Yung-Ning Pan

Stress effect on bone remodeling and osseointegration on dental implant with novel nano/microporous surface functionalization.

The objective of this study was to investigate the stress distributions of a surface-treated dental implant and bone tissue under physiological loading. For ensuring success of dental implant treatment, one must examine the magnitude and location of the maximum stresses. Stress analysis models were constructed from computer tomography data. Although several studies have investigated finite element models of dental implants, none have used an implant model with a nanoporous layer in a biomimetic geometrical mandible model. The novel implant surface used in this study, comprised of a microlevel porous containing a nanolevel porous structure, was complex and it was difficult to present due to the limitation of computer efficiency. However, this complex geometry was simplified using a film, to further investigate stresses resulting from 0 nm, 50 nm, 500 nm, 5 μm, and 50 μm surface treatment thicknesses. Results indicated that the stresses transferred more uniformly in implants with nanoporous surface treatments, and that the stresses decreased with increasing layer thickness. Our study showed that this could be potentially beneficial for understanding the stress properties of surface-treated layers for dental implants.

Internal Stress Control of Nickel-Phosphorus Electrodeposits Using Pulse Currents

Nickel-phosphorus deposits with various phosphorus contents and internal stresses were electroplated from a nickel sulfamate bath without an additive by varying the duty cycle and frequency of the pulse current. A reduction in the duty cycle increased the phosphorus content and decreased the internal tensile stresses in the deposit. At a 0.1 duty cycle, a deposit with slightly compressive internal stress was produced. A deposit with a thickness of several hundred micrometers was plated at 0.1 duty cycle on a copper plate with good adhesion. Because the waveform parameters of the pulse current strongly affects the current efficiency and the microstructure of the deposit, the internal stress of the deposit as a function of the current efficiency, phosphorus content, and grain size was measured and discussed.

Microstructure of Trivalent Chromium Conversion Coating on Electrogalvanized Steel Plate

The microstructure of trivalent chromium conversion coating on electrogalvanized steel plate has been characterized. The as-deposited coating consisted of three layers with a thin inner layer, a porous intermediate layer, and a thin outer layer. Baking at 90°C for 30 min reduced the population density and size of cracks in the coating. Meanwhile, the outer layer became denser, but the immediate layer became highly porous. During baking at elevated temperatures, the chemical species and voids within the coating redistribute, which, in turn, suppresses the formation of microcracks that are commonly seen in the hexavalent chromium counterpart.

Stress analysis during jaw movement based on vivo computed tomography images from patients with temporomandibular disorders

The purpose of this study is to develop three-dimensional (3D) finite element models of temporomandibular joints (TMJs) and to investigate stress distributions. To determine the causes of temporomandibular disorders (TMDs), the magnitude and location of the maximum stresses under physiological loading must be considered. Stress analysis TMD models were reconstructed from computed tomography (CT) data. Several studies have investigated finite element TMJ models, but few have used a bilateral mandible model that includes jaw closing and maximum opening. In this study, the authors defined an asymmetry index for the different stress values on each side joint; this index has not yet been investigated. According to clinical observation, one joint affects the other side joint during mastication. Three symptom-free volunteers and three symptomatic patients were selected as the control group (CG) and TMD group (TG), respectively. For the TG, data analysis indicated that the condyle was asymmetrical during jaw closing, while both the condyle and disc were slightly asymmetrical during jaw opening. The maximum stresses did not significantly differ between the CG and TG for either closing or opening of the jaw. The results of this study have a potential clinical benefit in terms of proving superior biomechanical behaviour.

Enhancement of biomechanical behavior on osseointegration of implant with SLAffinity.

The purpose of this study was to investigate stresses resulting from different thicknesses of hydroxyapatite- and titanium dioxide (TiO(2))-treated layers at the interface between temporomandibular joint (TMJ) implants and bones using three-dimensional finite element models. For ensuring osseointegration of implant treatment, one must examine the stresses of interface between implant and bone tissue. Treated layers on TMJ implants are a very important factor in clinical application. Several studies have investigated finite element models for TMJs, but few have examined a model for TMJ implants with treated layers. In this study, TMJ models were reconstructed using computer tomography data, and the effects of treated layer thickness on the stress field during jaw movement were investigated; this index has not yet been reported with respect to TMJ implant. The maximum stresses in the bone occurred at the position of the first screw. Data analysis indicated a greater decrease in this stress in the case of using TMJ implants with TiO(2)-treated layers, and the stresses decreased with increasing layer thicknesses. Results confirmed that the treated layers improve biomechanical properties of the TMJ implants and release abnormal stress concentration in them. The results of our study offer the potential clinical benefit of inducing superior biomechanical behavior in TMJ implants.

