• Progress in Superconductivity
• /
• 제8권1호
• /
• pp.119-121
• /
• 2006

We studied the mechanical and magnetic properties of Y-Ba-Cu-O superconductor with and without resin and Ag impregnation. Bulk YBCO superconductor was manufactured with the top-seeded melt-growth method. Typical sample of 40mm X 20mm X 3mm was made and then 8 holes with 0.5mm diameter were drilled arbitrally. Epoxy resin and $AgNO_3$ were systematically added into the holes to compare the mechanical and magnetic properties of YBCO superconductor before and after reinforcement of resin and Ag. Based on the result of 3 point bending, bending strength increased with increasing amounts of resin and carbon nano-tube. However, it was found that the levitation force decreased after making hole, compared with virgin sample without hole.

• 한국세라믹학회지
• /
• 제34권8호
• /
• pp.877-885
• /
• 1997

The dependence of strength, crack growth, fracture mode and degree of domain rearrangement of PZT ceramics on poling strength were studied. The PZT [(Pb0.94Sr0.06)(Zr0.46Ti0.54)O3+Nb(trace)] specimens were poled at 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 kv/mm, and the strength of the specimens was measured by 3 point flexure system. The bending strength of the specimen decreased in different modes according to the bending directions; xz, zx and yz plane direction with x axis of the poling direction in Cartesian coordinate system. The strength differences between the directions increased as the poling strength increased. The fracture mode transferred to intergranular fracture mode from transgranular one as the poling strength increased. The mechanical breakdown occurred when the poling strength higher than 3 kV/mm was applied to the specimen. It was observed that the crack length increased in the normal direction to the poling direction, however, decreased in the parallel direction to the poling direction when the poled PZT specimen was indented by the Vickers indenter. However, the crack produced by indentation continuously was continuously increased little by little after indentation on the specimen. The domain rearrangement occurred as the poling strength increased and the domains were rearranged more effectively when the electric field was continuously increased little by little.

• 한국세라믹학회지
• /
• 제38권12호
• /
• pp.1123-1131
• /
• 2001

재활용 $Al_2$O$_3$분말인 구조재료용 $Al_2$O$_3$세라믹스의 분쇄분말과 폐Al$_2$O$_3$흡착제의 첨가량과 입경에 따른 재생 $Al_2$O$_3$세라믹스의 소결특성을 조사하였다. 1,$650^{\circ}C$에서 5시간 소결한 순수 $Al_2$O$_3$시편을 급랭하여 분쇄한 -40과 +40$\mu$m의 $Al_2$O$_3$분말과 폐Al$_2$O$_3$흡착제를 순수한 $Al_2$O$_3$분말에 10~50wt% 첨가한 후, 재소결하여 재생 $Al_2$O$_3$세라믹스를 제조하였다. 재활용 $Al_2$O$_3$분말의 첨가량과 입경에 관계없이 소결온도가 증가함에 따라 시편의 밀도와 3점곡강도는 증가하였으나, 동일 소결온도에서는 재활용 $Al_2$O$_3$분말의 첨가량이 증가함에 따라 밀도와 3점곡강도는 감소하였다. ~30wt%의 $Al_2$O$_3$분쇄분말(-40$\mu$m), ~20wt%의 $Al_2$O$_3$분쇄분말(+40$\mu$m) 및 10wt%의 폐Al$_2$O$_3$흡착제를 첨가한 시편의 3점곡강도는 200MPa 이상이었다. 재생 $Al_2$O$_3$시편의 치밀화를 위하여 5~20wt%의 폐유리분말을 첨가하여 1200~1$650^{\circ}C$에서 5시간 소결한 시편은 폐유리분말의 첨가량이 증가함에 따라 최대 밀도와 3점곡강도를 나타내는 온도는 감소하였으나, 140$0^{\circ}C$이상에서는 페유리분말을 첨가하지 않은 시편에 비하여 밀도와 3점곡강도가 감소하여 재생 $Al_2$O$_3$세라믹스의 소결성 향상에는 기여하지 못하였다.

• 한국산업융합학회 논문집
• /
• 제27권4_2호
• /
• pp.973-980
• /
• 2024

Dependence of dynamic fracture path on loading velocity was observed from experimental results based on the three point bending fracture in cast iron. In this study, 3D and 2D numerical simulations are used to evaluate singular stress fields near crack tip and fracture mechanics parameters. Moving finite element technique, 2D and 3D Delauney automatic mesh generation and contact-noncontact evaluation is introduced into the numerical method. Dynamic fracture thoughness is decreased with increase of impact loading velocity. Fracture mode-ratio corresponds to initial kink angle of fracture path. The numerical result shows that the maximum hoop stress criterion cannot be applied to dynamic fracture of cast iron.

