Dr. Abdur-Rasheed Alao (CEng MIMechE, MASME) | UTB (original) (raw)
Papers by Dr. Abdur-Rasheed Alao (CEng MIMechE, MASME)
Precision engineering, Jun 1, 2024
IOP Conference Series: Materials Science and Engineering, 2021
Models are useful in controlling the process effectively and efficiently in micro electro dischar... more Models are useful in controlling the process effectively and efficiently in micro electro discharge machining (Micro-EDM). There are two types of models which are empirical models and theoretical models. Most of the models are basically formulated for conductive work materials. However, nowadays there is a trend to cut nonconductive materials using micro-EDM where the models developed for conductive materials are not applicable. There are only few models that are developed to cut nonconductive materials with micro EDM but these models have limitations. In this article, models for cutting conductive materials and nonconductive materials using micro EDM are compared in view of their applications.
Advanced Materials Research, 2011
Silicon being a typical hard-brittle material is difficult to machine to a good surface finish. A... more 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 a...
Journal of the Mechanical Behavior of Biomedical Materials, Jan 31, 2024
8TH BRUNEI INTERNATIONAL CONFERENCE ON ENGINEERING AND TECHNOLOGY 2021
Statistical analysis chip thickness in high-speed end milling using simulation approach
AIP Conference Proceedings, 2023
For load-bearing structural applications in engineering and medicine, presintered and sintered yt... more For load-bearing structural applications in engineering and medicine, presintered and sintered yttria tetragonal zirconia polycrystals (YTZPs) are usually CAD/CAM shaped by soft and hard machining, respectively. However, there is a need to analytically predict their machinability to know the better machinable material. This research aims to characterize brittleness and plasticity indices evaluated in terms of elastic modulus, hardness and fracture toughness for presintered and sintered YTZPs using microindentation techniques. Six indentations were made on the presintered and sintered samples at different loads ranging from 0.098 N-19.62 N. The hardness of both samples decreased as the load was increased indicative of the normal indentation size effect (NISE) occurrence. The NISE was analyzed by the Meyer's, proportional specimen resistance (PSR), modified proportional specimen resistance (MPSR), Hays-Kendall (HK) and elastoplastic deformation (EPD) models. For both materials, the Meyer law successfully described the NISE with the Meyer's index becoming less than 2. Models of PSR, MPSR, EPD and HK gave consistent intrinsic Vickers hardnesses for presintered and sintered YTZP materials. Because of its best correlation coefficient, however, the MPSR model successfully provided the best intrinsic Vickers hardness for presintered and sintered YTZP materials. Consequently, the intrinsic Vickers hardness is 0.742 GPa and 8.90 GPa for presintered and sintered YTZPs, respectively. Also, the brittleness and plasticity indices of presintered YTZP predicted better machinability and ductility of 0.742 μm. and 40, respectively. Therefore, presintered YTZP is considered better for CAD/CAM machining than sintered YTZP. This study provides a significant insight into a fast method of ranking materials in terms of machinability and ductility for specific applications.
AIP Conference
As part of the efforts towards green and sustainable machining strategies, this research project ... more As part of the efforts towards green and sustainable machining strategies, this research project investigated the use of MQL as an alternative towards flood cooling for drilling of 1-inch cylindrical mild steel rod using High Speed Steel (HSS) drill bit with diameter of 5 mm at the hole-depth of 10 mm. For this experiment, Design Expert statistical software is used to derive Design of Experiment (DOE) under Taguchi Orthogonal Array (OA) Design for cutting speeds of 650, 1050 and 2100 rpm and feed rate of 0.1, 0.2 and 0.3 mm/rev. Then, the experimental data obtained was analysed and the cutting parameter: cooling fluid, cutting speed and feed rate does in-fact, affect the surface roughness of drilled hole. As the cutting speed increases, the surface roughness decreases and when the feed rate decreases, the surface roughness increases, and these trends occurred for both types of lubrication system used. The analysed data were then optimized to find the best condition for the smallest surface roughness. It was then discovered with the use of MQL at cutting speed of 2100 rpm and feed rate of 0.1 mm/rev resulted in the smallest surface roughness.
