• 한국정밀공학회지
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• 제12권2호
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• pp.5-13
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• 1995

Various techniques to measure fracture toughness which is an important parameter to predict fracture behavious of structural materials have been reported. Among these mathods, this paper describes the micro-Vickers indentation crack method to estimate the fracture toughness of some WC-Co composites. Two indentation crack patterns (such as radial-median cracks (orhalf-penny cracks) and Palmqvist cracks generated during indentation) are referred precisely. The fracture toughness of WC-4.7wt%Co, WC-6wr%Co and WE-9wr%Co composites were estimated by using some equations given by Shetty et al., Nihara et al. in this study. We show the reliability of indentation method by comparing the results with those from literatures. The appropriate equation to estimate the fracture toughness in the case of WC-Co composite is given. In addition, some technical informations in terms of the crack length by indentation in estimating the existence of the surface residual stress that prevents to obtain an accurate fracture toughness are presented.

• 소성∙가공
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• 제33권5호
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• pp.315-321
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• 2024

Although achieving a high fracture toughness is essential for designing reliable aircraft components using aluminum alloys, only a limited number of studies have discussed the relationship between microstructure and fracture toughness. Therefore, in this study, the effects of dynamic recrystallization on the fracture toughness of Al7050 extruded alloy were investigated. Because of the temperature deviation in the extruded large component, incomplete dynamic recrystallization (DRX) occurred that results into the higher Kernel average misorientation (KAM) and sub-grain structure fraction compare with the complete DRX region. Although incomplete DRX changes KAM and sub-grain fraction, the strength and ductility difference between complete and incomplete DRX regions are not in big difference. The accumulated KAM reduces the plastic zone size, and both cleavage and a lower micro-void fraction are observed in the incomplete DRX region. Based on the different fracture behavior from different DRX behavior, the fracture toughness of the incomplete DRX is lower than that of the complete DRX region. This result implies how a different DRX behavior from temperature variation affects to the fracture toughness of high-strength aluminum alloys.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.300-305
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• 2003

Reduced activation ferritic (JLF-1) steel is leading candidates for blanket/first-wall structures of the D-T fusion reactor. In fusion application, structural materials will suffer effects of repeated changes of temperature. Therefore, the data base of tensile strength and fracture toughness at operated temperature $400^{\circ}C$ are very important. Fracture toughness ($J_{IC}$) and tensile tests were carried out at room temperature and elevated temperature ($400^{\circ}C$). Fracture toughness tests were performed with two type size to investigate the relationship between the constraint effect of a size and the fracture toughness resistance curve. As the results, the tensile strength and the fracture toughness values of the JLF-1 steel are slightly decreased with increasing temperature. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. The fracture toughness values of JLF-1 steel at room temperature and at $400^{\circ}C$ shows an excellent fracture toughness ($J_{IC}$) of about $530kJ/m^2\;and\;340kJ/m^2$, respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1240-1245
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• 2003

Reduced activation ferritic steel (JLF-1) is considered as a promising candidate material for blanket or first-wall structure of D-T fusion reactors. The fracture tests of fracture resistance curve (J-R curve) and $J_{IC}$ are desirable to investigate the exact fracture toughness of JLF-1 steel, since it has a high ductility. The fracture toughness of JLF-1 steel is affected by the configuration of test specimen such side groove, specimen thickness or specimen size. In this study, the fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The test results showed the standard specimen with the side groove of 40 % represented a valid fracture toughness. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. However, the fracture resistance curve of half size specimen was similar to that of the standard specimen.

