• 한국해양공학회지
• /
• 제25권6호
• /
• pp.91-96
• /
• 2011

In this paper, friction welded joints were constructed to investigate the mechanical properties of welded 15-mm diameter solid bars of Mg alloy (AZ31B). The main friction welding parameters were selected to endure reliable quality welds on the basis of visual examination, tensile tests, impact energy test, Vickers hardness surveys of the bonds in the area and heat affected zone (HAZ), and macrostructure investigations. The study reached the following conclusions. The tensile strength of the friction welded materials (271 MPa) was increased to about 100% of the AZ31B base metal (274 MPa) under the condition of a heating time of 1 s. The metal loss increased lineally with an increase in the heating time. The following optimal friction welding conditions were determined: rotating speed (n) = 2000 rpm, heating pressure (HP) = 35 MPa, upsetting pressure (UP) = 70 MPa, heating time (HT) = 1 s, and upsetting time (UT) = 5 s, for a metal loss (Mo) of 10.2 mm. The hardness distribution of the base metal (BM) showed HV55. All of the BM parts showed levels of hardness that were approximately similar to friction welded materials. The weld interface of the friction welded parts was strongly mixed, which showed a well-combined structure of macro-particles without particle growth or any defects. In addition, an acoustic emission (AE) technique was applied to derive the optimum condition for friction welding the Mg alloy nondestructively. The AE count and energy parameters were useful for evaluating the relationship between the tensile strength and AE parameters based on the friction welding conditions.

• 대한치과기공학회지
• /
• 제37권1호
• /
• pp.23-29
• /
• 2015

Purpose: The selective laser melting (SLM) process for dentistry, which is one of the additive manufacturing technologies (AM) allows for rapid production of a three-dimensional model with complex shape by directly melting metal powder. This process generates detailed items of a three-dimensional model shape through consolidation of a thin powder layer by utilizing both selective melting and laser beam simultaneously. In regard to SLM process, Fe-base powder, Ti-6AI-4V powder, AI-base powder, etc. have been researched. It is believed that the aforementioned technologies will be widely utilized in manufacturing metal parts using metal powder of raw material. This study chose Ni-Cr-Mo metal powder in order to manufacture metal powder materials that would be used in the selective laser melting for dentistry. Methods: This study manufactured metal powder using mechanical alloying technique (MA) among those metal powder manufacturing techniques. Moreover, this study aimed to utilize the metal powder manufactured after observing the characteristics of powder as preliminary data of Ni-Cr-Mo metal powder. This study could obtain the following conclusions within the experimental limitations. Results: As a result of mechanically alloying Ni-Cr-Mo powder over time, its mean particle size was $66.93{\mu}m$ $54.4{\mu}m$ and $45.39{\mu}m$ at 10h, 20h and 30h, respectively. The gtain form of metal powder by mechanical alloying technique was a sponge-like shape of irregular plate; however, the gtain form manufactured by high-pressure water aromization process had the following three types: globular type, chain type and oval type. Conclusion: This study found $37.65{\mu}m$ as the mean particle size of Ni-Cr-Mo metal powder, which was manufactured using water atomization technique under the following conditions: water atomization flux of 300 liter/min, hydraulic pressure of $400kgf/cm^2$ and injection angle of $45^{\circ}$. This study confirmed that the grain form of powder (solid particle form) would vary depending on the manufacturing process.

• 한국자기학회지
• /
• 제8권5호
• /
• pp.282-287
• /
• 1998

유리 기판위에 dc magnetron sputtering 방법으로 제작한Fe(50 $\AA$)/[Co(17 $\AA$)/Cu(24 $\AA$)]20 다층박막에 관하여 자기저항비의 기저층, 자성층, 비자성층의 증착률 및 열처리 의존성을 살펴보았다. 낮은 base 압력 중에서의 막의 증착은 Co/Cu 계면의 산화를 억제하여 자기저항비를 장가시켰다. 극대 자기저항비를 얻기위해 요구되는 증착률은 Fe는 1$\AA$)/s 이상, Cu는 2.8 $\AA$)/s 이었으며 Co는 증착률이 2 $\AA$/s 보다 높은 경우에 평탄한 자구형성을 이루어 자기적 향비가 높아지는 경향을 보였다. 40$0^{\circ}C$까지의 시료에 대한 역처리는 다층박막의 주기성을 유지한채 더 큰 결정립을 형성시켜 반강자성적으로 결합한 막의 부분이 증가함으로써 자기저항비를 증가시켰다.

