• 열처리공학회지
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• 제13권3호
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• pp.163-169
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• 2000

Recently, uncertainty of hardeness became a major concem for the people working on the laboratory evaluation and accreditation. It is required to indicate uncertainty of hardness tester on the report after calibration. In addition to this, uncertainty of certified hardness reference block is also required to indicate on the certification sheet. Method on the evaluation of uncertainty in hardness measurement is agreed only recently for Rockwell hardness C scale. In this paper, a preliminary calculation of uncertainty based on type B evaluation has been made for hardness testers which satisfies the requirements of Korean Standards. It was found that the tolerance limit of mean value specified in KS should be increased to be compatible with the calculated uncertainty.

• 소성∙가공
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• 제6권6호
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• pp.508-516
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• 1997

Forging process on sintered powder metals has been applied to produce automotive parts which require a high level of strength. In those parts, the measurement of relative density is very important because a low relative density density causes deterioration of strength. In the present study, an indentation force equation was proposed by which the result obtained from the hardness measurement is used to evaluate the relative density. This equation was applied to the prediction of the relative density in cylindrical specimens which were first sintered and then forged at the room temperature and at an elevated temperature. The experimental results were compared with predictions with and without consideration of the workhardening effect on the powder.

• 한국분말재료학회지
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• 제15권6호
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• pp.482-488
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• 2008

The indentation technique has been one of the most commonly used techniques for the measurement of the mechanical properties of materials due to its experimental ease and speed. Recently, the scope of indentation has been enlarged down to the nanometer range through the development of instrumentations capable of continuously measuring load and displacement. In addition to testing hardness, the elastic modulus of submicron area could be measured from an indentation load-displacement (P-h) curve. In this study, the hardness values of the constituent phases in Ti($C_{0.7}N_{0.3}$)-NbC-Ni cermets were evaluated by nanoindentation. SEM observation of the indented surface was indispensable in order to separate the hardness of each constituent phase since the Ti($C_{0.7}N_{0.3}$)-based cermets have relatively inhomogeneous microstructure. The measured values of hardness using nanoindentation were ${\sim}20$ GPa for hard phase and ${\sim}10$ GPa for binder phase. The effect of NbC addition on hardness was not obvious in this work.

• 대한치과기공학회지
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• 제18권1호
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• pp.15-25
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• 1996

This study is to measure and compare the hardness and tensile strength of each time after we recast seven times continually only with and metal alloy Chromium-Cobalt alloy used in the production of partial denture frame work. The result of the experiment were as follow; 1) The result of the hardness measurement The result of the first casting was $490.48{\pm}38.38$ and that of the second recasting was $455.18{\pm}35.61$ and form the third recasting. the result were $518.38{\pm}37.68$ and over. The change of the hardness difference between each recasting was as follow; The hardness difference between the first casting and the second recasting was $35.25{\pm}31.93$ and that between the second recasting and the third recasting was $63.20{\pm}54.02$. There was a statistically significant difference(P<0.01) in the above hardness, however, there was little difference on the whole. And after the third recasting, the hardness grew high a little bit. That is why low-melting metals such as Cr, Mn, Cu of alloy ingredient was evaporated or there was an effect of changes in metal crystal structure, I suppose. 2) The result of the tensile strength measurement. There was a statistically significant difference(P<0.01) between the first casting and the second, the fourth recasting, however. there was little difference in general.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 1991년도 추계학술발표회논문집
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• pp.45-47
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• 1991

In this research, we verify the relations between the mechanical hardness of a strip and the output of Residual Magnetic Flux Detector, which is installed in the end side of #2 CAL. First, we install the strip speed detector and get a hardness signal and a speed signal 2 seconds, and then do signal processing and send an output to a printer every 30 seconds. The system that performs above functions is Magnetic Hardness Data Acquisition & Processing System. We got the relation between output current and hardness for the strip of T3 BP through on-line tests. Seconds, we made a hardness Measurement Simulator and observed the speed characteristics of residual magnetic flux, with using it.

