bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Manufacturing Conditions for Hot-Gas-Aided Thermoplastic Tape Winding
Authors: Mazumdar S. K. , Hoa S. V.
Published: June 2014

Carbon/PEEK (APC-2) thermoplastic composite rings are manufactured by the thermoplastic tape winding process using hot nitrogen gas as a heat source. In the tape winding process, localized melting causes a high rate of heating and cooling, which demands different manufacturing conditions from hot pressing and autoclave processing. Heating rate and cooling rate are found to be more than 20,0000C/min and 5,0000C/min, respectively, and melt time is found to be in the range of 1 to 4 seconds for hot gas processing. Shorter melt times and higher heating rate during the on-line consolidation process require higher processing temperatures (greater than 600'C) for sufficient molecular interdiffusion. Higher molecular interdiff-usion would produce better interlaminar properties.

During the production of thermoplastic composite parts using the thermoplastic tape winding process, several parameters such as heat intensity, tape speed, consolidation pressure, preheating temperature of tape and tool material, and cooling rate can affect the properties of an end product. A judicious selection of such parameters can produce a composite part which has fewer voids, better consolidation, minimum residual stress, desired crystallinity and high quality. Effects of dominant processing parameters such as heat intensity, tape speed, and consolidation pressure on temperature distribution, processinduced deformation, quality of consolidation, and crystallinity are examined.
Ply-Level Failure Analysis of Thick-Section Composite Structures Based on "Smeared" Finite Element Results
Authors: Bonanni D. L. , Tacey R. K.
Published: June 2014

Conventional failure criteria for laminated composite materials require stresses and strains at the ply level. However, finite element analysis of practical thick-section composite structures is often based on equivalent homogeneous ("smeared" or effective) material models, which predict only laminate-averaged stresses and strains. This paper describes a post-processor to the ABAQUS general-purpose finite element code that performs ply-level failure analysis of a thick-section laminated composite structure given the results of a smeared ABAQUS analysis. The program, called ABAFAIL, provides ABAQUS users with an automated tool for composite first-ply failure analysis and produces thorough results that are easily interpreted. The ply-level stresses and strains required for failure analysis are extracted from the effective quantities at each node in the finite element model via a 3-D lamination theory. The failure criteria currently incorporated in ABAFAIL are Maximum Stress, Maximum Strain, Tsai-Hill, Tsai-Wu, and a modified version of Hashin's theory; other criteria can be easily added. Printed output includes failure indices and extrapolated failure loads. In addition, files may be obtained which are suitable for PATRAN visualization of failure index data.
Strain Distributions and Over-Stressed Volumes in Unidirectional Composites with Multiple Fiber Breaks
Authors: Pandey Parth , Sundaresan Mannur J.
Published: June 2014

A finite element technique was used for determining the strain distribution around fiber breaks in unidirectional composite monolayers subjected to tensile stress in the fiber direction. Various extents of damage, ranging from a single fiber break to ten adjacent fiber breaks, were considered. Both the fiber and the matrix were considered to be elastic. From the finite element results, the level of overloading in fibers around such damage and the volume of neighboring fibers subjected to overload were determined. To provide a detailed description of the stress distribution, this over-stressed volume was divided into sub-volumes corresponding to various strain levels and presented in the form of a histogram. Over-stressed volume histograms were generated for a variety of composite materials having various combinations of fiber volume fraction and matrix stiffness. In most cases, the stress concentration factor obtained from the finite element analysis was significantly greater than the corresponding value obtained by using the shear-lag model. The overstressed volume histograms are expected to be useful in the strength prediction of composite materials.
Integrating Material/Part/Process Design for Polymer Composites: A Knowledge-Based Problem-Solving Approach
Authors: Mcdowell James K. , Kamel Ahmed M. , Sticklen Jon , Hawley Martin C.
Published: June 2014

Polymer composites provide the opportunity to design the material as well as the part. The domain for composites design can be viewed along three dimensions, namely material design, part design, and process design. These dimensions are not independent, and their interactions create important bottlenecks in manufacturing. Integrating these material/part/process issues becomes increasingly important as composite materials penetrate the durable goods markets and as high-performance markets become more and more cost conscious. Often these bottlenecks are caused by lack of strategic knowledge or the application of knowledge in the wrong context. To address these challenges and facilitate the use of polymer composites, a problem-solving architecture for integrated material/part/process design is being developed that makes use of knowledge-based systems (KBS) technology. The goal is to bring to bear the necessary decision-making knowledge at important junctions in the design procedure. Our current implementations include a system for material design and a system for elementary process design in the form of process technology selection. These systems and the problem-solving architecture are founded on a particular approach to KBS known as Generic Task Theory. These software systems are described in terms of their behavior, the underlying domain assumptions, and the knowledge representation constructs and inferences used in design problem solving.
On the Thermoelastic Field in a Composite Material with Inhomogeneities
Authors: Huang Jin H.
Published: June 2014

