Abd Rahim Abu Bakar

Effect of Chemical Surface Modifications on the Properties of Woven Banana-Reinforced Unsaturated Polyester Composites

Chemical surface modifications involving 1% sodium hydroxide (NaOH) and 1% acrylic acid (AA) treatments are applied to woven banana fabric and it is used as reinforcement in an unsaturated polyester matrix. Vacuum bagging technique was used to prepare the woven banana fiber-reinforced unsaturated polyester composites with four different volume percentages of fibers (5, 10, 15, and 20%). The effects of fiber-loading and fiber surface treatments on the flexural, impact and water absorption properties of the composites were investigated. The acrylic acid treatment results in improved mechanical and water absorption properties of the composites compared to the alkali treatment and untreated fiber composites. The treatment effects on the banana fibers have been characterized by means of infrared spectroscopy (FTIR) and microscopy analysis (SEM). The moisture absorption test showed that acrylic acid-treated woven banana fabric composites exhibit less water absorption than both alkali-treated and untreated woven banana fabric composites.

Finite element analysis of wear and its effect on squeal generation

Abstract In the past, wear at the pad interface of disc brakes has rarely been accounted for in studies of brake squeal using the finite element method, and its effect on disc brake squeal has been investigated largely through experimental methods. In the present paper, wear taking place at this interface over time is simulated using a modified wear rate formula. The surface topographies of two new and unworn pairs of brake pads are measured. The same brake pads are tested under braking applications of three time durations. For each braking application, the static contact pressure distribution is measured using pressure-indicating film. The results are used to compare with the simulated results predicted by the three-dimensional finite element model of a real disc brake. The paper also investigates squeal generation due to the above braking applications using complex eigenvalue analysis that is available in a commercial software package. It is found that the predicted unstable frequency is very close to the observed squeal frequency and that they take place in the same braking duration.

Interface Pressure Distributions Through Structural Modifications

Due to the friction forces acting at the rotor and pads interface, the pressure distribution at the interface is asymmetric in a disc brake system of normal floatingtype caliper design. The asymmetry and the high unevenness of the interface pressure distribution cause uneven wear and shorten life of pads. It has been speculated that these undesirable features promote disc brake squeal. This paper investigates the contact (interface) pressure distributions at the rotor and piston-pad interface in response to several ideas of simulated structural (geometric or material) modifications. These modifications are made on the pads and/or at the interface between the piston and the back plate or at the pad guide. A detailed finite element model is constructed taking into account all significant contact interfaces between disc brake components. Sliding frictional contact is analyzed to obtain the interface pressure distributions. A plausible modification is identified which offers improved interface pressure distributions against wear. This work may also help create a good design of disc brakes for improved noise performance as well.

Brake pad surface topography part I: Contact pressure distribution

Recent studies carried out at the University of Liverpool showed that there was a variation in static contact pressure distributions on two new sets of pads even though they were tested with the same brake system under the same pressure. One of the possible reasons for this variation is due to brake pad surface topography. This paper investigates the effects of brake pad topography on contact pressure distributions. Pressurex ® , pressure indicating films are used to measure static contact pressure distribution. A detailed 3-D finite element model of a disc brake is also developed and takes into account pad surface profiles. A linear gauge is used to measure brake pad topography. Six different pad configurations are studied in this investigation. Results from the investigation could provide a better explanation of the variation in contact pressure distribution and in turn squeal generation.

Effects of Pad Surface Topography on Disc Brake Squeal

Brake squeal has always been a major NVH problem to many car makers due to significant number of warranty claims. Brake squeal is a high frequency noise (above 1 kHz) emanating from car disc brakes that get excited due to one or more mechanisms such as mode coupling, stick-slip, hammering and sprag-slip. This paper attempts to investigate the effects of brake pad surface topography on squeal generation. Two pairs of a non-asbestos organic (NAO) brake pad will be tested on a brake dynamometer test rig. Surface topography of the brake pad will be analyzed through microscopic techniques using energy dispersive X-ray analysis (EDX), and optical microscope.

