• Journal of the Korean Society of Safety
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• v.14 no.1
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• pp.25-32
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• 1999

The objective of this paper is to evaluate the fracture resistance characteristics of SA508 CL.1a carbon steel, TP347 stainless steel and their associated welds manufactured for primary coolant system of Ulchin 3,4 nuclear power plants. The effect of various parameters such as pipe size, welding method, chemical composition, crack plane orientation, metallography and fractography on the material properties were discussed. Test results showed that the effect of pipe size on fracture toughness is negligible while the effect of welding method on fracture toughness is significant. In addition, the drop of fracture toughness in the field fabrication weld of TP347 stainless steel is probably due to the large amount of $\sigma$-phase precipitated on the $\delta$-ferrite boundary and the large size dimples.

• Structural Engineering and Mechanics
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• v.56 no.2
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• pp.157-167
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• 2015

The impact behavior of epoxy-based nanocomposites reinforced with carbon nano tube (CNT), carbon nano fiber (CNF) and mixed contents of these nanoparticles was investigated using Izod impact test. The results showed that while the impact strength of nanocomposites containing 1 wt% of CNT and 1 wt% of CNF increased 19% and 13% respectively, addition of mixed contents of these nanofillers (0.5-0.5 wt%) demonstrated higher improvement (21%) in the impact resistance. The trend of the results is explained on the basis of different fracture mechanisms of nanocomposites. Furthermore, the fracture surface of specimens and the dispersion state of nanoenhancers have been studied using scanning electron microscopy (SEM) photographs.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.104.2-104.2
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• 2007

• The Journal of Advanced Prosthodontics
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• v.8 no.6
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• pp.489-493
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• 2016

PURPOSE. This in-vitro study aimed to evaluate the fracture resistances and failure modes of endodontically treated mandibular premolars restored with endocrowns and conventional post-core retained crowns. MATERIALS AND METHODS. Thirty mandibular premolars were assigned into three groups (n=10): GI, intact teeth; GE, teeth with endocrowns; GC, teeth with conventional post-core supported crowns. Except for the teeth in group GI, all specimens were cut to 1.5 mm above the cementoenamel junction and endodontically treated. Both endocrowns and conventional crowns were fabricated from lithium-disilicate blocks using a CEREC 3D CAD/CAM unit. All specimens were subjected to thermocycling and then to $45^{\circ}$ oblique compressive load until fracture occurred. The fracture resistance and failure mode of each specimen were recorded. Data were analyzed with one-way ANOVA and LSD Post Hoc Test (${\alpha}=.05$). RESULTS. The fracture resistances of GE and GC were significantly lower than that of GI (P<.01), while no significant difference was found between GE and GC (P=.702). As of the failure mode, most of the specimens in GE and GC were unfavorable while a higher occurrence of favorable failure mode was presented in GI. CONCLUSION. For the restoration of mandibular premolar, endocrown shows no advantage in fracture resistance when compared with the conventional method. Both of the two methods cannot rehabilitate endodontically treated teeth with the same fracture resistances that intact mandibular premolars have.

• The Journal of Korean Academy of Prosthodontics
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• v.60 no.2
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• pp.135-142
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• 2022

Purpose. This study aims to evaluate the combined effect of reduced thickness in different regions on the fracture resistance of monolithic zirconia crowns. Materials and methods. Seven nickel-chromium dies were generated from a 3D model of mandibular first molar using the digital scanner with the following geometries: 1.5 mm occlusal reduction, 1.0 mm deep chamfer. Based on the abutment model, Zirconia blocks (Luxen Zirconia) were selected to fabricate Sixty-three zirconia crowns with occlusal thicknesses of 0.3 mm, 0.5 mm, and 1.5 mm, and different axial thicknesses of 0.3 mm, 0.5 mm, and 1.0 mm. All crowns were cemented by resin cement. Next, the crowns were subjected to load-to-fracture test until fracture using an electronic universal testing machine. In addition, fracture patterns were observed with a scanning electron microscope (SEM). Two-way ANOVA and the Tuckey HSD test for post hoc analysis were used for statistical analysis (P < .05). Results. The mean values of fracture resistancerecorded was higher than the average biting force in the posterior region. The two-way ANOVA showed that the occlusal and axial thickness affected the fracture resistance significantly (P < .05). However, the effect of axial thickness on fracture resistance did not show a statistical difference when thicker than 0.5 mm. The observed failure modes were partial or complete fracture depending on the severity of crack propagation. Conclusion. Within the limitations of the present study, the CAD-CAM monolithic zirconia crown with extremely reduced thickness showed adequate fracture resistance to withstand occlusal load in molar regions. In addition, both occlusal and axial thickness affected the fracture resistance of the zirconia crown and showed different results as combined.

