• Journal of Industrial Technology
• /
• v.21 no.A
• /
• pp.329-336
• /
• 2001

In this study, a series of fatigue tests are carried out in order to estimate quantitatively the characteristics of fatigue crack growth rate for high strength steels of SM570, POSTEN60, and POSTEN80 steel, that is, the influence on fatigue crack growth rate according to the welding line, the characteristics of fatigue crack growth according to the welding method and the kinds of steel, and the characteristics of fatigue crack growth for base metal, heat affected zone and weld metal. From the test results, in case that the notch if parallel to welding line, it knows that the retardations of fatigue crack growth rate in crack tip at early stage increase remarkably than in case that the notch is perpendicular to welding line due to compressive residual stress. And the characteristics of fatigue crack growth rate according to welding method are that the dispersion of fatigue crack growth rate in case of FCAW method is smaller than that of SAW method. Also, it knows that the fatigue crack growth rate converges in high stress intensity factor range.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.9
• /
• pp.2145-2152
• /
• 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.

• Computers and Concrete
• /
• v.17 no.1
• /
• pp.107-127
• /
• 2016

Concrete is a heterogeneous material containing many weaknesses such as micro-cracks, pores and grain boundaries. The crack growth mechanism and failure behavior of concrete structures depend on the plastic deformation created by these weaknesses. In this article the non-linear finite element method is used to analyze the effect of presence of micro pore near a crack tip on both of the characteristics of crack tip plastic zone (its shape and size) and crack growth properties (such as crack growth length and crack initiation angle) under pure shear loading. The FE Code Franc2D/L is used to carry out these objectives. The effects of the crack-pore configurations and the spacing between micro pore and pre-excising crack tip on the characteristics of crack tip plastic zone and crack growth properties is highlighted. Based on the obtained results, the relative distance between the crack tip and the micro pore affects in very significant way the shape and the size of the crack tip plastic zone. Furthermore, crack growth length and crack initiation angle are mostly influenced by size and shape of plastic zone ahead of crack tip. Also the effects of pore decrease on the crack tip by variation of pore situation from linear to perpendicular configuration. The critical position for a micro pore is in front of the crack tip.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.5
• /
• pp.797-804
• /
• 2001

To obtain representative fatigue crack growth characteristic curve in residual stress field, fatigue crack growth test was carried out at various stress ratio and fatigue crack growth characteristic curve was represented using crack closure concept. Obtained results are as follows;K(sub)op/K(sub)max was independent of K(sub)max when R was lower than 0.5 and crack closure phenomenon was not observed when R is higher than 0.5. therefore neglecting crack closure behaviour, actual fatigue crack growth rate can be underestimated. Thus, considering crack closure phenomenon, fatigue crack growth characteristics curve of A 106 Gr B Steel weldment can be effectively estimated.

• Journal of the Korean Ceramic Society
• /
• v.33 no.10
• /
• pp.1095-1100
• /
• 1996

• Journal of Ocean Engineering and Technology
• /
• v.1 no.1
• /
• pp.104-110
• /
• 1987

Fatigue tests by axial loading (R = 0.05) were carried out to investigate fatigue crack growth characteristics of small surface cracks in 2 1/4 Cr-1 Mo steel at room temperature by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present test are determined as a function of the stress intensity factor range about a semi-elliptical crack, so that the application of linear fracture mechanics to the surface fatigue crack growth and to the fatigue crack growth into depth, and all the data obtained from tests were discussed in comparison with the data of Type 304 stainless steel and two type of mild steel under the same test conditions. The obtained results are as follows: 1)When the cycle ratios are same, surface fatigue crack length and its depth are almost same and fall within a narrow scatter band in spite of different stress levels. 2)Relations of the surface fatigue crack growth rate (da/dN) and fatigue crack growth rate into depth (db/dN) to its stress intensity factor range ($\Delta K_{Ia}, \Delta K_{Ib}$) can be plotted as a straight line at log-log diagram without dependence of stress level and coincide with the data of part-through crack in various steels.

• Proceedings of the KWS Conference
• /
• 1999.05a
• /
• pp.237-240
• /
• 1999

In this study, residual stresses of the weldment were calculated by finite element analysis(FEA) and experiment. And, the crack closure behaviour and fatigue crack growth characteristics in field of residual stress of A106 Gr B steel pipe weldment were investigated under various stress ratio. Obtained results are as follows. I) $K_{op}$ was independent of $K_{max}$, and load ratio in fatigue crack growth. 2) In variation of load ratio, the scatter band of crack growth curve was reduced by half considering crack closure. and 3) Neglecting crack closure behaviour, actual fatigue crack growth rate can be underestimated' and Actual fatigue crack growth rate can be overestimated by $K_{res}$, in tensile residual stress field.

• Journal of Welding and Joining
• /
• v.16 no.4
• /
• pp.47-54
• /
• 1998

Various equipments in plants are welded with two different materials and it is required to investigate the effects of fatigue crack propagation on the neighborhood of a welded portion. The characteristics of fatigue crack growth in the base metal of carbon and stainless steel, in the carbon and stainless steel sides located in the neighborhood of welded portion (carbon/stainless steel), respectively and welded portion, are investigated. The results show that the crack growth in the welded portion (carbon/stainless steel) is an average value of the crack growths in the carbon and stainless steel respectively located in the neighborhood of the welded portion. It is found that the crack growth in the welded portion is not significantly different from those in the carbon and stainless steel sides. Hence it can be concluded that the structure welded with two different materials wold not impede the integrity based on the fatigue crack growth.

• Journal of Advanced Marine Engineering and Technology
• /
• v.10 no.1
• /
• pp.65-73
• /
• 1986

Surface fatigue crack propagation tests by plane bending fatigue were conducted on the welding specimens of an aluminium alloy, A5083-0, having an edge through thickness notch to study the fatigue crack growth characteristics. Moreover, the experiments were performed in order to clarify the fatigue crack initiation and growth. The properties of fatigue crack growth were quantitatively inspected in welded metal, heat-affected zone and base metal of the welding specimens. The main results obtained are summarized as follows: 1. It is found that the hardness distributions of A5083-0 aluminium alloy weldments are quite different with those of steel material weldments, so that the hardness distribution becomes lower in the following order: base metal, heat-affected zone and weld metal. 2. It is observed that the grain size of this specimen weldment appears to be almost equal to the base metal, when TIC welding method is adopted. 3. In a surface fatigue crack initiation and growth, the fatigue crack does not begin by opening-closing mechanism until hardening is saturated at the crack tip. 4. The fatigue crack growth characteristics of A5083-0 alluminium alloy weldments can be concluded.$${\frac{da}{dn}}=C({\Delta}K)^n=3.8{\times}10^{-9}{({\frac}{1}{2}{\Delta}S_t{\sqrt{{\pi}a}})}^{2.4}$$

• 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.