• Korean Journal of Metals and Materials
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• v.50 no.6
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• pp.427-432
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• 2012

This paper presents the material properties of carbon steels for ships, and offshore structures (ASTM A131) are tested under a series of arctic and cryogenic temperature conditions. For material tension tests, among the ASTM 131 steels, Grades A and B of mild steel and Grade AH of high tensile steel have been used. The obtained mechanical properties of the materials from the material tension tests were applied in a 13,000TEU class container ship to define the effect of low temperature on the ultimate longitudinal strength of the target structure by using the ALPS/HULL intelligent supersize finite element method. The tensile coupon test results showed increased strength and nonuniform fracture strain behaviors within different grades and temperatures. Increasing the material strength resulted in increasing the ultimate longitudinal strength of the ship.

• Steel and Composite Structures
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• v.35 no.6
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• pp.739-752
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• 2020

This paper aims to investigate cyclic plasticity of a new type of high-performance austenitic stainless steel with both high strength and high ductility. The new stainless steel termed as QN1803 has high nitrogen and low nickel, which leads to reduction of cost ranging from 15% to 20%. Another virtue of the new material is its high initial yield strength and tensile strength. Its initial yield strength can be 40% to 50% higher than conventional stainless steel S30408. Elongation of QN1803 can also achieve approximately 50%, which is equivalent to the conventional one. QN1803 also has a corrosion resistance as good as that of S30408. In this paper, both experimental and numerical studies on the new material were conducted. Full-range true stress-true strain relationships under both monotonic and cyclic loading were obtained. A cyclic plasticity model based on the Chaboche model was developed, where a memory surface was newly added and the isotropic hardening rule was modified. A user-defined material subroutine was written, and the proposed cyclic plasticity model can well evaluate full-range hysteretic properties of the material under various loading histories.

• Journal of Welding and Joining
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• v.26 no.3
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• pp.61-66
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• 2008

As ships become to be larger than ever, the thicker plate and the higher tensile steel plate are used in naval shipyard. Though special chemical composition is needed for high-tensile steels, recent high-tensile steels are made by the TMCP(Thermo-Mechanical control process) skill. The increase of yield stress and tensile stress of TMCP steels is induced from bainite phase which is transformed from austenite, but that increased yield stress can be vanished by another additional thermal cycle like welding and heating. As thermal deformations are deeply related by yield stress of material, the study for prediction of plate deformation by heating should reflect principle of TMCP steels. This study developed an algorithm which can calculate inherent strain. In this algorithm, not only the mechanical principles of thermal deformations, but also the predicting of the portion of initial bainite is considered when calculating inherent strain. The simulations of plate deformation by these values showed good agreements with experimental results of normalizing steels and TMCP steels in welding and heating. Finally we made an inherent strain database of steels used in Class rule.

• Structural Engineering and Mechanics
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• v.48 no.6
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• pp.833-848
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• 2013

Nine rectangular-section of High Strength Concrete(HSC) beams were designed and casted based on the American Concrete Institute (ACI) code provisons with varying of tensile reinforcement ratio as (${\rho}_{min}$, $0.2_{{\rho}b}$, $0.3_{{\rho}b}$, $0.4_{{\rho}b}$, $0.5_{{\rho}b}$, $0.75_{{\rho}b}$, $0.85_{{\rho}b}$, $_{{\rho}b}$, $1.2_{{\rho}b}$). Steel and concrete strains and deflections were measured at different points of the beam's length for every incremental load up to failure. The ductility ratios were calculated and the moment-curvature and load-deflection curves were drawn. The results showed that the ductility ratio reduced to less than 2 when the tensile reinforcement ratio increased to $0.5_{{\rho}b}$. Comparison of the theoretical ductility coefficient from CSA94, NZS95 and ACI with the experimental ones shows that the three mentioned codes exhibit conservative values for low reinforced HSC beams. For over-reinforced HSC beams, only the CSA94 provision is more valid. ACI bending provision is 10 percent conservative for assessing of ultimate bending moment in low-reinforced HSC section while its results are valid for over-reinforced HSC sections. The ACI code provision is non-conservative for the modulus of rupture and needs to be reviewed.

• Transactions of Materials Processing
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• v.21 no.1
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• pp.58-66
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• 2012

The work roll surface temperature rises and falls repetitively during hot slab rolling because the work roll surface is cooled continuously by water. This study focused on Std. No. 7 to determine a cooling method which significantly reduces the tangential tensile stresses on the work roll surface of the hot slab mill at Hyundai Steel Co. in Korea. A series of finite element analyses were performed to compute the temperature distribution and the tensile stresses in the circumferential direction of the work roll. The virtual slab model was used to reduce the run time considerably by assigning a high temperature to the virtual slab. Except for the heat generated by plastic deformation, this is equivalent to the hot rolling condition that a high temperature slab (material) would experience when in contact with the work rolls. Results showed that when the virtual slab model was coupled with FE analysis, the run time was found to be reduced from 2000 hours to 70 hours. When the work roll surface cooled with a certain on-off patter of water spray, the magnitude of the tangential stresses on the work rolls were decreased by 54.1%, in comparison with those cooled by continuous water spraying. Savings of up to 83.3% in water usage are possible if the proposed water cooling method is adopted.

