• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.165-172
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• 2013

Power generating unit structures are designed and built to meet standard to secure its safety for expected life time. As the structures have been exposed to combined environment, degradation of structure material is accelerated and it can cause unexpected damage; evaluating precise mechanical properties of weak site like welded area is an essential research area as it is directly connected to safety issues. Existing measuring technique like tensile test requires specific size in testing specimen yet it is destructive method which is hard to apply on running structures. To overcome above mentioned limitation, IIT is getting limelight as it is non-destructive and simple method. In this study, latest technique is introduced to evaluate tensile property and residual stress by analyzing stress field occurs under the indenter while IIT is performed. Test on welded area, the weak site of nuclear structures have been practiced and confirmed that IIT can be usefully applied to evaluate integrity in industry.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1521-1528
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• 2011

We studied the material properties for reliability improvement in finite element analysis results for a nitrile butadiene rubber hub-bearing seal and for a carbon-filled rubber mount used in a vehicle. It was difficult to measure the material properties of hundreds of types of rubber for the mount design. Thus, we suggested that the engineering stressstrain relations from pure shear test data could be synthesized by using simple tension data and Poisson's ratio. We defined Poisson's ratio by using a function of principal stretches to synthesize the stress-strain relations for a pure shear test. A transformation of the pure shear data was applied to the experimental values to obtain the predicted results when the strain approaches 100%. In the finite element analysis for the contact force of a hub-bearing seal, the strain results that used the transformation of the pure shear data and simple tension data almost corresponded to the experimental values. Ogden constants were used to analyze.

• Composites Research
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• v.35 no.6
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• pp.425-430
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• 2022

In this study, the mechanical properties of the pressure vessel composite exposed to the thermal environment were evaluated to establish the standard for high temperature static pressure test of the pressure vessel for hydrogen bus. As the tensile strength of the composite material approaches the glass transition temperature of the epoxy resin, the strength decreases due to the deterioration of the epoxy resin. In addition, it was confirmed that the tensile strength increased again due to the post-curing of the epoxy resin during long-term exposure. Therefore, the accelerated stress rupture test conditions of the pressure vessel for the hydrogen bus should be set based on the epoxy resin properties of the carbon fiber composite material.

• Elastomers and Composites
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• v.42 no.1
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• pp.32-46
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• 2007

Mechanical properties of rubber material are very important in design procedure to assure the safety and reliability of the rubber components. In this paper, the material test and accelerated heat aging test were carried out. In order to investigate the effects of heat-aging on the material properties, hardness, elongation, stress-strain curves and dynamic characteristics were obtained from various test conditions. Also, rubber material coefficients were determined by both the uniaxical and equi-biaxial tensile tests.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.421-426
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• 2017

In this study, we propose a method for predicting the mechanical properties of the printed circuit board (PCB) that has transversely isotropic characteristics. Unlike the isotropic material, there is no specific test standard for acquisition of the transversely isotropic properties. In addition, common material test methods are not readily applicable to that type of laminated thin plate. Utilizing the natural frequency obtained by a modal test and the sizing optimization technique provided in $OptiStruct^{(R)}$, the mechanical properties of a PCB were derived to minimize the difference between test and analysis results. In addition, the validity of the predicted mechanical properties was confirmed by the MAC (Modal Assurance Criteria) value of each of the compared mode shapes. This proposed approach is expected to be extended to the structural analysis for the design verification of the top product that includes a PCB.

• Journal of Conservation Science
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• v.25 no.1
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• pp.77-86
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• 2009

The physical properties of the epoxy resins were studied with an addition of filler content and the application of artificial weathering test. When talc as a filler was added to the epoxy resin (L-30), the water resistance seemed to be increased because of the results of the reducing of water absorption rate and the increasing of contact angle. Although the adhesive strength of epoxy resins was not affected by the increasing amount of talc, its compressive strength was reduced. The physical properties of the epoxy resins had different trends according to the site environments. The artificial weathering test with the change of temperature and humidity showed that the changes of water absorption rate and colour differences of the epoxy resins containing talc were lower than the pure epoxy resin itself. However, the contact angle was higher. The artificial weathering test with ultraviolet irradiations showed the opposite result; the damage of epoxy resins was increased with the increasing of talc content. These mean the site environment of the stone monuments should be considered to determine the content of talc added to increase the durability of epoxy resin.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2009.11a
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• pp.173-174
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• 2009