AIP Conference Proceedings, 2023
For load-bearing structural applications in engineering and medicine, presintered and sintered yt... more For load-bearing structural applications in engineering and medicine, presintered and sintered yttria tetragonal zirconia polycrystals (YTZPs) are usually CAD/CAM shaped by soft and hard machining, respectively. However, there is a need to analytically predict their machinability to know the better machinable material. This research aims to characterize brittleness and plasticity indices evaluated in terms of elastic modulus, hardness and fracture toughness for presintered and sintered YTZPs using microindentation techniques. Six indentations were made on the presintered and sintered samples at different loads ranging from 0.098 N-19.62 N. The hardness of both samples decreased as the load was increased indicative of the normal indentation size effect (NISE) occurrence. The NISE was analyzed by the Meyer's, proportional specimen resistance (PSR), modified proportional specimen resistance (MPSR), Hays-Kendall (HK) and elastoplastic deformation (EPD) models. For both materials, the Meyer law successfully described the NISE with the Meyer's index becoming less than 2. Models of PSR, MPSR, EPD and HK gave consistent intrinsic Vickers hardnesses for presintered and sintered YTZP materials. Because of its best correlation coefficient, however, the MPSR model successfully provided the best intrinsic Vickers hardness for presintered and sintered YTZP materials. Consequently, the intrinsic Vickers hardness is 0.742 GPa and 8.90 GPa for presintered and sintered YTZPs, respectively. Also, the brittleness and plasticity indices of presintered YTZP predicted better machinability and ductility of 0.742 μm. and 40, respectively. Therefore, presintered YTZP is considered better for CAD/CAM machining than sintered YTZP. This study provides a significant insight into a fast method of ranking materials in terms of machinability and ductility for specific applications.
aspe.net
Silicon constitutes 90% of all semiconductors and it is an important material for making devices ... more Silicon constitutes 90% of all semiconductors and it is an important material for making devices in electronics, semi-conducting and optical industries. It is used as optical components in high-resolution thermal imaging systems and also finds applications in ...
Materials Research Express
Polymer-infiltrated zirconia-ceramic composite (PIZC) comprises a pre-sintered zirconia-ceramic m... more 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...
Alao, Abdur-Rasheed (2016) Fabrication and characterization of lithium metasilicate/disilicate gl... more Alao, Abdur-Rasheed (2016) Fabrication and characterization of lithium metasilicate/disilicate glass ceramics and yttria tetragonal zirconia polycrystals for dental restorations. PhD thesis, James Cook University.
Recent Advances in Structural Integrity Analysis - Proceedings of the International Congress (APCF/SIF-2014), 2014
ABSTRACT Zirconia is a unique material widely used in engineering, medicine and dentistry as load... more ABSTRACT Zirconia is a unique material widely used in engineering, medicine and dentistry as load-bearing structures, such as mechanical bearings, orthopedic bones and joints, dental implants, crowns and bridges. Zirconia structures can be shaped either in pre-sintered or sintered states by abrasive machining tools. However, abrasive machining inevitably induces surface and sub-surface cracks in both pre-sintered and sintered zirconia structures, resulting in poor surface quality and shortened lifespans of zirconia products. To predict the machinability of zirconia materials, it is necessary to simulate their fracture resistance behaviour. This research was undertaken to predict the resistance to machining-induced cracking for pre-sintered and sintered zirconia using nanoindentation which physically mimics abrasive machining with sharp grits. Mechanical characterization of the resistance to machining-induced cracking was performed using the Sakai model which incorporates fracture energy and ductility index. The characterization was performed at a peak load of 10 mN and loading rate of 0.1-2 mN/s. The results show that pre-sintered zirconia yielded a higher ductility and better resistance to machining-induced cracking. This work suggests that pre-sintered zirconia can sustain more mechanical damage and absorb more energy and can therefore be easily machined than the sintered zirconia.
