• Korean Journal of Materials Research
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• v.23 no.9
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• pp.525-530
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• 2013

This study investigated the continuous cooling transformation, microstructure, and mechanical properties of highstrength low-alloy steels containing B and Cu. Continuous cooling transformation diagrams under non-deformed and deformed conditions were constructed by means of dilatometry, metallographic methods, and hardness data. Based on the continuous cooling transformation behaviors, six kinds of steel specimens with different B and Cu contents were fabricated by a thermomechanical control process comprising controlled rolling and accelerated cooling. Then, tensile and Charpy impact tests were conducted to examine the correlation of the microstructure with mechanical properties. Deformation in the austenite region promoted the formation of quasi-polygonal ferrite and granular bainite with a significant increase in transformation start temperatures. The mechanical test results indicate that the B-added steel specimens had higher strength and lower upper-shelf energy than the B-free steel specimens without deterioration in low-temperature toughness because their microstructures were mostly composed of lower bainite and lath martensite with a small amount of degenerate upper bainite. On the other hand, the increase of Cu content from 0.5 wt.% to 1.5 wt.% noticeably increased yield and tensile strengths by 100 MPa without loss of ductility, which may be attributed to the enhanced solid solution hardening and precipitation hardening resulting from veryfine Cu precipitates formed during accelerated cooling.

• Journal of the Korean Society of Safety
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• v.23 no.1
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• pp.1-11
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• 2008

In this study, small punch test and tensile test were performed with specimens directly machined from an ASTM A53 grade B carbon steel pipe at which an explosion accident was occurred in the Heavy Oil Unit. Main damage mechanism of the pipe was known as a high temperature hydrogen attack(HTHA). Effects of HTHA on the mechanical strength change of the A53B steel were studied in detail. Small punch test results have showed that maximum reaction forces, SP energy and ductility were decreased at hydrogen attacked part of the pipe compared with sound part of the pipe. Yield strength and tensile ultimate strength were calculated with the obtained small punch test curve results using different methods and compared the estimation methods. Small punch test simulation has been also performed with the finite element method and then mechanical strength, equivalent strain and fracture toughness were calculated with the obtained numerical analysis results. It was shown that the fracture toughness data calculated from small punch equivalent energy obtained by the finite element analysis for SP test was very low at the hydrogen attacked part.

• Steel and Composite Structures
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• v.15 no.6
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• pp.659-677
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• 2013

This paper introduces new specimens of Steel-Carbon Fibre Reinforced Polymer composite developed in accordance with standard test method and definition for mechanical testing of steel (ASTM-A370). The main purpose of this research is to study the behaviour of steel-CFRP composite specimen under uniaxial tension to use it in beams in lieu of traditional steel bar reinforcement. Eighteen specimens were prepared and divided into six groups, depending upon the number of the layers of CFRP. Uniaxial tensile tests were conducted to determine yield strength and ultimate strength of specimens. Test results showed that the stress-strain curve of the composite specimen was bilinear prior to the fracture of CFRP laminate. The tested composite specimens displayed a large difference in strength with remarkable ductility. The ultimate load for Steel-Carbon Fibre Reinforced Polymer composite specimens was found using the model proposed by Wu et al. (2010) and nonlinear FE analysis. The ultimate loads obtained from FE analysis are found to be in good agreement with experimental ones. However, ultimate loads obtained applying Wu model are significantly different from experimental/FE ones. This suggested modification of Wu model. Modified Wu's model which gives a better estimate for the ultimate load of Steel-Carbon Fibre Reinforced Polymer (SCFRP) composite specimen is presented in this paper.

• Advances in concrete construction
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• v.10 no.4
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• pp.319-332
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• 2020

The impacts of reinforcing concrete matrix with steel fibers, polypropylene fibers and recycled plastic fibers using different volume fractions of 0.15%, 0.5%, 1.5% and 2.5% on the compressive and tensile characteristics are experimentally investigated in the current research. Also, flexural behavior of plain concrete (PC) beams, shear performance of reinforced concrete (RC) beams and compressive characteristics of both PC and RC columns reinforced with recycled plastic fibers were studied. The experimental results showed that the steel fibers improved the splitting tensile strength of concrete higher than both the polypropylene fibers and recycled plastic fibers. The end-hooked steel fibers had a positive effect on the compressive strength of concrete while, the polypropylene fibers, the recycled plastic fibers and the rounded steel fibers had a negative impact. Compressive strength of end-hooked steel fiber specimen with volume fraction of 2.5% exhibited the highest value among all tested samples of 32.48 MPa, 21.83% higher than the control specimen. The ultimate load, stiffness, ductility and failure patterns of PC and RC beams in addition to PC and RC columns strengthened with recycled plastic fibers enhanced remarkably compared to non-strengthened elements. The maximum ultimate load and stiffness of RC column reinforced with recycled plastic fibers with 1.5% volume fraction improved by 21 and 15%, respectively compared to non-reinforced RC column.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.157-168
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• 1995

