Journal of Reinforced Plastics and Composites recent issues

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.

Effect of Water on Mechanical Properties of Unsaturated Polyester--Acetylated Hydroxypropyl Guar Gum Composites

Shenoy, M.A., D'Melo, D.J. — Tue, 10 Nov 2009 09:19:03 PST

The use of natural, eco-friendly, renewable resources in composites, as a reinforcing material, requires chemical or physical treatment to improve compatibility with the polymer matrix. In the present study hydroxypropyl guar gum (HPG) was acetylated to investigate its influence on the behavior of its unsaturated polyester (UPR) composites on exposure to water. The kinetics of water diffusion and effect on mechanical properties were studied with respect to the degree of acetylation and filler concentration. The absorption behavior of all composites was found to follow Fick’s law. Mechanical properties of HPG composites were found to be superior compared to pure UPR and acetylated HPG composites.

Relationship of Rheological Study with Morphological Characteristics of Multicomponent (Talc and Calcium Carbonate) Filled Polypropylene Hybrid Composites

Jikan, S.S., Samsudin, M.S.F., Ariff, Z.M., Ishak, Z.A.M., Ariffin, A. — Tue, 10 Nov 2009 09:19:03 PST

Polypropylene (PP) copolymer reinforced with talc, CaCO₃, or multicomponent fillers (a combination of talc and CaCO₃) were compounded in a Brabender Plasti-Corder^® internal mixer. These compounds then experienced an extrusion process by means of a capillary rheometer. The rheological and morphological (SEM) properties of the extrudate were analyzed to investigate the effect of shear stress, filler type, and temperature. The rheological studies revealed that the incorporation of multicomponent fillers has increased the melt viscosity. However, different ratio of filler type demonstrates no significant effect. It is also shown that the system appears pseudoplastic over one range of shear rates but dilatant over another. The presence of filler seems to have a pronounced influence on dilatant flow in filled PP. Observation on SEM analysis at high shear stress showed that large CaCO₃ agglomerates are seen to be randomly dispersed whereas talc particles are more uniformly distributed and oriented to flow direction, suggesting better mixing.

Mechanical Properties of Coir/Glass Fiber Phenolic Resin Based Composites

Kumar, N. M., Reddy, G. V., Naidu, S. V., Rani, T. S., Subha, M.C.S. — Tue, 10 Nov 2009 09:19:03 PST

Phenolic resin based coir/glass hybrid composites were developed using compression molding followed by hand lay-up technique. Mechanical properties such as tensile and flexural properties of coir based hybrid composites were investigated as a function of fiber content and fiber volume fraction. This study is focused on the mechanical performance of coir based and its hybrid composites. Results showed that tensile properties increase with increasing fiber content. Mechanical properties of composites with increased glass fiber content have high values. The effect of alkali-treatment of fibers on the mechanical properties was also studied. Significant improvement in coir based composites by alkali-treatment was observed. Overall studies indicated that the short coir/ glass fabric hybrid polyester composites are promising candidates for structural applications where high strength and stiffness is required.

Large Shear Deformation of E-glass/ Polypropylene Woven Fabric Composites at Elevated Temperatures

Zhu, B., Yu, T.X., Tao, X.M. — Tue, 10 Nov 2009 09:19:03 PST

Stamping operation of textile composite sheets in industry involves a process of heating and cooling of the material. In the present article, the in-plane large shear deformation of woven fabric composite sheets at elevated temperatures is studied. Using the modified ‘picture frame’ test, the effects of temperature on the shear behavior of the material and the onset of wrinkling were investigated. In addition to the reduction in yarn width, the change of physical and mechanical properties of polypropylene (PP) fibers with temperature also plays a significant role. The initial shear stiffness of the composite sheets and the onset of wrinkling are reasonably explained by inter-yarn friction measurement. To simply consider the temperature effect, the introduction of a temperature-dependent factor for the simulation of stamping operation is suggested.

