Pultruded Composite Research Articles

Designing textile lay-up sequence of pultruded composite bridge deck using three-dimensional finite element analysis

The mechanical performance of pultruded composite bridge decks was evaluated focusing on the effect of the textile lay-up sequence on their bending rigidity. A composite deck with a multi-walled cross-section with variable thickness was chosen as the model structure and three types of textile lay-up sequences were considered for its manufacturing. Due to the varying thickness and corresponding lay-up sequence, a three dimensional finite element model was constructed for the pultruded composite decks and their material properties were calculated based on the properties of each constitutive layer. Then, the effect of the textile lay-up sequence on the bending rigidity of the pultruded composite decks was numerically calculated for two model problems: pure bending due to uniform pressure and modified three-points bending. Finally, to validate the current three-dimensional analysis, experiments were also carried out by manufacturing pultruded composite decks with the same size as the ones used in the field, in order to demonstrate that the current approach provides a useful method of designing textile lay-up sequences for specific pultruded composites.

Effect of filler and void content on mechanical properties of pultruded composite materials under shear loading

AbstractThis paper presents the results of an analytical investigation aimed at examining the mechanical behavior of fiber‐reinforced polymer matrix materials containing nonhomogeneous constituents such as fine clay fillers under shear loading. Analytical formulae that account for the presence of inhomogeneities in the matrix materials were developed for estimating the extensional and in‐plane shear moduli and Poisson's ratio. The analytical results were compared with the properties obtained from experiments. For the experiments, the pultruded composites containing clay fillers and voids as well as glass fiber and vinylester resin were selected, analyzed, and tested under shear loading. The effects of presence of constituents on the mechanical properties of matrix materials were also investigated based on the obtained volume fraction of their constituents. POLYM. COMPOS., 26:181–192, 2005. © 2005 Society of Plastics Engineers

Pultruded composite shear spike for repair of timber members

Use of pultruded composites to rejuvenate low aspect ratio timber beams is described. Loss of shear resistance is restored by inserting fiberglass pultruded rods from the bottom to the top of the beam, through areas of damage. An adhesive is incorporated during the process of insertion, which bonds the reinforcing rods in-place and fills adjacent cracks. Scale beam testing, with a variety of reinforcement cases, has been performed and the overall results are extremely positive, with test beams showing strong recovery of flexural properties and improvement in the strain to failure.

A micromechanical constitutive framework for the nonlinear viscoelastic behavior of pultruded composite materials

This study introduces a new three-dimensional (3D) micromechanical modeling approach for the nonlinear viscoelastic behavior of pultruded composites. The studied pultruded composite system consists of vinylester matrix reinforced with E-glass roving and continuous filament mat (CFM) layers. Micromechanical models are introduced for the roving and CFM layers each having a unit-cell with four fiber and matrix subcells. In addition, a sublaminate model is used to provide for a nonlinear equivalent continuum of a layered medium with alternating roving and CFM layers. The roving layer consists of unidirectional fibers embedded in the matrix; it is idealized as doubly periodic array of fiber with square cross-sections. The CFM layer consists of relatively long, swirl, and randomly oriented filaments. This system is idealized using a weighted-average response of two simplified micromodels with fiber and matrix dominated responses. A new iterative procedure is introduced along with a recursive integration method for the Schapery nonlinear viscoelastic model used for the isotropic matrix subcells of the two micromodels. The fiber medium is considered as transversely isotropic and linear elastic. Incremental micromechanical formulations of the above three micromodels are geared towards the time integration scheme in the matrix phase. New iterative numerical algorithms with predictor–corrector type steps are derived and implemented for the micromodels in order to satisfy the fiber and matrix viscoelastic constitutive relations along with the micromechanical equations in the form of traction continuity and strain compatibility between the subcells. Experimental creep tests are performed with coupons cut from E-glass/vinylester pultruded plate to calibrate and predict the nonlinear viscoelastic response. Three sets of pultruded specimens having off-axis angles: 0°, 45°, and 90° were tested at room temperature under different applied compression stress levels.