This paper concerns ellipsoidal inclusion problems in a three-dimensional composite material subjected to a far-field uniform heat flow. The eigenstrain formulation is developed to examine the thermoelastic field that results from two sources: one induced by the inclusion of thermal properties alone, and the other intensified by the inhomogeneity of elastic material constants. When the thermal conductivity and the thermal expansion coefficient of the inclusion are different from those of the surrounding matrix, the eigenstrain is utilized to simulate the thermal expansion strain and thermal expansion mismatch strain, respectively. It is shown that the eigenstrain is a homogeneous function of first degree, and the resulting thermoelastic field inside the ellipsoidal inclusion is therefore a homogeneous function of first degree. With these results in hand, the equivalent inclusion method is further employed to obtain the total thermoelastic field in the inhomogeneity which has elastic constants differing from those of the matrix.
Effect of Fiber Material on the Energy Absorption Behavior of Thermoplastic Composite Tubes
Authors: Hamada H. , Ramakrishna S.
Published: June 2014

The primary objective of this work is to identify the effect of fiber material on the energy-absorption characteristics of thermoplastic composite tubes. PEEK matrix composite tubes reinforced with AS4 carbon fiber, IM7 carbon fiber, and S2 glass fiber have been investigated. Seven fiber orientations (0) were used: unidirectional fibers parallel (0°) to the axis of the tube, ±5°, ±10°, ±15°, ±20°, ±25° and ±30°. A ±45° chamfer was ground onto one end of each specimen to initiate progressive crushing. The ±30° AS4/PEEK, ±30° IM7/PEEK, and ±25° and ±30° S2/PEEK tubes failed catastrophically, whereas all the other tube specimens crushed progressively in splaying mode. The energy absorption capability of all three types of tubes varied with the fiber orientation. The carbon-fiber-reinforced tubes displayed 20% higher specific energy absorption capability than the glass-fiber-reinforced tubes. Among the carbon-fiber-reinforced tubes, for intermediate fiber orientations, the AS4/PEEK tubes absorbed slightly higher energy than the IM7/PEEK tubes. Efforts have been made to relate the energy absorption capability to the failure processes in the crush zone.
Effect of Loading Path on the Stress-Strain Relation and Progressive Damage of a Polymer-Matrix Composite under Tension/Torsion Biaxial Loading
Authors: Tanaka T. , Fujii T. , Kamada M.
Published: June 2014

Strength and stress-strain properties of plain woven glass-fabric composites were measured under three different loading paths which gave the same final stress state. Thin-walled tubular specimens were used. The present study focused on progressive damage. In all tests, acoustic emissions (AE) were measured to distinguish damage accumulation such as debonding, matrix cracking and fiber breakage. Failed specimens were observed using an optical microscope. Based on the experimental results, a new yield criterion for glass-fabric composites was proposed. Damage accumulation and its sequence were both affected by loading path. The S-S relations up to failure were affected by the biaxial stress ratio a (the ratio between normal and shear stresses) and loading path. However, the strength did not depend on the loading path. The material failure was governed by the final stress condition regardless of the difference of loading path.
The Thermoplastic Laser-Assisted Consolidation Process-Mechanical and Microstructure Characterization
Authors: Agarwal Vivek , Mccullough R. L. , Schultz J. M.
Published: June 2014

The laser-assisted consolidation process can produce high-quality continuous-fiber composite parts in a single consolidation and winding step. Parts fabricated using this process were characterized for void content, crystallinity, and interlaminar strength and toughness. Optimum interlaminar properties were obtained at intermediate laser powers. Interlaminar properties were poor at high laser powers because of resin degradation. At low laser powers, poor properties were most likely caused by insufficient molecular interdiffusion. The void content of parts fabricated using this process was less than 2 percent, and the bulk crystallinity of 29% was not significantly different from that of the original prepreg tape.
An Investigation of Tensile Properties and a Simple Constitutive Model for a Random Continuous Fiber Thermoplastic Composite
Authors: Shaffer T. M. , Mallick P. K.
Published: June 2014

The tensile properties of a commercially available, random continuousfiber thermoplastic composite material are investigated at various strain rates and elevated temperatures. The material utilizes polypropylene (PP) for the matrix material, with random continuous E-glass fiber reinforcement. Tensile modulus, tensile strength, strain to peak stress, and strain energy are experimentally determined at strain rates varying from 0.000167 sec-1 to 0.0334 sec-5 and temperatures varying from 20 to 120'C. The material properties are found to have large scatter caused by local variations in fiber content and orientation. The tensile properties are independent of the strain rate but depend on the temperature. A model for the material response based on a simple power law equation is presented.
Evaluation of Materials for Composite Repair Applications
Authors: Mehrkam P. A. , Cochran R.
Published: June 2014

