Flexural behavior of methyl methacrylate modified unsaturated polyester polymer concrete beams reinforced with glass‐fiber‐reinforced polymer sheets

This study represents the behavior of flexural test of methyl methacrylate modified unsaturated polyester polymer concrete beam reinforced with glass‐fiber‐reinforced polymer (GFRP) sheets. The failure mode, load–deflection, ductility index, and separation load predictions according to the GFRP reinforcement thickness were tested and analyzed. The failure mode was found to occur at the bonded surface of the specimen with 10 layers of GFRP reinforcement. For the load–deflection curve, as the reinforcement thickness of the GFRP sheet increased, the crack load and ultimate load greatly increased, and the ductility index was found to be the highest for the beam with the thickness of the GFRP sheet at 10 layers (6 mm) or 13 layers (7.3 mm). The calculated results of separation load were found to match only the experimental results of the specimens where debonding occurred. The reinforcement effect was found to be most excellent in the polymer concrete with 10 layers of GFRP sheet reinforcement. The appropriate reinforcement ratio for the GFRP concrete beam suggested by this study was a fiber‐reinforced‐plastic cross‐sectional ratio of 0.007–0.008 for a polymer concrete cross‐sectional ratio of 1 (width) : 1.5 (depth). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Isothermal crystallization kinetics of silk fibroin fiber‐reinforced poly(ε‐caprolactone) biocomposites

BACKGROUND: Poly(ε‐caprolactone) (PCL) has attracted great attention due to its wide applications for pharmaceutical controlled released systems and implanted polymer devices. In this study, silk fibroin fiber (SF) obtained from degumming treatment of silk was used to prepare novel reinforced PCL biocomposites. The isothermal crystallization behavior of these composites was investigated using differential scanning calorimetry measurements. RESULTS: With a decrease of isothermal crystallization temperature (T_c) and an increase of fiber filler, the crystallization time of the SF/PCL composites becomes shorter, the crystallization rate constant (K) increases and the Avrami exponent (n) gradually decreases (being between 1 and 2). The crystallization of PCL and SF/PCL composites occurs in the same regime. With the gradual addition of fiber, lateral surface free energy (σ) is nearly unchanged, but fold surface free energy (σ_e) decreases. CONCLUSION: Heterogeneous nucleation is dominant and different growth morphologies coexist during the isothermal crystallization process of the SF/PCL hybrid systems. Although the introduction of SF obviously increases the overall crystallization rate of PCL, the growth rate constant and nucleation constant of PCL are reduced because of the confinement effect of fiber network structures on the molecular mobility of polymer molecular chains. Copyright © 2009 Society of Chemical Industry     

Mechanical characterization and modeling of poly (β‐hydroxybutyrate)‐co‐poly(β‐hydroxyvalerate)–Alfa fiber‐reinforced composites

The mechanical properties of biobased composites of poly(β‐hydroxybutyrate)‐co‐poly(β‐hydroxyvalerate) biopolymer continuously reinforced with unidirectional Alfa fibers are investigated via tensile testing of oriented composite laminates. Simple mechanical models for the elastic stiffness, strength, and nonlinear hardening of the biobased composites are proposed with an emphasis on techniques that only require the independent properties of the fiber and matrix to facilitate composite design. Rule of mixtures (ROM) approaches are found to effectively predict the elastic properties of the composites but generally overestimate strength. Modified ROM approaches that discount the contribution of the matrix in the fiber loading direction and the contribution of the fiber in the transverse loading direction provide the most accurate strength predictions. Apparent elastic properties for composites with varying fiber orientations are predicted using a modified orthotropic laminate plate method which was found to overestimate composite stiffness in off‐axis loading directions. Postyield nonlinear hardening is modeled using a calibrated continuum yield and plasticity model and demonstrated to provide a close match of the experimental results. POLYM. COMPOS., 35:1758–1766, 2014. © 2014 Society of Plastics Engineers     

