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Models for Calculating Equivalent Strengths of Periodic Wire-woven Structures
허해규(Hae-Kyu Hur),강기주(Ki-Ju Kang) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.4
This paper presents a simple procedure for calculating the equivalent stiffness and strength of uniform space-filling spatially wire-woven truss structures. To determine their continuum elastic constants, a hierarchical modeling of helically wire-woven structures is introduced, and a simple concept of strain energy density is considered to estimate the stiffness of uniform space filling trusses. With an explicit expression of wire-woven assemblies and repeating unit cells, the geometrical characteristics and boundary arrangements of wire-woven bulk kagome (WBK) and wire-woven bulk diamond (WBD) are surveyed respectively. Through this expression, independent elastic constants characterizing the WBK and WBO trusses are tailored to specific values by choosing the appropriate components of continuum stiffness. To find the equivalent modulus of WBK and WBD unit cells, the iso-strain assumption is applied to the sub-unit cell system, and then their equivalent modulus are compared between the different members of WBK and WBO trusses.
Micro-Cracked Textile Composite Structures’ Behavior on the Dynamic Impact Loading
허해규(Hae-Kyu Hur),김민성(Min-Sung Kim),정재권(Jae Kwon Jung),김용진(Yong Jin Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
This study is focused on an integrated numerical modeling enabling one to investigate the dynamic behavior and failure of 2-D textile composite and 3-D orthogonal woven composite structures weakened by micro-cracks and subjected to an impact load. The integrated numerical modeling is based on: Ⅰ) determination of governing equations via a three-level hierarchy: micro-mechanical unit cell analysis, layerwise analysis accounting for transverse strains and stresses, and structural analysis based on anisotropic plate layers, Ⅱ) development of an efficient computational approach enabling one to perform transient response analyses of 2-D plain woven and 3-D orthogonal woven composite structures featuring the matrix cracking and exposed to time-dependent loads, Ⅲ) determination of the structural characteristics of the textile-layered composites and their degraded features under various geometrical yarn shapes, and finally, Ⅳ) assessment of the implications of stiffness degradation on dynamic response to impact loads.
Equivalent Modulus of Concave/Convex Sub-unit Cell Composite Structures
허해규(Hae-Kyu Hur),강기주(Ki-Ju Kang) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
A geometrical modeling for studying mechanical characteristics for spatially twisted composite structures is developed. From a simple mathematical model for sub-unit cells, the elastic behavior of twisted and impregnated composite structures is estimated. To obtain the elastic properties, the strain energy density for the twisted composite sub-unit cells is introduced. In the numerical analysis, a system of anisotropic media is applied to the helically twisted composites' sub-unit cells. To calculate the equivalent stiffuess or compliance, the volume averaging method is presented to geometrical volumes of spatially twisted yams within the subunit cell. For the degraded elastic modulus, micro-mechanical equations of composites are used. In addition this study shows that the equivalent properties of sub-unit cells are considerably dependent on the geometrical architecture.
The Application of Cohesive Zone Modeling to Adhesively Bonded Structures
허해규(Hae-Kyu Hur),김민성(Min-Sung Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
In this paper, the use of cohesive zone modeling to analyze crack path in the adhesively bonded structures is presented. Cohesive zone modeling is implemented by a user element in the commercial finite element (FE) code ABAQUS. The developed cohesive user element describes reasonable solutions for the crack initiation, crack length and crack growth of adhesive joints. The cohesive user element is numerically demonstrated for generalized issues of composite structures: double cantilever beam (DCB) and end notched flexure (ENF). Accuracy of cohesive user element is investigated by comparing the finite element analysis solution to several analytical results and experimental data of DCB/ENF structures.