There are many adhesives and resins available for repair of composite aircraft structures. The selection of repair materials is based on several requirements, including the type of structure being repaired, structural loads, thermal stability, and process limitations of the material and structure. The Navy's requirement for performing repair actions at remote locations has placed a number of additional constraints on materials being developed for repair applications. Specifically, Navy field repair requirements impose the need for materials that are storable at ambient temperatures, processable with vacuum bag/heat blanket repair equipment, similar in mechanical properties to production materials, and compatible with field-level maintenance personnel capabilities and training. Developmental efforts at the Naval Air Warfare Center supporting naval aircraft in the fleet led to the evaluation of several materials for repair of complex shaped graphite/epoxy structures. The repair applications include structural bonding, wet lay-up patches, honeycomb core splicing, back side sealing, and filling small scratches. A series of materials supplied by Magnolia Plastics, including Magnobond 6362, 6367, 6371, 6391, 6392, 6396 and 6398, was tested to determine compatibility with repair procedures, mechanical strength, and thermal stability in an 820C (180'F) hot-wet environment. Results of the evaluation and potential applications for the materials are presented.
Analysis of Adhesively Bonded Composite Double Lap Joints
Authors: Tong L. , Kuruppu M. , Kelly D.
Published: June 2014

A new nonlinear formulation is developed for the governing equations for shear and peel stresses in adhesively bonded composite double-lap joints. The new formulation allows arbitrary nonlinear stress-strain characteristics in both shear and peel behavior. The equations are numerically integrated using a shooting technique and the Newton-Raphson method with an in-house-developed user-friendly interface. Numerical examples are presented to demonstrate the effect of the nonlinear adhesive behavior on the stress distributions. Failure loads are predicted using an interlaminar delamination failure criterion for three groups of adhesively bonded composite double-lap joints. It is shown that the failure loads predicted using the present nonlinear adhesive model correlate well with the measured failure loads, while the failure loads computed using the linear adhesive model are only about half of the measured failure loads.
Effect of Stacking Sequence on Failure of [±45/90/0]s Quasi-Isotropic Coupons with a Hole under Compression
Authors: Iyengar Nirmal , Gürdal Zafer
Published: June 2014

A combined experimental and numerical study of the compression response and the failure characteristics of various quasi-isotropic coupons with a hole obtained from a [±45/90/0]s quasi-isotropic laminate was carried out. Specimens with various quasi-isotropic stacking sequences of [±45+ l=O//90 + l=O/l=O]s, were acquired by cutting the coupons at various angles k from the quasi-isotropic laminate. Analysis of the coupons based on 2-D and 3-D finite element models were performed to evaluate the stresses around the hole. Two different compressive failure prediction techniques based on distinctly different failure modes, namely fiber kinking and delamination, have been evaluated. The validity of these techniques was measured against experimental data of quasiisotropic coupons tested.

The failure of the laminated coupons with a hole has been shown to be sensitive to the stacking sequence. It is also shown that a 2-D finite element model does not provide the required stacking sequence sensitivity. Thus, a 3-D analysis of the stress state in the vicinity of the hole is necessary. The study shows that no one mode of failure is responsible for limiting the strength for all laminate off-axis orientations, but rather the failure mode changes with change in stacking sequence. The analysis also substantiates the experimental data presented, that the peak strength of the laminate is achieved for a stacking sequence of [32.5/-57.5/77.5/-12.5], which corresponds to an off-axis angle of 12.5 with respect to the loading direction.
A Three-Dimensional Micromechanical Model of the Compressive Behavior of Unidirectional FRP Composites
Authors: Zhang Guigen , Latour Robert A.
Published: June 2014

A 3D model of fiber microbuckling assuming a square packed fiber array has been developed and analyzed under the assumption of fiber in-plane microbuckling. In this model, the fiber equilibrium equation is first developed as a function of uniaxial loading, material properties, and fiber/matrix interfacial stresses. By utilizing 3D boundary element modeling, the 3D stress distribution along the fiber/matrix interface is determined. The interfacial stresses obtained from the 3D boundary element analysis are then incorporated into the 3D equilibrium equation of fiber microbuckling to provide a closedform analytical solution of the 3D compressive fiber strength in unidirectional composites. Results show that the in-plane shear stress component is predominant, while one of the two out-of-plane stress components, which cannot be captured by a 2D model, is not negligible. Furthermore it is found that the in-plane interfacial shear stress is strongly dependent upon fiber spacing. These results indicate that the results for a 2D model are quite different from those of the 3D model. Therefore, the 3D model of compressive behavior of unidirectional composites is necessary in order to properly model the real interfacial stress distribution in a unidirectional composite subjected to axial compressive load. Because of the strong dependence of interfacial shear stress upon fiber spacing, more accurate calculation of in-plane interfacial shear stresses and theoretical fiber microbuckling strength will result from a 2D model if fiber spacing in the model is set to match that of a 3D model for a given 3D model-based fiber volume fraction.
Manufacturing of an Aileron Rib with Advanced Thermoplastic Composites
Authors: Hou Meng , Ye Lin , Mai Yiu-Wing
Published: June 2014

