Applied Mechanics and Materials Vol. 471

Abstract: Vibration transmissibility from a car body to pedal-pad could result to drivers discomfort and fatigue, which may lead to health problems. Vibration transmissibility occurs when the vehicle engine is turned on and vibration is transmitted from the car body to pedal-pad in this research Pedal-pad effective Amplitude Transmissibility (PEAT) value was used to predict suitable size of the pedal-pad that could provide comfortable operation of the pedal. In this study, the variables are the three different sizes of pedal-pads and data was recorded while the car was moving on the road at constant speed with three different sizes of pedal-pads. The data was measured in root mean square (r.m.s) unit, of the frequency weighted acceleration (m/s²) for every minute. The finding of the study shows that percentage PEAT_r.m.s of the three different sizes of pedal-pad is greater than 100%. It shows that vibrations to pedal-pads are greater than vibration from the car body consequentially it means that the foot on the pedal is exposed to higher vibration transmissibility than the foot on the floor.

Abstract: This paper presents an evaluation on elastomeric mount used to isolate vibration from powertrain to chassis or structure vehicle. The assessments started with measurement of noise inside compartment, and exhaust noise. This is followed by the measurement of vibration on both sides of elastomeric mounts. The noise in the compartment and exhaust noise is measured according to BS 6086: 1981 and BS ISO 5130: 2007. The noise in the compartment and vibration is tested in three conditions. Firstly, engine is run-up with load (driving at second gear); secondly, without load; and thirdly, without load but hanging. A microphone is fixed at the ear of the mannequin. The fast response and A weighting sound level meter were used for measurement noise in the compartment and exhaust noise. The vibration is measured in terms of acceleration on both sides of each elastomeric powertrain mounts. Two accelerometer transducers are fixed on both sides of powertrain elastomeric mounts. One side was identified as a source of vibration and the other as receiver of vibrations. The results showed that the pattern of overall vibration level on source and receiver increased from 1050 RPM (idling) to 4000 RPM on all test conditions. Vibration transmitted to chassis or receiver structure was analyzed using transmissibility concept. By evaluating test condition of engine run-up without load, informed that the front and rear mounts showed a high level transmissibility contributing to structure-borne noise.

Abstract: Determination of vehicle comfort is important because continuous exposure to the noise and vibration leads to health problems for the driver and passengers. In this paper, a vehicle comfort level classification system has been proposed to detect the comfort level in cars using artificial neural network. A database consisting of sound samples obtained from 30 local cars is used. In the stationary condition, the sound pressure level is measured at 1300 RPM, 2000 RPM and 3000 RPM. In the moving condition, the sound is recorded while the car is moving at 30 km/h up to 110 km/h. Subjective test is conducted to find the Jurys evaluation for the specific sound sample. The correlation between the subjective and the objective evaluation is also tested. The relationship between the subjective results and the sound metrics is modelled using Probabilistic Neural Network. It is found from the research that the Temporal Composite Feature gives better classification accuracy for both stationary and moving condition model, 89.51% and 85.61% respectively.

Abstract: This paper presents the estimation of vibration strength obtained from reception structure method. It describes a laboratory-based measurement procedure, which determines the strength of a vibration source in terms of its total squared free velocity. The source used in the experiment is a small electric fan motor. Here instead of using the usual flat rectangular plate, a thin stainless steel beam was used as the reception structure. The aim is to validate the data obtained from the reception method with that from the direct measurement. A good agreement is found between the two results, although small discrepancies occur due to the modal behavior of the beam.

Abstract: Moving vehicle will produce dynamic excitation and can be categorized in the study of noise, vibration and harshness (NVH). Studies of NVH can resolve issues associated with the use of a vehicle comfort. Exposure to some level of noise and vibration can be classified as a danger to vehicle passengers if they are exposed in a standard eight-hour time period. Therefore NVH aspect is the most important aspect in selecting a military vehicle other than the factor of safety, reliability, fuel consumption and maintenance costs. This study was carried out on Malaysian Army (MA) 3-tonne truck drivers who are exposed to noise and vibration produced by the truck. Vibration exposure at seat, steering wheel and body floor was measured using tri-axial and single axis accelerometers which were connected to a Brüel & Kjær Type 3649 vibration analyser, while noise exposure was measured at the drivers ear position using a DuO smart noise monitor. From the results obtained, both vibration and noise pressure levels increased proportionally with the increasing speed of the truck. In the long-term, will have an impact on the health of the truck drivers.

