Barry Ho - Academia.edu (original) (raw)
Papers by Barry Ho
Although it is very difficult to predict stock drainage behaviour on the PM, various drainage sen... more Although it is very difficult to predict stock drainage behaviour on the PM, various drainage sensors have been developed to give some indication of performance with respect to stock drainage, and to automatically control refiners. This paper provides an overview of the existing freeness sensors and describes their operating principles, and the variables which may influence their measuring accuracy.
is a unique organization whose charitable, educational, and scientific purpose evolves from the s... more is a unique organization whose charitable, educational, and scientific purpose evolves from the singular relationship between the Institute and the pulp and paper industry which has existed since 1929. The purpose of the Institute is fulfilled through three missions, which are: o to provide high quality students with a multidisciplinary graduate educational experience which is of the highest standard of excellence recognized by the national academic community and which enables them to perform to their maximum potential in a society with a technological base; and * to sustain an international position of leadership in dynamic scientific research which is participated in by both students and faculty and which is focused on areas of significance to the pulp and paper industry; and • to contribute to the economic and technical well-being of the nation through innovative educational, informational, and technical services. ACCREDITATION The Institute of Paper Science and Technology is accredited by the Commission on Colleges of the Southern Association of Colleges and Schools to award the Master of Science and Doctor of Philosophy degrees. NOTICE AND DISCLAIMER The Institute of Paper Science and Technology (IPST) has provided a high standard of professional service and has put forth its best efforts within the time and funds available for this project. The information and conclusions are advisory and are intended only for internal use by any company who may receive this report. Each company must decide for itself the best approach to solving any problems it may have and how, or whether, this reported information should be considered in its approach. IPST does not recommend particular products, procedures, materials, or service. These are included only in the interest of completeness within a laboratory context and budgetary constraint. Actual products, procedures, materials, and services used may differ and are peculiar to the operations of each company. In no event shall IPST or its employees and agents have any obligation or liability for damages including, but not limited to, consequential damages arising out of or in connection with any company's use of or inability to use the reported information. IPST provides no warranty or guaranty of results.
Georgia journal of science, 2021
A team of researchers from Valdosta State University (VSU) and Georgia Tech (GT) have been workin... more A team of researchers from Valdosta State University (VSU) and Georgia Tech (GT) have been working on a smart community project in collaboration with the city of Valdosta and two technology industries (Applied Information and Temple) to develop a connected vehicle smart system in all 128 intersections in the city of Valdosta. This one-year study will allow the City of Valdosta and its communities in the Lowndes county areas to develop a smart and connected traffic monitoring system to improve the movement of all types of vehicles and pedestrians in a safe and efficient manner. Using the funding from Georgia Tech’s Georgia Smart Communities Initiatives we are developing a more sophisticated Traffic Monitoring Center (TMC) and involving VSU engineering students in experiential learning and and undergraduate research to gain valuable training and experience related to smart systems in traffic management. The smart system will incorporate the Travelsafely App to apply preemption for the ten fire trucks, so that they can move easily through the intersections. The App will also provide the capabilities to notify drivers about bicycle riders, pedestrians, and others drivers and motorists in the area. Also notifications will be given to the drivers that are in the school or other speed zones about the changes in traffic lights. Furthermore, if a driver is about to run a red light, the App will give him/her a warning. We have made some progress related to the installation of the hardware in the cabinets of a few traffic lights and expect that it will be completed by the mid-spring in most signalized intersections. This study will describe the advance technology used and the recent results obtained from the smart city project program in Valdosta
