• Proceedings of the KWS Conference
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• 1994.05a
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• pp.39-43
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• 1994

The effects of ageing treatment on the mechanical properties of two Cu-bearing HSLA(High Strength Low Alloy) steels, HSLA-A and HSLA-B ,were studied by means of SEM, TEM, tensile, charpy impact and hardness tests. These steels showed excellent combination in strength and toughness at an ageing of $650^{\circ}C$ by the precipitation of $\varepsilon$-Cu and low carbon alloying. The peak strength was achieved at an ageing of 50$0^{\circ}C$ in both steels, while the impact energy was very low in this peak strength. With ageing temperature above this temperature, strength was decreased whereas impact energy increased. A marked increase in hardness above 675$^{\circ}C$ was associated with the formation of “M-A constituents” which forms during cooling from austenite-ferrite two phase region. The impact transition temperature of HSLA-A and HSLA-B steels were -l$25^{\circ}C$ and -145$^{\circ}C$, respectively.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.3 no.1
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• pp.35-39
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• 2000

The present study dealt with the relationships among the interfacial shear strength, the thickness of interfacial reaction layer and the impact value of $Nb/MoSi_2$ laminate composites. In addition, the tensile test was conducted to evaluate the fracture strain of $Nb/MoSi_2$ laminate composites. To change the thickness of the reaction layer, $Nb/MoSi_2$ laminate composites alternating sintered MoSi2 layers and Nb foils were fabricated as the parameter of hot press temperature. It has been found that the growth of the reaction layer increases the interfacial shear strength and decreases the impact value by localizing a plastic deformation of Nb foil. There also exist appropriate shear strength and the thickness of the reaction layer, which are capable of maximizing the fracture energy of $Nb/MoSi_2$.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.2
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• pp.13-20
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• 2019

This study was conducted in order to validate the nose shape factors of projectile in existing impact formulas for high-strength concrete in the event of collision with high-speed projectiles. In order to conduct the high-speed impact experiment, specified concrete strengths of 35, 100, and 120 MPa were prepared and tested in collision with both conical and hemispherical projectiles. The results showed that the measured penetration depth did not decrease linearly as concrete strength increased. Comparing the ratio penetration depth to the kinetic energy of the conical and hemispherical projectiles, the difference in the ratios for high strength concrete was observed to decline as concrete strength increased. However, in the modified NDRC and the Hughes formulas, the difference in the predicted penetration depth of the conical and hemispherical projectiles was constant despite increasing concrete strength. The modified NDRC and Hughes formulas should be improved upon so as to be applied to high strength concrete.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.4
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• pp.379-385
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• 2016

Door impact beam plays a key role in minimizing the occupant injury within the side impacted vehicle through preventing intrusion of the impacting vehicle. Steel pipe type door impact beam has been widely adopted since it has simple structure and the overall strength is easily determined according to the pipe size. The brackets welded at pipe ends connect the door impact beam and the door panels by spot welds. In this study, first, the effect of pipe thickness, bracket thickness and door mounting stiffness was respectively analyzed. Next, application of the tailor rolled pipe was examined and several alterations of the bracket mounting method were considered. Application of tailor rolled pipes with superior bracket mounting method showed remarkable strength enhancement and weight reduction possibility in comparison with the current door impact beam.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.250-255
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• 2000

Damage induced by low velocity impact loading in aircraft composite laminates is the form of failure which is occurred frequently in aircraft. Low velocity impact can be caused either by maintenance accidents with tool drops or by in-flight impacts with debris. As the consequences of impact loading in composite laminates, matrix cracking, delamination and eventually fiber breakage for higher impact energies can be occurred. Even when no visible impact damage is observed, damage can exist inside of composite laminates and the carrying load of the composite laminates is considerably reduced. The reduction of strength and stiffness by impact loading occurs in compressive loading due to laminate buckling in the delaminated areas. The objective of this study is to determine inside damage of composite laminates by impact loading and to determine residual compressive strength and the damage growth mechanisms of impacted composite laminates. For this purpose a series of impact and compression after impact tests are carried out on composite laminates made of carbon fiber reinforced epoxy resin matrix with lay up pattern of $[({\pm}45)(0/90)_2]s$ and $[({\pm}45)(0)_3(90)(0)_3({\pm}45)]$. UT-C scan is used to determine impact damage characteristics and CAI(Compression After Impact) tests are carried out to evaluate quantitatively reduction of compressive strength by impact loading.