Abstract: 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.

Abstract: The dynamic characterization of vehicle structures is a crucial step in NVH analysis and helps in refining the vibration and noise in new vehicles. This paper investigates the dynamic properties of two parts of the vehicle structure which are door and hood panels. Theoretical modal analysis which is referred to as Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA) or modal testing has been used as investigative tools. The paper investigates the structural dynamic properties of door and hood panels of a local car. ME'scope software was used to analyze the data obtained from Pulse to extract the dynamic properties of the panels. LS-DYNA software was used to analyze the dynamic behavior of the structure. The comparison between the results obtained from both analyses showed some similarity in frequencies and mode shapes. Finally the paper concludes that experimental modal analysis and finite element analysis can both be used to extract dynamic properties of structures.

Abstract: The first Noise, Vibration and Comfort (NVC2005) conference started with a humble beginning comprising of thirty technical papers presented. This conference was initially designed to be held bi-annually and continued to grow in numbers with 54 papers presented in 2007 and 57 papers in 2010. At the moment there are 81 papers that have already been accepted for presentation in the NVC2012 conference. This paper presents an analysis of sound and vibration research activities carried out in Malaysia from the papers presented since 2005 till 2012. However the findings might not be comprehensive since only papers presented by Malaysian researchers in the NVC conferences are being considered. It is suffice in giving a glimpse on the progress and development of sound and vibration research theme in Malaysia as most of the key researchers in this field are actively sharing their research findings in these conferences. The trend and development of new research niches in sound and vibration in Malaysia is also reported in this paper. Finally, strategic initiatives to promote research excellence in this field to a greater height are also proposed. These initiatives are presented based on the authors involvement in developing and managing research policies at the national level. Research and development (R&D) eco-system in Malaysia is changing rapidly, subsequently creating a demand for our researchers in this fraternity to realign their efforts in order to promote collaborative and multi-institutional research projects that are relevant for Malaysia.

Abstract: In the automobile industry, impact force is the main cause for material fatigue in lightweight vehicles. Bump-excited impact force is the most common case, which causes damage to vehicles and reduces the quality of the ride. Force identification is important to reflect the structure's health so that action such as structure modification can be taken before material fatigue. However, direct measurement by using force transducer is not practical due to difficulty in force sensor configuration. A methodology utilizing Operating Deflection Shape (ODS) analysis, Frequency Response Function (FRF) measurement and Modal Transformation Method (MTM) to evaluate the dynamic force is proposed here. This method is called indirect force measurement by using inverse technique. The performance of this approach was demonstrated via experiment. From the measured responses and measured dynamic characteristics of an automobile test rig, a real time mathematical manipulation can generate the systems input force. The force location is known in priori for impact excitation and therefore the inverse problem is well-posed. This method was tested using different force location with unique input force. It shows that high quality of curve fitting to extract the modal parameters such as damped natural frequency, modal damping and residue mode shape is essential to obtain a high accuracy force determination result.

Abstract: In this study, the investigations of the acoustic environments in the waiting areas in hospitals were conducted. The investigations were aimed on clarifying the actual conditions in two waiting areas in two hospitals in Kuala Lumpur. The investigations consist of both noise level measurements and questionnaire surveys, i.e. both physical and psychological aspects. Generally, physical aspects for both hospitals are strongly influenced by noise produced during general activities in waiting areas. Sound pressures data were collected approximately eight hours period in daytime and converted into different levels (L_Aeq and L_{eq, max}). It was found that the maximum permissible sound level L_Aeq in all waiting areas measured exceeded the guideline for community noise recommended by World Health Organization (WHO). In psychological aspects, respondents were interviewed in the course of a questionnaires survey dealing with nuisance occasioned by noise at actual conditions. Accumulate measured data is important for the further discussions and developments to overcome the problem. This paper gives a fundamental data for the help of future refinements.