• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.145-146
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• 2023

In this study, the effect of hybrid fiber reinforcement on the residual strength and impact resistance of high-strength cementitious composites exposed to high temperatures was investigated. A cementitious composites was manufactured in which 0.15 vol% of polypropylene fiber (PP) and 1.0 vol% of smooth steel fiber (SSF) were double-mixed, and a residual strength test was conducted while thermal stress was applied by heating test, and then a high-velocity impact test was performed. In the case of general cementitious composites, the rear surface is damaged due to explosion and low tensile strength during high temperature or impact, while hybrid fiber reinforced cementitious composites can repeatedly absorb and distribute stress until multiple fibers are damaged to suppress the propagation of impact and resistance to explosion. Therefore, this study analyzed the residual strength of cementitious composites exposed to high temperatures depending on whether hybrid fibers were mixed or not, and collected research data on fracture behavior through high-speed impact tests to evaluate impact resistance and mechanical properties.

• Structural Engineering and Mechanics
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• v.14 no.4
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• pp.455-472
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• 2002

The paper involves the study on the elastic and elasto-plastic stress wave propagation in the 1-D and 2-D solid media. The Smooth Particle Hydrodynamics equations governing the elastic and elasto-plastic large deformation dynamic response of solid structures are presented. The proposed additional stress points are introduced in the formulation to mitigate the tensile instability inherent in the SPH approach. Both incremental rate approach and leap-frog algorithm for time integration are introduced and the new solution algorithm is developed and implemented. Two examples on stress wave propagation in aluminium bar and 2-D elasto-plastic steel plate are included. Results from the proposed SPH approach are compared with available analytical values and finite element solutions. The comparison illustrates that the stress wave propagation problems can be effectively solved by the proposed SPH method. The study shows that the SPH simulation is a reliable and robust tool and can be used with confidence to treat transient dynamics such as linear and non-linear transient stress wave propagation problems.

• Journal of Welding and Joining
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• v.11 no.4
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• pp.91-102
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• 1993

The plasma sprayed $Cr_3C_2$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical and wear properties of the plasma sprayed $Cr_3C_2$-NiCr coating on steel plate were examined in this study. The pore in the coatings could be classified into two types, the one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occured at the interface of top coating and bond coating. It is though that the compressive residual stress increases with the increase of the top coating thickness. From the wear test, it was found that the wear rate increased with the increase of the sliding velocity regardless of the temperature. It is thought that the fracture toughness reduces with the increase of the sliding velocity at $30^{\circ}C$ and that the adhesion amount increases with the increase of the sliding velocity at $400^{\circ}C$ It is concluded that the wear mechanism at $30^{\circ}C$ is the fracture and pull-out of the carbide particles due to the fatigue on sliding surface, while the wear mechanism at $400^{\circ}C$ is the adhesion of the smeared layer formed during wear process.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.6
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• pp.101-107
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• 2003

Since stainless steel sheets have good mechanical properties, weldability, appearance and corrosion resistance, they are commonly used as one of the structural materials of the railroad cars or the commercial vehicles which are manufactured by the spat welding. Among the many kinds of spot welded lap joints, it can be found that multi-lap joints are employed in their body structure. But, fatigue strength of these joints is lower than that of base metal due to high stress concentration at the nugget edge of spot weld and is considerably influenced by welding conditions as well as the mechanical and geometrical factors. Thus, it is necessary to establish a reasonable and systematic design criterion for the long life design of the spot-welded body structures. In this paper, the stress distribution and deformation around the spot-welded multi-lap joints subjected to tensile shear load was numerically analyzed. Also, the $\Delta$P-Nf curve was obtained by fatigue tests. Using these results, $\Delta$P-Nf curves were rearranged in to the ${\Delta}{\sigma}$-Nf relation with the maximum stress at nugget edge of spot weld.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.710-717
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• 2000

Tensile and fracture toughness tests of the cold-rolled STS 304 steel plate for membrane material of LNG storage tank were performed at wide range of temperatures, 11 IK(boiling point of LNG), 153K , 193K and 293K(room temperature). Tensile strength significantly increases with a decrease in temperature, but the yield strength is relatively insensitive to temperature. Elongation at 193K abruptly decreases by 50% of that at 293K, and then decreases slightly in the temperature range of 193K to 111K. Strain hardening exponents at low temperatures are about four times as high as that at 293K. Elastic-plastic fracture toughness($J_c$) and tearing modulus($T_{mat}$) tend to decrease with a decrease in temperature. The $J_c$ values are inversely related to effective yield strength in the temperature range of 111K to 293K. These phenomena result from a significant increase in the amount of transformed martensite in low temperature regions.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.140-145
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• 2009

This paper deals with a stability evaluation of a butterfly valve using the body and disc of a valve seat. The experimental results of a strength evaluation are shown using STS316 stainless steel and spheroidal graphite cast iron (GCD450). The disc material was made from GCD450. The results of the strength analysis are as follows: Ultimate tensile strength 485MPa, Yield strength 370 MPa, Young's modulus $1.1{\times}10^5$, and Poisson's ratio v = 0.28. For the results of the disc analysis, the safety factor was about 4. This shows that a design was derived that satisfied the requirements of structural safety. However, some problems, such as the deflection and deformation of the disc, may occur when the sea water has back flow with a high pressure.

