• Polymer(Korea)
• /
• v.31 no.2
• /
• pp.123-129
• /
• 2007

Toughening mechanisms and mechanical properties of three different polyolefin-based composite systems we studied using the tensile, Izod impact and double-notch lout-point-bending (DN-4PB) test, which is well known be an effective tool for probing the failure mechanism (s) around the subcritically propagated crack tip. Microscopy observations such as optical microscopy and transmission electron microscopy were carried out lot the test samples. A detailed investigation clearly shows that a variety of toughening mechanisms, i.e., shear yielding, craze, particle-matrix debonding, rubber particle cavitation, crack deflection and bifurcation, are observed around crack tip damage zone. These toughening mechanisms are responsible for the observed, improved fracture toughness. Based on this study, DN-4PB technique is sufficient to obtain the information needed to describe the fracture behavior of polyolefin-based composites as well as their corresponding toughening mechanisms.

• Tunnel and Underground Space
• /
• v.26 no.3
• /
• pp.181-191
• /
• 2016

In geological storage of $CO_2$, the behavior of $CO_2$ is influenced by pore network of rock. In this study, the drilling cores from Pohang Basin were analyzed quantitatively using three-dimensional images acquired by X-ray micro computed tomography. The porosities of sandstone specimens around 740 m-depth (T1), 780 m-depth (T2) and 810 m-depth (T3) which were target strata were 25.22%, 23.97%, 6.28%, respectively. Equivalent diameter, volume, area, local thickness of pores inside the sandstone specimens were analyzed. As a result, the microstructural properties of T1 and T2 specimens were more suitable for geological storage of $CO_2$ than those of T3 specimens. The result of the study can be used as input data of the site for decision of injection condition, flow simulation and so on.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.4
• /
• pp.482-488
• /
• 2018

Generally, after stern tube bearing shows a significant increase in local load due to propeller load, which increases the potential adverse effects of bearing failure. To prevent this, research on regarding shaft alignment has been carried out with a focus on reducing the relative slope between the shaft and support bearing(s) under quasi-static conditions. However, for a more detailed evaluation of a shafting system, it is necessary to consider dynamic conditions. In this context, the results revealed that eccentric propeller force under transient conditions such as a rapid rudder turn at NCR, lead to fluid-induced instability and imbalanced vibration in the stern tube. In addition, compared with NCR condition, it has been confirmed that eccentric propeller forces given a rapid rudder starboard turn can lift a shaft from the stern tube bearing in the stern tube, contributes to load relief for the stern tube bearing.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.5C
• /
• pp.313-320
• /
• 2008

The discharge capacity testing apparatus using penetration method, being able to simulate in laboratory the condition of embedding plastic board drains in field, was developed to investigate consolidation characteristics of ground and to figure out discharge capacity of drains. The developed apparatus with a mandrel and penetrating device was designed to insert PBD into the ground prepared by previously applied pressure, being different from the conventional testing method that the drain was installed and the ground material was poured subsequently. Discharge capacity tests with the conventional apparatus as well as the newly developed one were performed to assess the applicability of the latter. As a result of tests, the conventional method showed delayed consolidation due to overall disturbance of ground and local deformation of drain caused by inhomogeneity of ground. Therefore discharge capacity of drain with the conventional apparatus was measured more or less larger than the expected values whereas discharge capacity with new one could be measured similar to the actual value in field.

• CORROSION AND PROTECTION
• /
• v.12 no.1
• /
• pp.30-38
• /
• 2013

Austenitic stainless steels and Ni-base alloys are widely used as structural materials for major components and piping system in pressurized water reactors (PWRs). These austenitic alloys are known to be susceptible to environmental assisted cracking (EAC), such as environmentally-assisted fatigue (EAF) and primary water stress corrosion cracking (PWSCC) during long-term exposure to PWR primary water environment. In this paper, the current understanding on the phenomena and mechanisms of these EAC are briefly introduced using experimental results and literature review. The mechanisms for EAF and PWSCC for austenitic stainless steels and Ni-base alloys are discussed. Currently, austenitic stainless steels are known to be more susceptible to EAF, while less susceptible to PWSCC than Ni-base alloys. The possible explanations to such behaviors are proposed and discussed in view of the role of hydrogen and internal oxidation.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.3
• /
• pp.116-122
• /
• 2007

