• Journal of Mechanical Science and Technology
• /
• v.18 no.5
• /
• pp.770-779
• /
• 2004

This paper describes the micro cutting of wear resistant tungsten carbides using PCD (Poly-Crystalline Diamond) cutting tools in performance with SEM (Scanning Electron Microscope) direct observation method. Turning experiments were also carried out on this alloy (V50) using a PCD cutting tool. One of the purposes of this study is to describe clearly the cutting mechanism of tungsten carbides and the behavior of WC particles in the deformation zone in orthogonal micro cutting. Other purposes are to achieve a systematic understanding of machining characteristics and the effects of machining parameters on cutting force, machined surface and tool wear rates by the outer turning of this alloy carried out using the PCD cutting tool during these various cutting conditions. A summary of the results are as follows: (1) From the SEM direct observation in cutting the tungsten carbide, WC particles are broken and come into contact with the tool edge directly. This causes tool wear in which portions scrape the tool in a strong manner. (2) There are two chip formation types. One is where the shear angle is comparatively small and the crack of the shear plane becomes wide. The other is a type where the shear angle is above 45 degrees and the crack of the shear plane does not widen. These differences are caused by the stress condition which gives rise to the friction at the shear plane. (3) The thrust cutting forces tend to increase more rapidly than the principal forces, as the depth of cut and the cutting speed are increased preferably in the orthogonal micro cutting. (4) The tool wear on the flank face was larger than that on the rake face in the orthogonal micro cutting. (5) Three components of cutting force in the conventional turning experiments were different in balance from ordinary cutting such as the cutting of steel or cast iron. Those expressed a large value of thrust force, principal force, and feed force. (6) From the viewpoint of high efficient cutting found within this research, a proper cutting speed was 15 m/min and a proper feed rate was 0.1 mm/rev. In this case, it was found that the tool life of a PCD tool was limited to a distance of approximately 230 m. (7) When the depth of cut was 0.1 mm, there was no influence of the feed rate on the feed force. The feed force tended to decrease, as the cutting distance was long, because the tool was worn and the tool edge retreated. (8) The main tool wear of a PCD tool in this research was due to the flank wear within the maximum value of $V_{max}$ being about 260 $\mu\textrm{m}$.

• Korean Journal of Agricultural Science
• /
• v.23 no.1
• /
• pp.25-38
• /
• 1996

To investigate the stability problem of irrigation-drainage channel excavation slope on soft ground, analyzed the behavior of the soft ground with excavation slope by the limit equilibrium method and the finite element method, and compared with field tests. The results of this study were summarized as follows; 1. When rapid drawdown the water level, the crack was occurred by the effect of the excess pore water pressure, and the pore water pressure was decreased slowly. 2. As the width of excavation was larger, the crack width was larger. And, excavated depth was deeper, the progressive failure was appeared. 3. When the soft ground excavation was small-scale, the minimum safety factor was more effected by cohesion(1.0, 1.5, 2.0, 2.5, 3.0) than excavated slope inclination(1:l, 1:1.5, 1:2). 4. As excavation was progressed, the settlement occurred on the top-slope due to plastic domain, and heaving was occurred at the bottom of excavation. 5. The maximum shear stress was appeared greatly as the base part of slope went down. Because of the increase of the maximum shear stress, tension area occurred and local failure possibility was increased. 6. As the excavation depth was increased, the maximum shear strain was appeared greatly at the base of slope and distribution pattern was concentrated beneath the middle of slope.

• Journal of Conservation Science
• /
• v.30 no.4
• /
• pp.427-438
• /
• 2014

To measure the depth and extension on the surface cracks of the stone monument, ultrasonic pulse velocity targeted at the Mulgyeseowon Stele in Changnyeong was used in this research. Additionally, to establish a long-term countermeasure of management and conservation for this stele, we have investigated the material properties and damage on it and have conducted a precise diagnosis by a variety of non-destructive techniques. Our research has revealed that stones of the stele are composed mainly of three rock types according to the parts of it, alkali-feldspar granite, gabbro and diorite. The result of the deterioration evaluation has occurred that cracks, which are observed from every direction in the body of the stele, are the significant factors to reduce structural stability. The ultrasonic velocity for an evaluation on the properties of the stele has revealed that the speed was high in the order of body, pedestal and crown. Furthermore, to understand the present condition and occurrences of the cracks which have measured in many different forms on the stele quantitatively, we have estimated from 0.6 to 24.1cm deep of the cracks by To-Tc method using ultrasonic velocity.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.37 no.2
• /
• pp.389-395
• /
• 2017

