Vinyl Ester Composites Research Articles

Mechanical properties of unidirectional aligned bagasse fibers/vinyl ester composite

Abstract The present study describes the preparation of aligned unidirectional bagasse fiber-reinforced vinyl ester (BFRVE) composites and their mechanical properties such as tensile, flexural, shear and impact strength. Composites were prepared by a hand lay-up technique developed in our laboratory with the help of a hot press. Mechanical properties were obtained for different fiber contents by varying the number of layers. The obtained tensile property values were compared with the theoretical results. The results show that the tensile strength increased linearly up to 44 wt% and then dropped. However, the tensile modulus increased linearly from 17 wt% to 60 wt%. In the case of flexural properties, the flexural strength increased up to 53 wt% and started to decrease. However, the flexural modulus also increased linearly up to 60 wt%. The impact strength values were higher than the matrix materials for all the specimens. The short beam shear strength values were also increased up to 53 wt% and then dropped. The modified Bowyer and Bader (MBB) model followed by the Hirsch model shows a very good agreement with experimental results in both tensile strength and modulus.

Modeling and Multiresponse Optimization of the Mechanical Properties of Roselle Fiber-Reinforced Vinyl Ester Composite

In this study, the roselle fiber-reinforced vinyl ester composites were prepared based on Taguchi’s L27 experimental design using hand lay-up technique. A gray-based Taguchi technique was used to optimize the process parameters with mechanical properties (multiple performance characteristics). The results also show that the fiber content is the most significant process parameter which greatly affects the mechanical properties. It was proved that the multiple performance characteristics of the plant-based natural fiber-reinforced polymer composites can be effectively improved by this method. The proposed response surface mathematical models to predict mechanical properties of composite were found statistically valid.

Manufacturing and Performance Evaluation of Polyurethane Composites Using One-Part and Two-Part Resin Systems

Polyurethane (PU)-based composites show superior performance compared to polyester and vinylester composites. The demand for PU composites is increasing in high technology as well as conventional applications such as infrastructure and automobile. In this study, glass fiber reinforced composite laminates using one-part and two-part PU resin are manufactured using vacuum-assisted resin transfer molding (VARTM) process. A new generation two-part thermoset PU resin system is investigated and compared with commercial one-part PU resin systems. The mechanical performance of glass fiber reinforced composites manufactured using two different PU resin systems is evaluated. Tensile and flexure tests are conducted on both neat resin and glass/PU composites. Low-velocity impact tests are performed on both types of glass fiber reinforced PU composite specimens. Mechanical properties including strength and modulus were measured and analyzed for the two resin systems. Differential scanning calorimetry (DSC) is used to study the cure behavior of both resin systems. A Brookfield LVDV-II programmable rotational type viscometer is employed to study the viscosity profiles of the resin systems. The influence of resin properties on the overall performance of glass fiber reinforced composites is discussed.

Optimization of Pultrusion Process for Kenaf Fibre Reinforced Vinyl Ester Composites

In pultrusion process, one of the major decisions to be made by the manufacturing engineer is about the setting of manufacturing process parameters such as pulling speed, gelation temperature, curing temperature and CaCo3 filler loading before the manufacturing process is commenced. The objective of this paper is to report on the optimization of the manufacturing process parameters during pultrusion process of kenaf fibre reinforced vinyl ester composites. Besides, the paper reveals the best combination parameter and the most contributed parameter in process of pultruded kenaf reinforced vinyl ester composite through analysis of variance (ANOVA).

