• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.1-6
• /
• 2004

In this study, the intrinsic static/dynamic fracture toughness of Al 7175=T74 is evaluated from the apparent static/ dynamic toughness of notched specimen, The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. Also, effective distance is applied to estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective In this study, the intrinsic static/dynamic fracture toughness of Al 7175=T74 is evaluated from the apparent static/ dynamic toughness of notched specimen, The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. Also, effective distance is applied to estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective distance can be used to evaluate the failure criterion of structure with notch.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.1358-1361
• /
• 2003

In this study, intrinsic static/dynamic fracture toughness of Al 7175-T74 are evaluated from the apparent static/dynamic toughness of notched specimen. The notch/crack critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The notch/crack critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, critical notch root radius can be predicted by notch/crack critical average stress fracture model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2002.04a
• /
• pp.84-87
• /
• 2002

In this study, intrinsic fracture toughness of Al 7175-T74 is evaluated from the apparent toughness of notched specimen. Modified average stress model is used to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched-cracked specimen. The modified average stress model is established the relation between notch radius and effective distance calculated by FEM analysis. The results show that fracture toughness decreases with decreasing of notch root radius. The true fracture toughness can be predicted from test results of apparent fracture toughness measured by using notched specimen.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.4 no.3
• /
• pp.19-25
• /
• 1984

In the welded structure, the most dengerous section is welded parts and almost fractures of welded structure occur from welded parts. Accordingly, in other to prevents of fracture, it is important seeking the fracture behavior of welded parts. In this study as basic investigation of fracture behavior of welded parts, it is investigated that local distribution of fracture toughness and effect of multipass electrode welding, also effect of release of residual stress were investigated, as the subjected. material, the used steel having fatigue history and unused steel were selected. As the result of this study, it is dear that the base metal of unused steel and heat affected zone and weld metal are different each other in fracture toughness, and it seems clear that the weld metal may will become source of fracture because of it having the most low fracture toughness. Especially, in the case of crack occur in the used steel, it will be the most brittle section in the structure because of it having low fracture toughness then weld metal. It affirmation that, if welded parts has not flaw, the multi pass electrode welding effective to improve of fracture toughness, also release of residual stress is none effective to improve of fracture toughness in this study.

• Journal of Welding and Joining
• /
• v.33 no.2
• /
• pp.32-39
• /
• 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.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.11a
• /
• pp.110-114
• /
• 2000

The Interlaminar fracture behavior of hybrid composite with non-woven carbon tissue was investigated under Mode I (DCB) and Mode II (ENF) loading condition. Hybrid composites were manufactured by means of inserting a non-woven tissue between prepreg layers. Two kinds of specimens were prepared from [0]$_{24}$ and [$0_{12}/0_{12}$]. Where, the symbol "/" means that a non-woven carbon tissue was located at 0/0 mid-plane of the specimen. The interlaminar fracture toughness of hybrid composites was compared with that of CFRP. The fracture surfaces of the specimens were observed using optical microscope and SEM, and the failure mechanism was discussed. The hybrid laminates, which are made by inserting non-woven carbon tissue between layers, were shown to be effective to remarkably improve Mode II fracture toughness.toughness.

• Journal of the Korean Ceramic Society
• /
• v.41 no.9
• /
• pp.690-695
• /
• 2004

In this study, inorganic (steel, asbestos and carbon) and organic (polyacryl and polyamide) fibers were used to investigate their reinforcing effects of the physical properties of Portland cement. From the load-displacement curve of each reinforced specimen, fracture strength, Young's module, fracture energy and fracture toughness were computed and compared with each other. In addition, the experiment of their impact toughness was carried out and compared with the fracture energy. For the improvement of fracture strength the inorganic (asbestos) fiber reinforcement was most effective, while the best reinforcing effect of impact toughness was achieved by organic (polyacryl) fiber. And steel fiber proved to be most adequate for improvement of both fracture strength and impact toughness. Steel fiber also showed the highest fracture energy and fracture toughness among all of the fibers.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.12
• /
• pp.3010-3017
• /
• 2000

For integrity evaluation of cracked or damaged structures, fracture toughness test results in ASTM are widely used. The fracture toughness values of the structures are used as an effective design criterion in nuclear plants and aircraft structures. Sometimes the difference of P-$\delta$ curve trend during the unloading /reloading cycle in the fracture toughness test using partial unloading compliance was observed. The phenomenon as a possible source of error in determining fracture toughness may be caused by the residual stress during unloading work-hardening and bucking of a specimen. Therefore, we evaluate the effect of bucking and compressive residual stress during the K-R and J-R testing using a finite element method.

• Journal of the Korean Society for Railway
• /
• v.8 no.2
• /
• pp.195-201
• /
• 2005

Mode II interlaminar fracture behaviors of carbon fabric/epoxy composites, which are applicable to tilting train carbodies, was investigated by the ENF (End notched flexure) test. The specimens were made of CF3327 plain woven fabric with epoxy and a starter delamination at one end was made by inserting Teflon film with the thickness of 12.5$mu$m or 25.0$mu$m. The equation for mode II interlaminar fracture toughness was suggested based on the effective crack length from the compliance of load-displacement curve. Mode II interlaminar fracture toughness was evaluated for several types of the specimens. Also crack propagating behaviors and fracture surfaces were examined through an optical travelling scope and a scanning electron microscope.

• Korean Journal of Metals and Materials
• /
• v.47 no.9
• /
• pp.533-541
• /
• 2009

Materials used for a reactor pressure vessel(RPV) are required high strength and toughness, which determine the safety margin and life of a reactor. Ni-Mo-Cr low alloy steel shows better mechanical properties than existing RPV steels due to higher Ni and Cr contents compared to the existing RPV steels. The present study focuses on effects of Ni, Cr contents on the cleavage fracture toughness of Ni-Mo-Cr low alloy steels in the transition temperature region. The fracture toughness was characterized by a 3-point bend test of precracked Charpy V-notch(PCVN) specimens based on ASTM E1921-08. The test results indicated that the fracture toughness was considerably improved with an increase of Ni and Cr contents. Especially, control of Cr content was more effective in improving fracture toughness than manipulating Ni content, though Charpy impact toughness was changed more extensively by adjusting Ni content. These differences between changes in the fracture toughness and that in the impact toughness were derived from microstructural features, such as martensite lath size and carbide precipitation behavior.