Dr Abdur-Rasheed Alao
@utb.edu.bn
Professor (Assistant), Mechanical Engineering
Universiti Teknologi Brunei
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Nur Imanina Shamsul Bahren, Ng Jia Ying, Mohd Ammar Akmal Aliuddin, and Abdur-Rasheed Alao
AIP Publishing
Angelyana Puyah Geruna, Mohammad Yeakub Ali, Seri Rahayu Ya'akub, Asri Mohammad, Abdur-Rasheed Alao, Muataz Al Hazza, and Erry Y. T. Adesta
AIP Publishing
Abdur-Rasheed Alao, Md Nur Adi Syafi Rafiuddin Eliza, and Ahmad Shamil Abd Rahman
IOP Publishing
Abstract Polymer-infiltrated zirconia-ceramic composite (PIZC) comprises a pre-sintered zirconia-ceramic matrix and a polymer. In this work, pre-sintered zirconia-ceramic was infiltrated with varied amounts of methacrylate-based polymer. Therefore, this paper reports the effect of polymer amount on the mechanical behavior of PIZC at 1100 °C–1300 °C pre-sintering temperatures. Conventional mechanical tests were performed to obtain the elastic modulus and fracture toughness while Vickers micro-indentations were employed to extract the Vickers hardness. Advanced mechanical behaviour analysis was characterized by plastic deformation resistance, elastic and plastic deformation components and brittleness index. Increasing the amount of polymer from 0 to 42% led to the corresponding decrease in elastic modulus, hardness and fracture toughness by at least 78, 85 and 75%, respectively. As the temperature was increased, both elastic modulus and hardness increased while the fracture toughness initially increased but decreased at higher temperature. Mechanical properties and polymer amount were well modelled by connected-grain models which usefully explained the densification process occurring at higher temperatures. Plastic deformation resistance and component and brittleness index confirmed better plastic properties for PIZC at higher polymer amounts and lower temperature. Therefore, in order to utilize the plastic properties of PIZC during the CAD/CAM process, these findings recommended the processing of PIZC at not-lower-than 26% polymer amount and 1100 °C, which could greatly facilitate its precision ductile machining mode realization. Finally, the results provide a technical guidance for the selection of appropriate polymer amount when fabricating dental restorations from this novel ceramic-composite.
Abdur-Rasheed Alao and Mohd Azmir Mohd Azhari
Journal of the Mechanical Behavior of Biomedical Materials Elsevier BV
Indentation size effect (ISE) and R-curve behaviour of Li2O-SiO2 and Li2O-2SiO2 glass ceramics are investigated using micro-indentation and indentation-strength (IS) techniques, respectively. Vickers micro-indentations were applied on both materials at the load of 0.10-19.6 N to determine the load influence on the measured hardness. For the IS-measured fracture toughness, the load ranged from 1.96 to 19.6 N. The hardness decreased with increasing load by 20% and 18% on Li2O-SiO2 and Li2O-2SiO2 glass ceramics, respectively, indicating the ISE behaviour on both materials. The fracture toughness increased with the load by 27% and 59% on Li2O-SiO2 and Li2O-2SiO2 glass ceramics, respectively, signifying the R-curve behaviour. The ISE behaviour of both materials was analysed using the Meyer's, Hays-Kendall (HK), proportional specimen resistance (PSR), Nix-Gao (NG), modified PSR (MPSR) and elastic plastic deformation (EPD) models while the R-curve behaviour was analysed by the fractional power law. The Meyer's index of both materials was less than 2, strongly confirming the ISE existence. The HK, PSR and NG models were only suitable to determine intrinsic Vickers hardness for Li2O-2SiO2 glass ceramic while the MPSR and EPD models were successful for both materials. The fractional power law gave higher R-curve steepness for Li2O-2SiO2 than Li2O-SiO2 glass ceramics. Also, material and brittleness indices predicted, respectively, higher quasi-plasticity and better machinability for Li2O-2SiO2 than Li2O-SiO2 glass ceramics indicating superior performance in the former to the latter. Finally, this study presents a new significant insight into the micro-mechanisms of fracture tolerance behaviour of these glass ceramics which is critical to their functional performance as structural ceramics.
Abdur-Rasheed Alao, Richard Stoll, Yu Zhang, and Ling Yin
Journal of the Mechanical Behavior of Biomedical Materials Elsevier BV
This paper reports on the process-fatigue relation of lithium disilicate glass ceramic (LDGC) using low-cycle, high-load Hertzian indentations with a rigid indenter to simulate teeth grinding/clenching of LDGC restorations with different surface asperities obtained in CAD/CAM milling, sintering, polishing and glazing. The maximum contact stresses were evaluated as functions of the number of load cycles and surface treatments using the Hertzian model. Indentation-induced surface damage was viewed using scanning electron microscopy (SEM) to understand the relationships among microstructures, surface asperities, crack morphology and propagation. Different processes and surface treatments significantly affected the maximum contact stresses of indented LDGC surfaces (ANOVA, p < 0.05), which were all significantly reduced with the number of cycles (ANOVA, p < 0.05). Quasi-plastic deformation was dominant in single-cycle indentation of all processed and treated surfaces. In higher cycle indentations, inner cone cracks were formed on all surfaces; median and transverse cracks were formed on the roughest surfaces processed by CAD/CAM milling and sintering. Ring cracks, fretting, pulverization, micro-bridges, surface smearing and wedging, and edge chippings were also propagated on all surfaces. The process-fatigue relation provides an understanding of the mechanical functions of surface asperities produced in different processes and treatments. It indicates that the mechanically assisted growth of surface asperities with different roughness strongly affected the indentation-induced surface damage. Finally, the smoothest surfaces produced by CAD/CAM milling, polishing and sintering sustained the highest contact stresses and the least fatigue damage at higher cycles, ensuring their superior fatigue performance compared to other processed LDGC surfaces.