Joining of fiber‐reinforced polymer tubes for high‐pressure applications

Fiber‐reinforced polymer composites offer superior performance particularly in harsh environments; hence, they are recognized as an attractive material, especially for the transportation of pressurized fluids. However, an extensive use of these composites has been hampered, in part due to unsatisfactory solutions for the joining of subcomponents, and insufficient knowledge on the associated damage behavior. A favorable connection design for a piping system can be an adhesively bonded joint. In this study, a unique adhesive injection technique is presented that joins composite pipe sections using filament‐wound overlap sleeve couplers. The purpose of the present study was to characterize the performance and associated damage behavior of a prototype‐size pipe structure joined by the above procedure. Internal pressure and axial traction were applied to specimens at various biaxial ratios. In addition to the experimental investigation, the joint geometry was also modeled numerically employing the finite element technique. This yielded a better understanding of the damage behavior and enabled a parametric study that provided recommendations for an improved joint design. POLYM. COMPOS., 27:99–109, 2006. © 2005 Society of Plastics Engineers     

Effect of bonded lengths and wrappings on energy capacity and debonding strain of reinforced concrete beams strengthened with carbon‐fiber‐reinforced polymer

In this study, a series of flexural tests were performed to evaluate the energy capacity and debonding strain of reinforced concrete beams strengthened with a carbon‐fiber‐reinforced polymer (CFRP). Seven reinforced concrete beams were fabricated and loaded up to failure in a three‐point bending test. The type of CFRP laminate (plate or sheet), bonded length (1.44 or 2.16 m), and wrapping of the CFRP sheet were selected as the key test variables. The test results showed that beams strengthened with CFRP sheets were more effective than those strengthened with CFRP plates. The CFRP‐strengthened beams showed an elastic energy greater than that of the control beam, but the opposite result was obtained for the plastic energy. The average debonding strains of the CFRP plates and sheets were 4,309 and 11,649 μ, respectively, which corresponded to 21.5% and 77.1% of their respective ultimate tensile. POLYM. COMPOS., 38:1418–1426, 2017. © 2015 Society of Plastics Engineers     

Effect of glass fiber‐reinforced polymer and epoxy injection on compressive strength of elevated temperature damaged concrete

Glass fiber‐reinforced polymer (GFRP) materials have received a great deal of interest among civil engineers during the past decade. This paper presents an overview of experimental studies carried out on GFRP‐wrapped and epoxy‐injected concrete samples exposed to elevated temperatures. For this purpose, 0.30, 0.35 and 0.40 water to binder (w/b) ratios were used. For each w/b ratio, normal aggregates were replaced by lightweight aggregates with a size fraction of 0–2 mm at three different volume fractions such as 10%, 20% and 30% of total aggregate volume. At the same time, a group of air‐entrained samples was also cast for each w/b ratios. Prepared samples were exposed to 600 °C for 3 h. The damaged samples were separately repaired by GFRP and epoxy injection. Before and after elevated temperature exposure, water absorption and compressive strength were tested. After repairing with GFRP and epoxy injection, only the compressive strength test was carried out. GFRP improved the compressive strength between 1–22% and 348–1403% for samples before and after being exposed to elevated temperatures, respectively. Epoxy injection increased the compressive strength of the samples, exposed to elevated temperature, between 1% and 123%. However, the epoxy injection process failed to recover the compressive strength of the samples before elevated temperature exposure. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of electron beam irradiation on the crystallization of silk fibroin fiber‐reinforced poly(ε‐caprolactone) biocomposites

