Recently, in newly constructed apartment buildings, the exterior wall structures have been characterized by thinness, having various openings, and a significantly low reinforcement ratio. In this study, a nonlinear finite element analysis was performed to investigate the crack damage characteristics of the exterior wall structure. The limited analysis models for a 10-story exterior wall were constructed based on the prototype apartment building, and nonlinear static analysis (push-over analysis) was performed. Based on the finite element (FE) analysis model, the parametric study was conducted to investigate the effects of various design parameters on the strength and crack width of the exterior walls. As the parameters, the vertical reinforcement ratio and horizontal reinforcement ratio of the wall, as well as the uniformly distributed longitudinal reinforcement ratio and shear reinforcement ratio of the connection beam, were addressed. The analysis results showed that the strength and deformation capacity of the prototype exterior walls were limited by the failure of the connection beam prior to the flexural yielding of the walls. Thus, the increase of wall reinforcement limitedly affected the failure modes, peak strengths, and crack damages. On the other hand, when the reinforcement ratio of the connection beams was increased, the peak strength was increased due to the increase in the load-carrying capacity of the connection beams. Further, the crack damage index decreased as the reinforcement ratio of the connection beam increased. In particular, it was more effective to increase the uniformly distributed longitudinal reinforcement ratio in the connection beams to decrease the crack damage of the coupling beams, regardless of the type of the prototype exterior walls.

Engineered Barrier Systems (EBS) are a key element of deep geological repositories (DGR) and play an important role in safely isolating radioactive materials from the ecosystem. In the environment of a DGR, gases can be generated due to several factors, including canister corrosion. If the gas production rate exceeds the diffusion rate, pore pressures may increase, potentially inducing structural deterioration that impairs the function of the buffer material. Therefore, understanding the hydraulic-mechanical behavior of EBS due to gas generation is essential for evaluating the longterm stability of DGR. This study employed X-ray computed tomography (CT) technology to observe cracks created inside the buffer material after laboratory-scale gas injection experiments. After CT scanning, we identified cracks more clearly using an image analysis method based on machine learning techniques, enabling us to examine internal crack patterns caused by gas injection. In the samples observed in this study, no cracks were observed penetrating the entire buffer block, and it was confirmed that most cracks were created through the radial surface of the block. This is similar to the results observed in the LASGIT field experiment in which the paths of the gas migration were observed through the interface between the container and the buffer material. This study confirmed the applicability of high-resolution X-ray CT imaging and image analysis techniques for qualitative analysis of internal crack patterns and cracks generated by gas breakthrough phenomena. This is expected to be used as basic data and crack analysis techniques in future research to understand gas migration in the buffer material.

In this study, In this study, structural analysis of a fuel tank for an SUV (sports utility vehicle) was performed for crack prevention design. Reservoir tank analysis was conducted for crack prevention design, and improvement measures for weak areas were discovered and reflected in the design. Pressure analysis was performed on the existing model to analyze weak areas. As a result of analysis through various design changes, it was found that the strength problem of the reservoir tank was due to the discontinuity of the rib inside the tank, and to improve this, it was necessary to minimize the discontinuity section.

본 연구는 Mori-Tanaka 방법 및 멀티스케일 접근 방법을 적용하여 CNT의 굴곡성을 고려한 CNT-복합재 보강 콘크리트 보에 대한 균열해석을 수행하였다. Ad-hoc Eshelby 텐서에 기반하여 CNT의 굴곡성을 기하학적으로 고려하여 폴리머와 합성 하는 방법을 적용하였다. 멀티스케일 방법이 기반하여 CNT 함유량 및 굴곡성 변화에 따른 복합재의 탄성계수 및 강도변화를 추정하였다. 본 해석모델은 기존 문헌과 비교검증하였다. 본 연구에서 도출한 결과는 CNT 함유량과 CNT 굴곡성의 상호관계를 도시하였다. CNT 보강 복합재 구조물의 해석에 있어서 CNT 굴곡성의 중요성을 입증하였다.

