Utilisation of indigenous resources for acoustical applications / Valliyappan D. Natarajan and Mohd Jailani Mohd Nor

This paper presents the development of novel sound absorbing materials based on natural indigenous resources particularly that of fibrous nature. Coir fiber in the form of stitched mat, which is porous and fuzzy, was utilized as the main sound absorbing component. Composite panels support the coir mat laterally. The panels were made from oil palm frond fibre (OPF) and rice husk (RH) bounded in either unsaturated polyester (UP) or polypropylene (PP) matrix. The acoustical properties of the composite structures were determined in an impedance tube based on the two-microphone transfer function method in the frequency range of 125Hz to 4000Hz. Overall results indicate that the coir mat-composite panel structure is a potential absorbent-barrier with not less than 50% of sound absorption. General improvements were achieved in the absorption properties over the entire frequency range using the more flexible RH-PP panel while superior low frequency absorption was attained using panel made of 50% volume fraction of OPF I RH mixture in UP. The product of this research offers exceptional cost-performance balance to the existing, relatively expensive noise control industry while reducing waste disposal problems in the plantation industry

Experimental Investigation on the Ballistic Resistance of Aluminium Plate under High Velocity Impact / Mohd Rozaiman Aziz ...[et al.]

Ballistic resistance has become towards researchers’ attention especially those in enforcement industry. In the ballistic resistance, researchers are keen to determine the lowest velocity of projectile that able to perforate a target. From result obtained, researchers can propose modification to enhance the survival of enforcement personnel. For an example, armor shield which is employed by enforcement personnel during gun fight. The main objective of this paper was to present the preliminary result of ballistic resistance of aluminium plate that will be used as a reference in the experiment works later. Future works will involve aluminium laminated with z-composite. In this study, the target was aluminium plate with thickness of 3 mm and fragment simulating projectile (FSP) acted as the projectile. The FSP was launched from gas gun which was located 2 meters from the aluminium plate. The velocity of FSP was varied by changing the charge weight. The experiment was carried-out at Science and Technology Research Institute for Defence (STRIDE), Batu Arang. From the experiment conducted, it was found the ballistic limit was equal to 257.7 m/s. Furthermore, there were two main modes of failure observed which were non-perforation and successful perforation. For non-perforation, the mode of failure was crater with and without FSP embedded into the plate. Meanwhile for the successful perforation, the mode of failure was a hole along with petals

Sound absorption properties at high sound frequency of open cell aluminium foam / Mohd Arifhakim Azizan...[et al.]

Open-cell aluminium foam is a type of metallic foam that has been industrialised years ago. It has been found that due to its porous characteristic, it is suitable for sound absorption. The porous characteristic of open-cell aluminium foam is closely related to its sound absorption properties. In this research, the open-cell aluminium foam was produced by infiltration casting method and its sound absorption properties were studied. Infiltration casting is a casting method that uses space holder material in the casting mould and later the mould is infiltrated with molten material by vacuuming and gas purging inside the mould. NaCl was used as the space holder material in order to form the porous structure. The size of NaCl grains is in the range between 1mm to 3 mm. The surface structure of the fabricated open-cell aluminium foam was then observed under an optical microscope while its sound absorption properties were determined using impedance tube test, respected to the ASTM E1050 designation to analyse sound absorption coefficient. It was found that at high sound frequency ranging from 800 Hz to 5000 Hz, open-cell aluminium foam produced from infiltration method gave a higher sound absorption for bigger pore open-cell aluminium foam

The Effect of Orifice Diameter to the Acoustic Signals Captured at the Cold Part of a Ranque-Hilsch Vortex Tube

In this study, acoustic analysis and thermofluid performance of a Ranque-Hilsch Vortex Tube (RHVT) is experimentally investigated under different orifice diameters at its cold tube. The orifice diameters used are 2mm, 3 mm, 4 mm, 5 mm and 6 mm. The inlet pressure (gage) is set at 10 psi, 15 psi, 20 psi and 25 psi for each orifice diameter. The sound produced by the tube is recorded using a microphone located outside the cold tube. The acoustic signal is processed using Fast-Fourier Transform (FFT) to obtain the frequency representation. Main frequencies are then extracted to constitute the signature of the signal for that specific configuration. It is observed that different orifice diameters give different signatures. These signatures are then associated with the thermofluid performance of the device to obtain the relation among the parameters