bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Unstitched and Stitched Laminates by Line Loading
Authors: Wu Enboa , Liau Jiunjie
Published: April 2011

Results of impact responses for both unstitched and stitched laminates to line-loading at low striking velocities are presented in this paper. These laminates, made of E-glass dry preform and having a (0°2/90°2)s stacking sequence, were fabricated by resin transfer molding. For the stitched laminates, Kevlar-29 untwisted roving of 3000 denier was used for the through-the-thickness reinforcement. Impact tests were conducted on a specially designed falling tower with a line-nosed impactor. It was found that the number of matrix cracks, the splitting crack lengths, the delamination areas, and the laminate residual deflections were all much reduced due to the stitching reinforcement. The major impact-induced damage mechanism gradually changed from delamination for the unstitched laminates to the plastic-hinge type of localized deformation at the impact location for the stitched specimens as the stitching density increased. Further, delamination damage in an unstitched laminate could be detected from the recorded strain and acceleration histories.
Monitoring the Integrity of Composite Structures
Authors: Donaldson Steven L. , Springer George S.
Published: April 2011

A method is proposed to predict the future load response of structures made of composite materials. The method makes the predictions on the basis of past loadstrain data. The method was developed for structures subjected to monotonically increasing or to random cyclic tensile loads. A computer code PREDICT was written which, in real time, can provide predicted values of residual strengths and number of cycles to failure from measured data. Tests were performed to evaluate the validity of the method using specimens made of different materials, lay-ups, and geometries. The specimens were subjected to monotonically increasing or to cyclic tensile loads. During the tests, the residual strengths and number of cycles to failure were predicted, and were compared to the actual value generated in the tests. The predicted and measured values were in good agreement lending confidence to the method.
Vibration Damping of Interleaved Carbon Fiber-Epoxy Composite Beams
Authors: Liao Fu-Sen , Su An-Chung , Hsu Tzu-Chien J.
Published: April 2011

Vibration-damping behavior of unidirectional and symmetric angle-ply carbon fiber-epoxy laminates as well as their interleaved counterparts with a layer of poly(ethylene-co-acrylic acid) (PEAA) at the mid-plane was examined. The introduction of the PEAA layer significantly improved the damping capability. The effectiveness of interleaving increased with the flexural modulus of the outer layers. In the case of unidirectional laminates, calculations based on a sandwich structure of isotropic layers quantitatively reproduced this trend. In the case of angle-ply laminates, however, the model predicted only part of the improvement experimentally observed. This was explained in terms of the bending of the angle-ply laminates in the transverse direction which would induce additional deformations in the interleaf layer and was not accounted for by the present model.
Response of SiC/Ti under Combined Loading. Part I: Theory and Experiment for Imperfect Bondin
Authors: Lissenden C. J. , Herakovich C. T. , Pindera M. J.
Published: April 2011

Results from cyclic multiaxial tests on unidirectional [04] and angle-ply [±45], silicon carbide/titanium (SiC/Ti) tubular specimens are compared with theoretical predictions from a micromechanical model that includes imperfect bonding between the fiber and matrix. Comparison of theory and experiment indicates that damage to the fiber/matrix interface often is a major factor in the stress-strain response of SiC/Ti composites. The axial shear (torsional) response of a [04] tube displayed a distinct knee associated with damage at the shear stress of 276 MPa (40 ksi). Transverse tensile (internal pressure) loading of a [04] tube and axial tensile loading of a [±45], tube resulted in inelastic deformation due to damage well before initial yielding was predicted to occur in perfectly bonded composites. Substantial differences were observed in the effects of damage on the response of [04] and [±45], tubes subjected to combined loading.
Mechanical Properties of CFRC Additionally Reinforced with CFRP Rods
Authors: Yamada Takashi , Yamada Kanji , Kubomura Kenji
Published: April 2011

Potential of using pitch-based high modulus carbon fiber was investigated as a reinforcement in cementitious composites for structural reinforced concrete (RC) members. For this purpose, effects of carbon fiber mechanical properties on the mechanical properties of CFRC reinforced with CFRP rods were studied through the three-point flexural test by using several pitch-based high modulus carbon fiber rods of varying fiber moduli and strengths. For the specimens with a fiber volume fraction larger than the critical volume fraction, the flexural strength is found to exceed the CFRC matrix strength and is linearly proportional to the sum of all rod strengths, and the flexural modulus after matrix cracking is found to also be linearly proportional to the sum of all rod stiffnesses.
Analysis of the Non-Viscous Flow Effect in Liquid Molding Process
Authors: Cai Zhong
Published: April 2011

