Fiber Reinforced Vinyl Ester Resin Research Articles

Influence of Carbon Nanotubes on Mechanical and Thermal Properties of Glass Fiber Reinforced Vinyl Ester Resin Composites

Carbon nanotubes (CNTs) were incorporated into glass fiber/ vinyl ester resins composites to improve their mechanical and thermal properties, especially the interlaminar shear and longitudinal compressive strengths which are belong to the matrix-dominanted properties and much weaker than the fiber-dominated properties. In this study, a higher temperature initiator was added to improve the polymerization degree and raise the transition temperature (Tg). Mechanical testing indicated that by adding 0.4 wt% CNTs, the nano-filled composites attributed to 21%, 16%, 10%, and 8% improvement in interlaminar shear strength, compressive strength, tensile strength and flexural strength with respect to their counterparts without CNTs, respectively. Moreover, Thermogravimetric analysis (TGA) also exhibits approximately 14°C higher decomposition temperature than those of conventional composites.

Thermo-mechanical correlations to erosion performance of short carbon fibre reinforced vinyl ester resin composites

Thermo-mechanical properties and erosion performance of short carbon fibre reinforced vinyl ester resin based isotropic polymer composites with four different fibre weight fractions have been investigated. The storage, loss and damping characteristics were analysed to assess the energy absorption/viscous recoverable energy dissipation and reinforcement efficiency of the composites as a function of fibre content in the temperature range of 0–140°C. The composite with 30wt.% of short carbon fibres has been observed to exhibit superior thermo-mechanical response with highest energy dissipation/damping ability accompanied with a constant storage modulus without any substantial decay till 60°C. The erosion rates (Er) of these composites are evaluated at different impingement angles (30–90°), fibre loadings (20–50wt.%), impact velocities (43–76m/s), stand-off distances (55–85mm) and erodent sizes (250–600μm) following the erosion test schedule in an air jet type test rig. An optimal parameter combination is determined and subsequently validated for erosion rate minimization following Taguchi method and by conducting confirmation experiments. A correlation between the loss-modulus inverse and the erosion rate has been observed which conceptually establishes a possible mechanistic equivalence between erosion and dynamic mechanical loading modes. The morphologies of eroded surface are examined by the scanning electron microscopy to investigate the nature of wear-craters, material damage mode and other qualitative attributes responsible for promoting erosion.

Cyclic fatigue behavior of carbon fiber reinforced vinylester resin composites manufactured by RTM and VARI

The mechanical behavior of [0°] 8 unidirectional, [+45°/0°/−45°/90°] S quasi-isotropic and [+45°/−45°] 3S angle-ply laminates produced by pressure or vacuum assisted resin infusion from toughened vinylester resin systems with unidirectional carbon fiber fabric reinforcement was investigated. The study included the determination of ultimate in-plane tension, compression and shear properties as well as the characterization of the cyclic fatigue behavior under stepwise increasing and constant amplitude loading. The experimental results showed a better fatigue performance of an epoxy-terminated butadiene-nitrile rubber modified VE resin system. Furthermore, the cyclic strength of the composites produced by VARI was lower compared to RTM composites. From the S– N curves of the quasi-isotropic material for R = +0.1, −1 and +10 the fatigue life diagram was determined.

Thermal degradation and decomposition of jute/vinylester composites

Thermal analysis of jute fibre reinforced vinylester resin with 30 vol% of fibre were performed by TG/DTG under dynamic conditions. The fibres were treated with alkaline solution at different temperatures and the final composition (cellulose, hemicellulose and lignin) of the fibre was determined by chemical analysis. Apparent activation energies were determined using a variety of conventional thermogravimetric methods. Two peaks were found in the composite differential curves: the first peak close to 327 and the second peak at 408°C. The apparent activation energy values for the second peak decreased when fibre were treated. The addition of the jute fibres produced a slightly decrease in the thermal stability of the composites.

Fracture criterion for kinking cracks in a tri-material adhesively bonded joint under mixed mode loading

The fracture behavior of a composite/adhesive/steel bonded joint was investigated by using double cantilever beam specimens. A starter crack is embedded at the steel/adhesive interface by inserting Teflon tape. The composite adherend is a random carbon fiber reinforced vinyl ester resin composite while the other adherend is cold rolled steel. The adhesive is a one-part epoxy that is heat cured. The Fernlund–Spelt mixed mode loading fixture was employed to generate five different mode mixities. Due to the dissimilar adherends, crack turning into the adhesive (or crack kinking) associated with joint failure, was observed. The bulk fracture toughness of the adhesive was measured separately by using standard compact tension specimens. The strain energy release rates for kinking cracks at the critical loads were calculated by a commercial finite element analysis software ABAQUS in conjunction with the virtual crack closure technique. Two fracture criteria related to strain energy release rates were examined. These are (1) maximum energy release rate criterion ( G max) and, (2) mode I facture criterion ( G II = 0). They are shown to be equivalent in this study. That is, crack kinking takes place at the angle close to maximum G or G I (also minimum G II, with a value that is approximately zero). The average value of G IC obtained from bulk adhesive tests using compact tension specimens is shown to be an accurate indicator of the mode I fracture toughness of the kinking cracks within the adhesive layer. It is concluded that the crack in tri-material adhesively bonded joint tends to initiate into the adhesive along a path that promotes failure in pure mode I, locally.

