Purpose -The purpose of this paper is to study the behavior of negative stiffness beams when arranged in a honeycomb configuration and to compare the energy absorption capacity of these negative stiffness honeycombs with regular honeycombs of equivalent relative densities. Design/methodology/approach -A negative stiffness honeycomb is fabricated in nylon 11 using selective laser sintering. Its force-displacement behavior is simulated with finite element analysis and experimentally evaluated under quasi-static displacement loading. Similarly, a hexagonal honeycomb of equivalent relative density is also fabricated and tested. The energy absorbed for both specimens is computed from the resulting force-displacement curves. The beam geometry of the negative stiffness honeycomb is optimized for maximum energy absorption per unit mass of material. Findings -Negative stiffness honeycombs exhibit relatively large positive stiffness, followed by a region of plateau stress as the cell walls buckle, similar to regular hexagonal honeycombs, but unlike regular honeycombs, they demonstrate full recovery after compression. Representative specimens are found to absorb about 65 per cent of the energy incident on them. Optimizing the negative stiffness beam geometry can result in energy-absorbing capacities comparable to regular honeycombs of similar relative densities. Research limitations/implications -The honeycombs were subject to quasi-static displacement loading. To study shock isolation under impact loads, force-controlled loading is desirable. However, the energy absorption performance of the negative stiffness honeycombs is expected to improve under force-controlled conditions. Additional experimentation is needed to investigate the rate sensitivity of the force-displacement behavior of the negative stiffness honeycombs, and specimens with various geometries should be investigated. Originality/value -The findings of this study indicate that recoverable energy absorption is possible using negative stiffness honeycombs without sacrificing the high energy-absorbing capacity of regular honeycombs. The honeycombs can find usefulness in a number of unique applications requiring recoverable shock isolation, such as bumpers, helmets and other personal protection devices. A patent application has been filed for the negative stiffness honeycomb design.
Background One of the goals of most undergraduate engineering curricula is to prepare students to solve openended design problems. Solving design problems requires applying technical knowledge to create original ideas and turn those into practical applications. However, the impact of engineering curricula on the innovation capabilities of undergraduate engineers is not well understood. Purpose (Hypothesis) This study seeks to provide insights into the research question of whether freshman undergraduate engineering students can be more innovative than seniors. Innovation is measured in terms of the originality of the solutions they propose for an open‐ended design problem, as well as the technical feasibility of those solutions for practical application. Design/Method Freshman‐ and senior‐level undergraduate engineering students were tasked with developing solutions to a specific design problem (a next‐generation alarm clock). Both levels of students used a modified 6‐3‐5/C‐sketch method for generating concepts. A fraction of both the freshman and the senior students also received innovation enhancement. Resulting concepts were analyzed for originality and technical feasibility. Results Freshman students generated concepts that were significantly more original than those of seniors, with no significant difference in quality or technical feasibility of the concepts generated by the two levels of students. Conclusions Within the limitations of the study, the findings suggest that freshman engineering students can be more innovative than their senior‐level counterparts. This motivates the need for additional studies to investigate the effect of factors such as skill acquisition and design curricula on the innovation capabilities of students.
Preliminary design of a complex system often involves exploring a broad design space. This may require repeated use of computationally expensive simulations. To ease the computational burden, surrogate models are built to provide rapid approximations of more expensive models. However, the surrogate models themselves are often expensive to build because they are based on repeated experiments with computationally expensive simulations. An alternative approach is to replace the detailed simulations with simplified approximate simulations, thereby sacrificing accuracy for reduced computational time. Naturally, surrogate models built from these approximate simulations are also imprecise. A strategy is needed for improving the precision of surrogate models based on approximate simulations without significantly increasing computational time. In this paper, a new approach is taken to integrate data from approximate and detailed simulations to build a surrogate model that describes the relationship between output and input parameters. Experimental results from approximate simulations form the bulk of the data, and they are used to build a model based on a Gaussian process. The fitted model is then “adjusted” by incorporating a small amount of data from detailed simulations to obtain a more accurate prediction model. The effectiveness of this approach is demonstrated with a design example involving cellular materials for an electronics cooling application. The emphasis is on the method and not on the results per se.
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