Journal of Reinforced Plastics and Composites current issue

Comparison of Stress Distributions of Dental Woven and Unidirectional Fiber-Reinforced Composite Crowns Under Different Loadings

Gungor, M. A., Artunc, C., Akan, E., Benli, S., Sayman, O. — Tue, 10 Nov 2009 09:41:02 PST

The aim of this numerical study was to investigate and compare the stresses occurring in dental woven and unidirectional experimental fiber-reinforced composite (FRC) crowns under different thermal and singular force loading conditions. For this reason, finite element models of FRC crown and tooth systems were performed by using the ANSYS program. Stress analyses of the models were carried out under thermal loading conditions heated from 37 to 55°C, cooled from 37 to 5°C, and 450 N singular force loading conditions at different angles. The results indicated that high stresses occurred in both woven and unidirectional FRC crowns under horizontal loadings because of bending moment. Thermal stresses exhibited small values that did not cause any damage. It can also be concluded that since the stress component of _z in the woven type FRC was smaller than that of unidirectional type FRC, use of the woven FRC might be beneficial in comparison with the unidirectional composite.

Ultrasonic Oscillations Effect on Extrusion Processing, Structure, and Properties of Blends of Propylene Based Plastomer and Ethylene/1-Octene Copolymer

Guo, W.-Y., Peng, B., Ruan, Q.-P. — Tue, 10 Nov 2009 09:41:02 PST

The effects of ultrasonic oscillations on extrusion processing, phase morphology, and compatibility as well as mechanical properties for blends of propylene based plastomer (DP) and ethylene/1-octene copolymer (EOC) were examined. The results show that introduction of ultrasonic oscillations into polymer melts in extrusion can in situ improve their processability, including the reduction of die pressure and shear viscosity under a constant shear rate (flow rate) and the increase of throughput under the same shear stress (die pressure). Scanning electron microscopy observation reveals that with ultrasonic oscillations, morphology of reduced disperse phase (EOC) size and good interfacial adhesion between EOC and DP matrix are formed in DP/EOC blends. The interfacial tension between DP and EOC melts obtained from the Palierne emulsion model decreases with applying ultrasonic oscillations. FTIR and GPC analysis indicate that in situ copolymer formation between DP and EOC happens with ultrasonic oscillations and copolymer consequently acts as compatibilizer for the blends. Accordingly, it leads to an elevation of stress at break and elongation at break of the blends.

Application of Vibrating Beam Method to Determine Dynamic Properties of Flexible Adhesives

Kadioglu, F., Adams, R. — Tue, 10 Nov 2009 09:41:02 PST

Nowadays, ductile adhesives are entering the arena of structural applications due to their high strains to failure that is able to tolerate possible stress—strain concentrations, and due to their high damping performance, which is useful for energy dissipation. In this article, dynamic properties of such an adhesive are investigated using a vibrating beam technique with free—free end conditions. For the measurements of flexural modulus and damping values of the adhesive, the free layer beam configuration with different layer thicknesses was used. It is shown that the technique is able to give the consistent results and the data can be used for design purposes. The results suggest that the dynamic properties of the adhesive are frequency dependent at room temperature, which means the adhesive has a viscoelastic behavior.

Polypropylene--Bamboo/Glass Fiber Hybrid Composites: Fabrication and Analysis of Mechanical, Morphological, Thermal, and Dynamic Mechanical Behavior

Samal, S. K., Mohanty, S., Nayak, S. K. — Tue, 10 Nov 2009 09:41:02 PST

Hybrid composites of polypropylene reinforced with bamboo and glass fibers (BGRP) were fabricated using an intermeshing counter rotating twin screw extruder followed by injection molding. Maleic anhydride grafted polypropylene (MAPP) has been used as a coupling agent to improve the interfacial interaction between the fibers and matrix. The mechanical properties of the hybrid composites were studied from tensile, flexural, and impact tests. Mechanical tests indicated an increase in tensile, flexural, and impact strength of the BGRP hybrid composites at a bamboo:glass fiber ratio of 15:15 ratio in the presence of 2 wt% of MAPP. Nearly, 69, 86, and 83% increase in tensile flexural and impact strength respectively has been observed as compared with virgin PP. The fiber matrix interfacial morphology of the tensile fractured specimens was studied using scanning electron microscopy (SEM) which showed less fiber pullout and comparatively less gaps between the fiber and the base matrix in the case of MAPP treated hybrid composites. The crystallization, melting behavior and thermal stability of the hybrid composites were investigated employing differential scanning electron microscopy (DSC) and thermogravimetric analysis (TGA). Thermogravimetric analysis (TGA) showed an increase in thermal stability of the matrix polymer with incorporation of bamboo and glass fibers, confirming the effect of hybridization and efficient fiber matrix interfacial adhesion. The dynamic mechanical analysis (DMA) showed an increase in storage modulus (E^') indicating higher stiffness in case of hybrid composites as compared with untreated composites and virgin matrix. The tan spectra presented a strong influence of fiber content and coupling agent on the and relaxation process of PP.

LRFD Approach for FRP-Reinforced Thermoplastic Beams

Razzaq, Z., Coskun, H., Li, X., Beach, R., Prabhakaran, R. — Tue, 10 Nov 2009 09:41:02 PST

Thermoplastic beams are currently being used primarily in marine and waterfront applications, and can be used in bridges and buildings. A summary is presented of an experimental and theoretical study of the flexural behavior of a commercially available thermoplastic beam known as Seatimber with simple supports and subjected to a gradually increasing midspan concentrated load. Theoretical predictions are based on a non-linear moment-curvature analysis coupled with a central finite-difference scheme. Simplified criteria for a load and resistance factor design (LRFD) approach is outlined and its use demonstrated through analysis and design examples.

