Pultruded Composites Research Articles

Pultruded fiber-reinforced polyurethane-toughened phenolic resin. II. Mechanical properties, thermal properties, and flame resistance

A novel process has been developed to toughen phenolic resin by polyurethane for fiber-reinforced pultruded composites. The mechanical properties of the composites (tensile strength, flexural strength, and notched Izod impact strength) approach maximum values at 10 wt% of the blocked polyurethane content. The fabricated composites show good mechanical properties and possess low void fraction. Notched Izod impact strength of the composite (with 5 wt% polyurethane content) increases by more than 30% compared to the virgin composite. The thermogravimetric analysis (TGA) showed that the temperature for the 5% weight loss of the phenolic/polyurethane copolymer decreases with the increasing of the polyurethane content; however, the thermal degradation temperature is still higher than 350°C. Differential scanning calorimetric analysis (DSC) showed that the onset point of copolymer is 20°C higher than that of the virgin one. The presence of the blocked polyurethane may hinder the polymerization of phenolic resin. The modified composite shows excellent dimensional stability. The copolymer composite also possesses good fire resistance. © 1996 John Wiley & Sons, Inc.

Material Characterization of Pultruded Laminates and Shapes

This paper discusses the material characterization of wide flange pultruded structural shapes (E-glass, Vinylester). The material was subjected to three loading conditions: tension, shear, and bending. Coupon samples were obtained from web and flanges of the I-section for tension and shear tests. Tensile properties were obtained from rectangular coupons with end tabs loaded in tension to failure. Shear properties were obtained from two different test methods: Iosipescu shear test method and torsion of rectangular samples. Experimentally determined material properties were compared to analytical predictions based on micro and macromechanics. Micromechanical models are used for the prediction of individual laminae (roving layers, continuous strand mat, nexus veils) properties. Classical lamination theory (CLT) is then used to predict the laminate properties. In addition, I-beams were tested in bending to evaluate their response and the experimental results were compared to predictions using Mechanics of Laminated Beams (MLB) approach. Results indicate a good correlation between experimental data and theoretical predictions, showing that the properties of pultruded composites can be predicted with sufficient accuracy. The superiority of the torsion test for determination of in-plane shear stiffness is demonstrated.

Effects of Pull Speed on Die Wall Temperatures for Flat Composites of Various Sizes

Properties of pultruded composites depend strongly on processing variables such as pull speed. Die wall temperatures may change depending on the size of the composite and the pull speed due to heat absorption or heat generation by the composite. It is the objective of this study to emphasize the importance of predicting and understanding the impact of die wall temperatures on centerline temperatures and degree of cure for composites of various thicknesses pultruded at different pull speeds. In order to accomplish this goal, a transient, three-dimensional numerical thermochemical heat transfer model for the heating section of the pultruder was developed. The governing energy and species equations for the composite were solved using a finite difference control volume scheme. The kinetic parameters for Shell EPON 9420 epoxy resin, determined using a heat flux type differential scanning calorimeter (DSC), were employed in this study. Previous researchers have tended to ignore the variations in die wall temperature distribution or have relied on experimentally obtained die wall temperature data to develop models and make predictions. This research overcomes those restrictions by completely predicting the temperature profiles in the entire die, thereby providing the pultrusion engineer with the tools to design a heating section of a pultrusion machine. An operational envelope has also been developed to establish guidelines for maximum pull speeds that can be used to obtain a specified degree of cure in the composite.

Temperature and Cure in Pultruded Composites Using Multi-Step Reaction Model for Resin

A numerical model has been developed to analyze the temperature and degree of cure profiles in pultruded composites. In pultruded composites the resin plays an important role in holding the fibers together in a structural unit and also transferring and distributing the applied load to the fibers. The degree of cure of the pultruded composite is an important phenomenon in the manufacturing process since it can be related to the mechanical properties. Therefore, the degree of cure of the resin plays a crucial role in the pultrusion process. The chemical reaction of the resin determines the degree of cure as well as the exothermic energy released by the resin. A one-step reaction model has been employed for the resin system in most of the previous research. For some resin systems, a one-step model may not produce good results; therefore, it was decided to pursue a multiple-independent-step reaction model that more closely follows the actual behavior of the resin. In this research, the effect of an approximate multiple-independent-step reaction model for the thermoset epoxy resin SHELL EPON 862/W was studied. The numerical model utilized a fixed control volume based finite difference approach [1]. This technique was used to solve the coupled, non-linear, three-dimensional steady-state energy and species equations for a cylindrical geometry. The species equation(s) utilized both a one-step Arrhenius reaction rate model as well as a multiple-independent-step Arrhenius reaction rate model for the resin. The kinetics parameters of the resin for a one-step reaction model were obtained from the differential scanning calorimeter (DSC) scans and for the multistep model a regression fit was made to obtain the kinetic parameters from the DSC scans. The numerical model was used to predict the temperature and degree of cure for the pultruded composite both inside the die and in the post-die region. These numerical results were compared with experimental measurements. The processing variables examined in this study were die-wall temperature setting, pull speed and fiber volume fraction.

