• Magazine of the Korean Society of Agricultural Engineers
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• v.30 no.1
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• pp.63-72
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• 1988

The primary objective of the study was to find the deformation characteristics of reinforced polymer concrete beams. A test program was carried out to compare the behavior in deformation of polyester and MMA concrete beams with cement concrete beams but with varying ratios of tensile reinforcement. From the results the following conclusions can be made. 1.The various strengths of polymer concrete ware very high compared to the strengths for cement concrete. Also, compared to conventional concrete beams, flexural strength of reinforced polymer concrete beams was distinctly higher for the same section and steel ratios. 2.The polymer concrete beams exhibit large deflections accompanied by relatively high strengths as compared to cement concrete beams. 3.The average ultimate strain at the extreme compression fiber of polymer concrete beams was 0.01 1 cm / cm, and this value was about three to four times as large as that of cement concrete beams, 4.The polymer concrete beams developed more cracks which were more wide crack distribution spacing than the cement concrete beams, and the beams failed in a more ductile manner. 5.The reinforcing steel ratio has a significant effect on the beam strength, load-deflection response, stress-strain curve, and crack pattern of polymer concrete beams.

• Journal of Powder Materials
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• v.1 no.2
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• pp.198-207
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• 1994

In order to find an optimal friction-welding condition for Ni-base ODS alloy (MA 754) produced by mechanical alloying, joint experiments were performed with various conditions of friction pressures (50~500 MPa), friction times (1~5 sec) and upset pressures (50~600 MPa). The optimal friction pressure and upset pressure must be above 400 MPa and 500 MPa, respectively, which are determined by tensile strengths and fracture features of as-welded joints. A maximum stress설h of 975 MPa could be obtained under these pressure conditions at friction time of 2 sec. Microstructural features of bonded interface by optical microscope and SEM revealed that the interface regions of all specimens are consisted with three distinct regions and defects such as voids, cracks and wavy interfaces exist in the joints produced under not-optimized conditions. EDS results showed that these defects include oxides composed with elements of Al, Y and Ti. The hardness on the bonded interface was higher than in the base metal region. Specimens fractured in bonded interface region had lower strength values compared to those fractured in base metal region. Surfaces of the former showed a typical intergranular fracture.

• Korean Journal of Materials Research
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• v.14 no.4
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• pp.239-245
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• 2004

Resistance spot weldability of coated steels for automobile applications was investigated. Test samples were prepared from commercial products of 0.8 mm in thickness. Based on the tensile-shear test, surface quality examination and cracking behavior, it was clear that aluminized steels showed good weldability. Microstructural inspection revealed that the coated materials was piled up at the split zone in the welding of aluminized steels. It was also demonstrated that no weld crack was found in the aluminized steel weld metal even the welding was carried out with higher current. However, through thickness cracks were detected at the weld metal of zinc coated steel. Small particles were found on the crack surface of zinc coated steel weld metal. It was thought that zinc vapor played key role to form the weld crack.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.39-46
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• 2001

It is noted that KS D 3507 pipe steel has several problems when it is used as a city gas pipe at medium pressure. So new pipe steel, KS D 3631, was developed in order to be used as a pipe for medium and low pressure and now it is being substituted for D 3507. In this study, several mechanical tests, such as tensile test, microhardness test, and Charpy impact test were conducted to get material properties of D 3507 and D 3631 pipe steels. And also microstructures at the weld and heat affected zones were observed for the two materials. From the Charpy test results $K_{IC}/$ was estimated for the upper and lower shelf and the critical crack length is calculated for supposed axial semi-elliptical surface cracks. And the burst pressure is estimated as a function of wear depth for a defective D 3631 pipe by using the finite element method. The burst pressure is also calculated for pipes with an axial crack by using the published equations.

• Computational Structural Engineering
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• v.10 no.1
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• pp.129-134
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• 1997

Interfacial stress singularity in a unidirectional two-dimensional laminate model consisting of an elastic fiber and a viscoelastic matrix has been investigated using the time-domain boundary element method. First, the interfacial singular stresses between the fiber and the matrix of a unidirectional laminate subjected to a uniform transverse tensile strain have been investigated near the free surface, but without any defect or any edge crack. Such a stress singularity might lead to fiber-matrix debonding or interfacial edge cracks. Then, the overall stress intensity factor for the case of a small interfacial edge crack of length a has been computed.

