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Composite structures used as aerosurfaces in aerodynamic applications are required to have a certain surface finish quality. In manufacturing of thermoplastic composites using automated fiber placement (AFP) for aerodynamic applications, it is not only desirable to achieve good consolidation by using AFP alone and avoiding secondary treatment in an autoclave, but also to achieve acceptable surface smoothness required for aerosurfaces. In this study, an in situ treatment called "repass" was implemented to achieve surface finish quality required for aerodynamic applications. Moreover, the effect of this in situ treatment on the quality of the thermoplastic laminates, including void content and crystallinity was investigated. Autoclavetreated samples were used as references for comparing surface quality and other quality indicators. [ABSTRACT FROM AUTHOR]

As shear premixing is an important process for the dispersion of nanoclays in polymeric resins, this article studies the effect of temperature, duration, speed of premixing, and also the interlamellar spacing of clay platelets on the dispersion of organoclay in epoxy by using a high speed premixing technique which can generate high shear. The quality of dispersion and intercalation/exfoliation of organoclay in epoxy after premixing (before adding hardener) was analyzed by means of X-ray diffraction (XRD) and rheological measurement. The dispersion and intercalation/exfoliation of organoclay in the epoxy nanocomposites (ENCs) after curing were characterized by TEM. The results illustrate that the intercalation/exfoliation of organoclay in epoxy at the premixing step is very much depending on the premixing parameters. This article also presents a model which takes into account the parameters such as the interlamellar spacing of clay platelets, the viscosity of the epoxy-clay mixtures, and the velocity of the mixer to explain their effect on the dispersion of clay in epoxy resin. The study focuses on the flow of epoxy clay in the high shear mixer to describe a model for predicting the processing conditions necessary for achieving delamination of the clay layers. Experimental results on the dispersion of clay are also provided to validate the model. The model provides a guide for the premixing parameters necessary to separate the clay layers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

The surface finish of composite plates made using Resin Transfer Molding of glass/polyester is studied. A surface profilometer is used to measure the surface profile and to record raw data. The objective is to develop an objective method (rather than using human judgment) to differentiate the quality of one surface from another. Initially commonly used current techniques are utilized to assess the quality of the surface finish. These include subjective evaluation through a survey of observations from a group of people; the use of the average amplitude of the signals, frequency analysis, and filtering. For surfaces that have approximate quality, human visual observation can differentiate the quality between the surfaces, but the objective methods (average amplitude, frequency spectrum, and filtering) cannot. A new objective technique is found to be able to distinguish surfaces of approximate quality. This uses the comparison between the parameters of a reference good surface to those of the surface under consideration. A comparative index can be obtained to indicate the degree of similarity between the surface under study and the reference (good) surface. [ABSTRACT FROM AUTHOR]

A new method for the determination of shrinkage and modulus development of thermoset resins is described. The method uses the change in the time of travel of longitudinal ultrasonic waves in a couplant to determine the change in height of a column of resin. This change in height is used to determine shrinkage. The method also uses the time of travel of ultrasonic waves through a column of resin to determine the modulus of the resin. The technique allows continuous monitoring of shrinkage and modulus as the material changes from the liquid state to the solid state. This method is used to determine the shrinkage and modulus development for a common epoxy resin. [ABSTRACT FROM AUTHOR]

The article discusses the dispersion of organoclay in epoxy resin, examining the effect of shear and temperature used to premix nanoclay and epoxy resin. Pristine and commercially treated clays tend to form stacks rather than individual platelets, the authors state. Topics include the intercalation/exfoliation and dispersion of the nanoclay in the resulting epoxy nanocomposites, the roles played by premixing and curing steps in the dispersion of organoclay, and controlling the micro-dispersion of the clay.

The article presents a study on the reinforcing impact of organoclay in glassy and rubbery resins. The researchers chose the EPON 828 resin from Resolution Performance Products LLC for the study and used amine-terminated polyoxypropylene diols as hardeners. They also obtained X-ray diffraction (XRD) patterns to evaluate the exfoliation/intercalation of the nanoclay. They found that toughness, modulus and tensile strength greatly improved in the rubbery system with the presence of Cloisite 30B.