Georgia journal of science, 2021
The purpose of this study is to describe the results obtained from analyses of survey data and ot... more The purpose of this study is to describe the results obtained from analyses of survey data and other data corresponding to a collaborative study between Valdosta State University (VSU), Georgia Tech, the City of Valdosta, and two technology development industries (Temple and Applied Information) to develop a new traffic management system in Valdosta that will provide improved safety, connectivity, and efficiency for the community including drivers, pedestrians, bikers and all transportation methods. The goal of the smart city project is to improve traffic management with the city, engage the local community and build a platform for community members to communicate with each other for all modes of travel around the city’s 128 intersection. Students, from the engineering programs at VSU have participated in a survey data to provide their feedback related to the application of the Travelsafely App, and the current traffic conditions in Valdosta. The App is developed by Applied Information and is used for traffic related communication and connects drivers, pedestrians, emergency vehicles, traffic lights and their surrounding environment to one another using mobile devices such as smart phones. Preliminary analyses of the survey data indicate that in general, most VSU engineering students are interested in applying the technology when driving in Valdosta. However, following the COVID-19 guidelines we will determine methods of community engagement to encourage the members of the VSU and Valdosta community to participate in the survey and become more familiar with the software and its benefits when driving in and around the city of Valdosta
Georgia journal of science, 2020
Advances in unusual types of renewable energy are expanding the possibilities for different types... more Advances in unusual types of renewable energy are expanding the possibilities for different types of resources that can be used to power electronics, power plants, smart phones, and other technology. Resources such as solar and wind power are most common, but other more unusual types such as cocoa shells, dance floors that convert kinetic energy into electricity, algae lipid oils, and geothermal energy are going through advances that might make it possible to move away from fossil fuels and focus on resources that are renewable. Common sources of renewable energy such as solar power are being explored in more unique ways such as space-based solar panels. Waves and tidal energy are also experiencing advances through methods of hydro turbines
We will report on the results of an externally funded project to improve student interest in engi... more We will report on the results of an externally funded project to improve student interest in engineering using project-based teaching and learning and Tablet Pc technology. Changes were made in some of the fundamental engineering courses to include hands-on projects, field trips and also invited speakers to the classroom. The results suggest that these changes can improve retention in engineering
Georgia journal of science, 2010
Camera-based web inspection sensors have been available in the paper industry for many years. How... more Camera-based web inspection sensors have been available in the paper industry for many years. However, in recent years because of a market demand for high-quality paper products, the need for realtime flaw-detection systems has increased significantly. In addition to flaw-detection capabilities, these systems should be capable of doing defect classification (e.g., relative to size and type of flaws) as well as defect localization (providing information on location of flaws). The technique employed in flaw detection and measurement principles used in common systems are based on laser, CCD (charge coupled device) camera, or infrared technology. The study was designed to determine the capabilities of commercially available CCD camerabased systems. A CCD camera-based commercial sensor was installed on a pilot paper coater machine with the production speed capability of 1524 m/min (5000 ft/min) that could accept paper rolls with a width of 76.2 cm (30 inches). Various paper grades consisting of newsprint, coated paper, coated board, and linerboard which had typical grade-related defects were provided by various paper mills for testing. The purpose of this manuscript is to describe the operational principle, capabilities, and performance of various sensors used in paper industry in detecting various flaws and defects and to provide a summary of the results obtained using a commercial sensor.
