Browsing by Subject "perturbation"
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Item Beam Deletion in Square Honeycombs for Improved Energy Absorption Under Quasi-Static In-Plane Compression(2022) Ramirez-Chavez, Irving E.; Lee, Christine; Bhate, DhruvWhen selecting cellular materials for energy absorption applications, there have traditionally been two choices: a periodic structure such as a honeycomb, or a stochastic one, as seen in foams. Both choices involve a global definition governing the allocation of the members of the structure, be they beams or surfaces. With Additive Manufacturing, the exploration of more complex structures enables the creation of aperiodicity through the local modification of periodic structures. This paper explores one application of this approach by deleting beams in square honeycombs, with the aim of avoiding localization of failure that generates significant undulations in the stress plateau under in-plane quasi-static compression. These perturbed structures show improved energy absorption behavior by generating higher Specific Energy Absorption for a given transmitted stress and relative density than their periodic counterparts. This work thus argues for further exploration of localized aperiodicity as an approach to finely tune energy absorption performance.Item Microwave Measurements of Nylon-12 Powder Ageing for Additive Manufacturing(University of Texas at Austin, 2017) Clark, N.; Lacan, F.; Porch, A.With repeated recycling, nylon powders used in Selective Laser Sintering are known to degrade and ultimately cause mechanical performance and surface finish deterioration in produced parts. In order to maintain consistent production and to reduce cost by minimising waste powder, it is desirable to monitor this degradation. However, any techniques used must be inexpensive, quick and simple in order to maintain industrial relevance; dielectric measurements by microwave cavity perturbation can offer these advantages. Here, samples are taken from a working SLS machine and their permittivity measured using microwave cavity perturbation operating around 2.5 GHz. A 2% reduction in effective dielectric constant and an 8% reduction in effective dielectric loss is observed between new powder and recycled feedstock. Furthermore, in-situ measurements simulating build chamber conditions show a similar trend.