• 한국정밀공학회지
• /
• 제20권2호
• /
• pp.154-161
• /
• 2003

The effects of specimen geometry, and loading conditions on the J-integral fur CCT (center cracked tension) specimens are investigated by using FEM. It is found that the J-integral tends to decrease according to the parallel tensile loading to crack line. Furthermore, it is verified that the compressive parallel loading to crack line is likely to increase the J-integral. A stress ratio of length to width of the center CCT specimen is confirmed to affect the J-integral significantly.

• Corrosion Science and Technology
• /
• 제15권2호
• /
• pp.58-68
• /
• 2016

Many industries need the universal standard or technique to obtain the identical CCT regardless of specimen geometries. This study aimed to determine an appropriate applied torque to the cylindrical specimen defining the apparatus and the procedure to measure the temperature of initiating crevice corrosion in tubular shape products such as pipes, tubes and round rods etc; the test method also proved applicable to the plate type specimen. A series of experiments for CCT measurements with the plate type and cylindrical stainless steel specimens of various diameters with different microstructures (austenitic and duplex) and PRENs were conducted to determine the relationship among geometries on CCT. Thus, the apparatus that could measure the CCT of stainless steels with both plate and cylindrical geometries was newly designed. The use of the apparatus facilitated the same CCT value for both geometries only if the specimens were made of the same alloy. The applied torque can be calculated for various diameters of the cylindrical specimens using the following relation; Applied torque, $Nm=-0.0012D^2+0.019D+2.4463$ (D; the diameter of cylindrical specimen, mm). However, upwards of 35 mm diameter cylindrical specimens require 1.58Nm, which is the same torque for the plate type specimen; in addition, this test method cannot be used for cylindrical specimens of less than 15 mm diameter.

• 수산해양기술연구
• /
• 제22권2호
• /
• pp.40-45
• /
• 1986

In this paper, the I-resistance curve of low-carbon steel with 3 mm thickness was investigated for various crack ratios. The experiments were carried out for the center cracked tension (CCT) specimen with about 50 mm width on an instron machine. The plane stress fracture toughness obtained by the Simpson's formula was Ii. = 24.96 kgffmm. Simpson's formula which considers crack growth in obtaining J integral showed more conservative lin than Rice's and Sumpter's. For materials that may be approximated by the Ramberg and Osgood stress strain law, the relevant crack parameters like the J integral, load line displacement are approximately normalized. Crack driving forces in terms of the I integral are computed for low-carbon steel CCT specimen using the above estimation scheme. Comparison of the prediction with actual experimental measurements by Simpson's formula showed good agreement for several different sized specimen.

• 대한기계학회논문집A
• /
• 제21권3호
• /
• pp.528-533
• /
• 1997

In the analysis of fatigue crack propagation behavior, the crack length is one of the most important factors. In the test of crack propagation, compliance method is widely used to detect crack length. The measurement of surface crack length is not so easy with compliance method. In this study, the image processing technique was applied to measure the surface crack length. CCD(Charge-coupled device) camera was used to observe the crack image and the computer program to detect crack length from stored crack image was developed. CCT(Center Cracked Tension) specimen was used to compare the compliance method with the image processing technique. The crack length which detected by the image processing techniques was found to be well consistent with that from the optical measurement.

• 한국생산제조학회지
• /
• 제8권1호
• /
• pp.119-125
• /
• 1999

The distribution of fatigue crack growth rate is subjected to the measuring interval and calculated method of growth rate. In this paper, in order to establish the method of determining the distribution of fatigue crack growth rate, which ignores those influences, a series of fatigue crack growth experiments and measuring intervals of crack length calculated reasonable are presented. The main conclusions obtained are summarized as follows: 1) As a result of the ΔP constant test and ΔK constant test, it is thought that an approximate measuring interval of 0.3~0.7mm is reasonable, which allows for few errors and is little subjected to the calculated method of crack growth rate. 2) After generally comparing the error estimation by using the experimental data of CCT specimen with the error rating of the CT specimens, it is possible that the fatigue test has few errors within the measuring interval, ξ(Δa/W)=0.0067~0.017, regardless of the dimension of specimen geometry.

