• Steel and Composite Structures
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• 제20권2호
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• pp.267-293
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• 2016

It is well known that, in order to accurately predict the behaviour of steel structures a requirement the definition of the mechanical behaviour of beam-to column joints is of primary importance. This goal can be achieved by means of the so-called component method, which, in order to obtain the whole behaviour of connections, provides to break up joints in basic components of deformability and resistance. One of the main joint components used to model bolted connections is the so-called equivalent T-stub in tension, which is normally used to predict the behaviour of bolted plates in bending starting from the behaviour of the single bolt rows. In past decades, significant research efforts have been devoted to the prediction of the behaviour of bolted T-stubs but, to date, no particular attention has been devoted to the characterization of their plastic deformation capacity. To this scope, the work presented in this paper, taking into account the existing technical literature, proposes a new theoretical model for predicting the whole behaviour up to failure of bolted T-stubs under monotonic loading conditions, including some complexities, such as the bolt/plate compatibility requirement and the bolt fracture, which are necessary to accurately evaluate the ultimate displacement. After presenting the advances of the proposed approach, a comparison between theoretical and experimental results is provided in order to verify its accuracy.

• 대한치과보철학회지
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• 제35권3호
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• pp.544-556
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• 1997

All ceramic restorations except In-Ceram Alumina system gave a good esthetics and an exellent marginal fidelity. The flexural strength of them had about 150MPa, so the indication is only single crown. By using In-ceram Alumina System(450Mpa), it is thought to be possible to construct bridge for its high flexural strength. But the prognosis is unclear, The purposes of this study are to clear short term prognosis of In-Ceram bridge restorations, to elucidate its clinical significance. Among 22 In-Ceram Bridge restored in our department, 11 In-Ceram bridges with follow up were used. The period of placement is from 1 to 18 months. The results were as follows : 1. Among follow up 11 bridges, 2 bridges were fractured. One is 4 unit in maxillary lateral incisors, the other is 3 unit bridge in maxillary canine and premolar. Including 11 bridge without follow up, failure rate is very low(2/22). 2. The fracture sites are connector areas between abutment and pontic. To maintain In-Ceram bridge for long term period, it is needed to remove the nonphysiologic occlusal force and to have sufficient thickness of alumina core. For estabilishing clinical use of In-Ceram bridges, it is thought to need clinical research during long term period.

• 한국자동차공학회논문집
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• 제13권4호
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• pp.174-181
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• 2005

In order to investigate the behavior of fatigue crack growth of SiC-particulate- reinforced Al-Si alloy composites, fatigue tests using single edge notched tension(SENT) specimens were performed. Composite materials were manufactured by using both permanent die casting and extrusion processes with different volume fractions of $10\%\;and\;20\%$. $SiC_p-reinfurced$ Al-Si composites showed the increased levels of threshold stress intensity factor range, ${\Delta}K_{th}$, for the increased volume fractions of SiC particles, which implies the increased fatigue crack growth resistance at the threshold or low ${\Delta}K$ levels, compared to the unreinforced Al-Si alloy. In the Paris region, however, the composites showed the increased rate of crack growth resulting in the unfavorable effects on the fatigue crack growth resistance. Critical stress intensity factor range at unstable crack growth leading to final fracture decreased as the volume fraction of SiC particle increased, because of the reduced fracture toughness of the composites. Extruded materials showed higher threshold and critical values than the cast materials.

• Journal of Welding and Joining
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• 제23권6호
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• pp.67-71
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• 2005

This paper is concerned with a study on fracture strength of composites in an adhesive single lap joint. The tests were carried out on joint specimens made with hybrid stacked composites consisting of the polyester and bamboo natural fiber layer. The main objective of this work was to evaluate the fracture properties adjacent to adhesive bonded joint of natural fiber reinforced composite specimens. From the results, natural fiber reinforced composites have lower tensile strength than the original polyester. But tensile-shear strength of natural fiber reinforced composites with bamboo layer far from adhesive bond is as high as that of the original polyester adhesive bonded joints. Spew filet at the end of the overlap reduced the stress concentration at the bonded area. Spew fillet and position of bamboo natural fiber layer have a peat effect on the tensile-shear strength of natural fiber reinforced composites including adhesive bonded joints.

• Steel and Composite Structures
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• 제31권5호
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• pp.517-527
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• 2019

To move forward in large steps rather than in small increments, the community would benefit from a systematic and comprehensive database of multi-scale composites and measured properties, driven by comprehensive studies with a full range of types of fiber-reinforced polymers. The multi-scale hierarchy is a promising chemical approach that provides superior performance in synergistically integrated microstructured fibers and nanostructured materials in composite applications. Achieving high-efficiency thermal conductivity and mechanical properties with a simple surface treatment on single-walled carbon nanotubes (SWCNTs) is important for multi-scale composites. The main purpose of the project is to introduce ozone-treated SWCNTs between an epoxy matrix and basalt fibers to improve mechanical properties and thermal conductivity by enhancing dispersion and interfacial adhesion. The obvious advantage of this approach is that it is much more effective than the conventional approach at improving the thermal conductivity and mechanical properties of materials under an equivalent load, and shows particularly significant improvement for high loads. Such an effort could accelerate the conversion of multi-scale composites into high performance materials and provide more rational guidance and fundamental understanding towards realizing the theoretical limits of thermal and mechanical properties.