Mechanical Performance of X-Truss/Foam Sandwich Construction

Zuoguang, Z., Jijun, H., Min, L., Yizuo, G., Zhijie, S. — Tue, 10 Nov 2009 09:19:03 PST

In order to improve the transverse mechanical performance of ordinary foam core sandwich, Z-pins of carbon fiber were inserted into the foam core forming a novel X-truss/foam sandwich construction. Mechanical behaviors of this new composite are mainly determined by its structure parameters, which offer many degrees of freedom to designers. Here, flatwise compression, shear, and bending tests were carried out to investigate the influence of structure parameters on mechanical behavior. These structure parameters include Z-pin inserted angle, volume fraction, and orientation of X-truss, etc. Based on the rule of mixture, equations have been derived to estimate the compression and shear properties, which conform to experimental results. With the increase of Z-pin inserted angle, compression performance is improved, while shear and bending performance decrease. The 45° angle offers the best properties of shear and bending behavior, whereas the 90° angle presents the best compression performance. In addition, using the theory of the Winkler foundation beam, a prediction equation of compression strength has been derived which indicates that larger diameter Z-pins can offer more efficient enhancement than smaller diameter ones in terms of compression behavior.

Effect of Load Levels and Plastic Type on Creep Behavior of Wood Sawdust/HDPE Composites

Najafi, A., Najafi, S. K. — Tue, 10 Nov 2009 09:19:03 PST

In this study, effect of load levels and plastic type on creep behavior of wood sawdust/ HDPE (high density polyethylene) composites was investigated. The composites were manufactured using a dry blend/hot press method. In this method, powder of plastic and dried sawdust were mixed in a high speed mixer and then the mixed powder was pressed at 190°C. Wood sawdust/HDPE composite panels were made from virgin and recycled high density polyethylene (as resin) and wood sawdust at 40% by weight HDPE loadings. Nominal density and dimensions of the panels were 1 g/cm³ and 35 x 35 x 1 cm, respectively. Short term flexural creep behaviors of the panels were studied at 10, 20, 30, and 40% of maximum bending load. Results indicated that the composites containing virgin HDPE exhibited higher creep deflection and by increasing the recycled HDPE content the creep deflection decreased in all load levels. At high levels of load, the behavior of composites becomes distinctly non-linear in character. Irrecoverable creep deflections are higher at high levels and lower virgin HDPE. Creep behavior in studied WPCs followed the Findley power law.

Hygrothermal Effect on the Compressive Strength of Uniaxial Fiber-Reinforced Polymer Matrix Composites

Upadhyay, P.C., Lyons, D.W., Wayne, W. S. — Tue, 10 Nov 2009 09:19:03 PST

Effect of temperature, moisture, and temperature and moisture combined (i.e., hygrothermal) on the compressive strength of four types of uniaxially fiber-reinforced polymer matrix composites (PMCs) have been evaluated using the theoretical model [12] of fibers microbuckling as the cause of failure under compression. The purpose is to show the severity of reduction in compressive strength of PMCs caused solely due to plasticization of the matrix, when the geometrical and material imperfection factors, which are almost unavoidable and cause further reduction in strength, are not incorporated and accounted for in the analysis.

The Effect of Curing Conditions and Fiber End Shapes on the Mechanical Properties of Composites

Atas, A., Arslan, N., Turkbas, E., Ozdemir, Z. — Tue, 10 Nov 2009 09:19:03 PST

The study consists of two main experimental parts. The aim of the first part of the study is to investigate the effects of the straight-short steel fibers and different curing conditions on the mechanical properties of the selected composite specimens. For this purpose, unreinforced (no fiber) specimens cured at room temperature (~20°C) and the straight-short steel fiber reinforced polyester—calcite composite specimens cured at room temperature and at different curing conditions of 40, 80, and 120°C for 4, 8, and 12 h, have been subjected to tensile tests. In the second part of the study, unreinforced specimens and polyester—calcite composite specimens with straight-short, woven, and three different end shaped fibers cured at room temperature have been tested according to the four-point bending test procedure so as to obtain the effects of the end shapes on the mechanical properties of the composite specimens.

