• Journal of Ocean Engineering and Technology
• /
• v.10 no.1
• /
• pp.36-46
• /
• 1996

This paper deals with determinig the proper friction welding condition and analyzing various mechanical properties of friction welded joints of sintered carbide tool materials(K20, P25, and SKDX5 for the blade part of drill or press punch) to alloy steel (SKH4, SCM440 for the shank part of drill or press punch), the alloy steel to aluminum(A6061 for the interlayer material between the blade part and the shank) and sintered carbide tool materials to alumminum. And also acoustic emission test will be carried out during fiction welding to evaluate the weld quality.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2007.10a
• /
• pp.234-237
• /
• 2007

Deep drawing of magnesium alloy sheet is conducted at elevated temperatures($200{\sim}300^{\circ}C$) to improve the press formability because of low formability at room temperature. Then magnesium alloy sheet formability is known to be very sensitive to the strain rate. In this paper, we conducted warm deep drawing tests of magnesium alloy AZ31 sheet for various punch velocities. We examined the forming velocity effect on the deep drawing formability and the correlation with the tensile test result.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2007.10a
• /
• pp.27-30
• /
• 2007

In order to measure the friction coefficient used in sheet metal forming analysis, a friction tester was manufactured and friction tests were performed in various forming conditions. Based on the friction coefficients measured, a mathematical friction model was constructed in terms of lubricant viscosity, blank holding force, punch velocity and sheet roughness. In addition, the effect of the number of forming parameters in the calculation of friction coefficient on the accuracy of sheet metal forming analysis was investigated by comparing the punch loads obtained from the FEM simulation, in which the friction coefficients were determined by a few parameters with the experimental measurement.

• Journal of the Korean institute of surface engineering
• /
• v.46 no.3
• /
• pp.126-132
• /
• 2013

It was investigated that the effects of hydrogen charging on the properties of 590 MPa Dual Phase(DP) steels at the surface layers. The hydrogen-charging time was changed from 5 to 50 hours and current densities from 100, 150, and 200 $mA/cm^2$, respectively. It was found that the hydrogen content in the specimen was increased with as the charging time and the current density. The microvickers hardness of the subsurface zone was increased from 215.3 HV to 239.5 HV due to the increase in current density and charging time. The comparison of the absorbed energies tested by a small-punch (SP) test showed that the absorbed energy of the specimen was greatly reduced from 436 to 283 $kgf-mm^2$ because of hydrogen embrittlement. It was confirmed that bulb aspects of fracture surface became more brittle with increasing hydrogen content.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.541-546
• /
• 2000

Recently, there have been increased mush concerns about repair and rehabilitation works for aged concrete structures to keep up with rapid economic growth in Korea since the early 1970's. In particular, it is believed in these days that there are significantly increasing number of aged concrete bridge slabs, which are strongly needed to construct and rehabilitate by innovative construction method. The objective of this research is to develop the new construction method of concrete slab in bridge structure, which can contribute to minimize the traffic congestion during the repair and rehabilitation works of aged concrete slab, and can also sufficiently assure the quality through the minimization of in-situ works at the site. I-beams with punch holes, which are substituted instead of main reinforcing steels in concrete slabs, will be manufactured in accordance with the specification in the factory, and will be preassembled into the panel. After erecting the preassembled panels in the site, concrete will be poured into the slab panel. This test is to investigate physical properties of I-Beam with punch holes itself, and then to investigate structural properties of assembled I-Beam panels through static and fatigue test, of which can be utilized for the development of new construction method of concrete slab in bridge structure.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2001.06a
• /
• pp.81-88
• /
• 2001

To study the influence of the shape of contacting bodies (especially the end profile) on slip regime, wear test is conducted in the case of the contact between tube and support. Two different end profiles of the support are used such as truncated wedge and rounded punch. During the test, 10, 30 and 50 N are applied as normal force and slip displacement varies between 10-200 $\mu\textrm{m}$. The tube and the support specimens are made of Zircaloy-4 and a specially designed wear tester is used. Tests are carried out in air at room temperature. Wear on the tube is examined by measuring microscope. Partial and gross slip regimes are classified from the observed wear shape. Surface roughness tester is also used to measure the wear depth and contour, from which wear volume is evaluated. The transition from partial to gross slip is also investigated by investigating the considerable increase of wear volume. From the result, the boundary between the partial and the gross slip is newly determined in the conventional fretting map for the present specific contact configuration. Since the transition is related with the amount of energy dissipation from the contact surface so is wear, it is regarded that wear can be restrained by designing a proper shape of support.

