• 동력기계공학회지
• /
• 제5권2호
• /
• pp.50-56
• /
• 2001

In this study, the effect of specimen thickness and stress ratio on fatigue crack growth in S45C steel was investigated. Acoustic emission was monitored during the fatigue crack growth test. Both crack closure and AE technique were used in assessing fatigue crack growth behavior. Constant amplitude loading tests were performed on CT type specimen with three different thicknesses and stress ratios. Crack closure was investigated to explain the influence of specimen thickness and stress ratio on the fatigue crack growth in the second growth region. The crack closure effect was decreased with specimen thickness and stress ratio.

• Journal of Mechanical Science and Technology
• /
• 제14권10호
• /
• pp.1041-1050
• /
• 2000

In this paper the effect of specimen thickness on fatigue crack growth with the spatial distribution of material properties is presented. Basically, the material resistance to fatigue crack growth is treated as a spatial stochastic process, which varies randomly on the crack surface. The theoretical autocorrelation functions of fatigue crack growth resistance with specimen thickness are discussed for several correlation lengths. Constant ${\Delta}K$ fatigue crack growth tests were also performed on CT type specimens with three different thicknesses of BS 4360 steel. Applying the proposed stochastic model and statistical analysis procedure, the experimental data were analyzed for different specimen thicknesses for determining the autocorrelation functions and probability distributions of the fatigue crack growth resistance.

• 한국안전학회지
• /
• 제9권3호
• /
• pp.22-27
• /
• 1994

For the $\beta$=1 specimen with constant thickness, Crack growth rate is smoothly increasing in the a-N curve. On the other hand for $\beta$=2 specimen with various thickness, the inflection point is observed in crack growth rate near the thickness interface. da/dN before the inflection point is increased, and da/dN after the point is decreased, compared to the $\beta$=1 specimen. da/dN near the thickness interface is approached zero. The descending point was observed earlier as $\beta$ increased. Considering the relation between da/dN and λ, the crack propagation rates for the case of $\beta$ =1 incrased almost linearly, however, the crack propagation rates for $\beta$=2,3 decreased more rapidly near the thickness interface. Additionally, the decreased point in da/dN for $\beta$=3 is farther from the thickness interface than the case for $\beta$ =2.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2001년도 추계학술대회 논문집
• /
• pp.232-237
• /
• 2001

The evaluation of specimen thickness effect of fatigue crack growth life by the simulation of probabilistic fatigue crack growth is presented. In this paper, the material resistance to fatigue crack growth is treated as a spatial stochastic process, which varies randomly on the crack surface. Using the previous experimental data, the non-Gaussian(eventually Weibull, in this report) random fields simulation method is applied. This method is useful to estimate the probability distribution of fatigue crack growth life and the variability due to specimen thickness by simulating material resistance to fatigue crack growth along a crack path.

• 한국해양공학회지
• /
• 제5권1호
• /
• pp.88-96
• /
• 1991

Fatigue life and retardtion behavior after through-thickness were examined experimentally by using a CT specimen and surface-cracked specimen. The material used was 3% Ni-Cr-Mo steel. The fatigue crack shape before through-thickness is almost semicircular, and the measured aspect ratio is larger than the value obtained by calculation using the K value proposed by Newman-Raju. It is found that the crack growth behavior on the back side after through-ghickness is unique and can be divided into three stages a, b and c. A retardation parameter has been used successfully to predict the growth of cracks in specimen, and in this time, retardation factor is 4.3. By using the crack propagation rule considering on retardation state and the K value proposed by the authors, the remarkable crack growth behavior and the change in crack shape can be evaluated quantitatively.

• 한국해양공학회지
• /
• 제10권4호
• /
• pp.51-57
• /
• 1996

A standard method for the evalution of the fracture toughness of the high polymer materials has not been fully developed in comparison with that for metallic materials, and has not yet established. In this paper, fracture toughness tests using polycarbonate specimens were carried out. The fracture thughness tests using polycabonate specimens were carried out. The fracture toughness of commercial polycarbonate were dependent on the specimen thickness. The specimen thickness is necessary above 8mm to obtain the valid $K_{IC}$. A cumulative counts were slightly dependent on specimen thickness.

• 한국해양공학회지
• /
• 제13권2호통권32호
• /
• pp.58-65
• /
• 1999

The effect of specimen thickness on fatigue crack growth rate was studied. The objective of the present study is to investigate the effect of specimen thickness on the fatigue crack growth behavior at various stress intensity factor ranges and also the variation of material restance to fatigue crack growth. The fatigue crack growth resistance was treated as a spatial stochastic process, which varies randomly on the crack path, Compact tension specimens with a LT orientation for structural steel were used. All testing was done at a constant stress intensity level. The experimental data were analyzed for the size effect to determine the Weibull distributions of the material resistance.

• Journal of the Korean Wood Science and Technology
• /
• 제9권3호
• /
• pp.24-30
• /
• 1981

This experiment was carried out to determine the drying time from green to oven dry and estimate the moisture content of wood, such as red lauan (Shorea Spp.), Douglas fir (Pseudotsuga menziesii), Birch (Betula platyphylla), and oak (Quercus aliena), at various thickness, paralleled to fiber, of specimen for M.C. by oven dry method (100-105$^{\circ}C$). The results obtained are summarized as follows: 1. The drying time from green to oven dry decreases as the thickness of specimen for M.C. becomes to be thined, and that time at 10mm thickness are 14 hrs, for birch wood and 24 hrs, for oak wood. 2. The relative formulae between thickness (X) of specimen for M.C. and drying lime (Y) from 12% to oven dry are showed in Fig. 3. 3. The M.C. based on the weight of specimen for M.C. at t% can be obtained from the formula (2), and the drying time to 1% are shorter than that time to oven dry by approximately three times.

• 한국공작기계학회논문집
• /
• 제15권3호
• /
• pp.120-126
• /
• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range$({\Delta}K)$ region and faster in high ${\Delta}K$ region than that of the base metal specimens.

• 한국산학기술학회논문지
• /
• 제15권2호
• /
• pp.646-652
• /
• 2014

본 논문의 목적은 AZ31 마그네슘합금의 균열성장거동의 경향을 묘사할 수 있는 실험적 피로균열전파모델을 시편두께 조건에서 평가하여 적합한 모델을 제시하는 것이다. 평가에 사용된 실험적 모델은 Paris-Erdogan 모델, Walker 모델, Forman 모델, 수정된 Forman 모델이며, 각 모델의 파라미터를 통계적으로 추정하기 위하여 최우추정법을 사용하였다. 두께조건이 피로균열전파거동 예측에 미치는 영향을 고려하면서 적합한 모델을 평가하기 위해 시편두께의 3가지 조건을 변화시키면서 피로균열전파실험을 수행하여 통계적 균열성장 데이터를 획득하였다. 시편두께 조건에 따라 마그네슘합금의 균열성장거동의 경향을 잘 묘사하는 모델은 Paris-Erdogan 모델과 Walker 모델이며, 모델의 파라미터 중 피로균열성장속도지수는 시편두께가 4.75mm와 6.60mm 조건에서 재료상수가 될 수 있음을 밝혀내었다. 그러나 시편두께가 두꺼운 경우에는 양상에 차이를 보이므로 모델 선정 시 신중한 판단이 요구된다.