High-temperature slurry erosion of vinylester matrix composites – The effect of test parameters

Glass fibre (GF) reinforced vinylester composites (VE-FRP) are commonly used materials in hydrometallurgical reactors, the pulp and paper industry and waste water treatment plants, due to their excellent chemical resistance combined with good mechanical performance. In these applications, materials can be subjected to erosion, elevated temperatures (as high as 95°C) and various chemical environments. However, studies on the slurry erosion of vinylester-based composites at high temperatures have not yet been reported.In this study, the erosion resistance of GF reinforced VE-FRP was investigated with a pilot-scale reactor. The effect of slurry concentration, erodent particle kinetic energy and slurry temperature was studied. The dominating wear mechanism was found to be abrasive wear. The VE-FRP structure was found to be prone to erosive turbulent flow and cavitation. Moreover, an increase in the erodent concentration of the slurry (10–20wt%) or in the total kinetic energy of the erodent particles (30–770kJ) increased the wear rate of the material markedly (up to 6 times higher weight loss). However, the total effect of different interrelated parameters was found to be complex. Consequently, it is recommended that predictions of the erosion rate of VE-FRP components are based on tests carried out in conditions that simulate the actual service environment.

Parametric analysis of mechanical properties of bagasse fiber-reinforced vinyl ester composites

In the present communication an effective parametric analysis on the mechanical properties (tensile and flexural strength) of bagasse fiber-reinforced vinyl ester (BFRVE) composites were conducted, and then the fabrication process parameters were optimized by using Taguchi and analysis of variance techniques. Composites plates were fabricated by Taguchi’s L18 experimental design as the function of process parameters such as fiber length, fiber content, fiber diameter, sodium hydroxide concentration and sodium hydroxide treatment duration. The optimum process parameters to obtain the maximum strength values were identified using signal-to-noise ratio calculations. Then, the results were analyzed to know the percentage contribution of each fabrication process parameter on the tensile and the flexural strength using analysis of variance. A multivariable non-linear regression model was developed to predict the strength values and compared with experimental strength values. The developed models were validated by 10 additional experimental results using the mean absolute percentage error (MAPE). The results reveal that the fiber content (40 wt%) is the most significant factor influencing the tensile and flexural strength. An acceptable level of mean absolute percentage errors (8.57% for tensile strength and 9.13% for flexural strength) was obtained in both cases. Finally, the results indicate that this model can be used efficiently for prediction of tensile and flexural strength of BFRVE composites without any further experiments.

Nonlinear response in glass fibre non-crimp fabric reinforced vinylester composites

This paper addresses the nonlinear stress-strain response in glass fibre non-crimp fabric reinforced vinylester composite laminates subjected to in-plane tensile loading. The nonlinearity is shown to be a combination of brittle and plastic failure. It is argued that the shift from plastic to brittle behaviour in the vinylester is caused by the state of stress triaxiality caused by the interaction between fibre and vinylester. A model combining damage and plasticity is calibrated and evaluated using data from extensive experimental testing. The onset of damage is predicted using the Puck failure criterion, and the evolution of damage is calibrated from the observed softening in plies loaded in transverse tension. Shear loading beyond linear elastic response is observed to result in irreversible strains. A yield criterion is implemented for shear deformation. A strain hardening law is fitted to the stress-strain response observed in shear loaded plies. Experimental results from a selection of laminates with different layups are used to verify the numerical models. A complete set of model parameters for predicting elastic behaviour, strength and post failure softening is presented for glass fibre non-crimped fabric reinforced vinylester. The predicted behaviour from using these model parameters are shown to be in good agreement with experimental results.

Environmental Durability of Vinyl Ester Composites Filled with Carbonized Jatropha Seed Shell

The durability of vinyl ester composites filled with carbonized jatropha seed shell was investigated in 5% NaOH solution, 5% HCl solution, and distilled water for 12 months. The environmental durability of the composites was determined by measuring weight changes, flexural properties, and tensile properties. Results showed weight gain and changes in the mechanical properties of the composites due to the soaking time in alkaline, acidic, and neutral environments. It was observed that vinyl ester composites had the highest tensile properties in alkaline environments. The highest flexural properties of the vinyl ester composites were observed in an alkaline environment. Scanning electron microscope image analysis revealed that the surface of the vinyl ester composites was rough and that the original luster was lost after soaking in alkaline solution, acidic solution, and distilled water for 12 months.

