• 한국해양공학회지
• /
• 제14권2호
• /
• pp.99-105
• /
• 2000

This paper describes the effect of specimen size on fatigue crack growth rate for the offshore structural high-tensile-strength steel BS4360 and machine structural steel SM45C. The purpose of the present study is to investigate the effect of stress ratio aspect ratio specimen width and specimen thickness of the fatigue crack growth behavior. Compact tension specimens with a LT orientation for BS4360 and SM45C steels were used, All testing was done at constant stress intensity factor range controlled fatigue crack growth condition. The investigation demonstrates that the fatigue crack growth rate is increased with increasing stress ratio and specimen thickness and is decreased with increasing specimen width. The fatigue crack growth rate is unaffected by aspect ratio until a/W=0.50 but is increased by increasing spect ratio from a/W=0.55.

• 한국가스학회지
• /
• 제1권1호
• /
• pp.95-100
• /
• 1997

금속재료의 탄소성파괴인성치 측정을 위해서 ASTM E399 시험법에 따라 단순 인장 시험편을 사용하여 유한요소해석을 하였으며 여기에서 얻어진 하중-균열개구변위 곡선을 이용하여 균열개시점을 찾고 이 점에서의 파괴인성치 $J_{IC}$를 구하였다. 탄소성 파괴인성치 J 값은 J 적분법 및 M. K. Tseng등에 의해서 제안된 계산식을 이용하여 구하였다. 해석된 값의 검증을 위해서 고강도 저합금강인 AISI 4130 재료를 이용한 기존 실험값과 비교하였으며 그 결과는 잘 일치함을 알 수 있다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2003년도 춘계학술대회 논문집
• /
• pp.729-732
• /
• 2003

The K-R design curve is an engineering method of linear-elastic fracture analysis under plane-stress loading conditions. By the way, linear-elastic fracture mechanics (LEFM) is valid only as long as nonlinear material deformation is confined to a small region surrounding the crack tip. Like general steels, it is virtually impossible to characterize the fracture behavior with LEFM, in many materials. Critical values of J contour integral or crack tip opening displacement (CTOD) give nearly size independent measures of fracture toughness, even for relatively large amounts of crack tip plasticity. Furthermore, the crack tip opening displacement is the only parameter that can be directly measured in the fracture test. On the other. the crack tip opening angle (CTOA) test is similar to CTOD experimentally. Moreover, the test is easier to measure the fracture toughness than other method. The shape of the CTOA curve depends on material fracture behavior and, on the opening configuration of the cracked structure. CTOA parameter describes crack tip conditions in elastic-plastic materials, and it can be used as a fracture criterion effectively. In this paper, CTOA test is performed for steel JS-SS400 hot-rolled thin plates under plane-stress loading conditions. Special experimental apparatuses are used to prevent specimens from buckling and to measure crack tip opening angle for thin compact tension (CT) specimens.

• 동력기계공학회지
• /
• 제15권1호
• /
• pp.39-44
• /
• 2011

This study was to investigate the effects of stress ratio and anisotropy on Fatigue Crack Propagation(FCP) behavior of rolled magnesium alloy AZ31B. The experimental materials were a Mg-Al-Zn magnesium alloy. The FCP test was conducted on compact tension specimen by a servo-hydraulic fatigue testing machine in air at room temperature. Compact tension specimens were prepared from the extruded parallel and vertical rolling direction. The test condition was frequency of 10Hz and sinusoidal load stress ratios are 0.1 and 0.7. The FCP rates was automatically measured by a compliance method. In the case of the FCP of AZ31B, the FCP of both direction of LT and TL by anisotropy of specimens are almost same value. In lower stress ratio, the FCP of the LT, TL specimens are increased in lower ${\Delta}K$ region but higher ${\Delta}K$ regions are almost same value. Finally, the result of observed the surface crack, it expressed the quasi-cleavage fracture in lower ${\Delta}K$ region and straight mark on the aspect of the facet in high ${\Delta}K$ region.

• 한국안전학회지
• /
• 제13권4호
• /
• pp.79-86
• /
• 1998

The effect of specimen thickness on fatigue crack growth behavior has been carried out by compact tension specimens of thickness of 3mm, 10mm and 25mm for maraging steel and Al 7075-T6. The closure points were determined during the test by means of a clip-gage situated at the notch mouth. Specimen thickness have no apparent influence on the fatigue crack growth rate of maraging steel, but the crack growth rate of 25mm thickness specimen for Al 7075-T6 is faster than that of 3 and 10mm specimens. The difference of crack growth rates can be successfully explained by considering the different stress state of plane strain and plain stress due to the variation of specimen thickness. Also the crack opening ratio of 25mm specimen is greater than those of 3 and 10mm specimens. When a side groove is introduced in a 10mm specimen, the crack growth rate is approximately similar to that of 25mm specimen. The effective thickness expression of $B_e=B_o-(B_o-B_N)^2B_o$ is the most appropriate to evaluate the crack growth rate of side-grooved specimen. Fatigue crack growth rates can be well described by $\Delta K_{eff}$ of the crack closure points in regardless of all thickness and side-grooved specimens.