Non-viscous flow effect in liquid molding processes has been analyzed and evaluated. Ergun equation is used to describe the non-viscous flow through fibrous media. Overall flow resistance of the fibrous media is considered as the summation of the viscous inertial components. The generalized permeability of the fibrous media is found to be not only a function of the structural parameters such as fiber diameter and porosity, but also related to the fluid properties and flow velocity. Two-dimensional mold filling flow equation has been established. In order to evaluate the magnitude of the non-viscous flow effect in various process conditions, solutions of simplified one-dimensional filling flow cases are discussed. Parametric study with numerical simulations has been carried out to assess the non-viscous flow effect on the filling time and the inlet fluid pressure.
Experimental and Analytical Studies of Failure Modes in Iosipescu Specimens under Biaxial Loadings
Authors: Bansal A. , Kumosa M.
Published: April 2011

This study is concerned with an extension of the traditional Iosipescu shear test to in-plane biaxial stress applications. A Biaxial Stress Test Fixture, which is based upon the original Iosipescu shear test and the Arcan in-plane stress method, is used to characterize mixed-mode failure phenomena in both isotropic (PMMA) and orthotropic (teak) Iosipescu specimens under externally applied biaxial loads. The fixture is used for generating failure data for a wide range of biaxial (dominated by shear) loading conditions. Finite element methods are used to evaluate the stress state at the notch tips (as a function of the notch-tip radius) of biaxially loaded Iosipescu specimens. In addition, a simplistic analytical approach has been applied to estimate the notch-tip stresses at the onset of failure. A high quality failure envelope has been generated for teak under a combination of shear and transverse tensile loading conditions. Results from the finite element analysis show that an absolute numerical evaluation of the stress distribution at the notch tips can be misleading if a linear-elastic material behavior is assumed. However, the analytical approach, which assumes a uniform stress state along the notch-root axis, is found to more accurately represent the notch-tip stresses. Preliminary results strongly indicate the potential of the Biaxial Iosipescu method as a reliable test procedure for biaxial stress applications.
Use of Composite Cylinder Model as Representative Volume Element for Unidirectional Fiber Composites
Authors: Tandon G. P.
Published: April 2011

The present work is concerned with the theoretical study of the elastic properties of unidirectional fiber composites. The approach to calculate the effective moduli of composite materials is generally based upon the premise of a representative volume element, or an element in which the strain and stress averages taken over large enough subregions of the specimen are the same for any such subregion. For purposes of computation, some model of a fiber composite must be assumed. The objective of this study is to demonstrate that the composite cylinder model can provide a good simulation for the representative volume element to define the response of a unidirectional composite for a wide range of elastic moduli and volume fraction provided the displacements are prescribed on the external surfaces. Results of the effective elastic moduli and microstresses within the constituents are compared with existing numerical solutions, both with and without partial interphase failure, to demonstrate the effectiveness of composite cylinder model to simulate composite behavior.
Nonlinear and First-Ply Failure Analyses of Laminated Composite Cross-Ply Plates
Authors: Kam T. Y. , Sher H. F.
Published: April 2011

A method is presented to study the nonlinear behaviors and first-ply failure strengths of centrally loaded laminated composite plates with semi-clamped edges. The method which is developed from the von Karman-Mindlin plate theory and the Ritz method is used to construct the nonlinear load-deflection curves of the composite plates with or without considering the reduction in plate stiffness induced by ply failure and predict the first-ply failure loads of the plates based on various commonly used strength-of-material type failure criteria. Experiments on laminated composite plates loaded to failure are performed to construct the experimental load-displacement curves of the plates. During testing, the first-ply failure loads of the plates are identified using the acoustic emission technique. The experimental results are used to investigate the capabilities of the present method in predicting the nonlinear behaviors and first-ply failure loads of the laminated composite plates. It has been found that when compared with the experimental load-deflection curves the present method with the consideration of stiffness reduction can yield reasonable results on load-deflection curve and even for some cases the ultimate strength. As for the determination of first-ply failure load, the inconsistent results predicted by the adopted failure criteria indicate that the strength-of-material approach may be inappropriate for the first-ply failure analysis of laminated composite plates. Hence, more research on failure mechanism and, especially, the development of appropriate failure criteria for composite laminates is needed.
A Thermal Viscoelastic Analysis for Thick-Walled Composite Cylinders
Authors: Chien Larry S. , Tzeng Jerome T.
Published: April 2011

The thermal viscoelastic behavior of thick-walled composite cylinders has been investigated. The analysis accounts for ply-by-ply variations of material properties, fiber orientations, and temperature changes. The Correspondence Principle is employed to convert the thermoviscoelastic problem to its corresponding thermoelasticity problem in Laplace transform space. A closed-form formulation is then developed for each layer, assuming a state of generalized plane strain, to solve for a general solution of the corresponding thermoelastic problem. A numerical method with implementation of parallel computing techniques was used to resolve the complex and large numerical system resulting from thick multi-ply cylinders. Finally, direct Laplace transform inversion is used to yield the quasi-static thermoviscoelastic solution.
Interactive Buckling Analysis of Fiber-Reinforced Thin-Walled Columns
Authors: Godoy L. A. , Barbero E. J. , Raftoyiannis I.
Published: April 2011

