, Aerodynamic Water Droplet with Strong Lightweight Bone Structure (“WaterBone”), was created by Andres Tovar, a mechanical engineering assistant professor at the School of Engineering and Technology at Indiana University-Purdue University Indianapolis, and his group of graduate students. The proposed design—which makes innovations in the structural layout, use of multi-materials, and the 3D printing manufacturing process—has the outer shape (envelope) of a water droplet with an embedded trabecular (graded porous) bone-like structure (spaceframe). The water droplet shape provides a low drag coefficient, while the spaceframe provides the mechanical strength and energy absorption capabilities (crashworthiness) required to protect the occupant in the event of a collision.
The envelope’s material is a polymer composite, which provides desirable characteristics of a monocoque design. The spaceframe’s material is functionally graded aluminum alloy foam. The layout of the proposed spaceframe is designed using a specialized and unique topology optimization algorithm (Hybrid Cellular Automaton, HCA) for crashworthiness. The monocoque-spaceframe design is built using additive manufacturing (3D printing) technology.
Novel multiscale structural layout. At the vehicle scale, the generated spaceframe has a structure similar to the one of long bone. In essence, the aerodynamic water droplet shape is protected by specialized ribcage that follows principles of Michell-type frame structures. At the component scale, each spaceframe tubular component is filled with a functionally graded bone-like cellular structure. Such complex, lightweight, multiscale structural layout is manufacturable using 3D printing technologies.
Novel lightweight multi-material design. The envelope’s polymer composite provides desirable safety characteristics of a monocoque design. The metallic (functionally graded cellular) spaceframe provides a level of protection similar to racercars that also use spaceframe design; however, the proposed design has less than 50% its weight with significantly lower part count. The result is a design of very light, strong, and safe (crashworthy) components with the possibility of utilizing a wide variety of plastics and metals.
Novel manufacturing process. Besides providing lightweight and innovative vehicle designs, 3D printing offers a number of benefits in comparison to current manufacturing processes: cleaner and environmentally friendlier operation that allows complex part production with minimal overall material wastage; free-form mass customization with reduced time to market; and low overall cost.
|The concept vehicle combines the shape of a water droplet and the spaceframe design similar to a ribcage. Each structural component has a graded porous structure similar to the one of a bone. Click to enlarge.|
The winning design was selected by a panel of experts in materials, crashworthiness, structures, manufacturing and safety.
HCA was proposed and developed by Dr. Tovar and collaborators with the support of Honda R&D Americas. Currently, the HCA algorithm is implemented by Livermore Software Technology Corporation (LSTC) in their commercial finite element analysis (FEA) software LS-DYNA. The topology optimization problem to be initially addressed is finding the material distribution that maximizes the internal energy (IE) and subject to a mass (M) constraint.
The main advantages of the HCA algorithm, says Dr. Tovar, are the proven convergence, its convergence rate, and its extension to solve a variety of topology problems. When applied to a single crashworthy vehicle component (e.g., a bumper), the HCA algorithm finds the material distribution that maximizes IE for a given mass target. However,while these designs may be sufficient for some vehicle components, this current strategy is not applicable to the design of crumple zone in the front and rear ends of the vehicle.
Other crashworthiness indicators must be considered: specific energy absorption (SEA); mean crushing force (MCF); peak crushing force (PCF); crash load efficiency (CLE); and progressive folding.
In order to address this crashworthiness problem, we have proposed a design algorithm that uses the “gray” design generated by HCA that is then clustered and optimized using sequential metamodel-based genetic programming. The multiscale design offers an optimal spaceframe design that maximizes internal energy, and the internal functionally graded cellular structure to manage the impact by extremizing crashworthiness indicators. The loading conditions for the optimal space frame two frontal pole impacts (full frontal and offset) and three side impacts (central and two offsets). The result is a lightweight structure that satisfies all safety standards.
Tovar will receive the $60,000 grand prize for his pioneering vehicle design concept. The remaining $90,000 in prize money will be divided between five additional submissions that were recognized for their ideas by both the Local Motors’ online community and LITECAR judging panel.
First runner up ($40,000): Sumit Lakhera and Feyzi Aras, Skeletos
Second runner up ($20,000): Wilburn Whittington, David Francis and Kyle Johnson, Metal Matrix Metallic Composites
Innovative design component ($10,000): Yuqing Zhou, Kazuhiro Saitou and Jeff Xu, Manta
Innovative safety component ($10,000): Alexander Rivera, Modular Sprung Pod Car
Community favorite ($10,000): Anthony Kim and Sheetanshu Tyagi, Apalis
The LITECAR Challenge launched on 2 January and voting concluded on 20 March. The submissions were evaluated on four main criteria: vehicle curb weight reduction, vehicle safety, innovation and supporting evidence.