The Engineering Graphics for Design course is one of the most important courses in freshman engin... more The Engineering Graphics for Design course is one of the most important courses in freshman engineering. However, one of the main challenges in teaching this course at Valdosta State University is handling a relatively large computer lab-based course and a wide range of skills and learning abilities in students. Many of our students are quick in learning computer tools and Commands in programs such as AutoCAD. Also, some students have good CAD drawing background from high school. But many have difficulty understanding 2-D or 3-D geometric and angular relations, geometric and trigonometric laws, and logical reasoning associated with fundamentals of engineering graphic. Recently, we have explored various pedagogical techniques to allow students to work on various self-paced CAD projects that are related to their field of interest in engineering. Also, we have included some team-based filed projects to increase interaction and collaborations among students. Furthermore, we added many online resources in D2L, and increased in-class and out-of-class support for students. Initial results shows an increased student success and course satisfaction among the students
Georgia journal of science, 2020
This study focuses on the design process and analysis of a hydraulic valve used to direct flow of... more This study focuses on the design process and analysis of a hydraulic valve used to direct flow of fluids with a low viscosity. Using Autodesk Inventor, a valve was designed to regulate the flow of fluids such as gasses or liquids with the use of mechanical levers and springs. While designing this valve, constraints and regulations were provided, along with the purpose of the machine, in order to ensure that the problem was being solved using a mechanical valve and not a different type of machine or tool. Constraints included size, material cost, and the project must have had the ability to direct and block the flow of fluids. A stress analysis and parametric analysis will be used on the valve. The stress analysis is to see where stress will be applied to the valve and how well the materials that were chosen preform. The parametric analysis will show how the valve reacts to different tasks and conditions, such as, different fluid types, temperatures, and pressures
The International journal of prosthodontics
The objective of this study was to analyze the relative effect of loading site, occlusal thicknes... more The objective of this study was to analyze the relative effect of loading site, occlusal thickness, ceramic flaws, elastic modulus of the cement, and voids in the cement layer on tensile stress that develops in molar glass-ceramic crowns under applied loads. Finite-element stress analyses were performed. Resin cement with a thickness of 0.05 mm was used. A central conical flaw (0.05 mm [diameter] x 0.05 mm) and a circular grooved flaw located under the cusp tips were included in all flaw cases. A void space confined within the occlusal region of the cement layer was also included in selected cases. For a ceramic thickness of 0.5 mm and a vertical distributed load applied at a distance of 1.3 mm from the vertical axis, the maximum tensile stresses were 100 MPa for a crown with flaws and a void, 87 MPa for a crown with no flaws and a void, and 75 MPa for a crown with flaws and no void. For a 1.5-mm-thick crown with flaws and a void, the tensile stress decreased to 22 MPa. When the loa...
Journal of Dental Research, 1993
The objective of this study was to test the hypothesis that quenching of porcelain in silicone oi... more The objective of this study was to test the hypothesis that quenching of porcelain in silicone oil rather than in compressed air will significantly increase the flexure strength by reducing the potential for crack formation during transient cooling. A secondary hypothesis to be tested is that the initial tempering temperature can be reduced significantly below the porcelain maturing temperature of 982°C but well above Tg without a decrease in strength. Opaque-body porcelain disks, 16 mm in diameter and 2 mm in thickness, with a thermal contraction mismatch (Δα) of -1.5,0, and +3.2 ppm/°C were tempered from initial temperatures of 650, 750, 850, and 982°C in silicone oil with kinematic viscosities of 50,1000, and 5000 centistokes. Porcelain disks were also subjected to three cooling procedures in air: slow cooling in a furnace (SC), free convective cooling in a laboratory bench (FC), and tempering (T) by blasting the surface of body porcelain with air. The crack size induced by a Vic...
Journal of Dental Research, 1988
For ceramic crowns, the recommended depth of tooth reduction from the incisal edge of anterior te... more For ceramic crowns, the recommended depth of tooth reduction from the incisal edge of anterior teeth is 1.5 mm to 2. 0 mm. Although some prosthodontists have suggested that incisal heights of ceramic which exceed 2 mm are associated with dangerously high intra-oral stresses, this theory has not been verified. The objective of this study was to test the hypothesis that the stress distribution in ceramic crowns designed for a prepared maxillary central incisor which are subjected to applied loading is relatively insensitive to the incisal length of ceramic. Finite element stress analyses were performed on three crown designs loaded with a horizontal or vertical force of 200 N along the lingual surface near the incisal edge. Ceramic crowns for maxillary central incisors were modeled with incisal lengths of 1.0 mm (Case I), 1.9 mm (Case II), and 4.0 mm (Case III). Zinc phosphate cement with a film thickness of 30 μm was included for each case. Plane-stress finite element analyses indica...
