• International Journal of Highway Engineering
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• v.14 no.3
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• pp.59-67
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• 2012

This study presents the evaluation of the patching materials that are used to repair the distress of asphalt pavement. Four kinds of patching materials currently used in practice were tested in both laboratory and field. The laboratory tests included the dry and soaked Marshall stability test, indirect tensile test, wheel tracking test and adhesive strength between the asphalt pavement and the repairing material was tested as a performance test. The field study was conducted using the slab samples placed on the location of vehicle tire passing and the performance of the repairing materials were investigated as passing the traffic load. The result of the laboratory tests were satisfied with the current design criteria and material standard except for water-immersion stability. Type C patching material showed the highest adhesive shear strength among the patching materials tested. However, the mature distress, such as rutting and stripping were monitored after construction in 10 days. It was found that performance of patching material is lack of quality behavior when they were applied in the field and required to develop and applu to prevent the mature distress of the current patching materials.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.2
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• pp.121-127
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• 2011

This paper presents an autonomous formation flight algorithm for micro aerial vehicles (MAVs) and its flight test results. Since MAVs have severe limits on the payload and flight time, formation of MAVs can help alleviate the mission load of each MAV by sharing the tasks or coverage areas. The proposed formation guidance law is designed using nonlinear dynamic inversion method based on 'Leader-Follower' formation geometric relationship. The sensing of other vehicles in a formation is achieved by sharing the vehicles' states using a high-speed radio data link. the designed formation law was simulated with flight data of MAV to verify its robustness against sensor noises. A series of test flights were performed to validate the proposed formation guidance law. The test result shows that the proposed formation flight algorithm with inter-communication is feasible and yields satisfactory results.

• Journal of Korean Society of Forest Science
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• v.88 no.2
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• pp.255-265
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• 1999

This study deals with forest soil characteristics and their effects on the trafficability of logging vehicles. The study area is the national experimental forest located in Kwangnung. This site has 20m length and is equally divided by 5 surveying ranges with 4m width, on which a tractor(FIATAGRI) attached with logging boogie can drive in 4 driving types, namely 1time-return unload, 1time-return with load of 780-790kg weight of 3 logs, 5 and 10times-return with same load. After one driving type on all surveying ranges, the soil hardness is surveyed 5 times with 3 several type tools, SHM-1 type, lang penetrometer(L-PNTM), and clegg impact soil tester(CIST). A disturbed degree of cover vegetation and sliding conditions of vehicle are also observed. As results, the soil type of the test site was SC by USCS and dry brown forest soil. The cover vegetation is gotten trambled under driving after 3-5 times-return, shrubs leaves are fully fallen and their bark are peeled, and after 10 times-return the cover vegetations were nearly disappeared. The test vehicle has neither slided nor was overthrown. The wheel tracks in the 1-3 ranges, of which unit weight(gd, gt) is high and soil moisture content(MC) is low, were only 1-2cm deep, but those in the 4-5 ranges, of which the gd, gt is low and the MC is high, were 5-7cm deep. In the soil hardness test, which was established in 5 test ranges by types of driving, the more driving times, the higher the hardness. The soil hardness surveyed by L-PNTM has changed slowly and that surveyed by SHM-1 type has risen sharply. In the ranges with higher specific gravity(Gs), higher unit weight, lower MC and higher liquid limit(LL) and plasticity index(PI) was the soil hardness high and the trafficability was good. In the ranges with opposite conditions, also in the ranges of the lower soil hardness, the trafficability must be not good, because the wheel track may be deep. The results from CIST attached with 4kg hammer was not better than expected. So it is recommended to use CIST with 2.5kg or 0.5kg hammer.

• Journal of Aerospace System Engineering
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• v.15 no.5
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• pp.81-88
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• 2021

In general, a non-explosive nylon wire cutting-based holding and release mechanism has been used to store and deploy deployable solar panels of CubeSat. However, with this method, accessing the solar panel's access port for charging the cube satellite's battery and electrical inspection and testing of the PCB and payloads while the solar panel is in storage is difficult. Additionally, the mechanism must have a reliable release function in an in-orbit environment, and reusability for stow and deploy of the solar panel, which is a hassle for the operator and difficult to maintain a consistent nylon wire fastening process. In this study, we proposed a pin-puller-based solar panel holding and release mechanism that can easily deploy a solar panel without cutting nylon wires by separating constraining pins. The proposed mechanism's release function and performance were verified through a solar panel deployment test and a maximum separation load measurement test. Through this, we also verified the design feasibility and effectiveness of the pin-puller-based separation device.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.74-79
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• 2019

The military vehicle produces electric power through an engine-integrated serial hybrid generator that is connected to the engine and does not have a separate generator installation space. However, depending on the mechanical characteristics of the connection between the generator and the engine, iron oxide for internal rusting and lubrication grew scattered. The iron oxide is adhered to the starter to deteriorate the starting performance, and there is a problem that the noise of the leg due to wear of the gear is increased. To solve this problem, the connection spline material and the surface treatment of the engine were improved and the shape was changed to a grease sealing type to prevent the generation of iron oxide inside. As the shape of the generator connector composing the shafting system was changed, the integrity of the structure was confirmed through the torsional endurance test. In addition, through the actual vehicle load test, it was verified that no corrosion occurred during the target life span without internal corrosion. It was confirmed that the anti-scattering structure of the grease effectively suppresses the generation of iron oxide, thereby reducing the noise generated from the generator. In this paper, we propose a fundamental solution to the degradation of the starter and the noise generation by preventing the back corrosion caused by the serial hybrid generator installed between the engine and the transmission.

