ASME IMECE2003 -43837 FORMATION OF MICROSCOPIC VOIDS IN RESIN TRANSFER MOLDED COMPOSITES

ABSTRACT Performance of composite materials usually suffers from process-induced defects such as dry spots or microscopic voids. While effects of void content in molded composites have been studied extensively, knowledge of void morphology and spatial distribution of voids in composites manufactured by resin transfer molding (RTM) remains limited. In this study, through-the-thickness void distribution for a diskshaped, E-glass/epoxy composite part manufactured by resin transfer molding is investigated. Microscopic image analysis is conducted through-the-thickness of a radial sample obtained from the molded composite disk. Voids are primarily found to concentrate within or adjacent to the fiber preforms. More than 93% of the voids are observed within the preform or in a so-called transition zone, next to a fibrous region. In addition, void content was found to fluctuate through-the-thickness of the composite. Variation up to 17% of the average void content of 2.15% is observed through-the-thicknesses of the eight layers studied. Microscopic analysis revealed that average size of voids near the mold surfaces is slightly larger than those located at the interior of the composite. In addition, average size of voids that are located within the fiber preform is observed to be smaller than those located in other regions of the composite. Finally, proximity to the surface is found to have no apparent effect on shape of voids within the composite

Ultrasound Findings in a Case of Myeloid Sarcoma of the Breast

Myeloid sarcoma is a rare, solid extramedullary tumor originating from immature granulocytic cells or monocytes. Breast involvement without an aleukemic or myeloproliferative disorder is very infrequent. A 21-year-old female patient was admitted with bilateral palpable breast masses for four months. The patient had given birth approximately one year ago. The ultrasonographic examination revealed multiple, oval shaped—some of them with microlubulated margins—hypoechoic, solid masses of which, the largest mass measured 4.5 . 2.5 cm, evaluated as BI-RADS 4. The histopthological examination suggested hematolymphoid neoplasm. In the differential diagnosis of solid breast lesions, myeloid sarcoma should be kept in mind even without hematological findings. Early diagnosis of this tumor is important for the effectiveness of the medical treatment

Effect of Preform Thickness and Volume Fraction on Injection Pressure and Mechanical Properties of Resin Transfer Molded Composites

An experimental study is performed to characterize the effect of the thickness of random preforms on injection pressure and mechanical properties of resin transfer molded (RTM) parts. Center-gated, disk-shaped parts are molded using two different chopped-strand glass fiber preforms. Both preforms have random microstructure but different planar densities (i.e., different uncompressed layer thicknesses). Tensile strength, short-beam shear strength, and elastic modulus are measured for parts molded with each preform type at three different fiber volume fractions of 6.84, 15.55, and 24.83%. Although mechanical properties are found to increase linearly with volume fraction, significant difference is not observed between disks containing thick and thin mats at equivalent fiber volume fraction.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Performance of Glass Woven Fabric Composites with Admicellar-Coated Thin Elastomeric Interphase

Adequate stress transfer between the inorganic reinforcement and surrounding polymeric matrix is essential for achieving enhanced structural integrity and extended lifetime performance of fiber-reinforced composites. The insertion of an elastomeric interlayer helps increase the stress-transfer capabilities across the fiber/matrix interface and considerably reduces crack initiation phenomena at the fiber ends. In this study, admicellar polymerization is used to modify the fiber/matrix interface in glass woven fabric composites by forming thickness-controlled poly(styrene-co-isoprene) coatings. These admicellar interphases have distinct characteristics (e.g., topology and surface coverage) depending on the surfactant/monomer (S/M) ratios used during the polymerization reaction. Overall, the admicellar coatings have a positive effect on the mechanical response of resin transfer molded (RTM), E-glass/epoxy parts. For instance, ultimate tensile strength (UTS) of composites with admicellar sizings improved 50 to 55% over the control desized samples. Interlaminar shear strength (ILSS) also showed increases ranging from 18 to 38% over the same control group. Interestingly, the flexural properties of these composites proved sensitive to the type of interphase formed for various admicellar polymerization conditions. Higher surface coverage and film connectedness in admicellar polymeric sizings are observed to enhance stress transfer at the interfacial region.Ye

Calorimetric and Rheological Measurements of Three Commercial Thermosetting Prepreg Epoxies