LNG 운반선은 선체와 화물창이 일체형인 멤브레인 타입을 적용한 대형선을 중심으로 건조되어 왔으나, 최근 친환경 연료인 LNG의 수요 증가 및 LNG 벙커링 인프라 확대로, 중소형 운반선에 대한 관심이 증가하고 있다. 본 연구에서는 중소형 LNG 운반선에 IMO B 형식 탱크를 적용하고 설계의 안정성 및 적합성을 검증하는 것을 목표로 하였고, B 형식 탱크를 적용하는 경우 필수적으로 수반되는 파괴역학 기반의 균열 진전 해석 및 가스 누출을 대비하여 설치되는 부분 2차 방벽의 크기의 결정을 위한 내용을 소개하였다. LNG 운반선 적용에 적용되는 국제 규정인 IGC 코드를 이용하여 설계 수명동안 균열 진전 해석에 적용될 응력 분포를 산정하는 방법을 제시하였고, Paris 법칙과 British Standard 7910 (BS 79110) 기반의 균열 진전 해석 프로그램을 개발하여 표면 균열 진전 해석을 수행하였다. 다음으로 2차 방벽의 크기를 결정하기 위하여, 초기 관통 균열의 크기를 가정할 수 있는 방법론을 제시하고, 균열 감지 후 회항 가능 기간인 15일 동안의 관통 균열 진전 해석을 수행하여 국제 규정에서 요구하는 B 형식 화물 탱크의 안정성 및 적합성을 검증하였다. 더 정확한 피로 균열 진전 해석을 위하여 코드 기반에 더하여 직접 해석을 통한 해석 절차 개발 및 검증이 필요할 것으로 사료된다.

This study presents the estimation of crack depth by analyzing temperatures extracted from thermal images and environmental parameters such as air temperature, air humidity, illumination. The statistics of all acquired features and the correlation coefficient among thermal images and environmental parameters are presented. The concrete crack depths were predicted by four different machine learning models: Multi-Layer Perceptron (MLP), Random Forest (RF), Gradient Boosting (GB), and AdaBoost (AB). The machine learning algorithms are validated by the coefficient of determination, accuracy, and Mean Absolute Percentage Error (MAPE). The AB model had a great performance among the four models due to the non-linearity of features and weak learner aggregation with weights on misclassified data. The maximum depth 11 of the base estimator in the AB model is efficient with high performance with 97.6% of accuracy and 0.07% of MAPE. Feature importances, permutation importance, and partial dependence are analyzed in the AB model. The results show that the marginal effect of air humidity, crack depth, and crack temperature in order is higher than that of the others.

Engine components subjected to cyclic thermal and mechanical loads may experience low-cycle or high-cycle fatigue failures. In particular, both of these failures can easily occur in aluminum cylinder heads, which are exposed to high temperatures and combustion pressures. Predicting the fatigue characteristics of the cylinder head are very important in the design stage of engine development. In this study, a finite element analysis was performed to predict the low-cycle thermal fatigue around exhaust ports of the cylinder head. Temperature distributions are obtained through the heat transfer analysis considering thermal cyclic test. The analysis result involves large plastic deformations, indicating compressive stresses at high temperatures and subsequently turn into tensile stresses at cold conditions. And the results showed that the critical regions such as exhaust port with large plastic strains coincided well with crack locations from thermal cyclic test. Next, design changes were made to the critical areas of the exhaust ports, and the results showed that the durability was improved by about 60% over the initial model and there were no problems in the thermal fatigue test.

본 논문은 균열선단 그리드 세분화기법을 소개하고 자연요소법을 이용한 균열해석에 이 기법을 적용함으로서 그 유효성을 고찰하였다. 유한요소법에 있어서의 국부적 h-세분화와 같이 높은 응력 특이성을 보이는 균열선단 주위를 따라 자연요소법 그리드를 국부적으로 세분화하였다. 본 논문에서 소개되는 그리드 세분화기법은 2단계로 구성되며, 1단계에서는 그리드 점들이 추가되고 2단계에서는 균열선단 절점을 공유하는 델라우니 삼각형들이 나뉘게 된다. 제안하는 그리드 세분화기법의 타당성과 균열해석에서의 유효성을 입증하기 위해 대칭 엣지 균열을 갖는 평면 변형률 상태의 사각 평판을 해석하였다. 수치해석 결과의 상대비교를 위해 균일한 자연요소 그리드를 이용한 균열해석도 수행하였으며, 균열선단이 세분화된 그리드는 균일한 그리드와는 달리 이론해와 조밀한 그리드와 유사한 균열선단 응력분포를 나타내었다. 또한, 총 그리드 절점수에 대한 해석결과의 전역 상대오차에서도 세분화된 그리드가 균일한 그리드에 비해 높은 수렴율 나타내었다.