Abdur-Rasheed Alao and Muhammad Haziq Danish Bujang
Ceramics International Elsevier BV
Abstract The mechanical behaviour of pre-crystallized and crystallized zirconia-reinforced lithium silicate glass ceramics (ZLS) using micro-indentation techniques is reported. Vickers micro-indentations were conducted on these materials at the load of 0.245 N–9.8 N and 4.9 N–9.8 N to determine the load effect on the hardness and fracture toughness, respectively. The hardness increased with the load by 78.2% (ANOVA, p
Abdur-Rasheed Alao
Elsevier BV
Abdur-Rasheed Alao, Richard Stoll, Xiao-Fei Song, John R. Abbott, Yu Zhang, Jaafar Abduo, and Ling Yin
Elsevier BV
Ling Yin, Yoshitaka Nakanishi, Abdur-Rasheed Alao, Xiao-Fei Song, Jaafar Abduo, and Yu Zhang
Elsevier BV
Abdur-Rasheed Alao, Richard Stoll, Xiao-Fei Song, Takashi Miyazaki, Yasuhiro Hotta, Yo Shibata, and Ling Yin
Elsevier BV
Abdur-Rasheed Alao and Ling Yin
Elsevier BV
Abdur-Rasheed Alao and Ling Yin
Elsevier BV
Abdur-Rasheed Alao and Ling Yin
Elsevier BV
Abdur-Rasheed Alao and Ling Yin
Elsevier BV
Abdur-Rasheed Alao and Ling Yin
Elsevier BV
Abdur-Rasheed Alao and Mohamed Konneh
Springer Science and Business Media LLC
Alao Abdur-Rasheed and Mohamed Konneh
Trans Tech Publications, Ltd.
Silicon being a typical hard-brittle material is difficult to machine to a good surface finish. Although ductile-mode machining (DMM) is often employed to machine this advanced material but this technique requires the use of expensive ultra-precision machine tools therefore limiting its applicability. However, by proper selection of grinding parameters, precision grinding which can be performed on conventional machine tools can be used to generate massive ductile surfaces thereby reducing the polishing time and improving the surface quality. Precision grinding should be planned with reliability in advance and the process has to be performed with high rates of reproducibility. Therefore, this study investigated the effect and optimization of grinding parameters using Taguchi optimization technique during precision grinding of silicon. Experimental studies were conducted under varying depths of cut, feed rates and spindle speeds. An orthogonal array (OA), signal-to-noise (S/N) ratio and the analysis of variance (ANOVA) were employed to find the minimum surface roughness value and to analyze the effect of the grinding parameters on the surface roughness. Confirmation tests were carried out in order to illustrate the effectiveness of the Taguchi method. The results show that feed rate mostly affected the surface roughness. The predicted roughness (Ra) of 34 nm was in agreement with the confirmation tests. Massive ductilestreaked surface was also found corresponding to the minimal surface finish determined from the optimal levels.
Alao Abdur-Rasheed
Trans Tech Publications, Ltd.
Conventional diamond cutting of ferrous materials is rarely economical due to the rapid tool wears which result from diffusion and graphitization of the tools. Conventional machining of hard-brittle materials like silicon and germanium results in surface and subsurface damage due to their brittle fracture. Although ductile mode machining (DMM) concept can be used to have a flawless machining on these materials but the mirror surfaces can only be realized on expensive ultraprecision machine tools because the critical depth of cut must be on the order of 1μm or less. Furthermore, there is a need to eliminate or reduce the use of cutting fluids during machining due to their attendant ecological hazards. However, grinding is one of the most difficult processes with regard to eliminating cutting fluids. Vibration assisted machining (VAM) can be used to minimize the problems enumerated above. VAM combines precision machining with small-amplitude tool vibration to improve the fabrication process. It has been applied to a number of processes ranging from turning, drilling to grinding. Therefore, this paper discusses DMM, the general overview of VAM, the basic kinematics of one-dimensional VAM; the advantages derived from using VAM and the ability of VAM to machine brittle materials in the ductile regime at increased depth of cut are described. Finally, the research directions in VAM are outlined.
Abdur Rasheed Alao and Mohamed Konneh
Inderscience Publishers
Silicon substrates are difficult to grind to good surface finishes using conventional machining. Ductile mode machining is often required to have flawless machining but this requires the use of expensive machine tools. However, precision grinding using conventional machine tools could generate large amounts of ductile streaks on ground silicon surfaces under good machining conditions. High wheel rotation, slow feed rate, small indentations and small grain sizes are the practical requirements to realise precision grinding of silicon. Therefore, this study examines the feasibility of quantitative determination of the criteria to realise precision grinding of silicon on an NC milling machine with factorial experimental design. The result shows massive ductile streaks at depth of cut, 20 μm; feed rate, 6.25 mm/min and spindle speed of 70,000 rpm with a 43 nm Ra. Spindle speed affects mostly the surface finish. The combined effects of depth of cut and feed rate on Ra and Rt which add to the complexity in the precision grinding process are investigated.