In this work, the manufacturing technology for an aileron rib for a civil aircraft with advanced CF/PEI thermoplastic composite materials was investigated. In particular, the compression molding method was applied and continuous-carbon-fiber fabric-reinforced polyetherimide (PEI) composite materials were used. The study was focused on the optimization of processing conditions which led to the production of highquality aileron ribs with CF/PEI thermoplastic composites. The design of processing molds and the relationships among the processing conditions, microstructures and mechanical properties (flexural stiffness and strength) of the produced composite parts were presented. The sample quality in relation to processing conditions was evaluated by C-scan, microscopic examination, void content measurement, and mechanical test programs.
Modeling of Heat Transfer and Crystallization in Thermoplastic Composite Tape Placement Process
Authors: Sonmez Fazil O. , Hahn H. Thomas
Published: June 2014

The crystallization behavior of thermoplastic composites during the tape placement process has been analyzed. A heat transfer analysis has been carried out using a finite element method. The heat transfer analysis is coupled with a crystallization kinetics model to predict the resulting morphology. In order to determine the heat intensity that could be applied to the laminate, a degradation kinetics model is added. The degradation kinetics model thus provides an upper bound for the heat input. The models relate the process parameters (e.g., roller velocity, roller pressure, heat input) to temperature and crystallinity distributions and degradation weight loss. These models are incorporated into a computer code to generate numerical results. By using this code, process conditions which are favorable to consolidation and also likely to produce optimum crystallinity levels are identified.
Effect of Stitching on Impact and Interlaminar Properties of Graphite/Epoxy Laminates
Authors: Sharma S. K. , Sankar B. V.
Published: June 2014

Effects of through-the-thickness stitching on the impact damage resistance, impact damage tolerance, and interlaminar fracture toughness (Mode I and Mode II) of plain woven and uniweave textile graphite/epoxy laminates were investigated. The uniweave textile was formed by weaving dry carbon-fiber tows with fiberglass fill tows. The content of fiberglass fill tows was 2.5% by weight. The plain woven laminates were manufactured using resin infusion molding and the uniweave laminates by resin transfer molding. Kevlar and glass yarns of various yarn numbers were used for stitching. Static Indentation-Flexure, Compression-After-Impact, Double Cantilever Beam and End-Notched Flexure tests were conducted. Stitching did not have any effect on the onset of impact damage. However, stitching leads to significant improvement (25-40%) in impact damage tolerance as measured by CAI strength and impact damage area. Mode I fracture toughness as characterized by critical strain energy release rate (G,Ic) was found to increase by at least an order higher (15-30 times) than the unstitched laminates. Mode II fracture toughness (GIIc) increased by 5-15 times over the unstitched laminates. New methods to estimate the Mode II critical strain energy release rate in the stitched laminates are presented. The stitched textile advanced composites are considered potentially superior to prepregs for high-volume, low-cost and high-performance structural materials.
Selection of Critical Thermal/Structural Design Parameters for a Metal/Composite Joint in a Composite Electronics Enclosure
Authors: Bailey L. E. , Roberts J. C. , Jones D. L.
Published: June 2014

An experiment was designed to determine the critical design parameters for a metal/composite joint in a composite electronic enclosure where both thermal and mechanical performance are important. A combination bolted and bonded single-lap joint that simulates the interface between the thermal wall and the card guide was studied under static loading with power supplied through a surface-mounted chip resistor. The following parameters were varied: fiber orientation, type of thermally conductive pitch fiber, type of adhesive, adhesive thickness, bolt spacing, bolt size, and input power. Load, strain, and temperature from five thermocouples were collected during a tensile test with a 0.02 in/ min. strain rate. A fractional factorial experimental design was used. A dual failure mechanism was consistently recorded: failure of the adhesive bond followed by bolt shear failure. Initial screening results indicated that a configuration can be achieved that significantly enhances both mechanical and thermal performance.
Analysis of the Fatigue Performance of Notched and Unnotched Graphite/Thermoplastic Composite Laminates
Authors: Whitworth H. A. , Llorente Steven G. , Croman Robert B.
Published: June 2014

The present investigation summarizes an evaluation of the effect of fatigue loading on continuous and long discontinuous fiber (LDF) composites manufactured using the AS4/PEKK (poly-ether-ketone-ketone) system. Approximately 100 static and fatigue specimens were tested in a two-phase experimental investigation. In the first phase, LDF AS4/PEKK thermoplastic specimens of 2 layups [0/90/ + 45]. were tested in static tension to determine their respective strengths. Constant amplitude fatigue tests were then conducted to evaluate the behavior of these two LDF composite laminates. Specimens surviving one million cycles were statically tested to failure. In the second phase of the investigation, continuous fiber AS4/PEKK thermoplastic laminates were tested in static tension and in fatigue to evaluate the effect of the discontinuous fiber on composite performance. The effect of a known stress concentration on both material systems was also investigated using specimens having a 0.635 cm center hole. Static tests confirmed a reduction (13%) in unnotched LDF strength compared with continuous fiber thermoplastics. One additional objective was to determine whether the presence of discontinuous fibers, and the resulting stress concentrations, would cause a severe reduction in LDF thermoplastic composite fatigue properties. This was not found to be the case.
Thermal Analysis for Thermoplastic Composite Tow/Tape Preheating and Pultrusion
Authors: Nejhad Mehrdad N. Ghasemi
Published: June 2014