In the medical industry, ionizing radiation has attracted increasing interest in recent years for the sterilization of biomedical materials due to its high effectiveness at relatively low cost and simple operation. In the study reported here, silk fibroin (SF) fiber was used to prepare novel reinforced poly(ε‐caprolactone) (PCL) biocomposites, and the effect of electron beam irradiation on both non‐isothermal and isothermal crystallization kinetics of the SF/PCL biocomposites was investigated. The models of Ozawa treatment, Avrami analysis and regime theory of crystal growth are applicable for describing the non‐isothermal and isothermal crystallization kinetics of the irradiated PCL and SF/PCL composites. Compared with non‐irradiated PCL and SF/PCL composites, the irradiated specimens exhibit the same crystallization regime (regime II) and similar lateral surface free energy (σ), except for smaller fold surface free energy (σ_e) and work of chain folding (q). The crosslinked PCL network formed in the irradiation process can act as a nucleation agent and accelerate the primary crystallization of PCL. However, the restriction effect of the crosslinked PCL network on the molecular chain mobility will reduce the overall crystallization rate of PCL, and this restriction effect appears stronger in the non‐isothermal crystallization process than in the isothermal crystallization process. Copyright © 2009 Society of Chemical Industry     

Axial load behavior of circular and square concrete columns confined with sprayed fiber‐reinforced polymer composites

Many experimental and theoretical investigations have been carried out to study the compressive strength of concrete confined externally with unidirectional fiber‐reinforced polymer (FRP) composites. These unidirectional FRP(s) include carbon, glass, aramid, polyethylene terephthalate, and polyethylene naphthalates. In this article, the performance of randomly distributed sprayed fiber‐reinforced polymer (SFRP) composites on the enhancement of strength and deformability of concrete column through external confinement is investigated. The salient features of SFRP are quick and easy application as well as the uniform tensile properties in all directions. In the present study, 24 small concrete specimens were loaded to failure under the uniaxial compression loading. The study parameters covered SFRP thickness, fiber length, and column sectional shape (circular and square). Test results showed that the external confinement by SFRP is significantly effective to increase the strength and deformability of confined concrete. Based on the experimental results, the performance of existing strength models developed for the unidirectional FRP is assessed to examine its applicability to the SFRP confinement. It is found that none of the existing models is capable of accurately predicting the strength of concrete confined with SFRP. Finally, new strength models based on a linear relationship between confined concrete compressive strength and lateral confining pressure are proposed to predict the compressive strength of circular and square sections. The strengths predicted by the proposed models are found to have a good agreement with experimental results. POLYM. COMPOS., 37:2557–2567, 2016. © 2015 Society of Plastics Engineers     

Durability of glass‐fiber‐reinforced polymer composites in an alkaline environment

This study investigated the aging of urethane and urethane‐modified vinyl ester (UMVE) GFRPs (glass fiber reinforced polymers) when they were exposed to alkaline solution for six months under a sustained load of 34.5 MPa or 16–20% of their tensile strength. The second experiment exposed both types of GFRP to alkaline solution without load for 6 months. The final experiment determined the alkaline solution diffusion coefficients into GFRP and neat polymer resin samples by measuring the change in mass of each sample as a function of time. After the GFRP samples were aged for 6 months, their tensile strengths were measured and compared with that of non‐aged samples to determine the aging effect. It was found that alkaline solution alone without sustained load did not significantly reduce or change the tensile strength of any GFRP sample. However, the presence of sustained load greatly increased the aging effect, particularly more for urethane GFRP than on UMVE GFRP. Urethane GFRP experienced a tensile strength reduction of 57.5%, while UMVE GFRP lost 27.3% of its original tensile strength. J. VINYL ADDIT. TECHNOL., 13:221–228, 2007. © 2007 Society of Plastics Engineers     

Fluorinated and oxyfluorinated short Kevlar fiber‐reinforced ethylene propylene polymer

The thermomechanical behavior of fluorinated and oxyfluorinated Kevlar fiber‐reinforced ethylene propylene (EP) composites has been studied. The composites have been prepared using brabender mixer and are cured using compression molding technique. FTIR study has been performed to understand the chemical reaction occurred due to modification of composites. Thermal behavior and crystallinity have been studied by DSC, TGA, DMTA, and XRD. These studies show that thermal stability, storage modulus, as well as crystallinity of the treated Kevlar fiber‐reinforced EP increases in comparison to the untreated derivative because the surface‐modified Kevlar fiber results in good adhesion between the fiber surface and EP matrix. Tensile strength increases in case of treated Kevlar fiber‐reinforced EP in comparison to the untreated one. SEM study supports all the above results. AFM results show that surface roughness increases because of the surface modification resulting from the incorporation of functional group‐induced Kevlar fiber. Polym. Compos. 27:205–212, 2006. © 2006 Society of Plastics Engineers     

