Laser straight cutting of zirconia tiles

B. S. Yilbas,S. S. Akhtar,C. Karatas 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.2

Laser straight cutting of zirconia is carried out. Temperature and stress fields developed in the cutting sections are predicted using the finite element code. The morphological changes in the cutting section are examined after incorporating the optical and scanning electron microscopes. The prediction of surface temperature is compared with its counterpart obtained from the thermocouple data. Temperature predictions agree well with the thermocouple data. The cut section is free from major cracks and dross attachment occurs at the kerf exit.

Laser cutting of triangular geometry into 2024 aluminum alloy: Influence of triangle size on thermal stress field

Bekir Sami Yilbas,Syed Sohail Akhtar,Omer Keles,Kurtulus Boran 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.8

Laser cutting of a triangular geometry into aluminum 2024 alloy is carried out. Thermal stress field in the cutting section is predictedusing the finite element code ABAQUS. Surface temperature predictions are validated through the thermocouple data. Morphologicalchanges in the cut section are examined incorporating optical and electron scanning microscopes. The effects of the size of the triangulargeometry on thermal stress field are also examined. It is found that surface temperature predictions agree well with thermocouple data. von Mises stress remains high in the region close to the corners of the triangular geometry, which is more pronounced for the small sizetriangle. This behavior is associated with the occurrence of the high cooling rates in this region. Laser cut edges are free from large scalesideways burning and large size burr attachments. However, some locally scattered dross attachments are observed at the kerf exit.

Laser cutting of Kevlar laminates: First and second law analysis

Bekir S. Yilbas,Ahmet Z. Sahin,C. Chatwin,Tahir Ayar 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.4

Kevlar laminates are difficult to machine using conventional machining methods because of their thermal and mechanical properties. Laser cutting offers advantages over conventional machining methods, such as precision of operation, non-frictional processing, and operational cost. This provides the motivation for the present study, which reports on laser cutting of Kevlar laminates of different thicknesses. The first and second law efficiencies of the cutting process are formulated and predicted in line with the experimental parameters. The laser cut surfaces are examined using optical and electron scanning microscopes. It is demonstrated that the first and second law efficiencies improve at high laser cutting speeds and low laser output power levels. For these conditions parallel sided kerfs with no sideways burning are produced.

Laser treatment of HVOF coating: model study and characterization

B. S. Yilbas,Z. Y. Taha-al,M. S. Hashmi 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.10

Laser short-pulse heating of metallic surface: Consideration of Seebeck effect

Bekir Sami Yilbas 한국물리학회 2009 Current Applied Physics Vol.9 No.3

In the present study, laser short-pulse heating is formulated using an electron kinetic theory approach. Temperature predictions are compared with that obtained from two-equation model. Seebeck effect is considered during the heating process. The predicted Seebeck coefficients are compared with the results based on the early formulation. Electron excess energy loss due to Seebeck effect is compared with electron mean energy. It is found that Seebeck coefficient decays sharply in the surface region due to sharp decay of electron temperature in this region. Seebeck coefficient obtained from the present study is in agreement with the predictions based on the early formulation, provided electron temperature is used in the previous formulation. However, Seebeck coefficient differs significantly once the lattice site temperature is used in the previous formulation. Electron excess energy loss due to Seebeck effect is considerably less than electron mean energy, i.e. the ratio is in the order of 10-5. In the present study, laser short-pulse heating is formulated using an electron kinetic theory approach. Temperature predictions are compared with that obtained from two-equation model. Seebeck effect is considered during the heating process. The predicted Seebeck coefficients are compared with the results based on the early formulation. Electron excess energy loss due to Seebeck effect is compared with electron mean energy. It is found that Seebeck coefficient decays sharply in the surface region due to sharp decay of electron temperature in this region. Seebeck coefficient obtained from the present study is in agreement with the predictions based on the early formulation, provided electron temperature is used in the previous formulation. However, Seebeck coefficient differs significantly once the lattice site temperature is used in the previous formulation. Electron excess energy loss due to Seebeck effect is considerably less than electron mean energy, i.e. the ratio is in the order of 10-5.

Improved formulation of electron kinetic theory approach for laser shortpulse heating: Thermal stress consideration

Bekir Sami Yilbas,A.F.M. Arif 한국물리학회 2009 Current Applied Physics Vol.9 No.6

Nonequilibrium energy transport between excited electrons and lattice site is re-formulated after considering the ballistic contribution of the electron energy to the energy transport process. The improved formulation of the electron kinetic theory predictions are compared with the previously obtained electron kinetic and two-equation models. Thermal stress developed in the region irradiated by a laser beam is formulated during the heating pulse. Copper with variable properties is used in the simulations. It is found that improved electron kinetic theory model predicts less temperature rise than that corresponding to previously formulated electron kinetic theory and two equation models in the surface region; in this case, electron temperature attains high values. Thermal stress developed is compressive and attains the maximum at some depth below the surface. The thermal stress level is well below the yielding limit of the substrate material. Nonequilibrium energy transport between excited electrons and lattice site is re-formulated after considering the ballistic contribution of the electron energy to the energy transport process. The improved formulation of the electron kinetic theory predictions are compared with the previously obtained electron kinetic and two-equation models. Thermal stress developed in the region irradiated by a laser beam is formulated during the heating pulse. Copper with variable properties is used in the simulations. It is found that improved electron kinetic theory model predicts less temperature rise than that corresponding to previously formulated electron kinetic theory and two equation models in the surface region; in this case, electron temperature attains high values. Thermal stress developed is compressive and attains the maximum at some depth below the surface. The thermal stress level is well below the yielding limit of the substrate material.