The concrete structures in Metropolitan city are usually exposed to carbonation and corrosion of embedded steel occurs due to the carbonation. In inspection and diagnosis of concrete structures, carbonation depth in sound concrete is mainly evaluated and service life for concrete structure is predicted based on the result. Generally, however, mass concrete structures such as columns have construction joint for suitable placing and also have cracks in early-age. In this study, carbonation depth in RC columns used for 20 years in metropolitan city is evaluated and also analyzed by considering the local conditions like sound, cracked, and joint area. The carbonation depth in cracked and joint area is more rapid than that in sound area, and it is thought to be more desirable to consider this effect in concrete structures with small cover depth. Furthermore, the technique for carbonation prediction in cracked concrete is derived in terms of crack width and the results from this technique are verified by comparing those from previous research.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.4 s.56
• /
• pp.116-125
• /
• 2009

Recently, modular system are popular in construction fields, and they are increasing their marcket share. To compare modular units, bolting and welding are most popular methods. However, the temperature around a welded part might be over than 1,300$^{\circ}C and the composite member might be exposed tp the direct welding heat about 20,000$^{\circ}C. This high welding heat makes decrease of the concrete strength. If the concrete strength seriously decreases, it can affect the behavior and safty of a structure. On this study, To prevent of concrete strength decreases by welding heat, we suggested method of to insert between steel and concrete.

• Journal of Korean Society of Steel Construction
• /
• v.17 no.5 s.78
• /
• pp.561-568
• /
• 2005

The object of this paper is to determine appropriateness for use of high-strength tensile bar as a tension web member. The gap K-joint of tensile bar types were compared with gap K-joint of square hollow section (SHS) types. For the same width-to-thickness ratio ($2{\gamma}=33.3$ ), tests were performed on four specimens of the SHS type and eight specimens of the tensile bar type. The comparison of capacity with the experimental results showed a capacity of the SHS type joint to be higher than that of the tensile bartype joint for the same brace-to-chord width ratio. Moreover, the capacity of the SHS type joints increased proportionally to the width ratio ${\beta}$), while tensile bar type joints increased as the tension width ratio (${\beta}2$). In failure mode, SHS-type specimens showed local buckling of the compression brace and plastic failure was observed between the tension brace and chord face, and with the tensile bar type specimens there appeared punching shear failure of the chord face at the toe of the connection plate. It is, therefore, concluded that width-to-thickness ratio should be lower than that of the hollow-section type and the relation between tension and compression width ratio should be considered.

• Journal of Navigation and Port Research
• /
• v.31 no.3 s.119
• /
• pp.235-245
• /
• 2007

Stiffened steel plates are basic structural members on the deck and bottom structure in ship, offshore. It has a number of one sided stiffeners in either one or both directions, the latter structure was called grillage structure. At the ship structural desgn stage, one of the major consideration is evaluation for ultimate strength of the hull girder. In general, it is accepted that hull girder strength can be represented by the local strength of the longitudinal stiffened panel. In case of considering hogging condition in a stormy sea, stiffened panel was acting on the bottom structure under axial compressive load induced hull girder bending moment, also simultaneously arising local bending moment induced lateral pressure load. In this paper, results of the structural analysis have been compared with another detailed FEA program and prediction from design guideline and a series analysis was conducted consideration of changing parameters for instance, analysis range, cross-section of stiffener, web height and amplitude of lateral pressure load subjected to combined load (axial compression and lateral pressure load). It has been found that finite element modeling is capable of predicting the behaviour and ultimate load capacity of a simply supported stiffened plate subjected to combined load of axial compression and lateral pressure load It is expected that these results will be used to examine the effect of interaction between lateral pressure and axial loads for the ultimate load-carrying capacity based on the Ultimate Limit State design guideline.

• Journal of the Korea Concrete Institute
• /
• v.23 no.2
• /
• pp.169-176
• /
• 2011

In this study, the flexural test for reinforced high performance fiber reinforced cementitious composites (R/HPFRCC) members has been conducted in order to investigate the flexural behavior including the effect of an ordinary tensile reinforcing bar. Through the test, it was observed that the flexural strength increased due to the stable tensile stress transfer of HPFRCC, even up to the ultimate state. In addition, no localized crack appeared until the yielding of the reinforcement. From the layered section analysis of the tested members, it was found that the analysis with the tensile model obtained from the tension stiffening test showed better agreement with the flexural test results, whereas the analysis with direct tension test results overestimated the flexural capacity. Through the experimental and analytical studies, two flexural failure modes have been defined in this paper; concrete crushing at the top compression layer or tensile failure at the bottom tensile layer of the beam section. Based on these two flexural failure modes, a simple formula that estimates the ultimate flexural strength of the member has been proposed in this paper. The proposed equations can be useful in a design and an analysis of R/HPFRCC members.