Fatigue crack growth retardation of 304 L stainless steel is studied using a neutron diffraction method. Three orthogonal strain components(crack growth, crack opening, and through-thickness direction) are measured in the vicinity of the crack tip along the crack propagation direction. The residual strain profiles (1) at the mid-thickness and (2) at the 1.5 mm away from the mid-thickness of the compact tension(CT) specimen are compared. Residual lattice strains at the 1.5 mm location are slightly higher than at the mid-thickness. The CT specimen is deformed in situ under applied loads, thereby providing evolution of the internal stress fields around the crack tip. A tensile overload results in an increased magnitude of the compressive residual stress field. In the crack growth retardation, it is found that the stresses are dispersed in the crack-wake region, where the highest compressive residual stresses are measured. Our neutron diffraction mapping results reveal that the dominant mechanism is by interrupting the transfer of stress concentration at the crack tip.

Tensile stress occurs and random crack develops in concrete pavement slab when it contracts by variation of temperature and humidity. The tensile stress decreases and the random cracks are minimized by saw cutting the slab and inducing the crack with regular spacing. The sawn or formed joint depth must extend to between 1/4 and 1/3 of the pavement depth to ensure the formation of a clean crack. The ‘Crack inducers (Triangular timber)’ have been installed at bottom of concrete slab to minimize concrete disturbance during initial age. In particular, it is often used to relatively thick airfield pavement compared to road. There are slabs of various thicknesses at the airfield, but the crack inducers are often designed to be installed uniformly without analyzed the joint behaviour to slab thickness. In this paper, the installation of crack inducer considering thickness variation is analyzed and applied. As a result, random cracks or joint freezing wasn’t occurred anywhere on the runway.

본 연구에서 페리다이나믹 이론 모델을 이용하여 준정적하중과 동적 하중, 균열전파와 분기균열 패턴 그리고 등방성재료, 직교 이방성 재료의 균열 진전 해석 등 다양한 조건을 고려한 전산 시뮬레이션을 수행하여 그 적합성을 검토하였다. 초기 균열은 없지만 중심에 홀이 있는 등방성 재료, 초기 균열이 존재하는 등방성 및 이방성 재료에 대한 전산 시뮬레이션이 수행되었다. 조정 동적 완화 기법이 사용되어 준정적 하중을 모사하였고, 이방성 재료 해석에서는 고전 연속체 역학과 페리다이나믹의 변형률 에너지를 고려한 균질화 방법이 사용되었다. 균열 전파와 분기 균열이 성공적으로 확인되었으며 파괴 거동의 시작과 그 방향 역시 페리다이나믹 이론으로 확인되었다. 페리다이나믹을 균질화 방법을 사용하여 비교적 복잡한 이방성 재료에 적용한 경우 역시 실험 결과 값과 비교하여 검증하였다.

Crack in concrete surfaces is one of the earliest signs of decomposition of the essential structure and constant exposure will cause serious damage to the structure and environment. In most of the safety assessment and fracture mechanic applications proposed that these cracks and defects eventually will grow and will have potential lead to in-service failure. Crack in concrete surfaces is one of the earliest signs of decomposition of the essential structure and constant exposure will cause serious damage to the structure and environment. Currently, non-destructive methods are getting popular in the field of inspecting defects in structure and one of them in trends is that using the thermographic image to detect hidden effects. However, the accuracy of the thermal camera, also called resolution, is highly dependent on camera variables such as lens, detector, sensitivity etc. Also, the most important question that needs to be answered for this research is what happens to the image in fog, rain or other climatic conditions where the camera detects crack which exceptionally smaller than most thermographic applications detects. This paper investigates the accuracy of thermal images obtained by the thermal camera under various weather condition and aims at providing information about optimum choice of environmental condition where the more favorable thermal images can be obtained and increase survey reliability and accuracy of the analysis.

본 논문에서는 이종재질로 구성된 세장비가 큰 보의 차원축소와 복원의 효율성과 정확성을 입증하기 위하여 VABS와 3차원 유한요소해석 모델의 결과와 비교하였다. 그리고 3차원 유한요소모델과 차원축소 모델을 가상균열닫힘법을 이용하여 에너지 해방률을 계산하였다. 원형과 사각형의 단면에 초기 크랙을 가진 수치모델을 이용하여 보의 차원축소와 복원기법 및 가상균 열닫힘법을 이용하여 복원해석 결과 및 에너지 해방률을 비교하여 효율성과 정확성을 입증하였다. 특히 제시된 에너지 해방률 계산 기법은 고고도 무인기의 날개, 헬리콥터 로터 블레이드, 풍력 블레이드, 틸트로터 등의 정적, 동적 모델링 및 수명평가에 활용될 수 있을 것이다.