• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.634-644
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• 2000

Fatigue crack growth and life is estimated by various fracture mechanical parameters but affected by load, material and environment. Fatigue character of component without surface notch cannot be e valuated by above-mentioned parameters due to microstructure of in-service material. Single fracture mechanical parameter or nondestructive parameter cannot predict fatigue damage in arbitrary boundary condition but multiple fracture mechanical parameters or nondestructive parameters can Fatigue crack growth modelling with three point representation scheme uses this merit but has limit on real-time monitoring. Therefore, this study shows fatigue damage model using backpropagatior. neural networks on the basis of X-ray half breadth ratio B/$B_o$ fractal dimension $D_f$ and fracture mechanical parameters can predict fatigue crack growth rate da/dN and cycle ratioN/$N_f$ at the same time within engineering estimated mean error(5%).

• Journal of Korean Society of Steel Construction
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• v.23 no.1
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• pp.29-39
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• 2011

With regard to steel construction, many studies have been performed to examine the structural behavior of the bolted connections domestically and in other countries. Especially, a domestic study was conducted on the block shear fracture and shear lag effect on the single-bolted angle connection in carbon steel. In this study, specimens were prepared with the end distance parallel to the loading direction and bolt arrangement ($1{\times}1$, $1{\times}2$), as the main variables. Then the fracture mode and the curling effect on the bolted angle connection in austenitic stainless steel were investigated. Moreover, the fracture mode and ultimate strength were compared, and the strength reduction by curling was estimated.

• Computers and Concrete
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• v.2 no.6
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• pp.499-516
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• 2005

A composite model is used to represent the heterogeneity of plain concrete consisting of coarse aggregates, mortar matrix and the mortar-aggregate interface. The composite elements of plain concrete are modeled using triangular finite element units which have six interface nodes along the sides. Fracture is captured through a constitutive single branch softening-fracture law at the interface nodes, which bounds the elastic domain inside each triangular unit. The inelastic displacement at an interface node represents the crack opening or sliding displacement and is conjugate to the internodal force. The path-dependent softening behaviour is developed within a quasi-prescribed displacement control formulation. The crack profile is restricted to the interface boundaries of the defined mesh. No re-meshing is carried out. Solutions to the rate formulation are obtained using a mathematical programming procedure in the form of a linear complementary problem. An event by event solution strategy is adopted to eliminate solutions with simultaneous formation of softening zones in symmetric problems. The composite plain concrete model is compared to experimental results for the tensile crack growth in a Brazilian test and three-point bending tests on different sized specimens. The model is also used to simulate wedge-type shear-compression failure directly under the loading platen of a Brazilian test.

• Structural Engineering and Mechanics
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• v.74 no.2
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• pp.283-296
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• 2020

The coupled hydro-mechanical loading conditions commonly occur in the geothermal and petroleum engineering projects, which is significantly important influence on the stability of rock masses. In this article, the influence of flaw inclination angle of fracture behaviors in rock-like materials subjected to both mechanical loads and internal hydraulic pressures is experimentally studied using the 3-D X-ray computed tomography combined with 3-D reconstruction techniques. Triaxial compression experiments under confining pressure of 8.0 MPa are first conducted for intact rock-like specimens using a rock mechanics testing system. Four pre-flawed rock-like specimens containing a single open flaw with different inclination angle under the coupled hydro-mechanical loading conditions are carried out. Then, the broken pre-flawed rock-like specimens are analyzed using a 3-D X-ray computed tomography (CT) scanning system. Subsequently, the internal damage behaviors of failed pre-flawed rock-like specimens are evaluated by the 3-D reconstruction techniques, according to the horizontal and vertical cross-sectional CT images. The present experimental does not only focus on the mechanical responses, but also pays attentions to the internal fracture characteristics of rock-like materials under the coupled hydro-mechanical loading conditions. The conclusion remarks are significant for predicting the rock instability in geothermal and unconventional petroleum engineering.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.3
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• pp.326-333
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• 2010

In this study, DAQ and TRA modules were applied to the CFRP single specimen testing method using AE. A method for crack identification in CFRP specimens based on k-mean clustering and wavelet transform analysis are presented. Mode I on DCB under vertical loading and mode II on 3-points ENF testing under share loading have been carried out, thereafter k-mean method for clustering AE data and wavelet transition method per amplitude have been applied to investigate characteristics of interfacial fracture in CFRP composite. It was found that the fracture mechanism of Carbon/Epoxy Composite to estimate of different type of fractures such as matrix(epoxy resin) cracking, delamination and fiber breakage same as AE amplitude distribution using a AE frequency analysis. In conclusion, the presented results provide a foundation for using wavelet analysis as efficient crack detection tool. The advantage of using wavelet analysis is that local features in a displacement response signal can be identified with a desired resolution, provided that the response signal to be analyzed picks up the perturbations caused by the presence of the crack.

• Computers and Concrete
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• v.13 no.4
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• pp.569-585
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• 2014

In this paper, a four-layer road structure consisting of an edge transverse crack is simulated using three-dimensional finite element method in order to capture the influence of a single-axle wheel load on the crack propagation through the asphalt concrete layer. Different positions of the vehicular load relative to the cracked area are considered in the analyses. Linear elastic fracture mechanics (LEFM) is used for investigating the effect of the traffic load on the behavior of a crack propagating within the asphalt concrete. The results obtained show that the crack front experiences all three modes of deformation i.e., mode I, mode II and mode III, and the corresponding stress intensity factors are highly affected by the crack geometry and the vehicle position. The results also show that for many loading situations, the contribution of shear deformation (due to mode II and mode III loading) is considerable.