Journal of the Mechanical Behavior of Biomedical Materials, 2021
Indentation size effect (ISE) and R-curve behaviour of Li2O-SiO2 and Li2O-2SiO2 glass ceramics ar... more 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.
Journal of the Mechanical Behavior of Biomedical Materials, 2021
This paper reports on the process-fatigue relation of lithium disilicate glass ceramic (LDGC) usi... more 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 *
Ceramics International, 2021
The mechanical behaviour of pre-crystallized and crystallized zirconia-reinforced lithium silicat... more 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 < 0.05) and 163% (ANOVA, p < 0.05) on pre-crystallized and crystallized ZLS, respectively, indicating the occurrence of the reverse indentation size effect (RISE) on both materials. The fracture toughness increased with the load by 20% and 12.3% on pre-crystallized and crystallized ZLS, respectively. Hardness data of both materials were analyzed using the Meyer's, indentation-induced cracking (IIC), proportional specimen resistance (PSR), modified PSR, Hays-Kendall and elastic plastic deformation (EPD) models. The Meyer's and IIC models described the RISE behaviour of both materials satisfactorily. The PSR, Hays-Kendall and EPD models provided consistent loadindependent hardnesses while the modified PSR model gave erratic load-independent hardnesses for both materials. The continuum model provided intrinsic compressive yield strengths of both materials which were consistent with those obtained from the EPD model and the Tabor relation, implying the EPD model as the most successful. The brittleness index predicted better machinability for crystallized ZLS than pre-crystallized ZLS. Finally, the variations of hardness and fracture toughness with load might account for the different micromaterial removal mechanisms in the sharp abrasive machining of these materials.
Journal of the Mechanical Behavior of Biomedical Materials, 2019
This paper applied non-linear theory of elasticity (NLTE) to partition indentation-induced deform... more This paper applied non-linear theory of elasticity (NLTE) to partition indentation-induced deformations into elasticity and plasticity for lithium metasilicate glass ceramic (LMGC), sintered and pressed lithium disilicate glass ceramics (SLDGC and PLDGC). It also used elastic plastic fracture mechanics (EPFM) approach to analytically predict machinability for these materials. Using the Sakai's series elastic and plastic deformation model that applied NLTE, the resistances to plasticity for LMGC, SLDGC and PLDGC were extracted from their respective indentation-extracted plane strain moduli and contact hardness values. Plane strain moduli and resistances to plasticity were used to calculate elasticity and plasticity for these materials. Furthermore, the EPFM approach in the Sakai-Nowak model was applied to deconvolute resistances to machining-induced cracking for these materials. All properties were extracted at 10 mN peak load and 0.1-2 mN/s loading rates to determine the loading-rate influence on these properties. The resistances to plasticity of LMGC and SLDGC were loading rate dependent (ANOVA, p < 0.05) and the resistance to plasticity of PLDGC was loading rate independent (ANOVA, p > 0.05). The strain rate sensitivity model was used to find the intrinsic resistances to plasticity for LMGC and SLDGC. The elastic displacement/deformation components were dominant for LMGC at all loading rates. For SLDGC and PLDGC, the deformation mechanisms were dynamic with the plastic and elastic deformation components dominating at low loading and high loading rates respectively, a phenomenon attributed to indentation energies. The decrease in plastic displacements for all materials with increase in loading rate was due to the strain hardening behaviour. Also, PLDGC revealed the highest absorbed energy followed by SLDGC and LMGC. Finally, PLDGC had the highest resistance to machining-induced cracking followed by SLDGC and LMGC. This study provides a quantitative basis to rank materials in terms of brittleness, ductility and resistance to mechanically-induced cracking.