• 한국자기학회지
• /
• 제9권3호
• /
• pp.166-172
• /
• 1999

본 연구에서는 마그네트론 스퍼터링 법으로 제작한 Mn-Ir/Ni-Fe/Zr/Si 다층막에서 Mn-Ir의 조성과 증착조건을 변화시키고 또한 Mn-Ir층의 두께를 조절한 후 자기적 특성과 미세구조에 대하여 고찰하였다. Mn-22at% Ir의 조성에서 219Oe의 가장 높은 Hex와 30Oe의 낮은 Hc를 얻을 수 있었다. 초기진공도가 3.0$\times$10-6Torr 이상 일때는 교환이방성이 사라지게 되었으며 이것은 Mn-Ir의 비정질화와 결정립미세화에 의한 것으로 판단된다.

• Geomechanics and Engineering
• /
• 제27권5호
• /
• pp.465-479
• /
• 2021

One of the important causes of building and infrastructure failure, such as bridges on pile foundations, is the placement of the piles in liquefiable soil that can become unstable under seismic loads. Therefore, the overarching aim of this study is to investigate the seismic behavior of a soil-pile system in liquefiable soil using three-dimensional numerical FEM analysis, including soil-pile interaction. Effective parameters on concrete pile response, involving the pile diameter, pile length, soil type, and base acceleration, were considered in the framework of finite element non-linear dynamic analysis. The constitutive model of soil was considered as elasto-plastic kinematic-isotropic hardening. First, the finite element model was verified by comparing the variations on the pile response with the measured data from the centrifuge tests, and there was a strong agreement between the numerical and experimental results. Totally 64 non-linear time-history analyses were conducted, and the responses were investigated in terms of the lateral displacement of the pile, the effect of the base acceleration in the pile behavior, the bending moment distribution in the pile body, and the pore pressure. The numerical analysis results demonstrated that the relationship between the pile lateral displacement and the maximum base acceleration is non-linear. Furthermore, increasing the pile diameter results in an increase in the passive pressure of the soil. Also, piles with small and big diameters are subjected to yielding under bending and shear states, respectively. It is concluded that an effective stress-based ground response analysis should be conducted when there is a liquefaction condition in order to determine the maximum bending moment and shear force generated within the pile.

• Geomechanics and Engineering
• /
• 제30권6호
• /
• pp.503-515
• /
• 2022

The permeability coefficient is an essential parameter for the study of seepage flow in fractured rock mass. This paper discusses the feasibility and application value of using readily available RQD (rock quality index) data to estimate mine water inflow and grouting quantity. Firstly, the influence of different fracture frequencies on permeability in a unit area was explored by combining numerical simulation and experiment, and the relationship between fracture frequencies and pressure and flow velocity at the monitoring point in fractured rock mass was obtained. Then, the stochastic function generation program was used to establish the flow analysis model in fractured rock mass to explore the relationship between flow velocity, pressure and analyze the universal law between fracture frequency and permeability. The concepts of fracture width and connectivity are introduced to modify the permeability calculation formula and grouting formula. Finally, based on the on-site grouting water control example, the rock mass quality index is used to estimate the mine water inflow and the grouting quantity. The results show that it is feasible to estimate the fracture frequency and then calculate the permeability coefficient by RQD. The relationship between fracture frequency and RQD is in accordance with exponential function, and the relationship between structure surface frequency and permeability is also in accordance with exponential function. The calculation results are in good agreement with the field monitoring results, which verifies the rationality of the calculation method. The relationship between the rock mass RQD index and the rock mass permeability established in this paper can be used to invert the mechanical parameters of the rock mass or to judge the permeability and safety of the rock mass by using the mechanical parameters of the rock mass, which is of great significance to the prediction of mine water inflow and the safety evaluation of water inrush disaster management.

