The characterization of additively manufactured cellular materials, such as honeycombs and lattices, is crucial to enabling their implementation in functional parts. One of the characterization methods commonly employed is mechanical testing under compression. This work focuses specifically on the dependence of these tests to the applied strain rate during the test over low strain rate regimes (considered here as 10−6 to 10−1 s−1). The paper is limited to the study of strain the rate dependence of hexagonal honeycomb structures manufactured with four different additive manufacturing processes: one polymer (fused deposition modeling, or material extrusion with ABS), one composite (nylon and continuous carbon fiber extrusion) and two metallic (laser powder bed fusion of Inconel 718 and electron beam melting of Ti6Al4V). The strain rate sensitivities of the effective elastic moduli, and the peak loads for all four processes were compared. Results show significant sensitivity to strain rate in the polymer and composite process for both these metrics, and mild sensitivity for the metallic honeycombs for the peak load. This study has implications for the characterization and modeling of all mechanical cellular materials and makes the case for evaluation and if appropriate, inclusion, of strain rate effects in all cellular material modeling.

Many researchers have proved the potential of autoparametric system in controlling stability and parametric resonance. In this paper, two different designs for auto-parametrically excited mass-spring-damper systems were studied: one system was controlled by rotational motion of the spring, and the other system was controlled by sliding motion of the spring. The theoretical models were developed to predict the behavior of the systems and also generated stability charts to analyze the systems. For each system, the numerical results from both the nonlinear equation and linearized equation were analyzed and compared. Simulation models were constructed to validate the analytical results. The error between simulation and theoretical results was within 2%. Both theoretical and simulation results displayed that the implementation of autoparametric system could help reduce the resonance by up to 33% and amplify the resonance by up to 34%.

Current methods of unmanned underwater locomotion do not meet stealth, robustness and efficiency. This work discuses about designing a Bioinspired UUV or Unmanned Underwater Vehicle that uses an undulating fin approximating to that of a cuttlefish fin locomotion. This propulsion method has higher maneuverability and ability to navigate while leaving its surroundings relatively undisturbed as compared to other propeller based systems. Mathematical models and control algorithms describing the complicated locomotion have been developed, and a simulation model is used to verify the theoretical results. This design of UUV can be utilized for underwater data collection and military applications without hampering the underwater wildlife.