• 한국기계가공학회지
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• 제20권1호
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• pp.42-47
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• 2021

Recently, many structures using lightweight materials have been developed. This study was conducted by using Al6061-T6 and carbon fiber reinforced plastic (CFRP), two common lightweight materials. In addition, the failure characteristics of an interface bonded between a single material and a heterogeneous bonding material were analyzed. The specimens bonded with CFRP and Al6061-T6 were utilized by the combination of the heterogeneous bonding material. The specimens had a double cantilevered shape and the bonding between the materials was achieved by applying a structural adhesive. The experiments were conducted in opening mode: the lower part of the samples was fixed, while their upper part was subjected to a forced displacement of 3 mm/min by using a tensile tester. Under the tested amount of strength, energy release rate, and considering the specimens' fracture characteristics in opening mode, the specimen "CFRP-Al" presented the maximum stress, followed by "Al" and "CFRP". We can hence conclude that the inhomogeneous material "CFRP-Al" is useful for the construction of lightweight structures bonded with structural adhesive.

• Journal of Yeungnam Medical Science
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• 제40권3호
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• pp.302-307
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• 2023

With recent developments in digital dentistry, research on techniques and materials for three-dimensional (3D) printing is actively underway. We report the clinical applications and outcomes of 3D printing of temporary crowns fabricated with polylactic acid (PLA) using a fused deposition modeling (FDM) printer. Five participants were recruited from among patients scheduled to be treated with a single full-coverage crown at a dental clinic in a university medical center from June to August 2022. We used 3D-printed crowns fabricated with PLA using an FDM printer as temporary crowns and were assessed for discomfort, fracture, and dislodging. The 3D-printed temporary crowns were maintained without fracture, dislodging, or discomfort until the permanent prosthesis was ready. The average time required for printing the temporary crowns was approximately 7 minutes. The 3D printing of temporary crowns with PLA using an FDM printer is a convenient process for dentists. However, these crowns have some limitations, such as rough surface texture and translucency; therefore, the 3D printing process should be improved to produce better prostheses.

• 화약ㆍ발파
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• 제34권1호
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• pp.11-18
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• 2016

도심지나 보안건물과 근접한 곳에서 폭약을 사용하는 발파작업이 수행되는 경우 지반진동 및 소음의 영향을 최소화 시킬 필요가 있다. 이러한 지반진동과 소음은 암반의 천공내에 장전된 폭약이 기폭되며 주변 암반을 파괴하고 남은 일부 충격에너지에 의하여 발생된다. 최근 천공 내 U형 철재장약홀더를 삽입하여 충격파의 전파방향을 제어하여 자유면방향으로 파쇄효과를 유지하며 암반 내로 전파하는 충격진동을 감쇄시키는 발파 공법이 제안되었다. 본 연구에서는 U형 철재장약홀더를 적용한 암반발파에서 충격파의 전파특성을 파악하기 위하여, AUTODYN 소프트웨어를 이용하여 장약홀더 내 장전된 폭약의 폭굉을 모사하고 주변암반에 전달된 충격파를 측정하였다. 또한 장약홀더 발파의 암파쇄 효과를 파악하기 위하여 동적파괴과정해석코드인 DFPA(Dynamic Fracture Process Analysis)를 적용하여 장약홀더를 이용한 장약조건을 고려한 2자유면 발파를 모사하였다. 일반발파의 장약조건을 고려한 충격파 발생 및 파괴과정해석을 추가적으로 수행하여 장약홀더의 암파쇄효과를 비교하였다.

• 대한기계학회논문집A
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• 제25권1호
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• pp.61-69
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• 2001

EFP(Fitness For Purpose) type defect assessment methodologies based on ECA(Engineering Critical Analysis) have been established and are in use for the structural integrity evaluation of gas pipelines. ECA usually includes the fracture mechanics analysis, and it is assumed that the J-integral uniquely characterizes the crack-tip stress-strain field. However, it has been proven that the J-integral alone can not be sufficient to characterize the crack-tip field under low levels of constraint with a single parameter. Since pipeline structures are made of ductile material, locally loaded in tension, cracks may experience low level of constraint, and therefore, J-dominance will be lost. For this reason, the level of constraint must be quantified to establish a precise assessment procedure for pipeline defects. The objective of this paper is to investigate the fracture behavior of a crack in gas pipeline(KS D 3507) by quantifying the level of constraint. For this purpose, tensile tests and CTOD tests were performed at room temperature(24$\^{C}$) and low temperature(-40$\^{C}$) to obtain the material properties. J-Q analyses were performed for SENB and SENT specimens based on 2-D finite element analyses, in order to investigate the in-plane constraint effects on pipeline defects. For precise assessment of cracks, especially shallow cracks, in KS D 3507 pipeline, constraint effect must be considered.

• 한국강구조학회 논문집
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• 제21권5호
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• pp.527-536
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• 2009

본 연구의 목적은 박판 탄소강 일면전단 2행 2열 볼트접합부의 블록전단파단거동과 면외변형의 영향을 조사하는 것이다. 하중직각 방향 연단거리, 볼트직경, 피치, 게이지 치수를 고정하고 블록전단파단이 발생하도록 실험체를 계획한다. 접합평판의 두께, 하중방향연단거리를 주요변수로 설정한다. 단순인장 실험을 실시하고 블록전단파단 양상, 최대내력을 현행의 설계기준식에 의한 예측치와 비교한다. 또한, 판 두께와 연단거리에 따른 하중방향과 직각방향으로 발생하는 면외변형의 발생조건을 조사하고 면외변형의 발생으로 인한 내력저하정도를 고찰한다.