• Korean Journal of Materials Research
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• v.5 no.3
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• pp.261-267
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• 1995

IN 617의 시편으로 1073K의 온도와 107과 180 MPA의 응력에서 $\varepsilon$=0.18까지 정압크\ulcorner을 한 직후 107 MPa로 응력을 낮추고 (응력강하시험), 또 다른 시편에는 180 ↔ 0.2 MPa의 응력으로 각각 17초씩 반복주기변형을 수행하여 정압크\ulcorner 변형시의 크\ulcorner곡선과 비교를 하엿다. 그 결과 IN 617 의 반복주기변형에서는 변형속도둔화(CCD)가 발생함을 알 수 있었고, 응력강하와 반복변형시험은 모두 거의 같은 모양의 회복 크\ulcorner곡선을 나타내었다. 이러한 회복 크\ulcorner은 아결정립크기와 자유전위밀도로서 그 회복기구를 설명할수 있었다.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.246-250
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• 1999

항공기 날개 및 동체의 보강재로 사용되는 스트링거가 압축하중을 받게되면 플렌지와 웹에서의 부분좌굴이 발생하고 이는 좌굴이 발생하지 않은 부분에 과도한 하중이 걸리게 하여 스트링거의 전체적인 하중지지능력을 현저히 감소시킨다. 이러한 손상의 형태가 크리플링(Crippling)이다. (중략)

• Composites Research
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• v.12 no.6
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• pp.65-73
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• 1999

Crippling stress and failure behavior of Z-section graphite/epoxy composite laminated stringers are investigated by the nonlinear finite element method. Stringers are idealized using 9-node laminated shell element. The complete unloading model is introduced into the finite element method for the progressive failure analysis. A modified Riks method is used to trace the post-failure equilibrium path after local buckling. Finite element results are validated with previous experimental results. The results show that the most important parameter affecting the crippling stress of Z-section stringers is the flange width. In terms of stacking sequence. the highest cripping stress is found at the stringer with $[{\pm}45/0/90]s$ lamination.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.7
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• pp.91-97
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• 1998

The analysis model is the infinite body consisted of power law creep material containing a rigid inclusion with line crack shape subjected to the arbitrarily directional stress on an infinite boundary. The crack analysis is performed using the complex pseudo-stress function. The strain rate intensity factor is determined in the closed form as new fracture mechanics parmeter which represents the magnitudes of stress and strain rate near the tip in power law creep material.

• Composites Research
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• v.14 no.3
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• pp.32-41
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• 2001

Z-section composite stringers with various lengths and flange-widths are tested in axial compression for the validation of a finite element algorithm to calculate the buckling and crippling stresses of composite laminated stringers. The stacking sequence considered is $[{\pm}45/0/90]s$. Strain gages are attached to each specimen, and deflection and end-shortening are obtained by two LVDTs. The buckling load is determined from the load vs. strain response, load vs. end-shortening curves, and load vs. out-of-plane deflection curves. The ultimate stress after local buckling is used as the crippling stress. Comparison between finite element and experimental results shows good agreement in the local buckling and crippling stresses.

• Journal of the KSME
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• v.19 no.4
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• pp.291-294
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• 1979

본 강좌에서는 취성파괴의 사고와 그 원인, 재료의 강도와 구조설계, 재료의 이상강도와 결함 크 랙의 변형과 파괴인성의 개요, 탄성파괴역학의 개요 등을 기술하겠다.