• Steel and Composite Structures
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• v.43 no.4
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• pp.465-481
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• 2022

This paper presents a comprehensive integrity assessment of welded structural components, including uniform high- and low-cycle fatigue assessment of welded plate joints and fatigue-induced fracture assessment of welded plate joints. This study reports a series of fatigue and fracture tests of welded plate joints under three-point bending. To unify the assessment protocol for high- and low-cycle fatigue of welded plate joints, this study develops a numerical damage assessment framework for both high- and low-cycle fatigue. The calibrated damage material parameters are validated through the smooth coupon specimens. The proposed damage-based fatigue assessment approach describes, with reasonable accuracy, the total fatigue life of welded plate joints under high- and low-cycle fatigue actions. Subsequently, the study performs a tearing assessment on the ductile crack extension of the fatigue-induced crack. The tearing assessment diagram derives from the load-deformation curve of a single-edge notched bend, SE(B) specimen and successfully predicts the load-crack extension relation for the reported welded plate joints during the stable tearing process.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.27 no.5
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• pp.472-477
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• 2005

This study investigated the mandibular fractures that were treated at the Seoul National University Boramae Hospital in order to analyze the characteristics of mandibular fractures and the relationship between the causes and injury patterns. A total of 141 patients with mandibular fractures who were treated between 1996 and 2004 were analyzed retrospectively. The male to female ratio in the patient group was 5.13:1, and the mean age was 33.7 years. The most common etiologic factor was assaults (45.4%), and which was followed by activities associated with daily-life (40.4%) includeding falls, stumbling, collisions, and traffic accidents (11.3%). Single fracture sites were present in 75 patients (53.2%), two or more fracture sites were observed in other patients, and a total of 211 fracture sites were observed. The mandibular angle fractures (46.7%) was the most common in case of single fractures, and symphysis and angle fractures (45.4%) was most common in multiple fractures. Through out overall fracture sites, the most common fracture site was the symphysis (41.2%), followed by the angle (32.2%) and condyle (18.5%). Among assault and falls-related injuries, the common involving sites were the symphysis, and followed by the body and condyle. In case of traffic accidents, the symphysis fracture was the most common, and which was followed by the condyle and angle fractures. This study documented the characteristics of the mandibular fractures. The results demonstrate that preventive measures according to these characteristics will need to be implemented in order to minimize the risk of maxillofacial injuries.

• The Journal of Korean Academy of Prosthodontics
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• v.61 no.2
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• pp.113-124
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• 2023

Purpose. The purpose of this study is to help increase the success rate by analyzing the types and characteristics of implant prosthesis and the survival rate. Materials and methods. Among implants placed between 2011 and 2020 at Sanbon Dental Hospital, College of Dentistry, Wonkwang University, a case restored by a prosthetic surgeon was investigated for the characteristics and correlation of failure. The causes of failure were classified as failure of osseointegration, peri-implantitis, fixture fracture, abutment fracture, screw fracture, screw loosening, prosthesis fracture, and loss of prosthesis retention. Prosthetic method, cantilever presence, placement location, etc. were analyzed for their correlation with implant failure. Results analysis was derived through Chi-square test and Kaplan-Meier survival analysis using SPSS ver 25.0 (IBM, Chicago, IL, USA). Results. A total of 2587 implants were placed, of which 1141 implants were restored with Single Crown and 1446 implants with Fixed Partial Denture, and the cumulative survival rate was 88.1%. The success rate of SC was 86.2% (984) and the success rate of FPD was 89.6% (1295), showing statistically significant differences, among which factors that had significant differences were abutment fracture, screw fracture, and screw loosening (P < .05). Conclusion. As a result of the 10-year follow-up, more failures occurred due to biomechanical factors than biological factors. Further studies on the success of implants will be needed in the future.

• The Journal of Advanced Prosthodontics
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• v.10 no.1
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• pp.65-72
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• 2018

PURPOSE. The aim of this in vitro study was to investigate the fracture resistance under chewing simulation of implant-supported posterior restorations (crowns cemented to hybrid-abutments) made of different all-ceramic materials. MATERIALS AND METHODS. Monolithic zirconia (MZr) and monolithic lithium disilicate (MLD) crowns for mandibular first molar were fabricated using computer-aided design/computer-aided manufacturing technology and then cemented to zirconia hybrid-abutments (Ti-based). Each group was divided into two subgroups (n=10): (A) control group, crowns were subjected to single load to fracture; (B) test group, crowns underwent chewing simulation using multiple loads for 1.2 million cycles at 1.2 Hz with simultaneous thermocycling between $5^{\circ}C$ and $55^{\circ}C$. Data was statistically analyzed with one-way ANOVA and a Post-Hoc test. RESULTS. All tested crowns survived chewing simulation resulting in 100% survival rate. However, wear facets were observed on all the crowns at the occlusal contact point. Fracture load of monolithic lithium disilicate crowns was statistically significantly lower than that of monolithic zirconia crowns. Also, fracture load was significantly reduced in both of the all-ceramic materials after exposure to chewing simulation and thermocycling. Crowns of all test groups exhibited cohesive fracture within the monolithic crown structure only, and no abutment fractures or screw loosening were observed. CONCLUSION. When supported by implants, monolithic zirconia restorations cemented to hybrid abutments withstand masticatory forces. Also, fatigue loading accompanied by simultaneous thermocycling significantly reduces the strength of both of the all-ceramic materials. Moreover, further research is needed to define potentials, limits, and long-term serviceability of the materials and hybrid abutments.