Durability of glass‐fiber‐reinforced polymer nanocomposites in an alkaline environment

This study was conducted to determine the effect of clay content in GFRP (glass‐fiber‐reinforced polymer) composite samples as they were aged in an alkaline solution. Two kinds of GFRP composite samples were prepared. One was E‐glass‐fiber‐reinforced vinyl ester polymer, and the other was nano‐GFRP composites prepared with the addition of 1 and 2 wt% of montmorillonite clay to the polymer matrix. These samples were aged in alkaline solution of pH 13.2 with and without sustained load. The load was 1335 N or 18.7% of the tensile strength of the composite samples. The aging was evaluated by measuring the reduction in tensile strength after 6 months. Also, absorption of alkaline solution into the plain and nano‐GFRP samples was investigated so as to elucidate the diffusion behaviors. It was found that for a short exposure time (e.g. 1 month) and without sustained load, dispersing 2 wt% of the nanoclay in the polymer matrix of the GFRP samples reduces the diffusivity by 39%. However, with the application of sustained load, the glass fiber composite samples deteriorate more with increasing clay content. The reduction in tensile strength was 7.1%, 12.1%, and 18.1% for the samples containing 0, 1, and 2 wt% of clay, respectively. J. VINYL. ADDIT. TECHNOL., 12:25–32, 2006. © 2006 Society of Plastics Engineers     

Study on short glass fiber‐reinforced poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) composites

Biobased non‐fossil polyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) containing 4.0 mol % 4‐hydroxybutyrate (4HB) was melt‐mixed with short glass fibers (SGF) via a co‐rotating twin‐screw extruder. The compositing conditions, average glass fiber length and distribution, thermal, crystallization, and mechanical properties of the P3/4HB/SGF composites were investigated. Calcium stearate, two kinds of paraffin wax and modified ethylene bis‐stearamide (TAF) were investigated as lubricants for the P3/4HB/SGF composites. It revealed that TAF is the most efficient lubricant of the P3/4HB/SGF composites. Coupling agents 2,2′‐(1,3‐phenylene)bis‐2‐oxazoline (1,3‐PBO) and pyromellitic dianhydride (PMDA) were used as end‐group crosslinkers to reduce the degradation of P3/4HB and increase the mechanical properties of the P3/4HB/SGF composites. It showed that 1,3‐PBO is the efficient coupling agent. The optimum condition of the P3/4HB/SGF composites is 1.5 phr TAF, 1.0 phr 1,3‐PBO, and 30 wt % glass fiber content. And the maximum of tensile strength, tensile modulus, and impact strength of the composites is 3.7, 6.6, 1.8 times of the neat P3/4HB polymer, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modeling and simulation of fiber‐reinforced polymer mold‐filling with phase change

A gas‐solid‐liquid three‐phase model for the simulation of fiber‐reinforced composites mold‐filling with phase change is established. The influence of fluid flow on the fibers is described by Newton's law of motion, and the influence of fibers on fluid flow is described by the momentum exchange source term in the model. A revised enthalpy method that can be used for both the melt and air in the mold cavity is proposed to describe the phase change during the mold‐filling. The finite‐volume method on a non‐staggered grid coupled with a level set method for viscoelastic‐Newtonian fluid flow is used to solve the model. The “frozen skin” layers are simulated successfully. Information regarding the fiber transformation and orientation is obtained in the mold‐filling process. The results show that fibers in the cavity are divided into five layers during the mold‐filling process, which is in accordance with experimental studies. Fibers have disturbance on these physical quantities, and the disturbance increases as the slenderness ratio increases. During mold‐filling process with two injection inlets, fiber orientation around the weld line area is in accordance with the experimental results. At the same time, single fiber's trajectory in the cavity, and physical quantities such as velocity, pressure, temperature, and stresses distributions in the cavity at end of mold‐filling process are also obtained. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42881.     