An analytical approximate model, leading to a closed form solution, is presented to account for buckling mode interaction in composite I section columns. Three buckling modes are considered in the analysis: a global mode (Euler mode about the weak axis); a primary local mode (rotation of the flanges and bending of the web); and a secondary local mode (bending of the flanges), which are modeled using analytical functions and four degrees of freedom. The fundamental state is shown to be linear and the three critical states for the isolated modes are found to be stable symmetric bifurcations. Mode interaction analysis in terms of the amplitudes of first order fields is carried out, for the first time, for prismatic sections of composite material. The tertiary (coupled) path involves coupling between the two local modes and it describes the sensitivity to imperfections of the buckling behavior of the composite column. A salient feature of the model presented is the closed form of the resulting solution, which enables the designer to easily perform parametric studies. Also, this is the first buckling mode interaction study for thin-walled composite columns. Numerical examples are presented to validate the results and to show the influence of the geometry and properties of the composite on the interaction phenomenon.
Some Scaling Rules for the Overall Thermal Conductivity in Porous Materials
Authors: Tzou Da Yu , Li Jing
Published: April 2011

The overall thermal conductivity in an isotropic porous medium containing cavities of various shapes is studied in this work. The cavity shapes under consideration include spherical and cylindrical pores, prelate and oblate spheroids, and cylindrical cavities with rectangular cross sections. The unique feature lies in the derivation of the scaling rules governing the overall thermal conductivity in porous media containing various shapes of internal cavities. The temperature distribution around the representative cavity surface, the central quantity in the present differential formulation, is obtained by the boundary element method employing the exterior formulation.
A Comparison of Energy Release Rates for Locally Buckled Laminates Containing Symmetrically and Asymmetrically Located Delaminations
Authors: Davidson Barry D. , Krafchak Todd M.
Published: April 2011

Results are presented from a study to determine energy release rate and mode ratio for a locally buckled, compression loaded laminate which contains either a single delamination or two symmetrically located delaminations. It is shown that, at a given applied load or displacement, significantly different values of energy release rate and mode ratio may exist in the two configurations. In general, the rate-of-increase of energy release rate with increasing displacement, as well as the percentage of crack-tip shearing mode at a given displacement, are higher in the configuration which contains two delaminations.
Measurement of the Three-Dimensional Permeability of Fiber Preforms Using Embedded Fiber Optic Sensors
Authors: Ahn Sung Hoon , Lee Woo Il , Springer George S.
Published: April 2011

An experimental technique is described which can be used to measure simultaneously the three principal permeabilities of fiber reforms made of continuous or short fibers. The technique utilizes embedded optical fibers for detecting the position of the liquid front inside the reform. Expressions were derived for calculating the permeabilities from the three-dimensional measurement of the liquid front. Permeabilities measured by the present fiber optic and by the conventional, pressure drop and flow visualization techniques were compared. Good agreements were found between the results of these techniques.
Progressive Crush Response of Multi-Element Foam-Filled Preform RTM Structures, I: Architecture and Rate Effects
Authors: Karbhari V. M.
Published: April 2011

The application of composites in automotive structures has been a topic of increasing interest in recent years. This has largely been driven by the need for energy efficiency, increased safety requirements, economics related to fabrication, and the designers need for enhanced flexibility in form through increased materials and processing options. The main objective of this study was to investigate the effect of multi-element preform fiber architectures for a resin transfer molded structural (rather than the tube-type element usually used) component on compressive response, progressive crush and energy absorption. Six different architectures based on a stiffened plate-type structural shape were tested under two loading rates, and behavioral characteristics in terms of failure loads, energy absorption per unit structural deformation, and damage mechanisms were studied. Absorbed energy is seen to increase with loading rate, whereas failure load decreases or remains constant. It is seen that the increasing use of braided layers in the rib section increases efficiency in terms of energy absorption per unit deformation. The use of specially placed fabric layers is also seen to open avenues as triggers for controllable sequences of damage modes.
The Macroscopic Elasticity of 3D Woven Composites
Authors: Cox B. N. , Dadkhah M. S.
Published: April 2011

The elastic properties of graphite/epoxy composites with three-dimensional interlock weave reinforcement have been measured over length scales somewhat greater than the characteristic length of the weave pattern. Orientation averaging models similar to those developed elsewhere over the last twenty years provide estimates of elastic constants that are in fair agreement with the experimental data. However, in-plane Young's moduli are consistently too high and properties related to the through-thickness reinforcement show considerable scatter. Most of the discrepancies can be attributed to waviness and other geometrical irregularities in nominally straight tow segments. Much improved agreement with in-plane properties is obtained by measuring and accounting for the out-of-plane waviness of in-plane tows. Other observed distortions of in-plane tows and irregularity in through-thickness tows are very difficult to quantify experimentally. There results a significant and apparently unavoidable uncertainty in predictions of properties that depend strongly on the through-thickness reinforcement. Nevertheless, the utility of orientation averaging models in applications where the in-plane properties are paramount is clearly verified.
Fracture Mechanics Analysis of the Fibre Fragmentation Test
Authors: Zhou Limin , Kim Jang-Kyo , Baillie Caroline , Mai Yiu-Wing
Published: April 2011

