• Computational Structural Engineering
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• v.7 no.4
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• pp.113-118
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• 1994

The purpose of this study is elastic plastic finite element analysis for standard fracture toughness specimens. The principles of elastic-plastic fracture mechanics are shortly summarized and the special requirements for computational tools are derived. Possibilities to model the crack tip singularities are mentioned. The relevant fracture parameters like J-Integral and COD and their correlation are evaluated from elastic plastic finite element calculations of standard fracture toughnes specimens. The size and form of the plastic zone are shown. The comparion between experiment and caculation is discussed as well as the application of the limit load analysis.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.12
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• pp.114-119
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• 1996

In the case of surface cracked plate specimen, we can not measure the fracture toughness of ductile materials by the ASTM E 813 standard method. In this report, using the Acoustic Emission method, we found out crack initiation point and investigated fracture toughness which was calculated by FEM. The method used in this paper shows that fracture toughnes by using AE technique is reliable.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2319-2325
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• 2000

This thesis studied that seven kinds of residual elements(inclusions) had influenced on fracture toughness($K_{IC}$) obtained by Begley-Logsdon and Rolfe-Novak model equation using tensile an d impact test data of I%CrMoV HP(high pressure) rotor steel. $K_{IC}$ design curve of ASME and fracture surface by SEM were also considered, obtained results are summarized as follows $K_{IC}$ was linearly increased with increase of temperature, effect of the inclusions was significantly over FATT. $K_{IC}$ at lower shelf temperature was quantitatively related to yield strength and was agreed well with Begley's equation. It was difficult to determine $K_{IC}$ because of specimen size and tester capacity at upper shelf temperature, but for this view point Rolfe-Novak's equation was useful. The degree of brittle fracture was dependent on FATT fundamentally, adding S, Sb to matrix decreased impact energy and adding Cu, As increased yield(tensile) strength, and the influence of the others minority inclusion was comparatively insignificant.

• Journal of Welding and Joining
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• v.9 no.4
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• pp.40-49
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• 1991

Both impact and fracture toughnesses were investigated with root gaps in FCAW weld metals at room temperature and 0.deg.C. The maximum impact value was obtained at the root gap of 16mm for 1G position weld metal, and the impact value of 3G position weld metals also showed the maximum impact value at the root gap of 12mm. However, the fracture toughnes(CTOD)values tend to decrease with increasing root gaps at both temperatures in 1G weld metal. Bending test also showed satisfactory results with all of root gaps investigated. Based on this result, it becomes possible to apply wide root gaps in real projects in both aspects of toughness and bending resistance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2405-2412
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• 2000

A cast stainless steel may experience an embrittlement when it is exposed to approximately 30$0^{\circ}C$ for long period. In the present investigation, The three classes of the thermally aged CF8M specimie n are prepared using an artificially accelerated aging method. Namely, after the specimen are held for 300, 1800 and 3600hrs. at 43$0^{\circ}C$ respectively, the specimens are quenched in water to room temperature. Load versus load line displacement curves and J-R curves are obtained using the unloading compliance method. $J_{IC}$ values are obtained following ASTM E 813-87 and ASTM E 813-81 methods. In addition to these methods, JIC values are obtained using SZW(stretch zone width) method described in JSME S 001-1981. The results of the unloading compliance method are $J_Q$=485.7 kJ/m$^2$ for virgin material, $J_{IC}$ of the degraded materials associated with 300, 1800 and 3600hrs are obtained 369.25 kJ/m$^2$, 311.02 kJ/m$^2$, 276.7 kJ/m$^2$, respectively. The results of SZW method are similar to those of the unloading compliance method. Through the elastic-plastic fracture toughness test, it is found that the value of $J_{IC}$ is decreased with increasing of the aging time. The results obtained through the investigation can provide reference data for a leak before break(LBB) of reactor coolant system of nuclear power plants.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.711-717
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• 1999

A multilayer-structure material containing ductile and brittle layer simultaneously was examined and compared with a single layer material using fracture mechanical properties. We found that impact strength of multilayer structure material was considerably higher than single layer's and toughness was enhanced by about two times or higher in similar glass transition temperature($T_g$) region and the same dimension. The superposition principle of impact pulse was used for interpretation of kinetic stress wave as a high-velocity crack proceeds in the plastic. It was understood that the optimum condition of ductile/brittle thickness ratio could be designed in the final toughness enhancement of multilayer.