• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.507-515
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• 2001

Significant improvements in bond strength between new and existing concrete can be achieved through the modification of the new concrete by latex. This study focuses on the investigation of bond strength of latex modified concrete. Pull-out bond test and uniaxial direct tensile bond test are adopted for evaluating the adhesion characteristics of latex modified concrete to conventional concrete substrate. The main experimental variables are test methods, latex-cement ratio, surface preparations and moisture levels. The results are as follows; The increase of latex-cement ratio substantially improves the adhesion between latex modified concrete and substrate. The effects of surface preparation at substrate into the bonding of latex modified concrete are quite different according to the conditions of surfaces. Thus, an adequate surface preparations are essential for good bond strength. Because the moisture level of the substrate may be critical to achieving bond, optimum moisture condition for a conventional concrete has evaluated in this study. The saturated condition of surface is the most appropriate moisture level among the considered, followed by dry condition and wet condition.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.8
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• pp.2033-2042
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• 1993

In conventional SCC susceptibility test, there are constant strain test, constant load test, slow strain rate test(SSRT) and K$_{ISCC}$ test. Among them, the SSRT method is much more aggressive in producing SCC than the other tests, so that the test time of it is considerably reduced. But this SSRT method has mostly been worked using the uniaxial tensile specimen untill now. Therefore, the SSRT method using the tensile specimen(Ten-SSRT) has much difficulty in SCC susceptibility evaluation of a localized region like weldment and the advantage material of high order. Recentely, the small punch(SP) test method using miniaturized small specimen is the very effective test method for fracture strength evaluation of a localized region like weldment and fusion reactor wall irradiated in the nuclear power plant. This paper investigated the possibility of SCC susceptibility evaluation by the SP-SSRT method using the miniaturized small specimen. Therefore, we obtained the result that the SP-SSRT had the possibility for the evaluations of SCC susceptibility for shorter time to corrosive environment compare to Ten-SSRT which was conventional method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.158-163
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• 2009

Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle. However, due to the low formability and large spring back at room temperature, titanium alloy sheets were usually formed by slow forming or hot forming with heating die and specimen. In the sheet metal forming area, FE simulation technique to optimize forming process is widely used. To achieve high accuracy FE simulation results, Identification of material properties and deformation characteristic such as yield function are very important. In this study, uniaxial tensile and biaxial tensile test of Ti-6Al-4V alloy sheet with thickness of 1.0mm were performed at elevated temperature of 873k. Biaxial tensile tests with cruciform specimen were performed until the specimen was breakdown to characterize the yield locus of Ti-6Al-4V alloy sheet. The experimental results for yield locus are compared with the theoretical predictions based on Von Mises, Hill, Logan-Hosford, and Balat's model. Among these Logan-Hosford's yield criterion well predicts the experimental results.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.5
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• pp.125-132
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• 2019

Ultra-high performance concrete (UHPC) has high compressive and tensile strengths due to the particle packing, and its ductile behavior can be ensured by utilizing steel fibers. However, since the UHPC members exhibit different characteristics of crack behavior and tensile behavior from normal concrete, the tension stiffening and cracking characteristics of the UHPC should be accurately modeled for the design and analysis of the UHPC members. In this study, uniaxial tension tests was conducted on the UHPC members with strands, where the test variables were diameter and reinforcing ratio of strands. Detailed analyses were also conducted to identify the tensile characteristics and crack behavior of the UHPC members. By comparing the test results with current code provisions and other models proposed by existing researchers, their applicability for estimation of crack behavior of the UHPC members was examined.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.1 s.244
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• pp.8-17
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• 2006

When subjected to severe shear deformation by ECAP, microstructure of Al2024 becomes extremely refined. To measure the strength of that, small punch(SP) testing method was adopted as a substitute for the conventional uniaxial tensile testing because the size of material processed by ECAP were limited to ${\psi}12\;mm$ in transverse direction. SP tests were performed with specimens in longitudinal and transverse directions of Al2024 ECAP metal. For comparing the strength values with those assessed by SP tests, uniaxial tensile tests were also conducted with specimens in longitudinal direction. Failure surfaces of the tested SP specimens showed that failure mode was shear deformation and Al 2024 ECAP metal has an anisotropy in strength. Thus, conventional equations proposed for assessing the strength characteristics were improper to assess those of Al2024 ECAP metal. In this paper a way of assessing the strength of Al 2024 ECAP metal was proposed and was proven to be effective.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.283-286
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• 2005

When subjected to severe shear deformation by ECAP, microstructure of Al2024 becomes nanocrystalline grained texture material. To measure the strength of that, small punch (SP) testing method was adopted as a substitute for the conventional uniaxial tensile testing because the size of material processed by ECAP were limited to $\varphi12mm$ in transverse direction. SP tests were performed with specimens in longitudinal and transverse directions of Al 2024 ECAP metal. For comparing the strength values with those assessed by SP tests, uniaxial tensile tests were also conducted with specimens in longitudinal direction. Failure surfaces of the tested SP specimens showed that failure mode was shear deformation and Al 2024 ECAP metal has an anisotropy in strength. Thus, conventional equations proposed for assessing the strength characteristics were improper to assess those of Al2024 ECAP metal. In this paper a way of assessing the strength of Al 2024 ECAP metal was proposed and was proven to be effective.

