Willey Yun Hsien Liew

Non-destructive concrete strength evaluation using smart piezoelectric transducer—a comparative study

Concrete strength monitoring, providing information related to the readiness of the structure for service, is important for the safety and resource planning in the construction industry. In this paper, a semi-analytical model of surface bonded piezoelectric (lead zirconate titanate) based wave propagation (WP) technique was developed for strength evaluation of mortar with different mix, throughout the curing process. Mechanical parameters of the mortar specimen were mathematically evaluated from the surface wave (R-wave) and pressure wave (P-wave) using elastic wave equations. These parameters were then empirically correlated to the strength. The model was found to be very robust as it could be generalized to account for different water to cement (W/C) ratio. The performance of the WP technique was then compared to the electromechanical impedance technique and other conventional techniques, such as the ultrasonic pulse velocity (UPV) test and the rebound hammer test. Results showed that the WP technique performed equally well as the conventional counterparts. The proposed technique is also advantageous over embedded WP technique and the UPV test, in terms of its capability to capture two types of waves for the evaluation of dynamic modulus of elasticity and Poissons ratio. A separate study was finally conducted to verify the applicability of this technique on heterogeneous concrete specimen. With the inherent capability of the WP technique in enabling autonomous, real-time, online and remote monitoring, it could potentially replace its conventional counterparts, in providing a more effective technique for the monitoring of concrete strength.

Increasing the bandwidth of the width-split piezoelectric energy harvester

A new method to maximize the output power of a piezoelectric energy harvesting system has been previously proposed by the authors. This can be achieved by reducing the mechanical damping through folding a given piezoelectric material equally and splitting it into smaller width. Experimental results have shown that the power harvested increases when the number of fold increases but with the trade off the optimal operating frequency range, which is referred as the bandwidth. This paper aims to improve the bandwidth by modifying the natural frequency of each split piezoelectric material and connecting them in parallel. Experimental results show that the bandwidth increases as the difference between the natural frequency of the reduced-width piezoelectric materials increases. Although these results are with trade off in reducing output power gain, the gain in the bandwidth per unit output power reduction is still increasing. This shows that the maximum output power of the harvesting system can be ensured with the width-splitting method and the bandwidth of the output can be widened by increasing the difference between the natural frequencies of the participating piezoelectric elements. This maximization method with wideband feature can be implemented at microscopic stage to be incorporated in the microelectronics devices such as MEMS.

Experimental Study on the Performance of Coated Carbide Tools in the Ultra-Precision Machining of Stainless Steel

Ultra-precision machines are widely used to turn aspherical or spherical profiles on mold inserts for the injection molding of optical lenses. During turning of a profile on a stainless steel mold insert, the cutting speed reduces significantly to 0 as the cutting tool is fed towards the center of the machined profile. This article reports on experiments carried out to study the wear of uncoated, physical vapor deposition (PVD) coated and chemical vapor deposition (CVD) coated carbide tools in the ultra-precision machining of STAVAX (modified AISI 420 stainless steel) at low speeds with and without a lubricant. A sprayed mixture of compressed air, liquid paraffin oil, and cyclomethicone was used as a lubricant. During machining at 44 m/min under dry condition, the rake face of the tool edge was predominantly subjected to abrasive wear. Reducing the speed to 10 m/min increased the flank wear and the severity of abrasive wear and caused the tool edge to fracture, leading to a deterioration of the surface finish. The lubricant was effective in preventing surface fracture, reducing flank wear, and improving the surface finish. Among the PVD-coated and the CVD-coated tools, the former tool type is more suitable to be used in ultra-precision machining. The CVD-coated tool vibrated rapidly, causing extensive fracture to take place on the flank face and the surface finish to be undulating. The experimental results obtained in the turning tests gave useful insight on the appropriate parameters and conditions to be used in the machining of a profile on a mold insert. The profile machined on the stainless steel mold insert with the PVD-coated carbide tool in the presence of natural oil had a superior form of accuracy and surface finish.

The effectiveness of palm oil methyl ester as lubricant additive in milling and four-ball tests

This paper examines the effectiveness of palm oil methyl ester (POME) as lubricant additive using the four-ball and milling tests. In milling 55 HRC-stavax® (modified AISI 420 stainless steel) under flood lubrication, three stages of tool wear occurred: 1) initial wear by delamination, attrition and abrasion; 2) cracking at the substrate, 3) followed by formation of individual surface fracture at the cracks which would then enlarge and coalesce to form a large fracture surface. Mineral oil sprayed in mist form was more effective in reducing the coating delamination and delaying the occurrence of cracking and fracture. The effectiveness of mineral oil in suppressing these wear modes could be enhanced by the presence of POME. The mechanism by which the POME suppressed these wear modes could be explained by the results obtained in the four-ball tests which showed that the presence of POME as additive in the mineral oil reduced the friction coefficient, severity of welding and increased the critical load for welding to occur.

The effects of width reduction on the damping of a cantilever beam and its application in increasing the harvesting power of piezoelectric energy harvester

Previous work shows that when a cantilever piezoelectric energy harvester with a given width is split into several pieces and then electrically connected in parallel, the output power increases substantially compared with when it acts in a single piece with a similar total width. It was hypothesized that this increase is due to the reduction in the damping of the width-reduced beam. As a result, the beam with the smaller width vibrates with higher amplitudes and therefore has higher energy harvesting capability. In this paper, this hypothesis is examined by measuring the damping of the cantilever beam as its width is reduced. It is shown that as the width decreases, the damping is reduced, which contributes to the increase in the harvested power. It is then shown that the harvested energy from an array of cantilever piezobeams with a certain total width is higher than that from a single-piece harvester of similar width.