The on-line consolidation of thermoplastic composites is a relatively new technology that can be used to manufacture composite parts with complex geometries. The localized melting/solidification technique employed in this process can reduce the residual stresses and allow for improved dimensional stability and performance. An additional advantage of this technique is elimination of the curing steps that are necessary in the processing of thermoset-matrix composites. This paper discusses analytical and numerical anisotropic thermal analysis for preheating and/or pultrusion of impregnated composite tows or tapes. Heat of melting/solidification is included in the form of a heat generation term. A separation of variable method is employed to solve the governing equations analytically. In the numerical analysis, the governing equations are discretized using a nonuniform mesh and solved employing a finite difference approach. The processing parameters, such as processing speed, heat intensity, heat source width, etc., as well as material properties are incorporated in the analysis. The maximum error between the analytical solution and the numerical result is found to be 1%.
Rheological Conditions for the Development of Fibrils in Blends of Liquid Crystalline and Conventional Polymers
Authors: Roetting O. , Hinrichsen G.
Published: June 2014

In blends of liquid crystalline polymers (LCP) with conventional thermoplastics, the development of infinite, thin and highly oriented LCP-fibrils is very important for a substantial mechanical reinforcement of the blends. Such fibrils can be produced by processing a coarse mixture of LCP and polyethyleneterephthalate (PET) powders in an extrusion apparatus in which preferentially elongational, but only weak shear flows occur. The rheological conditions for the success of this process are explained.
Injection Molding and Properties of Highly Filled Copper-Polyamide 11 Composites
Authors: Bέlanger B. , Sanschagrin B. , Fisa B.
Published: June 2014

Copper-polyamide-I1 composites containing up to 90 wt.% of spherical copper powder were made using three approaches: (1) conventional injection molding of dry copper-polyamide powder blends, (2) compounding of powder blends and subsequent injection molding of composite pellets, and (3) direct molding of powder blends on an injection machine equipped with a vacuum hopper. The conventional molding of powders results in products having a significant porosity, which originates from the air dragged into the machine with the powder. The other two approaches can be used to produce essentially void-free materials. The mechanical properties are affected by the state of the filler surface. The "as-atomized" copper (which has a rough surface covered with an oxide layer) adheres better to the polymer than that whose surface was reduced to pure metal by hydrogen.
Analysis of the On-Line Consolidation Process in Thermoplastic Composite Tape Placement
Authors: Sonmez Fazil O. , Hahn H. Thomas
Published: June 2014

The main objective of the present study is to establish the relationships between the process variables and the quality of thermoplastic composite laminates fabricated by tape placement. The quality parameters considered in the process modeling are interlaminar bond strength, weight loss through thermal degradation, and crystallinity. Stress, heat transfer, crystallization, degradation, and bonding models are developed. These models relate the process parameters (e.g., roller velocity, roller pressure, heat input) to temperature, stress, and crystallinity distributions, degradation weight loss, and degree of bonding within the composite. These relationships are used to develop a process window to ensure product quality. The process parameters are then optimized to reduce the lay-up time.
Recyclability of Waste Cord of Synthetic Fibers as Matrix Material for Thermoplastic Hybrid Composites
Authors: Kimura Teruo , Takeuchi Masanori , Nakanishi Koji
Published: June 2014

The hybrid composites were molded using the waste cord of synthetic fabrics as a matrix material, wherein continuous glass and carbon fibers were used for the reinforcements and were fed directly into the injection molding machine together with the waste cord. The measured tensile strength and tensile modulus of the molded composites were much higher than those of the matrix material, and they increase with increasing carbon fiber content. It is concluded that the molding system devised herein shows promise for contributing to the material recycling of waste cord of synthetic fabrics.
A Process Sensitivity Study of Composite Compressive Strength
Authors: Shin Daniel D. , Hahn H. Thomas
Published: June 2014

The effects of variations in curing parameters on the compressive strength of graphite/epoxy laminates were studied. The evaluated parameters were cure temperature, time, and pressure. Two specific settings were chosen for each parameter to form a unique processing envelope centered on the manufacturer's recommended cure cycle. Through factor analysis, high compressive strength was noticed with high cure temperature (204'C), low pressure (0.482 MPa), and long cure time (2.5 hours). This result suggests that deviation of cure time and temperature above the manufacturer's suggested cure cycle will still produce quality laminates. On the other hand, deviation below the manufacturer' s cure cycle will result in incomplete cure, which was evident in the experiment. Furthermore, according to the analysis of variance (ANOVA), the only factor that was significant at the 90% confidence level was cure time, while the cure temperature was slightly less significant. Therefore, cure time was the most sensitive to the compressive response. The next important parameters were cure temperature and pressure.
Damage Progression and Failure of Glass Fabric Composites Subjected to Tension/Tension and Tension/Shear Combined Stresses
Authors: Tanaka T. , Fujii T. , Ishikawa A.
Published: June 2014