An improved micromechanics analysis is developed for the stress transfer in the single fibre fragmentation test. Considering the partially debonded interface as the most general case, Griffith's fracture mechanics approach is employed to derive a debond criterion at the fibre-matrix interface. An average fibre strength model from the Weibull statistics is used to determine the mean fibre fragment length as a function of applied stress. A parametric study for a carbon fibre-epoxy matrix composite shows that there is a critical applied stress below which no interfacial debonding takes place. The Poisson effect increases the interface shear stress at the debonded region towards the fibre ends, which in turn discourages further debond propagation. The mean fibre fragment length is the sum of the bonded and debonded lengths, and is substantially smaller for the composite containing fibres with a higher surface treatment level at a given applied stress greater than the critical level.
Cross-Plied Cylindrical Composite Shells under Transverse End Load
Authors: Yuan F. G.
Published: April 2011

Analytical solutions for cross-plied composite shells under transverse end load are presented. Based on a Saint-Venant's semi-inverse method and the theory of cylindrically orthotropic elasticity, two connected partial differential equations are developed using Lekhnitskii's stress functions. Solutions are obtained using separation of variables and solved the governing equations sequentially. Special cases of a single transversely isotropic (00 ply) shell, p = 2 and/or t = 3 occurring in a layer are also briefly derived for stress and displacement response. To illustrate the fundamental nature of the problem, detailed distributions of radial strain and stress for two layups, [90/012 and [0/90]2, with two different midradius to thickness ratios are discussed.
An Accumulative Damage Model for Tensile and Shear Failures of Laminated Composite Plates
Authors: Shahid Iqbal , Chang Fu-Kuo
Published: April 2011

A progressive failure model was developed for predicting the accumulated damage and the effect of such damage on the in-plane response of laminated composite plates subjected to tensile and shear loads. Internal damage in composites induced by matrix cracking under in-plane tensile and shear loads was the primary concern. Free edge-induced damage was not considered.

The model assumes that the damage would accumulate uniformly in a laminate when it is subjected to uniformly distributed loads. The progressive failure model consists of two parts: constitutive modeling and damage accumulation prediction. Constitutive equations were established for relating the effective material properties of a damaged ply in a laminate to the extent of damage. Damage accumulation criteria were proposed by modifying the existing failure criteria for estimating the accumulated damage as a function of the applied loads.

A finite element analysis, designated as "PDCOMP," was developed based on the model. In order to verify the model, predictions from the analysis were compared with the experimental data available in the literature. Additional tests were also conducted to substantiate the model. Overall, the predictions agreed with the data quite well.
Notched Strength and Fracture Criterion in Fabric Composite Plates Containing a Circular Hole
Authors: Kim Jung-Kyu , Kim Do-Sik , Takeda Nobuo
Published: April 2011

The effects of the hole size and the specimen width on the fracture behavior of several woven fabric composite plates are experimentally investigated in tension. It is shown in this paper that the characteristic length ( d o) in the Point Stress Criterion (PSC) depends on the hole size and the specimen width. A modified PSC for predicting the notched strength is proposed. An excellent agreement is found between the experimental results and the analytical predictions using the modified PSC. When the unstable fracture occurred, the equivalent critical crack length ( a c) corresponding to the damage zone size is about twice the characteristic length. The characteristic length decreases with an increase in the notched strength. The critical energy release rate ( G c) corresponding to the unstable fracture criterion is independent of the hole size for the same specimen width. G c increases with an increase in the specimen width. These results can be explained by the correlation between the G c and the notch sensitivity factor (k).
Model Based Control of Voids and Product Thickness during Autoclave Curing of Carbon/Epoxy Composite Laminates
Authors: Joseph Babu , Hanratty Frieda Wang , Kardos John L.
Published: April 2011

In this article we present a novel feedback control strategy for the autoclave curing of carbon/epoxy laminates. The strategy utilizes an on-line model of the process to control the quality by adjusting the cure cycle. On line measurements are used to correct for modeling errors. The quality variables of interest here are the thickness of the product laminate and the maximum void size present in the laminate. Artificial neural networks are utilized to regress past operational data to generate nonlinear models for predicting the product quality. These models utilize properties of the raw material prepreg and secondary measurements taken while the process cycle is in progress. Some results of a control study done using a simulated model of a process for autoclaving a carbon fiber/epoxy resin system are also reported.