Journal of Dental Research, 1991
The objective of this study was to test the hypothesis that tempering stress can retard the growt... more The objective of this study was to test the hypothesis that tempering stress can retard the growth of surface cracks in layered porcelain discs with variable levels of contraction mismatch. Porcelain discs, 16 mm in diameter and 2 mm thick, were prepared with a 0.5-mm-thick layer of opaque porcelain (0) and a 1.5-mm-thick layer of body porcelain (B). The materials were selected to produce contraction coefficient differences, ao-aB, of +3.2, +0.7, -0.9, and -1.5 ppm/°C. Body porcelain discs with a thickness of 2 mm were used as the thermally compatible control specimens (Δα=0). The discs were fired to the maturing temperature of body porcelain (982°C) and were then subjected to three cooling procedures: slow cooling (SC) in a furnace, fast cooling (FC) in air, and tempering (T) by blasting the surface of the body porcelain with compressed and dried air for 90 s. The dimensions of cracks induced by a Vickers microhardness indenter under a load of 4.9 N were measured at baseline and si...
Journal of Biomedical Materials Research, 1998
The feasibility of simple tests or analytical methods for prediction of residual stress states in... more The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.
Journal of Applied Polymer Science, 1994
tî 4 _ The effects of thermal and mechanical fatigue on the flexural strength of G40-600/ PMR-15 ... more tî 4 _ The effects of thermal and mechanical fatigue on the flexural strength of G40-600/ PMR-15 cross-ply laminates with ply orientations of (02,902)2S and (902,02)2s are examined. The relative importance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45. Acoustic emission signals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine specimens for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, regardless of ply orientation, span-to-depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0° ply of specimens with high span-todepth ratios. Because of the complex failure modes, the flexural test results represent the "apparent" strengths rather than the true flexural or shear strengths for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strains during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32 to 260 °C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (-85 to 85 °C, 500 cycles. Mechanical cycling Polvmer matrix composites; Acoustic emission, Flexure test; Thermal cycling, Fatigue 24
Although it is very difficult to predict stock drainage behaviour on the PM, various drainage sen... more Although it is very difficult to predict stock drainage behaviour on the PM, various drainage sensors have been developed to give some indication of performance with respect to stock drainage, and to automatically control refiners. This paper provides an overview of the existing freeness sensors and describes their operating principles, and the variables which may influence their measuring accuracy.
is a unique organization whose charitable, educational, and scientific purpose evolves from the s... more is a unique organization whose charitable, educational, and scientific purpose evolves from the singular relationship between the Institute and the pulp and paper industry which has existed since 1929. The purpose of the Institute is fulfilled through three missions, which are: o to provide high quality students with a multidisciplinary graduate educational experience which is of the highest standard of excellence recognized by the national academic community and which enables them to perform to their maximum potential in a society with a technological base; and * to sustain an international position of leadership in dynamic scientific research which is participated in by both students and faculty and which is focused on areas of significance to the pulp and paper industry; and • to contribute to the economic and technical well-being of the nation through innovative educational, informational, and technical services. ACCREDITATION The Institute of Paper Science and Technology is accredited by the Commission on Colleges of the Southern Association of Colleges and Schools to award the Master of Science and Doctor of Philosophy degrees. NOTICE AND DISCLAIMER The Institute of Paper Science and Technology (IPST) has provided a high standard of professional service and has put forth its best efforts within the time and funds available for this project. The information and conclusions are advisory and are intended only for internal use by any company who may receive this report. Each company must decide for itself the best approach to solving any problems it may have and how, or whether, this reported information should be considered in its approach. IPST does not recommend particular products, procedures, materials, or service. These are included only in the interest of completeness within a laboratory context and budgetary constraint. Actual products, procedures, materials, and services used may differ and are peculiar to the operations of each company. In no event shall IPST or its employees and agents have any obligation or liability for damages including, but not limited to, consequential damages arising out of or in connection with any company's use of or inability to use the reported information. IPST provides no warranty or guaranty of results.