Damage progression and final failure of plain woven glass-fabric-reinforced composites subjected to tension/tension (or compression/tension and tension/shear combined stresses) were studied. Normal stresses (a, and a2) were applied to tubular specimens parallel to the material axes as well as shear stress (T12). At tension/shear combined stress state, the S-S relation up to failure was strongly affected by the biaxial stress ratio, a (=/ra1T2). However, in the tension/tension combined stress state, the S-S relation was not strongly affected by the alternative biaxial stress ratio,fl (=u1/a2), although the stress combination at final failure changes with respect to/p. The S-S curve under tension/tension combined stress is represented by two straight lines that intersect each other at the knee point. The Tsai-Wu failure criterion fits well the experimental failure envelope under tension/shear combined stress. while the maximum stress theory fits better than the Tsai-Wu failure criterion under tension/tension (and compression/tension) combined stress. The initial yield stress condition under tension/tension combined stress was represented by a square that was based on the knee stresses at/? = 1/0 and 0/1. Internal damage and its accumulation do not affect the biaxial strength under tension/tension and tension/shear combined stresses.
Vibration of Variable Thickness Orthotropic Plates Using Eigensensitivity Analysis
Authors: Barton Oscar , Raouf Raouf A.
Published: June 2014

An approximate closed-form expression is presented which can be used to compute the fundamental frequency of orthotropic laminates of variable thickness. The quadratic expression is derived for a laminate with a general thickness variation in one direction, and explicit results are provided for a laminate with a linear thickness variation. The desired expression is determined by casting the governing differential equation into discrete form using the Ritz method and expanding the discrete equations in a Maclaurin series about the off-diagonal elements of both the stiffness and mass matrices. Simply supported and clamped boundary conditions are analyzed using both beam shape functions and orthogonal polynomials. Results are compared with those obtained numerically using the Rayleigh-Ritz approach for several laminate tapers $ and plate aspect ratios R.
Integral Micro-Mechanical Interlock (IMMI) Joints for Polymer-Matrix Composite Structures
Authors: Messler Robert W. , Genc Suat
Published: June 2014

A relatively new concept for producing joints in structures made from polymers with potential for polymer-matrix composites is presented, described, positioned, and organized. Named here integral micro-mechanical interlocking or IMMI (pronounced "eye-my") joints, the concept is derived from several different traditional integral attachment approaches, but on a finer scale. As such, IMMIs offer the freedom from fasteners and fastening tools and the ease of assembly sought in design for assembly (DFA) philosophy, with expected improvements in strength compared to joints in polymer-matrix composites made by conventional mechanical fastening or adhesive bonding. The position of IMMIs within an overall hierarchy ofjoining methods is shown, and three fundamental approaches are identified, described, and illustrated, depending on whether the interlock is accomplished in a rigid, elastic, or plastic fashion. An IMMI design matrix is also presented that shows general performance expectations in shear, tension, and overall load-carrying capability and utility. The overall intent of the paper is education, organization, and stimulation of thinking.
Characterization of a Fiber-Reinforced New Fully Aromatic Liquid Crystalline Polymer
Authors: la Mantia F. P. , Sortino G. , Scaffaro R. , Bertolini G. , Montani E. , Pedretti U.
Published: June 2014

A new rigid liquid crystalline polymer that demonstrates good mechanical and thermomechanical properties and acceptable processing temperature has been recently synthesized and characterized. The melting temperature and some thermomechanical properties do not seem, however, suitable for use in some applications at high temperature or in the presence of aggressive fluids. The use of appropriate inorganic fillers can overcome these shortcomings. In this work the new LCP, polymerized in a bench-scale apparatus, and the same sample filled with carbon fibers are characterized. The properties of the carbon fiber filled LCP are compared with those of another filled wholly aromatic commercial LCP, a carbon filled semirigid LCP, and the same semirigid LCP reinforced with glass fibers.

In general, the mechanical properties of the filled LCP sample increase remarkably when the filler concentration is about 20%; however, with further increases in filler content, a decrease is observed. The thermal and chemical resistance of this new rigid LCP seems slightly influenced by the addition of fibers, while the thermal resistance of the other two LCP samples is remarkably improved.
Mechanics of Stochastic Fibrous Networks
Authors: Sastry A. M. , Cheng X. , Wang C. W.
Published: June 2014

Point-bonded fibrous networks are used in a variety of engineering applications, including reinforcement for polymeric composites, paper, and electrochemical substrates, among many others. An understanding of the nature of the deformation of these irregular microstructures is key to developing useful manufacturing guidelines for their cost-effective production. The current approach allows such analysis, through use of a stochastic approach in constructing the network. Resulting network properties are compared with those in more regular arrays. Ultimately, determination of local deformations in these kinds of networks will be used to predict local deformation due to flow front progression in fibrous preforms for production of polymeric composite materials.
Creation of Conducting Networks among Particles in Polymer Melts by Chaotic Mixing
Authors: Danescu R. I. , Zumbrunnen D. A.
Published: June 2014