Mechanical and Wear Characterization of GF Reinforced Vinyl Ester Resin Composites with Different Co-Monomers

Chauhan, S., Kumar, A., Patnaik, A., Satapathy, A., Singh, I. — Tue, 10 Nov 2009 09:19:03 PST

This article reports the mechanical characterization and sliding wear behavior of glass fiber-reinforced vinyl ester resins of varying acid values, based on epoxy-novalocs in the presence of three different comonomers (styrene, methyl acrylate and butyl acrylate) as reactive diluents. It presents a special account of the optimization of fabrication techniques of glass fiber-reinforced vinyl ester resin composites. It outlines optimum reaction conditions such as temperature, time, monomer type and initiator concentration. The experimental plan consisted of preparation of vinyl ester resin followed by the composite samples. Mechanical characterization was done and a comparison was made between the different samples. It was found that these composites have fairly good tensile and flexural properties. The composites with styrene and butyl acrylate as co-monomers had similar tensile strength which was higher than that of the composite with methyl acrylate. Hardness values of the three composites were almost the same without any significant effect of the comonomer type. Volumetric wear rate was estimated for these samples under various test conditions. A steady wear rate regime after certain amount of sliding was observed all the three cases.

Effect of Processing Temperatures on Mechanical Properties of Oil Palm Empty Fruit Bunch-Filled PVC Extrudates

Bakar, A. A., Hassan, A., Yusof, A. F. M. — Tue, 13 Oct 2009 02:32:21 PDT

The influence of extrusion processing temperature profiles on the mechanical properties of oil palm empty fruit bunch-filled poly(vinyl chloride) extrudates was investigated. Only the poly(vinyl chloride) (PVC), acrylic and chlorinated polyethylene extrudates filled with 10 phr oil palm empty fruit bunch (OPEFB) were able to be extruded successfully as the extrusion processing temperature profiles increased. The extrudates containing 20 phr OPEFB were severely distorted even though the processing temperature was increased to the maximum level. The impact strength, flexural modulus and strength, and yield stress and strain at break of extrudates filled with 10 phr OPEFB were insignificantly affected by the increase of extrusion processing temperature and fusion level of PVC.

Some Studies in Metal Matrix Composites Machining using Response Surface Methodology

Gaitonde, V.N., Karnik, S.R., Davim, J. P. — Tue, 13 Oct 2009 02:32:21 PDT

The present study establishes the relationship between cutting conditions and machinability characteristics during the turning of metal matrix composites (MMC). The investigation aims at determining the effects of cutting speed and feed rate on machining force, cutting power, and specific cutting force by developing second-order mathematical models using response surface methodology (RSM). Aluminum alloy reinforced with 20% of SiC particulates (A 356/20/SiCp-T6) were machined using a polycrystalline diamond (PCD) tool. The experiments have been planned as a full factorial design of experiments (FFD). The analysis of variance (ANOVA) was performed to check the adequacy of the mathematical models. The parametric analysis reveals that the machining force and cutting power increase with increase in feed rate while the specific cutting force decreases.

Mechanical and Microstructural Evaluation of Polymer Matrix Composites Filled with Recycled Industrial Waste

Diniz Melo, J. D., Dos Santos, E. A. — Tue, 13 Oct 2009 02:32:21 PDT

In this study, the influence of the addition of industrial waste of polyester and EVA (ethylene vinyl acetate) on the mechanical properties of polyester resin was studied. Specimens were fabricated and tested for the evaluation of flexural properties and Charpy impact resistance. Properties of the filled materials were measured and compared to those of the plain resin. The effect of particle size and filler content was also investigated. Then, fracture surfaces were analyzed by scanning electron microscopy (SEM). The results indicate reductions in flexural strength and strain to failure with the addition of particulate fillers. However, an increase of about 6% in impact resistance was observed in composites with 12.5 wt% of EVA.

Effect of Multi-walled Carbon Nanotubes on Mechanical Properties of Feldspar Filled Polypropylene Composites

Ansari, M.N.M., Ismail, H., Zein, S.H.S. — Tue, 13 Oct 2009 02:32:22 PDT

In this study, the effect of multi-walled carbon nanotube (MWCNT) reinforcement on mechanical and morphological properties of MWCNT reinforced feldspar/polypropylene composites was investigated. The composites were compounded in a Polydrive Thermo Haake R600 internal mixer at 180°C and at 50 rpm of rotor speed. Polyethylene co-acrylic acid (PEAA) was used as a processing aid in this study. The structure and dimensions of the MWCNTs were characterized using a transmission electron microscope (TEM). The tensile strength, elongation at break, Young’s modulus, flexural strength, flexural modulus, and impact strength increased with the addition of 0.1 wt% of MWCNT. The morphology and degree of dispersion of the MWCNTs in the feldspar/PP composites at different MWCNT loading was investigated using scanning electron microscopy (SEM). Results indicate that MWCNTs are well distributed and dispersed in feldspar/PP composites particularly at low filler loading, i.e., 0.1 wt%.