The effects of Mo additions on the microstructure and the room temperature deformation behavior of polysynthetically twinned (PST) crystals of TiAl were studied in order to get a basic conception for alloying additions on the two-phase TiAl compounds with the lamellar structure. It was found that the Mo additions in TiAl PST crystals increase both the yield stress and tensile elongation to fracture but the increase in yield stress deppend on the angle $\Phi$at which the lamellar boundaries lie from the loading axis. The large difference in yield stress between specimens deformed parallel($\Phi = 0^\circ$)or perpendicular($\Phi = 90^\circ$) to the loading axis and those deformed in intermediate orientations could be plained by the difference in Mo content between the TiAl and the $$Ti_{3}Al$ phases. It was also found that the Mo-doped specimens with intermediate orientation fail by cracking zigzag across to the lamellar boundaris, which is the same fracture mode as that of binary specimens with intermediate orientations tested in vacuum This suggests that Mo atoms are thought to play a role to reduce the environmental embrittlement of binary PST crystals, resulting in increasing the tensile ductility.

• Transactions of Materials Processing
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• v.16 no.5 s.95
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• pp.391-395
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• 2007

Semi-solid Al-Zn-Mg alloys were produced by using a cooling plate method in order to investigate the extrudability. Al melt was poured on cooling plate which was adjusted at $60^{\circ}$ with respect to the horizontal plane, and the melt was cooled by water circulation underneath. Obtained Semi-solid feedstock has globular microstructure but also contains considerable amount of gas pore. Due to the pore, tensile elongation of the semi-solid feedstock was very low and it doesn't show yield point phenomenon. Isothermal hot extrusion was carried out using at $400^{\circ}C$ with a ram speed of 1mm/sec and an extrusion ratio of 25:1. The extruded bar show noticeably improved tensile ductility and strength because pore volume fraction decreased from 5% to 0.8% after extrusion. Mechanical properties of the semi-solid extruded bar were compared with that of commercial casting alloy.

• International Journal of Concrete Structures and Materials
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• v.3 no.2
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• pp.119-126
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• 2009

This paper provides a brief summary of the performance of an innovative slip hardening twisted steel fiber in comparison with other fibers including straight steel smooth fiber, high strength steel hooked fiber, SPECTRA (high molecular weight polyethylene) fiber and PVA fiber. First the pull-out of a single fiber is compared under static loading conditions, and slip rate-sensitivity is evaluated. The unique large slip capacity of T-fiber during pullout is based on its untwisting fiber pullout mechanism, which leads to high equivalent bond strength and composites with high ductility. Due to this large slip capacity a smaller amount of T-fibers is needed to obtain strain hardening tensile behavior of fiber reinforced cementitious composites. Second, the performance of different composites using T-fibers and other fibers subjected to tensile and flexural loadings is described and compared. Third, strain rate effect on the behavior of composites reinforced with different types and amounts of fibers is presented to clarify the potential application of HPFRCC for seismic, impact and blast loadings.

• Journal of Korea Foundry Society
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• v.30 no.1
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• pp.29-33
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• 2010

The microstructure of Al-5%Mg based alloy mainly consists of aluminum matrix with a small amount of AlMn phase. The addition of Sc or Zn to the base alloy significantly improved the as-cast tensile strength, while the addition of Fe deteriorated both strength and ductility. Although the Al-5%Mg based alloy was not heat-treatable, aging hardening could be observed in the case that Sc or Zn was added to the base alloy. TEM analysis showed that very fine AlSc or AlMgZn precipitates were formed after T6 heat treatment, resulting in enhanced strength. The corrosion resistance measured as corrosion potential was found to decrease a little by adding Zn, whereas other alloying elements were not clearly influential.

• Steel and Composite Structures
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• v.17 no.3
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• pp.253-269
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• 2014

Among the various alternatives to make a steel tubular member connection, making a slotted and gusset plate welded connection is one of the most frequently preferred alternatives. This type of connection is essentially an end connection that is made by slotting the tube longitudinally, inserting the gusset plate and then placing longitudinal fillet welds at the tube-to-plate interface. In this paper an experimental study on the behaviour of such connections in stainless steel is presented. 24 specimens were tested under concentrically applied axial tensile forces for varying tube-to-gusset plate weld lengths. Both circular and box section members were considered in the test program. Load-deformation curves were obtained and comparisons were made in terms of strength and ductility. The results obtained from the study were then critically examined and compared with currently available design guidance for slotted gusset plate welded tubular end connections. It is noted that no specific rules exist in international specifications on structural stainless steel which cover the design of such connections. Therefore, the results of this study are compared with the existing design rules for carbon steel.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.69-74
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• 2016

Because the pure titanium has superior corrosion resistance and formability compared with different material, it is widely used as material of welded heat exchanger. When the welding of heat exchanger is carried out, certain area in which welding start and end are overlapped occurs. The humping of back bead is formed in the overlap area due to partial penetration. Thus in this study, the experiments were carried out by changing the length and wave shape of overlap area, and then the weldabiliay was evaluated through the observation of microstructure, the measurement of hardness and tensile-shear strength test in the overlap area. When overlap length was 9.8mm, humping bead was suppressed. The microstructure of overlap area coarsened and its hardness increased due to remelting. As a result of tensile-shear strength test in the overlap area according to applying the wave shape control, it was confirmed that the overlap area applied wave shape control had more excellent yield strength and ductility.