Chaotic mixing of a nonconducting thermoplastic melt and initially coarse clusters of conducting particles has been investigated to assess opportunities for the in-situ formation of extended particle networks. Upon capture by solidification, such extended networks may render the composite electrically conducting. Chaotic advection of small, spherical, non-interacting particles was studied computationally and experimentally in a cavity formed between two offset cylinders. Numerical tracking of individual particles was performed under conditions where global chaotic mixing prevailed. Formation mechanisms were identified at various stages of mixing. After mixing, networks comprising interconnected particles were identified as electrical pathways. Micrographs of composites produced experimentally by two-dimensional chaotic mixing of thermoplastics with conducting carbon black showed structures resembling those predicted by the simulations and provided further insights into formation mechanisms. The electrical resistivity of the composites is also compared to composites produced by conventional means.
Virtual Prototyping in Polymer Composites
Authors: Lenz Timothy J. , Hawley Martin C. , Sticklen Jon , McDowell James K. , Scanlon John F. , Wigell Gary A.
Published: June 2014

Polymer composites have no standardized design procedure that guides a conscientious consideration of the multiple interactions among materials, manufacturing, and geometry. Intelligent decision support systems can enable such considerations during the critical conceptual design phase, where function and general structure are more significant than detailed geometry. This paper focuses on the knowledge representation and inference strategies in an intelligent decision support system for the conceptual design of polymer composite assemblies. The conceptualized function and structure of an assembly are represented in functional and configuration knowledge models. The specific domain application is retrofitting an existing metal assembly using polymer composite materials.
Optimizing Lamination of Hybrid Thick-Walled Cylindrical Shell under External Pressure by Using a Genetic Algorithm
Authors: Byon(G. Ben) O. , Nishi Y. , Sato S.
Published: June 2014

The effects of thermal residual stresses, strains, and stacking sequences resulting from hybrid composite material system selection on the design of thick-walled cross-ply cylindrical shells are discussed by using a simple and accurate finite cylindrical element method formulated by Byon and Vinson [1]. It is seen that beneficial effects can be realized in the cylindrical shells by utilizing a hybrid of graphite/epoxy and E-glass/epoxy material systems. An optimal stacking sequence of hybrid composite cylindrical shell is also proposed to give the smallest value of tensile strain in the through-the-thickness direction. This paper describes an optimal stacking sequence of a thick-walled cross-ply cylindrical shell laminated with hybrid composite materials determined by a genetic algorithm (GA) and shows that this method is useful for such an optimization problem.
Skin-Stiffener Stresses in Composite Plates and Shallow Shells
Authors: Robeson Mark E.
Published: June 2014

The development of an approximate analysis for predicting stresses in the skin-stiffener interface region of composite plates and shallow shells is presented. The analysis determines interlaminar normal stress and transverse shear stresses in the direction of the stiffener axial coordinate and the direction of the in-plane coordinate perpendicular to the stiffener axis. The analysis accounts for skin-stiffener interfaces with nonzero thickness and for curvature in the skin and stiffener. The interlaminar normal stress and transverse shear stresses at the interface are applied to the lower face of the skin and the upper face of the stiffener flange as unknown functions, and the displacements in the skin and flange are related through the deformation of the interface bond layer. The Rayleigh-Ritz method is used to determine the unknown functions that yield the interlaminar stresses at the skin-stiffener interface. Distributions of the interface stresses are presented, and these results show that the stresses are greatest at the edge of the stiffener flange. In addition, results from the skinstiffener analysis have been compared with results from other analyses, and all of these results were found to be in close agreement.
Analysis of a Fiber Composite Cylinder Laminated with an Elastic-Plastic Aluminum Liner under Internal Pressure Loading
Authors: Swanson Stephen R. , Offolter Matt
Published: June 2014

The basic equations are given for the analysis of a fiber composite cylinder wrapped over a ductile liner. The stiffness of the laminated cylinder is based on classical lamination theory along with thin-shell assumptions, in the linear range. After yielding of the liner, an incremental tangent matrix is employed, based on classical plasticity theory. Comparisons of the stiffness and residual strain predictions with experiments are given and show good agreement.
On the Elastic Behavior of a Cross-Ply Composite Pin-Joint with Clearance Fits
Authors: Di Scalea F. Lanza , Cappello F. , Cloudt G. L.
Published: June 2014

The effect of pin/hole clearance fits on the elastic membranal behavior of a cross-ply fiber glass-reinforced epoxy laminate plate loaded in tension through a pin is examined by a finite element nonlinear contact analysis. No a priori assumption is made on the distribution of the contact pressure on the surface of the hole. Friction effects are not included. The numerical results correlate well with Hertzian theory of contact. It is demonstrated that clearance increases the peak compressive stress in the plate up to a factor of 3000% with respect to the perfect-fit case. Clearance also shifts the location of the peak tensile stress towards the pin/hole contact arc and decreases its magnitude by 4% with respect to the perfect-fit case. The degree of clearance does not significantly influence the stress distribution in the plate outside the contact arc.
On the Effect of Interference Fits in Composite Pin-Joints
Authors: Di Scalea F. Lanza , Cappello F. , Cloud G. L.
Published: June 2014