Analysis of the tensile properties of natural fiber and particulate reinforced polymer composites using a statistical approach

Abstract In the present study, the effect of fiber and (5% wt) coconut shell powder (CSP) loading on the tensile properties of randomly oriented roselle fiber reinforced vinyl ester (RV) composites was carried out. Composite specimens were fabricated using the hand lay-up technique. It was observed that tensile properties of vinyl ester composites increase upon reinforcement with roselle fibers and CSP particles. The reinforcement of roselle fibers has significant effects on the tensile strength and modulus of the composite. The fractographic study was carried out on the surface of fractured composite specimens using scanning electron microscopy. A better interfacial adhesion, fiber dispersion and less fiber pull out on the surface of fractured composite specimens were identified. The tensile strength of RV composites has also been statistically analyzed by two-parameter Weibull distribution. Twenty-five tension tests were carried out. The results obtained varied between 37.89 MPa and 45.07 MPa. Furthermore, the inspection of the developed distribution was examined by the Kolmogorov-Smirnov (KS) test. The results show that the gained two-parameter Weibull distribution can be used to express the tensile strength and predict its values accurately.

Effect of long-term exposure to marine environments on the flexural properties of carbon fiber vinylester composites

Marine industries are increasingly embracing carbon fiber–vinylester resin composites as structural materials for military and civilian naval crafts. This move is driven by the ability of vinylester to better tolerate ultraviolet (UV) radiation and moisture as compared to other resins. Vinylester composites, even with long-term exposure to UV and moisture, exhibit limited surface damage which has a minor effect on their bulk properties. However, this surface-confined damage can impact the composite flexural strength which can be critical for marine crafts; particularly, as marine crafts are often subjected to out-of-plane loads (e.g., hull slamming). This work reports on a series of experiments aimed to investigate the individual and synergistic damaging effects of UV radiation and moisture on the flexural properties of carbon fiber vinylester composites. Results show that marine environment-induced damage can significantly reduce the flexural strength of carbon fiber–vinylester laminas (−10% to −40%).

Thermo‐physical, thermal degradation, and flexural properties of betel nut husk fiber reinforced vinyl ester composites

This study aims to investigate the thermo‐physical, mechanical, and thermal degradation properties of betel nut husk (BNH) fiber reinforced vinyl ester (VE) composites. These properties were evaluated as a function of fiber maturity, fiber content, and fiber orientation. Thermo‐physical properties were analyzed experimentally using a hot disk TPS method. The introduction of BNH was found to reduce the thermal conductivity of neat VE. The thermal conductivity and thermal diffusivity of BNH reinforced VE composites decreased with the increase in fiber content. Short fiber BNH reinforced VE composites showed the lowest thermal conductivity as compared to the unidirectional and random nonwoven composites. The TGA analysis shows lower resin transition peak for the BNH reinforced VE composites than the peak of neat VE. Fiber maturity had a notable effect on the flexural modulus of the BNH fiber reinforced VE composites. Incorporation of 10 wt% BNH fibers into the composite has increased the composites' flexural modulus by 46.37%. However, further increases in the fiber content reduced both flexural strength and modulus of the composites. POLYM. COMPOS., 37:2008–2017, 2016. © 2015 Society of Plastics Engineers

Particle swarm and simulated annealing based intuitive search optimization of flexural behaviors in bioparticles impregnated coir fiber–vinyl ester composites

The present investigation is focused on evaluation and optimization of flexural behaviors of bio‐particulates impregnated coir–vinyl ester composites. The bio‐particulates such as termite mound soil, groundnut and rice husk were selected and the composite fabrications were planned as per Design of Experiments with the different levels of fiber length, fiber content, and particulate content. The flexural strength of fabricated composites was evaluated as per ASTM D 790‐10. The fractography study was carried out on tested specimens using Scanning Electron Micrographs. The nonlinear regression models were developed for the prediction of flexural behaviors over the specified range of conditions. The fabrication parameters for the better value of flexural behaviors were determined using particle swarm and simulated annealing algorithms. The optimum conditions are further refined and validated experimentally using intuitive search algorithm. It was confirmed that the termite mound soil, ground nut and rice husk impregnated coir–vinyl ester composites exhibited better value of flexural strengths of 33.5 MPa, 36 MPa, and 38.4 MPa, respectively. POLYM. COMPOS., 37:1765–1774, 2016. © 2014 Society of Plastics Engineers

