• Journal of Welding and Joining
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• 제7권3호
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• pp.28-35
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• 1989

It was reported that the toughness for welded region was influenced by various factors such as the gradient for prior austenite grain size, the variation of microhardness and the characteristic microstructure depending on distance from the fusion boundary. Therefore, in order to evaluate the fracture strength of the weldment in which the microstructures change continuously, it is important to assess the peculiar strength of each microstructure in welded region. It was known that the small punch(SP) test technique which was originally developed to study the irradiation damage effect for the structures of nuclear power plant was also useful to investigate the strength evaluating of nonhomogeneous materials. In this paper, by means of a small punch test technique the possibility of evaluating strength of parent and welded region in SS41 and SM53B steels was investigated. The obtained results are summerized as follows: 1) The small punch test which showed markedly the ductile-brittle transition behavior in this experiment may be applied to evaluation for the fracture strength of welded region. 2) It was shown that the ductile-brittle regime lied in Region III(plastic membrane stretching region) of the flow characteristics observed in SP test. 3) The SP test technique which shows a more precipitous energy change transition behavior than the other test technique is able to estimate the more precise transition temperature. 4) It could be seen that in comparision with the structure of parent the structure of weld HAZ in SS41 steel was improved while it in SM53B steel was deteriorated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.111-116
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• 2001

Small punch-creep(SP-Creep) test technique has been applied for evaluating the creep characteristics for high temperature materials. However, in order to evaluate the damage and predict the remaining life, it is necessary to establish a quantitative correlation between SP-Creep and uniaxial-creep test results. This paper presents analytical and experimental results of useful correlation between SP-Creep and uniaxial-creep properties for 9Cr1MoVNb steel at $600{\sim}650^{\circ}C$ in terms of stress(load) and activation energy during creep deformation. Especially, the activation energy obtained from SP-Creep test is linearly related to that from uniaxial-creep test at $650^{\circ}C$ as follows: $Q_{sp-p}{\fallingdotseq}1.37\;Q_{TEN},\;Q_{sp-{\sigma}}{\fallingdotseq}1.53\;Q_{TEN}$.

• 한국가스학회:학술대회논문집
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• 한국가스학회 1997년도 추계학술발표회 논문집
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• pp.78-85
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• 1997

Indentation and small punch tests are very powerful methods to monitor the materials reliability since they are very simple, easy and almost non-destructive. First, recently-developed continuous indentation test can provide the more material properties such as hardness, elastic modulus, yield strength, work-hardening exponent, etc., than the conventional hardness test. In our study, the true stress-strain curve was derived from the indentation load-depth curve for spherical indentation. In detail, the strain was able to be obtained from plastic depth/contact radius ratio, and the flow stress was from mean contact pressure through the analysis of elastic-plastic indentation stress field. Secondly, the small punch test was studied to evaluate the fracture toughness and defomation properties such as elastic modulus and yield strength. Like the indentation test, this test can be applied without severe damage of the target structure.

• Journal of Welding and Joining
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• 제12권4호
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• pp.63-75
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• 1994

The conventional SCC(stress corrosion cracking) test methods have much difficulty in evaluating the SCC behaviors of the localized zone like HAZ, bond line and weld metal because of the specimen size. Accordingly, the purpose of this paper is to develop the new SCC test method of the welded zone by evaluating the SCC susceptibility on parent metal and various microstructures of the welded zone by SP(small punch) test method using miniaturized small specimen and SSRT(slow strain rate test) method(SP-SSRT). Besides, this study is to verify the efficiency of the SP-SSRT results through AE(acoustic emission) test which is a useful technique to monitor the microfracture processes of the material. From the results of SCC susceptibility, SEM observation and AE test, it can be concluded that the SP-SSRT test using miniaturized small specimen(10mm*10mm*0.5mm) will be a good test method to evaluate the SCC susceptibility on the local zone such as the welded zone.

• 에너지공학
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• 제18권1호
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• pp.56-62
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• 2009

본 연구에서는 X65강의 용접부에 전기화학적 방법으로 수소를 장입한 이후에, 소형펀치시험편을 사용하여 기계적 강도를 평가하고 파면을 분석하였다. 모재부의 경우와는 다르게 용접부에서는 수소장입정도에 따라 강도저하가 민감하게 나타나는 거동을 보였다. 수소장입시 전류밀도, 온도, 장입시간의 변화에 따라 강도 및 연신율 등의 기계적 성질이 민감하게 변화하였다. 특히, 전류밀도가 높고 장입시간이 길어짐에 따라서 강도의 저하가 크게 나타났으나, 상대적으로 전해질 온도의 영향은 비교적 작게 나타났다. 또한 주사전자현미경을 통해 관찰한 시험편의 파면에서 수소침투된 표면근처의 재료에서 취성파면이 발견되었으며, 이는 강도의 저하 거동과 일치되는 경향이다. 수소취화 거동 평가 연구를 위해 본 연구에서 채택한 시험시스템은 재현성이 높게 나타나고 있으며, 이 방법을 이용한 재료의 강도평가 결과 매우 높은 신뢰성을 보이고 있다. 따라서 소형펀치시험과 전기분극법을 이용함으로써 X65강 용접부의 수소취화에 의한 강도변화를 민감하게 평가할 수 있었다. 산출된 데이터의 통계적인 처리를 통해 강도변화값을 예측할 수 있었음도 보였다.

