• Journal of Ocean Engineering and Technology
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• v.21 no.3 s.76
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• pp.71-76
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• 2007

Recently, many industries have been employing the application of laser beam welding, due to the resulting high welding quality, such as smaller width of melting and heat affective zone, smaller welding deformation, and fine grains of weldment, compared to arc welding. However, in order to appropriately utilize this welding process with steel structure, the characteristics of welding residual stresses and fracture toughness in welded joints are to be investigated for reliability. Therefore, in this study, the mechanical properties of weldments by arc and laser welding are investigated using FEM to confirm the weldability of laser welding to the general structural steel (HT50). The Charpy impact test and 3-points bending CTOD test are carried out in the range of temperatures between $-60^{\circ}C\;and\;20^{\circ}C$, in order to understand the effect on the fracture toughness of weldments. From the research results, it has been found that the maximum residual stress appears at the center of plate thickness, and that the fracture toughness is influenced by strength mis-match.

• Journal of Welding and Joining
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• v.3 no.1
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• pp.22-31
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• 1985

Hot straining embrittlement is one of the most important factors which cause the brittle fracture initiation even in the service temperature in the case of mild steel and high tensile steel. Therefore it is necessary to analyze thoroughly the hot straining embrittlement occurred in weld HAZ of the structural steels. The behaviors of plastic deformation and fracture toughness at the notch tip of the hot strained weld HAZ in structural steels (SB 41 KS, SA 588-Grade A ASTM) have been studied by the recrystallization technique and crack opening displacement (COD) test method. The obtained results are summarized as follows; 1. The plastic zone is formed at the notch tip of weld HAZ owing to nomotonic and cyclic hot stran, and the maximum plastic strain increases with the accumulated hot straining amounts. 2. The distribution of the effective strain at the plastic deformed zone in HAZ can be determined as follows; (.epsilon. over bar $_{p}$ )$_{\chi}$=.epsilon. over bar $_{cr}$ ( $R_{/chi}$/.chi.)$^{m}$ where, .epsilon. over bar $_{cr}$ : (SB 41; .epsilon. over bar $_{cr}$ = 0.2, SA 588; .epsilon. over bar $_{cr}$ = 0.1) 3. The embrittlement of weld HAZ in SB 41 and SA 588 is influenced by hot strain, and the degree of embrittlement becomes deeper with hot straining amounts. 4. The embrittlement of weld HAZ of SB 41 is not influenced by the hot straining amounts until .epsilon. over bar $_{max}$ = 0.36, $R_{\chi}$ = 0.065mm, however the embrittlement of structure in SA 588 is considerably influenced even by a small quantity of the hot straining amounts.s.

• Computers and Concrete
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• v.29 no.6
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• pp.393-405
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• 2022

Lightweight concrete is a superior material due to its light weight and high strength. There however remain significant lacunae in engineering knowledge with regards to shear failure of lightweight fiber reinforced concrete beams. The main aim of the present study is to investigate the optimum usage of steel fibers in lightweight fiber reinforced concrete (LWFRC). Multi-scale finite element model calibrated with experimental results is developed to study the effect of steel fibers on the mechanical properties of LWFRC beams. To decrease the amount of steel fibers, it is preferred to reinforce only the middle section of the LWFRC beams, where the flexural stresses are higher. For numerical simulation, a multi-scale finite element model was developed. The cement matrix was modeled as homogeneous and uniform material and both steel fibers and lightweight coarse aggregates were randomly distributed within the matrix. Considering more realistic assumptions, the bonding between fibers and cement matrix was considered with the Cohesive Zone Model (CZM) and its parameters were determined using the model update method. Furthermore, conformity of Load-Crack Mouth Opening Displacement (CMOD) curves obtained from numerical modeling and experimental test results of notched beams under center-point loading tests were investigated. Validating the finite element model results with experimental tests, the effects of fibers' volume fraction, and the length of the reinforced middle section, on flexural and residual strengths of LWFRC, were studied. Results indicate that using steel fibers in a specified length of the concrete beam with high flexural stresses, and considerable savings can be achieved in using steel fibers. Reducing the length of the reinforced middle section from 50 to 30 cm in specimens containing 10 kg/m3 of steel fibers, resulting in a considerable decrease of the used steel fibers by four times, whereas only a 7% reduction in bearing capacity was observed. Therefore, determining an appropriate length of the reinforced middle section is an essential parameter in reducing fibers, usage leading to more affordable construction costs.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.193-200
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• 2023