Practical multi-objective controller for preventing noise and vibration in an automobile wiper system

This paper presents an approach using a multi-objective controller to prevent noise and vibration generated by the wiper blade during its wiping operation. Firstly, this paper focuses on the experimental approach to collect noise and vibration data from a car wiper system during its operation and secondly, to develop black box model of the wiper system using nonparametric approach of system identification known as nonlinear auto regressive exogenous Elman neural network (NARXENN). Finally, a novel closed loop iterative input shaping controller whose parameters are tuned simultaneously by a Pareto based multi objective genetic algorithm (MOGA) are proposed and simulated in such a way that it can prevent unwanted noise and vibration in the wiper system. The main contribution of this work rather the previous studies of automobile wiper system is to develop a novel multi-objective control strategy whereby an automobile wiper blade is moved within its sweep workspace in the least amount of time with minimum noise and vibration.

The properties of vinyl ester composites reinforced with different types of woven fabric and hollow phenolic microspheres

This study compares the effects of hollow polymeric microspheres (PHMS) on specific mechanical properties and thermal properties of glass, basalt, and carbon woven fabric reinforced vinyl ester composites. The specific flexural and specific impact strengths of the composites were marginally increased with the addition of PHMS; however, it was at the expense of reduced specific flexural modulus. The thermal stability of the neat vinyl ester was improved with the addition of woven glass and carbon, but was consequently reduced with the further inclusion of PHMS. SEM observations identified the presence of the combined failure mechanism of fibers and PHMS. In short, the major reinforcing effect of the woven fiber-reinforced vinyl ester composites is governed by the type of fiber used, while the addition of PHMS enhanced the ductility of the composites.

Effects of External Hard Particles on Brake Noise of Disc Braking System

The open design and position of disc brake that is closed to road surfaces enable contaminants to enter the brake gap and caused noise and tribological disturbance at the brake interface. Contaminants such as dirt and soil can be present and are expected to influence the occurrence of brake squeal that produce an annoying sound during braking action. The objective of this study was to examine the effect of external hard particles at different disc sliding speed on generation of brake squeal using a brake dynamometer. Different rotational speed of disc brake was selected and the experiments squeal noise data was collected and analyzed using the Fast Fourier Transformation (FFT) analyzer. From the experiments, the presence of external particle and the rotation speed of disc brake promotes the generation of brake squeal phenomenon by changing the surface roughness and effective contact of brake interface. Results obtained from the experiment also showed that higher rotating disc generate higher sound level meter or squeal frequency and increase numbers of squeal noise generated.

The Study of Disc Brake Noise on Three Different Types of Friction Materials

This work investigates the effect of road grit particles and material compositions on disc brake squeal noise. Three different Non Asbestos Organic (NAO) brake pad samples and road particles with a size range between 400 μm to 500 μm are used in the squeal experiment. The relationship between the existence of road particle with the noise occurrence were studied through the change in pressure level, friction coefficient (CoF), sound pressure level (SPL) and material composition. The material compositions were analyzed before and after squealing condition using energy dispersive X-ray analysis (EDX). Result has shown the road particles contribute to the emission of squeal noise and the increasing of some material composition of brake friction material components.

Influence of Silica Sand Particles on Disc Brake Squeal Noise

Researchers in recent years begin to explore on tribological behavior of automotive brake squeal phenomena which covers the morphology, chemical composition, friction and wear, phase composition and third body or friction film distribution. However less effort has been made to study the tribological on the influence of small particles on brake squeal. During braking condition, both rotor and pads are exposed to road environmental particle which may affect pads surface condition. In order to assess the influence of this particle on brake squeal a series of squeal tests were performed. Silica sand grit particles with a size range between 400 to 200 μm which most available on the road surface were used in this experiment. Brake pad and disc surface characteristics were analyzed before and after squealing condition using Scanning Electron Microscope (SEM) and Energy dispersive X-ray analysis (EDX). The result shows that the silica sand particles had influence the squeal and surface behavior of the brake pad.