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Jonathan Lawrence - One of the best experts on this subject based on the ideXlab platform.
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evaluation of fracture toughness of zro2 and si3n4 engineering ceramics following co2 and fibre laser surface treatment
Optics and Lasers in Engineering, 2011Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:The fracture toughness property (K1c) of Si3N4 and ZrO2 engineering ceramics was investigated by means of CO2 and a fibre laser surface treatment. Near surface modifications in the hardness was investigated by employing the Vickers indentation method. Crack lengths and geometry were then measured by using the optical. A co-ordinate measuring machine was used to investigate the diamond indentations and to measure the lengths of the cracks. Thereafter, computational and analytical methods were employed to determine the K1C. An increase in the K1C of both ceramics was found by the CO2 and the fibre laser surface treatment in comparison to the as-received surfaces. The K1C of the CO2 laser radiated surface of the Si3N4 was over 3 % higher in comparison to that of the fibre laser treated surface. This was by softening of the near surface layer of the Si3N4 which comprised of lower in hardness, which in turn increased the crack resistance. The effects were not similar with the ZrO2 ceramic to that of the Si3N4 as the fibre laser radiation in this case had produced a rise of 34% compared to that of the CO2 laser radiation. This occurred due to propagation of lower crack resulting from the Vickers indentation test during the fibre laser surface treatment which inherently affected the end K1C though an induced compressive stress layer. The K1C modification of the two ceramics treated by the CO2 and the fibre laser was also believed to be influenced by the different laser wavelength and its absorption co-efficient, the beam delivery system as well as the differences in the brightness of the two lasers used.
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fracture toughness modifications by means of co2 laser beam surface processing of a silicon nitride engineering ceramic
36th International MATADOR Conference, 2010Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:Surface treatment of an Si3N4 engineering ceramic with a CO2 laser was carried out to identify changes in the fracture toughness (K1c). A Vickers macro hardness indentation method was adopted to determine the K1C prior to and after the CO2 laser treatment. After determination of the surface integrity, crack geometry, crack lengths and the dimensions of the diamond indentations, computational and analytical methods were employed to calculate the K1c. A decrease in the surface hardness of nearly 7% and of 44% in the resulting crack lengths was found after laser treatment. This inherently led to a 64% increase in the K1c for the Si3N4. This could have occurred due to melting and redistribution of the melt zone which softened the near (top) surface layer forming a degree of oxidation, causing the surface of the engineering ceramic to transform into a new composition.
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fracture toughness modification by using a fibre laser surface treatment of a silicon nitride engineering ceramic
Journal of Materials Science, 2010Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:Surface treatment of a silicon nitride (Si3N4) engineering ceramic with fibre laser radiation was conducted to identify changes in the fracture toughness as measured by K1c. A Vickers macro-hardness indentation method was adopted to determine the K1c of the Si3N4 before and after fibre laser surface treatment. Optical and a scanning electron microscopy (SEM), a co-ordinate measuring machine and a focus variation technique were used to observe and measure the dimensions of the Vickers indentation, the resulting crack lengths, as well as the crack geometry within the as-received and fibre laser-treated Si3N4. Thereafter, computational and analytical methods were employed to determine the K1c using various empirical equations. The equation K1c = 0.016 (E/Hv)1/2 (P/c3/2) produced most accurate results in generating K1c values within the range from 4 to 6 MPa m1/2. From this it was found that the indentation load, hardness, along with the resulting crack lengths in particular, were the most influential parameters within the K1c equation used. An increase in the near surface hardness of 4% was found with the Si3N4 in comparison with the as-received surface, which meant that the fibre laser-treated surface of the Si3N4 became harder and more brittle, indicating that the surface was more prone to cracking after the fibre laser treatment. Yet, the resulting crack lengths from the Vickers indentation tests were reduced by 37% for the Si3N4 which in turn led to increase in the K1c by 47% in comparison with the as-received surface. It is postulated that the fibre laser treatment induced a compressive stress layer by gaining an increase in the dislocation movement during elevated temperatures from the fibre laser surface processing. This inherently increased the compressive stress within the Si3N4 and minimized the crack propagation during the Vickers indentation test, which led to the fibre laser-radiated surface of the Si3N4 engineering ceramic to have more resistance to crack propagation.