Hygrothermal Aging Effect on Fatigue Behavior of GLARE

Da Silva, D.A., Botelho, E.C., Rezende, M.C. — Tue, 13 Oct 2009 02:32:22 PDT

This article reports on the experimental characterization of the fatigue behavior of GLARE laminate taking into account the hygrothermal effects. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. The importance of temperature at the time of conditioning plays an important role in environmental degradation of such composite materials. In this work, the experiments showed that the hygrothermal conditioning can induce significant changes in the material properties. Due to the effect of the hygrothermal aging, both the tensile and fatigue values of the studied systems have been reduced, that is, the absorbed moisture has deleterious effects on the physical properties of metal—fiber composite laminates.

Buckling and Post-buckling Behavior of Compression Loaded Composite Panels with Hat Stiffeners

Elaldi, F., Colak, L. — Tue, 13 Oct 2009 02:32:22 PDT

The aim of this study was to explore easy technologies for manufacturing of integral composite structures to evaluate the manufacturing concepts. This has been done by determining the buckling and post-buckling behavior of hat-stiffened composite panels under compression loading. A shadow Moiré technique was used to monitor the out-of-plane displacement of the skin panel. The experimental results of hat-stiffened panels for initial buckling and post-buckled response of the panels were compared with numerical results obtained from linear and non-linear finite element methods. It was found to be in reasonably good agreement with each other. The panels showed good post-buckling strength and total failure began with the local buckling of the hat stiffeners.

Damped Response of Symmetric Laminated Composite Beams to Moving Load with Different Boundary Conditions

Kiral, Z. — Tue, 13 Oct 2009 02:32:22 PDT

The aim of this study is to present the damped dynamic response of a symmetric laminated composite beam with different boundary conditions. A three-dimensional finite element model based on the classical laminated plate theory is used together with the Newmark integration method in order to obtain the dynamic response of the beam. A computer code written in MATLAB^® was developed in order to perform the dynamic analyses. The proportional damping which is referred to as Rayleigh damping is employed in the dynamic analyses. The impulse, step and moving load responses of the composite beam are presented for different damping ratios. The effect of the damping ratio on the dynamic magnification value, which is defined as the ratio between the dynamic and static displacements calculated for the mid point of the beam, is investigated. The normalized time values at which the maximum mid-point displacements occur are presented. The results reported in this article show that the largest dynamic magnification values are recorded for a pinned—pinned beam and the dynamic magnification values decrease as the damping ratio increases.

A Study on the Effect of Epoxy Molding Compound (EMC) Rheology During Encapsulation of Stacked-CHIP Scale Packages (S-CSP)

Abdullah, M. K., Abdullah, M.Z., Mujeebu, M.A., Kamaruddin, S., Ariff, Z.M. — Tue, 13 Oct 2009 02:32:22 PDT

The numerical and experimental investigations of three-dimensional (3-D) mold filling during encapsulation process in stacked-chip scale package (S-CSP) are presented. The finite difference method (FDM) based on Navier—Stokes equations has been employed for the flow analysis in the mold cavity. The mold flow is assumed to be non-Newtonian and non-isothermal. The proposed models can take care of polymer rheology with cure effect (Castro—Macosko model) and without cure effect (Cross model). A package with five, six, and seven overhang stacking dies without wire bonds is considered for simulation. The epoxy molding compound (EMC) used is HITACHI CEL-9200. The effects of gap between die top and mold cap surface, and between adjacent dies on flow rheology are analyzed and presented. The flow retardation in the limitation region (gap region) and smooth flow in the free region of the package is being predicted. Higher initial conversion of EMC demonstrated higher viscosity and slower melt front advancement especially under the overhang area of same die stacking region and critical gap between the die and mold cap. The void mechanism occurred due to unbalanced mold flow and critical gap clearance. The simulation results are verified with those obtained from a typical electronic industry and found in good agreement. From the results; the Castro—Macosko model is found to be more stable and reliable on the flow rheology.