• Korean Journal of Materials Research
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• v.30 no.4
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• pp.197-203
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• 2020

Abdominal organs are the most vulnerable body parts under vehicle trauma, and there is high mortality from acute injuries in accidents. There are various ways to reduce this high mortality; one method is Resuscitative Endovascular Balloon Occlusion of the Aorta, which has recently become very popular as a minimally invasive alternative in the emergent management of patients with non-compressible hemorrhages below the diaphragm. However, high safety factor for patients is applied in actual clinical practice because there is no exact standard for the operating time. Therefore, in this study, the effects of the mechanical behavior of organ tissues for the duodenum, kidney, and liver on the operating time of Resuscitative Endovascular Balloon Occlusion of the Aorta is investigated in order to obtain data needed to establish standards of operating time. In characteristic analysis of organ tissues, uniaxial tensile test and compression test are conducted according to the operating time.

• Smart Structures and Systems
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• v.30 no.1
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• pp.49-62
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• 2022

Experimental and discrete element methods were used to investigate the effects of triple joints lengths and triple joint angle on the failure behavior of rock mass under uniaxial compressive test. Concrete samples with dimension of 20 cm × 20 cm × 5 cm were prepared. Within the specimen, three imbedded joint were provided. The joint lengths were 2 cm, 4cm and 6 cm. In constant joint lengths, the angle between middle joint and other joints were 30°, 60°, 90°, 120° and 150°. Totally 15 different models were tested under compression test. The axial load rate on the model was 0.05 mm/min. Concurrent with experimental tests, the models containing triple joints, length and joint angle are similar to the experiments, were numerical by Particle flow code in two dimensions (PFC2D). Loading rate in numerical modelling was 0.05 mm/min. Tensile strength of material was 1 MPa. The results show that the failure behaviors of rock samples containing triple joints were governed by both of the angle and the length of the triple joints. The uniaxial compressive strengths (UCS) of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. Furthermore, it was shown that the compressive behavior of discontinuities is related to the number of the induced tensile cracks which are increased by decreasing the joint length. Along with the damage failure of the samples, the acoustic emission (AE) activities are excited. There were only a few AE hits in the initial stage of loading, then AE hits rapidly grow before the applied stress reached its peak. In addition, every stress drop was accompanied by a large number of AE hits. Finally, the failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

• Design & Manufacturing
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• v.14 no.1
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• pp.49-55
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• 2020

In this study, the fatigue behavior and fatigue life characteristics of PA2200 specimens fabricated by SLS 3D printer were studied. Fatigue tests were performed according to the standard specification (ASTM E468) and fatigue life curves were obtained. In order to perform the fatigue test, mechanical properties were measured according to the test speed of the simple tensile test, and the self-heating temperature of the specimen according to the test speed was measured using an infrared temperature measuring camera in consideration of heat generation due to plastic deformation. There was no significant difference within the set test speed range and the average self-heating temperature was measured at 38.5 ℃. The mechanical strength at the measured temperature showed a relatively small difference from the mechanical strength at room temperature. Fatigue test conditions were established through the preceding experiments, and the loading conditions below the tensile strength at room temperature 23 ℃ were set as the cyclic load. The maximum number of replicates was less than 100,000 cycles, and the fracture behavior of the specimens with the repeated loads showed the characteristics of Racheting. It was confirmed that SLS 3D printing PA2200 material could be applied to the Basquin's S-N diagram for the fatigue life curve of metal materials. SEM images of the fracture surface was obtained to analyze the relationship between the characteristics of the fracture surface and the number of repetitions until failure. Brittle fracture, crazing fracture, grain melting, and porous fracture surface were observed. It was shown that the larger the area of crazing damage, the longer the number of repetitions until fracture.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.255-259
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• 2001

The spring constant of a micro coil spring was measured by uniaxial tensile test. The inner diameter of it is $35{\mu}m$ and the pitch size is about $23{\mu}m$. A suing constant measurement system was developed. It consists of control units, load cell units, linear stages and several specially designed jigs and fixtures. Load and displacement are measured using a commercial load cell of 1000g capacity and a magnetic scale of $0.5{\mu}m$ resolution. In this study, a method to measure the spring constant of micro coil spring is presented and the relationship between misalignment of specimen and measurement error is discussed.