Georgia journal of science, 2021
A team of researchers from Valdosta State University (VSU) and Georgia Tech (GT) have been workin... more A team of researchers from Valdosta State University (VSU) and Georgia Tech (GT) have been working on a smart community project in collaboration with the city of Valdosta and two technology industries (Applied Information and Temple) to develop a connected vehicle smart system in all 128 intersections in the city of Valdosta. This one-year study will allow the City of Valdosta and its communities in the Lowndes county areas to develop a smart and connected traffic monitoring system to improve the movement of all types of vehicles and pedestrians in a safe and efficient manner. Using the funding from Georgia Tech’s Georgia Smart Communities Initiatives we are developing a more sophisticated Traffic Monitoring Center (TMC) and involving VSU engineering students in experiential learning and and undergraduate research to gain valuable training and experience related to smart systems in traffic management. The smart system will incorporate the Travelsafely App to apply preemption for the ten fire trucks, so that they can move easily through the intersections. The App will also provide the capabilities to notify drivers about bicycle riders, pedestrians, and others drivers and motorists in the area. Also notifications will be given to the drivers that are in the school or other speed zones about the changes in traffic lights. Furthermore, if a driver is about to run a red light, the App will give him/her a warning. We have made some progress related to the installation of the hardware in the cabinets of a few traffic lights and expect that it will be completed by the mid-spring in most signalized intersections. This study will describe the advance technology used and the recent results obtained from the smart city project program in Valdosta
Georgia journal of science, 2021
The purpose of this study is to describe the results obtained from analyses of survey data and ot... more The purpose of this study is to describe the results obtained from analyses of survey data and other data corresponding to a collaborative study between Valdosta State University (VSU), Georgia Tech, the City of Valdosta, and two technology development industries (Temple and Applied Information) to develop a new traffic management system in Valdosta that will provide improved safety, connectivity, and efficiency for the community including drivers, pedestrians, bikers and all transportation methods. The goal of the smart city project is to improve traffic management with the city, engage the local community and build a platform for community members to communicate with each other for all modes of travel around the city’s 128 intersection. Students, from the engineering programs at VSU have participated in a survey data to provide their feedback related to the application of the Travelsafely App, and the current traffic conditions in Valdosta. The App is developed by Applied Information and is used for traffic related communication and connects drivers, pedestrians, emergency vehicles, traffic lights and their surrounding environment to one another using mobile devices such as smart phones. Preliminary analyses of the survey data indicate that in general, most VSU engineering students are interested in applying the technology when driving in Valdosta. However, following the COVID-19 guidelines we will determine methods of community engagement to encourage the members of the VSU and Valdosta community to participate in the survey and become more familiar with the software and its benefits when driving in and around the city of Valdosta
Georgia journal of science, 2020
Advances in unusual types of renewable energy are expanding the possibilities for different types... more Advances in unusual types of renewable energy are expanding the possibilities for different types of resources that can be used to power electronics, power plants, smart phones, and other technology. Resources such as solar and wind power are most common, but other more unusual types such as cocoa shells, dance floors that convert kinetic energy into electricity, algae lipid oils, and geothermal energy are going through advances that might make it possible to move away from fossil fuels and focus on resources that are renewable. Common sources of renewable energy such as solar power are being explored in more unique ways such as space-based solar panels. Waves and tidal energy are also experiencing advances through methods of hydro turbines
We will report on the results of an externally funded project to improve student interest in engi... more We will report on the results of an externally funded project to improve student interest in engineering using project-based teaching and learning and Tablet Pc technology. Changes were made in some of the fundamental engineering courses to include hands-on projects, field trips and also invited speakers to the classroom. The results suggest that these changes can improve retention in engineering
Georgia journal of science, 2010
Camera-based web inspection sensors have been available in the paper industry for many years. How... more Camera-based web inspection sensors have been available in the paper industry for many years. However, in recent years because of a market demand for high-quality paper products, the need for realtime flaw-detection systems has increased significantly. In addition to flaw-detection capabilities, these systems should be capable of doing defect classification (e.g., relative to size and type of flaws) as well as defect localization (providing information on location of flaws). The technique employed in flaw detection and measurement principles used in common systems are based on laser, CCD (charge coupled device) camera, or infrared technology. The study was designed to determine the capabilities of commercially available CCD camerabased systems. A CCD camera-based commercial sensor was installed on a pilot paper coater machine with the production speed capability of 1524 m/min (5000 ft/min) that could accept paper rolls with a width of 76.2 cm (30 inches). Various paper grades consisting of newsprint, coated paper, coated board, and linerboard which had typical grade-related defects were provided by various paper mills for testing. The purpose of this manuscript is to describe the operational principle, capabilities, and performance of various sensors used in paper industry in detecting various flaws and defects and to provide a summary of the results obtained using a commercial sensor.