• Journal of Welding and Joining
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• v.15 no.1
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• pp.46-54
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• 1997

The object of this paper is to evaluate SCC(stress corrosion cracking) susceptibility for parent metal and bond line region of weld joints which have the various weld heat input condtions in TMCP(thermo-mechanical control process) steel by SP-SSRT(small punch-slow strain rate test) method. And the SCC test results of TMCP steel are compared with those of the conventional HT50 steel which has te almost same tensile strength level like TMCP steel. The loading rate used was $3\times10^{-4}$mm/min and the corrosive environment was synthetic sea water. According to the test results, in the case of parent metal, TMCP steel showed higher SCC susceptibility than HT50 steel because of the high plastic strain level of ferrite microstructure obtained by accelerated cooling. And in the case of bond line, the both TMCP steel and HT50 steel showed low load-displacement behaviors and higher SCC susceptibility above 0.6. These results may be caused by theembrittled martensite structure on HT50 steel and by the coarsened grain and the proeutectoid ferrite structure obtained by the impart of accelerated cooling effect on TMCP steel.

• Smart Structures and Systems
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• v.19 no.4
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• pp.371-382
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• 2017

Concrete filled steel tubes are extensively applied in engineering structures due to their resistance to high tensile and compressive load and convenience in construction. But one major flaw, their vulnerability to environmental attack, can severely reduce the strength and life of these structures. Degradation due to corrosion of steel confining the concrete is one of the major durability problems faced by civil engineers to maintain these structures. The problem accelerates as inner surface of steel tube is in contact with concrete which serves as electrolyte. If it remains unnoticed, it further accelerates and can be catastrophic. This paper discusses a non-destructive degradation monitoring technique for early detection corrosion in steel tubes in CFST members. Due to corrosion, damage in the form of debonding and pitting occurs in steel sections. Guided ultrasonic waves have been used as a feasible and attractive solution for the detection and monitoring of corrosion damages in CFST sections. Guided waves have been utilized to monitor the effect of notch and debond defects in concrete filled steel tubes simulating pitting and delamination of steel tubes from surrounding concrete caused by corrosion. Pulse transmission has been used to monitor the healthy and simulated damaged specimens. A methodology is developed and successfully applied for the monitoring of concrete filled steel tubular sections undergoing accelerated chloride corrosion. The ultrasonic signals efficiently narrate the state of steel tube undergoing corrosion.

• Steel and Composite Structures
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• v.33 no.4
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• pp.489-507
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• 2019

In order to obtain high bearing capacity and good ductility simultaneously, a structural column with hybrid normal and high strength steel (HNHSS) welded box section has been developed. Residual stress is an important factor that can influence the behaviour of a structural member in steel structures. Accordingly, the magnitudes and distributions of residual stresses in HNHSS welded box sections were investigated experimentally using the sectioning method. In this study, the following four box sections were tested: one normal strength steel (NSS) section, one high strength steel (HSS) section, and two HNHSS sections. Based on the experimental data from previous studies and the test results of this study, the effects of the width-to-thickness ratio of plate, yield strength of plate, and the plate thickness of the residual stresses of welded box sections were investigated in detail. A unified residual stress model for NSS, HSS and HNHSS welded box sections was proposed, and the corresponding simplified prediction equations for the maximum tensile residual stress ratio (${\sigma}_{rt}/f_y$) and average compressive residual stress ratio (${\sigma}_{rc}/f_y$) in the model were quantitatively established. The predicted magnitudes and distributions of residual stresses for four tested sections in this study by using the proposed residual stress model were compared with the experimental results, and the feasibility of this proposed model was shown to be in good agreement.

• Transactions of Materials Processing
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• v.32 no.5
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• pp.255-267
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• 2023

Recently, 3D printing using a material extrusion method is used in various fields. Since plastic material has lower strength than steel, research to increase the strength is continuously being conducted. This study investigates the lattice structure for additive manufacturing of six 3D infill patterns (octet, quarter cubic, cubic, cubic subdivision, triangles and cross 3D) which consist of tetragons, hexagonal trusses, equilateral triangles and cross shapes. Consequently, in the tensile strength considering the weight and printing time, octet, quarter cubic, cubic and triangles patterns tended to increase linearly as the infill density increased, except for the infill density of 20%. However, the tensile strength/weight performed better than the infill density of 100% when the cubic subdivision pattern had the infill density of 20% and the cross 3D pattern had the infill density of 40%. Considering the weight and printing time, the infill patterns of high tensile strength were octet, quarter cubic, cubic, cubic subdivision, triangles and cross 3D order.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.621-630
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• 2006

Twelve beams made of lightweight high-strength concrete were tested to determine their diagonal cracking and ultimate shear capacities. A total of 12 beams without(4 beams) and with lightweight(8 beams) were tested in a stiff testing facility, and complete load-midspan deflection curves, including the maximum capacities portion, were obtained. The variables in the test program were concrete strength, which varied 35.4 MPa, 65.3 MPa; shear span-depth ratios a/d=1.5, 2.5, 3.5, 4.5; and tensile steel ratio between 0.57 and 2.3 percent. Also, we divided beam by diagonal tension crack and ultimate shearing strength to propose an equation. In addition, it analyzed comparison mutually applying existing proposal and guide. $V_{cr}$ was as result that AIK recommendations and Zsutty proposal decrease more than a/d=2.5, increased some in Mathey's proposal equation. $V_{cr,\exp}/V_{cr,cal}$ showed tendency of overestimation according to increase of tensile steel ratio and compressive strength of concrete. On the other hand, $V_{cr,\exp}/V_{cr,cal}$ is superior in conformability with an experiment result Zsutty's proposal among other equations. The proposal equation hew that expect $V_{cr}/V_u$, rationally about shearing strength. Therefore, shear strength an equation is considered to be utilized usefully evaluating capacity by change of the shear span depth ratio of lightweight concrete, tensile steel ratio, and compressive strength of the concrete in this research.