• Journal of Welding and Joining
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• 제33권2호
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• pp.32-39
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• 2015

This study examined the welding residual stress and fracture toughness of 78mm thick steel electro gas welding (EGW) and flux cored arc welding (FCAW) welded joints by numerical analyses of the thermal elasto-plastic behavior and fracture toughness(KIC). The residual stress, fracture toughness characteristics and production mechanism on the welded joints were clarified. Moreover, the effects of the welding process (EGW and FCAW) on the welding residual stresses and fracture toughness of welded joints were evaluated. The results showed that the new welding process (EGW) appears to be an effective substitute for the existing welding process (FCAW) in a thick steel plate with high strength.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.9-15
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• 2001

In the case of a crack propagation, a portion of the work of inelastic deformation near the crack tip is dissipated as heat. In order to understand the thermal effect on fracture toughness, tensile test was carried out using thermocouples to monitor the variation of temperature with SA516 Gr70. The experimental results show that the temperature of specimen was increased $3.6^{\circ}C$ at static load condition. And the thermal effect was investigated connected with the steady-state stress in the vicinity of a crack propagation in the elastic-plastic C-T specimen theoretically. And fracture toughness, the energy to make crack surfaces, presented correctively. The fracture toughness with considering heat at the blunting of the crack tip ws lower about 19.3% than that of ignoring heat. So, it is resonable to apply the fracture toughness with considering thermal energy and it would be good explanation for constraint effect depending on the configuration in the presence of excessive plasticity.

• 한국주조공학회지
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• 제10권5호
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• pp.408-416
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• 1990

The application of this new design approach called fracture mechanics allow one to determine the maximum allowable stress from the knowledge of the largest expected flow size and the plane strain fracture toughness of a material. In this study we examined the relation between retained austenite, mechanical property and fracture toughness accompanied by austempering heat treatment. Fracture toughness values and retained austenite volume were higher with the ADI(austempered ductile iron) which were austempered at $380^{\circ}C$ than austempered at $320^{\circ}C$. Additionally, fracture toughness values were increased for 1~2 hour austempering time but it was slowly decreased for 5 hour ADI maintaining the predominant fracture toughness($K_{IC}:83MPa{\sqrt{m}}$) is obtained following condition, namely, austempering temperature and time ($380^{\circ}C$ and 1 hour).

• 한국세라믹학회지
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• 제31권3호
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• pp.305-311
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• 1994

In this paper, a change of fracture toughness and hardness in PZT-PYW ceramics system before and after poling treatment was measured to investigate the effect of composition on the mechanical properties in PZT-PYW ceramics. The hardness of the PZT-PYW ceramics increased with increasing mole fraction of PYW. The fracture toughness achieved maximum values for x=0.03. Both of the hardness and the fracture toughness also increased with poling treatment. The variation of both hardness and fracture toughness with increasing PYW mole fracture was explained by the change in microstructures such as grain size and second phase. The difference in hardness and fracture toughness in the electrically poled and unpoled specimens was also explained on the bases of internal stress.

• 한국정밀공학회지
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• 제20권8호
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• pp.153-157
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• 2003

In the present work, the effect of plasma treatment of aluminum on the fracture toughness of CFRP/aluminum composites was investigated. The surface of the aluminum was treated by a DC plasma. The plasma treatment was carried out at volume ratio of acetylene gas to nitrogen gas of 5:5 and the treatment time used was 30 sec. Cracked lap shear specimens of aluminum/CFRP composites were made using secondary bonding procedure. Fracture toughness of aluminum/CFRP composites was determined using the work factor approach. Then, the fracture toughness of plasma-treated aluminum/CFRP composites was compared with that of untreated aluminum/CFRP composites. The results showed that the fracture toughness of plasma-treated aluminum/CFRP composites was about 50 % higher than that of untreated aluminum/CFRP composites.

• 한국안전학회지
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• 제16권2호
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• pp.1-6
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• 2001

In the case of a crack propagation a portion of the work of inelastic deformation near the crack tip is dissipated as heat. In order to understand the thermal effect on fracture toughness, tensile tests were carried out using thermocouples to monitor the variation of temperature. The experimental results show that the temperature of specimen was increased $5.4^{\circ}C$ at static load condition. And the thermal effect is investigated connected with the steady-state stress in the vicinity of a crack propagation in the elastic-plastic C-T specimen theoretically. And fracture toughness, the energy to make crack surfaces, presented correctively. The fracture toughness with considering heat at the blunting of the crack tip is lower about 16.9％ than that of ignoring heat. So, it is resonable to apply the fracture toughness with considering thermal energy and it would be good explanation for constraint effect depending on the configuration in the presence of excessive plasticity.