• Polymer(Korea)
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• v.28 no.1
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• pp.77-85
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• 2004

It has been widely used ultra high molecular weight polyethylene (UHMWPE) for the biomaterials due to its excellent mechanical properties and biocompatibility. In the case of blend of UHMPE with another polymeric biomaterials, however, UHMWPE might have low blend compatibility due to surface inertness. In this study, in order to improve the mechanical properties of poly(methyl methacrylate) (PMMA) bone cement by means of the impregnation of UHMWPE powder, we developed the novel surface modification method by the mixture of methyl methacrylate (MMA) and xylene. We investigated the variation of composition of MMA/xylene. It was confirmed by the analysis of Fourier transform infrared-attenuated total reflectance, scanning electron microscope, universal transverse mercator, and digital thermometer. The maximum mechanical strength of surface modified UHMWPE powder impregnated PMMA bone cement compound was observed the ratio of 1 : 1 (v/v％) MMA/xylene. Also its curing temperature decreased from 103 $^{\circ}C$ to 58 ∼ 73 $^{\circ}C$ The mechanism of surface modification of UHMWPE powder by the mixture of MMA/xylene has been proposed.

• Journal of the Korean Society of Safety
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• v.14 no.1
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• pp.208-215
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• 1999

The creep behavior of a rapidly solidified and consolidated Al-9.45wt%Fe-4.45wt%Cr alloy were investigated in the stress range 40 to 115 MPa and temperature range 300(0.53Tm) to 441$^{\circ}C$(0.66Tm). It is of use to available aerospace and automobile industries for the improved performance of materials used at high temperature. Because Al alloys with improved creep resistance offer the potential for lower weight and reduced costs in aerospace and automobile components (e.g., structural members and engine parts) through the replacement of heavier and more costly materials, the safety in use at high temperature is good. The alloy is characterized by high stress exponents and activation energies for creep, which are greatly dependent on the stress and temperature. Because the creep stress is seen to cause a strongly significant enhancement of coarsening, the coarsening rate of the dispersed particles in all crept specimens is faster than that in isothermally annealed specimens. Dislocations connecting dispersoids are observed more cofrequently in crept specimens with higher stress and lower temperature. The creep strain rates in the power law creep regime were found to be predicted much better by the Shorty and Rosler/Arzt equation with the inclusion of a threshold stress and dislocation detachment mechanism. The dispersoids in this alloy were acting a source of void nucleation that finally leaded to ductile fracture within the grain so called intergranular. Each void was initiated, grown and failed at the dispersoids in the aluminium matrix. Grain boundary accommodation of the slip produced, which result in initiation of the void and then final transgranular fracture. Therefore, it was confirmed that these dispersoids played an important role in the fracture mechanism by the formation of $Al_{13}Fe_4$, $Al_{13}Cr_2$ and $Al_2O_3$.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10b
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• pp.151-152
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• 2003

전보[1]에서 PMMA 코어 플라스틱 광섬유의 클래드 재료로 사용하기 위하여 MMA/불소계메타크릴레이트(FAMA) 공중합체를 제조하고 FAMA 종류 및 함량에 따른 굴절률, 내열성의 변화를 살펴보았다. FAMA의 함량이 증가함에 따라 굴절률은 효과적으로 낮출 수 있었으나 유리전이온도와 계면접착력은 감소하여 내열성 및 PMMA와의 계면 접착력을 향상시킬 수 있는 새로운 화학구조의 클래드 재료 설계가 필요하였다. (중략)

• Polymer(Korea)
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• v.28 no.1
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• pp.86-91
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• 2004

Hydrogels with enhanced biocompatibility and biostability were prepared by copolymerization of 2-hydroxyethyl methacrylate (HEMA) and sodium methacrylate (SMA) at high monomer concentration to replace a sponge which has limited applications as an implant material. It was found that incorporation of SMA moiety suppressed cytotoxicity. P(HEMA-co-SMA) hydrogel prepared at SMA feed ratio of 0.05 showed minimal cytotoxicity as compared with a normal cell culture plate. The adhesion and the spreading of cells were preferred on the surface of the hydrogel prepared with SMA feed ratio of 0.01. On the other hand, the hydrogel prepared with SMA feed ratio of 0.05 showed lower cell adhesion. Histological findings revealed no evidence of significant foreign body reaction in the tissues around the copolymer hydrogels. Conclusively, it is suggested that the hydrogels prepared by copolymerization of HEMA and SMA at high monomer concentration are strong candidates for an implant material with excellent biocompatibility and biostability.