• Magazine of the Korea Concrete Institute
• /
• v.1 no.2
• /
• pp.101-112
• /
• 1989

콘크리트에 선형파괴역할의 적용가능성을 연구한 많은 논문이 발표되었다. 본 논문에서는 CLWL-DCB식편을 이용한 콘크리트의 개구형파괴를 연구하였다. 표면구열길이는 리프리카를 사용하여 직접적인 방법으로 측정하였고, 이 결과은 실험에서 얻은 측정가중과 구열개구변위의 관계곡선을 이용하여 분석하였다. 감계응력강도계수와 감계구열선단위는 Two Parameter 모델을 사용하여 유효구열선단에서 구하였다. LEFM 구열단면과 실험으로 구한 구열단면으로부터 폐쇄압력을 얻기 위하여 중첩법을 적용하여 5종의 균열모델을 평가하였다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.5 no.2
• /
• pp.121-131
• /
• 1985

The characteristic of fatigue crack growth in the homogeneous or the soft welded connections used SWS-53 steel and HT-80 steel as base metals is examined by fractographic analysis. As a result of this analysis, the fact that the characteristic of fatigue crack growth which is observed and measured at the surface has wide application to engineering practice is verified. Also, the fact that the welded parts of HT-80 steel have much danger of brittle fracture is prooved. Considering that the striations are observed at the welded parts of SWS-58 steel and the spacing of striations has higher numerical value than da/dN, we can prove that inner fatigue crack growth may develop in zig-zag directions.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.3
• /
• pp.636-645
• /
• 1990

Analytically induced wear mechanism of elastic body under Hertzian contact is applied in acutual wear test of ceramics. There are two types of wear in ceramics, a large scale wear and a small scale wear. The large scale wear is commensurable with Hertzian contact area and the small scale wear with real contact area. Nondimensional parameter, S$_{c}$, is introduced and fully examined to estimate or predict wear rate of ceramics. Ceramic wear for S$_{c}$.leq.0.8 is in small scale wear and for S$_{c}$;geq.1.6 in large scale wear. wear.

• Journal of the korean Society of Automotive Engineers
• /
• v.14 no.2
• /
• pp.65-75
• /
• 1992

An analytical scheme for predicting the crack aspect pattern of materials which contain twin surface cracks was developed. Fatigue tests were performed on twin surface cracked PMMA plate specimens to obtain the interaction factor accounting for the interference effect of adjacent cracks. Here, the interaction factor is defined as the ratio of the stress intensity factor for twin surface cracks to that for a single surface crack. From the analysis of the fatigue test result, the interaction factor was presented as the ninth-order polynomial expression having a function of dimensionless crack spacing ratio. Then the polynomial expression was incorporated into the prediction program of the crack aspect pattern for twin surface cracked materials. And, the interaction effect and the coalescence condition of adjacent cracks were simplified in the newly developed prediction scheme of the crack aspect pattern. The predicted crack growth pattern using the prediction scheme was compared with test data from PMMA specimen. The predicted pattern agreed well with the test data.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.2
• /
• pp.492-501
• /
• 1990

It was known that the fracture incidences of offshore structure were mostly originated from the surface defects. Especially, in the case of the welded structures, since the welded region has some defects and incomplete beads which are apt to behave like the surface cracks, it has been necessary to evaluate the environmental effects on crack growth at HAZ for the design crack growth behaviour at multi-pall HAZ for SWS41 steel under free corrosion and cathodic protection(-0.9V vs Ag/Agcl) conditions. The results are summarized as follows ; (1) Crack growth rate of the as weld in air was faster than that of the parent and PWHT specimens over all .DELTA.K rang. (2) In free corrosion test, surface crack growth rate of the as welded was decreased in comparison with that of the parents. (3) In fatigue test under cathodic protection, cathodic electric potential(-0.9V vs Ag/Agcl) for the SWS41 steel parent was effective, while for the as welded ineffective. (4) There was a tendency that the exponent(m) of the Paris' equation was decreased in order of microhardness magnititude in air and under cathodic protection conditions and vise versa in free corrosion. (5) Fracture surface has dimples and ductile striations in air test, but transgranular cracks and brittle striations under cathodic protection test.

