• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.4
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• pp.80-88
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• 1997

An experimental investigation of the fatigue through crack growth behavior under simple stepped variable loading condition has been performed using Al7075-T651. Experiments were carried out by using cantilever bending type specimens, with chevron notches on a small electro-magnetic test machine. Tensile overloads have a retarding effect on the fatigue crack growth rates, therefore tensile overloads were used for the beneficial effect on the fatigue life. While in most cases compressive overloads have only a vanishing effect on crack growth rates, some experiments with single edge crack tension specimens reveal a marked growth retardation. The stress ratios used in this investigations varies from R=0.32 to 0.81, from R=0.04 to 0.76, from R=-0.15 to 0.73, and from R=-0.33 to 0.68 and the peak load for each case was not varied. The crack growth and crack closure were measured by Kikukawa's compliance method with a strain gauge mounted on the backside of each specimens. The results obtained are as follows. When the stepped variable load was applied, the smaller the stress ration was, the larger the delayed retardation of the crack growth rate was. The fatigue crack growh rate data obtained for through cracks were plotted well against the effective stress intensity factor range from 4.0 to 20.0MP{a^{SQRT}m}. It was found that the effective stress intensity factor range ratio was related well to the opening stress intensity factor, the maximum stress intensity factor, and crack length.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1288-1296
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• 2000

In this study, fatigue crack behavior between arbitrarily located defects was investigated by experiment. Especially, stress interaction between micro hole defects and fatigue cracking, and fatigue crack initiation life following the variation of location of micro hole defects were considered. In addition, crack initiation position by micro hole stress interaction and the relationship between stress concentration factor and fatigue initiation life are studied in detail.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.4 no.4
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• pp.25-32
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• 1995

This study is to inspect the influence of the initial residual stress on fatigue crack growth behavior after the distribution of the initial residual stress is measured when the crack is growing from the compressive residual stress field. Also, the tensile residual stress field. Also, the influence of the variation of residual stress distribution on fatigue crack growth behavior at the crack tip is studied when the initial crack occurs on weld metal, bead interface and HAZ (Heat Affected Zone), respectively. For this purpose, CT-type specimen that crack parallel to the welding bead were manufactured by butt welding on the Al. Alloy 1100-O plate.

• Journal of Welding and Joining
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• v.5 no.1
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• pp.73-80
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• 1987

During PWHT, it is well known that residual stress in weld HAZ is one of the reasons for PWHT embitterment. In case of static loading, it was experimentally found that fracture toughness of weld HAZ was dependant upon PWHT conditions. However, the effects of PWHT on fatigue behavior are not clearly verified. Therefore, in this paper, the effects of heating rate PWHT conditions and residual stress simulated in weld HAZ of Cr-Mo steel on fatigue crack propagation behavior were evaluated by fatigue Testing and SEM observation. The obtained results are summarized as follows; 1. Applied stress($10 Kgf/mm^2$) in weld HAZ during PWHT tneded to decrease fatigue strength and to increase fatigue crack growth rate. 2. Applied stress and slow heating rate of 60.deg. C/hr during PWHT contributed to precipitin of impurity elements as well as carbide, which promoted the fatigue crack growth. 3. Fatigue crack growth rate decreased at the heating rate of 220.deg. C/hr in contrast with 600.deg. C/hr and 60.deg. C/hr.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.201-212
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• 2001

If defects are located far apart, fatigue cracks are independently initiated from them and gradually approach other cracks so that the fatigue life becomes influenced by the crack growth behavior of those interacting cracks. In this study, the effect of the stress interaction between defects on the fatigue crack propagation behavior is investigated experimentally and these results are verified by finite element method. In addition, fatigue crack propagation behaviors under micro hole interaction field are studied.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.127-131
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• 2000

The dynamic photoelasticity with the aid of Cranz-Shardin type high speed camera system is utilized to record the dynamically propagating behavior of an interface crack. This paper investigates determined the effects of the hole (existed on the path of the crack propagation) on the crack propagation behavior by comparing the experiment isochromatic fringes to the theoretical stress fields.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1349-1353
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• 2003

Previous researches for fiber reinforced composite material(FRCM) have been evaluated the fatigue delamination behavior using the traditional fracture mechanics parameters. Therefore. previous researches for FRCM have not generally been firmed yet. Because delamination growth behavior in FRCM should be consider relationship between delamination area, A$\sub$D/ and crack length, a instead of traditional fracture mechanics parameters. Especially, in case of delamination behavior for FRCM without crack should be considering equivalent crack, i.e., pseudo crack, a$\sub$p/, using the fracture behavior of FRCM with crack. The major purpose of this study was to evaluate the delamination for FRCM without crack. The details of the studies are as follow : 1) Relationship between crack growth rate, da/dN and stress intensity factor, ΔK in FRCM containing a saw-cut and circular hole with crack. 2) Propose of PSEUDO CRACK MODEL for the delamination in FRCM without crack. 3) Analysis of crack propagation energy, E$\sub$crack/ using a total energy, E$\sub$total/ and delamination growth energy, E$\sub$del/.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.5
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• pp.1108-1114
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• 2001

The fatigue crack propagation behavior of the SA516-Grade 70 steel which is used for pressure vessels was experimentally examined under the condition of at room temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ with stress ration of R=0.1 and 0.3. The fatigue crack propagation rate , da/dN, related with the stress intensity factor range, $\vartriangle$N, was influenced by the stress ration within the stable growth of fatigue crack(Region II) with an increase in $\vartriangle$N. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations revels that the differences of the fatigue crack growth characteristics between room and high temperatures are mainly explained by the crack and oxide-induced by high temperature.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.4
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• pp.117-124
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• 2003

The lightness of components required in automobile and machinery industry is requiring high strength of components. In particular, manufacturing process and new materials development for solving the fatigue fracture problem attendant upon high strength of suspension of automobile are actively advanced. In this paper, the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in high temperatures($100^{\circ}C$, $150^{\circ}C$, $180^{\circ}C$) was investigated with considering fracture mechanics. So, we can obtain followings. (1)Compressive residual stress decreases in high temperature, that is, with increasing temperature. (2)The effect of compressive residual stress on fatigue crack growth behavior in high temperature increases below $\Delta$K=17~19MPa (3)It was investigated by SEM that the constraint of compressive residual stress for plastic zone of fatigue crack tip was decreased in high temperature as compared with room temperature.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.1
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• pp.57-65
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• 1991

It is experimented under rotary bending stress that the spacing of two micro hole flaws is adjacent and that it is distant. In order to observe the behavior of fatigue crack propagation, two kinds of specimens are tested under constant stress and periodic overstressing. Although the crack occurs faster when two micro-hole flaws are adjacent than when they are distant, but there is no difference of the number of fracture cycles between two. The crack propagates slower under low-high block stress than under high-constant stress, and it propagates faster under high-low block stress than under low-constant stress. The influence of two-step block stress is serious right after the stress varies.