• The Korean Journal of Rheology
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• v.8 no.2
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• pp.129-138
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• 1996

접착강도는 접착제의 점탄성을 반영한 온도·속도 의존성을 나타낸다는 것이 잘 알 려져있다. 특히 유리전이온도(Tg)에서의 역학적 완화기구가 접착층의 변형을 수반하는 접착 층의 변형을 수반하는 접착강도에 크게 영향을 미치고 있다. 또한 접착계의 모드I의 변형에 너지 해방율(GIC)를 측정할때에도 접착제의 변형과 파괴가 발생하기 접착제의 점탄성이 그 값에 어떠한 영향을 미치는 지에 흥미가 깊다. 본 연구에서는 2종류의 에폭시 수지를 블랜 드한 접착제를 이용하여 일정한 측정조건에서 인장 접착강도와 GIC의 상관관계에 대하여서 도 토론하였다.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.529-534
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• 1998

To find out an adequate failure criterion in two-dimensional linear elastic crack problems, finite element programs, SED, which determine stress intensity factors $K_I, K_{II}$, crack angle and peak load by the minimum strain energy density failure criterion were developed. In this program, the conventional quadratic isoparametric elements were used in all regions except the crack tip zone where triangular singular elements with 6 nodes were used. The results of SED were compared with the results of those which followed by the maximum circumferential tensile stress criteria and those by the maximum energy release rate criteria and those by Jenq and Shah`s experiments of the same geometry and material properties. The maximum energy release rate criteria were better close to those of the Jenq and Shah`s experiments than the maximum circumferential tensile stress criteria and the minimum strain energy density criteria.

• Journal of Magnetics
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• v.15 no.4
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• pp.173-178
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• 2010

A new kind of magnetic rubber, Fe dispersed ethylene propylene monomer (EPM), was prepared by a conventional technique using a two roll mill. The magnetic fillers of Fe-nanoparicles were coated by low density polyethylene (LDPE). The purpose of surface treatment of nanoparticles by LDPE is to enhance wettability and lubricancy of the fillers in a polymer matrix. The mechanical strength and microstructure of the magnetic rubber were characterized by tensile strength test and scanning electron microscopy (SEM). Results revealed that the Fe nanoparticles were relatively well dispersed in an EPM matrix. It was found that the nano- Fe dispersed magnetic rubber showed higher coercivity and tensile strength than those of micron- Fe dispersed one.

• Advances in concrete construction
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• v.16 no.6
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• pp.277-290
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• 2023

In order to study the mechanical properties of basalt fiber reinforced ultra-fine fly ash concrete (BFUFARC), the effects of ultra-fine fly ash (UFA) content, basalt fiber content, basalt fiber length and water reducing agent content on the compressive strength, splitting tensile strength and flexural strength of the composite material were studied through experimental and theoretical analysis. Also, a scanning electron microscope (SEM) was employed to analyze the mesoscopic structure in the fracture surface of composite material specimens at magnifications of 500 and 3500. Besides, the energy release rate (G_c) and surface free energy (γ_s) of crack tip cracking on BFUFARC in different basalt fiber content were studied from the perspective of fracture mechanics. Further, the cracking resistance, reinforcement, and toughening mechanisms of basalt fibers on concrete substrate were revealed by surface free energy of BFUFARC. The experimental results indicated that basalt fiber content is the main influence factor on the splitting tensile strength of BFUFARC. In case that fiber content increased from 0 to 0.3%, the concrete surface free energy at the tip of single-sided crack showed a trend of increased at first and then decreased. The surface free energy reached at maximum, about 3.59 × 10^-5 MN/m. During the process of increasing fiber content from 0 to 0.1%, G_C-2_γS showed a gradually decreasing trend. As a result, an appropriate amount of basalt fiber can play a preventing cracking role by increasing the concrete surface free energy, further effectively improve the concrete splitting tensile performance.