Impact fatigue of glass fibre–vinylester resin composites

Abstract An impact fatigue study has been made for the first time on 63.5% glass fibre reinforced vinylester resin, notched composites. The study was conducted using a pendulum type repeated impact apparatus specially designed and fabricated for determining single and repeated impact strengths. Well-defined impact fatigue ( S – N ) behaviour, having a progressive endurance below the threshold single cycle impact fracture strength, with a limit, has been demonstrated. Fractographic analysis revealed fracture by primary debonding, with fibre breakage and pull-out in the tensile zone, but a shear fracture of fibre bundles in the compressive zone of the specimen. Residual strength measured after impact fatigued showed retention of the property at high impact energy levels, up to about 10 2 impact cycles, thereafter a gradual drop to about 10 3 impact cycles followed by a rapid drop. The residual modulus and toughness showed a gradual drop with the increasing number of impacts endured. It is suggested that a few large cracks and an increased volume of microcracks in the matrix, with damaged fibres at high and low impact endurances, respectively, account for the failures of the composites under impact fatigue.

Behaviour ofE-glass fibre reinforced vinylester resin composites under impact fatigue

An impact fatigue study has been made for the first time on 63.5% glass fibre reinforced vinylester resin notched composites. The study was conducted in a pendulum type repeated impact apparatus especially designed and fabricated for determining single and repeated impact strengths. A well-defined impact fatigue (S-N) behaviour, having a progressive endurance below the threshold single cycle impact fracture stress with decreasing applied stress has been demonstrated. Fractographic analysis revealed fracture by primary debonding having fibre breakage and pullout at the tensile zone, but a shear fracture of fibre bundles at the compressive zone of the specimen. The residual strength, modulus and toughness showed retention of the properties at high impact stress levels up to 1000 impacts followed by a sharp drop. Cumulative residual stresses with each number of impacts not withstanding the static fatigue failure at long endurances have been ascribed for the composite failures under the repeated impact stresses.

Effects of moisture on the mechanical properties of glass fibre reinforced vinylester resin composites

Glass fibre reinforced vinylester resin composites incorporating varying amounts of fibres (63.5, 55.75, 48.48, 38.63 and 27.48 wt%) were characterized for their mechanical properties both as prepared and after treatment with boiling water for 2, 4, 6, 8 and 24 h. Weights of the samples were found to increase to a saturation at about 8 h with boiling water treatment. In keeping with the composite principle, the mechanical properties improved with fibre loading. However, the properties were relatively inferior when treated with boiling water for longer hours attributing to ingress of moisture by capillary action through the interface between the fibre and the resin matrix. Considering the rates of moisture absorption and correlating with the mechanical properties, it was observed that the deteriorating effects were predominant up to 4 h treatment with boiling water. Estimation of defect concentrations for 63.5 wt% of nascent fibre reinforced composites as well as those composites treated with boiling water for 24 h were 56.93% and 64.16% respectively. Similarly, 27.48 wt% nascent fibre reinforced composites and those composites with boiling water treatment showed the estimation of defect concentrations of 39.94% and 50.55% respectively. SEM study of the fractured surfaces showed heavy fibre pull-out in the tensile zone whilst shear fracture of the fibre bundles was predominant at the compressive zone of the samples tested for flexural strength properties.

A Viscoelastic Analysis of the Creep Behaviour of a Chopped Strand Mat E-Glass Fibre Reinforced Vinylester Resin

The viscoelastic response of a chopped strand mat E-glass fibre reinforced vinylester resin has been studied over a wide range of applied stress levels. At low applied stress levels, the material exhibited a linear viscoelastic response well represented by Schapery's power law model with constant C and n terms. At higher stresses nonlinear behaviour was observed which apparently is caused by the multiplicity of complex local phenomena associated with and preceding damage development (plastic deformation of the matrix, interfacial slippage, fiber-matrix debonding). The limits of linear viscoelastic behaviour and of damage initiation – about 0.48% strain or 42 MPa – coincide for this material. However, for successful modelisation of uniaxial creep strain in the nonlinear range a modified power law is proposed which uses stress-dependent creep parameters C and n.

Durability of Closed-End Pressurized GRP Pipes under Hygrothermal Conditions. Part I: Monotonic Tests

Environmental factors are of extreme importance with respect to the ser-vice life of composite components based on polymeric engineering matrices. Part I deals with the role of matrix ductility and chemical environmental degradation on the composites mechanical properties. Part II is concerned with the lifetime prediction of GRP filament wound pipes under low pressure levels and hygrothermal conditions. There composites are an E glass fiber reinforced polyester resin and an ECR glass fiber reinforced vinylester resin. The mechanical behavior of the pipes before and after exposure to water for different duration is studied through internal pressurizing tests with closed end procedure. The results indicate that in the hoop direction, fibers carry the complete load while in the axial direction there is a substantial contribution from the matrix. The use of elasticity theory appears as an appropriate method to describe the mechanical behavior of the pressurized pipes under monotonic loading conditions. In the hoop direction the behavior is governed by the fibers one whereas in the axial direction damage must be accounted for in the elastic law. Chain scission effects on the mechanical properties are investigated. Experimental results show that the mechanical properties, the damage mechanisms and the failure mode of the pipes are changed by water uptake. Relations between the mechanical properties and the exposure duration based on physical considerations are assessed, allowing for the definition of a damage parameter related to hygrothermal degradation. Environmental effects (swelling and chain scission) mainly affect the yielding pressure and the pressure to failure, whereas load condition and initial defects affect the axial modulus. This leads to the definition of two independent damage parameters.