• The Journal of Korean Academy of Prosthodontics
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• v.47 no.2
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• pp.191-198
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• 2009

Statement of problem: Ceramics have been important materials for the restoration of teeth. The demands of patients for tooth-colored restorations and the availability of various dental ceramics has driven the increased use of new types of dental ceramic materials. Improved physical properties of theses materials have expanded its use even in posterior crowns and fixed partial dentures. However, ceramic still has limitation such as low loading capability. This is critical for long-span bridge, because bridge is more subject to tensile force. Purpose: The wire reinforced ceramic was designed to increase the fracture resistance of ceramic restoration. The purpose of this study was to evaluate the fracture resistance of wire reinforced ceramic. Material and methods: Heat pressed ceramic(ingot No.200 : IPS Empress 2, Ivoclar Vivadent, Liechtenstein) and Ni-Cr wire(Alfa Aesar, Johnson Matthey Company, USA) of 0.41 mm diameter were used in this study. Five groups of twelve uniform sized ceramic specimens(width 4 mm, thickness 2 mm, length 15 mm) were fabricated. Each group had different wire arrangement. Wireless ceramic was used as control group. The experimental groups were divided according to wire number and position. One, two and three strands of wires were positioned on the longitudinal axis of specimen. In another experimental group, three strands of wires positioned on the longitudinal axis and five strands of wires positioned on the transverse axis. Three-point bending test was done with universal testing machine(Z020, Zwick, Germany) to compare the flexural modulus, flexural strength, strain at fracture and fracture toughness of each group. Fractured ceramic specimens were cross-sectioned with caborundum disc and grinded with sandpaper to observe interface between ceramic and Ni-Cr wire. The interface between ceramic and Ni-Cr wire was analyzed with scanning electron microscope(JSM-6360, JEOL, Japan) under platinum coating. Results: The results obtained were as follows: 1. The average and standard deviation in flexural modulus, flexural strength and fracture toughness showed no statistical differences between control and experimental groups. However, strain was significantly increased in wire inserted ceramics(P<.001). 2. Control group showed wedge fracture aspects across specimen, while experimental groups showed cracks across specimen. 3. Scanning electron microscopic image of cross-sectioned and longitudinally-sectioned specimens showed no gap at the interface between ceramic and Ni-Cr wire. Conclusion: The results of this study showed that wire inserted ceramics have a high strain characteristic. However, wire inserted ceramics was not enough to use at posterior area of mouth in relation to flexural modulus and flexural strength. Therefore, we need further studies.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.473-478
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• 2009

The purpose of this study is to evaluate the behaviour of the plastic deformed zone at crack tip on the standard Charpy specimens which were taken from the multi-passed weld block of the pressure vessel steel. Notch was machined on the standard Charpy test specimens and pre-crack which was located around the fusion line was made under the repeat load. Four point bend and acoustic emission tests were carried out simultaneously. The size of plastic region at crack tip was calculated using stress intensity factor. Relationships between characteristics of acoustic emission and plastic zone size at crack tip were discussed through the cumulative AE energy. Regardless of the specimens, AE signals were absent within the elastic region almost and most of AE signals were produced at the plastic deformation region from yield point to the mid-point between yield and maximum load. More AE signals for the weldment were produced compared with the base-metal and PWHT specimen. Relations between plastic deformed zones at crack tip and cumulative AE energy for the weldment and PWHT specimen were different quietly from the base-metal. Besides, number of AE counts for the weldment was the larger than those of the base-metal and PWHT specimen.