• Structural Engineering and Mechanics
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• v.22 no.2
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• pp.223-240
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• 2006

Taking into account the geometrical and material nonlinearities, an ultimate behavior of reinforced concrete cooling tower shell in hyperbolic configuration is presented. The design wind pressures suggested in the guidelines of the US (ACI) and Germany (VGB), with or without the effect of internal suction, are employed in the analysis to examine the qualitative and quantitative characteristics of each design wind pressure. The geometrical nonlinearity is incorporated by the Green-Lagrange strain tensor. The nonlinear features of concrete, such as the nonlinear stress-strain relation in compression, the tensile cracking with the smeared crack model, an effect of tension stiffening, are taken into account. The biaxial stress state in concrete is represented by an improved work-hardening plasticity model. From the perspective of quality of wind pressures, the two guidelines are determined as highly correlated each other. Through the extensive analysis on the Niederaussem cooling tower in Germany, not only the ultimate load is determined but also the mechanism of failure, distribution of cracks, damage processes, stress redistributions, and mean crack width are examined.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.240-245
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• 2005

There has been a strong demand on more economic and lower depth girder bridges for short and medium span range, PRECOM, which is a new type steel-concrete composite girder, has been developed to realize a more economic bridge system with a lower depth girder. In the PRECOM girder bridge, a steel plate girder is simply supported and then concrete form is hung to girder. Thus, the self-weight of the concrete is loaded to the steel girder. To increase the resistance of concrete in the lower casing against tensile stress, compressive force is introduced by prestressed tendon To evaluate the manufacturability and performances of the completed bridge, four 15-m girders and a bridge specimen with two 20m girders wvere constructed. The camber during the construction and introduction of an appropriate compressive force was evaluated. Dynamic data were obtained through the modal testing of the completed girders. Static loading test was also conducted to examine cracks and evaluate the decrease in stiffness and failure behavior under extreme conditions.

• Elastomers and Composites
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• v.53 no.3
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• pp.168-174
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• 2018

Natural rubber (NR) and bromo-isobutylene-isoprene rubber (BIIR) were compounded with other formulation chemicals through polymer blending via a mechanical mixing method. After rubber vulcanization by hot-press compression molding, the cure characteristics, mechanical properties, and ozone resistance of the NR/BIIR blends were measured. As the BIIR content increased, the maximum torque of the blends decreased, while the optimum cure time and scorch time tended to increase. Furthermore, the hardness of the blends increased with increasing BIIR content, reaching the maximum value at 75 wt% BIIR, and decreased with a further increase in the BIIR loading. The tensile strength and elongation at break decreased with an increase in the BIIR content, reaching the minimum value at 75 wt% BIIR, and increased with a further increase in the BIIR content. In the ozone resistance test, cracks were not generated when the BIIR content was more than 75 wt%.

• Structural Engineering and Mechanics
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• v.36 no.6
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• pp.729-744
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• 2010

There is world wide concern for safety of nuclear power installations after the terrorist attack on World Trade Center in 2001 and several other civilian structures in the last decade. The nuclear containment structure in many countries is a double shell structure (outer shell a RCC and inner a prestressed concrete). The outer reinforced concrete shell protects the inner shell and is designed for external loading like impact and blast. A comparative study of non-linear response of reinforced concrete nuclear containment cylindrical shell subjected to impact of an aircraft (Phantom) and explosion of different amounts of blast charges have been presented here. A material model which takes into account the strain rate sensitivity in dynamic loading situations, plastic and visco-plastic behavior in three dimensional stress state and cracking in tension has been developed earlier and implemented into a finite element code which has been validated with published literature. The analysis has been made using the developed software. Significant conclusions have been drawn for dissimilarity in response (deflections, stresses, cracks etc.) of the shell for impact and blast loading.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.1326-1331
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• 2006

The precast concrete deck is one of suitable solutions for replacement and new construction in urban area. However, the precast concrete deck could be a weak point of the steel plate girder bridges structurally due to the connections between precast panels in the longitudinal direction. Thereafter, it is necessary for improvement of durability and load carrying capacity to introduce the prestress force in the longitudinal direction Some cracks of connections at the precast concrete deck may be occurred due to live loads, the difference of temperature and long-term effects. The shrinkage and creep of concrete may significantly affect long-term behaviors which occur tensile stresses at the precast concrete deck of steel plate girder bridges. In this study, the time-dependant analysis program has been developed to determine the initial prestress force in the longitudinal direction considering loss of stress at the precast concrete deck. Also it has been estimated the initial prestress force by construction stages and shapes of girder.