• Journal of Mechanical Science and Technology
• /
• v.14 no.10
• /
• 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.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.23 no.7 s.166
• /
• pp.1139-1146
• /
• 1999

Reliability analysis of structures based on fracture mechanics requires knowledge on statistical characteristics of the parameter C and m in the fatigue crack growth law, $da/dN=C({\Delta}K)^m$. The purpose of the present study is to investigate if it is possible to predict fatigue crack growth rate by only the fluctuation of the parameter C. In this study, Paris-Erdogan law is adopted, where the author treat the parameter C as random and m as constant. The fluctuation of crack growth rate is assumed only due to the parameter C. The growth resistance coefficient of material to fatigue crack growth (Z=1/C) was treated as a spatial stochastic process, which varies randomly on the crack path. The theoretical crack growth rates at various stress intensity factor range are discussed. Constant ${\Delta}K$ fatigue crack growth tests were performed on the structural steel, SM45C. The experimental data were analyzed to determine the autocorrelation function and Weibull distributions of the fatigue crack growth resistance. And also, the effect of the parameter m of Paris' law due to variation of fatigue crack growth resistance was discussed.

• Journal of Power System Engineering
• /
• v.15 no.6
• /
• pp.73-80
• /
• 2011

The experimental investigation focuses on an influence of artificial aging time in longitudinal butt welded Al 6013-T4 aluminum alloy on the fatigue crack growth resistance. The preferred welding processes for this alloy are frequently tungsten inert gas welding (TIG) process due to its comparatively easier applicability and better weldability than other gas metal arc welding. Fatigue crack growth tests were carried out on compact tension specimens (CT) in longitudinal butt TIG welded after T82 heat treatment was varied in three artificial aging times of 6 hours, 18 hours and 24 hours. Of the three artificial aging times, 24 hours of artificial aging time are offering better resistance against the growing fatigue cracks. The superior fatigue crack growth resistance preferred spatial variation of materials within each specimen in the Paris equation based on reliability theory and fatigue crack growth rate by crack length are found to be the reasons for superior fatigue resistance of 24 hours of artificial aging time was compared to other joints. The highest of crack propagation resistance occurs in artificial aging times of 24 hours due to the increase in grain size (fine grained microstructures).

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.6
• /
• pp.898-905
• /
• 1986

In order to obtain the microstructure improving fatigue crack propagation resistance of steels, fatigue crack propagation behavior of martensite-ferrite dual phase steels is investigated in terms of crack deflection and crack closure. The results obtained are as follows; (1) .DELTA.K$_{th}$ and fatigue crack propagation resistance in low .DELTA.K region increases with increasing hardness of second phase. But the difference of this crack propagation resistance decreases with increasing .DELTA.D. (2) In low .DELTA.K region, crack closure increases with increasing hardness of second phase, when the materials have all the sam volume fractionof second phase, or when yield strengths are similar in all materials. (3) These crack closure can be explained by fracture surface roughness due to crack deflection.n.

• Journal of Ocean Engineering and Technology
• /
• v.13 no.2 s.32
• /
• 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 Ocean Engineering and Technology
• /
• v.1 no.2
• /
• pp.93-100
• /
• 1987

Corrosion fatigue cracking of the austenitic stainless steel(bese metal & heat affected zone by TIG weld) was studied experimentally under the environments of various specific resistance and air. The characteristics of corrosion fatigue crack growth rate and the environmental constants of paris' rule were investigated for SUS 304 weldments in the various specific resistance. The influences of stress intensity factor range and corrosion on the crack growth rate were compared. The characteristics of corrosion fatigue cracking for the weldments were inspected from mechanical, electrochemical and microstructural point of view. Main results obtained are as follows: 1) As the specific resistance decreases, the environmental constant C of paris'rule increases(hence the corrosion fatigue crack growth rate is rapid), but the environmental constant m decreases, so the effect of corrosion to the crack growth rate is more susceptible than thet of stress intensity factor range. 2) As the stress intensity factor range decreases, the corrosion fatigue crack growth rate of heat affected zone is more susceptible than that of the base metal. 3) The corrosion fatigue crack growth rate of the heat affected zone is more rapid than that of the base metal, because of the phenomenon of softening and the less noble potential coused by wedlding heat cycle. 4) The corrosion fatigue cracking of SUS 304 weldment appears transgranular fracture.

• Journal of Welding and Joining
• /
• v.12 no.4
• /
• pp.117-126
• /
• 1994

APAL (Aramid Patched ALuminum alloy) was manufactured, which was a material that was consisting of a A12024-T3 aluminum alloy plate bonded to single-side of it with aramid/epoxy laminates. The aramid/epoxy laminates were bonded to it in condition of 1, 2 ply and fiber orientation of .+-.45, 0.deg./90.deg. Fatigue crack propagation tests were performed at stress ratio R-0.2, 0.5 with Al 2024-T3, APAL 45-1P, APAL 0/90-1P, APAL 45-2P, APAL 0/90-2P specimens to examine behavior of retardation in fatigue crack propagation. All the APAL specimens showed superior fatigue crack resistance. Number of cycle spended for crack to propagate from $a_{M}$=37 to $a_{M}$=65 mm in case of APAL 0/90-2P specimen was half that of Al 2024-T3 specimen. Fatigue crack propagation rate of APAL 0/90 specimens were retarded more compared to APAL 45 specimens and the amounts of retardation at R=0.5 were larger than that at R=0.2. It was found that the retardation in fatigue crack propagation was caused by intact fibers in the wake of crack.ack.

• Journal of Ocean Engineering and Technology
• /
• v.8 no.2
• /
• pp.47-55
• /
• 1994

The purpose of the present study is to investigate the effect of specimen thickness on statistical properties of crack growth resistance. In this study, the resistance S$\delta$$_h$(x) to fatigue crack growth was treated as a spatial stochastic process. which varies randomly on the crack surface. The theoretical autocorrelation functions of the resistance to fatigue crack growth considering specimen thickness are discussed for several correlation lengths. The main results obtained are : (1) The theoretical autocorrelation functions of S$\delta$$_h$(x) are almost independent of specimen of specimen thickness except for the origin. (2) The variance increases with decreasing specimen thickness.

• Journal of Ocean Engineering and Technology
• /
• v.9 no.1
• /
• pp.132-141
• /
• 1995

The purpose of the present study is to investigate the statistical characteristics of m and C in the fatigue crack propagation law, da/dN=C(.DELTA.K)/sup m/ and to studies on the randomness of fatigue crack propagation and retardation behavior. Fatigue tests were perfomed on 32 CT specimens of SPV50 steel under the same one condition. First, the value of m and C were determined for each specimen, and all the data were analyzed statistically. second, the material's resistance to fatigue crack propagation is modeled as a stchastic process, which varies randomly along the crack path. The statistical analysis of the material resistance is performed with the data obtained by constant load controlled tests. Finally, retardation behavior was examined experimentally by using a CT specimen, and a retardation parameters were analyzed statistically.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2001.10a
• /
• 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.