• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.7-13
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• 2012

A lack of study on the dynamic tensile strengths of Sn-based solder joints at high strain rates was the motivation for the present study. A modified miniature Charpy impact testing machine instrumented with an impact sensor was built to quantitatively evaluate the dynamic impact strength of a solder joint under tensile impact loading. This study evaluated the tensile strength of lead-free solder ball joints at strain rates from $1.8{\times}10^3s^{-1}$ and $8.5{\times}10^3s^{-1}$. The maximum tensile strength of the solder ball joint decreases as the load speed increases in the testing range. This tensile strength represented that of the interface because of the interfacial fracture site. The tensile strengths of solder joints between Sn-3.0Ag-0.5Cu and copper substrate were between 21.7 MPa and 8.6 MPa in the high strain range.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.6
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• pp.66-75
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• 1994

In this paper, the effects of temperature change on the impact damages of CF/PEEK laminates are experimentally investigated. Composite laminates used in this experiment are CF/PEEK orthotropic laminated plates, which have two-interfaces$[0^{\circ}_4/90^{\circ}_4]_{9+} A steel ball launched by the air gun collides against CFRP laminates to generate impact damage. The delamination damages are oberved by a scanning acoustic microscope. And various relations are experimentally observed including the impact energy vs. delamination area, the specimen temperature vs. transverse crack, and the impact energy vs. residual bending strength of carbon fiber peek composite laminates subjected to FOD(Foreign Object Damage) under high temperatures.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.1930-1938
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• 1994

In this paper, the effects of temperature change on the impact of CFRP laminates was experimentally studied. Composite laminates used for this experiment are CFRP orthotropic laminated plates, which have two-interfaces$[0_6^{\circ}/90_7^{\circ}]_s$ and four-interfaces$[0_3^{\circ}/90_6^{\circ}/0_3^{\circ}]_s$. The interrelations between the impact energy vs. delamination area, the impact energy vs. residual bending strength, and the interlayer delamination area vs. the decrease of the residual flexural strength of carbon fiber epoxy composite laminates subjected to FOD(Foreign Object Damage) under high temperatures were experimentally observed.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.11
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• pp.124-131
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• 1996

The dynamic material property of Mn-B ally high-strength steel is investigated through the rod impact test which is one of simple test methods for the analysis of the material behavior under high-strain-rate. Rod impact test is performed to produce the deformed shape of rod and analyzed by the one-dimensional theory based on conservation law and the two-dimensional hydrocode AUTODYN-2D. The dynamic yield stress is determined and compared with the static yield stress to investigate the strain-rate sensitivity of Mn-B alloy high-strength steel.

• Elastomers and Composites
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• v.28 no.4
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• pp.283-292
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• 1993

The morphology and impact strength of alloys of high density polyethylene(HDPE) and nylon-6(PA) with modified $ethylene-{\alpha}-olefin$ copolymer(OCP) as compatibilizer and impact modifier were measured by the scanning electron microscope(SEM) and the notched Izod impact test(and the high rate impact test), respectively. HDPE is incompatible with PA and specimens obtained from simple mechanical mixing show the inferior properties. However, it was indicated that OCP played roles of not only impact modifier but also compatibilizer. High rate impact test results were different from those of the notched Izod impact test, but in both tests OCP was effective for HDPE/PA blends. From SEM observation, the size of the dispersed phase in alloys prepared with OCP is much smaller than that of alloys without OCP and the interfacial adhesion of alloys prepared with OCP is also better. Toughening mechanism of polymer blends was discussed by combining the morphology analysis with mechanical and thermal properties.

• Journal of Technologic Dentistry
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• v.21 no.1
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• pp.55-65
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• 1999

So far, I Conducted an examination with focus on the type, characteristic, and test methods of impact test. which is a type of mechanical that evaluate materials. As mentioned previously, in testing soldering strength of soldering is the load when the object under experiment is broken down with the result of flexibility test or peel test. In this method, a hevay load is necessary until alloy of parent metal is bended, if the alloy of the parent metal has a large mechanical quality(peel strength or resisting power). Once the alloy of the parent metal is bended, however, it tends to come into pieces abruply form the part where soldered. Therefore, a metal has a high breakdown value if the degree of strength of its parent metal is high even if the result of measurement indicates otherwise. Thus, the result of the test did not correspond to the clinical result. Therefore, this study concludes as the following from a test of strength of soldering by mean of conducting an impact test, which is a type of mechanical evaluation methods : 1. Among various impact tests, a charpy thpe is more appropriate than the izod type in testing strength of soldering. 2. As far as test piece is concerned, to use subsized impact test piece is appropriate in the impact test in that it does not have notch. 3. In the matter of analysis, it is appropriate to measure absorbing energy which results from rupture of test piece.