Sensitivity and uncertainty analyses for ignition of fiber‐reinforced polymer panels

The ignition characteristics of combustible solids are affected by many factors such as material properties, external heating source, and surrounding environmental conditions. In practice, these factors can vary significantly from one application to another. Thus, it is important to evaluate the sensitivity and uncertainty aspects of the effect of these factors on ignition. This study attempts to achieve this goal through sensitivity and uncertainty analyses on the piloted ignition of fiber‐reinforced polymer (FRP) composite panels. A Monte Carlo simulation using the Latin hypercube sampling method was employed to conduct sensitivity and uncertainty analyses. An integral model combining a general thermal thickness model with a heating rate‐related ignition temperature criterion was used as the ignition prediction model. Time‐to‐ignition was evaluated as the output parameter against the variations of input parameters such as material properties, external heating source, and surrounding environmental conditions. In addition, to identifying important sensitivity factors and uncertainty ranges of piloted ignition, a critical thermal thickness was found for the composite panels. These findings can serve as guides for the fire safety design of FRP composite materials for various applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Concentration effect of γ‐glycidoxypropyltrimethoxysilane on the mechanical properties of glass fiber–epoxy composites

In this study, glass fibers were modified using γ‐glycidoxypropyltrimethoxysilane of different concentrations to improve the interfacial adhesion at interfaces between fibers and matrix. Effects of γ‐glycidoxypropyltrimethoxysilane on mechanical properties and fracture behavior of glass fiber/epoxy composites were investigated experimentally. Mechanical properties of the composites have been investigated by tensile tests, short beam tests, and flexural tests. The short‐beam method was used to measure the interlaminar shear strength (ILSS) of laminates. The tensile and flexural properties of composites were characterized by tensile and three‐point bending tests, respectively. The fracture surfaces of the composites were observed with a scanning electron microscope. On comparing the results obtained for the different concentrations of silane solution, it was found that the 0.5% GPS silane treatment provided the best mechanical properties. The ILSS value of heat‐cleaned glass fiber reinforced composite is enhanced by ∼59% as a result of the glass fiber treatment with 0.5% γ‐GPS. Also, an improvement of about 37% in tensile strength, about 78% in flexural strength of the composite with the 0.5% γ‐GPS treatment of glass fibers was observed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

A review on oil palm empty fruit bunch fiber‐reinforced polymer composite materials

Natural fiber‐reinforced polymer composite materials have emerged in a wide spectrum of area of the polymer science. The composite produced from these types of materials are low density, low cost, comparable specific properties, and most importantly they are environmental friendly. The composite materials produced from oil palm fibers and commercially available polymers have offered some specific properties that can be comparable to conventional synthetic fiber composite materials. However, these properties are greatly dependent on the compatibility of oil palm fibers and matrix phase with moisture absorption as one of the critical issues that becomes the drawbacks of the oil palm fiber polymer composite materials. Apparently, it greatly affects the physical as well as mechanical properties of the composite materials. The present review reports the work on oil palm empty fruit bunch (OPEFB) fiber‐reinforced polymer composites with some interest on the OPEFB physical structure, and chemical compositions. Finally, the incorporation of OPEFB into polymeric materials leads to several interesting consequences on the water absorption characteristics and the mechanical properties, which have been reviewed. POLYM. COMPOS., 31:2079–2101, 2010. © 2010 Society of Plastics Engineers     