Overnight hospital stay and/or extended recovery period may allow long-duration oral and maxillofacial surgeries in the operating room of a dental hospital in an outpatient setting: a single-center experience

Filiz Uzumcugil,Aysun Ankay Yilbas,Basak Akca,Demet Basak Ozkaragoz,Selen Adiloğ,lu,Hıfzı Hakan Tuz,Meral Kanbak 대한구강악안면외과학회 2020 대한구강악안면외과학회지 Vol.46 No.2

Objectives: The requirement for overnight hospital stay should be considered preoperatively according to patient-related factors, type of surgery, and anesthetic management plan. In this study, we aimed to define the major factors that influence consideration of overnight hospital stay in patients undergoing oral and maxillofacial (OMF) surgery in an operating room (OR) of a dental hospital in an outpatient setting. Materials and Methods: The records of patients who underwent oral procedures under general anesthesia between 2014-2017 were reviewed. Results: A total of 821 patients underwent oral procedures under general anesthesia; 631 of them underwent OMF surgery in the OR of a dental hospital, and 174 of these patients were hospitalized for overnight stay. There was no significant difference in the number of patients with comorbidities between the outpatient and hospitalized patient groups (P=0.389). The duration of surgery was longer in the hospitalized patient group (105.25±57.48 vs 189.62±82.03 minutes; P<0.001). Double-jaw (n=15; 310.00±54.21 minutes) and iliac crest grafting surgeries (n=59; 211.86±61.02 minutes) had the longest durations. Patients who underwent iliac crest grafting had the highest rates of hospitalization (79%). The overall recovery period was longer in outpatients (119.40±41.60 vs 149.83±52.04; P<0.001). Conclusion: Duration of surgery was the main determinant in considering whether a patient required overnight hospital stay. However, patients with an American Society of Anesthesiology physical status score <3 may be scheduled for OMF surgery in the OR of a dental hospital in an outpatient setting regardless of duration of surgery if overnight hospital stay is planned or an extended recovery period is provided until patients meet the discharge criteria.

Laser repetitive pulse heating and melt pool formation at the surface

S. Z. Shuja,B. S. Yilbas,O. Momin 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.2

In this paper, laser repetitive pulse heating of steel surface is conducted to predict temperature and melt pool geometry in the irradiated region. The enthalpy porosity method is incorporated to account for the phase change in the irradiated surface. The flow field in the melt pool is simulated after considering the Marangoni effect. To examine the influence of the laser pulse intensity distribution on the formation and flow field in the melt pool, the laser pulse intensity parameter (β) is introduced in the analysis. An experiment is conducted to compare the melt pool geometry predicted from the simulation and that obtained from the experiment. The melt pool size is significantly affected by the intensity parameter (i.e., the melt pool is too shallow for high-intensity parameters). The predicted melt pool geometry is in agreement with the experimental results.

Laser short-pulse heating of silicon film with the presence of metallic substrate

S.B. Mansour,B.S.Yilbas 한국물리학회 2010 Current Applied Physics Vol.10 No.5

Laser interaction of silicon film located at he top of metallic substrate is examined and energy transport in electron and lattice sub-systems are formulated using the electron kinetic theory approach. The simulations are repeated for different substrate materials, namely gold, silver, and copper. It is found that electron temperature in the silicon film rises in the vicinity of the silicon-metallic substrate interface, despite the fact that energy absorption from the irradiated filed is significantly low in the silicon film. Lattice site temperature rises rapidly in the early heating period at the interface. Inaddition, lattice site temperature increase is higher in the silicon film than that corresponding to the metallic substrate.

Body Surface Area Is Not a Reliable Predictor of Tracheal Tube Size in Children

Filiz Uzumcugil,Emre Can Celebioglu,Demet Basak Ozkaragoz,Aysun Ankay Yilbas,Basak Akca,Nazgol Lotfinagsh,Bilge Celebioglu 대한이비인후과학회 2018 Clinical and Experimental Otorhinolaryngology Vol.11 No.4

Objectives. The age-based Cole formula has been employed for the estimation of endotracheal tube (ETT) size due to its ease of use, but may not appropriately consider growth rates among children. Child growth is assessed by calculating the body surface area (BSA). The association between the outer diameter of an appropriate uncuffed-endotracheal-tube (ETT-OD) and the BSA values of patients at 24–96 months of age was our primary outcome. Methods. Cole formula, BSA, age, height, weight and ultrasound measurement of subglottic-transverse-diameter were evaluated for correlations with correct uncuffed ETT-OD. The Cole formula, BSA, and ultrasound measurements were analyzed for estimation rates in all patients and age subgroups. The maximum allowed error for the estimation of ETT-OD was ≤0.3 mm. Patients’ tracheas were intubated with tubes chosen by Cole formula and correct ETT-OD values were determined using leak test. ETT exchange rates were recorded. Results. One-hundred twenty-seven patients were analyzed for the determination of estimation rates. Thirteen patients aged ≥72 months were intubated with cuffed ETT-OD of 8.4 mm and were accepted to need uncuffed ETT-OD >8.4 mm in order to be included in estimation rates, but excluded from correlations for size analysis. One-hundred fourteen patients were analyzed for correlations between correct ETT-OD (determined by the leak test) and outcome parameters. Cole formula, ultrasonography, and BSA had similar correct estimation rates. All three parameters had higher underestimation rates as age increased. Conclusion. The Cole formula, BSA, and ultrasonography had similar estimation rates in patients aged ≥24 to ≤96 months. BSA had a correct estimation rate of 40.2% and may not be reliable in clinical practice to predict uncuffed-ETT-size.