• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.4-5
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• 2021

In irregular curtain walls, the nominal stress required for each member varies greatly depending on the shape, so it is inefficient to design members based on the maximum required stress. Then, built-up members are absolutely necessary, but built-up members manufactured by Manpower-welding cannot be constructed in an irregular curtain wall building because it' not precise. In order to address the problems, this paper presents why Robotic-laser-welding should be used in irregular curtain walls using Gwanggyo Galleria Department Store involving 3D printing as an example. Results verify the performance of Robot-Laser-Welding as an efficient solution for precise steel curtain wall members.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.239-250
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• 2000

This study investigates the mechanical behavior on trough rib to crossbeam joint in orthotropic steel plate decks, specially emphasizing on the effect of diaphragm inside trough rib on the fatigue behavior of slit by static and fatigue tests. In particular, the effects of diaphragm on in-plane stress and out-of-plane stress, stress concentration, propagation of fatigue cracks at the silt are studied. With the result of experiment and numerical analysis, we have estimated the fatigue strength using the nominal stress and hot-sport stress. The details with diaphragm have occurred about 50% stress reduction at trough rib part of trough rib to crossbeam joint than the detail without diaphragm, however, the lower parts of crossbeam have occurred much more stress. Initial crack size or slit have an considerable influence on the propagation of fatigue cracks due to V-notch. The fatigue strength category of the details without diaphragm has higher value than fatigue limit, whereas that of the details with diaphragm is estimated lower than fatigue limit.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.85-99
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• 1998

This paper describes an experimental study to examine collapse causes of the lifting cable due to brittle failure of an fitting anchor under the lifting works. Also, in this study an collapse mechanism that was obtained from stress analysis was compared with an actual collapse procedure. Fractographical analysis as well as chemical component test, tension test and Charpy V-Notch impact test for the fractured steel members were carried out. And then, its results were compared with that of normal steel members. Circumferential surface flaws were developed at internal facets of the fitting anchor before tensile stress occurred. Hence, a higher stress than nominal stress was occurred at flaws by stress concentration at the crack tip. Also, stress intensity factor of members increased by crack size of the potential flaws. Because the stress intensity factor at the crack tip was greater than critical values(fracture toughness), brittle fracture occurred under the lifting works. It is judged that the main collapse of the lifting cable is due to brittle fracture of the fitting anchor.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.233-246
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• 2014

Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it's been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.5
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• pp.304-308
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• 2005

The effects of diethylhexyl phthalate (DEHP) on various oxidative stress responses in liver, kidney and gill tissues of freshwater bagrid catfish Pseudobagrus fulvidraco were investigated under laboratory conditions. Bagrid catfish were intraperitoneally injected with sunflower seed oil containing nominal concentrations of 0, 300 or 900mg DEHP per kilogram of body weight for 3 days and the effects after last injection were assessed in liver, kidney and gill tissues of the exposed organisms. The oxidative stress responses of fish were evaluated by analyzing the level of glutathione (GSH), as well as the activities of antioxidant enzymes such as glutathione S-transferase (GST), glutathione peroxidase (GPx) and glutathione reductase (GR). After exposure to the DEHP, there were significant decrease in GR, GPx activity and GSH content in liver of fish exposed to 900 mg DEHP per kilogram of body weight compared to the control group. Compared with the control group, significant decreases in renal GPx and GR activity were observed in the DEHP treatment groups (900 mg $kg^{-1}$ bw). However, no significant difference was observed in any oxidative stress responses in gills between the DEHP-treated and the untreated group of fish. The findings of the present investigation show that DEHP induce oxidative stress and the liver was the most affected organ followed by the kidney and gills. Furthermore, the changes of GPx and GR activities may be important indicators of oxidative stress responses but additional study is required to confirm the oxidative stress of DEHP.

• Journal of Welding and Joining
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• v.12 no.1
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• pp.102-115
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• 1994

This paper is to evaluate the fatigue strength of lap joints of materials applied to LNG carrier cargo containment of GAZ-TRANSPORT(GT) type, which was welded by manual and automatic TIG welding process. The thicknesses of lapped members were 1.5mm/1.5mm or 1.5mm/0.7mm in Invar to Invar joint, and 1.5mm/8.0mm in Invar to stainless steel joint, respectively. These lap joints were mainly applied to the membrance fabrication of GT-LNG carrier. Fatigue tests of Invar/Inar lap joints were conducted under the stress ratio R=0 at room temperature. The effect of mean stress and cumulative fatigue damage on the allowable stress of Invar lap joint was evaluated on the basis of test results. Fatigue test was also conducted on Inver/Stainless steel lap joints welded by automatic TIG process without filler metals. The fatigue test of the joint was carried out under the same conditions as those of Invar/invar lap joints. The fatigue strength of the joint welded without filler metal was comparable to those welded with filler metal quoted from reference. The fatigue strength of Invar/stainless steel lap joint was only dependent on the lap throat thickness, and not on the welding process. Based on test results, the applicability of TIG welding process without filler metal in Invar/stainless steel lap joint was reviewed by controlling welding variables to assure the valid throat thickness of lap joints.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.875-881
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• 2013

