• Journal of Mechanical Science and Technology
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• 제14권3호
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• pp.314-319
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• 2000

Back-face strain compliance (BFS compliance) for the four-point bend specimen has been calibrated for various crack length ratios. Finite element technique was employed to simulate four-point loading and calculate back-face strain of the bend specimen. The numerically determined strain variation along the back face indicates that the sensitivity to gage placement increases with crack length and back-face strain at the gage length less than O.2W, where W is the width of the bend specimen, can be measured within 5% deviation of the maximum BFS. Non-dimensional back-face strain compliance, -E'BCW, was calibrated with FE analysis and experiment. The experimentally determined compliance indicates good agreement with the numerical compliance and can be expressed as a function of crack length ratio.

• 한국산학기술학회논문지
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• 제17권12호
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• pp.686-691
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• 2016

용접강구조물에서는 용접비드와 같은 응력집중부가 많이 존재한다. 또한 용접부에서는 용접결함이 발생할 가능성이 많다. 반복적인 피로하중이 응력집중부에 작용하면 응력집중부에서 피로균열이 발생하고, 발생된 균열의 전파에 의해 피로파괴사고를 일으킨다. 따라서 피로파괴사고를 미연에 방지하기 위하여 균열발생수명과 균열전파수명과 같은 피로수명의 파악이 필요하다. 본 연구에서는 피로균열전파특성 연구에 사용되는 컴플라이언스를 도출하였다. 이 컴플라이언스는 피로균열의 자동화 측정에 활용할 수 있다. 본 연구에서는 CT시험편에 대하여 in-house FEM program을 사용하여 컴플라이언스를 계산하였다. 이 계산결과는 저자의 앞선 연구에서 본 프로그램을 사용하여 계산한 J integral의 계산결과와 대비하여 a/W와의 관계를 제시하였다. 그리고 또한 CT시험편 Back Face의 중앙부로부터 위아래 방향의 스트레인 분포에 계산을 실시하였다. 이 분포에서는 중심으로부터 위아래로 갈수록 스트레인이 감소하는 경향을 나타내었다. 이상의 계산과정으로부터 균열진전시험의 자동수행을 위한 컴플라이언스를 얻을 수 있었다. 이것으로부터 CT 시험편의 피로균열진전시험의 자동화에 활용이 가능하게 되었다.

• 대한기계학회논문집
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• 제17권9호
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• pp.2145-2152
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• 1993

The objective of this paper is to examine the detection limit, growth characteristics and notch curvature radius in short crack problem. Measurement techniques such as ultrasonic method and back-face strain compliance method were adopted. The fatigue crack growth rate of the short crack is slower than that of a long crack for a notched specimen. The characteristic of crack growth and crack closure is same as the case of a delay of crack growth caused by constant amplitude load for an ideal crack or single peak overload for a fatigue crack. The short crack is detected effectively by ultrasonic method. A short surface crack occurs in the middle of specimen thickness and is transient to a through crack depth is larger than the notch curvature radius.

• 한국산업융합학회 논문집
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• 제10권1호
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• pp.39-46
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• 2007

The objective of this paper is to examine the detection limit, growth characteristics and notch curvature radius in short crack problem. Measurement techniques such as ultrasonic method and back-face strain compliance method were adapted. The fatigue crack growth rate of the short crack is slower than that of a long crack for a notched specimen. The short crack is detected effectively by ultrasonic method. A short surface crack occurs in the middle of specimen thickness and is transient to a through crack when maximum crack depth is larger than the notch curvature radius.

• 한국정밀공학회지
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• 제9권1호
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• pp.106-117
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• 1992

In this study, the propagation behaviour and the closure phenomena of physically small surface cracks were investigated by the techinque of the Kikukawa-unloading elastic compliance method using a back face strain gage. The surface cracks initiated and propagated from notched specimens under constant amplitude bending load. The crack shape (aspect ratio) with approximately semi-circular at the early stage was changed to semi-elliptical as the cracks grew larger. The crack depth (a) could be expressed uniquenly by the crack length (c). The dependence of the crack propagation rate on the stress ratio R was strongly related in the lower ${\Delta}K$ range. The deceleration of the surface crack propagation rate was prominent in lower R during the crack length was small. When the propagation rate was rearranged with the effective stress intensity factor range ${\Delta}$K_{eff} the dependence of the crack propagation rate on the stress ratio R was found to be diminshed. These were caused by the crack closure phenomena that was most prominent at the lower propagation rate. The mechanism of crack closure phenomena was dominated by the plasticity-induced mechanism.