A Parametric Study on Admittance Signatures of a PZT Transducer Under Free Vibration

Piezoelectric material is proven to be a versatile collocated sensor and actuator. Its specific application includes electromechanical impedance (EMI)-based structural health monitoring (SHM). To date, several EMI models are available in the literature but parametric studies are scarcely available. This study aims at providing a parametric study on selected models, considering a freely vibrating piezoelectric transducer. The effect of varying mechanical and electrical parameters of the transducer on the admittance signatures was investigated. The theoretical results were compared against the experiments. Accuracy of the model was successfully refined upon model updating.

Dry Sliding Behaviour of AlCrN and TiN Coatings

This paper examines the friction behaviour of AlCrN and TiN PVD coatings in atmospheric air and vacuum using a ball-on-disc and a reciprocating tribotesters. Comparative study on the coating sliding in air and in high vacuum environment provides important insight on the effect of oxidation on the friction behaviour of the coatings. Other important factors such as load, sliding velocity, temperature effects on the frictional behaviour of these coatings were also investigated. In the ball-on-disc tests carried out in vacuum, (i) TiN gave lower coefficient of friction (COF) than AlCrN, indicating that TiN was more lubricous, (ii) higher speed resulted in lower COF, and (iii) the COF of both coatings were lower than that produced in air. In ambient air, (i) AlCrN gave lower COF than TiN with high wear debris retention on the sliding interface due to the effect of oxidation, and (ii) higher speed resulted in lower COF, similar to that observed in vacuum. In the reciprocating tests, at low load, increasing the temperature from room temperature to 150 °C resulted in a reduction in the COF. However, at high load, the temperature virtually did not affect the COF. Higher nominal load resulted in lower COF while higher speed resulted in higher COF.

Influence of Alkali Treatment and Nanoclay Content on the Properties of Rice Husk Filled Polyester Composites

The effect of alkali treatment and nanoclay addition on the mechanical properties and water absorption behavior of rice husk particle (RHP) reinforced unsaturated polyester (UP) composites was investigated. Thermogravimetric analysis (TGA) indicated that the alkali treatment removed most of the hemicellulose and impurities from the RHP with the tensile strength, tensile modulus, flexural strength and flexural modulus of the resulting composites being improved by alkali treatment. The results indicated that the 5% sodium hydroxide concentration had the optimum performance on mechanical strength and water absorption resistance. Furthermore, the influence of nanoclay addition (1, 3 and 5 wt%) on the properties of optimum alkali treated RHP-UP composites was investigated with the lowest content (1 wt%) of nanoclay showing the highest mechanical performance. However, further addition of nanoclay improved the moisture absorption resistance of the composites. Good interface bonding between the filler and matrix was observed from scanning electron micrographs for the optimum RHP alkali treated and nanoclay dispersed RHP-UP composites.

An EOQ Based Multi-Storage Location of Spare Part Inventories: A Case Study

Spare parts inventory management is very important to ensure smooth operation of maintenance department. The main objectives of inventory management of spare parts are to ensure the availability of spares and materials for the maintenance tasks and increase the productivity of the maintenance department. This research centred on the development of the Computerised Inventory Management System (CIMS) for the maintenance team at Weida Integrated Industries Sdn. Bhd. The inventory management technique used to control the spare parts inventory in this research was the basic Economic Order Quantity models (EOQ). However, the CIMS developed is unique as it has the ability in handling inventories in multiple-storage locations. The CIMS was written using the Visual Basic 2010 software. This CIMS has the abilities to keep records and process the spare parts information effectively and faster besides helping the user to perform spare parts ordering tasks compared to the current manual recording. In addition, the ordering quantity and frequency for the CIMS is determined through the EOQ technique. However, observation indicates that the overall average inventory level currently at the factory is lower than the expected overall average inventory level produced by the CIMS. This is due to the fact that the CIMS was unable to consider the opening stock in ordering the inventories. Therefore, further improvements are needed to optimize the performance of the system such as using the EOQ with the reorder point technique, the periodic or continuous review system.

The Effect of Cooling Rate in Molten Salt Electro-Carburisation Process

In the recent development of a new process of electro-carburisation of mild steel in 800 °C molten carbonate based salts, further investigation has been carried out to study the effects of the cooling rate after the electro-carburisation process. In the process, the mild steel to be carburised was made the cathode and an inert SnO2 as anode. Salt mixture of Na2CO3-NaCl (mole ratio 4:1) was used as the electrolyte, and the process was carried out at voltage range of 1.0 to 2.5 V for 60 minutes, and thereafter cooled at certain rate. As revealed by the optical microscopy, the microstructural changes in samples that have been electro-carburised and thereafter cooled either rapidly or naturally in air, were featured by the increase of the carbon rich in the martensite structure at the expense of the original ferrite phase near the surface of the samples. Micro-hardness profiles measured from the surface to the centre of the electro-carburised sample presented clear evidence of carbon penetration as a function of the electrolysis voltage, and significant effects of cooling rate after the electro-carburisation process.