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laser surface treatment of engineering ceramics and the effects thereof on fracture toughness
28th International Congress on Applications of Lasers and Electro-Optics ICALEO 2009, 2009Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:Surface treatment of Si3N4 and ZrO2 engineering ceramics with a CO2 laser and a fibre laser was conducted to identify changes in the fracture toughness (K1c). Vickers macro hardness indentation tests were employed prior to and after the laser treatment to investigate the near surface changes in the hardness of the engineering ceramics. Optical microscopy was then used to observe the near surface integrity, crack lengths and crack geometry within the engineering ceramics. A co-ordinate measuring machine was used to observe the diamond indentations and to measure the lengths of the cracks in the ceramics. Thereafter, computational and analytical methods were employed to determine the K1c. A decrease in the near surface hardness and the resulting crack lengths was found with both materials after the laser treatment. This in turn led to increase in the K1c for both engineering ceramics. A rise in K1c of 64 % for Si3N4 and 40 % was obtained for ZrO2 ceramics using the CO2 laser treatment. Fibre laser treatment induced 50 % increase with ZrO2 and 51 % with Si3N4 ceramics. The likely cause of this increase is the softening of the near (top) surface layer through some degree of melting and redistribution of the melt zone, along with surface oxidation that changed the engineering ceramics composition.Surface treatment of Si3N4 and ZrO2 engineering ceramics with a CO2 laser and a fibre laser was conducted to identify changes in the fracture toughness (K1c). Vickers macro hardness indentation tests were employed prior to and after the laser treatment to investigate the near surface changes in the hardness of the engineering ceramics. Optical microscopy was then used to observe the near surface integrity, crack lengths and crack geometry within the engineering ceramics. A co-ordinate measuring machine was used to observe the diamond indentations and to measure the lengths of the cracks in the ceramics. Thereafter, computational and analytical methods were employed to determine the K1c. A decrease in the near surface hardness and the resulting crack lengths was found with both materials after the laser treatment. This in turn led to increase in the K1c for both engineering ceramics. A rise in K1c of 64 % for Si3N4 and 40 % was obtained for ZrO2 ceramics using the CO2 laser treatment. Fibre laser treatment...
Brian R Lawn - One of the best experts on this subject based on the ideXlab platform.
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transverse fracture of brittle bilayers relevance to failure of all ceramic dental crowns
Journal of Biomedical Materials Research Part B, 2006Co-Authors: Sanjit Bhowmick, Ilja Hermann, Brian R LawnAbstract:This study examines the behavior of cracks approaching interfaces in all-ceramic dental crown-like bilayers. Flat specimens are fabricated by fusing porcelain veneers onto yttria-tetragonal-zirconia-polycrystal (Y-TZP) and alumina core ceramic plates, with veneer/core matching to minimize residual thermal expansion mismatch stresses. Vickers indentations are placed on either side of the interfaces, at systematically decreasing distances, so that the lead corner cracks approach and intersect the interfaces in a normal orientation. Cracks originating in the porcelain arrest at the boundaries and, after further diminution in indentation distance, deflect along the interface without penetration into the tough core ceramic. Cracks initiating in the core ceramic pass unimpeded into the weaker porcelain without deflection, and with abrupt increase in crack size. These latter cracks, because of their lack of containment within the core layer, are regarded as especially dangerous. Implications concerning the design of optimal dental crowns in relation to materials optimization are considered. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
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fatigue sensitivity of y tzp to microscale sharp contact flaws
Journal of Biomedical Materials Research Part B, 2005Co-Authors: Yu Zhang, Brian R LawnAbstract:The strength degrading effects of sharp-contact damage are examined for Y-TZP ceramic plates bonded to a plastic substrate. Contacts are made with Vickers and Berkovich diamond indenters at low loads (0.1 N to 100 N) in the ceramic lower surfaces prior to bonding to the substrates. The indentations remain in the subthreshold region, that is, without visible corner radial cracks, over the lower region (< 10 N) of the load range. A concentrated load is then applied sinusoidally to the ceramic upper surface, with the loading axis centered on the subsurface indentation flaw, thereby subjecting the flaw to cyclic tension. Relative to polished surfaces, the indentations diminish the single-cycle strength by an amount that increases with increasing indentation load. The critical number of cycles required to cause failure from the indentation flaws is then measured at specified maximum lower surface tensile stresses. At each indentation load, the strength of the ceramic plates diminishes with increased cycling. The scale of degradation is compared with that from previous studies on Y-TZP surfaces containing larger-scale surface damage: sandblast damage, as used in dental crown prepara- tion; and blunt-contact trauma from a spherical indenter at 3000 N. These other damage modes are shown to be equivalent in their strength-degrading capacity to diamond pyramid indentations in the microscale load range 0.1 N to 1 N, attesting to the highly deleterious nature of sharp particulate contacts. The mechanism of fatigue is considered in terms of microcrack evolution within the indentation damage zone. © 2004 Wiley Periodicals, Inc.* J Biomed Mater Res Part B: Appl Biomater 72B: 388 -392, 2005
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thermal shock resistance of silicon nitrides using an indentation quench test
Journal of the American Ceramic Society, 2004Co-Authors: Seung Kun Lee, James D Moretti, Michael J Readey, Brian R LawnAbstract:Thermal shock resistance of silicon nitrides is investigated using an indentation–quench method. Four commercially available silicon nitrides with different microstructures are investigated. The extension of Vickers radial cracks is measured as a function of quenching temperature for each material, up to the critical temperature for failure. An indentation fracture mechanics analysis is used to account for the crack responses, with due allowance for R-curve behavior. The analysis confirms the important role of microstructure in thermal shock resistance.