Load and resistance factor design (LRFD) approach for bolted joints in pultruded composites

The application of glass fiber-reinforced polymeric matrix composites in civil engineering structures has been increasing rapidly in recent years. Pultruded composites are attractive for structural applications because of their continuous production and excellent mechanical properties. The present study is intended to be a step in understanding bolted joints in pultruded composites. Specifically, bolted connections in pultruded plates are investigated for their block shear and net tension failure modes. Configurations and dimensions have been selected to highlight the block shear and net tension failure phenomena and to compare the behavior of composites to the standard practice in the case of steel connections. Specimens with single and multiple holes have been tested in tension under bolt-loading conditions. Some of the specimens were instrumented with strain gages and the load-strain responses were monitored. The failed specimens were examined for the cracks and fracture patterns. The results have been analyzed using the strength calculations similar to those used in the load and resistance factor design (LRFD) procedures for steel structures. Two LRFD-type formulae for block shear and net tension failure for pultruded composites are proposed in the present paper. It was found that the failures in the bolt-loaded pultruded specimens could be predicted reasonably well with the proposed formulae. The use of these formulae is also demonstrated by means of examples. The proposed resistance factors are checked with additional test results.

Die and post-die temperature and cure in graphite/epoxy composites

A numerical model has been developed to analyze the die and post-die temperature and degree of cure profiles in pultruded composites. The model utilizes a fixed control volume based finite difference approach (S. V. Patankar, Numerical Heat Transfer and Fluid Flow. McGraw-Hill, NY, 1980). The method was used to solve the coupled non-linear three-dimensional steady-state energy and species equations for a cylindrical coordinate system. The species equation utilizes the one step Arrhenius reaction rate equation for an epoxy resin system. The kinetic parameters used for the epoxy resin to predict the temperature and degree of cure profiles were obtained from the differential scanning calorimeter (DSC) scans. The model is used to predict the temperature and degree of cure for the pultruded composite both inside the die and in the post-die sections. The post-die curing is important since the composite processing temperature is quite high and curing continues for some time even after the composite exits the die. The processing conditions examined in this study were die wall temperature settings, pull speed and fiber volume fraction.

Manufacturing model for three-dimensional irregular pultruded graphite/epoxy composites

Pultrusion is one of the most cost-effective and least laborious techniques of producing structural composite materials. Detailed computer modelling is required for the improved manufacturing and advancement of pultruded composites. This research involves a numerical three-dimensional investigation of the thermochemical aspects of the design and manufacture of pultruded composite materials of various geometries by investigating axially, and in cross-sectional contour form, the transient temperature and curing characteristics for graphite/epoxy composites. The behaviour of the exothermic chemical reaction on the temperature profiles and the degree of cure is discussed. A numerical model based on Patankar's finite difference technique was formulated for solving the governing energy and species equations used in modelling the entire heating section of the industrial PTI Pulstar 804 pultrusion machine. The chemical kinetic parameters of the Epon 9420 epoxy resin were determined using a differential scanning calorimeter. Computer modelling has the ability of enhancing the understanding of the thermal and curing mechanisms without disrupting the performance of composites and can act as a useful tool to improve manufacturing. The cost-effective nature of pre-fabrication modelling allows manufacturers to be more competitive in producing structural shaped composites.

Poly (ϵ-caprolactam)-poly (butadiene- co-acrylonitrile) block copolymers II. Processability and properties of pultruded glass-fiber-reinforced composites

Uni-directional glass-fiber-reinforced Nylon 6 and poly(ϵ-caprolactam)-poly(butadiene- co-acrylonitrile) block copolymers (NY6/ ATBN) have been prepared by a novel thermoplastic pultrusion process. The effects of processing parameters, ATBN (amine-terminated butadiene-acrylonitrile copolymer) content and glass fiber content on the mechanical and thermal properties of pultruded composites were studied. Results show that NY6/ATBN (less than 15 wt.% ATBN) composites possess good fiber wet-out and very low void content (below 1 vol.%). The intrinsic viscosity of NY6/ATBN in pultruded composites is more than 1.1, and the pulling rate is between 25 and 50 cm/min at a die temperature of 180–200 °C. The NY6/ATBN composites show the highest notched Izod impact strength compared with glass-fiber-reinforced Nylon 6, PMMA, PPS and ABS resin composites.

