• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.852-855
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• 2002

In order to investigate the fracture behaviors(penetration modes) and resistance to penetration during ballistic impact of surface hardening treated Aluminum, Titanium alloy laminates, ballistic tests were conducted. In this paper, Anodized Al 5083-H131 alloy laminates and nitrified Ti (Gr.2) alloy laminates were used to achieve higher surface hardness. Surface hardness test were conducted using a Micro victor's hardness tester and thickness of surface hardening treated specimens was measured by video microscope. Resistance to penetration is determined by the protection ballistic limit($V_50$), a statistical velocity with 50% probability far complete penetration. Fracture behaviors and ballistic tolerance, described by penetration modes, are respectfully observed at and above ballistic limit velocities, as a result of $V_50$ test and Projectile Through Plates (PTP) test methods. PTP tests were conducted with $0^{\circ}$ obliquity at room temperature using 5.56mm ball projectile. $V_50$ tests with $0^{\circ}$ obliquity at room temperature were conducted with projectiles that were able to achieve near or complete penetration during PTP tests.

• Journal of Korea Foundry Society
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• v.31 no.2
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• pp.71-78
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• 2011

This study aims to investigate the formability of bipolar plates for fuel cell fabricated by vacuum die casting of ALDC 6. Cavity shape of mold is thin walled plate (size: $200mm{\times}200mm{\times}0.8mm$) with a serpentine channel (active area: $50mm{\times}50mm$). Before bipolar plate was made by HPDC, computational filling behavior and solidification was performed by MAGMA soft. The final mold design for location and direction of channel was determined by computational simulation. Also, according to injection speed conditions, simulation result was compared to actual die casting experimental result. When vacuum pressure, injection speed of low and high region is 350 mbar, 0.3 m/s and 2.5 m/s respectively, products had few casting defects. On the other hand, at the same as injection speed, without vacuum pressure, products had many casting defects between end of the channel and overflow.

• Journal of the Korean Vacuum Society
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• v.6 no.4
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• pp.293-297
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• 1997

Using trace etching method in this study, we measure the energy of argon ions generated in VEBA System which is composed of Marx Generater and Pulse Forming Line. In this system the electron beam of 240 kV, 30 kA, 60 ns is generated. Argon ions are formed through the electron beam ionization of a gas cloud injected by a fast puff valve. Thus argon ions are accelerated into vacuum drift tube by a virtual cathode and seperated with electron beam, consequently, they heat the trace etching plates made of aluminum thin films. The energy of argon ions are determined by the number of aluminum thin films penetrated by the ions. This experimental value corresponds with the theoretical value.

• Structural Engineering and Mechanics
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• v.62 no.6
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• pp.739-748
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• 2017

Notches such as slots are typical geometric features on mechanical components that promote fatigue crack initiation. Unlike for components with open hole type notches, there are no conventional treatments to enhance fatigue behavior of components with slots. In this work we evaluate the viability of applying laser shock peening (LSP) to extend the fatigue life of 6061-T6 aluminum components with slots. The feasibility of using LSP is evaluated not only on damage free notched specimens, but also on samples with previous fatigue damage. For the LSP treatment a convergent lens was used to deliver 0.85 J and 6 ns laser pulses 1.5 mm in diameter by a Q-switch Nd: YAG laser, operating at 10 Hz with 1064 nm of wavelength. Residual stress distribution was assessed by the hole drilling method. A fatigue analysis of the notched specimens was conducted using the commercial code FE-Safe and different multiaxial fatigue criteria to predict fatigue lives of samples with and without LSP. The residual stress field produced by the LSP process was estimated by a finite element simulation of the process. A good comparison of the predicted and experimental fatigue lives was observed. The beneficial effect of LSP in extending fatigue life of notched components with and without previous damage is demonstrated.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.174-179
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• 2001

In order to investigate the fracture behaviors(perforation modes) and resistance to perforation during ballistic impact of aluminum alloy plate, ballistic tests were conducted. Depth of penetration experiments with 5.56mm-diameter ball projectile launched into 25mm-thickness Al 5052-H34 targets were conducted. A powder gun launched the 3.55g projectiles at striking velocities between 0.6 and 1.0 km/s. radiography of the damaged targets showed different penetration modes as striking velocities increased. Resistance to perforation is determined by the protection ballistic limit($V_{50}$), a statistical velocity with 50% probability for complete perforation. Fracture behaviors and ballistic tolerance, described by perforation modes, are respectfully observed at and above ballistic limit velocities, as a result of $V_{50}$ test and Projectile Through Plates (PTP) test methods. PTP tests were conducted with $0^{\circ}$ obliquity at room temperature using 5.56mm ball projectile. $V_{50}$ tests with $0^{\circ}$ obliquity at room temperature were conducted with projectiles that were able to achieve near or complete perforation during PTP tests. The effect of various impact velocity are studied with depth of penetration.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.62-69
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• 1986