• Journal of Advanced Marine Engineering and Technology
• /
• 제32권8호
• /
• pp.1240-1247
• /
• 2008

Leakage trouble on the sea water pipeline in engine room is often resulted from a localized corrosion due to severe corrosive environment caused by both high speed and high pressure of sea water flowing through the inner pipe. In addition, when the ship is in stand-by or emergency condition, underwater welding to control the leakage of sea water from a hole of its pipe is very important in an industrial safety point of view. In this study possibility of underwater welding to control leakage of sea water and corrosion property of its welding zone were investigated with the electrochemical methods by parameters of welding methods and welding electrodes when underwater welding is achieved with a such case that sea water is being leaked out with a height at 50mm from a hole of $2.5mm{\emptyset}$ of test pipe. Corrosion resistance of weld metal zone is better than the base metal and its hardness is higher than that of the base metal. However corrosion potential of weld metal zone showed a negative value than that of the base metal, therefore weld metal zone is preferentially corroded rather than the base metal by performance of galvanic cell due to difference of corrosion potential between weld metal zone and base metal. Eventually it is suggested that leakage of sea water is successfully controlled by underwater welding,

• The Journal of Advanced Prosthodontics
• /
• 제2권3호
• /
• pp.102-105
• /
• 2010

PURPOSE. The aims of this study were to suggest a method of fabrication of the record base using a light-polymerized resin by applying the two-phase fabrication method for the improvement of the fit of the record base and to compare the degree of fit according to the separation site. MATERIALS AND METHODS. In the edentulous cast of maxilla, four test groups were considered. In the first, second, third, and fourth test groups (n = 12 in each group) the separation was done at 0, 5, 10, and 15 mm, respectively below the alveolar crest along the palatal plane. For the control group, the record base was made without separating the two sections. The light-body silicone material was injected into the fitting surface of the record base. It was then placed onto the cast and finger pressure was applied to stabilize it in a seated position followed by immediate placement onto the universal test device. Finally, the mass of the impression material was measured after it was removed. ANOVA was performed using the SAS program. For the post-hoc test, the Wilcoxon Rank-Sum test and the Tukey-Kramer HSD test were performed ($\alpha$ = 0.05). RESULTS. The control group and Group 3, 4 showed significant differences. The Group 3 and 4 showed significantly smaller inside gaps than the control group which was not made with the two-phase fabrication method. CONCLUSION. The two-stage polymerized technique can improve the fit of the denture base particularly when the separation was made at 10 to 15 mm from the alveolar crest.

• 대한기계학회논문집
• /
• 제13권1호
• /
• pp.178-189
• /
• 1989

본 연구에서는 우선 승용차의 1/10 모형의 형상을 더욱 단순화시킨 2차원 자동차형 물체를 대상으로 하여 그 주위의 압력, 속도 및 난류량의 분포를 측정하고, 또한 울터프트(wool tuft)를 이용한 유동가시화법으로 후류구조를 파악함으로써 향후 계속될 실험적 및 수치해석적 연구의 기초를 마련하고자 한다.

• Coupled systems mechanics
• /
• 제13권4호
• /
• pp.311-335
• /
• 2024

This work aims to show a model to estimate the minimum cost (Thickness and area of steel in X and Y directions) for design a circular isolated footing with eccentric column that considers that the surface in contact with the ground works partially under compression. The formulation is shown by integration to find the moments, the bending shears and the punching shear using the pressure volume under the footing. Some researchers show the minimum cost design for circular isolated footings for an eccentric column assuming that the contact area works completely in compression, others consider the contact surface with the ground working partially in compression for a column in the center of the base. Three numerical examples are developed to obtain the complete design, which are: Example 1 for a column in the center of the base,Example 2 for a column at a distance of 1.50 m from the center of the base in the X direction, Example 3 for a column at a distance of 1.50 m from the center of the base in both directions. Also, a comparison of the new model against the model proposed by other authors is presented. The comparison shows that the new model generates a great saving of up to 43.74% for minimum area and 48.44% for minimum cost design in a column located in the center of the base, and when the column is located at a distance of radius/2 starting from the center of the base in the X direction generates great savings of up to 45.24% for minimum area and 31.80% for minimum cost design. Therefore, it is advisable to use the model presented in this study.