The Engineering Graphics for Design course is one of the most important courses in freshman engin... more The Engineering Graphics for Design course is one of the most important courses in freshman engineering. However, one of the main challenges in teaching this course at Valdosta State University is handling a relatively large computer lab-based course and a wide range of skills and learning abilities in students. Many of our students are quick in learning computer tools and Commands in programs such as AutoCAD. Also, some students have good CAD drawing background from high school. But many have difficulty understanding 2-D or 3-D geometric and angular relations, geometric and trigonometric laws, and logical reasoning associated with fundamentals of engineering graphic. Recently, we have explored various pedagogical techniques to allow students to work on various self-paced CAD projects that are related to their field of interest in engineering. Also, we have included some team-based filed projects to increase interaction and collaborations among students. Furthermore, we added many online resources in D2L, and increased in-class and out-of-class support for students. Initial results shows an increased student success and course satisfaction among the students
Georgia journal of science, 2020
This study focuses on the design process and analysis of a hydraulic valve used to direct flow of... more This study focuses on the design process and analysis of a hydraulic valve used to direct flow of fluids with a low viscosity. Using Autodesk Inventor, a valve was designed to regulate the flow of fluids such as gasses or liquids with the use of mechanical levers and springs. While designing this valve, constraints and regulations were provided, along with the purpose of the machine, in order to ensure that the problem was being solved using a mechanical valve and not a different type of machine or tool. Constraints included size, material cost, and the project must have had the ability to direct and block the flow of fluids. A stress analysis and parametric analysis will be used on the valve. The stress analysis is to see where stress will be applied to the valve and how well the materials that were chosen preform. The parametric analysis will show how the valve reacts to different tasks and conditions, such as, different fluid types, temperatures, and pressures
The International journal of prosthodontics
The objective of this study was to analyze the relative effect of loading site, occlusal thicknes... more The objective of this study was to analyze the relative effect of loading site, occlusal thickness, ceramic flaws, elastic modulus of the cement, and voids in the cement layer on tensile stress that develops in molar glass-ceramic crowns under applied loads. Finite-element stress analyses were performed. Resin cement with a thickness of 0.05 mm was used. A central conical flaw (0.05 mm [diameter] x 0.05 mm) and a circular grooved flaw located under the cusp tips were included in all flaw cases. A void space confined within the occlusal region of the cement layer was also included in selected cases. For a ceramic thickness of 0.5 mm and a vertical distributed load applied at a distance of 1.3 mm from the vertical axis, the maximum tensile stresses were 100 MPa for a crown with flaws and a void, 87 MPa for a crown with no flaws and a void, and 75 MPa for a crown with flaws and no void. For a 1.5-mm-thick crown with flaws and a void, the tensile stress decreased to 22 MPa. When the loa...