Pultruded fibre-reinforced furfuryl alcohol resin composites: 2. Static, dynamic mechanical and thermal properties

Abstract A novel process has been developed to manufacture pultruded fibre-reinforced furfuryl alcohol (FA) resin composites. In this paper, the effects of fibre reinforcement type and content on the static, dynamic mechanical and thermal properties of the FA resin pultruded composites are investigated. The mechanical properties increase with increasing volume content of the glass or carbon fibres, with the glass fibre-reinforced furfuryl alcohol (GF/FA) composite exhibiting maximum mechanical property values at a filler content of 5 phr. High catalyst content and die temperatures are necessary for manufacturing FA pultruded composites with high filler content. GF/FA pultruded composites retain their mechanical properties at elevated temperatures better than do unsaturated polyester pultruded composites. Dynamic mechanical analysis revealed that the dynamic storage modulus of the GF/FA pultruded composites increases with increasing post-cure time. Tan δ of GF/FA decreases and its glass transition temperature increases with decreasing pulling rate or increasing post-cure time. The glass and carbon fibre-reinforced FA pultruded composites possess high heat distortion temperature and good flexural properties, in comparison with other pultruded composites.

Ultrasonic and vibration methods for the characterization of pultruded composites

Characterization of unidirectional fiber reinforced glass/epoxy pultruded composites using ultrasonics (high frequency, 1-5 MHz) and the impulse-frequency response vibration (intermediate frequency, 50-100 Hz) technique, is demonstrated here. This paper compares the response of both of these non-destructive test techniques to the changes in the pultrusion process variables and to the indeed contaminants introduced during manufacturing. The ultrasonic methods use multi-mode techniques of wave velocity and attenuation measurements to measure the viscoelastic constants of the pultruded composite while the vibration technique provides the dynamic flexural modulus and loss factor (damping) measurements. Quasi-destructive assays were also performed using a low frequency (1-50 Hz) Dynamic Mechanical Analyser (DMA) to verify the state of pultruded samples with induced contaminants (simulated porosity and interfacial debonding) and the results compared with the non-destructive measurements. Mathematical models to describe the influence of porosity and debonding agents on the material properties were derived based on statistical regression analysis procedures. Results indicate that the peak damping value of the tan δ curve obtained from the DMA is a sensitive parameter to detect abnormalities in the finished product. The ultrasonic velocity and dynamic flexural modulus measurements provide useful information on the stiffness characteristics while the attention and loss factor can be related to the anomaly-sensitive damping properties of the material.

Mass and volume fraction properties of pultruded glass fibre-reinforced composites

With the expansion of pultruded composites into the construction industry, there exists a need for further studies on the properties of these materials. This paper presents the results from a series of tests on the physical properties of pultruded composite materials. Specimens cut from structural shapes, plates, gratings and rebars have been tested by using a supplementary procedure to the ASTM D2584-68 Standard Test Method for Ignition Loss of Cured Reinforced Resins. This supplementary procedure is used to remove the filler material added to the resin during the pultrusion process. The results from this series of tests have been used to show the wide variations that exist in specimens cut from similar samples of pultruded material. Also, pictorial illustrations are given of several representative samples of the post burnout fibre architecture of the pultruded composites.

Pultruded fiber reinforced blocked polyurethane (PU) composites. I. Processability and mechanical properties

AbstractThis paper presents a proprietary process developed to manufacture polyurethane (PU) pultruded composites. The blocked isocyanate (NCO)‐terminated PU prepolymer synthesized in this study was prepared from ε‐caprolactam blocked blends of toluene diisocyanate (TDI) and branched polyester. The processability and mechanical properties of various fibers (glass, carbon, and Kevlar 49 aramid fiber) reinforced PU composites have been studied. From the investigation of the pot life of resins, the reactivity of resins, and fiber wet‐out, it was found that the blocked PU prepolymers with chain extender showed excellent processability for pultrusion. Results show that the mechanical properties (i.e., tensile strength, specific tensile strength, flexural strength, specific flexural strength, flexural modulus, and impact strength) increase with fiber content. Kevlar fiber/PU composites possess the highest impact strength and specific tensile strength, whereas carbon fiber/PU composites show the highest tensile strength, flexural strength, specific flexural strength, and flexural modulus. Experimental results of tensile strength of all composites except carbon fiber/PU composites follow the rule of mixtures. The deviation of property of carbon fiber/PU composite is due to fiber breakage during processing. Pultruded fiber reinforced PU composites showed excellent tensile and impact strength compared to other pultruded composites studied.