A study was carried out to improve the field implementation of asphalt surface reinforcement method which is a preventive maintenance. Mean Texture Depth (MTD) was measured to quantify the surface condition and used to determine the optimum application rate. Determining the application rate using MTD can reduce the material loss from 30% to 15%. In order to reduce the curing time to 30 minutes, the heat capacity of $317kcal/m^2$ is required. Therefore, the design capacity of the heating curing device requires more than 380,000 kcal/hr. The asphalt surface reinforcement method is preferably applied at a time when slight cracking occurs before the permanent deformation becomes serious. Through the analysis of the pavement survey data, it was decided to apply the surface reinforcement method at the crack rate of 3~4%. Heating the surface reinforcement agent to $50^{\circ}C$ improves workability and ensures sufficient penetration depth even at a crack width of 1 mm. The results will be utilized as basic data for the development of automated construction equipment for efficiency improvement.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.15 no.3
• /
• pp.3059-3088
• /
• 1973

The Object of research was laid on the dry paddy field which had a low level of underground water, rather than on a paddy field with a high level of underground water. In the treatment of the clay paddy field before transplanting we employed 3 kinds of methods; deep plowing, development of cracks by drying the surface of the field under which pipe drain was built. This study was to find which one, among these three methods, is the most effective to let roots extend to deep zone and increase the yield of rice and at the same time, for trafficability of large scale machinery which will be introduced to the harvest, in the light of the earth bearing capacity in relation with underground drainage. In the treatments of plots, 1) the kyong plot was plowed 39 days before transplanting and dried, 2) the kyun plot was plowed again 2days before transplanting after plowing 39 days before transplanting, leveling field surface in the saturation with water and developing the cracks by drying, 3) the kyunam plot was plowed again 2 days before transplanting after setting the drainage pipe and at the same time plowing 39 days before transplanting, leveling field surface in the saturation with water and developing the cracks by drying. Also each plot above had three different levels of soil depth, respectively; that is 15cm, 25cm, 35cm. The kyong plot with 15cm-depth was he control. The results obtained were as follows; 1. The kyunam plot showed a remarkably lager amount of water consumption by better underground drainage than the kyong and the kyun plot, and the kyong plot indicated a greater amount of water consumption than the kyun plot. Therefore the amount of available rainfall was decreased in the order of kyunam>kyong>kyun. The net duty of water decreased in the order of kyunam>kyong>kyun and its showed about 105cm in depth at the kyunam plot, about 70cm in depth at the kyong plot and about 45cm in depth at kyun plot, regardless of soil depth. 2. According to the tendency that the weight of the total root was effected by the maximum depth of the crack, it seemed that the root development was more affected by the depth of the crack than by only the crack itself. The weight of the total roots tended to increase as the depth of the crack got deeper and deeper, and the weight of the total roots was increased in the order of kyun<kyunam<kyong. 3. In the growing of the plant height, the difference did not appear at the beginning of growing(peak period of tillering) of any plot, But for the mid period of growing(ending period of tillering) to the period of young panicle formation, the deeper the depth of plot is, the more the growing goes down. On the contrary at the late period of growing, growth was more vigorous in the plot with deep depth than in the plot with shallow depth. Since the midperiod of growing, in the light of experimental treatment, the kyun plot was not better in growing than the other two plots and no remarkable defference was shown between the kyunam and the kyong plot, but the kyunam plot had the tendency of superiority in growing plant height. 4. As the depth of plot went deeper, the decreasing tendency was shown in the number of tillers through a whole period of growingi. When the above results were observed concering each plot of experimental treatment, the kyun plot was always smaller in the number of tiilers than the kyunam and the kvong plot, and the kyong plot was slightly larger than the kyunam plot in the number of tillers. 5. When each plot of the different experimental treatments was compared with the control plot(15-kyong), yield(weight of grains) was increased by 17% for the 35-kyong plot, by 10% for the 35-kyunam and yields for the other plots were less or nomore than the control plot. On the whole, as the depth of plot went deeper, yields for plots was increased in the order of kyong>kyunam>kyun. 1% of significance between the levels of depths and 5% of significance between the treatments were shown. 6. The depth of consumptive water which was more effective on the weight of grains is that of the last half period. When the depth of consumptive water was increased at the range of less than 2.7cm/day in the 15cm plot, 3.0cm/day in the 25cm plot and 3.3cm/day in the 35cm plot, the weight of grains was increased, and at the same time the weight of grains was increased as the depth of plot went deeper. The deeper plots was of advantage to the productivity at the same depth of consumptive water. 7. The increase in the weight of grains in propertion to the weighte of root showed a tendency to increase depending on the depth of plot at each plot of the same weight of roots. The weight of roots and grains together increasezd in the order of kyun>kyunam>kyong, considering each treatment of experimental plot. The weight of grains was in relation to the minimum water content ratio during the midperiod of surface drainage and the average earth temperature was mainly affected by the minimum water content ratio because it was relatively increased in proportion to the water content ratio(at less than 40%) 8. The weight ratio of straw to grain showed an increasing tendency at the plot of shallow depth and had a relation of an inversely exponental function to the weight of roots. At the same depth of plot except the 15cm plot, the weight ratio of straw to grain was increased in proportion to the depth of consumptive water. The weight of grains was increased as the depth of consumptive water was increased to some extent, but at the same time the weight of ratio of straw to grain was increased. 9. At a certain texture of soils the increase in the amount of the cracks depends on meteorological conditions, especially increase in amounts of pan evaporation. So if it rains during the progressing of field drying the cracks largely decrease. The amount of cracks of clay soil had relation of inversely exponental function to the water content ratio(at more than 25%). The maximum depth of crack kept generally a constant value at less than 30% of water content ratio. 10. The cone index showed the tendency that it was propertional to the amount of cracks within a certain limit but more or less inversely proportional over a certain limit. The water content ratio at the limit may be about 25%. 11. The increase in the cone index with the progressing of time after final surface drainage showed the tendency that it was proportional to the depth of consumptive water at the last half of growing period. Based on the same depth of if the cone index in the kyunam plot was much larger than in the other two plots and that in the kyong plot was much smaller than in the kyun plott, as long as the depth of plot was deeper, especially in the 35-kyong plot. 12. In the light of a situation where water content ratio of soil decreased and the cone index increased after final surface drainage the porogress of the field dryness was much more rapid in the kyunam plot than in the kyong plot and the kyun plot, especially slowest in the kyong plot. In the plot with deeper zone the progress was much slower. The progress requiring the value of the cone index, $2.5kg/cm^2$, that working machinary can move easily on the field changed with the time of final surface drainage and the amount of rainfall, but without nay rain it required, in the kyunam plot, about 44mm in total amount of pan evaporation and more than 50mm in the other two plots. Therefore the drying in the kyunam plot was generally more rapid in the kyunam plot was generally more rapid over 2days than in the kyun plot, and especially may be more rapid over 5days than in the 35-kyong plot.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.2
• /
• pp.235-253
• /
• 2018