The cure kinetics of three different thermosetting resins are investigated using differential scanning calorimetry and oscillatory shear rheometry. For the latter, two different types of plates are used, smooth plates and grooved plates; the latter are used to improve sample–plate contact. In addition, oscillatory compression rheology is used; however, machine compliance prevents accurate measurements at high conversions. A fractional conversion is defined based on the maximum storage modulus achieved at a given temperature, and is compared to the fractional conversion calculated from enthalpy measurements. As expected, the rates of reaction derived from these fractional conversions are very different for calorimetry and rheometry. However, the rates of reaction using the two types of plates are identical, although the grooved plates give much more reproducible storage moduli. A number of previously used mathematical expressions are employed to fit the calorimetric and rheological data, and the activation energies calculated from these fits are compared.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Effect of Nanoclay Content on Void Morphology in Resin Transfer Molded Composites

Effects of nanoclay content on morphology and spatial distribution of voids in resin transfer molded nanoclay/E-glass/epoxy composite disks are investigated. Closite®25A nanoclay loads of 2, 5, and 10wt% are mixed by sonication with a low-viscosity epoxy resin prior to filling the mold cavity containing 13.6% E-glass preform by volume. A disk without nanoclay is also molded. Once the molded composites are cured, voids on radial composite samples are evaluated via microscopic image analysis. The addition of nanoclay is found to result in a significant increase in the apparent viscosity of the clay-epoxy mixture, thus increasing the molding pressure. Void occurrence is observed to increase considerably with increasing nanoclay content, from 2.1% in the composite without nanoclay to 5.1 and 8.3% in the composites molded with 5 and 10wt% nanoclay, respectively. However, the composite with 2wt% nanoclay yields the lowest void content of 0.7%. Voids are observed to be, in average, smaller after the addition of nanoclay at all nanoclay concentrations. Presence of nanoclay in the impregnating resin induces at least 60% reduction in voids located inside fiber tows, which are trapped by the fluid front motion during impregnation. Irregularly shaped voids are also observed to decrease with increasing nanoclay content. A nonuniform void content and morphology is observed radially, which seems to be affected by the flow kinematics as well as possible breakdown and filtration of clay clusters.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Filtration and Breakdown of Clay Clusters during Resin Transfer Molding of Nanoclay/Glass/Epoxy Composites

Dispersion of nanoclay clusters during resin transfer molding of nanoclay/glass/epoxy disks is investigated. In addition to a center-gated disk containing only 14% glass fibers, three nanocomposite disks are fabricated with the addition of 2, 5 or 10 wt% Cloisite® 25A nanoclay. The spatial distribution of nanoclay clusters along the radial axis of the nanocomposite disks are characterized at two length scales. Clusters larger than 1.5 μm are characterized by performing image analysis on the SEM micrographs whereas smaller nanoclay clusters are identified by wavelength dispersive spectrometry. Results obtained from image analysis indicate that nanoclay clusters are filtered out by as much as 50% in the flow direction by the glass fiber preforms. In addition, increasing nanoclay content led to higher filtration, suggesting that cluster formation is more prominent at higher nanoclay loadings. Cluster size distribution analyses revealed that the outer edges of the disks, on average, contain finer nanoclay particles. For instance, the outer edge of the nanocomposite with 2% clay contains 22% more small nanoclay clusters compared to center of the disk. Glass transition temperature, Tg, of four specimens obtained from each molded disks is characterized under oscillatory shear. Glass transition temperature of the samples are shown to increase with the nanoclay content, yielding a 40% higher Tg at 10% nanoclay loading compared to glass/epoxy composite without clay. Increasing glass transition temperature with increasing nanoclay content may be an indication of intercalation of nanoclay within the epoxy matrix.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

The Effect of Insulin Like Growth Factor-1 on Recovery of Facial Nerve Crush Injury

Objectives The aim of this study is to investigate the efficacy of locally applied insulin-like growth factor 1 (IGF-1) on the recovery of facial nerve functions after crush injury in a rabbit model. Methods The rabbits were randomly assigned into three groups. Group 1 consisted of the rabbits with crush injury alone; group 2, the animals applied saline solution onto the crushed facial nerve and group 3, IGF-1 implemented to the nerve in the same manner. Facial nerve injury was first electrophysiologically studied on 10th and 42nd days of the procedure. The damage to the facial nerves was then investigated histopathologically, after sacrification of the animals. Results In the electrophysiological study, compound muscle action potential amplitudes of the crushed nerves in the second group were decreased. In pathological specimens of the first and second groups, the orders of axons were distorted; demyelination and proliferation of Schwann cells were observed. However, in IGF-1 treated group axonal order and myelin were preserved, and Schwann cell proliferation was close to normal (P<0.05). Conclusion Local application of IGF-1 in a slow releasing gel was found efficacious in the recovery of the facial nerve crush injury in rabbits. IGF-1 was considered worthy of being tried in clinical studies in facial nerve injury cases