Effect of matrix properties on the fatigue damage initiation and its growth in plain woven carbon fabric vinylester composites

The influence of matrix properties including the fracture toughness and carbon fiber (CF)/vinylester (VE) adhesion on the static tensile properties and tension–tension fatigue properties of CF/VE composites has been investigated. An appropriate chemical modification of VE resin improved the tensile strength up to 37.3% and extended the fatigue life of CF/VE composites greatly by several ten times than that using regular VE resin as matrix. Under static loading different failure modes appeared and strain at failure changed due to chemical modification of VE altering the fracture toughness and CF/VE adhesion. Based on TSA (thermoelastic stress analysis) and SEM (scanning electron microscopy) observation, it was revealed that the fracture toughness of matrix dominated the initiation and growth of matrix cracks in CF/VE composites at fatigue initial stage. Transverse cracks formed by linkage of individual matrix crack occurred at interface or matrix that depended on CF/VE adhesive strength. At fatigue middle stage, local delamination tended to initiate early in composites fabricated by resin with lower fracture toughness. High CF/VE adhesive strength also brought a positive effect on the resistance to delamination growth resulting in remarkable extension in fatigue life of composites. The coupling effect of fracture toughness of matrix and CF/VE adhesion on the mechanical properties especially fatigue performance of CF/VE composites was investigated.

Tribological Behavior of Micrometer- and Submicrometer-Size Cenosphere Particulate-Filled Glass Fiber–Reinforced Vinylester Composites Under Dry and Water-Lubricated Sliding Conditions

In this work, the tribological behavior of micrometer and submicrometer cenosphere particulate–filled E-glass fiber–reinforced vinylester composites have been investigated on a pin-on-disc tester under dry sliding and water-lubricated sliding conditions. Three different uniform sizes of cenosphere particles (2 μm, 900 nm, 400 nm) were used as fillers in the glass fiber–reinforced vinylester composites. The weight fraction of cenosphere particles has been varied in the ranges from 5, 10, 15, to 20 wt%. The experimental results show that all of the composites exhibited lower coefficient of friction and lower wear resistance under water-lubricated sliding conditions than under dry sliding. It has been noted that the submicrometer size (400 nm) cenosphere particulates as fillers contributed significantly to improve the wear resistance. It has also been noted that 10 wt% of the cenosphere particles is the most effective in reducing the wear rate and coefficient of friction. Effects of various wear parameters such as applied normal loads, sliding speeds, particle size, and particle content on the tribological behavior were also discussed. In order to understand the wear mechanism, the morphologies of the worn surface were analyzed by means of scanning electron microscopy (SEM) for composite specimens under both dry and water-lubricated sliding conditions.

Optimization of Mechanical Behaviors of Red Mud Particulated Coir–Vinyl Ester Composites Using Intuitive Analysis Based on Response Surface Methodology and Simulated Annealing

Addition of red mud particles into coir fiber reinforced vinyl ester composites is investigated in this study. Red mud is the caustic insoluble waste residue generated during the alumina production from bauxite. The composites were fabricated by varying weight percentage of the red mud and length of the coir fiber in polymer matrix composites. The compression molding process was used for fabricating the composites and static mechanical tests like flexural and impact were conducted as per ASTM standards. The non linear regression models were developed and optimum conditions for better mechanical behavior were determined using Response Surface Methodology and Simulated Annealing algorithms. An intuitive analysis was conducted to determine the better value of mechanical behaviors within the ranges of fabrication parameters.