Procedia CIRP, 2017
Zirconia is widely used for load-bearing functional structures in medicine and dentistry. The qua... more Zirconia is widely used for load-bearing functional structures in medicine and dentistry. The quality of engineered zirconia surfaces determines not only the fracture and fatigue behaviour but also the low temperature degradation (ageing sensitivity), bacterial colonization and bonding strength of zirconia devices. This paper reviews the current manufacturing techniques for fabrication of zirconia surfaces in biomedical applications, particularly, in tooth and joint replacements, and influences of the zirconia surface quality on their functional behaviours. It discusses emerging manufacturing techniques and challenges for fabrication of zirconia surfaces in biomedical applications.
Journal of the mechanical behavior of biomedical materials, Oct 15, 2017
This paper studied surface fracture, roughness and morphology, phase transformations, and materia... more This paper studied surface fracture, roughness and morphology, phase transformations, and material removal mechanisms of lithium metasilicate/disilicate glass ceramics (LMGC/LDGC) in CAD/CAM-milling and subsequent surface treatments. LMGC (IPS e.max CAD) blocks were milled using a chairside dental CAD/CAM milling unit and then treated in sintering, polishing and glazing processes. X-ray diffraction was performed on all processed surfaces. Scanning electron microscopy (SEM) was applied to analyse surface fracture and morphology. Surface roughness was quantitatively characterized by the arithmetic average surface roughness Ra and the maximum roughness Rz using desktop SEM-assisted morphology analytical software. The CAD/CAM milling induced extensive brittle cracks and crystal pulverization on LMGC surfaces, which indicate that the dominant removal mechanism was the fracture mode. Polishing and sintering of the milled LMGC lowered the surface roughness (ANOVA, p < 0.05), respectivel...
Volume 1: Processing, 2016
Dental caries is a ubiquitous disease and nearly 100% of the population is affected worldwide. Co... more Dental caries is a ubiquitous disease and nearly 100% of the population is affected worldwide. Consequently, reliable dental restorations are in high demand. More and more patients expect and request esthetics and biosafety, and desire metal-free prostheses. Both biocompatible and esthetic ceramics and digital processing of prostheses have been developed to meet these demands. This paper reviews the current status of abrasive machining involved in affordable digital dental ceramic restorations with regard to dental ceramic materials, dental CAD/CAM systems, and extra/intraoral dental handpiece adjustments. It highlights the importance and challenge of abrasive machining technologies in manufacturing of affordable and reliable dental restorations with cutting-edge materials.
Journal of the Mechanical Behavior of Biomedical Materials, 2017
This paper studied the surface quality (damage, morphology, and phase transformation) of yttria-s... more This paper studied the surface quality (damage, morphology, and phase transformation) of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in CAD/CAM milling, and subsequent polishing, sintering and sandblasting processes applied in dental restorations. X-ray diffraction and scanning electron microscopy (SEM) were used to scan all processed surfaces to determine phase transformations and analyse surface damage morphology, respectively. The average surface roughness (Ra) and maximum roughness (Rz) for all processed surfaces were measured using desk-top SEM-assisted morphology analytical software. X-ray diffraction patterns prove the sintering-induced monoclinic-tetragonal phase transformation while the sandblasting-induced phase transformation was not detected. The CAD/CAM milling of pre-sintered Y-TZP produced very rough surfaces with extensive fractures and cracks. Simply polishing or sintering of milled pre-sintered surfaces did not significantly improve their surface roughness (ANOVA, p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;0.05). Neither sintering-polishing of the milled surfaces could effectively improve the surface roughness (ANOVA, p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;0.05). The best surface morphology was produced in the milling-polishing-sintering process, achieving Ra=0.21±0.03µm and Rz=1.73±0.04µm, which meets the threshold for bacterial retention. Sandblasting of intaglios with smaller abrasives was recommended as larger abrasive produced visible surface defects. This study provides technical insights into process selection for Y-TZP to achieve the improved restorative quality.
