The present study describes the processing and mechanical characterization of two different fibers (glass and carbon) and two different fabric architectures (woven roving and stitch bonded) made into composites with Dow Chemical's Derakane 510A-40, a brominated vinyl ester (VE) resin. Both E-glass and T700 carbon fibers are coated with VE compatible sizing. The composite panels are fabricated by the vacuum assisted resin transfer molding (VARTM), the specimens are machined, and the mechanical tests are conducted as per the accepted test standards. Tension, compression, in-plane shear, and interlaminar shear properties are measured and their associated failure modes are compared with each other. The specific properties of the composites are compared with that of the marine steel. The carbon composites have superior properties, higher specific strength, and specific modulus than the marine steel. The glass composites have higher specific strength but lower specific modulus than marine steel. The glass composites are well suited for constructing ship hulls which are only strength critical. The topside (upper) structures of the ship are stiffness critical. The carbon composites are applicable to both the topside and the hull structures of the ship to reduce the total weight. The straightness of the fiber and the FOE sizing are the possible reasons for the superior performance of the carbon composites. The predicted elastic constants based on the simple micromechanical equations of the composites agree very well with the experimental data.
The concept of electrospun polymer nanofiber fabric interleaving to enhance dynamic properties, impact damage resistance, fracture toughness and resistance, and delamination onset life was evaluated. Polymer nanofabric interleaving increased the laminate thickness and weight by an order of 1%, and its impact on in-plane mechanical properties of the composite laminate would be statistically zero. On the other hand, its influence on interlaminar fracture toughness and resistance, impact damage resistance, and damping is substantial. Results of this study showed that interleaving AS4/3501-6 composite laminate increased the damping by 13%, reduced the impact damage size to one-third, increased fracture toughness and resistance by 1.5 times and one-third, respectively, significantly increased delamination onset life, and increased the fatigue threshold energy release rate by two-thirds. These improvements are comparable to that of the commercial T800H/3900-2 composite but with no thickness increase penalty, loss of in-plane properties, or multiple glass transition temperatures. Nomenclature A = cross-sectional area of cantilever beam, m 2 a IC = initial delamination length for the fracture test at = acceleration at any time t a 0 = initial delamination length da = delamination extension E 0 = material storage modulus, Pa E 00 = material loss modulus, Pa Et = instantaneous energy at any time t G I = mode I energy release rate G IC = initiation mode I fracture toughness G I max = maximum cyclic mode I energy release rate G IR = plateaued mode I fracture resistance G R = fracture resistance g = acceleration due to gravity, 9:81 m=s 2 L = length of the cantilever beam M = effective mass of the impactor system M a = mass of the impactor and the accelerometer system N 1% = number of cycles for 1% compliance increase Pt = instantaneous impact force, N R = ratio of minimum and maximum cyclic displacement I min = I max T g = glass transition temperature t = time, s tan = damping factor V 0 = initial velocity of the impactor at the time of impact = delamination length correction parameter IC = critical load-point displacement when the delamination starts to grow in the fracture test I max = maximum value of cyclic displacement I min = minimum value of cyclic displacement = mass density of the cantilever beam
Dynamic Mechanical Analysis (DMA) is one of the most powerful tools to study the behavior of plastic and polymer composite materials. Unfortunately, as observed in literature and from author's experiences, there are discrepancies in the measurement of storage modulus using DMA, particularly for high modulus materials like carbon fiber composites. This is because of lack of guidelines for DMA testing of materials. This paper systematically studied the DMA testing of composites for both rectangular and cylindrical beam type specimens, identified the problems, made corrections and established simple test guidelines. Using these guidelines a wide variety of materials were tested and the test results are presented. Some of the test results were compared with the ASTM D790 bend test results.
This study systematically assessed the measurement of dynamic properties of a range of fiber reinforced composite materials using dynamic mechanical analysis (DMA) instrument. The discrepancy in the moduli from DMA to ASTM tests was investigated. The study showed that proper specimen preparation, maintaining appropriate aspect ratio (span to thickness ratio) to reduce the transverse shear deformation, and sufficient loading are critical to measure correct properties from DMA test. The guidelines on aspect ratio and loading for plastics to high-modulus carbon fiber composites are presented as a design chart and equations, respectively. The study also found that the glass transition temperature (T g ) was independent of specimen aspect ratio and T g is lower for multidirectional composites when compared with its unidirectional composites. The particle interleaved T800H/3900-2 composite showed two glass transition temperatures (140 and 1988C), the lower value is due to the effect of interleaving by thermoplastic particles, and the higher value is the T g of its base matrix. This lowering of T g would have significant effect on the application temperature of the material. This phenomenon was not observed here to fore in the literature. POLYM. COMPOS., 30:962-969, 2009. ª
For the first time, this study explores how the incorporation of ZnO nanowires (ZnO NW) in the interface affects moisture absorption and resultant mechanical properties of glass and carbon composites. ZnO NW were coated onto glass and carbon fabrics to modify the fiber/matrix interface in the composites. Moisture absorption, longitudinal tension, short beam shear, and mode‐I fracture tests were conducted. While the moisture absorption was found to decrease the interlaminar shear strength (ILSS) of glass composite, it was found to decrease the ILSS, tensile properties, and fracture toughness of carbon composites. The incorporation of ZnO NW was found to decrease the moisture absorption in both glass and carbon composites, increase the tensile modulus of dry and wet glass composites by ~17%, and prevent the delamination failure of wet carbon composites in tensile tests. Also, ZnO NW incorporation was found to increase the fracture toughness of all composites with a maximum of 141% improvement for dry carbon composite. Importantly, ZnO NW incorporation was believed to increase the stiffness and prevent bending failure of DCB arm in wet carbon composites. The uniqueness of this article includes demonstrating the benefits of ZnO NW to reduce the moisture absorption in composites and to reduce the extent of fiber/matrix interface degradation in wet carbon composites.
This article investigates the dispersion of nanoclay and its effect on the properties of nanoclay/epoxy nanocomposites developed using a high-shear mixing technique. Epon 828, Nanomer 1.30 E, and a compatible amine-curing agent (Epikure W) were the materials used. The dispersion of nanoclay was studied using XRD and TEM at different levels of magnification. Even though nanoclays were found to have exfoliated based on XRD's d-spacing data (>8 nm), they remained as tactoids based on TEM data. The effect of curing on the dispersion of nanoclay was also studied using XRD analysis, which showed polymerization of resin in-between the nanoclay layers during curing. This polymerization was only helpful for the exfoliation of nanoclay, it could not completely delaminate and disperse the individual nanoclay layers. The nanocomposites were characterized using dynamic mechanical analysis and ASTM standard fracture tests. Measured elastic modulus was compared with the predicted modulus using modified Halpin-Tsai model. The experimental value was less than the predicted value and the difference was attributed to the poor dispersion of nanoclays. However, addition of 5.3 wt% nanoclay increased the storage modulus and the fracture toughness of epoxy resin by 21% and 16%, respectively. The fracture morphologies indicated that the major toughening mechanism was due to crack deflection around nanoclay tactoids.
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