Repair of damage in aircraft composite sound-absorbing panels

This work is focused on analysis of mechanical behaviour of aircraft engine's sound-absorbing panels (SAPs) exposed to in-service damage. Its aim is to suggest techniques of local repair of damaged SAPs and estimation of their post-repair residual strength. Fibreglass laminate panels with tubular core and perforated elements were studied for this purpose. A mechanical behaviour of structural elements of the panels was modelled with the finite-element (FE) analysis, with through rupture considered as an in-service defect. A technique of defect repair without dismantling parts from the structure is introduced using a novel vacuumless technology. This procedure was implemented on specially produced samples and simulated with FE. Residual strength of repaired samples was compared with that of standard and ruptured ones in tension experiments and FE analysis. Conclusions about applicability limits of the presented method are provided

Acoustic field restoration and control in closed technical areas by applying the synergy of numerical and analytical models

The noise in the industrial companies is caused by operation of the mechanisms and equipment and during various technological operations. The effect of these excitation sources on the acoustic field is very different and the control of these processes with a purpose to reduce the noise is usually very complicated and sometimes impossible. The main objective of this work was to analyze how the FE and analytical models synergy uses such type of tasks. Using the described methodology, which is based on consistent application of numerical and analytical models, and the limited experimental research data can significantly reduce the costs of investigation for the study and evaluation of acoustic fields generated by a variety of sources in closed technical space

Incorporation of Cyclotriphosphazenes as pendant groups to the sago network

Cyclotriphosphazene-incorporated sago wastes as pendant groups have been prepared and structurally characterized using FT-IR and SEM. The chemically modified sago wastes composite was applied with binders and developed as sound absorbing panels. These panels are a class of organic-inorganic based materials that exhibit excellent fire retardant properties. Sound absorbance test has given a higher value at 250, 500 and 2000 Hz, which indicates the suitability of the panel for used in medium frequency. The panel was 51% lighter compared to fiberboard. The function and basic manufacturing of sound absorbers products was aligned with the present products in the market

Sustainable multiple resonator sound absorbers made from fruit stones and air gap

[EN] This article investigates the sound absorption coefficient of materials manufactured from natural wastes. Fruit stones from some crops are one of the most available natural wastes in the Mediterranean Region. Recycled and vegetable products are becoming an interesting alternative to traditional materials to be used as sound-absorbing panels. Fruit stones can be profitable for a number of applications, such as biomass to produce energy. This research work intends to demonstrate that one of their applications can be ecological sound absorbers in building acoustics. Different four fruit stone samples, with different air gap volume percentages, display similar behaviour to multiple Helmholtz resonators (MHRs). By adding a 40 mm-thick rockwool layer, the sound absorption coefficients are compared for each sample. The experimental results allow establishing some analogies between MHRs and the new absorbing materials according to thickness, fruit type and the air gap volume. These fruit stones have been demonstrated as a good choice from acoustic and sustainable points of view.Juliá Sanchis, E.; Segura Alcaraz, JG.; Montava-Belda, I.; Gadea Borrell, JM. (2022). Sustainable multiple resonator sound absorbers made from fruit stones and air gap. Alexandria Engineering Journal. 61(12):10219-10231. https://doi.org/10.1016/j.aej.2022.03.0631021910231611

Sustainable Panels with Recycled Materials for Building Applications: Environmental and Acoustic Characterization☆

Abstract Sound absorption materials structure is generally based on porous synthetic media (rock wool, glass wool, polyurethane, polyester, ect.): they have expensive production processes, important energy consumptions, and high environmental impact. Recycled materials are becoming an interesting alternative, due to their good acoustic behavior, similar to traditional porous materials; they also allow low impact production costs, thanks to the use of wastes derived from other production cycles. This work focuses on the evaluation of the acoustic absorption properties of new panels made of recycled paper and other scrap materials, as wool and nonwoven polyester fabric: different samples were produced and tested by means of impedance tube, according to ISO 10534-2. In order to present the environmental benefits, Life Cycle Assessment was carried out in terms of primary embodied energy and greenhouse gas emissions, considering a "cradle-to-gate" approach. Furthermore, the behavior of innovative absorption materials was investigated in order to improve the acoustic performance of a lecture room, by means of an acoustic simulation software. A comparison with traditional materials was also carried out for both acoustic and environmental aspects. In the simulation model, calibrated by an in-situ experimental campaign of the main acoustic quality indexes (Reverberation Time, Clarity and Definition Indexes, Speech Transmission Index), different acoustic correction solutions were implemented: both the new recycled and traditional panels were applied as wall and ceiling absorbers. The analysis of the acoustic absorption trends, in 100 - 5000 Hz frequencies range, shows that the new materials are suitable as acoustic correction systems, especially the panel composed by waste paper and wool fibers. The LCA analysis results show that, considering the same acoustic performance, the recycled panels allow to reduce the environmental effects and the global production costs

Acoustic wave propagation through panels that are made of used tea bags

These days more than ever, society habits raise the necessity to consider the future of the environment. This presentation will tackle the aspect of more eco-friendly sound absorbing materials, more specifically analyzing the properties of consumed tea bags, starting from the collection up to the application and measurement of the final product. Many good options are often avoided, or not implemented for the lack of reliable properties analysis, encouraging existing materials to be chosen instead. The more information could be found about new materials, the more these could have a chance to be used, compared, or eventually improved. Sound absorbing panels that are made of tea bags were designed and developed to investigate sound transmission through tea-bag panels. Measurements were carried out on tea-bag panels in an impedance tube using a transfer function method to determine their sound absorption and transmission loss. Furthermore, the impedance gun system was used to determine acoustical properties of larger panels. Results show that 70 mm thick panels give an absorption coefficient higher than 0.8 between 500 Hz and 1600 Hz while 17 mm thick panels give an absorption coefficient that is mostly effective at higher frequencies. Up to 9 dB sound transmission loss is obtained at some frequencies

SOUND ABSORBING MATERIALS FROM RECYCLED RUBBER PRODUCTS

This paper concerns the results of comparative research into the acoustical properties of rubber granulates derived from the recycling of conveyor belts production waste. In the process of recycling it is possible to obtain pure granulated rubber and forms contaminated with cotton fibres with a predominance of rubber grains or of cotton fabric. Rubber granulate in the contaminated form is characterized by sound-absorbing properties similar to those of the average-quality mineral wool and other fibrous materials. It can be used as the core of sound-absorbing panels in anti-noise protections. The research results can be used both in the design of acoustical protection as well as in the course of the recycling process of other waste products for obtaining materials with sound absorbing properties