• Korea-Australia Rheology Journal
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• v.18 no.1
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• pp.1-8
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• 2006

Blend of bisphenol-A polycarbonate (PC) and (acrylonitrile-styrene-acrylic rubber) terpolymer (ASA) having excellent balance in the interfacial properties and mechanical strength was developed for the automobile applications. Since interfacial adhesion between PC and styrne-acrylonitrile copolymer (SAN) matrix of ASA is not strong enough, two different types of compatibilizers, i.e, diblock copolymer composed of tetramethyl polycarbonate (TMPC) and SAN (TMPC-b-SAN) and poly(methyl methacrylate) (PMMA) were examined to improve interfacial adhesion between PC and SAN. TMPC-b-SAN was more effective than PMMA in increasing interfacial adhesion between PC and SAN matrix of ASA (or weld-line strength of PC/ASA blend). When blend composition was fixed, PC/ASA blends exhibited similar mechanical properties except impact strength and weld-line strength. Impact strength of PCI ASA blend at low temperature was influenced by rubber particle size and its morphology. PC/ASA blends containing commercially available PMMA as compatibilizer also exhibited excellent balance in mechanical properties and interfacial adhesion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1836-1842
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• 1996

In this paper, static and fatigue bending strengths of CFRP(carbon fiber reinforced plastic laminates having impact damage(FOD) are evaluated. Composite laminates used for this experiment are CF/EPOXY and CF/PEEK orthotropy laminated plates, which have two-interfaces[${0^0}_4{90^0}_4}$]$_sym$. A steel ball launched by the air gun colides against CFRP laminates to generate impact damages. The damage growth during bending fatigue test is observed by the scanning acoustic microscope(SAM). When the impacted side is compressed, the residual fatigue bending strength of CF/PEEK specimen P is greater that that of CF/EPOXY SPECIMEN B. On the other hand, when the impacted side is in tension, the residual fatigue bending strength of CF/PEEK speicemen P is smaller than that of CF/EPOXY specimen B. In the case of impacted-side compression, fracture is proposed from the transverse crack generated near impact point. On the other hand, fracture is developed toward the impact point from the edge of interface-b delamination in the case of impacted-side tension.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.6
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• pp.247-258
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• 2000

It is thought that impact damages and hygrothermals can affect to CFRP (Carbon-fiber reinforced plastic) composite laminated due to the sensitivity on the composite laminated Therefore, this paper focuses on the fracture mechanisms experimentally based on a scanning acoustic microscope (SAM) when subjected to impact damages, i.e., foreign object damages(FOD), and also the influence of impact damages and hygrothermals on residual fatigue bending strength of CFRP laminates. Composite laminates used in the experiment are CF/EPOXY orthotropy laminated plates, which constist of two-interfaces [04/904]s. A steel ball launched by an air gun collides against CFRP laminates to generate impact damages. Bending fatigue tests are periodically interrupted for a nondestructive evaluation (NDE) measurement of the progrossive damages to built the fracture mechanism by impact damages, and three-point fatigue bending tests are carried out to investigate the influence of hygrothermals on the effect on the residual bending fatigue strength of CFRP laminates.

• Steel and Composite Structures
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• v.17 no.2
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• pp.199-213
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• 2014

The damage characters of scarf repaired composite laminates subjected to low-velocity impact with various energy levels at different locations are studied experimentally. The results are compared with those of the original laminates which have no initial damage and don't need repair. The impact load-time history of the specimens, the velocity-time curves of the impactor, the post impact compressive strength of the specimens and the C-scan photographs of the damaged regions are obtained. The delamination threshold load and damage character of the specimen section at impact point are also studied. The results have shown that the impact response of a repaired composite laminate is sensitive to the location of the impact. The impact load and the delamination threshold load have shown different characters for specimens with different impact locations. The debonding characters of the adhesive and compressive strength after impact of the specimens are also influenced by impact locations.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.498-500
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• 1999

Polyacetals with melamine were investigated in terms of mechanical properties. It was found that tensile strength, impact strength and elongation were decreased with the increase of melamine content up to 30 par, flexural strength had no remarkable changes. For master-batch using polyurethane as carrier resin, in which the ratio of polyurethane to melamine was 2:1, tensile strength and flexural strength were decreased and impact strength remained unchanged with melamine me content.