• Korean Journal of Materials Research
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• v.12 no.6
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• pp.436-441
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• 2002

Effect of Sn addition on the stress corrosion cracking(SCC) resistance of the Al-Cu-Mn cast alley was investigated by C-ring teat and electrical conductivity measurement, The electrical conductivity and SCC resistance increased by Sn addition. The alley containing 0,10%Sn showed maximum electrical conductivity and the best SCC resistance. At the same composition, the electrical conductivity and SCC resistance increased from peak aged condition to ever aged condition. The PFZ and coarse precipitates along the grain boundary were observed from TEM micrographs. The fracture mode of the alloy was confirmed as intergranular type and showed brittle fracture surface. The SCC mechanism of the alloy was concluded as the anodic dissolution model, The maximum hardness was increased from 130Hv in the Sn-free alloy to 156Hv in the 0.10%Sn added alloy.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.05a
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• pp.73-77
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• 2008

In this study, we would like to study on the application of roof exposure waterproofing method of joint stability through shiplap rubberized asphalt color sheet to complement problem of fracture, exfoliation and water leakage by existing roof exposure sheet waterproofing material joint weakness. Accordingly, examined basis performance and stability for joint that shiplap rubberized asphalt color sheet through test of that tensile strength, bonding strength, water permeability after bonding, peel resistance after bonding, lengthen resistance after bonding and hang resistance after bonding. The results of this study, waterproofing method to using shiplap rubberized asphalt color sheet is judged to solved fracture, exfoliation and water leakage problems happened in joint by problem was joint of exposure sheet by minimizing gap of joint being integration by shiplap.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.116-123
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• 2006

During the last two decades, many researchers investigated influences of stress triaxiality on ductile fracture for various specimens and structures. With respect to a transferability issue, the local approach reflecting micro-mechanical specifics is one of effective methods to predict constraint effects. In this paper, the applicability of the local approach was examined through a series of finite element analyses incorporating modified GTN (Gurson-Tvergaard-Needleman) and Rousselier models as well as fracture toughness tests. To achieve this goal, fracture resistance (J-R) curves of several types of compact tension (CT) specimens with various crack length, with various thickness and with/without 20% side- grooves were estimated. Then. the constraint effects were examined by comparing the numerically estimated J-R curves with experimentally determined ones. The assessment results showed that the damage models might be used as useful tool for fracture toughness estimation and both the crack length and thickness effects should be considered for realistic structural integrity evaluation.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.13-18
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• 2004

The objective of this study is to investigate fracture toughness and fatigue crack propagation behavior in the Reduced Activation Ferritic Steel (RAFs) JLF-I. The fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The fatigue crack propagation behavior of the JLF-I steel was investigated by the constant-amplitude loading test for the stress ratios R=O.I, 0.3 and 0.5 respectively. The effects of stress ratios and specimen size on the fatigue crack growth behaviors for JLF-I steel were discussed within the Paris law. The test results showed the standard CT 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. The fatigue crack propagation rate of a half size specimen was similar to that of a full size specimen at the stress ratios of 0.1, 0.3 and 0.5 respectively. The fatigue crack propagation behavior of this material were evaluated by using a half size specimen.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.1-7
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• 2012

The fracture resistance and tensile properties of $Y_2O_3$ oxide dispersion strengthened steel containing 9 wt% Cr(9Cr-ODS) were measured at various temperatures up to $700^{\circ}C$. The fracture characteristics were compared with those of commercial E911 ferritic/martensitic steel. The strength of 9Cr-ODS was at least 30% higher than that of E911 steel at the test temperatures below $500^{\circ}C$. The strength difference between the two materials was almost diminished at $700^{\circ}C$. 9Cr-ODS showed cleavage fracture behavior at room temperature and unstable crack growth behaviors at $300^{\circ}C$ and $500^{\circ}C$. The J-R fracture resistance of 9Cr-ODS was much lower than that of E911 steel at all temperatures. It was deduced that the coarse $Cr_2O_3$ particles that were formed during the alloying process provided the crack initiation sites of cleavage fracture in 9Cr-ODS.