Crack propagation analysis of mode-I fracture in pultruded composites using micromechanical constitutive models

An experimental and analytical study is carried out to characterize the fracture behavior of fiber reinforced plastic pultruded composites. The composite material system used in this study consists of roving and continuous filament mat (CFM) layers with E-glass fiber and polyester matrix. Eccentrically loaded single-edge-notch-tension ESE(T) fracture toughness specimen were cut from a thick pultruded plate, with the roving orientation transverse to the loading direction. Three-dimensional micromechanical constitutive models for the CFM and roving layers are developed. The micromodels can generate the effective nonlinear behavior while recognizing the in situ response at the fiber and matrix levels. The ability of the proposed micromodels to predict the effective elastic properties as well as the nonlinear response under multi-axial stress states is verified and compared to the stress–strain response from a series of off-axis tests. The micromodels are implemented in a finite element code with a cohesive layer to model the nonlinear fracture behavior of a pultruded composite material with different crack configurations. The properties for the cohesive layer were calibrated from one ESE(T) specimen with a crack to width ratio, a/ W of 0.5. Good prediction is demonstrated for a range of notch sizes and geometries. The use of cohesive elements with nonlinear micromodels is effective in modeling the transverse mode-I crack growth behavior in pultruded composites.

Nonlinear behavior of pultruded FRP composites

Abstract Coupon tests are investigated and used to calibrate three-dimensional (3D) micromechanical models and to verify their prediction for the nonlinear elastic behavior of pultruded fiber reinforced plastic composites. The tested composite material system is made from E-glass/vinylester pultruded composite plate with both glass roving and continuous filament mat (CFM) layers. Tension, compression, and shear tests were performed, using off-axis coupons cut with different roving reinforcement orientations. The overall linear elastic properties are identified along with the nonlinear stress–strain behavior under in-plane multi-axial tension and compression loading. The tests were carried out for coupons with off-axis angles: 0, 15, 30,45, 60, and 90°, where each test was repeated three to five times. Finite element analyses are used to simulate the off-axis tests and examine the effects of coupon geometry, end-clamping condition, and off-axis orientation, on the spatial distribution of the axial strains at the center of the coupons. Lower initial elastic modulus and a softer nonlinear stress–strain responses were consistently observed in the tension tests compared to those in compression, for all off-axis (roving) orientations. The nonlinear behavior can be attributed to the relatively low overall fiber volume fractions (FVFs) in pultruded composites and the existence of manufacturing defects, such as voids and microcracks. It is also shown that the end-clamping effects for the tested geometry are relatively small at the center and allow extracting the nonlinear stress–strain response of the anisotropic material. The analytical part of this study includes two (3D) micromechanical models for the roving and CFM layers. Shear tests are used to calibrate the in situ nonlinear elastic properties of the matrix. Good prediction ability is shown by the proposed micromodels in capturing the stress–strain behavior in the off-axis tests.

Three-Dimensional Micromechanics-Based Constitutive Framework for Analysis of Pultruded Composite Structures

A new 3D micromechanics-based framework is proposed for the nonlinear analysis of pultruded fiber-reinforced polymeric composites. The proposed 3D modeling framework is a nested multiscale approach that explicitly recognizes the response of the composite systems (layers) within the cross section of the pultruded member. These layers can have reinforcements in the form of roving, continuous filament mat (CFM), and/or woven fabrics. Different 3D micromechanical models for the layers can be used to recognize the basic response of the fiber and matrix materials. The framework is implemented with both shell and 3D finite elements. The 3D lamination theory is used to generate a homogenized nonlinear effective response for a through-thickness representative stacking sequence. The proposed modeling framework for pultruded composites is used to predict the stiffness and nonlinear stress-strain response of E-glass/vinylester pultruded materials reinforced with roving and CFM. The roving layer is idealized using a 3D nonlinear micromechanics model for a unidirectional fiber- reinforced material. A simple nonlinear micromechanics model for the CFM layer is also applied. The proposed model shows very good predictive capabilities of the overall effective properties and the nonlinear response of pultruded composites, based on the in situ material properties, and the volume fractions of the constituents. Experimental data from off-axis tests of pultruded plates under uniaxial compression are used to verify the proposed model. The proposed framework can be easily incorporated within displacement-based finite-element models of composite structures.