• Nuclear Engineering and Technology
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• 제48권3호
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• pp.758-764
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• 2016

Specimens of stainless steel reactor internals were irradiated with 240 keV protons and 6 MeV Xe ions at room temperature. Nanoindentation constant stiffness measurement tests were carried out to study the hardness variations. An irradiation hardening effect was observed in proton- and Xe-irradiated specimens and more irradiation damage causes a larger hardness increment. The Nix-Gao model was used to extract the bulk-equivalent hardness of irradiation-damaged region and critical indentation depth. A different hardening level under H and Xe irradiation was obtained and the discrepancies of displacement damage rate and ion species may be the probable reasons. It was observed that the hardness of Xe-irradiated specimens saturate at about 2 displacement/atom (dpa), whereas in the case of proton irradiation, the saturation hardness may be more than 7 dpa. This discrepancy may be due to the different damage distributions.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.146-156
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• 2020

Two High Tensile Strength Steel (EH47) plates with thickness of 70 mm were butt-welded together by multi-pass Submerged Arc Welding (SAW), also the hardness and welding residual stress were investigated experimentally. Based on Thermal-Elastic-Plastic Finite Element (TEP FE) computation, the thermal cycles during entire welding process were obtained, and the HAZ hardness of multi-pass butt welded joint was computed by the hardenability algorithm with considering microstructure evolution. Good agreement of HAZ hardness between the measurement and computational result is observed. The evolution of each phase was drawn to clarify the influence mechanism of thermal cycle on HAZ hardness. Welding residual stress was predicted with considering mechanical response, which was dominantly determined by last cap welds through analyzing its formation process.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 춘계학술대회 논문집
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• pp.853-854
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• 2012

• 한국해양공학회지
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• 제13권3호통권33호
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• pp.92-99
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• 1999

High temperature and pressure materials in power plant are degraded by creep damage, if they are exposed to constant loads for long times, which occurs in load bearing structures of pressurized components operationg at elevated temperatures. Many conventional measurement techniques such as replica method, electric resistance method, and hardness test method for measuring creep damgage have been used. So far, the replica method is mainly used for the inspection of high temperature and pressure components. This technique is, however, restricted to applications at the surface of the testpieces and cannot be used to material inside. In this paper, ultrasonic evaluation for the detection of creep damage in the form of cavaties on grain boundaries or intergranular microcracks were carried out. And the absolute measuring method of quantitative ultrasonic velocity technique for Cr-Mo material degradation was analyzed. As a result of ultrasonic tests for crept for specimens, we founded that the sound velocity was decreased as increase of creep life fraction(${phi}c$) and also, confirmed that hardness was decreased as increase of creep life fraction(${phi}c$).

• 보존과학회지
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• 제25권4호
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• pp.431-438
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• 2009

풍납토성에서 출토된 한성백제시대 토기를 중심으로 다양한 경도측정 방법을 적용하여 토기의 굳기에 따른 적절한 측정방법 및 조건을 연구하였다. 연구를 위한 토기시료는 육안관찰과 모스경도계를 이용하여 굳기의 서열별로 선정하였으며, 표면 경도측정에는 초음파 및 에코팁 경도측정법을 적용하였고, 단면에는 로크웰 표충경도(로크웰 슈퍼피셜)와 마이크로비커스 경도측정법을 적용하였다. 그 결과, 표면 경도에서는 두 방법 모두 정밀한 측정에 많은 어려움이 있었으며 육안 및 모스경도에 따른 분류와 일치하는 경향성을 관찰할 수 없었다. 단면 경도측정 결과에서는, 로크웰 표충경도 측정법의 경우, 연질 토기의 측정에 보다 유리한 것으로 나타났으며, 1/16" 강구 압입자를 사용하여 15kgf의 시험하중으로 측정할 경우 가장 재현성이 좋은 측정값을 얻을 수 있음을 확인하였다. 반면, 마이크로비커스 측정법의 경우, 경질 토기의 측정에 보다 유리한 특성을 보였으며, 시험하중 100gf에서 가장 재현성과 정밀도가 높은 측정값을 얻을 수 있었다. 또한, 로크웰 표충경도법과 마이크로비커스 측정법은 모두 그 측정값이 고고학적 견해에 따른 육안분류와 거의 일치하는 경향성을 나타내었다. 이러한 결과는 향후 토기에 대한 고고학적 견해의 객관성을 뒷받침할 수 있는 매우 유용한 도구로써 기계적 경도측정값이 이용될 수 있음을 보여주는 것으로, 향후 이를 이용한 활발한 연구가 가능해 질 것으로 판단된다.