In this study, the buckling restoration at CFRP 3-Point bending specimen composed of 30°, 45°and 60° is investigated when the pressure at the lowest position on the compressed specimen is eliminated. The fracture configuration and stress contour of the specimen can be seen according to the laminate angle of fiber. The result of this study is thought to apply the data for the safe design of CFRP structure.

PURPOSES : The objective of this study is to evaluate the effect of size and depth of cavities on the pavement failure using the full-scale accelerated pavement testing. METHODS: A full-scale testbed was constructed by installing the artificial cavities at a depth of 0.3 m and 0.7 m from the pavement surface for accelerated pavement testing. The cavities were made of ice with a dimension of 0.5 m*0.5 m*0.3 m, and the thickness of asphalt and base layer were 0.2 m and 0.3 m, respectively. The ground penetrating radar and endoscope testing were conducted to determine the shape and location of cavities. The falling weight deflectometer testing was also performed on the cavity and intact sections to estimate the difference of structural capacity between the two sections. A wheel loading of 80 kN was applied on the pavement section with a speed of 10 km/h in accelerated pavement testing. The permanent deformation was measured periodically at a given number of repetitions. The correlation between the depth and size of cavities and pavement failure was investigated using the accelerated pavement testing results. RESULTS : It is found from FWD testing that the center deflection of cavity section is 10% greater than that of the intact section, indicating the 25% reduction of modulus in subbase layer due to the occurrence of the cavity. The measured permanent deformation of the intact section is approximately 10 mm at 90,000 load repetitions. However, for a cavity section of 0.7 m depth, a permanent deformation of 30 mm was measured at 90,000 load repetitions, which is three times greater than that of the intact section. At cavity section of 0.3 m, the permanent deformation reached up to approximately 90 mm and an elliptical hole occurred at pavement surface after testing. CONCLUSIONS : This study is aimed at determining the pavement failure mechanism due to the occurrence of cavities under the pavement using accelerated pavement testing. In the future, the accelerated pavement testing will be conducted at a pavement section with different depths and sizes of cavities. Test results will be utilized to establish the criteria of risk in road collapse based on the various conditions.

PURPOSES: This study identifies the causes and the mechanism of the occurrence of underground cavities. METHODS: A case study on cave-in and a series of model tests with a small soil chamber were conducted. RESULTS: A hypothesis about the mechanism of the cave-in in road was established, and the basic influencing factors on underground cavity expansion were identified. CONCLUSIONS: It was found that the characteristics of shear strength of soil and direction of water flow had a larger influence on cavity formation and expansion than the characteristics of internal erosion. In addition, large cavities suddenly expanded when cavities were caused owing to breakage of buried sewer pipe.

Aquatic ecosystems are receiving various harmful effects due to anthropogenic chemical pollutions. To protect wildlife, risk assessments of the chemicals are conducted using reference indexes of toxicity estimated by species-level laboratory tests and/or micro-/mesocosm community-level studies. However, the existing micro-/mesocosm communities are structurally too complicated, and it is also difficult to compare the experimental results directly with those from species-level tests. Here, we developed a procedure of a simple bi-trophic microcosm experiment which contains the common species (a green algae, Pseudokirchneriella subcapitata and a cladoceran, Daphnia magna) for testing chemical toxicities. For the proper operation of bitrophic microcosm experiment, the minimum required concentration of primary producer (P. subcapitata) is 5×105 cells mL-1. The microcosm system showed higher stability when the initially introduced D. magna population was composed of neonates (<24-h old) than adults and those mixture. This simple microcosm system would be an applicable tool to estimate the disturbing impacts of pollutants on plant-herbivore interactions, and linking the species- and population-/community level risk assessments in the future studies.

PURPOSES : The objective of this study was to evaluate the results of the dynamic immersion test (DIT) through digital image analysis (DIA). METHODS : The asphalt binder retained post DIT was inspected visually by more than three investigators. However, because visual observations can be subjective, depending on the inspector’s skills and knowledge, DIA was also performed. The threshold value for the DIA was determined by a mesh analysis, in which the digital image to be analyzed is divided into very small meshes. In addition, the bitumen bond strength (BBS) test was also performed to the compare the visual results with the mechanical values. RESULTS AND CONCLUSIONS : Depending on the materials used, various methods can be used to predict the behavior of retained asphalt. However, the increasing ratio in the trend of retained asphalt shows different behaviors among the evaluation methods. In this study, the results of the visual observations were significantly different from those of the DIA, the mesh analysis, and the BBS tests. Thus, DIA is an appropriate method for evaluating the results of the DIT. However, in order to use this technique in the field, it is necessary to determine a more reasonable threshold value by performing DIA on various materials.