• 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.

• Journal of the Korean Wood Science and Technology
• /
• 제43권6호
• /
• pp.868-875
• /
• 2015

목구조물 접합부에 기존의 슬릿(slit)형 강판을 대체하기 위해서 FRP (Fiber Reinforced Plastic) 보강적층판을 제작하였다. 보강재, 접착제 종류에 따라 총 4가지 타입의 FRP 보강적층판을 제작하였으며, 접합부 적용 전 KSF 3021과 KSF 2160에 의거한 박리실험과 ASTM D5045-99에서 제안한 Compact Tension (CT)형 파괴인성 시험을 실시하였다. 접착성능 시험결과 GFRP textile, GFRP sheet, GFRP Textile-Sheet 타입의 FRP 보강적층판은 침지 및 내수침지박리 시험에서 모두 KS 기준인 박리율 5% 이하를 만족하였다. 그러나 Aramid 타입의 시험편은 침지박리율 4.8%로 기준을 만족하였으나 내수침지박리율 70%로 합격기준을 만족하지 못하였다. 파괴인성 시험결과 단판만을 교차적층 시킨 대조군시험편보다 목재 대비 보강재 체적비를 23%로 함으로서 FRP 보강적층판의 내력이 2~4배 증가하였다. 그중에서도 GFRP Textile-Sheet 타입의 시험편이 하중 평행방향의 유리섬유 배열로 인해 할렬파단을 억제하면서 대조군 대비 응력확대계수 비가 61% 증가되어 파괴를 가장 크게 억제하는 것으로 확인되었다. FRP 보강적층판과 비금속 dowels을 사용한 접합부의 인장형 전단내력은 금속접합에 비해 약 12% 낮은 내력이 측정되었다.

• 한국해양공학회지
• /
• 제8권2호
• /
• pp.38-46
• /
• 1994

The method of JSME S001-83 and ASTM E813-87 have been adapted for evaluation of the elastic-plastic fracture toughness J sub(IC) of SB41 steel. This SB41 steel have the characteristics of low-stength CT specimens. The test results obtained have been considered and compared on the basis of resulted data from two kinds of methods(JSME S001-83, ASTM E813-87) and two kinds of specimen configurations(smooth, side-grooved). On the basis of results from consideration and comparison, the difficulties for its application were presented in case when the standard ASTM E813-87 method was employed for the measurement of J sub(IC) in SB41 steel. A modified method was applied for measuring J sub(IC) in SB41 steel that it used the blunting line real-measured by experiment instead of the standard blunting line theoretically determined, and the result from that procedure was analyzed and the usefulness of that method was examined and considered.

• 열처리공학회지
• /
• 제14권4호
• /
• pp.212-219
• /
• 2001

The fatigue test was carried out to evaluate the fatigue characteristics of fire resistance steel for frame structure and heat affected zone (HAZ) by the one side Gas Metal Arc Welding (GMAW). In this paper, the fatigue crack growth behavior was investigated with the compact tension specimen of base metal and the HAZ according to chemical composition and rolling end temperature, respectively. And the acoustic emission signals obtained from the fatigue test were analyzed by the time-frequency analysis method as a nondestructive evaluation. Main results obtained are summarized as follows; The hardness was appeared softening phenomenon that weld metal and HAZ are lower than that of base metal. Fatigue life of welded specimen was longer than that of base metal. m was 3~4.5 in base metal and 3.8~5.8 in HAZ. The main frequency range of acoustic emission signal analyzed from time-frequency method is different with the range by noise and crack. Also, it could be classified that it was also generated by fracture mechanics of dimple, inclusion etc.

• 한국항해항만학회지
• /
• 제26권4호
• /
• pp.435-440
• /
• 2002

잔류응력이 판의 파괴 특성에 미치는 영향의 정량적 평가를 위하여, 균열이 존재하는 CT(Compact Tension) 시편에 가스 토오치 (gas torch)를 이용한 국부 가열을 실시하여 인위적인 잔류응력을 생성시키고, 열탄소성 유한요소해석을 통하여 생성된 잔류응력장을 평가하였으며, 잔류응력이 존재하는 시편과 잔류응력이 존재하지 않는 시편에 대한 파괴인성 실험을 실시하여 이들의 결과를 파괴저항 선도 상에서 비교, 분석함으로써 압축 잔류응력이 파괴 특성에 미치는 영향을 정량화하였다.