Optimal heat treatment conditions and properties of bimetal (high Cr cast iron/alloyed steel) hammers

Abstract This study intended to establish the optimal heat treatment conditions for the desired hardness and wear resistance property for the bimetal hammers developed by the authors. The objective of this study is to attain bimetal hammers that have a tough Cr–Ni alloyed steel shank and a high wear resistant high Cr cast iron head to replace conventional single alloy (high Mn steel) hammers. The results show that the optimal heat treatment condition obtained for the bimetal hammers is: destabilisation: 1000–1050°C for 2 h, quench: FAC and tempering: 480–500°C for 6 h. By employing this optimal heat treatment condition, the highest hardness value can be attained along with the best wear resistance property for the head portion and acceptable toughness for the shank portion. The microstructure of the head portion that corresponds to the optimal properties consists of eutectic M7C3 carbides, secondary M7C3 carbides, tempered martensite and almost nil retained austenite.

Production of Selected Key Ductile Iron Castings Used in Large-Scale Windmills

Both the optimal alloy design and microstructures that conform to the mechanical properties requirements of selected key components used in large-scale windmills have been established in this study. The target specifications in this study are EN-GJS-350-22U-LT, EN-GJS-350-22U-LT and EN-GJS-700-2U. In order to meet the impact requirement of spec. EN-GJS-350-22U-LT, the Si content should be kept below 1.97%, and also the maximum pearlite content shouldn’t exceed 7.8%. On the other hand, Si content below 2.15% and pearlite content below 12.5% were registered for specification EN-GJS-400-18U-LT. On the other hand, the optimal alloy designs that can comply with specification EN-GJS-700-2U include 0.25%Mn+0.6%Cu+0.05%Sn, 0.25%Mn+0.8%Cu+0.01%Sn and 0.45%Mn+0.6%Cu+0.01%Sn. Furthermore, based upon the experimental results, multiple regression analyses have been performed to correlate the mechanical properties with chemical compositions and microstructures. The derived regression equations can be used to attain the optimal alloy design for castings with target specifications. Furthermore, by employing these regression equations, the mechanical properties can be predicted based upon the chemical compositions and microstructures of cast irons.

Alloy Design and Microstructure Control for the Production of Heavy Ductile Irons Used in Large-Scale Windmills

The primary purpose of this research is to establish the optimal alloy design and microstructure for achieving the desired mechanical properties (tensile strength, yield strength, elongation and low temperature impact value) of key components used in large-scale windmills. In order to meet the impact requirement (I-40°C≥10J) of spec. EN-GJS-350-22U-LT, the Si content should be kept below 1.97%, and also the maximum pearlite content shouldn’t exceed 7.8%. On the other hand, the optimal alloy designs that can comply with specification EN-GJS-700-2U include 0.25%Mn+0.8%Cu+0.01%Sn , 0.25%Mn+0.6%Cu+0.05%Sn and 0.45%Mn+0.6%Cu+0.01%Sn. Furthermore, based upon the experimental results, multiple regression analyses have been performed to correlate the mechanical properties with chemical compositions and microstructures. The derived regression equations can be used to attain the optimal alloy design for castings with targeted specifications. Furthermore, by employing these regression equations, the mechanical properties can be predicted based upon the chemical compositions and microstructures of cast irons.

Research on the Wear Resistance of High-Chromium White Cast Iron and Multi-Component White Cast Iron

The pin-on-disk wear test and solid particle erosion test were used to investigate the wear resistance property of both high chromium white cast iron and multi-component white cast iron with optimal alloy compositions and heat treatment conditions. Experimental results indicate that a linear relationship between the wear lose and the testing time exists for high chromium white cast irons. Apparent scratch grooves and sheared pits appeared on the specimen surface. Subsurface observations found pit depths of some 4.5~8.0 mm. Crack propagation routes were clearly visible along the martensitic grain boundaries for alloys in the as-quenched state. Tempering treatment increases the toughness of the alloy, resulting in an increase in the resistance to crack formation. On the other hand, the multi-component white cast irons exhibited a non-linear relationship between the wear lose and the testing time. Relatively shallow scratches were found on the specimen surface, and pit depths of about 4.0 mm were observed through subsurface observations. Tempering at 570°C caused a reduction in hardness of the alloy, and therefore, the fracture mode tends to be ductile. As a result, deformation only occurred in crater regions with no clear evidence of spreading.

Simulation of the Phase Diagrams for High-Chromium White Cast Irons and Multi-Component White Cast Irons

In this study, simulation or computation of the phase diagrams for specific alloys of the high-Cr white cast irons and the multi-component white cast irons was performed by employing Thermo Calc software package and appropriate thermodynamics modules. The phase diagrams constructed were verified by thermal analysis (DSC), optical microscopy and X-ray diffraction analysis. Both the obtained phase transition points via DSC and the microstructures observed by optical microscopy and XRD analysis match well with the phase diagrams.