• 대한기계학회논문집
• /
• 제16권1호
• /
• pp.63-69
• /
• 1992

본 연구에서는 특히 앞서 지적한 표면균열의 진전거동에 관한 연구와도 관련 하여 측면홈을 가진 중앙관통균열(side-grooved center cracked tension) 시험편에 대 해 피로균열 진전실험을 수행하고, 평면변형률 조건의 만족여부 및 응력강도계수 평가 방법에 관하여 검토하여 비교적 새로운 결과를 얻었으므로 여기에 보고하고자 한다.

• 대한기계학회논문집A
• /
• 제29권8호
• /
• pp.1118-1122
• /
• 2005

The direct current potential drop (DCPD) method and the unloading compliance (UC) method with a crack opening displacement gauge were applied simultaneously to the Zr-2.5Nb curved compact tension (CCT) specimens to determine which of the two methods can precisely determine the crack initiation point and hence the crack length for evaluation of their fracture toughness. The DCPD method detected the crack initiation at a smaller load-line displacement compared to the UC method. As a verification, a direct observation of the fracture surfaces on the curved compact tension specimens was made on the CCT specimens experiencing either 0.8 to 1.0 mm load line displacement or various loads from $50\%\;to\;80\%$ of the maximum peak load, or $P_{max}$. The DCPD method is concluded to be more precise in determining the crack initiation and fracture toughness, J in Zr-2.5Nb CCT specimens than the UC method.

• 대한기계학회논문집A
• /
• 제37권11호
• /
• pp.1355-1360
• /
• 2013

균열이 발생된 고체추진제는 연소면적 증가에 따른 과연소 현상으로 인해 로켓의 손상 또는 파괴까지 일어날 수 있기 때문에 파괴인성을 평가하는 것은 매우 중요하다. 이 재료에 파괴인성에 미치는 온도 및 두께의 영향을 확인하기 위하여, 시험 온도는 $-60^{\circ}C$에서 $60^{\circ}C$ 범위, 시편의 두께는 4, 12.5, 24.5 mm 의 3 종류로 변화하여 Center cracked tension(CCT) 시편을 이용하여 파괴인성을 평가하였다. 본 시험 결과로부터 파괴인성은 온도 증가와 함께 감소하는 경향을 보이고 두께 변화에 대한 파괴인성은 $-60^{\circ}C$를 제외한 다른 온도조건에서 두께 12.5 mm 일 때 가장 크게 나타나고 있다. 고체추진제의 파괴인성은 $-60^{\circ}C$부근에서 유리전이거동에 의한 변화하는 것을 알 수 있다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집A
• /
• pp.93-98
• /
• 2000

Unpredictable failures can occur due to the DHC (delayed hydride cracking) or the degradation of fracture toughness by hydride embrittlement in CANDU pressure tube which can result from the absorption of hydrogen or deuterium in the high temperature coolant. To investigate the hydride embrittlement of CANDU Zr-2.5Nb pressure tube, the transverse tensile test and the fracture toughness test were performed from room temperature to $300^{\circ}C$ using three different specimens which have an AR (As Received), 100, and 200 ppm hydrogen. As the amount of absorbed hydrogen was increased, the transverse yield strength and the ultimate tensile strength were also increased. In addition, as the test temperature became higher they were decreased linearly. While, at room temperature, the hydrogenbsorbed specimens represented the embrittlement which resulted in sudden decreasing of fracture toughness, the fracture characteristics became ductile such as AR specimen at high temperatures. Through the observation of fracture surface using SEM, it was found that the stress state of mixed mode could be related to the fissure which was believed to decrease the global fracture toughness.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.78-83
• /
• 2003

The aim of this study is to investigate the effect of hydrogen embrittlement od Zr-2.5Nb CANDU pressure tube. The test were performed at three hydrogen contents for transverse tensile and CCT specimens while the test temperatures were changed (RT to 300$^{\circ}C$). The specimens were directly machined from the tube retaining original curvature using electric discharge machine. Both the transverse tensile and the fracture toughness tests showed the hydrogen embrittlement clearly at RT but this phenomenon was disappeared while the test temperature arrived over 250$^{\circ}C$. From the fracture toughness test, it was found that fracture toughness dJ/da was increased up to 200$^{\circ}C$ and then decreased.