Flexural Tests of Phenol Formaldehyde and Slg Composites: Pilot Study

Cardona, F., Rogers, D., Gurney, R., Trada, M., Ku, H. — Tue, 10 Nov 2009 09:41:02 PST

Phenol formaldehyde was filled with Envirospheres slg to increase the strength of the composite for structural applications by a research center on composites, University of Southern Queensland (USQ). In order to reduce costs, the center wished to fill with as much slg as possible, subject to maintaining sufficient strength of the composites in structural applications. This project varied the wt% of the slg in the composites which were then subjected to flexural tests. The results showed that composite with 25 wt% of the slg produced the highest flexural strength and Young’s modulus combined with a reasonable fluidity for casting; the highest flexural strain was achieved when the slg was 10 wt%.

Kinetics Analysis of Thermal Degradation Reaction of PVA and PVA/Starch Blends

Zhou, X.-Y., Jia, D.-M., Cui, Y.-F., Xie, D. — Tue, 10 Nov 2009 09:41:02 PST

The kinetics of thermal degradation of PVA and PVA/starch (40/60) blends were investigated by thermogravimetry (TGA) and derivative thermogravimetry (DTG). Experiments under non-isothermal conditions were carried out for samples in nitrogen at heating rates of 5, 10, 15 and 20°C/min. The Kissinger, Flynn—Wall—Ozawa, and Coats—Redfern methods were used to calculate the activation energy of degradation and determine the degradation mechanism for PVA and PVA/starch blends. The results showed that these three methods were suitable and effective to describe the thermal degradation of PVA and PVA/starch blends. The thermal stability of PVA/ starch blends is higher than that of PVA suggesting that the addition of starch improved the thermal stability of PVA. The thermal degradation of the PVA/starch blends could be separated into three distinct stages. The Coats—Redfern method showed that the degradation mechanism of PVA and PVA/starch blends was a nucleation and growth mechanism in which PVA went to the A₃ mechanism and PVA/starch blends went to the A₄ mechanism.

Effect of Cellulose Fiber Reinforcement on the Temperature Dependent Mechanical Performance of Nylon 6

Tajvidi, M., Feizmand, M., Falk, R. H., Felton, C. — Tue, 10 Nov 2009 09:41:02 PST

In order to quantify the effect of temperature on the mechanical properties of pure nylon 6 and its composite with cellulose fibers (containing 25 wt% cellulose fibers), the materials were sampled and tested at three representative temperatures of 256, 296, and 336 K. Flexural and tensile tests were performed and the reductions in mechanical properties were evaluated. The highest reductions were observed in stiffness (modulus) values and the cellulose fibers remarkably enhanced the high temperature resistance of nylon. The reductions in mechanical properties were well explained by a simple quadratic curve fitting procedure applied to experimental data. Dynamic mechanical analysis (DMA) was also performed to study the effect of temperature on mechanical performance. No shifting in glass transition temperature was observed, but the composite material showed less viscous behavior as seen by its lower mechanical loss factor (tan ) values in the rubbery state. The results of the present study will be helpful in determining the end-use application of these composite materials.

Correlated Rules between Complex Structure of Composite Components and Manufacturing Defects in Autoclave Molding Technology

Wang, X., Zhang, Z., Xie, F., Li, M., Dai, D., Wang, F. — Tue, 10 Nov 2009 09:41:02 PST

Based on statistical analysis, considerable defect information obtained by nondestructive identification (NDI) techniques for composite components, different type defects which often form in autoclave molding of composites were summarized, and the effect rules of complex structure in composite components on manufacturing defects were also revealed. Combined with statistical results and defect micrographs, the strong correlation between geometric characteristics (for instance, thickness, gradient of thickness variation, curvature radius) in composite components and controllability of manufacturing defects was discussed in detail. It was found that delamination, pore, void, and rich resin were the four main defects in autoclave molding, and that the ratio of defect appearance was remarkably influenced by complex structure of composite components. Especially, geometric characteristics of composite components had a significant influence on the defect type and defect ratio. For example, too thin or too thick components, too small radius and abrupt change of thickness in components would obviously increase the ratio of defect production. Thickness, curvature radius, and gradient of thickness variation would probably lead to the defects of delamination and void, and gradient of thickness variation would also result in rich resin around the overlap region of long fiber and short fiber in the thickness transition zone.

Influence of Solvents on the MWCNT/Adhesive Grade Epoxy Nanocomposites Preparation

Sharma, S.C., Sheshadri, T.S., Krishna, M., Murthy, H.N. N., Jose, J. — Tue, 10 Nov 2009 09:41:02 PST

In this article, the effect of two solvents, namely dimethyl formamide (DMF) and N-methyl pyrrolidone (NMP), on the dispersion effectiveness and the resulting electrical and mechanical properties of multi-walled carbonanotubes (MNCNT) filled structural adhesive grade epoxy nanocomposites was studied. The solvents were used mainly to reduce the viscosity of the resin system to effectively disperse the nanofiller. The dispersion was carried out under vacuum using high energy sonic waves. SEM was undertaken to study the dispersion effectiveness. Electrical resistivity, tensile properties, and glass transition of the nanocomposites were studied. Between DMF and NMP, the former proved better in terms of dispersion effectiveness and the resulting electrical and mechanical properties of the nanocomposites. Addition of MWCNT into AV138M resulted in an increase in glass transition temperature irrespective of the solvent used and in both cases percolation threshold was found with respect to reduction in electrical resistivity of the nanocomposites. Less agglomeration and hence better interaction between CNT and epoxy was observed in the samples prepared using DMF compared with that using NMP.