Pusat Pengajian Kejuruteraan Mekanikal - Tesis

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Analysis Of Piston Secondary Motion
(2014-04)
April 2014
In an internal combustion engme, the piston performs secondary motion besides the primary reciprocating motion. The clearance between the piston skirt and cylinder liner allows the piston to move in the lateral direction and rotational motion about the piston pin axis. The piston secondary motion created impact between the piston skirt and the cylinder liner that radiates unwanted engine noise and increases friction loss. A measurement system consists of three laser displacements sensors are developed to capture the instantaneous piston motion and posture directly from the piston assembly under motorized condition. The laser spots aimed at the piston crown with machined profile in order to obtain the rotational and lateral motion of the piston. The instantaneous piston motion showed that the likelihood of contact between the piston skirt and the cylinder liner increases with the occurrence of the piston secondary motion. In addition, a non-linear model of the piston with reciprocating, lateral and rotational degree of freedom is developed to investigate the piston secondary motion and the piston slap induced vibration behavior of the single cylinder engine.
Cascaded cylindrical micro-perforated panel for noise broadband attenuation
(2023-04-01)
Mohamad Izudin Bin Alisah
This research presents an analysis of cascaded cylindrical micro-perforated panel (MPP) for absorbing the sound of a flow system in a circular duct application. This is important for the cases where the noise source comes from multi direction as actual application would not in single direction. Since the typical MPP has limited narrow band attenuation, it is necessary to have a specific MPP to radiate noise from circular direction and broadband attenuation. The aim of this study is to model using simplified transfer matrix method, optimized via genetic algorithm and demonstrate the effectiveness of cascaded cylindrical micro-perforated panel on vacuum cleaner. Cascaded cylindrical MPP is a special class of cylindrical MPP, where two cylindrical MPPs are arranged in series to improve sound attenuation. The manufacturing of MPP primarily involves the machining of micro perforations because the small holes are not readily made using injection moulding due to the complexity of the die, flow control of the molten polymer through the small orifices and dimensional stability, making it unsuitable for mass production. This limitation can be overcome with the use of additive manufacturing (AM) technology based fused deposition method (FDM), where the micro perforations can be designed and manufactured, with relatively larger tolerances. Moreover, parametric studies on basis of perforation diameter, perforation ratio, depth of air cavity on the diameter of the duct and length ratio are carried out. Result shows that the transmission loss performance of cascaded cylindrical MPP can be improved by reducing the perforation diameter and by correct selection of perforation ratio and air cavity depth value. Experimental validation ensures that the manufactured cascaded cylindrical MPP is performed according to design. The application of transfer TMM framework was aligned with similar trend with boundary element method (BEM) and measured result via two-load method measurement. Small shift of the transmission loss peak values attributed to perforations in printed structures that were not perfectly circular in shape. The average Root Mean Square Error (RMSE) obtained was 3.04 dB. A case study is demonstrated here in the design and additive manufacturing of cascaded cylindrical MPP to attenuate peak noise at 1650 Hz. The manufactured cascaded cylindrical MPP is installed on a vacuum cleaner duct, and the measurement of sound power level shows a reduction of 5.2 dB (A).