The main contribution of this paper is the successful demonstration of a neural network model based feedback control strategy for autoclave curing. While discussion in this paper is limited to control of the autoclave process, the methodology suggested is also equally applicable to other composite manufacturing processes.
Life Predictions of Metal Matrix Composite Laminates under Isothermal and Nonisothermal Fatigue
Authors: Gao Zhanjun , Zhao Huixia
Published: April 2011

A remarkably simple model is proposed in this paper to predict the fatigue life of titanium matrix composite (TMC) laminates under thermomechanical fatigue. It is shown that the maximum applied stress, together with the associated temperature, represents a critical state of loading, of the fatigue process. This critical state of loading dictates a unique state of damage represented by stiffness reduction of the off-axis plies and viscoplastic deformation of the total laminate. As far as the fatigue life prediction is concerned, it is not necessary to know how the damage evolves, and what the stress-strain response is in each loading cycle. After a relatively small number of loading cycles, the stress of 00 fibers saturates to a stable level, and further damage is dominated by the 0° plies of the laminate. The fatigues life is determined by the saturated stiffness, cumulated nonelastic strain and the maximum applied stress.

The model is based on a firm understanding of the fundamental damage mechanisms in the TMC laminates under various mechanical and thermal loading. Damage mechanisms and fatigue lives of isothermal, in-phase and out-of-phase fatigue are unified and examined using the concept of critical state of loading. The predictions of fatigue life are shown to be in a good agreement with experimental data of [0/90]2 s, [02/±45] s and [0/±45/90] s made of SCS-6/Titanium for room temperature fatigue, as well as in-phase and out-of-phase thermomechanical fatigue.

The most important feature that separates the present research from the existing approaches is its simple and clear representation of the physics involved in the fatigue damage and failure of TMC. The key to the success of the model is the simple fact that failure is controlled by fibers in 0° plies for any laminates containing 00 plies. The data needed to predict the life of any laminates, containing 0° and off-axis plies, under various thermomechanical fatigues are minimal and obtained essentially from a unidirectional laminate. No fatigue life data for the laminates themselves are used to calibrate the model or to determine curve fining parameters. The model makes it possible to establish a data base for different unidirectional laminate and predict the fatigue life of a laminate based on the data of its laminate and the laminate stacking sequence.
First-Order Approximations for the Effective Shearing Viscosities of Continuous-Fiber Suspensions
Authors: Coffin Douglas W. , Pipes R. Byron. , Šimáček Pavel
Published: April 2011

The effective shearing viscosities required to model aligned-continuous-fiber suspensions as a transversely isotropic fluid are investigated. Relations for the longitudinal shearing viscosity and the transverse shearing viscosity are developed by considering the kinematics of adjacent rigid fibers interacting with the viscous fluid matrix in states of shear deformation. This simple micromechanical analysis revealed that the longitudinal and transverse shearing viscosities of the medium may be considered to be equal. The present prediction for the in-plane shearing viscosity accounts for the constraint of fiber inextensibility and differs from previous relations [4-6]. In addition, the relationships presented herein were used in Reference [11], but development and discussion of these relationships, as given in the following, are lacking in the literature. Predictions for both Newtonian and shear thinning Carreau matrix fluids are presented and compared to results of a finite-element analysis as well as the earlier work of Christensen [10]. Finally, these simple relations are compared to experimental observations in order to evaluate their validity.
Elastic Tailoring of Laminated Composite Plate by Anisotropic Piezoelectric Polymers-Theory, Computation, and Experiment
Authors: Yu Jeoung Yoel , Kang Woo Young , Kim Seung Jo
Published: April 2011

Using the fact that polyvinylidene fluoride polymer (PVDF) has the anisotropic property, the experimental and numerical investigations were performed to study the static behavior of lasted composite plate when the PVDF was used as a continuous actuator. In this way, it was confirmed that not only the directionality of the composite material, but also the directionality of the PVDF could influence the deformation of the structure. With combination of the different layer angles of both composite and PVDF, several deformed states of the structure, i.e., bending, pure torsion, bending-torsion coupling were obtained. Pure torsional motion was produced when orthotropic electromechanical coupling of PVDF is used. Stronger pure torsional motion was also observed through tailoring of composite layer angle [+451-45] without orthotropic electro-mechanical coupling. But the PVDF has advantage over the composite in producing the pure twist motion since it is very easy to tailor. An efficient finite element method based on first order shear deformation theory which treats both actuators and plate as plies of an integrated laminated plate was developed and various numerical verifications were performed. The computed results were also compared with the experimental results and agreed well. Finally, the effects of various layer angles of both continuous piezo actuator and CFRP composite plate were examined. As results, desired specific deformed shapes of the structure can be generated by selecting appropriate combination of layer angles of both materials, and these results can be used to maximize the directional characteristics of PVDF and composite materials.
Effects of Processing Temperature and Layup on Springback
Authors: Sarrazin Hugo , Kim Beomkeun , Ahn Sung-Hoon , Springer George S.
Published: April 2011