The object of this article is to study the stress distribution of particles dispersed in polymer and its effect on strength. Micro-scale finite element cracking models are formulated to study strengthening of hard particles-dispersed polymer. Two aspects are studied. First, the effect of particle aspect ratio, particle modulus and inter-particle distance on stress shielding zones around particles is investigated. Second, the effect of stress shielding zones on initiation of crack propagation is investigated. [ABSTRACT FROM AUTHOR]

The article presents a study on the effect of different organoclays and mixing methods on the cure kinetics and properties of epoxy nanocomposites based on Epon828 and Epicure3046. The two kinds of organoclay used in the study were I.30E and C.30B. It is concluded that the presence of nanoclay and the quality of clay dispersion affect the cure kinetics and mechanical properties of epoxy nanocomposite.

The toughening mechanism of epoxy resin mixed with micro/nano particles is investigated in this study. The effects of particle size on maximum stresses are studied. Analytical cell models of fracture are proposed to probe the toughening mechanism. These models are based on the assumption that increase of fracture surface area is a main factor to improve the toughness of the material. These models give the correlation of parameters (material properties, volume fraction, size, and amount of particles and epoxy resin) and the fracture toughness, and build the upper limit of toughness improvement. Some significant results are obtained for understanding the toughening mechanism of epoxy resin with micro/nano particles. [ABSTRACT FROM AUTHOR]

Single layers of triaxial woven fabric composites have been used to make communication satellite reflectors due to their extremely light weight with good stiffness and strength property. Special superfinite elements have been developed for the analysis of these lightweight materials. These superfinite elements are used for the deflection and stress analysis of a membrane sector of the satellite reflector subjected to lateral pressure. Due to the significant difference in the size of the satellite structure (order of meters) and the size of the superfinite elements (order of millimeters) it is not possible to model the satellite structure using the superfinite elements and computer facilities available in most labs (personal computers). In the process of finding a solution to this problem, a special similitude behavior for the deflection of the curved panels made of triaxial fabrics was discovered. Using this behavior, the deflection of a large-size reflector panel (order of meters) can be analyzed using models in the millimeters size range. Stresses in the triax reflector model were also calculated. However, no special similitude behavior was obtained for the stresses. [ABSTRACT FROM AUTHOR]

Investigates the effect of organo-nanoclay on the cure mechanism and kinetics of epoxy nanocomposites. Models used for differential scanning calorimetry cure data; Activation energy; Glass transition temperature.

Presents a study which evaluated thermal deformation behavior of triaxial woven fabric composites with open holes. Description of the thermal deformation models; Analysis of thermal deformation behavior; Conclusions.

Experimental investigation of the characteristics of the interface between a base laminate [08]T and a repair laminate [08]T was carried out through Mode II fracture tests, compliance calibration tests, and microscopic observations. The material used for manufacturing the test samples is unidirectional carbon fiber prepreg (Newport Composites NCT-301 graphite/epoxy). The laminate lay-up used in all experiments was [016]T.The specimens were subjected to variations in the autoclave pressure in the repair curing cycle. A standard sample (reference) was subjected to the manufacture recommended cure cycle. The repair samples were subjected to the manufacturer recommended curing cycle (for temperature) with different values for pressure.Results show a significant effect of pressure. However, the effect of the magnitude of the pressure is not significant after some threshold values. More than 28% drop in the fracture toughness is experienced by the lack of bonding between the older previously cured matrix and the newly added composite laminate. There is some difference between the Mode-II test and compliance calibration test, but no preference, in terms of accuracy, can be given to what method to be used to obtain Mode II fracture toughness. [ABSTRACT FROM PUBLISHER]

A round-robin test programme has been carried out to characterise the mode I interlaminar fracture behaviour of E-glass woven fabric reinforced vinyl ester matrix composites. Special emphasis has been placed on the effect of silane coupling agent on the stability of interlaminar crack propagation and fracture toughness. Sixteen laboratories participated in this programme. Each laboratory was supplied with composite laminates of thicknesses of its own choice and conducted the tests according to its own procedures. The results showed that variations in interlaminar fracture toughness between laboratories were very large in spite of slight differences in the test procedures used, such as specimen dimensions, test speed and data reduction schemes. Nevertheless, the general trends were clearly identified with respect to different silane coupling agents. Other observations and the implications are discussed. [ABSTRACT FROM AUTHOR]