Fabrication and molecular dynamics analysis of polydimethylsiloxane antimicrobial nanostructure
(2023-04-01)
Nur Liyana Binti Mohd Shamsuddin
The topographically surface modification using lithography techniques is an alternative approach to create antimicrobial surfaces. The micro/nano structure surfaces mimic the naturally-occur surfaces that are able to repel bacterial attachment or rupture the bacterial cell wall once attached to the surfaces. Nevertheless, the conventional photolithography technique has limits on light diffraction. An electron beam lithography (EBL) the being explored in fabricating the desired micro-and nanofeatures on large areas. This study aimed to fabricate micro/nanostructured of polydimethylsiloxane (PDMS) with antimicrobial properties. The pattern definition process produce the micro/nanohole array on the PMMA/Si mould and the pattern was transferred onto the PDMS using replica moulding (soft lithography) technique. Large-scale Atomic/Molecules Parallel Simulator (LAMMPS) was employed for molecular dynamics (MD) simulation to determine stress-strain response under compression. The adhesion of the Methicillin-resistant Staphylococcus aureus (MRSA) cells was observed and bactericidal efficiency count via the viable plate count method. The PDMS micro/nanostructures arrays of 200 to 300 nm in base diameter and 30-160 nm in height successfully fabricated. The simulated compressive modulus and ultimate compressive strength of PDMS nanostructure was decreased with the increase in simulated temperature. The cell viability diminished by almost 80% and FESEM images showed the cells were deformed and ruptured once attached to the PDMS surface. The topographic features of the PDMS micro/nanostructured surface enhanced the bactericidal properties of the film, which effectively inhibit bacterial attachment and cell proliferation.
Flow characteristics and heat transfer enhancement of synthetic jet impinging on heated plate
(2023-02-01)
Azmi Bin Husin
Downsizing electronic components while increasing their performance will increase heat generation exponentially. The excessive heat produced in electronic components can cause premature failure. Hence, maintaining the operating temperature at optimal conditions becomes more challenging. A synthetic jet is one of the under-developing forced cooling systems. The capability to produce continuous high fluid flow without additional fluid supply systems, high reliability and simple construction are the synthetic jet device's main advantages to be considered as a future active cooling system. The present research work was focused on enhancing the flow and the heat transfer rate by synthetic jet. The effect of the straight, nozzle and diffuser-shaped orifices were studied to see the flow characteristic of the speaker-driven synthetic jet. Additionally, the exit velocity was investigated to see the opening angle effect of the diffuser-shaped orifice. Then, the cooling performance of synthetic jet impinges on a flat heated surface was further investigated in the numerical work. Moreover, the effect of various heat source inputs, the gap between the orifice to the cooling surface, the opening angle of the diffuser shape orifice and the speaker’s diaphragm amplitude were extensively studied. The flow and heat transfer characteristics of the synthetic jet were numerically simulated using commercial computational fluid dynamic software. A three-dimension model with a moving boundary method was developed to achieve the objective of the current study. The flow is assumed to be incompressible and turbulent. The Unsteady Reynolds-averaged Navier-Stokes equations with Shear Stress Transport k-ω model are chosen to solve the governing equations for the synthetic jet flow. The user-defined functions that represent the movement of the speaker's diaphragm were utilized to increase the accuracy of the numerical model. In the flow study, the numerical model successfully captured the streamline of the synthetic jet flow generated by the speaker actuator. The ejection centreline velocity from the diffuser shape orifices was higher than straight and nozzle shape orifices. The most significant change in centreline velocity was observed when the opening angle switched from 0o to 30o. The maximum acceptable opening angle was 60o because the change of the centreline velocity at the opening angle of 90o and 120o were almost insignificant. The location of vortex formation near the centreline of the orifice help to increase the velocity during the ejection of the synthetic jet. In the heat transfer study, the distance between the orifice and the heated surface has significant heat transfer characteristics. The smaller gap (H=10mm) is suitable for centred or point cooling while the greater gap (H=30mm) shows a more uniform temperature distribution on the heated surface. Considering the opening angle of the diffuser shape orifice with suitable speaker diaphragm amplitude improved the cooling performance of the speaker-driven synthetic jet impinging on the flat heated surface. The heat transfer performance for the opening angle of 90o is better than 45o at a higher diaphragm amplitude.