As CFRP as the single material has various material properties, it has been used at many fields. CFRP is utilized at the mechanical structure on the basis of the brittle fracture property and the performance of vibration damping. CFRP composed of multiple axes has the high natural frequency. It is shown to have more reinforced material property with the fiber design. This paper investigates the fatigue property of the bonded specimen for mode 1 at the laminate angles of 30°, 45° and 60°. According to the fiber design, each specimen bonded with the laminate angle is shown to have different fatigue property repectively. As the laminate angle is increased, the reaction force tends to be increased. In this paper, the laminate angle through the fiber design of CFRP is applied and the fatigue property at mode 1 is investigated. Through the study result, The safety of fatigue fracture is also checked at applying to the composite structure.

Damages of large embankment dams by recent strong earthquakes in the world highlight the importance of seismic security of dams. Some of recent dam construction projects for water storage and hydropower are located in highly seismic zone, hence the seismic performance evaluation is an important issue. While state-of-the-art numerical analysis technology is generally utilized in practice for seismic performance evaluation of large dams, physical modeling is also carried out where new construction technology is involved or numerical analysis technology cannot simulate the behavior appropriately. Geotechnical centrifuge modeling is widely adopted in earthquake engineering to simulate the seismic behavior of large earth structures, but sometimes it can’t be applied for large embankment dams due to various limitations. This study proposes a dynamic centrifuge testing method for large embankment dams and evaluated its applicability. Scaling relations for a case which model scale and g-level are different could be derived considering the stress conditions and predominant period of the structure, which is equivalent to previously suggested scaling relations. The scaling principles and testing method could be verified by modified modeling of models using a model at different acceleration levels. Finally, its applicability was examined by centrifuge tests for an embankment dam in Korea.

현재 아스팔트 포장 분야는 최근의 이상기후(집중호우 및 폭설)로 인하여 수분으로 인한 파손(점착력 약화로 인한 박리 및 포트홀)이 증가하고 있는 실정이다. 이에 국토교통부에서는 『아스팔트 혼합물 생산 및 시공 지침(2014)』의 재료 선정 과정에서 동적수침 시험을 통하여 피복잔류율이 50% 미만이면 박리방 지 재료를 사용토록 규정하고 있다. EN 12697-11에 규정되어있는 동적수침 시험은 골재와 아스팔트 사 이의 박리 저항성 평가하고 이 결과를 통해 아스팔트 혼합물의 수분 저항성을 평가하는 시험법으로, 피복 잔류율 평가는 검사자의 주관적인 육안 평가를 통해 이루어지기 때문에 시험결과의 객관성 및 신뢰성이 부족하다고 할 수 있다. 본 연구에서는 동적수침시험의 객관성 및 신뢰성 향상을 위하여, Digital Image Analysis(DIA)를 도입하였으며, Mesh Analysis를 통하여 DIA의 기준값을 선정하였다. Mesh Analysis 를 위하여 시험 후 건조된 시료를 동일한 조건에서 스캔하여 총 400(20×20) 개의 mesh로 나누어 각 셀 에 대한 피복율을 육안조사를 통하여 총 5 단계의 가중치를 적용하여 계산하였다. DIA는 이미지 파일을 화소(Pixel) 값을 기반으로 처리하는 기법으로, Mesh Analysis에 이용된 25비트 컬러 이미지 파일을 그 레이 이미지(화소값 0(검정색)~255(흰색))로 변환한 후 기준값을 바탕으로 변환된 흑백의 이미지를 이용 하여 피복율을 계산하는 분석방법이다. 보다 객관적인 피복율 비교를 위하여 BBS 시험을 수행하여 얻어 진 점착력을 피복율과 비교하였다. Fig. 1(a)는 피복율과 점착력의 비교결과, Fig. 1(b)는 AP-3를 기준으 로 계산된 피복율과 점착력의 재료에 따른 변동비율 결과를 보여준다. Fig. 1에서 육안평가 결과의 경향은 다른 평가방법과 다른 경향을 나타냈으며 즉, 육안평가는 시료 종 류에 따른 피복율 경향 파악에는 적합한 방법이 될 수는 있으나, 객관적인 피복율 평가에는 미흡한 것으 로 판단된다. 반면에 DIA는 Mesh Analysis 및 BBS 결과와 비교적 유사한 경향을 보였으며, 동적수침시 험의 피복율 평가에 DIA를 적용하는 것은 결과의 신뢰성 및 객관성 측면에서 도움이 될 수 있을 것으로 판단된다.