• Journal of the Korean institute of surface engineering
• /
• v.46 no.5
• /
• pp.229-233
• /
• 2013

The small punch(SP) tests that can be applied to high strength sheet steel in automobile were carried out to evaluate the behavior of hydrogen embrittlement of DP sheet steels. In order to charge hydrogen at DP sheet steels, DP sheet steels were treated by the electrochemical hydrogen charging method under the charging conditions of current densities of 100, 150 and 200 $mA/cm^2$ for charging times of 5, 10, 25 and 50 hrs. Respectively, After hydrogen charging with experimental conditions, SP tests were performed. From the SP results, the correlations between the variation of bulb diameters and bulb heights with the hydrogen charging conditions were analysed. It was shown that the variation of bulb diameters were not significant with the hydrogen embrittlement due to the amounts of hydrogen charging. On the other hand, the bulb heights were observed to decrease with increasing hydrogen contents. It was thought that these results of the variation of bulb shapes after SP tests would be estimated as the index of evaluation of hydrogen embrittlement.

• Proceedings of the Korean Institute of Industrial Safety Conference
• /
• 2003.05a
• /
• pp.147-152
• /
• 2003

원자로 압력용기 저합금강들은 원자로 가동 중 중성자 조사에 의해 재질열화 (material degradation)가 발생한다. 그러므로 계속적인 재질열화의 평가는 발전소의 수명을 예측, 평가하기 위해서 매우 중요하다. 그러나 표준시편을 이용한 인장시험, 충격시험 및 파괴인성 시험법 등은 조사시편의 크기 및 수량에 제한이 따르고, 높은 방사능으로 인해 시험편의 취급에도 제약을 받게 된다. 따라서 소형시편을 이용한 재료의 손상평가기술의 필요성이 부각되었고, 소형펀치시험(small punch test, SP test)은 그 중 하나의 유용한 시험 방법이다.(중략)

• Journal of the Korean institute of surface engineering
• /
• v.47 no.1
• /
• pp.13-19
• /
• 2014

The various surface treated conditions of Fe-3.0%Ni-0.7%Cr-1.4%Mn-X steel such as as-received, ion nitriding, DLC coated, DLC coated after nitriding for 3 hrs and 6 hrs were investigated to evaluate the beneficial effect for plastic mold steel. Micro Vickers hardness tester was used to estimate nitriding depth from the hardness profile and to measure hardness on the surface. Elastic modulus and residual stress were measured by a nanoindentator. Scratch test and SP (small ball punch test) were utilized to assess the adhesive strength of DLC coating. The depth of nitriding layer was measured as $50{\mu}m$ for the condition of 3 hrs nitriding and $90{\mu}m$ for that of 6 hrs nitriding. Hardness, elastic modulus, residual stress of DLC coating were 20.37 GPa, 162.78 GPa and -1456 MPa respectively. Residual stress on the surface of DLC coating after nitriding could increase to -3914 MPa by introducing nitriding before DLC coating. During the 'Ball-On-Disc' test ${\gamma}^{\prime}$ particles pulled out from the surface of nitrized layer tend to enhance abrasive wear mode since the fraction of ${\gamma}^{\prime}$ (Fe4N) in ion-nitrized layer is known to increases with nitriding time. Thus the specific wear rate of the nitriding layer increased. Comparing with nitriding the specific wear rate in work piece disc as well as ball decreased prominently in DLC coating due to the remarkable reduction in friction coefficient.

• Journal of the Korean institute of surface engineering
• /
• v.45 no.3
• /
• pp.130-135
• /
• 2012

Hydrogen charging was electrochemically conducted at high strength DP steels and TRIP steel with varying charging time. The penetration depths and the mechanical properties with charging conditions were investigated through the distribution of micro-hardness and the microstructural observation of the subsurface zone. The micro-Vickers hardness was measured to evaluate the hydrogen embrittlement of subsurface zone in addition to the microscope investigation. It was shown that the hydrogen amounts decreased in DP steels and TRIP steel with increasing hydrogen charging time. As shown by micro-Vickers hardness test and small punch test results, micro-Vickers hardness and SP energy for DP steels and TRIP steel decreased with increasing hydrogen charging time, for constant value of charging current density. SEM investigation results for the hydrogen contained samples showed that the major fracture behavior was brittle fracture which results in dimples on fractured surface and the size of dimples were decreased with increasing hydrogen charging time. These results indicate that hydrogen embrittlement is the major cause for the fracture of high strength steels and also micro-Vickers hardness test and small punch test is a valuable test method for hydrogen embrittlement of high strength sheet steels.