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.

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.

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.

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.

Torque Analysis of A Twisted Singles Wires

Hur, Hae-Kyu(허해규),Kang, Ki-Ju(강기주) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

A simple model is introduced to predict the response of wire strands subjected to a coupled axial torsion. The derivation of wire strands is based on wire configurations and material properties. And also the number of wires is considered to predict the stiffness of wire strands. The equilibrium equations of twisted wire elements are derived by using the components of forces and torques, and the numerical results are investigated from the different loading conditions.

Developing Stiffness Matrix for Analyzing Spatially Twisted Wires

Hae-Kyu Hur(허해규),Ki-Ju Kang(강기주) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

A new analytical model called spatially twisted wires is proposed in this paper with the objective of predicting three-dimensional stiffness matrix of a uniform space-filling wire-woven truss; wire-woven bulk kagome (WBK) and wire-woven bulk diamond (WBD). The stiffness matrix of order 12 by 12 for a helically wound wire is formulated using Castiglianos theorem. Effects of transverse shear forces and tangential thrust are taken into account. From numerical examples, the accuracy of this developed element is checked and shows that the WBD/WBK sub-unit cell stiffness is considerably dependent on the spatially twisted region.

Numerical Analysis of the Effective Elastic Properties for Quadrilateral Grid Sandwich Structures

Hae-Kyu Hur(허해규),Chang-Min Cho(조창민) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11

A simple model is introduced to predict the flexibility of square honeycomb-core sandwich panels. The derivation of flexibility is based on the core configurations and material properties of face sheets and cores. And the unit cell or the repeating unit cell of square honeycomb cores is considered to predict the stiffness of sandwich panels. The equivalent moduli of unit cells or repeating unit cells are derived by using the concept of strain energy approach. To calculate equivalent moduli, the finite element approach is applied to the plate theory, i.e. classical laminated plate theory. The results of strain energy and flexibility approaches are compared together, and then a good accuracy is found.

Ballistic Impact Analyses Using a Cohesive Element Approach

Hae-Kyu Hur(허해규),Jae Kwon Jung(정재권),Jungsun Hwang(황정선),Jeong-Ho Han(한정호),Yong Jin Kim(김용진) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

In this study, a cohesive element approach is introduced to get a better understanding of the ballistic impact and contact phenomena of structures. To simulate the ballistic impact problem, this study considers two contact schemes for un-cracked elements and cracked elements between the projectile and the target. In the first contact algorithm, a simple contact methodology is applied to represent the un-cracked elements of target and projectile structures during the contact phenomena. With a various impact and contact models, the un-cracked contact phenomena are valuated. Within the second contact approach, the concept of cohesive zone modeling is introduced to depict cracks or fragmentation problems related to the brittle material impact, and also a simple application for contact algorithms is considered to depict post-rupture cracks and post-rupture crack surfaces during the impact and contact processing. To simulate the high velocity impact and the penetration phenomena, the finite element method and the cohesive element method based on a simple erosion contact algorithm and a discontinuous cracking scheme are introduced. For the effect of mesh sensitivity, this study implements various mesh sizes of target structures, and then different dynamic behavior of structures subjected to ballistic impact loading are suggested. Finally, the comparisons of the present predictions with other available ones are carried out, and the excellent agreement is reported.

Multi-scale Modeling of Transverse Impact on a Ballistic Fabric Composite

Hae-Kyu Hur(허해규),Soo-Yong Lee(이수용),Jung-Sun Park(박정선) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.4

A methodology has been developed to obtain dynamic response of planar woven textile composites subjected to impact loading. The yarn modeling is obtained using concepts of a repeating unit cell (RUC) and a unit cell (UC), and the geometrical architecture of RUC and UC on the yarn assembly is derived from mathematical equations based on yarn surfaces. The yarn material modulus is estimated from multi-scaled hierarchical system of composite structures. To estimate the mechanical characteristics of composites, this work uses a simple multi-scale concept for fiber, yarn, assembled yarn and RUC assembly. The focus of this paper is the effects of yarn geometry and hierarchical system on the dynamic behavior of ballistic fabric composites, starting from the mechanical behavior of multi-scaled components.

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.