Precision engineering, Jun 1, 2024
IOP Conference Series: Materials Science and Engineering, 2021
Models are useful in controlling the process effectively and efficiently in micro electro dischar... more Models are useful in controlling the process effectively and efficiently in micro electro discharge machining (Micro-EDM). There are two types of models which are empirical models and theoretical models. Most of the models are basically formulated for conductive work materials. However, nowadays there is a trend to cut nonconductive materials using micro-EDM where the models developed for conductive materials are not applicable. There are only few models that are developed to cut nonconductive materials with micro EDM but these models have limitations. In this article, models for cutting conductive materials and nonconductive materials using micro EDM are compared in view of their applications.
Advanced Materials Research, 2011
Silicon being a typical hard-brittle material is difficult to machine to a good surface finish. A... more 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 a...
Journal of the Mechanical Behavior of Biomedical Materials, Jan 31, 2024
8TH BRUNEI INTERNATIONAL CONFERENCE ON ENGINEERING AND TECHNOLOGY 2021
Statistical analysis chip thickness in high-speed end milling using simulation approach
AIP Conference Proceedings, 2023
For load-bearing structural applications in engineering and medicine, presintered and sintered yt... more For load-bearing structural applications in engineering and medicine, presintered and sintered yttria tetragonal zirconia polycrystals (YTZPs) are usually CAD/CAM shaped by soft and hard machining, respectively. However, there is a need to analytically predict their machinability to know the better machinable material. This research aims to characterize brittleness and plasticity indices evaluated in terms of elastic modulus, hardness and fracture toughness for presintered and sintered YTZPs using microindentation techniques. Six indentations were made on the presintered and sintered samples at different loads ranging from 0.098 N-19.62 N. The hardness of both samples decreased as the load was increased indicative of the normal indentation size effect (NISE) occurrence. The NISE was analyzed by the Meyer's, proportional specimen resistance (PSR), modified proportional specimen resistance (MPSR), Hays-Kendall (HK) and elastoplastic deformation (EPD) models. For both materials, the Meyer law successfully described the NISE with the Meyer's index becoming less than 2. Models of PSR, MPSR, EPD and HK gave consistent intrinsic Vickers hardnesses for presintered and sintered YTZP materials. Because of its best correlation coefficient, however, the MPSR model successfully provided the best intrinsic Vickers hardness for presintered and sintered YTZP materials. Consequently, the intrinsic Vickers hardness is 0.742 GPa and 8.90 GPa for presintered and sintered YTZPs, respectively. Also, the brittleness and plasticity indices of presintered YTZP predicted better machinability and ductility of 0.742 μm. and 40, respectively. Therefore, presintered YTZP is considered better for CAD/CAM machining than sintered YTZP. This study provides a significant insight into a fast method of ranking materials in terms of machinability and ductility for specific applications.
AIP Conference
As part of the efforts towards green and sustainable machining strategies, this research project ... more As part of the efforts towards green and sustainable machining strategies, this research project investigated the use of MQL as an alternative towards flood cooling for drilling of 1-inch cylindrical mild steel rod using High Speed Steel (HSS) drill bit with diameter of 5 mm at the hole-depth of 10 mm. For this experiment, Design Expert statistical software is used to derive Design of Experiment (DOE) under Taguchi Orthogonal Array (OA) Design for cutting speeds of 650, 1050 and 2100 rpm and feed rate of 0.1, 0.2 and 0.3 mm/rev. Then, the experimental data obtained was analysed and the cutting parameter: cooling fluid, cutting speed and feed rate does in-fact, affect the surface roughness of drilled hole. As the cutting speed increases, the surface roughness decreases and when the feed rate decreases, the surface roughness increases, and these trends occurred for both types of lubrication system used. The analysed data were then optimized to find the best condition for the smallest surface roughness. It was then discovered with the use of MQL at cutting speed of 2100 rpm and feed rate of 0.1 mm/rev resulted in the smallest surface roughness.