• Magazine of the Korea Concrete Institute
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• v.7 no.1
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• pp.109-116
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• 1995

In tnis study, the impact factors of a simply supported highway bridge due to a vehicle moving across the span are presented. This variable has received cons~derable attention in recent years, both analytically and experimentally. The KBDC specification equation has a maximum 30 percent value which decreases with span length. The results of field tests showed that the dynamic load effects are mostly lower t.hari present KBDC value and that the impact factor does not vary significantly with spar1 as implied in KHUC. The rnain parameters affecting lmpact are the br dge approach. bumps, and other pavement roughness. In thls study, based on test results, three values of impact factors are provided by correlating the roughness of the surface to the deck condition survey values. The present study proposes reasonable impact factors for the strength evaluation of highway bridges. This study may be extended to the evaluation of existing brdges.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.491-497
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• 2014

The corrosion of steel reinforcement in reinforced concrete bridge decks significantly affects the degradation of the capacity. Due to the advantageous characteristics such as high tensile strength and non-corrosive property, fiber reinforced polymer (FRP) has been gathering much interest from designers and engineers for possible usage as a alternative reinforcement for a steel reinforcing bar. However, its application has not been widespread, because there data for short- and long-term performance data of FRP reinforced concrete members are insufficient. In this paper, seven full-scale decks with dimensions of $4000{\times}3000{\times}240mm$ were prepared and tested to failure in the laboratory. The test parameter was the bottom reinforcement ratio in transverse direction. The decks were subjected to various levels of concentrated cyclic load with a contact area of $577{\times}231mm$ to simulate the vehicle loading of DB-24 truck wheel loads acting on the center span of the deck. It was observed that the glass FRP (GFRP) reinforced deck on a restraint girder is strongly effected to the level of the applied load rather than the bottom reinforcement ratio. The study results showed that the maximum load less than 58% of the maximum static load can be applied to the deck to resist a fatigue load of 2 million cycles. The fatigue life of the GFRP decks from this study showed the lower and higher fatigue performance than that of ordinary steel and CFRP rebar reinforced concrete deck. respectively.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.65-73
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• 2002

Underground flexible pipes for electric cables are subject to external loads and surrounding soil pressure. Particularly, strain of flexible pipes is of great concern in terms of safety and maintenance for electric cables. In this paper, stress and strain of flexible pipes with various depth are compared using traditional formula, FEM analysis and model soil box test. The results show that theoretical values are more conservative in strain in comparison with model soil box test and FEM analysis. Considering the strain criteria - maximum 3.5%, flexible pipes can be buried at the depth of 40cm without additional soil improvement. From the result of this study, deformation formula compatible with the field condition was proposed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.203-209
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• 2010

In this study, the fatigue characteristics and life of a woven glass fabric/epoxy laminate composite applied to railway vehicles was evaluated. The fatigue test was conducted using a tension-tension load with a stress ratio R of 0.1 and frequency of 5 Hz. Two types of woven glass fabric/epoxy laminate composite was used in the fatigue test: with and without carbon/epoxy ply reinforcement. In addition, the fatigue life of the woven glass fabric/epoxy laminate composite was compared with that of aluminum 6005, which is used in the car body and underframe structures of railway vehicles. The test results showed that the failure strength and life of the woven glass fabric/epoxy laminate composite reinforced with three carbon/epoxy plies had a remarkable improvement compared with that of the bare specimen without reinforcement.

• Journal of the Korean Institute of Gas
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• v.25 no.5
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• pp.52-56
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• 2021

With the development of an eco-friendly environment and the automobile industry, research is being actively conducted to increase thermal efficiency and reduce exhaust gas through complete combustion in internal combustion engine vehicles. In particular, research is underway to increase engine load and output by understanding the volatility and combustion characteristics of gasoline, and research is underway to reduce soot and harmful gases and realize optimal efficiency based on the distillation and combustion characteristics of diesel fuel. . Therefore, in this study, based on the contents of KS M ISO 3045 on the distillation test method for petroleum products according to the Korean industrial standard, distillation experiments were conducted based on gasoline and diesel from 4 refineries marketed and used in Korea. The distillation experiment confirmed the correlation with the distillation temperature according to the amount of distillation, and the distillation characteristics were analyzed by comparing the distilled fuel to confirm the suitability of meeting the test standards.