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fatigue sensitivity of y tzp to microscale sharp contact flaws
Journal of Biomedical Materials Research, 2004Co-Authors: Yu Zhang, Brian R LawnAbstract:The strength degrading effects of sharp-contact damage are examined for Y-TZP ceramic plates bonded to a plastic substrate. Contacts are made with Vickers and Berkovich diamond indenters at low loads (0.1 N to 100 N) in the ceramic lower surfaces prior to bonding to the substrates. The indentations remain in the subthreshold region, that is, without visible corner radial cracks, over the lower region (< 10 N) of the load range. A concentrated load is then applied sinusoidally to the ceramic upper surface, with the loading axis centered on the subsurface indentation flaw, thereby subjecting the flaw to cyclic tension. Relative to polished surfaces, the indentations diminish the single-cycle strength by an amount that increases with increasing indentation load. The critical number of cycles required to cause failure from the indentation flaws is then measured at specified maximum lower surface tensile stresses. At each indentation load, the strength of the ceramic plates diminishes with increased cycling. The scale of degradation is compared with that from previous studies on Y-TZP surfaces containing larger-scale surface damage: sandblast damage, as used in dental crown preparation; and blunt-contact trauma from a spherical indenter at 3000 N. These other damage modes are shown to be equivalent in their strength-degrading capacity to diamond pyramid indentations in the microscale load range 0.1 N to 1 N, attesting to the highly deleterious nature of sharp particulate contacts. The mechanism of fatigue is considered in terms of microcrack evolution within the indentation damage zone.
Pratik Shukla - One of the best experts on this subject based on the ideXlab platform.
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evaluation of fracture toughness of zro2 and si3n4 engineering ceramics following co2 and fibre laser surface treatment
Optics and Lasers in Engineering, 2011Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:The fracture toughness property (K1c) of Si3N4 and ZrO2 engineering ceramics was investigated by means of CO2 and a fibre laser surface treatment. Near surface modifications in the hardness was investigated by employing the Vickers indentation method. Crack lengths and geometry were then measured by using the optical. A co-ordinate measuring machine was used to investigate the diamond indentations and to measure the lengths of the cracks. Thereafter, computational and analytical methods were employed to determine the K1C. An increase in the K1C of both ceramics was found by the CO2 and the fibre laser surface treatment in comparison to the as-received surfaces. The K1C of the CO2 laser radiated surface of the Si3N4 was over 3 % higher in comparison to that of the fibre laser treated surface. This was by softening of the near surface layer of the Si3N4 which comprised of lower in hardness, which in turn increased the crack resistance. The effects were not similar with the ZrO2 ceramic to that of the Si3N4 as the fibre laser radiation in this case had produced a rise of 34% compared to that of the CO2 laser radiation. This occurred due to propagation of lower crack resulting from the Vickers indentation test during the fibre laser surface treatment which inherently affected the end K1C though an induced compressive stress layer. The K1C modification of the two ceramics treated by the CO2 and the fibre laser was also believed to be influenced by the different laser wavelength and its absorption co-efficient, the beam delivery system as well as the differences in the brightness of the two lasers used.
