Che Husna Azhari

Microstructural characteristics on the surface and subsurface of semimetallic automotive friction materials during braking process

Abstract In this study, a series of friction tests on semimetallic automotive friction materials were conducted on a friction test machine by pressing test samples against a rotating cast iron brake disc, thus simulating actual braking. After each friction test, the morphological changes of the wear surface and subsurface were investigated using scanning electron microscopy. Microstructural examinations showed that the major wear mechanisms in operation during braking are comprised of the following: (i) abrasive, (ii) adhesive, (iii) fatigue, (iv) delamination, and (v) thermal. The wear mechanism and wear transition are found to be influenced by the applied loads and braking times. In the study of the subsurface morphology, microcracks generated in the subsurface are thought to be due to the following phenomena; (i) growth of microvoids, (ii) coalescence of microvoids, (iii) coalescence of second phase particles, and (iv) coalescence of microvoids and second phase particles. The microcracks generated in the subsurface grew and propagated parallel to the sliding surface as the braking times as well as applied loads are increased. Finally, the microcracks grew and joined each other producing wear particles on subsequent braking. These mechanical and thermal failures manifested a complex wear mechanism, causing plastic collapse in the local region which subsequently produced wear particles in different shapes depending on the modes of failure.

Correlation of filler loading and silane coupling agent on the physical characteristics of epoxidized natural rubber-alumina nanoparticles composites

Studies were conducted on the effects of filler loading and 3-aminopropyltriethoxysilane (SCA) on the physical characteristics of epoxidized natural rubber (ENR)-alumina nanoparticles composites (ENRAN). The filler loading varied from 10, 20, 30, 40, 50, and 60 phr in the absence and presence of 2 phr SCA in every formulation. The alumina nanoparticles have a positive interaction with the ENR matrix since they increase the glass transition temperature of the composites [Mohamad, N., Muchtar, A., Ghazali, M.J., Dahlan, H.M. and Azhari, C.H. (2008). The Effect of Filler on Epoxidized Natural Rubber-Alumina Nanoparticles Composites, Eur. J. Sci. Res., 24: 538—547]. The addition of SCA decreased the maximum torque (MH) and the torque difference (MH-ML) of ENRANs compound as well as causing the curing process to occur at a very fast rate. The spherical alumina particles were dispersed in ENR matrix and a uniform particle distribution was observed under scanning electron microscope enabling the increase of the torque values in the composites.

An experimental investigation on the response of woven natural silk fiber/epoxy sandwich composite panels under low velocity impact

This paper presents results of dynamic deformation behavior of woven natural silk/epoxy sandwich composite panels. The specimens were prepared in configurations of reinforced woven natural silk fiber (RWNSF)/Epoxy/Foam, RWNSF/Epoxy/Coremat; RWNSF/Epoxy/Honeycomb and reinforced RWNSF/Epoxy (control material) using hand-lay-up method. Each of the three core material was sandwiched between reinforced woven natural silk fiber/Epoxy composite facesheet. Drop weight impact test was carried out under 32 J impact energy. Degree of damages inflicted on the contact surface, through thickness and rear surface were analyzed, sandwich composites performed better than the reinforced (control material). Failure mechanism involved interlaminar matrix cracking, layer debonding, delamination and fibre breakage.

Analysis of the Sound of the Kompang for Computer Music Synthesis

This paper presents an analysis of the properties and the characteristics of sound made by a kompang for computer music synthesis. The kompang is a Malay traditional musical instrument with a circular membrane made from goatskin. It is classified as a membranophone. The sound samples used for analysis are the sound produced by the kompang as the instrument is played traditionally, by striking it with the palm near the centre of the membrane and striking it with the fingers near the boundary of the membrane. The sound samples are analyzed using time and frequency domain analysis. Time domain analysis uses waveform examination and amplitude envelope detection, while frequency domain analysis uses the fast Fourier transform analysis and the short time Fourier transform analysis. The sample waveforms, frequency content, and spectrogram are obtained. The results show that when the kompang is struck at the centre of the membrane, the sound has a longer attack and decay period and a larger amount of frequency content than when it is struck near the edge of the membrane. Like most membranophones, sound produced by the kompang does not have a pitch since the normal modes of the excited kompang do not have frequencies that are integral multiples of a number.