• 대한치과교정학회지
• /
• 제22권3호
• /
• pp.647-656
• /
• 1992

The purpose of this study was to evaluate the elastic memory process in cold worked stainless steel wire and the effect of heat treatment on it. 0.018 inch round and $0.019\times0.025$ inch rectangular wire (ORMCO stainless wire) were used in this study. Each wire type had 4 groups: non-heat treatment group, furnace heat treatment group, electric current heat treatment group, and bending after heat treatment group. Each group was consisted of 10 specimens. With the Jig, each wire was bent into v-shape uniformly, and width of two free ends of each v-shaped wire was measured by caliper (to the point of 0.1 mm correctly) at time interval of offjig, after heat treatment, 1, 2, 3, 4 hours, 1, 2, 3, 4, 5, 6 days, 1, 2, 3, 4 weeks after. The results were as follows: 1. In non-heat treatment group and bending after heat treatment group, elastic memory process was occured $60\%$ within 1 hour, and more than $90\%$ within 1 week. 2. In furnace and electric current heat treatment group, almost all elastic memory process was occured during teat treatment, and then specimen was stabilized dimensionally. 3. Magnitude of deformation by elastic memory was greater in heat treatment group than non heat treatment group and bending after heat treatment group. 4. There was no remarkable difference in deformation pattern between 0.018 inch round wire and $0.019\times0.025$ inch rectangular wire.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 2008년도 추계학술발표대회 및 제15회 신소재 심포지엄
• /
• pp.27.2-27.2
• /
• 2008

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
• /
• pp.180-183
• /
• 2001

Glass fiber reinforced plastic(CFHP) tent pole fabricated by the pultrusion process with unidirectional glass fiber is two times as heavy as aluminum tent pole owing to the low specific modulus The first objective of this research is the design the high strength and light weight tent pole compete with. the second is the develope glass fiber carbon fiber hybrid tent pole pultrusion process. the third is the evaluate the mechanical properties of the hybrid tent pole compare to these of the duralumin tent pole.

• Composites Research
• /
• 제13권3호
• /
• pp.1-8
• /
• 2000

Excellent environmental durability and handy installation procedure as well as high specific strength and stiffness have introduced fiber-reinforced polymeric composite materials into the civil and architectural engineering field. This study presents the considerably enhanced strength characteristics of the mortal beams by being reinforced with epoxy-bonded carbon fiber sheets(CFS). Three point bending and Charpy impact tests were performed on both of bare and reinforced mortar specimens. The influences of length, and the number of reinforcing plies were investigated. Strength reduction due to pre-existent notch was lessened dramatically. The acoustic emission(AE) measurement revealed the progressive damage process in reinforced specimens.

• 한국세라믹학회지
• /
• 제31권10호
• /
• pp.1197-1201
• /
• 1994

The fracture strength and fracture modes were studied in 3Y-TZP/NiNi bonding which change their interfacial structure with bonding condition. Average 4-point bending strength of 200 MPa to 400 MPa were achieved. The formation of Ti-oxide phase at the interface critically influenced the bonding strength and fracture mode. The fracture surface of Ti-oxide free interface contained multiphase in some case including ZrO2. From the result it was confirmed that in order to maximize the bonding strength crack deflection from interface to ceramic was required.

• 대한기계학회논문집A
• /
• 제38권12호
• /
• pp.1387-1394
• /
• 2014

광탄성 실험법에 의해 측정된 등색프린지 차수를 응력으로 변환시키기 위해서는 광탄성 재료 응력 프린지 상수를 알아야 한다. 광탄성 재료 응력 프린지 상수는 단순 인장시편 또는 압축하중을 받는 원형디스크를 이용하여 측정하는 방법 등이 있다. 이들 방법에서는 시편에 여러 하중을 가하여 하중에 응답하는 프린지 차수의 관계를 최소자승법 등을 이용하여 재료 상수를 결정한다. 본 논문에서는 4점 굽힘 시편에 하중을 가하여 나타나는 프린지로부터 재료 응력 프린지 상수를 결정하였다. 4점 굽힘 시편의 순수 굽힘 구간에서는 주응력 방향이 일정하므로 4단계 위상이동법의 적용이 가능하다. 이 방법은 원형편광기에서 검광판을 0, ${\pi}/4$, ${\pi}/2$, 그리고 $3{\pi}/4$ 라디안 회전시켜 얻은 4개의 광탄성 프린지를 필요로 한다. 4점 굽힘 시편을 이용한 재료의 프린지 상수를 결정하는 방법에서는 일정 하중을 가하여 서로 다른 위치에서도 측정할 수 있는 장점이 있다. 이 방법으로 측정된 재료 응력 프린지 상수는 제조회사에서 제시한 범위이내에 분포하였다.