Tests were performed to assess the effects of processing conditions and laminate layup on the change in shape (springback). Twelve inch long and one inch wide coupons made of Fiberite T300/976 graphite/epoxy were tested. Coupons of different layups were cured using different types of molds and different types of vacuum bagging arrangements. The curing was performed with different temperature cycles. Springback was measured from the change in shape of initially flat coupons. The results indicated the effects of the applied temperature, applied pressure, material of the mold, arrangement of the teflon surrounding the coupon, and laminate layup on springback.
High Strain Rate Response of Angle-Ply Glass/Epoxy Laminates
Authors: Staab George H. , Gilat Amos
Published: April 2011

The effects of strain rate on the mechanical behavior of Scotchply Type 1002 glass/epoxy angle-ply laminates is investigated. High strain rate tests (approximately 103 sec−1) using a direct tension split Hopkinson bar apparatus and quasi-static tests (strain rate of approximately 10−4 sec−1) using a servo-hydraulic testing machine have been conducted. Results indicate that the maximum normal stress experienced by glass/epoxy laminates is higher for dynamic than for quasi-static loading conditions. Although both fibers and matrix are sensitive to the strain rate, the fibers influence laminate rate sensitivity more than the matrix.
Local Buckling of Delaminated Beams and Plates Using Continuous Analysis
Authors: Wang James Ting-Shun , Cheng Shou-Hsiung , Lin Chien-Chang
Published: April 2011

The study presents a continuous analysis method for determining the buckling load of delaminated beams and plates. Investigations include beam-plates with end rotational restraints using the Stokes' transformation technique and orthotropic plates with simple supports. The analysis allows structures to have a multiple number of delaminations of various shapes and sizes, and at any locations. The method treats the discontinuous structure as a body without delamination but with a force system added at a number of discrete points in the delaminated region so as to make the net interracial tractions to vanish at these points. Hence, the procedure solves problems of delaminated structures directly as a continuous system. Fourier series in conjunction with the Stokes' transformation is used which provides a unified solution for problems with different end conditions. Numerical results accounting for the effects of delamination length, location and shape; boundary conditions and stiffness of adhesive layer, to the local buckling load are presented for illustrative purposes. The method of analysis presented in the study is simple in concept, yet so effective and accurate in solving such discontinuous structures which would otherwise be extremely difficult if not impossible to analyze
Geometrical Parameters in Composite Repair
Authors: Zimmerman Kristin , Liu Dahsin
Published: April 2011

This paper presents a systematic investigation of the geometrical effects on composite repair. Although fiber geometry, matrix property, adhesive bonding, and reinforcing patch are important parameters in composite repair, the bond line geometry is the primary concern in this study. Various bond line configurations are investigated. The experimental results can be used for optimizing the composite repair design.
Numerical Modeling of Fiber Push-Out Test in Metallic and Intermetallic Matrix Composites-Mechanics of the Failure Process
Authors: Ananth C. R. , Chandra N.
Published: April 2011

The application of push-out test to characterize the mechanical behavior of interfaces in Metallic and Intermetallic Matrix Composites (MMCs and IMCs) is studied using Finite Element Method. A stress based criterion for debonding, and frictional resistance based criterion for interfacial sliding are used in the proposed model to predict the interfacial behavior during the push-out test. The complexities involved in modeling the process, and interpretation of the experimental results in the case of MMCs and IMCs, as compared with Ceramic Matrix Composites (CMCs) are addressed. The mechanics of interface failure is analyzed and an attempt is made to capture the debonding sequence during a thin-slice push-out test. The effect of different material and testing variables on the experimental observations are studied. The influence of processing induced residual stresses on interface behavior during the push-out test is examined in detail, with the main focus on the role of residual shear stresses in a thin-slice push-out test. The elastic-plastic behavior of the matrix and the temperature dependency of the constitutive properties are included in the analysis. The push-out behavior at elevated temperatures is also studied. The effect of temperature on the peak load in push-out tests, predicted using the proposed model, qualitatively agrees with the experimental observations.
Buckling of Laminated Plates with Adhesive Joints
Authors: Yeh Meng-Kao , You Yui-Long
Published: April 2011

The buckling behavior of laminated plates with adhesive joints under uniaxial compression was investigated analytically and experimentally. For the analysis, a two-dimensional nonlinear finite element code was developed and the buckling loads of the laminated plates were extracted from the calculation of the smallest eigenvalue. A testing frame was used to measure experimentally the buckling strength and deformation of the specimen with a single-stepped lap joint. The buckling loads decreased as the length of adhesive layer decreased and the thickness of adhesive layer increased. When the stacking sequence of the composite laminates was [θ/−θ]2 s, the buckling loads decreased as o increased. Close agreement was obtained between the analytical predictions and the experimental results. Improved buckling strengths of the composite laminates were obtained when the difference between the Young's modulus of adhesive and the longitudinal modulus of the laminated plates was decreased.
On the Apparent Bending Isotropy in Clamped Elliptic Composite Laminates
Authors: Lee S-W. R. , Sun C. T.
Published: April 2011

