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09.05 Additive Manufacturing for Acoustic Applications

Optimization of 3D printed porous materials accounting for manufacturing defects
Time: 12:40 pm

Author: Jean Boulvert

Abstract ID: 2314

Open-cell materials are well-known for their low price, low weight, and broadband acoustic behavior. They form one of the most used class of acoustic treatments but suffer from a lack of versatility when made by conventional manufacturing processes. Recent advances in additive manufacturing allow to produce porous materials having a controlled microstructure. In this way, the design of treatments including porous materials is not limited to a catalog of existing media. The macroscopic behavior is governed by the micro-geometry of the porous medium, which can be estimated by numerical models. Then, acoustic treatments can be optimized numerically using predicting models and minimization algorithms. However, additive manufacturing induces defects often too complex to be accounted for numerically. In this presentation, a method allowing to obtain the parametric model of the intrinsic behavior of a 3D-printed porous material is presented. The corrected model is used in the optimization of several porous treatments; namely, graded porous materials, folded porous materials and metaporous surfaces. These treatments are versatile and display remarkable properties. They provide quasi-perfect absorption at several frequencies that can be out of reach of standard porous treatments in normal or oblique incidence. Experimental validations confirm the relevance of the proposed design processes.

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3D printed multifunctional, load-bearing, low-frequency sound absorbers
Time: 1:00 pm

Author: Bhisham Sharma

Abstract ID: 3177

Cellular porous materials are an attractive choice for lightweight structural design. However, though their open porous architecture is ideally suited for multifunctional applications, their use is typically limited by the pore sizes achievable by traditional as well as advanced fabrication processes. Here, we present an alternative route towards overcoming this pore size limitation by leveraging our recent success in printing fibrous structures. This is achieved by superimposing a fibrous network on a load-bearing, open-celled porous architecture. The multifunctional structure is 3D printed using a novel technique that enables us to simultaneously print a load-bearing scaffold and the necessary fibrous network. The acoustic properties of the printed structures are tested using a normal-incidence impedance tube method. Our results show that such structures can provide very high absorption at low frequencies while retaining the mechanical performance of the underlying architected structure.

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Evaluation of additively manufactured stacks for thermo-acoustic devices
Time: 1:20 pm

Author: James Manimala

Abstract ID: 2683

The thermo-acoustic effect provides a means to convert acoustic energy to heat and vice versa without the need for moving parts. This is especially useful to construct mechanically-simple and robust energy harvesting devices, although there are limitations to the power-to-volume ratio achievable. The mechanical and thermal properties as well as geometry of the porous stack that forms a set of acoustic waveguides in thermo-acoustic devices are key to its performance. In this study, we evaluate various additively manufactured polymer stacks against more conventional ceramic stacks using a benchtop thermos-acoustic refrigerator rig that uses air at ambient pressure as its working fluid. Influence of stack parameters such as material, length, location, porosity and pore geometry are examined using experiments and correlated to simulations using DeltaEC, a software tool based on Rott’s linear approximation. Structure-performance relationships are established by extracting scaling laws for power-to-volume ratio and frequency-thermal gradient dependencies. It is found that additively manufactured stacks can deliver performance comparable to ceramic stacks while being more affordable and customizable for thermo-acoustic transduction applications.

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