Groundwater flow induced by cracks in a buried pipe causes ground loss in the vicinity of it which can lead to underground cavities and sinkhole problems. In this study, the ground collapse mechanism and the failure mode based on an aperture in the pipe located in cohesionless ground were investigated through a series of physical model studies. As the influence parameters, size of the crack, flow velocity in the pipe, groundwater level, ground cover depth and ground composition were adopted in order to examine how each of the parameters affected the behavior of the ground collapse. Influence of every experimental condition was evaluated by the final shape of ground failure (failure mode) and the amount of ground loss. According to the results, the failure mode appeared to be a 'Y' shape which featured a discontinuous change of the angle of erosion when a groundwater level was equal to the height of the ground depth. While in the case of a water table getting higher than the level of ground cover depth, the shape of the failure mode turned to be a 'V' shape that had a constant erosion angle. As the height of the ground depth increased, it was revealed that a mechanism where a vertically collapsed area which consisted of a width proportional to the ground height and a constant length occurred was repeated.

• Journal of the Korea Concrete Institute
• /
• v.22 no.2
• /
• pp.199-208
• /
• 2010

In order to substitute FRP bar for steel bar in new structures, it is necessary to establish a reliable design code. But relatively little research has been conducted on the material in Korea. So, a total of 22 beam specimens (18 GFRP reinforced concrete and 4 conventional steel reinforced concrete) were constructed and tested. In the first phase of the experiment, it was carried out to observe flexural behavior, and collect deflection and crack data. In order to eliminate of the uncertainty by the shear reinforcements and induce flexural failure mode, any stirrup were not used and only shear span-depth ratio were adjusted. However, almost beams were broken by shear and the ACI 440.1R, CSA S806, which were used to design test beams, showed considerable deviation between prediction and test results of shear strengths. Therefore in the second phase of the study, shear failure modes and behavior were observed. A standard specimen had dimensions of 3,300 mm long ${\times}$ 800 mm wide ${\times}$ 200 mm effective depth. Clear span and shear span were 2,800 mm, 1,200 mm respectively. Control shear span-depth ratio was 6.0. Four-point bending test over simple support was conducted. Variables of the specimens were concrete compressive strength, type and elastic modulus of reinforcement, shear span-depth ratio, effective reinforcement ratio, the effect of bundle placing method and cover thickness.