The flexural behavior of clamped elliptic composite laminates is studied. Both symmetric and asymmetric laminates are investigated. Closed form solutions are discussed for laminates subjected to uniform transverse loading. The appparent bending isotropy is identified for clamped elliptic laminates for which the deflection can be represented by an equivalent isotropic plate. An invariant characteristic bending stiffness is found for circular symmetric laminates. It is shown that the characteristic bending stiffness of quasi-isotropic laminates can be obtained directly from the in-plane effective moduli of the laminate. For laminates under nonuniform loading, the apparent bending isotropy may not exist. However, a numerical study shows that, for clamped circular π/4 quasi-isotropic laminates subjected to axisymmetric loading, the solution of isotropic plates can be adopted as a good approximation.
Analytical/Experimental Evaluation of Hybrid Commingled Carbon/Glass/Epoxy Thick-Section Composites under Compression
Authors: Chaudhuri Reaz A. , Garala Himatlal J.
Published: April 2011

This paper outlines a current effort at improving the compressive strength of carbon fiber reinforced composites (CFRC) by using a hybrid carbon/glass commingling concept. Prior investigations into the hydrostatic strength of thick-section carbon fiber reinforced composite cylinders resulted in failures which were significantly lower (50 to 70% of design pressure) than anticipated. The formation and propagation of fiber kink bands at the microscopic level, triggered by the fiber misalignment defects formed during the manufacturing process, leading to a shear crippling failure at the macroscopic level is the dominant compressive failure mode in the presence of fiber misalignment or waviness. It is theorized that one way to improve compressive strength is through the use of a commingled (at the tow level) hybrid fiber system. A novel fracture mechanics based concept for commingling a small percentage of glass with carbon fibers to suppress compressive failures due to inelastic micro-buckling of fibers and kink band propagation is developed. A Griffith type fracture criterion for a mode II crack growth, based on the principle of energy balance, is introduced to derive the hitherto unknown concept of kink toughness (i.e., resistance to kink band propagation), and to determine the required glass-carbon ratio for possible enhancement of toughness against the kink band propagation. The width of a kink band normalized with respect to a characteristic length scale, such as thickness of a matrix impregnated fiber tow can be used as a practical measure for kink toughness. Preliminary experimental data suggest enhancement of the compressive and flexural strengths of the composite material even with a small percentage (15%) of glass fibers in commingled hybrid composites. Most significantly, inspection of the failed compression test coupons clearly demonstrates that introduction of this small percentage of glass fibers is effective in changing the failure mode away from the catastrophic kink band failure mode. Furthermore, it may be noted that the flexural hybrid commingled glass/carbon/epoxy composite specimens have failed in tension, which is in sharp contrast to what has been observed in their baseline carbon/epoxy counterparts.
Finite Element Analysis of Effective Thermal Conductivity of Filled Polymeric Composites
Authors: Ramani Karthik , Vaidyanathan Aparna
Published: April 2011

A novel method to predict the macroscopic effective thermal conductivity of filled composites, based on its microstructural characteristics is developed and validated. A finite element method which incorporates the effect of microstructural characteristics such as filler aspect ratio, interfacial thermal resistance, volume fraction, and filler and fiber dispersion to determine the effective thermal conductivity of a composite with circular and rectangular fillers is presented. Filler interactions and chain formation effects are included in the model. To overcome the laborious task of repeated finite element model generation, an algorithm which generates the positions and orientations of the fillers in the matrix is developed. The automated model development capability is used to create several microstructures for finite element analysis. The trends predicted by the finite element models are compared with existing analytical models and available experimental results. The advantage of this method over existing analytical and semi-empirical models is that it can handle interactive effects, provide a detail heat flux pattern, and also model high filler volume fractions.
Analytical Models for Low Cost Manufacturing of Composite Components by Filament Winding, Part II: Inverse Kinematics
Authors: Mazumdar S. K. , Hoa S. V.
Published: April 2011

There are no available techniques for the prediction of fiber angle distribution for various mandrel shapes under different conditions of mandrel's rotations and delivery point motions. In the present paper a novel approach based on the geometric and trigonometric relations is developed for predicting the fiber laydown path for a given equation of motion for the delivery point. This is important during the start-up and reversal periods of the filament winding operation. During the start-up period, the delivery point accelerates from a velocity of zero to a final value in some interval of time, whereas during the reversal period the delivery point decelerates to zero velocity and then accelerates to a final velocity.