• Nuclear Engineering and Technology
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• v.49 no.7
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• pp.1472-1482
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• 2017

Zirconium alloy cladding tube specimens were irradiated at $380^{\circ}C$ up to a fast neutron fluence of $7.5{\times}10^{24}n/m^2$ in a research reactor to investigate the effect of neutron irradiation on hydride reorientation and mechanical property degradation. Cool-down tests from $400^{\circ}C$ to $200^{\circ}C$ under 150 MPa tensile hoop stress were performed. These tests indicate that the irradiated specimens generated a smaller radial hydride fraction than did the unirradiated specimens and that higher hydrogen content generated a smaller radial hydride fraction. The irradiated specimens of 500 ppm-H showed smaller ultimate tensile strength and plastic strain than those characteristics of the 250 ppm-H specimens. This mechanical property degradation caused by neutron irradiation can be explained by tensile hoop stress-induced microcrack formation on the hydrides in the irradiation-damaged matrix and subsequent microcrack propagation along the hydrides and/or through the matrix.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.83-86
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• 2001

This paper presents an investigation of the contribution of fibers in energy absorption during impact and the effect of resin types on properties of the high strength polyethylene (Spectra-900 PE) composite. In high strength polyethylene fiber, main impact energy absorbing mechanism was tensile breakage and deformation of fiber. Two types of resin were examined : Unsaturated polyester (UP) and Epoxy. Tensile and 3-point bending test have been performed to investigate the changes of mechanical properties. In tensile and flexural testes, the Spectra Composite prepregged with UP showed higher properties than Spectra Composite prepregged with epoxy.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.2
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• pp.80-85
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• 1999

The purpose of this work is to investigate fatigue damage of quasi-isotropic laminates under tensile loading in different directions. Low cycle fatigue tests of [0/-60/+60]a laminates and [+30/-30/90]s lamina tes were carried out. Material systems used are AS4/Epoxy and AS4/PEEK. The fatigue damage of [+30/-30/90]s is very different from that of [0/-60/+60]s. The position of delamination generated at AS4/Epoxy and AS$/PEEK laminates were differentiated by the matrix difference that is, we suppose, the value of both GIcr(critical energy release rate of mode-I) and GIIIcr(critical energy release rate of mode-III) difference.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.6
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• pp.477-482
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• 2008

The influence of dislocation substructure of metallic materials on ultrasonic velocity has been experimentally investigated. The test materials of pure Cu, brass (Cu-35Zn), 2.25Cr-1Mo steel, and AISI 316 with different stacking fault energy (SFE) are plastically deformed in order to generate dislocation substructures. The longitudinal wave velocit $(C_L)$ decreases as a function of tensile strain in each material. The $C_L$ of Cu-35Zn and AISI 316 decreases monotonously with tensile strain, but $C_L$ of Cu and 2.25Cr-1Mo steel shows plateau phenomena due to the stable dislocation substructure. The variation of ultrasonic velocity with the extent of dislocation damping and dislocation substructures is discussed.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.1
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• pp.36-43
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• 2015

Since the crack generation and its propagation caused by welding defects is one of the main hull damage patterns, the simulation of crack propagation process has an important significance for ship safety. Based on interface element method, a finite element model to simulate crack propagation is studied in the paper. A Lennard-Jones type potential function is employed to define potential energy of the interface element. Tensile tests of steel flat plates with initial central crack are carried out. Surface energy density and spring critical stress that are suitable for the simulation of crack propagation are determined by comparing numerical calculation and tests results. Based on a large number of simulation results, the curve of simulation correction parameter plotted against the crack length is calculated.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 1999.04b
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• pp.232-238
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• 1999

The reinforcement of wheat straw pulp sheets with softwood kraft was studied, with special emphasis on the impact of softwood kraft beating and the proportion softwood kraft in straw pulp. the reinforcement was evaluated by measuring the tensile stiffness sand in-plane fracture behavior of samples. the results were compared with a mechanical pulp (TMP) and with a hardwood birch kraft, both reinforced with the same softwood kraft. Wheat straw pulp forms strong interfiber bonds. Therefore, its tensile stiffness and tensile strength are larger than TMP used. In-plane tear tests showed that a pure wheat straw pulp sheet has low fracture energy and correspondingly a narrow fracture process zone. The fracture energy of the reinforced straw sheets was found to increase linearly with the proportion of both unbeaten and beaten softwood pulps.