The Finite Element Method is used to determine the effect of pin/hole interference fits on the elastic membranal behavior of an orthotropic plate loaded in tension through a pin. A complete contact analysis is performed to handle the nonlinear contact problem. The study encompasses two levels of interference fits, two degrees of anisotropy of the plate, and two load levels. Friction effects are not included. Experimental results from Digital Speckle Pattern Interferometry are also presented. It is shown that the stress changes in the plate vary linearly with load when no pin/plate separation occurs. It is also shown that interference fits can have beneficial effects on the static and fatigue behavior of the plate.
Viscoelastic Response of Composite Overwrapped Cylinders
Authors: Tzeng Jerome T.
Published: June 2014

Creep and stress relaxation behavior of composite overwrapped cylinders are investigated based on anisotropic viscoelasticity. The analysis accounts for ply-by-ply variations of material properties, ply orientations, and temperature gradients through the thickness of cylinders. Fiber-reinforced composite materials generally illustrate extreme anisotropy in viscoelastic behavior. The viscoelasticity exists mainly in matrix-dominant properties such as transverse and shear, while the fiber-dominant properties behave more like elastic media. The study of thermal and mechanical stress relaxation in an overwrapped composite cylinder shows that the viscoelastic characteristics of composite cylinders are quite different from those of isotropic cylinders. Poisson effects from the creep behavior in the transverse properties of the composite can result in a drastic change of stress and strain state of the cylinder.
Influence of Processing on Morphology, Interface, and Delamination in PEEK/Carbon Composites
Authors: Vu-Khanh T. , Frikha S.
Published: June 2014

It is well known that the mechanical properties of thermoplastic composites depend upon processing parameters such as cooling rate, melting temperature, and residence time at the melt temperature. This is due to the change in matrix morphology, fiber/matrix interaction, and interphase structure with processing conditions. In previous works on carbon fiber/PEEK composites, it has been found that an increase in the melting temperature and the residence time improves the short-beam-shear strength of the composite, and increasing the cooling rate results in a decrease in this strength. Crystallinity at the interface appeared to be efficient only if there is a strong physico-chemical interaction between the matrix and the fiber. Moreover, transcrystallinity does not seem to be the primary factor responsible for a good fiber/matrix interaction in thermoplastic composite materials. The purpose of this work is to foster the understanding of the role of morphology in the bulk matrix and at the fiber/matrix interphase in the composite performance. The morphology of the matrix is observed by optical microscopy and compared with the analysis results from differential scanning calorimetry (DSC). The composite performance is investigated by Mode-I and Mode-Il delamination tests. The results show that the transcrystalline region strongly depends on the molding parameters and controls the fiber/matrix interfacial strength in the composite. A better-defined spherulite structure is observed with specific molding temperature and residence time at melt temperature. The cooling rate also strongly affects the fiber/matrix interaction and the transcrystalline phase. The Mode-I delamination performance is controlled mainly by the matrix morphology, whereas the Mode-Il delamination resistance is related to the fiber/matrix interfacial strength and the interphase structure in the composite.
Manufacturing and Testing of Thermoplastic Composite High Load Hinge
Authors: Hou Meng , Ye Lin , Mai Yiu-Wing
Published: June 2014

A composite hinge has been designed to replace an existing metallic hinge on an aircraft aileron. The new design aims to reduce the manufacturing cost while maintaining the operating loads and conditions. Thermoplastic composite hinges were produced from solvent-impregnated fiber fabric-reinforced polyetherimide prepreg. To get fully consolidated thermoplastic composite parts with high quality, optimum forming conditions such as forming temperature, holding time, and forming pressure were determined by an impregnation model. The final void content in the thermoplastic composite hinge was less than 0.2%. A special test rig was designed to test the hinges under the worst loading condition expected during operations. Composite hinges with different fiber orientation and flange/web thickness ratio were tested up to failure. All hinges behaved linearly up to the onset of the first crack growth in the tensile section. After this event, non-linear behavior was observed. The main failure mode observed in all hinges appeared to be delamination in the tensile section. The load at which first delamination started was found to be in the range of 15-17 k N, depending on the fiber orientation and flange/web thickness ratio in the hinges, and catastrophic failure was not observed up to the specified maximum load of 25 k N. The ultimate load expected during the operation of the metallic hinge was met by the thermoplastic hinges.
Demonstration of a Dynamic Polymer Composite Connector
Authors: Stoll Frederick , Gibson Ronald F. , Zhao Wenzhong , Yang Shuo , Husain Noman , Bettinger David
Published: June 2014

This paper introduces the dynamic polymer composite (DPC) connector concept for creating structural joints of tubular composite members. DPC connectors are fiber-reinforced tubular elements featuring pretensioned circumferential fibers and a thermoplastic matrix. Application of heat softens the thermoplastic, allowing the circumferential fibers to clamp the connector onto the tubes to be joined. A laboratory demonstration of the DPC connector concept is described. General design relationships are presented to relate the basic performance measures to material properties and prestress levels. The need to maximize certain properties of the prestressing fiber and the thermoplastic matrix is discussed.