Kudzu fiber‐reinforced polypropylene composite

Kudzu fiber‐reinforced polypropylene composites were prepared, and their mechanical and thermal properties were determined. To enhance the adhesion between the kudzu fiber and the polypropylene matrix, maleic anhydride‐grafted polypropylene (MAPP) was used as a compatibilizer. A continuous improvement in both tensile modulus and tensile strength was observed up to a MAPP concentration of 35 wt %. Increases of 24 and 54% were obtained for tensile modulus and tensile strength, respectively. Scanning electron microscopy (SEM) showed improved dispersion and adhesion with MAPP. Fourier transform infrared (FTIR) spectroscopy showed an increase in hydrogen bonding with an increase in MAPP content. Differential scanning calorimetry (DSC) analysis indicated little change in the melting temperature of the composites with changes in MAPP content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1961–1969, 2002     

Cellulose fiber‐reinforced polylactic acid

Polymer composites from polylactic acid (PLA) and two types of cellulose fibers obtained either by acid hydrolysis of microcrystalline cellulose (HMCC) or by mechanical disintegration of regenerated wood fibers (MF) were prepared and characterized. To enhance the compatibility of the cellulose fibers with PLA matrix, a surface treatment based on 3‐aminopropyltriethoxysilane (APS) was performed. The Fourier Transform Infrared (FTIR) spectroscopy was used to determine the chemical groups involved in the surface modification reaction. The silanization treatment resulted in different modifications on both types of cellulose fibers because of their different structural and morphological characteristics. The composites were prepared by incorporating 2.5% of the treated or untreated HMCC and MF into a PLA matrix using a melt‐compounding technique. An improved adhesion between the two phases of the composite materials was observed by scanning electron microscopy thanks to treatment. The dynamic mechanical thermal analyses showed that both untreated and silane treated fibers led to an improvement of the storage modulus of PLA in the glassy state. A higher enhancement of the storage modulus in the case of PLA/HMCC composites than the composites containing MF was obtained as a result of the high aspect ratio of these fibers which allows better matrix‐to‐filler stress transfer. Furthermore, the storage modulus of PLA composites was enhanced by silanization even at higher temperatures especially after thermal treatment. The cellulose fibers addition in PLA matrix modified significantly the relaxation phenomenon as observed in tan δ curves, emphasizing strongly modified molecular mobility of PLA macromolecules and crystallization changes. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers.     

Kenaf fiber‐reinforced copolyester biocomposites

In this study the morphology and properties of a biodegradable aliphatic–aromatic copolyester mixed with kenaf fiber were investigated. Untreated kenaf fiber, as well as kenaf fiber treated with NaOH, and with NaOH followed by silane coupling agent treatment at various concentrations, were used as fillers in the composites. The biocomposites were prepared by melt‐mixing and a 10 wt% fiber loading was used for all the composites. The properties of the biocomposites were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), tensile properties, environmental scanning electron microscopy (ESEM), and biodegradability. The extent of silane initiated grafting was followed by gel content determination. The presence of fiber and fiber treatment influenced the determined properties in a variety of ways, but the best balance of properties were found for the copolyester mixed with alkali‐treated fiber. This composite showed improved thermal, thermomechanical, and mechanical properties. The introduction of alkali treatment caused increased surface roughness in the fiber, which resulted in mechanical interlocking between the filler and the matrix, while silane treatment slightly reduced the properties. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Modeling tensile response of fiber‐reinforced polymer composites using discrete element method

An advanced discrete element method (DEM), coupled with imaging techniques, of the tensile response of carbon fiber‐reinforced composite materials is presented in this article. DEM was developed using the image‐based shape structural model to determine the composites' elastic modulus, stress–strain response, and tensile strength. The developed model utilizes the microfabric micromechanical discrete element modeling technique. Clusters of very small bonded discrete elements were used to model the two composite constituents (matrix and reinforcement). The microparameters of each discrete element were determined from the macrocharacteristics of each constituent. The results from the developed model were compared with the results from an experimental case study. The results obtained from DEM simulations are within the coefficient of variation of the experimental values. The comparison indicates that the image‐based DEM micromechanical model accurately determines the elastic modulus and tensile strength of the molded carbon fiber‐reinforced polymer composite. POLYM. COMPOS., 34:877–886, 2013. © 2013 Society of Plastics Engineers