AIP Conference Proceedings, 2023
For load-bearing structural applications in engineering and medicine, presintered and sintered yt... more For load-bearing structural applications in engineering and medicine, presintered and sintered yttria tetragonal zirconia polycrystals (YTZPs) are usually CAD/CAM shaped by soft and hard machining, respectively. However, there is a need to analytically predict their machinability to know the better machinable material. This research aims to characterize brittleness and plasticity indices evaluated in terms of elastic modulus, hardness and fracture toughness for presintered and sintered YTZPs using microindentation techniques. Six indentations were made on the presintered and sintered samples at different loads ranging from 0.098 N-19.62 N. The hardness of both samples decreased as the load was increased indicative of the normal indentation size effect (NISE) occurrence. The NISE was analyzed by the Meyer's, proportional specimen resistance (PSR), modified proportional specimen resistance (MPSR), Hays-Kendall (HK) and elastoplastic deformation (EPD) models. For both materials, the Meyer law successfully described the NISE with the Meyer's index becoming less than 2. Models of PSR, MPSR, EPD and HK gave consistent intrinsic Vickers hardnesses for presintered and sintered YTZP materials. Because of its best correlation coefficient, however, the MPSR model successfully provided the best intrinsic Vickers hardness for presintered and sintered YTZP materials. Consequently, the intrinsic Vickers hardness is 0.742 GPa and 8.90 GPa for presintered and sintered YTZPs, respectively. Also, the brittleness and plasticity indices of presintered YTZP predicted better machinability and ductility of 0.742 μm. and 40, respectively. Therefore, presintered YTZP is considered better for CAD/CAM machining than sintered YTZP. This study provides a significant insight into a fast method of ranking materials in terms of machinability and ductility for specific applications.
aspe.net
Silicon constitutes 90% of all semiconductors and it is an important material for making devices ... more Silicon constitutes 90% of all semiconductors and it is an important material for making devices in electronics, semi-conducting and optical industries. It is used as optical components in high-resolution thermal imaging systems and also finds applications in ...
Materials Research Express
Polymer-infiltrated zirconia-ceramic composite (PIZC) comprises a pre-sintered zirconia-ceramic m... more 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...
Alao, Abdur-Rasheed (2016) Fabrication and characterization of lithium metasilicate/disilicate gl... more Alao, Abdur-Rasheed (2016) Fabrication and characterization of lithium metasilicate/disilicate glass ceramics and yttria tetragonal zirconia polycrystals for dental restorations. PhD thesis, James Cook University.
Recent Advances in Structural Integrity Analysis - Proceedings of the International Congress (APCF/SIF-2014), 2014
ABSTRACT Zirconia is a unique material widely used in engineering, medicine and dentistry as load... more ABSTRACT Zirconia is a unique material widely used in engineering, medicine and dentistry as load-bearing structures, such as mechanical bearings, orthopedic bones and joints, dental implants, crowns and bridges. Zirconia structures can be shaped either in pre-sintered or sintered states by abrasive machining tools. However, abrasive machining inevitably induces surface and sub-surface cracks in both pre-sintered and sintered zirconia structures, resulting in poor surface quality and shortened lifespans of zirconia products. To predict the machinability of zirconia materials, it is necessary to simulate their fracture resistance behaviour. This research was undertaken to predict the resistance to machining-induced cracking for pre-sintered and sintered zirconia using nanoindentation which physically mimics abrasive machining with sharp grits. Mechanical characterization of the resistance to machining-induced cracking was performed using the Sakai model which incorporates fracture energy and ductility index. The characterization was performed at a peak load of 10 mN and loading rate of 0.1-2 mN/s. The results show that pre-sintered zirconia yielded a higher ductility and better resistance to machining-induced cracking. This work suggests that pre-sintered zirconia can sustain more mechanical damage and absorb more energy and can therefore be easily machined than the sintered zirconia.