• 대한기계학회논문집A
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• 제26권1호
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• pp.171-178
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• 2002

An effect is made in this study to deepen understanding of small punch(SP) creep testing which has been a round for about 10 years as a substitute for the conventional uniaxial creep testing. Even though considerable numbers of SP creep test program have been performed, most of the tests were aimed at measuring creep rupture lives only. Very flew studies showed interest on the meaning of what we were really measuring during the SP creep tests. In this paper meanings of the parameters measured during the SP creep testing, such as punch load and punch displacement rate are investigated using finite element analysis. It was shown that the measured parameters must represent the stress and strain rates of the material at the annular region located at about 0.65 mm from the center of the SP specimen. The material in this location would go through constant maximum stress and strain rate during the testing. Experimental verification is also discussed.

• 대한금속재료학회지
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• 제48권11호
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• pp.965-973
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• 2010

The small punch creep (SPC) test has recently received much attention as a new alternative to the conventional uniaxial creep test because it needs only a miniature-sized specimen directly detached from an operating system or component without any serious sampling damages. However, it is difficult to obtain the equivalent uniaxial creep data directly from the SPC data. As a specimen is deformed by a punch in the SPC test, the test result is sensitive to the friction between them. Finite element analyses with various friction coefficients was performed and showed a tendency of increased SPC life with an increased friction coefficient. The necking position predicted by the SPC simulation with a proper friction coefficient showed good agreement with that observed from the real SPC test. Finally, a noble method to convert the SPC load and displacement rate into the equivalent uniaxial creep stress and strain rate, respectively, was established in this study.

• 한국초전도ㆍ저온공학회논문지
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• 제25권4호
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• pp.70-74
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• 2023

The Small Punch Test (SPT) was developed to evaluate the softening and embrittlement of materials such as power plants and nuclear fusion reactors by taking samples in the field. Specimens used in the SPT are very thin and small disk-shaped compared to specimens for general tensile test, and thus have economic advantages in terms of miniaturization and repeatability of the test. The cryogenic SPT can also be miniaturized and has a significantly lower heat capacity than conventional universal test machines. This leads to reduced cooling and warm-up times. In this study, the cryogenic SPT was developed by modifying the existing room temperature SPT to be cooled by liquid nitrogen using a super bellows and a thermal insulation structure. Since the cryogenic SPT was first developed, basic experiments were conducted to verify the effectiveness of it. For the validation, aluminum alloy 6061- T6 specimens were tested for mechanical properties at room and cryogenic temperature. The results of the corrected tensile properties from the SPT experiment results were compared with known room temperature and cryogenic properties. Based on the correction results, the effectiveness of the cryogenic SPT test was confirmed, and the surface fracture characteristics of the material were analyzed using a 3d image scanner. In the future, we plan to conduct property evaluation according to the development of various alloy materials.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.31-36
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• 2003

In this study a relationship between SP curves and tensile properties was investigated by FE analysis on SP test with various assumed tensile properties. For the accuracy of FE analysis, SP test and tensile test were performed and those results were compared with FE analysis results. The yield load(Py) defined from the intersection point of two lines tangent to the elastic bending region and plastic bending region. And it was related specifically with yield stress(${\sigma}_0$) in FE analysis result curves. The slopes of FE analysis result curves normalized by yield stress(${\sigma}_0$) reflected the change of tensile properties regardless of yield stress(${\sigma}_0$) variation. Empirical relations were derived from these results. Tensile properties from these relations showed good agreement in FE analysis curve and tested curve.

• 대한기계학회논문집A
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• 제25권12호
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• pp.1995-2001
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• 2001

In this study, a small punch creep(SP-Creep) test using miniaturized specimen(10${\times}$10${\times}$0.5mm) is described to develop the new creep test method for high temperature structural materials. The SP-Creep test is applied to 2.25Cr-lMo(STBA24) steel which is widely used as boiler tube material. The test temperatures applied for the creep deformation of miniaturized specimens are between 550∼600$^{\circ}C$. The SP-Creep curves depend definitely on applied load and creep temperature, and show the three stages of creep behavior like in conventional uniaxial tensile creep curves. The load exponent of miniaturized specimen decreases with increasing test temperature, and its behavior is similar to stress exponent behavior of uniaxial creep test. The creep activation energy obtained from the relationship between SP-Creep rate and test temperature decreases as the applied load increases. A predicting equation or SP-Creep rate for 2.25Cr-lMo steel is suggested. and a good agreement between experimental and calculated data has been found.