최근 대도시에서 빈번하게 발생하는 도로함몰로 인해 국민들의 불안감이 증대되는 가운데 도로함몰 발 생 원인 및 위험도 평가를 위한 기초연구가 필요한 실정이다. 이를 위해 한국건설기술연구원에서 보유한 포장가속시험기(Accelerated Pavement Tester, APT) 운영을 통해 동공 심도 및 크기에 따라 아스팔트 포장체 파손에 미치는 영향을 파악하고자 한다. 먼저 예비실험 및 동공 관련 문헌조사 결과 동공 생성에 얼음이 적합한 것으로 판단되어 테스트베드 구축 시 가로×세로×높이가 50cm×50cm×30cm인 얼음을 주문 제작하여 포장가속시험기 바퀴축의 중앙에 깊이 0.3m와 0.7m 지점에 매설하였다. 동공 매설 깊이 와 크기를 결정한 기준은 일본의 도로함몰 위험도 등급 기준과 서울시에서 발생된 동공의 심도 중 그 빈 도가 높은 위치를 선정하였다. 동공 매설 시 내시경 촬영을 위한 관을 매립하여 동공 생성 여부 및 함몰 진행상황을 모니터링 하였다. 테스트베드 구축한 후 FWD 장비를 이용하여 동공을 매설한 동공구간과 매설하지 않은 건전구간의 구 조적 지지력을 측정하였으며, 동공구간이 건전구간보다 처짐값이 약 10% 정도 낮은 것으로 파악되었다. 1차 포장가속시험 후(운행횟수 90,000회) 소성변형량 측정 결과 건전구간은 약 10mm 정도의 소성변형이 발생했으나 동공구간은 약 30mm정도 발생하여 약 3배의 차이가 나는 것으로 파악되었다.

Tracked vehicles for military application such as tank and armored vehicle are operated in severe conditions of driving on gravel road and muddy water including river-crossing. Thus, coating on such vehicles requires more robust characteristics of coating in adhesion, corrosion(salt-spray) resistance and water resistance than those of vehicles for civil applications. Currently, coatings applied on the military equipments are mostly based on the U.S. military specification(known as Mil-SPEC). Typical specifications for primer materials for military application are MIL-P-23377 and MIL-P-53022. And for topcoat, coating material of KDS 8010-1004 specification is typically applied. However, as MIL-P-23377 or MIL-P-530224 is applied for primer coating not only on the tank and armored vehicle at system level but also on the sub-components of these equipments, there has been a need for test data for determining the feasibility of alternatively applying either of these two coatings for primer coat. Therefore, in this study, coating characteristics are compared with respect to these two different primer coating materials so that the feasibility of alternatively applying them is investigated.

This study aims at analyzing the property of the structural body bonded with alumimum foam by the utilization of the aluminum foam of closed type used generally with impact absorbent. The structural bodies bonded with the aluminum foam of DCB and TDCB are designed in this study, and then the fatigue analysis and experiment are carried out. At fatigue analysis, the maximum load happens at all of each specimen models when the fatigue life of 0 to 50 cycle is proceeded. And from the point of time that the maximum load happens, the load at the bonded surface is seen to be decreased in cases of analysis and experiment. As the specimen thickness is increased, the maximum load happened at specimen is increased. It is confirmed that the result of fatigue analysis becomes similar to that of fatigue experiment for verification. It is thought that the study data on various specimen thicknesses can be secured simply without the extra fatigue experimental procedure. By using this study result, the mechanical properties of the structural bodies bonded with the alumimum foams of DCB and TDCB with mode Ⅲ type can be thought to be analyzed effectively.

Buzz, squeak, rattle noise that are referred as BSR have become important part in vehicle's quality because vehicle NVH(noise vibration harshness) reduction technology of main parts like engine and drive-line has made great progress except BSR noise. BSR test is progressed by composing many road excitation power spectrum density(PSD) profiles into a composite PSD profile. Shakers which are input by composite PSD profile make time histories(time-acceleration data) by aggregate of a large number of harmonics related with composite PSD profile in general. But when only composite PSD profile is input to shaker, the time histories from shakers exhibits Gaussian distribution characteristics and can't reflect all road excitation PSD profiles. In this study, we search other studies that try to solve the problems occurring when a shaker is input only PSD profile and analyze time histories resulted from BSR test to check ways of shaker's operation.

Because aluminum foam is porous material, the frature property is different from that of non-porous material. This aluminum foam can be used with the joint bonded with adhesive in order to utilize the light weight to the maximum. So, the study of fracture property on bonded surface can be important. In this study, the analyses on the specimens with two kinds of configuration as DCB(Double Cantilever Beams) and TDCB(Tapered Double Cantilever Beams) aluminum foams of mode Ⅲ type bonded with adhesive are carried out and compared with each other. And the fracture properties the adhesive surfaces of the structure with bonded aluminum foams are studied as the static experiments on these verifications are done. DCB and TDCB specimens used in this study have the variable of thickness(t) as 35mm, 45mm and 55mm. As the result of this study, the range of reaction forces are 0.3 to 0.8 kN and 0.5 to 1.2 kN at DCB and TDCB specimens respectively. The results of the static experiments can also be confirmed with these similar results. These study results can be obtained by only a simulation without the special experimental procedures. The mechanical properties of the bonded structures composed of DCB and TDCB aluminum foams with mode Ⅲ type can be thought to be analyzed effectively.