Journal of the Mechanical Behavior of Biomedical Materials, 2021
Indentation size effect (ISE) and R-curve behaviour of Li2O-SiO2 and Li2O-2SiO2 glass ceramics ar... more 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.
Journal of the Mechanical Behavior of Biomedical Materials, 2021
This paper reports on the process-fatigue relation of lithium disilicate glass ceramic (LDGC) usi... more 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 *
Ceramics International, 2021
The mechanical behaviour of pre-crystallized and crystallized zirconia-reinforced lithium silicat... more 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 < 0.05) and 163% (ANOVA, p < 0.05) on pre-crystallized and crystallized ZLS, respectively, indicating the occurrence of the reverse indentation size effect (RISE) on both materials. The fracture toughness increased with the load by 20% and 12.3% on pre-crystallized and crystallized ZLS, respectively. Hardness data of both materials were analyzed using the Meyer's, indentation-induced cracking (IIC), proportional specimen resistance (PSR), modified PSR, Hays-Kendall and elastic plastic deformation (EPD) models. The Meyer's and IIC models described the RISE behaviour of both materials satisfactorily. The PSR, Hays-Kendall and EPD models provided consistent loadindependent hardnesses while the modified PSR model gave erratic load-independent hardnesses for both materials. The continuum model provided intrinsic compressive yield strengths of both materials which were consistent with those obtained from the EPD model and the Tabor relation, implying the EPD model as the most successful. The brittleness index predicted better machinability for crystallized ZLS than pre-crystallized ZLS. Finally, the variations of hardness and fracture toughness with load might account for the different micromaterial removal mechanisms in the sharp abrasive machining of these materials.
Journal of the Mechanical Behavior of Biomedical Materials, 2019
This paper applied non-linear theory of elasticity (NLTE) to partition indentation-induced deform... more This paper applied non-linear theory of elasticity (NLTE) to partition indentation-induced deformations into elasticity and plasticity for lithium metasilicate glass ceramic (LMGC), sintered and pressed lithium disilicate glass ceramics (SLDGC and PLDGC). It also used elastic plastic fracture mechanics (EPFM) approach to analytically predict machinability for these materials. Using the Sakai's series elastic and plastic deformation model that applied NLTE, the resistances to plasticity for LMGC, SLDGC and PLDGC were extracted from their respective indentation-extracted plane strain moduli and contact hardness values. Plane strain moduli and resistances to plasticity were used to calculate elasticity and plasticity for these materials. Furthermore, the EPFM approach in the Sakai-Nowak model was applied to deconvolute resistances to machining-induced cracking for these materials. All properties were extracted at 10 mN peak load and 0.1-2 mN/s loading rates to determine the loading-rate influence on these properties. The resistances to plasticity of LMGC and SLDGC were loading rate dependent (ANOVA, p < 0.05) and the resistance to plasticity of PLDGC was loading rate independent (ANOVA, p > 0.05). The strain rate sensitivity model was used to find the intrinsic resistances to plasticity for LMGC and SLDGC. The elastic displacement/deformation components were dominant for LMGC at all loading rates. For SLDGC and PLDGC, the deformation mechanisms were dynamic with the plastic and elastic deformation components dominating at low loading and high loading rates respectively, a phenomenon attributed to indentation energies. The decrease in plastic displacements for all materials with increase in loading rate was due to the strain hardening behaviour. Also, PLDGC revealed the highest absorbed energy followed by SLDGC and LMGC. Finally, PLDGC had the highest resistance to machining-induced cracking followed by SLDGC and LMGC. This study provides a quantitative basis to rank materials in terms of brittleness, ductility and resistance to mechanically-induced cracking.
