Effect of the addition of t-ZrO2 on the material properties of β-TCP/PCL composites

Using poly-methyl methacrylate as a pore-forming agent, porous β-tricalcium phosphate (β-TCP)/t-ZrO₂ composites were fabricated depending on the volume percentages (vol.%) of t-ZrO₂ powder. In the porous sintered bodies, hybrid pores, about 20 and 200 μm in diameter, were homogenously dispersed in the β-TCP/t-ZrO₂ matrix and showed good interconnection. On the other hand, β-TCP-(t-ZrO₂)/polycaprolactone (PCL) composites were fabricated by the melt infiltration process using porous β-TCP/t-ZrO₂ bodies. The relative density of the β-TCP-(t-ZrO₂)/PCL composites increased as the vol.% of t-ZrO₂ increased and its maximum value was about 98.6%. However, the hardness, bending strength and elastic modulus of β-TCP-(t-ZrO₂)/PCL composites decreased due to the low densification of porous β-TCP/t-ZrO₂ bodies as the volume percentages of t-ZrO₂ content increased. The values (using 20 vol.% of t-ZrO₂) were 11.4 Hv, 25.5 MPa and 17.2 GPa, respectively.     

Fabrication of a Continuously Oriented Porous Al2O3 Body and Its In Vitro Study

Continuously oriented porous Al₂O₃ bodies were fabricated by a multi-pass extrusion process using C powders and ethylene vinyl acetate as an agent for pore forming and as a binder, respectively. The main pore size can be easily controlled by increasing the number of extrusion passes. The edges of the pore frame showed a rough surface having many fine pores about 0.2–1 μm in size. In the continuously porous Al₂O₃ bodies having 150 μm pore size, the values of the relative density and bending strength were about 63% and 90 MPa, respectively. These values were higher than those of an Al₂O₃ porous body made by a common process. From the in vitro study using human osteoblast-like MG-63 cells, it was confirmed that the cells grew well and adhered to the top surface and inside pores, as well as the outside wall of the continuously porous Al₂O₃ body. Without the directionality, the cells showed some spindle-shaped, three-dimensional, and network-type structures.     

Fabrication of pore-gradient Al2O3–ZrO2 sintered bodies by fibrous monolithic process

Functionally pore-gradient Al₂O₃–ZrO₂ composites where the porosity is dependent on the extrusion ratio and number of shell layer were fabricated by a fibrous monolithic process. The size and volume fraction of the pores were controlled by different numbers of shell layers, which contained various sizes and a different volume percentage of the pore-forming agent. In the pore-gradient, Al₂O₃–ZrO₂ bodies having a dense core part, some defects such as cracks, swelling and delamination occurred during the sintering process due to the low extrusion ratio. However, these defects were completely removed as the extrusion ratio increased, and the shell layers as well as the core part had a continuously porous structure. In the shell part, various sizes of pores from 70 to 250 μm in diameter were observed.     

Design of hole-clinching process for joining of dissimilar materials – Al6061-T4 alloy with DP780 steel,hot-pressed 22MnB5 steel,and carbon fiber reinforced plastic

The mechanical joining of dissimilar materials is a key technology in the automotive industry as it enables the realization of car bodies that incorporate multiple materials. However, it remains difficult to join materials such as aluminum alloy to high-strength/low-ductility materials such as advanced high-strength steel, hot-pressed steel, and carbon fiber reinforced plastic by using joining methods that are based on forming technology. The purpose of this study is to develop a new joining process, called “hole clinching,” for these material combinations. In the hole-clinching process, the ductile material is positioned uppermost and the brittle material—into which a hole is formed—is positioned below that. The upper sheet is indented into a die cavity through the hole in the lower sheet and spread so that the two sheets interlock geometrically. In this study, hole-clinching tools were designed based on the geometrical relationship between the forming volume and the joint strength. Finite element analysis and practical experiments were performed to verify the practicality of the hole-clinching process. The cross-sections of the hole-clinched joints formed in our experiments were in good agreement with the results of the finite element analysis. Then, a single-lap shear test was performed to evaluate the joint strength. The hole-clinched joints, regardless of the material combinations, provided a joint strength in excess of the desired 2.5 kN. These results point to the applicability of the hole-clinching process to the joining of dissimilar materials.     