Development and Characterization of Amine Terminated Poly(Ethylene Glycol) Benzoate Modified Epoxy and E Glass Fiber Composites

Jena, R. K., Bhat, A.H., Maji, S., Behera, D., Banthia, A.K. — Tue, 13 Oct 2009 02:32:22 PDT

The E glass woven fabrics have been used as a reinforcing agent with amine terminated poly(ethylene glycol) benzoate (ATPEGB) modified epoxy as a matrix, for the preparation of fiber reinforced plastic (FRP) composites. The composite materials so obtained were subjected to dynamic mechanical analysis at a fixed frequency of 1 Hz. The volume fraction of glass was about 0.45. The concentration of ATPEGB in the matrix was varied gradually from 0 to 30 phr (phr stands for parts per hundred parts of resin). To investigate the effect of ATPEGB concentration on the dynamic mechanical properties of the composites, it was found that the tan peak temperature and storage modulus gradually decrease with incorporation of ATPEGB. However, the tan peak value increases upto 10 phr of ATPEGB concentration and decreases thereafter. Flexural strength of the composites increases slightly up to 10 phr of ATPEGB concentration and decreases thereafter. However, the impact strength of the composites increases significantly up to 10 phr of ATPEGB concentration and decreases thereafter. Scanning electron microscope (SEM) analysis of the fracture surface indicates massive plastic deformation in modified epoxy-based composites.

Performance Evaluation of Treated--Untreated Jute--Carbon and Glass--Carbon Hybrid Composites of Bisphenol-C based Mixed Epoxy--Phenolic Resins

Patel, V.A., Bhuva, B.D., Parsania, P.H. — Tue, 13 Oct 2009 02:32:22 PDT

Jute—carbon and glass—carbon hybrid composites of mixed matrix material [epoxy resin of bisphenol-C (EBC) and bisphenol-C-formaldehyde (BCF) of 50 wt% of the fibers] have been prepared by hand lay-up technique at 150°C under 7.6MPa pressure for 2h. Alkali-treated jute fibers have been acrylated to improve their physico-chemical properties. Tensile strength, flexural strength, electric strength, and volume resistivity of untreated (JCEBCF-50), treated (TJCEBCF-50) jute—carbon and glass—carbon (GCEBCF-50) composites are 10 MPa, 17 MPa, 1.60 kV/mm, and 5.9 x 10¹² -cm; 14.65 MPa, 19.33 MPa, 2.09 kV/mm, and 6.79 x 10¹² -cm; and 21.4 MPa, 24.53 MPa, 1.62 kV/mm, and 5.71 x 10¹² -cm, respectively. Alkali treatment and acrylation of jute fibers resulted in 46.50, 13.71, 24.40, and 15.15% improvement in tensile, flexural, electric strengths and volume resistivity, respectively. Water uptake tendency of jute—carbon composite is considerably reduced upon alkali treatment and acrylation of jute fiber. Observed equilibrium water content in all the three composites is HCl > H₂O > NaCl. Observed reduction in water uptake in TJCEBCF-50 is due to esterification of hydrophilic OH groups. In boiling water saturation time is reduced 20 times for JCEBCF-50 and TJCEBCF-50, and 16 times for GCEBCF-50 without any damage. Hybrid composites may be useful for low load bearing application and also in marine field.

A Three-Parameter Bond Strength Model for FRP--Concrete Interface

Wu, Z., Islam, S.M., Said, H. — Thu, 17 Sep 2009 03:35:51 PDT

The success of most strengthening or retrofitting technologies for concrete structures by using external bonded FRP sheets depends highly on the interface bond between FRP sheets and concrete substrates. This article presents a simplified, but more rational and accurate three-parameter bond strength model for FRP—concrete interface based on statistical analysis, in which main parameters of bond strength behavior are considered. An extensive database consisting of 311 experimental data of simple FRP-to-concrete bonded joints has been assembled to calibrate the parameters of the proposed model and examine its validity. Then, the performance of the proposed model has been compared with the performance of other existing bond strength models using the assembled database. Results have confirmed the validity of the proposed model and shown its superiority over other existing models.