A global/local approach using partial hybrid elements is presented to study the interlaminar stress distribution around delamination crack tips in composite laminates subjected to out-of-plane loading. The cracked composite laminate is modeled with three types of elements. 20-node three-dimensional sublaminate partial hybrid elements are used in the local region where the stress gradients are expected to be sharp, 8-node degenerated partial hybrid plate elements are used in the global region and 15-node transition elements are employed to connect the local and global regions. The results show that the global/local approach yields accurate solutions with much less active degrees of freedom, less consumption of computer space and CPU time as compared with the conventional displacement element. Experiments are performed for cross-ply laminates with midplane delamination crack subjected to three-point bending. The predicted critical loads by finite element analysis based on both a strength-based criterion and a fracture mechanics approach are in good agreement with the experimental data. [ABSTRACT FROM PUBLISHER]

To produce high-quality composites with high density and low void content, the knowledge of cure process is very important, and the sensors capable of monitoring the cure process are therefore desirable.Since the term of "fully processed" should be a reflection of the ultimate material application, the objectives of the present work are to monitor how material properties have been developed during the cure and justify when "end-of-cure" has been achieved by measuring chemical and mechanical properties of the curing composites. As a reference, differential scanning calorimetry is used to evaluate the degree of cure while fiber-optic sensors are used to measure the evolution of process-induced strains, and ultrasonic sensors are used to monitor the development of viscoelastic properties of the curing composites. Moreover, an ultrasonic cure monitoring system has been developed, by using conventional broadband ultrasonic sensors together with clad buffer rods. The major merits of this system can be summarized as (i) workable inside an autoclave at high temperature (for example, up to 2500C if by water-cooling) and internal pressure (for example, 100 psi); (ii) high signal to spurious ultrasonic noise ratio, and high signal strength; (iii) suitable for longitudinal or shear wave measurement in reflection/transmission mode. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

The effect of pressure in the repair curing cycle on the characteristics of the interface region between a base laminate and a repair laminate was established through mode I fracture tests and microscopic observations. More than 50% drop in the fracture toughness is experienced for repair samples as compared to standard samples. There is significant difference in fracture toughness between repair samples cured at 0 pressure and repair samples cured at a given pressure. The effect of variation in the level of repair curing pressure for the repair samples on the fracture toughness is insignificant. It was found that increasing the pressure has the effect of reducing the amount of voids, increasing crack growth stability, and to a much less degree, increasing the fracture toughness. [ABSTRACT FROM PUBLISHER]

A box beam made of fiber glass reinforced vinyl ester was subjected to static loading over a period of three months. Four point bending was used. Three different loads were examined, each load was applied for a period of one month. Displacement at the center of the beam and strain gage values were recorded. The results show that creep is significant during the first month of initial loading. During the subsequent two months, even though the loads were larger which resulted in larger elastic strains, creep rates are smaller. A design exercise is carried out to demonstrate the feasibility in using fiber reinforced composites for making structural elements for building applications. [ABSTRACT FROM PUBLISHER]

One of the important problems in the application of sheet molding compounds (SMC) in automobiles is how to join different structures together. In a previ- ous paper [1] a comparison between (adhesive) bonding strength and (metal) bolting strength was studied. It was found that bolting gave better joining strength than bonding. However, bolting creates stress concentration in the SMC and may be inconvenient in some applications. [ABSTRACT FROM PUBLISHER]

Filament winding technique is not used to its overall capacity because of insufficient understanding of the kinematics of filament winding. In order to effectively utilize the capability of filament winding technique, a Geometric Approach based on the algebraic and trigonometric relations is presented to determine the machine motions for generating desired fiber distribution on axisymmetric, non-axisymmetric, cylindrical, and non-cylindrical mandrel shapes.Analytical models thus developed are found to be extremely useful tools for laying down the fiber on predetermined path in lieu of costly techniques such as teach-in-programming, simulation, CAD/CAM, etc. It is suggested that a sophisticated filament winding machine is not always necessary to fabricate a complex structure. A filament winding machine with two and three degrees of freedom can perform the same task on various types of mandrel surface with fewer driven parts, higher accuracy, and lower manufacturing cost. Present method determines the machine motion in a few seconds and provides exact solution in generating the desired fiber winding angle on certain types of mandrel surface which has polygonal cross-sections.Based on the Geometric Approach, a user friendly computer program "DIRECTIKIN" is developed to study the direct kinematics of filament winding. Using the program "DIRECIXIN, effects of location of the delivery point, fiber winding angle distribution, and mandrel shape geometry on winding motions are discussed. Experimental verification of the model is performed on a McClean Anderson filament winding machine for cylindrical and non-cylindrical mandrels. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]