Fatigue surface crack growth was studied in 7075-T651 aluminum alloy plates subjected largely to bending loads. The surface crack length and its depth were measurement by the unloading elastic compliance method. The surface crack growth rate dc/dN, on the surface and da/dN, in the depth direction were obtained by the secant method. The stress intensity factor range .DELTA.K was computed by means of Newman and Raju equation. The aspect ratio a/c was presented in form of a/c=0.815-0.853(a/T). The effect of the stress ratio on the stable surface crack growth rates under increasing .DELTA.T is larger in lower .DELTA.K, while the relation between dc/dN, da/dN and the effective stress intensity factor range .DELTA.K$_{eff}$ is weakly dependent on the stress ratio.o.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.2
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• pp.55-60
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• 2000

A comparison of Riveted and bonded repairs, bearing and net tension failures, and Al 6061-T6 plates is presented. The results are then compared with previous papers about bonded repairs on different patch materials and shapes. Aluminum alloys, including Al 6061-T6, have a face-centered-cubic crystal structure. Under normal circumstances, these types of crystal structures do not exhibit cleavage fractures even at very low temperatures. In aluminum-base structures, the cracked plate structures are frequently repaired using mechanical fasteners-either rivets of bolts- even though patch-bonding techniques are applied to repair and reinforce the structure. Static test results indicate that the riveted repairs are affected by the position of the rivers. When using the same size of patch, the bonded repair technique is stronger; the rate of elongation is also increased. Form FEM analysis, it is revealed the origin of patch debonding in patch-bonded structures is the edge of the patch along to the tensile strength.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.6 s.237
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• pp.822-827
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• 2005

The characteristics of elastic waves emanating from crack initiation and propagation in 6061 aluminum alloy subjected to fatigue loading with different stress ratio was investigated. The objective of this study is to determine the properties of the signals generated from each stage of fatigue crack growth. AS a crack propagates, substantial elastic wave occurred just prior to penetration. Then it decreased and the crack penetrated. The waveforms and their power spectra were found to be dependent on the different stress ratio associated with the signals. It is determined that high-frequency signal $0.5{\sim}0.75$ MHz is most likely emitted during crack propagation at peak load of fatigue cycle which release the highest energy. It is determined that 0.3 MHz is closely related to crack closure effect. The frequency peaks below 0.25 MHz may be attributed to fretting or hydraulic noise.

• Transactions of Materials Processing
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• v.21 no.5
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• pp.305-311
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• 2012

One of the main methods of building LNG tankers uses the Moss spherical tank design since it can be precisely analyzed with respect to reliability and safety of construction by stress analysis. Aluminum alloy 5083 is generally used in the Moss spherical tank design for the wall in constructing the LNG tanker. This aluminum alloy does not have low temperature brittleness, but has good corrosion resistance, good weldability, and excellent material properties for the application. The Moss spherical tank is constructed with several sections of A5083 thick plate with curved surfaces, which are welded together. It is essential to predict the amount of springback for the deformed thick plates in design to insure a reliable construction because the structure needs to be assembled into a perfect sphere. Unless the initial construction meets the design, there are additional processing costs for reworking to meet the specifications as well as a cost penalty paid to a consumer. In this paper, FE analyses were conducted to predict the amount of springback for various forming conditions and forming processes. The various forming processes were evaluated with respect to reducing springback and compared with the conventional forming process used for curved surfaces of thick Al plate.

• Structural Engineering and Mechanics
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• v.75 no.5
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• pp.559-569
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• 2020

In the present study, the fracture toughness of U-shaped notches made of aluminum alloy Al7075-T6 under combined tension/out-of-plane shear loading conditions (mixed mode I/III) is studied by theoretical and experimental methods. In the experimental part, U-notched test samples are loaded using a previously developed fixture under mixed mode I/III loading and their load-carrying capacity (LCC) is measured. Then, due to the presence of considerable plasticity in the notch vicinity at crack initiation instance, using the Equivalent Material Concept (EMC) and with the help of the point stress (PS) and mean stress (MS) brittle failure criteria, the LCC of the tested samples is predicted theoretically. The EMC equates a ductile material with a virtual brittle material in order to avoid performing elastic-plastic analysis. Because of the very good match between the EMC-PS and EMC-MS combined criteria with the experimental results, the use of the combination of the criteria with EMC is recommended for designing U-notched aluminum plates in engineering structures. Meanwhile, because of nearly the same accuracy of the two criteria and the simplicity of the PS criterion relations, the use of EMC-PS failure model in design of notched Al7075-T6 components is superior to the EMC-MS criterion.