"방사성폐기물 고화체의 물성시험"에 사용되는 시편을 실험실적으로 제조한 소규모 모의 고화체 시편과 고화공정에서 직접 채취한 소규모 시편, 200L 드럼으로부터 코아시편을 채취 가공하여 만든 시편과 같이 3종류가 있다. 고화공정에서 발생되는 고화체는 일반적으로 200 L 드럼에 주입되며, 고화체의 균일성 정도는 고화공정의 특성, 폐기물/고화매질 혼합비, 200 L 고화체 드럼의 냉각방식에 따라 다르다. 따라서, 실험실에서 제조한 시편과 공정에서 채취한 소규모 시편을 실제 고화공정을 대표할 수 없으며 또한 실제 발생된 고화체의 조성과도 동일하다고 볼 수 없다. 따라서 200 L 실드럼에서부터 코아시편을 채취하여 만든 시편이 고화공정과도 고화체를 대표할 수 있는 시편으로 볼 수 있다. 기 발생고화체(시멘트와 파리핀 고화체 및 잡고체 폐기물)의 영구처분을 위하여 과기부 고시 05-18호 "폐기물 인도기준" 규정과 한국방사성폐기물관리공단의 중 저준위 방사성폐기물 인수기주(안)의 준수 여부를 평가하기 위하여 각 원전의 대표 드럼에 대하여 특성평가시험인 압축강도, 침출, 침수, 열 순환, 내방사성 영향시험을 수행하기위해 실 드럼으로부터 원통형 코아시편을 채취하여 이를 시험검사에 필요한 시험시편으로 가공한 후 표준 특성시험법을 이용하여 물성들을 평가하며 특성평가시험을 위한 시편으로는 L/D=2, L/D=1인 두 종류의 시편을 가공하였으며 압축, 침수, 열순환 및 방사선조사시편은 L/D=2 시편을 제조하였고 침출시험시편은 L/D=1인 시편을 채취하였다.

• Composites Research
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• v.23 no.5
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• pp.8-14
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• 2010

Three types of glass woven fabrics (plain, balanced twill, and unbalanced twill) having various sample sizes and aspect ratios were tested using the bias-extension tests. Real-time deformation images, force, and displacement data were collected. For the bias-extension test, the shear angle of the fabrics from the equation based on the crosshead displacement and fabric size was compared with direct manual measurements of the warp and weft angles as well as the optical measurement software. To determine the shear force, an analytical equation was introduced considering the kinematics of the bias-extension test. The obtained shear behaviors were further compared with the results by the trellis-frame test. The optical measurement methods showed that the mathematical method was reasonable before the shear angle of the fabrics reaches $30^{\circ}$ in the bias-extension tests. Also, the bias-extension test gave consistent behaviors with the trellis-frame test only for isotropic and homogeneous fabrics such as balanced plain and twill weaves.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.306-314
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• 2006

Instrumented indentation technique is a new way to evaluate nondestructive such mechanical properties as flow properties, residual stress and fracture toughness by analyzing indentation load-depth curves. This study evaluated quantitatively the flow properties of steels and residual stress of weldments. First, flow properties can be evaluated by defining a representative stress and strain from analysis of deformation behavior beneath the rigid spherical indenter and the parameters obtained from instrumented indentation tests. For estimating residual stress, the deviatoric-stress part of the residual stress affects the indentation load-depth curve, so that by analyzing the difference between the residual-stress-induced indentation curve and residual-stress-free curve, the quantitative residual stress of the target region can be evaluated. The algorithm for flow property evaluation was verified by comparison with uniaxial tensile test and the residual stress evaluation model was compared to mechanical cutting and ED-XRD results.

• Journal of Adhesion and Interface
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• v.6 no.2
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• pp.13-20
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• 2005

Interfacial shear strength (IFSS) of environmentally friendly natural fiber reinforced polymer composites plays a very important role in controlling the overall mechanical performance. The IFSS of various Ramie and Kenaf fibers/epoxy composites was evaluated using the combination of micromechanical test and nondestructive acoustic emission (AE) to find out optimal conditions for desirable final performance. Dynamic contact angle was measured for Ramie and Kenaf fibers and correlated the wettability properties with interfacial adhesion. Mechanical properties of Ramie and Kenaf fibers were investigated using single-fiber tensile test and analyzed statistically by both uni-and bimodal Weibull distributions. An influence of clamping effect on a real elongation for both Ramie and Kenaf fibers were evaluated as well. Two different microfailure modes, axial debonding and fibril fracture coming from fiber bundles and single fiber composites (SFC) were observed under tension and compression.