Hydrogen absorption and diffusion in niti shape memory alloy
(2023-05-01)
Ng Ching Wei
Nickel titanium (NiTi) alloy is a popular biomaterial in biomedical implants and orthodontic applications. In orthodontic treatment, the usage of NiTi archwire in combination with dental bracket is capable of delivering constant force on the treated tooth, to induce tooth movement. The contact between NiTi archwire and stainless steel brackets could form a galvanic couple in the oral cavity, while giving rise to hydrogen absorption into archwire. The absorption of hydrogen atoms impairs its shape memory behavior and functionality in orthodontic treatment. The deterioration of shape memory behavior of NiTi archwire may persist and worsen over the treatment duration, owing to the inner diffusion of hydrogen interstitial atoms into deeper core of the matrix. This study investigated the effect of hydrogen absorption and diffusion over time toward shape memory and load-deflection behavior of NiTi alloy wires. Two different NiTi wires were use, the industrial round wire, and the commercial rectangular orthodontic wire. At room temperature, the round wire was at martensitic phase, and the rectangular wire was at austenite phase. The absorption of hydrogen into wire specimens was induced via electrolytic charging. The inward diffusion of hydrogen over time was achieved via aging at room temperature. The differential scanning calorimetry showed that the absorption and diffusion of hydrogen in martensitic NiTi round wire suppressed the size of thermal martensite phase transformation peaks. Furthermore, the additional hydrogen-related phase transformation peaks were also observed after hydrogenation, while its peak size and enthalpies increased over the aging duration. The tensile deformation behavior was also largely affected, of which the stress-induced martensitic phase transformation exhibited a non-flat plateau with the formation of force curvatures at the onset and ending stages, respectively. The loading force, as deduced from its load-deflection behavior via three-point bending deformation also increased slightly. This impaired its strain recovery. The effect of hydrogen charging towards load-deflection behavior of rectangular austenitic NiTi wire via three-point bending test was only detected after charging for 16 and 24 hours. The strain recovery of the wire deteriorated over aging time in the unloading stage of load-deflection curve. The largest residual deflection was 0.65 mm for the 24-hour-charged and 7-day-aged wire specimen, as compared to 0.03 mm for the as-received specimen. In a three-bracket bending test, the hydrogen charging caused the wire to fracture during the loading stage. Likewise, the hydrogen diffusion via aging led to the large residual deflections upon complete unloading, of which its magnitude increased from 0.12 mm for the as-received specimen, to 0.70 mm after charging for 24 hours and aging for 7 days, at a maximum deflection of 4 mm. After prolonged aging, the effect of inner diffusion of hydrogen has caused obstruction towards the reverse stress-induced martensite phase transformation, thus causing the unloading force curve to occur at lower force levels.
Reducing work-related injuries: a comparative analysis of patient transfer devices for healthcare professional
(2023-09-01)
Mitchelle Law Jyy Jinn
Work-related musculoskeletal disorders (WMSDs) are a common problem among healthcare workers. For WMSDs risks assessment, the Rapid Entire Body Assessment (REBA) is widely used. However, previous studies have used a constant estimated external force as load input in REBA, which does not consider the load variations due to patient and nurse postural changes. A method to input the actual load to REBA through instantaneous measurement is needed. Despite the risk-reducing benefits, the adoption rates for patient transfer devices are still low. Surveys are prone to cognitive judgement and biases and cannot capture instantaneous user emotions. Emotional evaluation of patient transfer devices has not been done before. Whether an evaluation tool of the National Aeronautics and Space Administration Task Load Index (NASA-TLX) can capture both perceived workload and instantaneous emotions, or whether facial expression analysis is necessary to quantify emotions, is unknown. This thesis aimed to identify the WMSDs risks of patient transfer devices through REBA with instantaneous measured force, to quantify the nurses' perceived workload, technology acceptance, and instantaneous emotional states during the use of patient transfer devices, and to quantify the relationship between the perceived workloads and instantaneous emotions via facial expression. Seven nurses were recruited to carry out tasks using a sliding board, motorised transfer, walking belt, and floor lift. The postural and ground reaction force data were used for the calculation of external load as load input for the REBA system. User experience was obtained through a technology acceptance questionnaire, NASA-TLX, and facial expression analysis. Motorised transfer obtained the lowest REBA score (3.33 ± 0.56), and floor lift as an intervention, still reported high REBA scores (7.73 ± 0.51). The motorised transfer had a higher technological acceptance (p = 0.016) and lower perceived workload (p = 0.004) than the sliding board. The floor lift significantly reduced perceived workload compared to the walking belt (p = 0.018), but acceptance scores did not significantly differ (p= 0.098). Despite good feedback on the interventions for the NASA-TLX and technology acceptance surveys, all devices, including the motorised transfer and floor lift, showed a high negative valence of over 80 in facial expression analysis. The motorised transfer had relatively better valence scores (82.87 ±12.60), while the floor lift had the highest negative valence (99.16±1.93). This study contributes to WMSDs risk assessment by using REBA with instantaneous measured force and introducing facial expression analysis to understand user emotions while using patient transfer assistive devices.