• Journal of the KSME
• /
• v.17 no.1
• /
• pp.32-39
• /
• 1977

파괴역할적으로 피로문제를 다룰 때는 언제나 crack의 존재를 전재로 한다. 재료가 피로하중을 받아 파괴에이르는 과정의 설명은, 일차적으로는 피로에의한 crack의 발생이고, 다음단계로는 발 생한 crack들의 상호연결 또는 성장을 거쳐 최종적으로 파단에 이른다는 순서로 이루어진다고 보 기 때문이다. 또한, crack의 존재를 전제로 하더래도 crack청단의 응력장이 탄성론적으로 해석될 수 있어야함도 절대적인 전제가 되고 있다. 모든 피로제엔 각경형태의 crack발생, 성장이 관찰되 고 있는데, 이들 모든 crack들이다. 파괴역학적으로 다루어 질 수 있는 것은 물론 아니고, 아직도 K해석이 도어있지 않은 crack들이 많이 남아 있는 것이다. 예컨대 회전굽힘 피로시험편에서 관찰 되는 각종 형태의 표면피로 crack들은 응력해석의 곤란 때문에 아직은 이들에 적용시킬 K의 표 식이 없는 실정이라 하겠다. 이들 crack에 대해서는 K해석 뿐만 아니고, 피로역학적인 다른 Factor 즉 $r_{p}$라든가 .phi.같은 것들도 이해색상태에 있어 이 분야에의 연구가 많이 기대되고 있는 실정이다. Crack에 대한 연구는, 그것이 파괴의 전제가 되기 때문에 큰 의의를 갖는다고 보 겠는데 표면 Crack이 연결 또는 성장해서 시편의 전주를 완전히 일주 했어도 그것만으로는 바로 재료의 파괴에 직결이 되지 않는 것도 이 시험편의 특색이라 하겠다. 물론 회전굽힘 피로시험편 외에도 K해석이 되어있지 않은 경우는 아직도 많으며, K가 해석되어 있는 경우에 대해서도 정확 한 경계조건 등을 잘 검토해 가면서 응용함이 옳을 것이다. 화전굽힘피로의 경우나 그밖의 예에 서와같이 정확한 K해석이 이루어져 있지 않드래도 연구자에 따라 "Effective Streess Intensity Factor"라는 것을 쓰는 예도 왕왕있는데, 이에는 상당한 검토와 타당성제가 요구되고 있으며, 그 사용가능성여부에 대해서는 논란이 많이 따르는데 상례이기도 하다. 몇가지의 피로구열해석예를 들어보기로 한다. 들어보기로 한다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.1
• /
• pp.87-95
• /
• 1990

Rotating bending fatigue tests of an authentic steel 304 were performed at various temperatures such as room temperature, $538^{\circ}$ and $593^{\circ}C$. The plastic replica method was also applied in order to estimate the fatigue life on the basis of serial observation of small fatigue crack initiation and growth on the pit specimen surface. The fatigue crack growth behavior of 304 stainless steel was investigated within the frame work of elastic-plastic fracture mechanics within a narrow scatterband in spite of different stress levels at elevated temperature as at room temperature. The growth law of small surface crack is determined uniquely by the term. $\DELTA\sigma^{n}a$ where $\DELTA\sigma$ is the stress amplitude, a is the crack length, and n is a constant. It is found that the small crack growth behavior is basically equivalent to the S-$N_{f}$ relationship, where S and $N_{f}$ are stress and number of cycles to failure, and the fatigue life prediction is in good agreement with the experimental results.

• Journal of Conservation Science
• /
• v.18 s.18
• /
• pp.19-32
• /
• 2006

The stone pagoda of the Bunhwangsa temple made by piling small brick-shaped stones. The major rock forming stone bricks are andesites with variable genesis. Rock properties of the pagoda roof stone suffer partly including multiple peel-offs, exfoliation, decomposition like onion peels, cracks forming round lines and falling off stone pieces. The stylobates and tabernacles in all the four directions the pagoda are mostly composed of granitic rocks. Those rock properties are heavily contaminated by lichens and mosses with the often marks of inorganic contamination by secondary hydrates that are dark black or yellowish brown. Within the four tabernacles and northern pagoda body situated to relatively high humidity. There are even light gray precipitate looking like stalactites between the northern and western rocks of the body Their major minerals are calcite, gypsum and clays. The stone lion standing in the southeast and northeast side are alkali granite, while that in the southwest and northwest lithic tuff. Total rock properties of the pagoda are 9,708 pieces, among the all properties, fractured blocks are 11.0%, fall out blocks are 6.7% and covered blocks by precipitates are 7.0%, respectively. The pagoda has highly deteriorated the functions of the rock properties due to physical, chemical and biological weathering, therefore, we suggest that this pagoda has need to do long term monitoring and synthetic conservation researches.