Over the past decade, there has been an increase in the intentional design of meso-structured materials that are optimized to target desired material properties. This paper reviews and critically compares common numerical methodologies and optimization techniques used to design these meso-structures by analyzing the methods themselves and published applications and results. Most of the reviewed research targets mechanical material properties, including effective stiffness and crushing energy absorption. The numerical methodologies reviewed include topology and size/shape optimization methods such as homogenization, Solid Isotropic Material with Penalization, and level sets. The optimization techniques reviewed include genetic algorithms (GAs), particle swarm optimization (PSO), gradient based, and exhaustive search methods. The research reviewed shows notable patterns. The literature reveals a push to apply topology optimization in an ever-growing number of 3-dimensional applications. Additionally, researchers are beginning to apply topology optimization and size/shape optimization to multiphysics problems. The research also shows notable gaps. Although PSOs are comparable evolutionary algorithms to GAs, the use of GAs dominates over PSOs. These patterns and gaps, along with others, are discussed in terms of possible future research in the design of meso-structured materials.
A systematic unit cell synthesis approach is presented for designing metamaterials from a unit cell level, which are made out of linearly elastic constitutive materials to achieve tunable nonlinear deformation characteristics. This method is expected to serve as an alternative to classical Topology Optimization methods (solid isotropic material with penalization or homogenization) in specific cases by carrying out unit cell synthesis and subsequent size optimization (SO). The unit cells are developed by synthesizing elemental components with simple geometries that display geometric nonlinearity under deformation. The idea is to replace the physical nonlinear behavior of the target material by adding geometric nonlinearities associated with the deforming entities and thus, achieve large overall deformations with small linear strains in each deformed entity. A case study is presented, which uses the proposed method to design a metamaterial that mimics the nonlinear deformation behavior of a military tank track rubber pad under compression. Two unit cell concepts that successfully match the nonlinear target rubber compression curve are evaluated. Conclusions and scope for future work to develop the method are discussed.
A system was created for sand traction performance testing of tire prototypes for extraterrestrial use by NASA. The system consists of a suspended sand-filled trough that rotates when driven by the prototype. Sensors are used to determine traction slippage of prototypes, providing a quantitative measure of relative prototype performance. This paper describes system improvements to better simulate extraterrestrial environments and more accurately measure prototype performance. A tire prototype hard stop was designed and built to prevent damage associated with the tire assembly resting in the trough. A rock obstacle was created to simulate rough terrain. A sensor system was designed to more accurately determine tire velocity. Various concepts were developed and prototyped to groom the sand during testing. Computational hardware and software upgrades were made to better facilitate the data acquisition processes. An instructional video was created to explain operational procedures. The sensor system will be integrated with the software and a sand grooming concept will be implemented.
The interaction between tires and soft soils is a complex process that has not yet been fully understood. Attempts to create analytical models which realistically simulate these interactions have proven to be exceedingly time consuming for each tire model and have achieved only limited success. Thus, the exploration and evaluation of traction concepts by analytical means is impractical. This paper posits that significantly more reliable, rapid, and cost effective development is achieved through the prototyping and experimental evaluation of traction concepts. Here, three traction prototypes are developed and evaluated by undergraduate teams in the course of an academic semester. These concepts explore the performance of grousers, inverted geometry (dimples), and cellular materials respectively using a wheel endurance and soft-soil traction testing system at Clemson University. Each concept is tested at different acceleration rates from 0–10km/h and at different loads while measuring the slip between the tire and soil surfaces. The results of experimental evaluation indicate that cellular materials present a unique slip profile which is superior to that of the two other purely geometric concepts studied. The worst performance was seen on the inverse geometry concept which presented a behavior of steadily increasing slip with respect to wheel velocity regardless of acceleration. Grousers also presented this behavior but only at higher accelerations. This suggests that not only that prototyping is preferable, but that traditional soft-soil traction approaches may be in error.
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