Effect of various water immersions on mechanical properties of roselle fiber–vinyl ester composites

In the present communication, the effect of water absorptions on mechanical properties of roselle fiber reinforced vinyl ester composites prepared by wet hand lay‐up method was studied. Water absorption tests were conducted by immersing composite specimens into three different water environments, namely distilled water, ground water, and sea water, which were at room temperature, for a period of 10 days. The water absorption behavior of composite was found to follow a non‐Fickian behavior. The maximum water absorption percent and diffusion coefficient were determined from the obtained water absorption curves. The scanning electron microscopy was used for the fractographic studies on the fractured surface of composite. The results show that composites exposed to sea water environment absorb more water absorption percent than that of other water environments. It was observed that the water absorption percent increased with increasing fiber loading. Mechanical properties of dry composite specimens were compared with wet composite specimens. Mechanical properties were found to decrease with an increasing percentage of water uptakes. POLYM. COMPOS., 36:1638–1646, 2015. © 2014 Society of Plastics Engineers

Mechanical and thermal properties of josapine pineapple leaf fiber (PALF) and PALF-reinforced vinyl ester composites

Although the pineapple leaf fibers (PALF) are long known as domestic threading material in Malaysia, they are currently of little use despite being mechanically and environmentally sound. This study evaluated some selected properties of Josapine PALF and PALF-vinyl ester composites as well as the effects of simple abrasive combing and pretreatments on fiber and composite properties. Using PALF vascular bundles extracted from different parts of the leaves did not significantly affect PALF-vinyl ester composite mechanical properties. At low weight fraction and consolidating pressure, PALF fibers regardless of diameters and locations performed equally well in enhancing composite flexural properties under static loading. Finer bundles enhanced PALF-vinyl ester composite toughness indicated by tests at higher speeds. Abrasive combing produces cleaner and finer bundles suitable for reinforcing composites for applications not requiring high toughness.

Mathematical Modeling and Optimization of Mechanical Properties of Short Coir Fiber-Reinforced Vinyl Ester Composite Using Genetic Algorithm Method

The tensile, flexural, and impact properties of coir-fiber reinforced vinyl ester composites were evaluated. The short coir fibers with different proportions in fiber length and fiber content were used as reinforcements in polymer-based matrices. The mathematical models of tensile, flexural, and impact properties were developed using statistical packages and optimized using the genetic algorithm method to find the optimum fiber parameters for maximum value of mechanical properties.

Degradation in fatigue behavior of carbon fiber–vinyl ester based composites due to sea environment

This study focuses on the effect of confined and one sided sea water confinement on the cyclic fatigue behavior of carbon fiber reinforced vinyl ester composites that serve as facings materials for naval sandwich structures. Experimental results for facings yielded failures under much lower number of cycles when fatigued under immersed conditions surrounded by sea water than in air. Water penetrates the matrix resin through diffusion and fiber/matrix interface by capillary action through micro-cracks or inter-layer delaminations. During fatigue loading, its inability to drain during the downward (compressive) cyclic loading and the near incompressibility of water induces an internal pore water pressures which dominates the progressive failure mechanism. Sea water induced fatigue degradation data and resulting microstructure changes are obtained using high resolution X-ray micro-tomography along with the implications for marine composites.

Desirability Fuzzy Multiple Criteria Optimization of Process Parameters in CNC Turning of GFRP/ Vinyl Ester Composites

Although, Glass fiber reinforced vinyl ester resin is used for the production of many electrical components, automotive structural parts, sporting goods and high performance marine equipments, very little is known about its machining aspects. In this study, a hybrid multiple criteria optimization algorithm involving desirability index and fuzzy inference system coupled with Taguchi methodology is used to evaluate the optimal cutting parameters setting, in order to satisfy contradictory requirements of quality and productivity. Woven fabric based GFRP/ Vinyl ester tubes are finish turned using PCD cutting tool. Four process parameters, each at three levels are selected for the study viz. cutting tool nose radius, cutting speed, feed rate and depth of cut. Individual desirability indices of the three performance measures, viz. surface roughness, tangential cutting force and material removal rate are converted into a single multi-performance characteristics index (MPCI) using fuzzy inference system, which is then optimized using Taguchi analysis.