• 한국정밀공학회지
• /
• 제32권1호
• /
• pp.57-61
• /
• 2015

A spindle unit is very important in machine tools. It has a direct effect on machining accuracy. The static and dynamic characteristics of the spindle unit should be considered in the initial design stage for manufacturing of precision product. This study describes an investigation for deriving design stability of a 20,000rpm heavy-cutting spindle for precision machining. Static and dynamic characteristics of the spindle, such as deformation, stress, natural frequency and mode shapes are analyzed using finite element analysis. The 20,000rpm heavy-cutting spindle is confirmed that it is successfully designed through finite element analysis.

• Tribology and Lubricants
• /
• 제31권4호
• /
• pp.148-156
• /
• 2015

In the study, a design process for ensuring optimal clearance in a fuel injection pump(FIP) is suggested. Structure analysis and hydrodynamic lubrication analysis are performed to determine the optimal clearance. The FIP is simulated using Hypermesh, Abaqus 6.12 to evaluate the reduction of clearance when the maximum supply pressure is applied. The reduction in clearance is caused by the difference in the deformations between the barrel and plunger. When the deformation of the plunger is larger than that of the barrel, a reduction in clearance at the head part occurs. On the other hand, the maximum clearance reduction equals the maximum deformation in the stem part, because the deformation of barrel does not occur in this region. The clearance of FIP should be designed to be larger than maximum reduction of clearance in order to avoid contact between the plunger and barrel. In addition, the two-dimensional Reynolds equation is used to evaluate lubrication characteristics with variations of viscosity, clearance and nozzle for a laminar, incompressible, unsteady state flow. The equation is discretized using the finite difference method. The lubrication characteristics of FIP are investigated by comparing film parameter, which is the ratio of the minimum film thickness and surface roughness. The optimal clearance of FIP is to be designed by considering the maximum reduction in clearance, lubrication characteristics, machining limits and tolerance of clearance.

• 한국도로학회논문집
• /
• 제14권4호
• /
• pp.29-36
• /
• 2012

PURPOSES : Plastic deformation is frequently made in intersection asphalt pavement at its early age due to deceleration and stoppage of vehicles. This study has been performed to provide a mechanistic basis for reasonable selection of paving method to minimize the plastic deformation at intersection. METHODS : Pavement layer, temperature, traffic volume of the intersections managed by the Daejeon Regional Construction and Management Administration were collected to calculate asphalt dynamic modulus with pavement depth by using a prediction equation suggested by the Korean pavement design guide. Performance of ordinary dense-graded asphalt pavement, polymer modified asphalt pavement, and fiber reinforced asphalt pavement was analyzed by finite element method and the results were used in a performance model to predict the plastic deformation. RESULTS : In aspect of performance, the three paving methods were usable under low traffic while the fiber reinforced asphalt pavement was the most suitable under heavy traffic. CONCLUSIONS : Reasonable paving method suitable for traffic characteristics in the intersection might be decided by considering economic feasibility.

• 대한조선학회논문집
• /
• 제53권3호
• /
• pp.195-200
• /
• 2016

In this study, compression tests for the polyisocyanurate foam which is recognized as the insulation material for the storage tank of the liquefied natural gas (LNG) were carried out for investigation of the material characteristic of mechanical behavior. Deformation recovery ratio according to the various initial deformation levels were estimated and the mechanical behavior of foams that are experienced compressive deformation was also obtained experimentally. The test results were analyzed based on the conditions of initially applied strain level and engineering strain rate.

• 대한기계학회논문집A
• /
• 제29권1호
• /
• pp.132-138
• /
• 2005

In heavy industrial fields such as power plant and chemical plant, it is often necessary to restore damaged part of large machinery and structure which is installed in the hazard working place. In this paper, to estimate stress distribution which occurs during damage and restoration of cylindrical beam structure, the finite element technique has been used. A finite element model was verified by experiment for non deformed cylindrical beam structure. The displacements and elastic recovery have an excellent agreement between experiment and finite element analysis. The variations of stress distribution on deformation and restoration procedure for surfaces have been examined. The maximum von Mises stress appears in the surface for deformation and restoration procedure. In deformation procedure, the maximum stress occurs in the vicinity of support body. In restoration procedure, the maximum stress occurs in the vicinity of the fixing body. The fixing body allows avoiding stress concentration in adjacent support structure boundary.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제7권5호
• /
• pp.805-816
• /
• 2015

In the present study, external restraints imposed normal to the plate during the cooling stage were determined to be effective for reduction of the angular distortion of butt-welded or fillet-welded plate. A welding analysis model under external force during the cooling stage was idealized as a prismatic member subjected to pure bending. The external restraint was represented by vertical force on both sides of the work piece and bending stress forms in the transverse direction. The additional bending stress distribution across the plate thickness was reflected in the improved inherent strain model, and a set of inherent strain charts with different levels of bending stress were newly calculated. From an elastic linear FE analysis using the inherent strain values taken from the chart and comparing them with those from a 3D thermal elasto-plastic FE analysis, welding deformation can be calculated.

• Journal of Welding and Joining
• /
• 제23권4호
• /
• pp.48-52
• /
• 2005

To estimate welding deformation for large steel structures, either experiment result with small specimen or analysis result of FEM with small numerical model is used. Consequently, it is important to decide the welding length of specimen and numerical model not to have an effect on welding deformation for accurate estimation of whole welding deformation. This study experimentally clarifies the effect of welding length on angular distortion due to welding by varying welding length of specimens, but fixing width and thickness of specimens on V-groove butt welding, fillet welding and bead on plate welding. As a resell the critical welding length on fillet welding and on bead on plate welding is over 500mm and on V-groove butt welding is over 1,000mm.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제7권1호
• /
• pp.157-173
• /
• 2015

In the present study, the existing equivalent stain method is improved to make up for its weaknesses. The improved inherent strain model is built considering more sophisticated three dimensional constraints which are embodied by six cubic elements attached on three sides of a core cubic element. From a few case studies, it is found that the inherent strain is mainly affected by the changes in restraints induced by changes of temperature-dependent material properties of the restraining elements. On the other hand, the degree of restraints is identified to be little influential to the inherent strain. Thus, the effect of temperature gradients over plate thickness and plate transverse direction normal to welding is reflected in the calculation of the inherent strain chart. The welding deformation can be calculated by an elastic FE analysis using the inherent strain values taken from the inherent strain chart.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2013년도 춘계학술대회 논문집
• /
• pp.809-810
• /
• 2013

• Journal of Welding and Joining
• /
• 제30권6호
• /
• pp.120-125
• /
• 2012

Because ships and offshore structures have very large dimensions and complicated shapes, it is difficult to determine the deformation or internal stress in the structure by simple lab tests. Thus, a rigorous analysis by using the computer simulation technology is essential for obtaining their distortions by considering the entire production process characteristics. The rapid development of computer technology made it possible to analyze the heat transfer phenomena, deformation and phase transformation in the welded joint. For large shell structures, shell elements modeling contributed primarily to this development. But if a welding is done by multi-pass, shell elements whose thickness are unchangeable can hard to describe the local situation. Recently, it was researched how to introduce the imaginary temperature for V grooved multi-layer butt welding in strain-boundary method (a kind of shrinkage methodologies). In the present study, we formulated the imaginary temperature for the double bevel and double V groove by considering the thickness change of each pass through the bead and the thickness directions simultaneously and also demonstrated the feasibility of the formula by applying it to the thermal distortion analysis of the erection process of crane pedestal.