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fracture toughness modifications by means of co2 laser beam surface processing of a silicon nitride engineering ceramic
36th International MATADOR Conference, 2010Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:Surface treatment of an Si3N4 engineering ceramic with a CO2 laser was carried out to identify changes in the fracture toughness (K1c). A Vickers macro hardness indentation method was adopted to determine the K1C prior to and after the CO2 laser treatment. After determination of the surface integrity, crack geometry, crack lengths and the dimensions of the diamond indentations, computational and analytical methods were employed to calculate the K1c. A decrease in the surface hardness of nearly 7% and of 44% in the resulting crack lengths was found after laser treatment. This inherently led to a 64% increase in the K1c for the Si3N4. This could have occurred due to melting and redistribution of the melt zone which softened the near (top) surface layer forming a degree of oxidation, causing the surface of the engineering ceramic to transform into a new composition.
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fracture toughness modification by using a fibre laser surface treatment of a silicon nitride engineering ceramic
Journal of Materials Science, 2010Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:Surface treatment of a silicon nitride (Si3N4) engineering ceramic with fibre laser radiation was conducted to identify changes in the fracture toughness as measured by K1c. A Vickers macro-hardness indentation method was adopted to determine the K1c of the Si3N4 before and after fibre laser surface treatment. Optical and a scanning electron microscopy (SEM), a co-ordinate measuring machine and a focus variation technique were used to observe and measure the dimensions of the Vickers indentation, the resulting crack lengths, as well as the crack geometry within the as-received and fibre laser-treated Si3N4. Thereafter, computational and analytical methods were employed to determine the K1c using various empirical equations. The equation K1c = 0.016 (E/Hv)1/2 (P/c3/2) produced most accurate results in generating K1c values within the range from 4 to 6 MPa m1/2. From this it was found that the indentation load, hardness, along with the resulting crack lengths in particular, were the most influential parameters within the K1c equation used. An increase in the near surface hardness of 4% was found with the Si3N4 in comparison with the as-received surface, which meant that the fibre laser-treated surface of the Si3N4 became harder and more brittle, indicating that the surface was more prone to cracking after the fibre laser treatment. Yet, the resulting crack lengths from the Vickers indentation tests were reduced by 37% for the Si3N4 which in turn led to increase in the K1c by 47% in comparison with the as-received surface. It is postulated that the fibre laser treatment induced a compressive stress layer by gaining an increase in the dislocation movement during elevated temperatures from the fibre laser surface processing. This inherently increased the compressive stress within the Si3N4 and minimized the crack propagation during the Vickers indentation test, which led to the fibre laser-radiated surface of the Si3N4 engineering ceramic to have more resistance to crack propagation.
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laser surface treatment of engineering ceramics and the effects thereof on fracture toughness
28th International Congress on Applications of Lasers and Electro-Optics ICALEO 2009, 2009Co-Authors: Pratik Shukla, Jonathan LawrenceAbstract:Surface treatment of Si3N4 and ZrO2 engineering ceramics with a CO2 laser and a fibre laser was conducted to identify changes in the fracture toughness (K1c). Vickers macro hardness indentation tests were employed prior to and after the laser treatment to investigate the near surface changes in the hardness of the engineering ceramics. Optical microscopy was then used to observe the near surface integrity, crack lengths and crack geometry within the engineering ceramics. A co-ordinate measuring machine was used to observe the diamond indentations and to measure the lengths of the cracks in the ceramics. Thereafter, computational and analytical methods were employed to determine the K1c. A decrease in the near surface hardness and the resulting crack lengths was found with both materials after the laser treatment. This in turn led to increase in the K1c for both engineering ceramics. A rise in K1c of 64 % for Si3N4 and 40 % was obtained for ZrO2 ceramics using the CO2 laser treatment. Fibre laser treatment induced 50 % increase with ZrO2 and 51 % with Si3N4 ceramics. The likely cause of this increase is the softening of the near (top) surface layer through some degree of melting and redistribution of the melt zone, along with surface oxidation that changed the engineering ceramics composition.Surface treatment of Si3N4 and ZrO2 engineering ceramics with a CO2 laser and a fibre laser was conducted to identify changes in the fracture toughness (K1c). Vickers macro hardness indentation tests were employed prior to and after the laser treatment to investigate the near surface changes in the hardness of the engineering ceramics. Optical microscopy was then used to observe the near surface integrity, crack lengths and crack geometry within the engineering ceramics. A co-ordinate measuring machine was used to observe the diamond indentations and to measure the lengths of the cracks in the ceramics. Thereafter, computational and analytical methods were employed to determine the K1c. A decrease in the near surface hardness and the resulting crack lengths was found with both materials after the laser treatment. This in turn led to increase in the K1c for both engineering ceramics. A rise in K1c of 64 % for Si3N4 and 40 % was obtained for ZrO2 ceramics using the CO2 laser treatment. Fibre laser treatment...