MULTISCALE CHARACTERIZATION OF NANOCOMPOSITES FABRICATED BY COPULVERIZATION OF EPOXY RESIN AND NANOCLAY IMECE2005-80380

ABSTRACT INTRODUCTION Effect of nanoclay on the thermo-mechanical properties of BT250E-1 epoxy resin is investigated. Nanocomposite parts containing 0, 2 and 10wt. % of Cloisite ® 30B nanoclay are fabricated by copulverization of nanoclay with epoxy resin at -25°C. Desired amounts of solid epoxy resin and nanoclay are placed into a grinder and copulverized for 20 seconds. The resulting fine powder is then cured using an APA2000 rheometer by using the time-temperature profile provided by the resin supplier. Five disk-shaped parts for each nanoclay content are fabricated. Two rectangular samples are cut out from each disk and used for characterization of mechanical properties and microstructure. Physical properties of polymers can be altered significantly by the addition of particulates. Traditionally, particulates such as calcium carbonate are added to reduce cost at the expense of strength. However, development of nano-scale particulates in the last two decades resulted in materials such as carbon nanotubes and nanoclay, which might improve mechanical performance in addition to other thermo-physical properties. Nanoclay, contrary to carbon nanotubes, is cost effective owing to its abundance in the nature and low processing cost Transmission electron microscopy indicates several nanovoids trapped in the intra-cluster regions. The existence of these voids is also verified by density measurements of the cured samples of the epoxy with and without nanoclay. The reduction observed in the flexural strength is believed to be due to these nanovoids and nanoclay agglomeration. Researchers often achieved promising results when they utilized nanoclay with various thermoplastic resin

ASME IMECE2003 -43838 COMBINED EDGE AND ANISOTROPY EFFECTS ON FICKIAN MASS DIFFUSION IN POLYMER COMPOSITES IMECE2003-43838

ABSTRACT INTRODUCTION The common methods used to determine the diffusion coefficients of polymer composites are based on the solution of Fickian diffusion equation in one-dimensional rectangular domain. However, these diffusivities usually involve errors primarily due to finite sample dimensions and anisotropy introduced by fiber reinforcements. In this study, the solution of transient, three-dimensional anisotropic Fickian diffusion equation is non-dimensionalized using six parameters. The solution is then used to analyze the combined contribution of finite sample dimensions and anisotropy to the errors involved in diffusion constants calculated by one-dimensional methods. The small time solution of the Fickian diffusion equation in three-dimensional domain is used to analyze the slope used in diffusivity calculations. It is shown that the diffusion coefficient calculated by one-dimensional approach is exact only if the correct slope of percent mass gain versus root square time curve at t=0 is used. However, it has also been shown that depending on the part geometry and degree of anisotropy, there might be considerable differences between the measured slope from the experimental data and the actual slope at t=0. The mismatch between the slopes results in as much as 50% errors in estimates of diffusion coefficients. The degree of control on the final material properties and the ability to impose directional dependency have contributed to increased usage of fiber reinforced polymers. However, unlike conventional materials, their excessive susceptibility to environmental conditions is one of their primary shortcomings. Among the environmental factors, ingress of moisture is shown to degrade material properties considerably, and thus decrease the expected service life of a product [1][2] Using the three-dimensional solution in non-dimensional form, the magnitudes of these errors are studied. A least square curve fit method, which yields accurate anisotropic diffusion coefficients, is proposed. The method is demonstrated on artificially generated experimental data for a polymer composite containing 50% unidirectional reinforcement. The anisotropic diffusion coefficients used to generate the data are recovered with less than 1% error. It is essential for a realistic design to consider the possible moisture diffusion in and out of the designed part and potential structural degradations associated with it. Therefore, predicting the time scale or essentially the rate of diffusion is important. Among the several factors influencing the moisture uptake, researchers often investigated the effects of environmental conditions such as temperatur