The failure of a bolted joint owing to stress corrosion cracking (SCC) has been considered one of the most important structural integrity issues in a nuclear power plant. In this study, the failure possibility of bolting, which is used to support the steam generator of a pressurized water reactor, owing to SCC and brittle fracture was evaluated in accordance with guidelines proposed by the Electric Power Research Institute, which are called the Reference Flaw Factor method. For this evaluation, first, detailed finite element stress analyses were conducted to obtain the actual nominal stresses of bolting in which either service loads or bolt preloads were considered. Based on these nominal stresses, the structural integrity of bolting was addressed from the viewpoints of SCC and toughness. In addition, the accuracy of the EPRI Reference Flaw Factor for assessing bolting failure was investigated using finite element fracture mechanics analyses.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.1-9
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• 1985

In-plane tension fatigue tests (R = 0.05) were carried out to investigate the initiation and propagation behaviors of micro-surface-fatigue cracks on smooth surfaces of a mild steel. Also, the investigations of saturated cyclic strain which can be obtained by the fatigue tests have been made via the cyclic strain intensity factor, .DELTA. $K_{\epsilon}$/, for the purpose of unifying two approaches of the study of fatigue; the one approach is based on the fracture mechanics concept and the other on lowcycle fatigue concept. Some of the results are as follows; The growth rate, d(2a)/dN, of small cracks cannot be represented by one straight line as a function of .DELTA.K for various of the nominal stress range, .DELTA..sigma., and is higher than that of a larger through crack. The rearrangement of the d(2a)/dN by .DELTA..epsilon..root..pi.s( = .DELTA. $K_{\epsilon}$/) with the stress range .DELTA..epsilon. in .DELTA.K replaced by .DELTA..epsilon., strain range, gives one straight line of the .DELTA. $K_{\epsilon}$-d(2a)/dN relation for various values of stress range .DELTA.$_{\epsilon}$../.X>../.

• Steel and Composite Structures
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• v.39 no.4
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• pp.453-469
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• 2021

The cracking at the transverse diaphragm cutout is one of the most severe fatigue failures threatening orthotropic steel decks (OSDs), whose mechanisms and crack treatment techniques have not been fully studied. In this paper, full-scale experiments were first performed to investigate the fatigue performance of polished cutouts involving the effect of an artificial geometrical defect. Following this, comparative experimental testing for defective cutouts strengthened with carbon fiber-reinforced polymer (CFRP) was carried out. Numerical finite element analysis was also performed to verify and explain the experimental observations. Results show that the combinative effect of the wheel load and thermal residual stress constitutes the external driving force for the fatigue cracking of the cutout. Initial geometrical defects are confirmed as a critical factor affecting the fatigue cracking. The principal stress 6 mm away from the free edge of the cutout can be adopted as the nominal stress of the cutout during fatigue evaluation, and the fatigue resistance of polished cutouts is higher than Grade A in AASHTO specification. The bonded CFRP system is highly effective in extending the fatigue life of the defective cutouts. The present study provides some new insights into the fatigue evaluation and repair of OSDs.

• Transactions of Materials Processing
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• v.33 no.1
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• pp.18-35
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• 2024

In the present work, the evolution rules for the internal variables including continuum damage factors are obtained using the thermodynamic framework, which are in turn facilitated to derive the elastic-plastic constitutive relation for the particulate composites. Using the Mori-Tanaka scheme, the homogenization on state and internal variables such as back-stress and damage factors is carried out to procure the rate independent plasticity relations. Moreover, the degradation of mechanical properties of constituents is depicted by the distinctive damages such that the phase and interfacial damages are treated individually accordingly, whereas the kinematic hardening is depicted by combining the Armstrong-Frederick and Phillips' back-stress evolutions. On the other hand, the present constitutive relation for each phase is expressed in terms of the respective damage-free effective quantities, then, followed by transformation into the damage affected overall nominal relations using the aforementioned homogenization concentration factors. An emphasis is placed on the qualitative analyses for strain localization by observing the perturbation growth instead of the conventional bifurcation analyses. It turns out that the proposed constitutive model offers a wide range of strain localization behavior depending on the evolution of various internal variable descriptions.