• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 춘계학술대회 논문집
• /
• pp.275-278
• /
• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it finds use in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. In order to design optimal structural parts made of INCONEL 718, accurate understanding of material's mechanical properties, dynamic behavior and fracture characteristic as a function of strain rates are required. This paper concerned with the dynamic material properties of the INCONEL 718 for the various strain rates. The dynamic response of the INCONEL 718 at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is from the split Hopkinson pressure bar test. Based on the experimental results, the effects of strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure are evaluated. Experimental results from both quasi-static and high strain rate up to the 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of INCONEL 718.

• 한국세라믹학회지
• /
• 제35권5호
• /
• pp.429-436
• /
• 1998

The mechanical properties and damage mode of {{{{ {Y}_{2 } {O}_{3} }}-doped tetragonal (Y-TZP) can-didated as biomaterials were performed under indentation stress-strain curve critical load for yield and cracking strength degradation and fatigue behavior with Hertzian indentation tests. This material shows the brittle behavior which is confirmed by indentation stress-strain response. The critical load for cracking(Pc) is much higher than that for yields (Py) indicating crack resistance Strength were strongly dependant on contact area and there were no degradation when the indenter size was ${\gamma}$=3.18 mm suggesting that Y-TZP should be highly damage tolerant to the blunt contacts. Multi-cycle contact were found to be innocuous up to {{{{ {10 }^{6 } }} cycles at 500N and {{{{ {10 }^{5 } }} cycles at 1000N in water. On the other hand contacts at {{{{ {10 }^{6 } }} cycles at 1000 N in water did show some signs of incipient degradation. By contrast contacts with Vickers indenter pro-duced substantial strength losses at much lower loads suggesting that the mechanical integrity of this ma-terial would be compromised by inadvertent sharp contacts.

• 한국세라믹학회지
• /
• 제35권7호
• /
• pp.671-678
• /
• 1998

Hertzian indentation tests with sphere indenters were used to study the mechanical properties of glass-in-filtrated alumina and spinel composites and evaluated the effect of preform microstructure and evaluated the effect of preform microstructure and glass con-tents on contanct damage and strength. The spinel composite showed more brittle behavior than the alumina composite which is verified from indentation stress-strain curve cone cracks and quasi-plastic deformation developed at subsurface. Failure originated from either cone cracks(brittle mode) or deformation zone(quasi-plastic mode) above critical load for cracking(Pc) and yield ({{{{ {P }_{Y } }}) with the brittle mode more dominant in the spinels and the quasi-plastic mode more dominant in the aluminas. Even though brittle mode was dominant in the spinel composites the strength degradation from accumulation of damage above these critical loads was conspicuously small suggesting that the glass-infiltrated composites should be highly damage tolerant to the blunt contacts.

• 한국세라믹학회지
• /
• 제41권7호
• /
• pp.541-547
• /
• 2004

일반적으로 혼합분말의 소결에서 작은 입자에 큰 입자의 첨가는 소결성의 저하를 가져온다. 본 연구에서는 이러한 원리를 이용하여 작은 SiC 입자에 큰 SiC 휘스커 또는 큰 SiC 입자를 첨가하여 소결성을 저하시키고, YAG(Y$_3$A1$_{5}$O$_{12}$)상을 소결 첨가제로 사용함으로서 다공질 SiC 세라믹스를 제조하였다. 제조된 다공질 SiC 세라믹스의 기공율은 큰 입자의 함량과 소결 압력을 제어함으로서 0.3-39% 범위에서 제어할 수 있었다. 기공율은 큰 입자의 함량이 증가함에 따라 증가하였고, SiC 휘스커를 첨가하는 것이 큰 SiC 입자를 첨가하는 것 보다 기공율을 높이는데 효과적이었다. 제조된 다공질 세라믹스에서 기체의 통기성은 기공율이 증가함에 따라 증가하였고, 굽힘강도는 기공율이 증가함에 따라 감소하였다. 기공율이 18% 이상인 다공질 SiC 세라믹스의 경우에 주목할 만한 변형율이 관찰되었다.

• 한국압력기기공학회 논문집
• /
• 제13권2호
• /
• pp.75-83
• /
• 2017

In severe accident conditions of light water reactors, the loss of coolant may cause problems in integrity of zirconium fuel cladding. Under the condition of the loss of coolant, the zirconium fuel cladding can be exposed to high temperature steam and reacted with them by producing of hydrogen, which is caused by the failure in oxidation resistance of zirconium cladding materials during the loss of coolant accident scenarios. In order to avoid these problems, we develop a multi-metallic layered composite (MMLC) fuel cladding which compromises between the neutronic advantages of zirconium-based alloys and the accident-tolerance of non-zirconium-based metallic materials. Cold pilgering process is a common tube manufacturing process, which is complex material forming operation in highly non-steady state, where the materials undergo a long series of deformation resulting in both diameter and thickness reduction. During the cold pilgering process, MMLC claddings need to reduce the outside diameter and wall thickness. However, multi-layers of the tube are expected to occur different deformation processes because each layer has different mechanical properties. To improve the utilization of the pilgering process, 3-dimensional computational analyses have been made using a finite element modeling technique. We also analyze the dimensional change, strain and stress distribution at MMLC tube by considering the behavior of rolls such as stroke rate and feed rate.