Study On The Effect Of Tool Nose Wear On Surface Roughness And Dimensional Deviation Of Workpiece In Finish Turning Using Machine Vision
(2009-02)
Haghighi, Hamidreza Shahabi
The aim of this research is to study the effect of tool nose wear, which is in contact with the surface profile of workpiece directly, on Ra using a developed machine vision in finish turning operation.
Synthesis of stretchable conductive polymer for electronics circuit application
(2023-04-01)
Sana Zulfiqar
Stretchable electronic circuits (SECs) have become very popular nowadays in various mechanical, electrical and biomedical engineering applications. They are comprised of flexible and stretchable substrate as well as conductive ink, and electronic components. The stretchability and flexibility of SECs can be controlled by the proper selection of materials and designs for the substrate and conductive ink. Moreover, the material used to develop the conductive ink must exhibit high electrical conductivity and good adhesion with the substrate to obtain a high quality of stretchable printed circuit. This study focussed on the synthesis, material modelling and the examination of various properties of polymeric substrate and conductive ink by different thermal, mechanical and electrical testing. For synthesis, PDMS-OH was used as a binder or elastomer in both the formulations and silver powder as a conductive filler for silver-based conductive ink. The mechanical properties of these materials were evaluated by simple UTM under tensile loading. The modulus of elasticity and tensile strength of the substrate and ink were found as 0.48 MPa and 2.18 MPa at 300% stretchability, and 5.72 MPa and 1.195 MPa with the yield stress of 0.86 MPa at 137% stretchability before rupture, respectively. Afterwards, the thermal analysis of the conductive ink was carried out by DSC and TGA. From DSC, the glass transition and melting temperatures of the cured ink were found as 130°C and 297.43°C, correspondingly. The thermal degradation was studied by TGA in which the weight loss occurred at different ranges of temperature. The residue of silver particles was obtained as 82.62% after complete analysis. This proves that the current formulation of the ink becomes more viscous at higher temperatures. Moreover, the storage modulus, loss modulus and damping ratio of the ink were calculated using DMA analysis. As a result, the silver ink exhibited low loss modulus value than the storage modulus, which proves that the current formulation of the ink was more elastic in nature rather viscous. Farther the micro mechanical analysis, the hardness and reduced modulus of the conductive were computed by nanoindentation technique. In addition, the surface analysis of the ink was done by OM and SEM. As a result, the silver particles were homogeneously spread throughout the surface of the ink. The electrical conductivity was measured by 2-point multi-meter before and after application of load. It was found as 1002 S/cm without loading, while, the resistance of the ink increased from 0.042 Ω to 25 Ω at 60% strain during loading and decreased from 25 Ω to 0.0767 Ω at 0% after unloading. Finally, the stress-strain data of respective material were utilized to characterize the material properties using hyper-elastic constitutive models for the substrate and multi-linear plastic models for the conductive ink. The curve fitting was done using three solvers, Abaqus, GRG and C-PSO algorithm. As a consequence, the Reduced Polynomial (𝑁=6) model under C-PSO algorithm was considered as the best fit hyper-elastic model than others. The validation of this hyper-elastic model was then executed through FE analysis. Consequently, the experimental results were in a good agreement with the simulated results.

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