Influence of Cut-Out Variables on Buckling Behavior of Composite Plates

Yazici, M. — Thu, 17 Sep 2009 03:35:51 PDT

Cut-outs are often found in composite structures. These are provided with structural components for ventilation and sometimes to lighten the structure. This article addresses the effects of a cut-out on the buckling behavior of rectangular plates made of polymer matrix composites. While the loaded edges are modeled in simply supported boundary conditions, the unloaded edges are taken as free. Finite element analysis is also performed to predict the effects of cut-outs on the buckling behavior of these plates. Several key findings and behavioral characteristics are discussed. These findings include the effects of cut-out size, cut-out orientation, and corner fillet radius conditions.

Some overall important findings of these studies are that the critical buckling loads are not changed by increasing cut-out orientation angle and hole corner fillet radius. The maximum variation was obtained as 5.91% by increasing the hole orientation angle in the buckling loads.

Effect of Particle Size, Fiber Content and Compatibilizer on the Long-term Water Absorption and Thickness Swelling Behavior of Reed Flour/Polypropylene Composites

Tajvidi, M., Azad, F. — Thu, 17 Sep 2009 03:35:51 PDT

Reed (Phalaris sp.) flour was used to produce natural fiber polypropylene composites and effects of particle size, compatibilizer, and fiber content on the physical properties of the produced composites were evaluated. The particle sizes ranged from 40 mesh to smaller than 100 mesh sizes and fiber contents were 60% and 70% by weight. Composites were made through the extrusion process. Particle size proved to have very significant effects on both water absorption and thickness swelling of the composite formulations. The lowest water absorption and thickness swelling values were obtained at the lower fiber content and smallest particle size. Water diffusion coefficients were also smaller for smaller particle sizes and at lower fiber contents. The effect of compatibilzer was positive in terms of enhancing the dimensional stability of the composites. Composites containing the smallest particle size exhibited different water absorption and thickness swelling behaviors as seen in their considerably longer time required to reach maximum values.

Dimensional and Geometric Deviations Induced by Drilling of Polymeric Composite

Faria, P.E., Campos Rubio, J.C., Abrao, A.M., Davim, J.P. — Thu, 17 Sep 2009 03:35:51 PDT

Tool material, tool wear, and machining parameters drastically affect the quality of holes produced in polymeric composites and, therefore, the performance of the finished component. This article investigates the influence of the above-mentioned factors on thrust force, diameter, and roundness deviations on holes generated after drilling glass fiber reinforced epoxy resin. High speed steel and cemented carbide drills were tested as tool materials and the results indicated that the high speed steel drill presented severe wear after drilling 1000 holes, thus promoting high thrust force and roundness deviation values, in addition to hole diameter figures considerably smaller than the nominal value. On the other hand, after drilling 10,000 holes the carbide drill presented lower wear land and, consequently, lower thrust force values, producing holes with superior dimensional and geometric quality.

Comparison of Inelastic Behaviors of Lead-Free and Sn--Pb Solder Joints

Tsai, H.-C., Jong, W.-R., Chang, H.-T. — Thu, 17 Sep 2009 03:35:51 PDT

In this study, finite element analysis is used to investigate the inelastic behaviors of lead-free solders, 96.5Sn—3.5Ag and 95.5Sn—3.9Ag—0.6Cu, and classical 63Sn—37Pb solder-bumped wafer level chip scale package (WLCSP) on printed circuit board (PCB) assemblies subjected to four different temperature cycle tests. The behaviors of equivalent strain range and strain energy density at the outmost corner solder joint adjoining to the upper pad are examined. It is found that: (1) the 95.5Sn—3.9Ag—0.6Cu solder has the best performance on the effect of plastic behavior among these three solder alloys, but it accumulates more plastic strain while the number of temperature cycling increased; (2) the 96.5Sn—3.5Ag solder alloy can sustain more creep than others; (3) the difference exists between using the equivalent total strain range and the strain energy density, respectively, to assess the thermo-mechanical behaviors of the solder-bumped WLCSP on PCB assemblies.