Perspectives for Titanium-Derived Fillers Usage on Denture Base Composite Construction: A Review Article

Poly(methyl methacrylate) (PMMA) is an extensively used material in dentistry because of its aesthetics, processability, and reparability. However, PMMA is still far from being ideal in fulfilling the mechanical requirements of prosthesis. PMMA-based denture base polymers exhibit low fracture resistance and radiopacity behavior. Efforts to improve the mechanical and radiopacity properties of denture base materials through inclusion of silica-based fillers are ongoing. Although silane-treated siliceous fillers are commonly used, they are not sufficiently strong. They also exhibit cracks, which either cut through the glass fillers or propagate around the filler particles. This defect occurs when the dental composites are placed in aqueous oral environment because of the hydrolytic degradation of silica-based fillers and silane-coupling agents. The clinical problem of using silanes in adhesion promotion is bond degradation over time in oral environment. In addition, silanes do not bond effectively to nonsilica-based dental restorative materials. This review presents titanium-derived fillers as alternatives to siliceous fillers. Titanate-coupling agents are found to be effective couplers in treating Ti-based fillers because of their chemical compatibility and relatively high stability in aqueous environment.

Rheological Characteristics of Epoxidized Natural Rubber Modified Bitumen

Polymer modified bitumens have tended to be the most popular among the various types of modified binders that are available worldwide. Polymer modification significantly alters the rheological characteristics of the binder, thereby requiring the use of fundamental rheological testing methods to provide an indication of the performance of the binder and subsequently the asphalt mixture. In this paper the characterization of bitumen modified with epoxidized natural rubber (ENR) was done with four percentages of ENR content. The effects of the modifier on the conventional properties, storage stability and rheological properties were investigated. The results indicated that storage stability of ENR modified bitumens (ENRMB) were mainly dependent on the ENR content. ENR reduced the temperature susceptibility. The degree of the improvement generally increased with ENR content up to 9%.

MATLAB based image analysis software for characterization of microstructure materials

This paper presents MATLAB based image analysis software specially developed to perform characteristic analysis of microstructures images such as the Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) etc. The developed software is user-friendly with graphical user interface (GUI), allows dynamic 2D and 3D visualization and performs standard statistical analysis to analyze the microstructure morphology automatically. Two examples are given to show the effectiveness of the software.

Energy Absorption Capability of Axially Compressed Woven Natural Ramie/Green Epoxy Square Composite Tubes

This study focuses on failure response and energy absorption of woven ramie epoxy square composite tubes when exposed to the axial quasi-static compression test. Hand lay-up technique was used to prepare the rectangular composite tubes composed of 12 layers of ramie fabric with a thickness of 1.7 mm and 50-, 80-, and 120-mm-long tubes. The measured parameters were specific energy absorption, energy absorption, and peak load. The total energy absorption increased with the increase in the length of the tubes. The failure mode of the tested tubes was examined, and the mid-length and local buckling were considered as the main sources of failure. The woven natural ramie was used in the textiles for years. However, the results of this paper can be significant because of the limited research employing woven ramie as reinforcement for composites.

Crashworthy characteristics of axial quasi-statically compressed Bombyx mori composite cylindrical tubes: Experimental

The study investigated the energy absorption response and load carrying capability of Bombyx mori (B. mori) natural silk fibre/epoxy composite cylindrical tubes subjected to an axial quasi-static crushing test. The reinforced cylindrical composite tubes were prepared using hand lay-up technique. Varied numbers of B. mori layers, 12, 24 and 30 were used to fabricate the tubes; their corresponding diameters were 33.3, 62.3 and 80.6 respectively. The crashworthiness of the cylindrical tube was analyzed by measuring the specific energy absorption, peak load and total energy absorption as a function of tube diameter/number of layers under a quasi-static axial compression load. Failure mechanisms of the tubes were analyzed using scan electron microscopy (SEM) and high resolution photographs obtained during test. Generally, the result showed increase in crashworthiness behaviour as the numbers of B. mori layers increased. The 12 layer tube (33.3 mm diameter) showed a progressive crushing failure starting from the upper half; the 24 layer tube (62.3 mm diameter) depict a mid-length crack failure, while the 30 layer tube (80.6 mm diameter) showed a progressive crushing failure from the lower side of the tube. The SEM micrographs of suggest that failure mechanism includes: matrix crack, fiber delamination, fiber pull out, tear and fibre breakage.

Review of titanate coupling agents and their application for dental composite fabrication

Silane is a dominant coupler that is widely used in dentistry to promote adhesion among the components of dental composites. Silica-based fillers can be easily silanized because of their similarly ordered structure. However, silane is hydrolytically degraded in the aqueous oral environment and inefficiently bonds to non-silica fillers. Thus, the development of hydrolytically stable dental composites is an important objective in the research on dental materials. Titanate coupling agents (TCAs) exhibit satisfactory interfacial bonding, enhanced homogeneous filler dispersion, and improved mechanical properties of the composites. Titanates also provide superior hydrolytic stability in wet environments, which should be considered in fabricating dental composites. The addition of a small amount of titanates can improve the resistance of the composites to moisture. This paper reviews the effects of the instability of silanes in moisture on the performance of dental composites and presents TCAs as alternative couplers to silanes for fabricating dental composites.