Flexural and shear properties of unidirectional pultruded composites

Three point bend tests were performed on pultruded half-round cross-section rods of glass fibre-reinforced polyester and glass fibre-reinforced epoxy, the tests being arranged so that the specimen was unloaded as soon as the deflection corresponding to the maximum load was reached. This testing method enabled the fracture mechanisms at maximum loads to be mapped as a function of the loading rate and the span-to-depth ratios. An effect highlighted by this map is that a specimen tested at intermediate span-to-depth ratios may result in a purely tensile fracture at low loading rates and a purely shear fracture at high loading rates. This behaviour is interpreted as being due to the fact that the increase in loading rate increases the brittleness of the material, subsequently increasing the defect sensitivity and leading to a shear fracture. This explanation is supported by fracture surface observations. In addition, it was found that the shear strength increases significantly with increasing load rate up to 5000 mm min −1 and then starts to decrease slightly. The decrease in shear strength at very high loading rates was found to correspond to multiple cracking behaviour rather than to a longitudinal fracture plane as for intermediate loading rates.

Pultruded fiber reinforced thermoplastic poly(methyl methacrylate) composites. Part II: Mechanical and thermal properties

AbstractA novel process has been developed to manufacture poly(methyl methacrylate) (PMMA) pultruded parts. The mechanical and dynamic mechanical properties, environmental effects, postformability of pultruded composites and properties of various fiber (glass, carbon and Kevlar 49 aramid fiber) reinforced PMMA composites have been studied. Results show that the mechanical and thermal properties (i.e. tensile strength, flexural strength and modulus, impact strength and HDT) increase with fiber content. Kevlar fiber/PMMA composites possess the highest impact strength and HDT, while carbon fiber/PMMA composites show the highest tensile strength, tensile and flexural modulus, and glass fiber/PMMA composites show the highest flexural strength. Experimental tensile strengths of all composites except carbon fiber/PMMA composites follow the rule of mixtures. The deviation of carbon fiber/PMMA composite is due to the fiber breakage during processing. Pultruded glass fiber reinforced PMMA composites exhibit good weather resistance. They can be postformed by thermoforming, and mechanical properties can be improved by postforming. The dynamic shear storage modulus (G′) of pultruded glass fiber reinforced PMMA composites increased with decreasing pulling rate, and G′ was higher than that of pultruded Nylon 6 and polyester composites.

Loading rate effect as a function of the span-to-depth ratio in three-point bend testing of unidirectional pultruded composites

Three-point bend tests were performed on pultruded half-round cross-section rods of glass fibre-reinforced polyester and glass fibre-reinforced epoxy, the tests being arranged so that the specimen was unloaded as soon as the deflection corresponding to the maximum load was reached. This testing method enabled the fracture mechanisms at maximum loads to be mapped as a function of the loading rate and the span-to-depth ratios. An effect highlighted by this map is that a specimen tested at intermediate span-to-depth ratios may result in a purely tensile fracture at low loading rates and a purely shear fracture at high loading rates. This behaviour is interpreted as being due to the fact that the increase in loading rate increases the brittleness of the material, subsequently increasing the defect sensitivity and leading to a shear fracture. This explanation is supported by fracture surface observations. In addition, it was found that the shear strength increases significantly with increasing loading rate up to 5000 mm min −1 and then starts to decrease slightly. The decrease in shear strength at very high loading rates was found to correspond to multiple cracking behaviour rather than to a longitudinal fracture plane as for intermediate loading rates.

A Comparison of Methods for Determining the Shear Properties of Glass/Resin Unidirectional Composites

Abstract This paper describes and compares three methods of test for determining the interfacial adhesive strength of the glass/resin bond in reinforced plastic (RP) unidirectional composites. Measurement of the shear properties of these materials is of fundamental importance to the fiberglass manufacturer developing optimum sizing systems for the surface treatment of glass fibers used as plastics reinforcements. A new test, developed explicitly for the shear strength determination of pultruded cylindrical composites, is described and data obtained thereby are compared with similar results obtained by torsional and short-beam methods. Unlike this new notched-rod test, both the latter tests may occasionally give tensile rather than shear failures, thus rendering their usefulness questionable, since the shear strength of the composite has not been measured under such circumstances. Contrary to earlier work of other researchers, the current experiments suggest that the shear strength of the RP composite may exceed that of the resin matrix when the bond at the glass/resin interface has been optimized.