Reducing Fiber Readout of Structural Composite Panels

Wang, C.S., Iobst, S. A. — Thu, 17 Sep 2009 03:35:51 PDT

A new molding process concept aimed at producing fabric-based structural composites with minimized out-of-mold surface fiber readout was proposed and validated in this study. The process first incorporates and lightly cures resins in fiber reinforcements to form fabric preforms. The partially cured preforms are subsequently over-molded with fresh resins to produce the finished panels. The concept was demonstrated using a vinyl ester resin reinforced with a large roving, plain weave glass fabric. By controlling the volumetric shrinkage of resin matrices through adding low profile additives and fillers, the proposed molding process successfully produced composite panels with significantly reduced surface fiber readout as indicated by surface profiles and corresponding Ra values measured by optical profilometry. The results also indicated that the surface texture of the fabric-based structural composites can eventually be made comparable to that of an ELPO-coated steel sheet.

Stress and Strain Behavior of Slender Concrete Columns Retrofitted with CFRP Composites

Sadeghian, P., Shekari, A. H., Mousavi, F. — Thu, 17 Sep 2009 03:35:51 PDT

This article presents the results of experimental studies about axial stress—strain behavior of retrofitted slender concrete columns with CFRP composites. In this study, 30 unreinforced concrete cylinders 100 mm diameter with variable height of 200, 400, 600, 800, and 1000 mm were prepared and retrofitted. In each group, a plain specimen (unwrapped) and five wrapped specimens with different fiber orientations (0, 0/0, 90/0, 45, and 45/0) were tested under compressive axial force up to failure. At the end, analytical models were proposed for ultimate strength and ultimate strain of the slender specimens. The results have shown that the CFRP composites are most effective in increasing the strength and ductility of slender columns.

Nanocarbon Film as a Percolation Network for Nanocarbon/Polymer Composites

Sandu, I., Florescu, L. G., Fleaca, C., Dragomirescu, A. — Thu, 17 Sep 2009 03:35:51 PDT

Starting with a nanocarbon film, which has some special characteristics, the present study uses this film as a cluster of connected particles that induces the percolation of electrical carrier in composites. The composite is formed through the free infiltration of the polymer through the filler’s aggregates. This method forms nanocarbon/polymer composites which have an electrical conductivity more than three orders of magnitude greater than those prepared by mixing.

Wear Performance of Tetrazine Modified Multiwalled Carbon Nanotube/Epoxy Composites

Aibo, Z., Wei, L., Ming, L., Yaping, Z. — Thu, 17 Sep 2009 03:35:51 PDT

A graft-amino functional group was built on the surface of multi-walled carbon nanotubes (MWNTs) by the receation of tetrazine with -bond of MWNTs. A kind of multi-walled carbon nanotube (MWNT)/epoxy composite was prepared by means of tetrazine modified multiwalled carbon nanotube at elevated temperature. The interface properties of MWNT/epoxy composites were improved by the building of a chemical bond between the graft-amino group on the wall of nano-carbon tubes and epoxy functional group. The reaction mechanism is presented in Figure 2. The state of MWNT after modification was characterized by transmission electron microscopy (TEM) and Perkin Elmer Spectrum (FTIR). It was found that the morphology and structure of MWNT show great changes by treated tetrazine and MWNT was found well-dispersed in the matrix. The MWNT/epoxy (EP) composite exhibited a lower friction coefficient and lower wear rate compared to those without tetrazine modification. The friction coefficient of the composites is 6.5% lower than that of untreated MWNTs/EP composites and the wear rate is 71.4% lower. The dispersion of MWNTs has remarkable effect on the tribological properties of the composites and is presented in Figure 3.

Preparation and Characterization of Poly Acrylic Acid-Locust Bean Gum

Mahmoud, R. I. — Thu, 17 Sep 2009 03:35:52 PDT

Polymerization of acrylic acid (AA) with native locust bean gum (LBG) was carried out with the use of the peroxydiphosphate (PDP)/Fe²⁺(FAS) redox initiation system. The factors affecting the efficiency of the redox system and the polymerization process were studied. These factors included the concentration of AA, PDP, FAS, duration of reaction, and polymerization temperature. The polymerization reaction was studied with respect to percentage of total conversion (TC), whereas the resultant polymerization product (i.e., composite) was analyzed for the polymer yield. The latter refers to the percentages of the graft yield (GY), the graft efficiency (GE), homopolymer (HP) and total conversion (TC). The apparent viscosity of the composite at different rates of shear was also examined. The characteristic of the grafted product was evaluated by thermal decomposition TGA in the temperature range (0—700°C). Tentative mechanisms, including different chemical events that can occur thoughout the whole course of polymerization process, are reported.