Equations of motion for the delivery point are presented to have smooth start-up and reversal periods. Closed form solution are developed to compute the fiber winding angle distribution on various types of cylindrical mandrels with axisymmetric and non-axisymmetric cross-sections, whereas numerical solutions are presented for non-cylindrical mandrels. Fiber slackening phenomena during a reversal period is discussed.

Based on the current approach, an interactive computer program INVERSEKIN is developed to determine fiber winding angle distributions for a given equation of motion, mandrel shape geometry and experimental set-up conditions. Effects of winding parameters on fiber position and fiber winding angle distributions are discussed. Experimental verification of the model is done on a McClean Anderson filament winding machine for a conical mandrel for various equations of delivery point motion.
Influence of Stress Ratio on Fatigue Behavior in the Transverse Direction of Unidirectional CFRPS
Authors: Miyano Yasushi , Nakada Masayuki , McMurray Michael K.
Published: April 2011

The dependence of flexural fatigue behavior in the transverse direction of two unidirectional carbon fiber reinforced plastics(CFRP) upon stress ratio (σ min/σ max) has been studied at several constant temperatures. The two CFRP contain the same type of carbon fiber but different matrix resins, one a general type and one a high glass-transition temperature type matrix resin. Three-point bending fatigue tests were performed at various constant temperatures under various stress ratios. As the stress ratio decreases from one to zero, the flexural fatigue strength near room temperature (well below the glass-transition temperature) decreases while the strength at temperatures close to the glass-transition temperature increases. These observations indicate that the flexural fatigue strength at room temperature depends on stress amplitude and thus is controlled mainly by fatigue damage, while the strength near the glass-transition temperature depends on mean stress and, therefore, is controlled by creep damage.
Design, Analysis and Fabrication of a Graphite/Epoxy Electronics Enclosure Flanged Aperture, with Supporting Electromagnetic Interference Test Data
Authors: Roberts Jack C. , Wienhold Paul D.
Published: April 2011

The structural design of a rectangular metal electronics enclosure for airborne or space applications is straightforward and contained in a number of texts. However, the design of a composite electronics enclosure, optimized for weight and structural and thermal load paths, has not been addressed. In particular, the design of flanges that attach the walls to one another or the enclosure to its cover is an important topic because of the need for EMI shielding and flange structural stability in a random vibration environment. Several carbon fabric/epoxy flanged aperture (two overlapping flanges with gap) designs were considered for integration into a composite electronics enclosure. The design evaluation was based on structural integrity, EMI shielding effectiveness, ease of fabrication, development time, number of parts, total cost, and total weight. The most promising design consisted of two overlapping "L" flanges with a double EMI gasket in the aperture. This design was analyzed for instability of the flanged aperture, local buckling of the individual flanges between fasteners, and bearing and shearout of the flanged aperture. Laminate configurations used in the structural analysis consisted of [(0°)]3, [(0°), (45°)] s, and [(0°), (45°), 0.076 mm thick syntactic foam core, (45°), (0°)]. The preliminary analysis indicated that the [(0°)] 3 laminate configuration would fail by local buckling between flanges. The [(0°), (45°), 0.076 mm thick syntactic foam core, (45°), (0°)] laminate had the highest margins of safety in overall flanged aperture instability, local buckling, bearing, and shearout. This configuration was thought to be the best lay-up because large margins of safety would be needed in random vibration to compensate for the unknown torsional and bending loads in the flanges. EMI shielding tests on a Ni plated carbon fabric flanged aperture from 200 MHz to 40 GHz showed that the geometry of the flange alone provided significant shielding over that of an open hole. The shielding effectiveness of the Ni plated carbon fabric/epoxy flanged aperture with EMI gasket was equivalent to that of a continuous solid Ni plated carbon fabric/epoxy panel. The [(00), (450)], and [(00), (450), 0.076 mm thick syntactic foam core, (45°), (00)] laminate configurations are currently being incorporated into a finite element model of the electronics enclosure.
Application of GPS Tensors to Fiber Reinforced Composites
Authors: Xie Z. -Y. , Chandra N.
Published: April 2011

In this paper we propose a pair of two new tensors called GPS tensors S and D for the concentric cylindrical inclusion problem. GPS tensor S relates the strain in the inclusion constrained by the matrix of finite radius to the uniform transformation strain (eigenstrain), whereas tensor D relates the strain in the matrix to the same eigenstrain. The tensorial form of relationship to the inclusion problem allows us to derive explicit expressions for a larger class of transformation problems, including thermal residual stress problems. Since GPS tensors take the fiber volume fraction into account explicitly, we are able to study the effect of matrix properties and fiber volume fraction on the spatial distribution of thermal residual stress. GPS tensors are also used in the evaluation of effective material properties by using the self-consistent method. Very good agreement between analytical results using GPS tensors and experimental data is observed for graphite/epoxy and glass/epoxy composites.