복합재료 패널의 굽힘 및 비틀림 하중에 대한 유한요소 해석
허해규,박정선,이수용 한국 항공대학교 항공산업기술연구소 1996 航空宇宙産業技術硏究所 硏究誌 Vol.6 No.-
This study is to investigate the stiffness degradation in a composite laminated panel including matrix cracks subjected to bending and twisting moments. Micromechanics theory on the composite material is derived by introducing crack density. Iterative numerical scheme is developed to calculate the degraded composite stiffness which has nonlinear relation due to crack density. For the structural analysis of the composite panel, the finite element analysis is used. Structural responses of the composite panel are examined for various laminated angles and crack density under bending and twisting moments. Also, the effect of crack opening and closing is considered in the examination. It is realised that the matrix cracks may cause sever stiffness reduction and should be considered in the composite laminated panel.
Geometrical Modeling Applied to Spatially Twisted Wire Structures
Hae-Kyu Hur(허해규),Ki-Ju Kang(강기주) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.4
In this work, a simple geometrical modeling is introduced to get a better understanding of spatially twisted structures. With a simple mathematical model of wire assemblies, their geometrical characteristics and boundary arrangements are surveyed, and a few limitations to form a rope-like structure and a periodic wire-woven bulk kagome structure as yarn-based assemblies are estimated. To simplify the geometric arrangements of twisted yarns, this work considers the twisted yarns as a three-dimensional solid structure, and then the mathematical model of wire structures is extended to two types of wire assemblies having an elliptical or a circular cross-section, respectively. The effect of wire cross-section is studied by geometrical parameters, i.e. ellipse ratios and volume fractions of yarns. This work proposes a methodology that one can estimate a range of actual design limitations by parametrically varying the amount of ellipticity.
Micro-scale Modeling for Predicting Tension Modulus of Plain Woven Composites
Hur, Hae-Kyu(허해규),Kang, Ki-Ju(강기주) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
A simple model is introduced to predict the tension modulus of 2-D plain weave fabric (PWF) composites based on a micro-scale configuration depicted with sinusoidal shape functions. The material properties of 2-D PWF composites are calculated by a micro-mechanical curved beam model and strain energy of unit cells. Finally, the obtained numerical results are compared with available data suggested in the previous literature.
Mechanical Compression Behavior of Tube Wire-woven Bulk Kagome
Hae-Kyu Hur(허해규),Byung-Kon Lee(이병곤),Ki-Ju Kang(강기주) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
This study suggests a new type of wire-woven bulk kagome (WBK) structures constituting of helically woven tube-wires. The present work consists of two parts; the experiments and the numerical analysis. In the numerical simulation, to implement the compression behavior of tube-WBK trusses, the numerical model is postulated with perfect unit cells and specified by appropriate boundary conditions. Two different tube-wires are introduced to check the mechanical compression behavior under compression. In the experiment, the uniaxial compression test is fulfilled by a universal testing machine with the same dimension of numerical models, and then the stress-strain curve is calculated from the measured displacement of tube-WBKs. From the comparisons between the prediction of finite element analyses and the experimental data for tube-wires, this work finds that the mechanical compression behavior of tube-WBKs is considerably dependent on the geometry of helically woven tube-wires.
Geometrical Modeling and Characteristics of Wire-woven Bulk Kagome Structures
Hae-Kyu Hur(허해규),Ki-Ju Kang(강기주) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
A simple geometrical modeling for wire-woven bulk kagome (WBK) structures is developed and demonstrated to describe the three-dimensional architecture of WBK unit cells that account for helically interwoven wires in the spatially curved directions. To represent the three-dimensional shape of wire-woven bulk kagome trusses, this work uses several geometrical parameters and a simple three-dimensional mesh-generation scheme based on the concept of WBK unit cells. The current geometrical methodology for WBK unit cells is valuated by the exact volume of WBK unit cells. Very good agreement between the current predicted volume and the exact volume on the WBK unit cell is achieved. Two geometrical types of helically woven wires, concave WBKs and convex WBK unit cells, are derived using the simple geometrical equations of the spirally inter-/outer-woven wire shapes and also investigated geometrical characteristics between these concave and convex WBK unit cells.