Journal of Dental Research, 1993
The objective of this study was to test the hypothesis that quenching of porcelain in silicone oi... more The objective of this study was to test the hypothesis that quenching of porcelain in silicone oil rather than in compressed air will significantly increase the flexure strength by reducing the potential for crack formation during transient cooling. A secondary hypothesis to be tested is that the initial tempering temperature can be reduced significantly below the porcelain maturing temperature of 982°C but well above Tg without a decrease in strength. Opaque-body porcelain disks, 16 mm in diameter and 2 mm in thickness, with a thermal contraction mismatch (Δα) of -1.5,0, and +3.2 ppm/°C were tempered from initial temperatures of 650, 750, 850, and 982°C in silicone oil with kinematic viscosities of 50,1000, and 5000 centistokes. Porcelain disks were also subjected to three cooling procedures in air: slow cooling in a furnace (SC), free convective cooling in a laboratory bench (FC), and tempering (T) by blasting the surface of body porcelain with air. The crack size induced by a Vic...
Journal of Dental Research, 1988
For ceramic crowns, the recommended depth of tooth reduction from the incisal edge of anterior te... more For ceramic crowns, the recommended depth of tooth reduction from the incisal edge of anterior teeth is 1.5 mm to 2. 0 mm. Although some prosthodontists have suggested that incisal heights of ceramic which exceed 2 mm are associated with dangerously high intra-oral stresses, this theory has not been verified. The objective of this study was to test the hypothesis that the stress distribution in ceramic crowns designed for a prepared maxillary central incisor which are subjected to applied loading is relatively insensitive to the incisal length of ceramic. Finite element stress analyses were performed on three crown designs loaded with a horizontal or vertical force of 200 N along the lingual surface near the incisal edge. Ceramic crowns for maxillary central incisors were modeled with incisal lengths of 1.0 mm (Case I), 1.9 mm (Case II), and 4.0 mm (Case III). Zinc phosphate cement with a film thickness of 30 μm was included for each case. Plane-stress finite element analyses indica...
Journal of Dental Research, 1991
The objective of this study was to test the hypothesis that tempering stress can retard the growt... more The objective of this study was to test the hypothesis that tempering stress can retard the growth of surface cracks in layered porcelain discs with variable levels of contraction mismatch. Porcelain discs, 16 mm in diameter and 2 mm thick, were prepared with a 0.5-mm-thick layer of opaque porcelain (0) and a 1.5-mm-thick layer of body porcelain (B). The materials were selected to produce contraction coefficient differences, ao-aB, of +3.2, +0.7, -0.9, and -1.5 ppm/°C. Body porcelain discs with a thickness of 2 mm were used as the thermally compatible control specimens (Δα=0). The discs were fired to the maturing temperature of body porcelain (982°C) and were then subjected to three cooling procedures: slow cooling (SC) in a furnace, fast cooling (FC) in air, and tempering (T) by blasting the surface of the body porcelain with compressed and dried air for 90 s. The dimensions of cracks induced by a Vickers microhardness indenter under a load of 4.9 N were measured at baseline and si...
Journal of Biomedical Materials Research, 1998
The feasibility of simple tests or analytical methods for prediction of residual stress states in... more The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.
Journal of Applied Polymer Science, 1994
tî 4 _ The effects of thermal and mechanical fatigue on the flexural strength of G40-600/ PMR-15 ... more tî 4 _ The effects of thermal and mechanical fatigue on the flexural strength of G40-600/ PMR-15 cross-ply laminates with ply orientations of (02,902)2S and (902,02)2s are examined. The relative importance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45. Acoustic emission signals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine specimens for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, regardless of ply orientation, span-to-depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0° ply of specimens with high span-todepth ratios. Because of the complex failure modes, the flexural test results represent the "apparent" strengths rather than the true flexural or shear strengths for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strains during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32 to 260 °C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (-85 to 85 °C, 500 cycles. Mechanical cycling Polvmer matrix composites; Acoustic emission, Flexure test; Thermal cycling, Fatigue 24