This paper investigates the effect of directional alignment of steel fibers using an electromagnetic field on the flexural fracture behavior of steel fiber reinforced concrete. A specially designed and manufactured solenoid, capable of aligning steel fibers in the longitudinal direction of the beam specimen, was employed for this purpose. Beam specimens with a design strength of 30 MPa were produced, and failure tests were conducted on specimens exposed to electromagnetic fields and those without exposure. Experimental variables included the mixing ratio and aspect ratio of steel fibers. The results of the experiments revealed a slight increase in flexural strength and crack mouth opening displacement at the maximum load for specimens exposed to the electromagnetic field. Notably, a significant enhancement in fracture energy was observed.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.177-185
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• 2016

This paper concerns the flexural behavior of steel fiber-reinforced ultra-high-performance concrete (UHPC) beams with compressive strength of 150 MPa. It presents experimental research results of hybrid steel fiber-reinforced UHPC beams with steel fiber content of 1.5% by volume and steel reinforcement ratio of less than 0.02. This study aims at investigating of compressive and tensile behavior of UHPC to perform a reasonable prediction for flexural capacity of UHPC beams. Tensile behavior modeling was performed using load-crack mouth opening displacement relationship obtained from bending test. The experimental results show that steel fiber-reinforced UHPC is in favor of cracking resistance and ductility of beams. The ductility indices range from 1.6 to 3.0, which means high ductility of hybrid steel fiber-reinforced UHPC. Test results and numerical analysis results for the moment-curvature relationship are compared. Though the numerical analysis results for the bending capacity of the UHPC beam without rebar is larger than test result, the overall comparative results show that the bending capacity of steel fiber-reinforced UHPC beams with compressive strength of 150 MPa can be predicted by using the established method in this paper.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.93-102
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• 2016

The purpose of this paper is to investigate the flexural behavior of high-strength steel fiber-reinforced concrete beams with compressive strength of 130 MPa. The paper presents experimental research results of steel fiber-reinforced concrete beams with steel fiber content of 1.0% by volume and steel reinforcement ratio of less than 0.02. Both of normal-strength rebar and high-strength rebar were used in the test beams. Modeling as well as compressive and tensile strength test of high-strength steel fiber-reinforced concrete was performed to predict the bending strength of concrete beams. Tension modeling was performed by using inverse analysis in which load-crack mouth opening displacement relationship was considered. The experimental results show that high-strength steel fiber-reinforced concrete beams and the addition of high-strength rebar is in favor of cracking resistance and ductile behavior of beams. For beams reinforced with normal-strength rebar, the ratio of bending strength prediction to the test result ranged from 0.81 to 1.42, whereas for beams reinforced with high-strength rebar, the ratio of bending strength prediction to the test result ranged from 0.92 to 1.07. The comparison of bending strength from numerical analysis with the test results showed a reasonable agreement.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.279-286
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• 2019

In this study, an experimental study on the tensile properties of steel fiber-reinforced ultra high strength concrete(UHSC) with a standard compressive strength of 180MPa was performed. Steel fibers with a volume ratio of 1% were mixed to prepare direct tensile strength specimens and prism specimens for the three-point bending test. The fabricated specimens were set up in the middle section of the specimen to induce cracks, and the test was carried out according to each evaluation method. First, the stress-strain curves were analyzed by performing direct tensile strength tests to investigate the behavior characteristics of concrete after cracking. In addition, the load-CMOD curve was obtained through the three-point bending test, and the inverse analysis was performed to evaluate the stress-strain curve. Tensile behavior characteristics of the direct tensile test and the three-point bending test of the indirect test were similar. In addition, the tensile stress-strain curve modeling presented in the SC structural design guidelines was performed, and the comparative analysis of the measured and predicted values was performed. When the material reduction factor of 1.0 was applied, the predicted value was similar to the measured value up to the strain of 0.02, but when the material reduction factor of 0.8 was applied, the predicted value was close to the lower limit of the measured value. In addition, when the strain was greater than 0.02, the predicted value by SC structural design guideline to underestimated the measured value.