• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1415-1422
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• 2011

Sheet aluminum alloys used in manufacturing of machine structures for transportation show the difference of crack growth speed depending on thickness under the constant fatigue stress condition. The referred thickness effect is a major fatigue failure property of sheet aluminum alloys. In this work, we identified the thickness effect in fatigue test of thick plate and thin plate of Al 2024-T3 alloy under the constant fatigue stress condition, and presented the thickness effect to a correlative equation, $U_{i}^{equ}=f(R_t)$ which is determined by the shape factor, thickness ratio, $R_t$ and the loading factor, equivalent effective stress intensity ratio depending on thickness, $U_{i}^{equ}$. And we analyzed quantitatively the crack growth retardation behavior in thin plate compared to thick plate by the thickness effect using ${\Delta}K$ conversion method. We obtained such values as decrement of thickness(DoT), decrement of stress intensity factor range, ${\Delta}K$ (DoS) and identified the relation between them to present the nature of thickness effect in this work.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.1
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• pp.119-125
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• 1999

The distribution of fatigue crack growth rate is subjected to the measuring interval and calculated method of growth rate. In this paper, in order to establish the method of determining the distribution of fatigue crack growth rate, which ignores those influences, a series of fatigue crack growth experiments and measuring intervals of crack length calculated reasonable are presented. The main conclusions obtained are summarized as follows: 1) As a result of the ΔP constant test and ΔK constant test, it is thought that an approximate measuring interval of 0.3~0.7mm is reasonable, which allows for few errors and is little subjected to the calculated method of crack growth rate. 2) After generally comparing the error estimation by using the experimental data of CCT specimen with the error rating of the CT specimens, it is possible that the fatigue test has few errors within the measuring interval, ξ(Δa/W)=0.0067~0.017, regardless of the dimension of specimen geometry.

• 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/.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1277-1286
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• 2001

Aluminum 5052/Aramid Fiber Reinforced Plastic(Al5052/AFRP) laminates are applied to the fuselage-wing intersection. The Al5052/AFRP laminates suffer from the cyclic bending moment of variable amplitude during the service. Therefore, the influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in Al5052/AFRP laminate was investigated in this study. Al5052/AFRP laminate composite consists of three thin sheets of Al5052 and two layers of unidirectional aramid fibers. The cyclic bending moment fatigue tests were performed with five different levels of bending moment. The shape and size of the delamination zone formed along the fatigue crack between Al5052 sheet and aramid fiber-adhesive layer were measured by an ultrasonic C-scan. The relationships between da/dN and ΔK, between the cyclic bending moment and the delamination zone size, and between the fiber bridging mechanism and the delamination zone were studied. Fiber failures were not observed in the delamination zone in this study. It represents that the fiber bridging modification factor should turn out to increase and that the fatigue crack growth rate should decrease. The shape of delamination zone turns out to be semi-elliptic with the contour decreased non-linearly toward the crack tip.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.10
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• pp.61-68
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• 2001

Turbine blade in nuclear plant is subject to cyclic bending fatigue by high steam pressure. Especially, fatigue fracture is caused by low stress below yielding stress. Photograph by SEM doesn't have striation but photograph by AFM has striation on the fatigue fractured surface of 12% Cr steel used in turbine blade. Surface roughness $R_q$ has the linear relation with respect to stress intensity factor range ΔK and is increased linearly according to load amplitude $\textit{\Delta}P$. In this study loading condition applied to turbine blade is predicted by the relation between the gradient of $R_q$ to $\textit{\Delta}K$ and load amplitude $\textit{\Delta}P$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.4
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• pp.592-601
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• 2001

Fiber reinforced metal laminates(FRMLs) are new types of hybrid materials. FRMLs consists of high strength metal(Al 5052-H34) and laminated fiber with structural adhesive bond. The mixture ratio effect of epoxy resin$.$curing agent$.$accelerator on the fatigue behavior of FRMLs was investigated in this study. The epoxy, diglycidylether of bisphenol A(DGEBA), was cured by methylene dianiline(MDA) with or without an accelerator(K-54). Eight different kinds of resin mixture ratios were selected for the test ; five kinds of FRMLs(1) and three others of FRMLs(2). The relationship between da/dN and ΔK with variation of resin mixture ratio was studied. FRMLs(1) and FRMLs(2) indicated approximately 2 times and 2.2 times more improved maximum bending strengths in comparison with those of Al 5052-H34. The resin mixture ratio <1:1> in case of FRMLs(1) indicated the maximum fatigue life, while the resin mixture ratio <1:1:0.2> in case of FRMLs(2) indicated the maximum fatigue life. As results, FRMLs(2) turned out to have more effective characteristics on the fatigue properties and the bending strength than those of FRMLs(1).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.6 s.177
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• pp.1584-1592
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• 2000

Reversed plane bending fatigue tests were conducted on SiC whisker reinforced aluminum composite which were consolidated by squeeze casting process. Initiation and growth of small surface fatigue c racks were investigated by means of a plastic replica technique. The fatigue crack initiated in the vicinity of SiC whisker/matrix interface. It was found that a fatigue crack deflected along SiC whisker and grew in a zig-zag manner microscopically, although the crack propagated along the direction normal to the loading axis macroscopically. The coalescence of micro-cracks was observed in the tests conducted at high stress levels, but were not evident in tests in which lower levels of stress were applied. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn -ΔK realtionship.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.3
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• pp.281-288
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• 2004

The hybrid composite material (Al/GFRP laminates) are applied to the fuselage and wing in a aircraft. Therefore, Al/GFRP laminates suffer from the cyclic bending moments. This study was to evaluate the effect of fiber stacking angle on the fatigue crack propagation and delamination behavior using the relationship between crack growth rate (da/dN) and stress intensity factor range (ΔK) in Al/GFRP laminates under cyclic bending moment. The variable delamination growth behavior in case of three different type of fiber orientations, i.e., [Al/O$_2$/Al], [Al/+45$_2$/Al] and [Al/90$_2$/Al] at the interface of Al layer and glass fiber layer was measured by ultrasonic C-scan images. As results of this study, It represent that the delamination shape should turns out to have more effective characteristics on the fiber stacking angle. The extension of the delamination zone in case of [Al/+45$_2$/Al] and [Al/90$_2$/Al] were not formed along the fatigue crack profile. The shape of delamination zone depend on fiber stacking angle and the variable type with the delamination contour decreased non-linearly toward the crack tip at the Al layer.