Numerical investigation on NOX formation in oxygen-CH4 MILD combustion with air leakage

In this paper, we focus on formation of NO_X under oxy-fuel MILD combustion using JHC (jet-in hot co-flow) burner. The effect of the different oxygen dilution ratio in the co-flow is analyzed for MILD combustion formation and also for characterizing NO_X emission. RANS (Reynolds averaged Navier Stokes) with the modified k-ε equation and EDC (eddy dissipation concept) model were applied for 2D-axisymmetric computational domain using the Ansys Fluent. It is found that the effect of the oxygen concentration rather than the composition of dilution gas is more significant for the formation of the MILD combustion and as the oxygen concentration of the dilution gas increases under MILD combustion conditions, the region with D_a < 1 expressed as MILD regime tends to be decreased. The effect of a diluted oxygen concentration in the oxy-fuel combustion on NO_x emission under MILD condition is found to be much greater than the amount of air leakage into co-flow, and NO emissions are almost unaffected by the increase of N₂ concentration in case of MILD combustion condition within practical air leak ranges.

     

Fabrication of calcium phosphate-calcium sulfate injectable bone substitute using chitosan and citric acid

In this study, an injectable bone substitute (IBS) consisting of citric acid, chitosan solution as the liquid phase and tetra calcium phosphate (TTCP), dicalcium phosphate anhydrous (DCPA) and calcium sulfate hemihydrate (CSH) powders as the solid phase was prepared. Four groups containing different percentages (0–30%) of calcium sulfate hemihydrate (CSH, CaSO₄ · 0.5H₂O) were investigated. Initial setting times for IBS with CSH were longer than those without CSH. The setting times for all compositions were in the range of 25–45 min. The injectability was improved by the addition of CSH in the present system. Scanning electron microscopy images showed that fiber-like crystallization appeared in the cements. The enhancement of crystallinity was confirmed by XRD profiles where the peak intensity of HAp increased with incubation time and the addition of CSH. Also, the compressive strength increased with the addition of CSH. The maximum compressive strength obtained for IBS was with 20% CSH after 28-day incubation in 100% humidity at 37°C.     

Enhanced osteoconduction and angiogenesis of a three dimensional continuously porous Al2O3 implant

A 3-dimensional alumina (Al₂0₃) implant consisting of a continuous porous structure was fabricated using a fibrous monolithic process and its biocompatibility was evaluated through in vitro procedures and in vivo angiogenesis. In vitro experiments were carried out using human osteoblast like cells, MG-63 and osteoclast-like cells, Raw-264.7. Cellular proliferation and growth behavior were examined on the specimen surfaces by SEM. Highly condensed, circular cells with three-dimensional network like growth pattern was observed inside the pore surfaces using MG-63 cells. In contrast, the osteoclast-like Raw 264.7 cells had a multi-layered pebblestone appearance with interconnections. Moreover, the crystalline-like nodules generated by osteoblasts cultured on an Al₂O₃ porous body were shown to have resulted from the in vitro mineralization of calcium-phosphate deposits. To investigate the in vivo angiogenesis, 3-dimensional Al₂O₃ porous bodies were implanted into the subcutaneous tissues of rats. The porous bodies were completely filled with fibroblasts at 4 weeks and the formation of new blood vessels inside the porous body was observed at 6 weeks.     

Fabrication of bioglass infiltrated Al2O3–(m-ZrO2) composites

Using 80 vol.% of poly methyl methacrylate (PMMA) as a pore-forming agent to obtain interconnected porous bodies, porous Al₂O₃–(m-ZrO₂) bodies were successfully fabricated. The pores were about 200 μm in diameter and were homogeneously dispersed in the Al₂O₃–25 vol.% (m-ZrO₂) matrix. To obtain Al₂O₃–(m-ZrO₂)/bioglass composites, the molten bioglass was infiltrated into porous Al₂O₃–(m-ZrO₂) bodies at 1400°C. The material properties of the Al₂O₃–(m-ZrO₂)/bioglass composites, such as relative density, hardness, compressive strength, fracture toughness and elastic modulus were investigated.     

A precision stopping measurement device to automatically detect position errors of an urban train at railway stations

International Journal of Control, Automation and Systems - Precision stopping of an urban train at a railway station with platform screen doors is essential to passenger safety and timely revenue...     

Microstructure and mechanical properties of porous yttria stabilized zirconia ceramic using poly methyl methacrylate powder

Porous t-ZrO₂ ceramic was fabricated by pressureless sintering, using commercial t-ZrO₂ and different volume percentages of poly methyl methacrylate (PMMA) powders (20–80%). The spherical pores ranged from about 120 to 170 μm in diameter. By increasing the PMMA content, the number of pores, material properties and pore morphology were changed dramatically. The values of relative density, elastic modulus, bending strength and hardness of the 60 vol.% PMMA content sample, sintered at 1550 °C, were about 43%, 40 GPa, 170 MPa and 248 Hv, respectively.