• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1259-1268
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• 1995

The stress distribution around micro holes and the behavior of stress interaction between micro holes are considerd in the study. Several conclusions are extracted as follows : (1) The stress interaction varies with the distance e between micro holes. When the two micro holes are spaced in such a manner that theri two closest points are separated by a distance of micro hole radius (e=1), stress distribution is affected by a opposite micro hole in all the closest region. In addition, if two closest points are seperated by twice the distance of a micro hole radius (e=2), stress distribution is affected by a opposite micro hole in the region of -0.8.leq.x/r.leq.0.8 and the interaction effect can be neglected for e=4. (2)If the depth becomes larger than the radius, or the radius varies, the shape and magnitude of stress distribution around micro holes varies. (3) Hoop stress around a micro hole for the two dimensional configuration is larger than that of the three dimensional micro hole located on the surface of material for .theta. < 60.deg., but it is reversed for .theta > 60.deg.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.2
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• pp.154-161
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• 1995

In order to analysis of the stress distribution around flaws and the interaction effects between fatigue cracks, stress around micro hole was analyzed by Finite Element Method(F.E.M.) and micro hole specimens were tested using rotary bending fatigue machine and twisting fatigue machine to identify stress effects for fatigue cracks initiating from micro holes and interaction effects between micro holes. The results are as follows : Interaction effects of .sigma. $_{y}$for the micro hole side is larger than the large micro hole side when the interval between micro holes is near. Stress concentration factor increase as the diameter of micro hole becomes smaller. But, stress field of micro hole is smaller than that of large micro hole at h .leq. r (h:depth of micro hole, r:radius of micro hole) and that of large hole is larger than that of small micro hole at h >r expect the small range from micro hole.e.

• International Journal of Precision Engineering and Manufacturing
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• v.3 no.2
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• pp.72-77
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• 2002

In this paper, a simple method to measure the residual stress in microstructure is presented. In order to find the residual stress in micro-machined beam, the first natural frequency of the beam that has the residual stress inside is analyzed using Rayleigh's energy method. Micro gold electroplated structure is fabricated by surface micro-machining process including electroplating. The made structure is an approximate shape of clamped-clamped beam and its 1 st natural frequency is measured by resonance method. For the better estimation of the residual stress, an equivalent length of micro-fabricated beam to ideal beam is calculated by FEM. The residual stress was estimated from the equivalent length and the measured natural frequency. It was found that a tensile stress was residue in the micro beam structure.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.12
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• pp.195-200
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• 2000

In order to find a residual stress in the micro-machined beam, first natural frequency of the beam that has the residual stress inside is analyzed using the Rayleigh's energy method. Micro gold electroplated structure is fabricated by surface micro-machining process. The made structure is clamped-clamped beam and its 1st natural frequency is measured by resonance method. For the better estimation of the residual stress, an equivalent length of micro-machined beam to ideal beam is calculated by FEM. The residual stress is estimated from the equivalent length and the measured natural frequency.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.179-186
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• 2005

A comparative study of stress distributions in the maxillary bone with three different types of abutment was conducted. Finite element analysis was adopted to determine stress generated in the bone with the different implant systems with micro threads (Onebody type implant, Internal type implant, and External type implant). It was found that the types of abutments and the number of micro threads have significant influence on the stress distribution in the maxillary bone. They were due to the difference in the load transfer mechanism and the size of contact area between abutment and fixture. Also the maximum effective stress in the maxillary bone was increased with increasing inclination angle of load. It was concluded that the maximum effective stress in the bone was the lowest by the internal implant among the maximum effective stresses by other two types of implants and by appropriate number of micro threads, and that the specific number of micro thread was existed to decrease the maximum effective stress in the maxillary bone due to different implant systems and loading conditions.

• Journal of the Korean Society of Safety
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• v.14 no.3
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• pp.25-32
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• 1999

This study has been performed to investigate the stress distribution around defects that behave as stress concentrators. Besides, the effect of stress interaction effects on the initiation of primary cracks were also investigated by rotary bending fatigue tests which were performed with specimens drilled micro surface defects and the stress distribution was analyzed using Finite Element Method. In addition, the stress interaction effects around defects and cracks were investigated by comparing the results of experiments and F.E.M. The results obtained are summarized as follows ; 1) Area which slip and micro cracks initiated at micro surface defects is between the maximum shear stress points and this area is over than ${\pm}30^{\circ}$ from the maximum stress point along the defect edge. 2) The stress interaction effect for the small size defect is larger than that of large size defect when the interval between them is near 3) Interval which there is no shear stress interaction effect analyzed by F.E.M. is larger than that of experimental results.

• Journal of Ocean Engineering and Technology
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• v.1 no.2
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• pp.74-82
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• 1987

This study has been made to investigate into the behavior of fatigue limit, of fatigue crack initiation, and of fatigue crack propagation under the condition of rotating bending stress; specifically on the independency of stress field as well as the crack behavior of surface micro hole defect, which is made artificially through the specimen. The results obtained can be summarized as followa; 1) For the single micro hole defect, initiation of fatigue crack is occurred at both tips of microhole defect simultaneosly along the slip which are produced in the range of maximum principal stress arround micro hole defect independent of the size of micro hole defect. 2) For the neighbored deuble micro hole defects with equal size, in the range ($\frac{L}{r}$)ratio $\gtrsim$ 3 defined as the size of micro hole defect(2r) to the distance between the centers of micro hole defects (2L), the crack behavior of the micro hole defects is same as single one. However, for the range of $\frac{L}{r}$<3, the interference effect becomes significant as the ratio approaches to 1.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.560-566
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• 2000

Many researchers have dealt with the problems of fracture mechanics. Generally, these researches are concerned with crack in isotropic material without other micro defects. Actual structure, however, may contain micro defects as well as crack in manufacture processing or operation. If it contains mi defects near a crack, some different characteristics will be appear in fracture behaviors of the crack. This study examines the effect of the micro defect on stress intensity factor of center slant crack rectangular plate subjected to uniform uniaxial tensile stress. In this study, boundary element method(BEM) is used for analysis in stress intensity factor(SIF).

• New & Renewable Energy
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• v.6 no.1
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• pp.38-45
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• 2010

Abstract Under the physical stress on photovoltaic (PV) module, it will be warped according to elongation of the front glass and then micro-crack will be occurred in the thermally sealed solar cell. This micro-crack leads to drop of short circuit current of the PV module. This is because of increase of resistance component by micro-crack. Micro-crack at specific solar cell in the module lessens the durability of PV module with reduced output, hot-spot caused by solar cell output mismatch and increased resistance component. This study shows the relation between electrical characteristics and micro- cracks due to mechanical stress on PV module.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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• pp.128-139
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• 1998

In this paper, a finite element method for predicting the temperature and stress distributions in micro-machining is presented. The work material is oxygen-free-high-conductivity copper(OFHC copper) and its flow stress is taken as a function of strain, strain rate and temperature in order to reflect realistic behavior in machining process. From the simulation, a lot of information on the micro-machining process can be obtained; cutting force, cutting temperature, chip shape, distributions of temperature and stress, etc. The calculated cutting force was found to agree with the experiment result with the consideration of friction characteristics on chip-tool contact region. Because of considering the tool edge radius, this cutting model using the finite element method can analyze the micro-machining with the very small depth of cut, almost the same size of tool edge radius, and can observe the 'size effect' characteristic. Also the effects of temperature and friction on micro-machining were investigated.