Procedia CIRP, 2017
Zirconia is widely used for load-bearing functional structures in medicine and dentistry. The qua... more Zirconia is widely used for load-bearing functional structures in medicine and dentistry. The quality of engineered zirconia surfaces determines not only the fracture and fatigue behaviour but also the low temperature degradation (ageing sensitivity), bacterial colonization and bonding strength of zirconia devices. This paper reviews the current manufacturing techniques for fabrication of zirconia surfaces in biomedical applications, particularly, in tooth and joint replacements, and influences of the zirconia surface quality on their functional behaviours. It discusses emerging manufacturing techniques and challenges for fabrication of zirconia surfaces in biomedical applications.
Journal of the mechanical behavior of biomedical materials, Oct 15, 2017
This paper studied surface fracture, roughness and morphology, phase transformations, and materia... more This paper studied surface fracture, roughness and morphology, phase transformations, and material removal mechanisms of lithium metasilicate/disilicate glass ceramics (LMGC/LDGC) in CAD/CAM-milling and subsequent surface treatments. LMGC (IPS e.max CAD) blocks were milled using a chairside dental CAD/CAM milling unit and then treated in sintering, polishing and glazing processes. X-ray diffraction was performed on all processed surfaces. Scanning electron microscopy (SEM) was applied to analyse surface fracture and morphology. Surface roughness was quantitatively characterized by the arithmetic average surface roughness Ra and the maximum roughness Rz using desktop SEM-assisted morphology analytical software. The CAD/CAM milling induced extensive brittle cracks and crystal pulverization on LMGC surfaces, which indicate that the dominant removal mechanism was the fracture mode. Polishing and sintering of the milled LMGC lowered the surface roughness (ANOVA, p < 0.05), respectivel...
Volume 1: Processing, 2016
Dental caries is a ubiquitous disease and nearly 100% of the population is affected worldwide. Co... more Dental caries is a ubiquitous disease and nearly 100% of the population is affected worldwide. Consequently, reliable dental restorations are in high demand. More and more patients expect and request esthetics and biosafety, and desire metal-free prostheses. Both biocompatible and esthetic ceramics and digital processing of prostheses have been developed to meet these demands. This paper reviews the current status of abrasive machining involved in affordable digital dental ceramic restorations with regard to dental ceramic materials, dental CAD/CAM systems, and extra/intraoral dental handpiece adjustments. It highlights the importance and challenge of abrasive machining technologies in manufacturing of affordable and reliable dental restorations with cutting-edge materials.
Journal of the Mechanical Behavior of Biomedical Materials, 2017
This paper studied the surface quality (damage, morphology, and phase transformation) of yttria-s... more This paper studied the surface quality (damage, morphology, and phase transformation) of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in CAD/CAM milling, and subsequent polishing, sintering and sandblasting processes applied in dental restorations. X-ray diffraction and scanning electron microscopy (SEM) were used to scan all processed surfaces to determine phase transformations and analyse surface damage morphology, respectively. The average surface roughness (Ra) and maximum roughness (Rz) for all processed surfaces were measured using desk-top SEM-assisted morphology analytical software. X-ray diffraction patterns prove the sintering-induced monoclinic-tetragonal phase transformation while the sandblasting-induced phase transformation was not detected. The CAD/CAM milling of pre-sintered Y-TZP produced very rough surfaces with extensive fractures and cracks. Simply polishing or sintering of milled pre-sintered surfaces did not significantly improve their surface roughness (ANOVA, p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;0.05). Neither sintering-polishing of the milled surfaces could effectively improve the surface roughness (ANOVA, p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;0.05). The best surface morphology was produced in the milling-polishing-sintering process, achieving Ra=0.21±0.03µm and Rz=1.73±0.04µm, which meets the threshold for bacterial retention. Sandblasting of intaglios with smaller abrasives was recommended as larger abrasive produced visible surface defects. This study provides technical insights into process selection for Y-TZP to achieve the improved restorative quality.