Mechanical properties, thermal stability, and flame retardance of pultruded fiber-reinforced poly(ethylene oxide)-toughened novolak-type phenolic resin

The mechanical properties (flexural modulus, static tensile strength, notched Izod impact strength), miscibility, thermal stability, and flame retardance of a poly(ethylene oxide) (PEO)-toughened phenolic resin glass pultruded composite were investigated. The mechanical properties of a pultruded glass fiber-reinforced modified phenolic resin composite increased while the soft segment of PEO absorbs the loads in the network of brittle phenolic resin. The phenolic/PEO blend is completely miscible, from the results of differential scanning calorimetry. Its thermal degradation temperature is always higher than 370°C and decreased with increasing PEO content. The morphology of the interface between the fiber and matrix is well wetted-out with increasing PEO content from the result with a scanning electron microscope (SEM). The modified phenolic composite also shows excellent flame retardance that is UL-94, V-0, and the limited oxygen index is more than 55. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1129–1136, 1998

Blocked diisocyanate polyester-toughened novolak-type phenolic resin: Synthesis, characterization, and properties of composites

A blocked diisocyanate polyester was synthesized to copolymerize with novolak-type phenolic resin. From the results of IR and NMR spectra, it was found that the blocked diisocyanate polyester reacts with the hydroxyl group of the novolak-type phenolic resin at high temperature. The deblocking temperature for the novolak-type phenolic resin is 120°C. The blocking agent, ε-caprolactam, is convenient for this system. The copolymer exhibited a single glass transition temperature and a negative deviation of the glass transition temperature. The results showed that the copolymer system is miscible and the molecular motion of the copolymer is increased with the addition of a modifier. The interface between the modified phenolic resin and the glass fiber is improved and the tensile strength of pultruded composite is increased with the modifier content. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1119–1127, 1998

Simulation of temperature and curing profiles in pultruded composite rods

Pultrusion is one of many composite manufacturing techniques with potential for rapid and cost-effective production. In this paper, an iterative procedure is developed for simulation of the pultrusion process for polymer-matrix composites. The procedure involves both heat-transfer and curing sub-models. A two-dimensional finite-element model was applied to simulate heat transfer and temperature profiles inside the die during the pultrusion process, and this was coupled with a numerical approximation of the curing kinetics for thermosetting polymer resins. Major pultrusion mechanisms (heat transfer and degree of curing) can be simulated for two-dimensional pultruded polymer-matrix composites. The pultrusion process of AS4/Epon 9420/9470/537 carbon-fibre/epoxy composite rods was simulated and the results compared with those obtained in a previous publication. The approach developed in this work can easily be adopted to tailor the two-dimensional pultrusion processes in practical applications.

Influence of resin additives on failure behaviour of pultruded glass/polyester composites shapes

Pultrusion is one of the t;astest and most costetTectivc processes by which composites can be mam~t'actured. Lately, the uses of pultruded composites have proliferated to include a number of new structural applications [1, 2]. These composite structures have desirable properties in corrosive and chemical environments. For all these reasons, pultruded composite structures are becoming more and more competitive with steel and concrete for construction. With the increasing possibilities of using pultruded composites in the construction industry, the need for full characterization [3, 4] of these materials becomes essential. Some studies [5-7] have dealt with the effect of different processing parameters on the mechanical and thermal properties of pultruded profiles. A recent study [8] has examined the mass and volume fraction properties of pultruded glass/polyester and glass/vinylester composites. The authors concluded that a wide variation of these parameters exist in specimens cut from similar samples of pultruded materials. In the same study, an attempt to identify the filler types and to separate the fillers from the reinforcement was successfully carried out. As mentioned before, it is of vital importance to quantify the effect of resin additive on the mechanical properties of pultruded profiles. In general, fillers are used with resins (here, unsaturated polyester) to help reduce cost. They are much more expensive than the resin itself as well as the most reinforcing agents. However, there are other advantages associated with the use of fillers. Their use permits higher curin~ temperatures by reducing the concentration of" reactive materials, which, in turn. tends to reduce the peak exotherm temperature. Clays and carbonates arc th,~ most commonly used fillers. Furthermore, other types of additives can be used such as dyes and pigments, flame-retardant substances (antimony trioxide) and ultraviolet absorbers. In order to produce a good final profile, all these substances must be compatible with the resins. the catalyst and the accelerators used. In thi~ work. ll~e considered profile shape is a UPN (channel) geometry of O0 :x 35 × 8 >,~ 8 ram. The localization ol II~e different reintbrcements in the cross section is shown in Fig. i. The glass fibre reinforcement is constituted by a contilmous strand mat (fibre randomly odemed) and by unidirectional fibre called direci co\ms. The matrix set is conslituted with a mixture of two different kinds o1" p,dycster tmsaturated isophtalic

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.

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.

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.