• Journal of the Korean Society of Safety
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• v.30 no.3
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• pp.7-12
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• 2015

CFRP composites are used as primary structural members in various industrial fields because their specific strength and specific stiffness are excellent in comparison to conventional metals. Their usage is expanding to high added-value industrial fields because they are more than 50% lighter than metals, and have excellent heat resistance and wear resistance. However, when CFRP composites suffer impact damage, destruction of fiber and interface delamination occur. This causes an unexpected deterioration of strength, and for this reason it is very difficult to ensure the reliability of the excellent mechanical properties. Therefore, for the destruction mechanism in bending with impact damage, this study investigated the reinforcement data regarding various external loads by identifying the consequential strength deterioration. Specimens were damaged by impact with a steel ball propelled by air pressure. Decrease in bending strength caused by the tension and compression of the impact side, and depending on the lamination direction of fiber and interface inside the specimen. From the bending test it was found that the bending strength reduced when the impact energy increased. Especially in the case of compression on the impact side, as tensile stress occurred at the damage starting point, causing rapid failure and a substantially reduced failure strength.

• Korean Journal of Materials Research
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• v.12 no.1
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• pp.10-15
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• 2002

Melt blends of maleic anhydride grafted polypropylerle(PP-g-MA) and Nylon 6 were prepared to study the influence of chemical reaction between the two polymer components. By adding the MA grafted polystyrene pold (ethylene/butadiene) and polystyrene[SEBS-g-MA] as the compatible modifiers to reinforce the impact resistance, the Izod impact strength, high rate impact strength and morphology were studied. The notched Izod impact strength increased with the content of PP-g-MA and SEBS- g-MA. The energy of high rate impact strength increased as the thickness of specimen increased, while, it increased as the specimen displacement decreased. In the morphology observed by SEM, finally, we confirmed the improvement of the compatibilization and interfacial adhesion with the content of SEBS-g-MA. The continuous phase of PP-g-MA was the main cause of the modified properties.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.3
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• pp.121-126
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• 2014

High-nitrogen Fe-18Mn-18Cr-N austenitic steels with higher yield strength have been recently developed and used for generator retaining rings because they have non-magnetic, high strength, high ductility, and good corrosion resistance. In the present study, a high-nitrogen Fe-18Mn-18Cr-0.61N austenitic steel was fabricated and then tensile and Charpy impact tests were conducted on them in order to investigate the effect of cold working on the mechanical properties. Although the yield and tensile strengths usually increased with cold working, the ductility and impact toughness significantly decreased after cold working. On the other hand, the high-nitrogen austenitic steel exhibited a ductile-brittle transition due to unusual brittle fracture at low temperatures despite having a face-centered cubic structure. The ductile-brittle transition temperature obtained from Charpy impact tests could be remarkably increased by $60^{\circ}C$ after 20% cold working because of the enhanced cleavage-like brittle fracture.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.3 s.258
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• pp.295-303
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• 2007

Degradation behaviors of filament-winded composites have been evaluated under the accelerated environmental test of high temperature, water immersion and thermal impact conditions. Two kinds of laminated composites coated by an urethane resin have been used: carbon-fiber reinforced epoxy(T700/Epon-826, CFRP) and glass-fiber reinforced phenolic (E-glass/phenolic, GFRP). For tensile strength of $0^{\circ}$ composites, CFRP showed little degradation while GFRP did high reduction by 25% under the influence of high temperature and water However for water-immersed $90^{\circ}$ composites tensile strength of both CFRP and GFRP showed high reduction. Bending strength and modulus of $90^{\circ}$ composites were largely reduced in water-immersion as well as high temperature environment. Urethane coating on the composite surface improved the bending properties by 20%, however hardly showed such improvement for water-immersed $90^{\circ}$ composites. In case of shear strength and modulus, both CFRP and GFRP showed high reduction by water-Immersion test but did a slight increase by high temperature and thermal impact conditions.