• Transactions of Materials Processing
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• v.29 no.4
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• pp.179-187
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• 2020

Existing composite forming processes such as the autoclave, prepreg compression forming (PCF), RTM, etc. require high production costs because of their long processing time. On the other hand, microwave heating process (MHP) can reduce the production costs since both mold and composite material can be heated directly. The aim of this study is to manufacture a mold consisting of polytetrafluoroethylene (PTFE), quartz glass, stainless steel clamps, and polyether ether ketone (PEEK) bolts for fabricating FML based on self-reinforced polypropylene (SRPP) using the MHP. First, the flame test was carried out prior to the MHP to check the temperature on the mold and whether the spark occurred at the mold and the edge of the FML. Second, the uniaxial tensile test was then conducted to obtain the mechanical properties of the FML manufactured by the MHP. The mechanical properties were compared with those of the FML fabricated by the PCF. As a result, the MHP using the PTFE mold can manufacture the FML more rapidly than the PCF, and obtain acceptable mechanical properties.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.2
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• pp.31-39
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• 2019

Cracked component analysis is needed for structural integrity analysis under seismic loading. Under large amplitude cyclic loading conditions, the change in material properties can be complex, depending on the magnitude of plastic strain. Therefore the cracked component analysis under cyclic loading should consider appropriate cyclic hardening model. This study introduces a procedure for determining an appropriate cyclic hardening model for cracked component analysis. The test material was nuclear-grade TP316 stainless steel. The material cyclic hardening was simulated using the Chaboche combined hardening model. The kinematic hardening model was determined from standard tensile test to cover the high and wide strain range. The isotropic hardening model was determined by simulating C(T) test under cyclic loading using ABAQUS debonding analysis. The suitability of the material hardening model was verified by comparing load-displacement curves of cyclic C(T) tests under different load ratios.

• Journal of Korea Foundry Society
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• v.35 no.1
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• pp.1-7
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• 2015

In this study, we investigated the effect of carbon on mechanical properties with different austempering conditions of high carbon(0.7~1.3wt.%C)-2.0wt.%Si steels. The specimens were austenitized at 850, 925 and $1020^{\circ}C$, and austempered at 260, 320 and $380^{\circ}C$ for the various period of time from 3 min to 300 min. After heat treatment, the evolution of stage I and stage II was identified with optical microscope, XRD and hardness test. When the austempering temperature was $260^{\circ}C$, the microstructure consisted of the lower ausferrite while the upper ausferrite micro-structure was formed at $380^{\circ}C$. As the austempering temperature increases from 260 to $380^{\circ}C$, the tensile strength decreases and elongation increases. In addition, when carbon content increases, tensile strength and elongation decrease.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4146-4158
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• 2022

Ultra-high performance concrete (UHPC) has been widely utilized in military and civil protective structures to resist intensive loadings attributed to its excellent properties, e.g., high tensile/compressive strength, high dynamic toughness and impact resistance. At present, aiming to improve the defects of the traditional vertical concrete cask (VCC), i.e., the external storage facility of spent fuel, with normal strength concrete (NSC) shield, e.g., heavy weight and difficult to fabricate/transform, the feasibility of UHPC applied in the shield of VCC is numerically examined considering its high radiation and corrosion resistance. Firstly, the finite element (FE) analyses approach and material model parameters of NSC and UHPC are verified based on the 1/3 scaled VCC tip-over test and drop hammer test on UHPC members, respectively. Then, the refined FE model of prototypical VCC is established and utilized to examine its dynamic behaviors and damage distribution in accidental tip-over and end-drop events, in which the various influential factors, e.g., UHPC shield thickness, concrete ground thickness, and sealing methods of steel container are considered. In conclusion, by quantitatively evaluating the safety of VCC in terms of the shield damage and vibrations, it is found that adopting the 300 mm-thick UHPC shield instead of the conventional 650 mm-thick NSC shield can reduce about 1/3 of the total weight of VCC, i.e., about 50 t, and 37% floor space, as well as guarantee the structural integrity of VCC during the accidental drop simultaneously. Besides, based on the parametric analyses, the thickness of concrete ground in the VCC storage site is recommended as less than 500 mm, and the welded connection is recommended for the sealing method of steel containers.