Dongil Kwon - One of the best experts on this subject based on the ideXlab platform.
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effect of contact angle on contact morphology and vickers hardness measurement in instrumented indentation testing
International Journal of Mechanical Sciences, 2014Co-Authors: Seungkyun Kang, Dongil KwonAbstract:Abstract We derive a general contact-depth function for the Vickers indenter by modifying a scaling relation between yield strain and indentation depth ratio, which is comprised of indenter angle, plastic constraint factor, and indentation depth ratio. The validity of this function is demonstrated by using various indenters of different angles. A method for calibrating the actual contact area of an imperfectly shaped Vickers indenter is suggested that yields a better evaluation of Vickers hardness in the instrumented indentation test.
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conventional vickers and true instrumented indentation hardness determined by instrumented indentation tests
Journal of Materials Research, 2010Co-Authors: Seungkyun Kang, Chanpyoung Park, Dongil KwonAbstract:We evaluate Vickers hardness and true instrumented indentation test (IIT) hardness of 24 metals over a wide range of mechanical properties using just IIT parameters by taking into account the real contact morphology beneath the Vickers indenter. Correlating the conventional Vickers hardness, indentation contact morphology, and IIT parameters for the 24 metals reveals relationships between contact depths and apparent material properties. We report the conventional Vickers and true IIT hardnesses measured only from IIT contact depths; these agree well with directly measured hardnesses within ±6% for Vickers hardness and ±10% for true IIT hardness.
Michel Nganbe - One of the best experts on this subject based on the ideXlab platform.
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role of microstructural features in toughness improvement of zirconia toughened alumina
Journal of Minerals and Materials Characterization and Engineering, 2016Co-Authors: Olaniyi Fakolujo, Ali Akba Merati, Mariusz Ielawski, Mano Olduc, Michel NganbeAbstract:Ceramics constitute an integral part of highly efficient armours due to their low density, high hardness, strength and stiffness. However, they lack toughness and multi-hit capability. Therefore, zirconia toughened alumina is investigated. The hardness is evaluated using Vickers, Knoop and instrumented indentations, while the fracture toughness is evaluated using the indentation technique and Charpy tests. The strength is evaluated using ring-on-ring, four point bend and drop weight tests. The Young’s modulus is evaluated using the unloading instrumented indentation curves. Microstructure, porosity and density are characterised using ultrasonic scanning, Archimedes principle, optical and scanning electron microscopy. Results show an indentation size effect on all mechanical properties. A substantial improvement in toughness is achieved through retardation of crack initiation by tetragonal-to-monoclinic phase transformation in zirconia particles, crack deviation thanks to appropriate grain structure, as well as energy absorption by densification due to remaining porosity. This improved toughness is expected to promote multi-hit capability.
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instrumented and vickers indentation for the characterization of stiffness hardness and toughness of zirconia toughened al2o3 and sic armor
Journal of Materials Science & Technology, 2015Co-Authors: A Nastic, Olaniyi Fakolujo, Ali Akbar Merati, Mariusz Bielawski, Manon Bolduc, Michel NganbeAbstract:Instrumented and Vickers indentation testing and microstructure analysis were used to investigate zirconia toughened alumina (ZTA) and silicon carbide (SiC). Several equations were studied to relate the Vickers indentation hardness, Young's modulus and crack behavior to the fracture toughness. The fracture in SiC is unstable and occurs primarily by cleavage leading to a relatively low toughness of 3 MPa m1/2, which may be inappropriate for multi-hit capability. ZTA absorbs energy by plastic deformation, pore collapse, crack deviation and crack bridging and exhibits time dependent creep. With a relatively high toughness around 6.6 MPa m1/2, ZTA is promising for multi-hit capability. The higher accuracy of median equations in calculating the indentation fracture toughness and the relatively high c/a ratios above 2.5 suggest median type cracking for both SiC and ZTA. The Young's modulus of both ceramics was most accurately measured at lower indentation loads of about 0.5 kgf, while more accurate hardness and fracture toughness values were obtained at intermediate and at higher indentation loads beyond 5 kgf, respectively. A strong indentation size effect (ISE) was observed in both materials. The load independent hardness of SiC is 2563 HV, putting it far above the standard armor hardness requirement of 1500 HV that is barely met by ZTA.