• Restorative Dentistry and Endodontics
• /
• v.13 no.2
• /
• pp.337-348
• /
• 1988

The purpose of this study was to examine the fracture strength and characteristics of teeth with MOD cavity preparation. Freshly extracted sound maxillary premolars were cleaned and stored in normal saline solution $37^{\circ}C$ for 72 hours before experiments. The roots of teeth were embedded in a self-curing resin, and the exposed crown were maintained in a vertical position by a modelling wax in a brass ring. The MOD cavities were prepared with No. 57 carbide bur under high speed to a depth of 2.0mm and a width of 2.0mm(Fig.1). All the prepared teeth specimens were divided into 7 groups according to the mode of cavity form and restorative materials (Table 1, 2): Group I, unpreapred, intact teeth as control Group II, prepared cavity without restoration Group III, prepared teeth restored with amalgam Group IV, prepared teeth restored with composite resin (P-10) Group V, prepared teeth with beveled enamel margins restored with composite resin (P-10) Group VI, prepared teeth restored with light-cured composite resin (P-30) Group VII, prepard teeth with beveled enamel margins restored with light-cured composite resin (P-30) After placement of restorations, all of the specimens were stored in water at $37^{\circ}C$ for 72 hours before testing. All of the specimens were tested on the Instron Universal Testing machine (No. 6025) in order to evaluate the strength of fracture. One metal ball 5.0mm in diameter contacting the specimens parallel to the occlusal surface was used to in this study (Fig. 1). The fracture characteristics of the specimens were examined with naked eye and in the scanning electron microscope (JSM-20). The results obtained from this study were as follows: 1. The mean fracture strength was the highest in group VI and that in group II was the lowest. 2. The progress of crack of teeth propagated into the pulp cavity. 3. In case of the group of the restored teeth, the crack occurred to be accompanied with cuspal fracture. 4. The crack of restored teeth was initiated along the pulpo-axial line angle of the cavity.

• Journal of Conservation Science
• /
• v.24
• /
• pp.1-11
• /
• 2008

The Unhyungung Water Container in the possession of the Seoul Museum of History in Korea is consisted of a calcareous marble developed laminated bedding and numerous argillaceous veinlets. This monument should need to conservation treatment because of black discoloration and seriously numerous cracks. Vertical and horizontal cracks in the monument are developed following stratification and argillaceous veinlets that are relatively low coherence between the rock materials. We have proved that the material inducing discoloration on the surface is carbon which is formed by deposited organic matters. As the result of the ultrasonic measurements, although highly surface weathering degree, the physical properties of the Unhyungung Water Container is confirmed slightly weathered state. The depths of cracks in the monument are calculated at maximum 60mm in some cracks completely penetrating into the wall and at minimum 9mm in the other crack. The cracks, developed following veinlet, are revealed that there penetrate from an outer wall to an inside wall for the monument. And most depths of cracks, developed following stratification, are calculated 20 to 30mm. This result will offer a significant data for conservation of the Unhyungung Water Container.

• International Journal of Highway Engineering
• /
• v.11 no.2
• /
• pp.141-149
• /
• 2009

This study was conducted to investigate the causes that induce the T-shape cracks at the joints in the jointed concrete pavements(JCPs). The finite element models of JCP including dowel bars were developed and the stress distribution in the slab was investigated under environmental loads. To investigate the effect of dowel bars on the transverse stresses at the joints that induce the T-shape cracks, the slab curling behavior was analyzed with and without dowel bars. In addition, the stress concentration was investigated when the dowel bar was not installed at the mid-depth of the slab. The results of this study showed that the transverse stresses were not affected by the dowel bars if the dowel bars were installed at the mid-depth of the slab. However, if the dowel bars were not installed at the mid-depth, the transverse stresses were concentrated at the dowel bar locations when the slab curled. The stress concentration was dependent on the contact characteristics between the dowel bar and concrete, and was significantly large when the dowel bar not installed at the mid-depth was located far from the edge of the slab. Therefore, to mitigate T-shape cracking in JCP, dowel bars should be very carefully installed and leveled at the proper locations.