High Elongation Fibers Research Articles

Integrative tensile prediction and parametric analysis of unidirectional carbon/basalt hybrid fiber reinforced polymer composites by bundle-based modeling

In this study, the previous bundle-based concept, in which the impregnated fiber bundle is considered as a basic element, was adopted to model unidirectional hybrid fiber-reinforced polymer (FRP) composites in a full-scale manner. Hybrid composites with carbon and basalt fibers were modeled and validated using previous experimental data. A comprehensive parametric study of the constituent properties was performed to determine their sensitivities to overall behaviors. On this basis, an optimization framework was developed to reflect the integrative performance and cost-performance of hybrids. The simulation obtained a saturation point of the matrix shear strength of approximately 70 MPa, beyond which the overall behavior rarely changed. A dispersed arrangement of the fiber bundles could significantly delay the damage propagation and enhance the overall behavior only at low contents of high-elongation fibers. In the present case, the mean ultimate strength can be improved from 1063 MPa to 1315 MPa. The sensitivity analysis indicated that for the elastic moduli of fibers, carbon fiber strength, and Weibull shape parameter of basalt fibers, trade-offs must be considered to balance the overall ultimate strain, strength, ductility, and hybrid effect. The bundle-based modeling concept provides a fast and convenient approach to evaluate the global behavior of hybrids.

Fragmentation model for tensile behavior of intermingled hybrid composites and optimal mixing ratio

A numerical fragmentation model is proposed to predict the mechanical response of intermingled, unidirectional hybrid composites under tensile loads. The model is based on a previously developed for unidirectional composites considering the critical number of fiber breaks and the correction of the fiber-matrix interfacial strength. Hybrids comprising two reinforcements are considered, and the energetic contribution of reinforcements is evaluated during the damage process. Additionally, the pseudo-ductile strain, yield strength, and the level of degradation of each reinforcement are estimated. The present model is compared with a progressive failure model and micromechanical finite element simulations, obtaining some similarities in the stress-strain behavior. Results show that both low elongation and high elongation fiber sub-composite experience a linear tensile response where fibers remain intact (IF), and fragmentation (FM) where breaking appears. The sliding/separation phenomenon (SS) occurs in one of the sub-composites when crack saturation is obtained, and failure occurs when the other one undergoes the crack saturation. Results also show that the IF, FM, and SS phenomena are conditioned by the fiber mixing ratio, α. The model allows estimating the optimal value of α for which the highest pseudo-ductile strain and hybrid effect are reached.

Mechanical and Tribological Characterization of Hybrid Composites: A Review

Abstract A review on the mechanical and tribological characterization of hybrid fibers reinforced polymer (FRP) composite materials is presented in this article. Fiber reinforced polymer composites are used in aircraft, boats, ships, helicopters, sporting equipments, chemical processing instruments and automobiles. Using more than one fibers in a single polymer matrix gives the more improvements than single fiber polymer composites. Hybridization (A mixture of fibers, during a process known as hybridization, so as to take advantage of the two fibers) in the field of FRPs can enhance the mechanical characteristics of particular fibre-reinforced polymer composite. By the addition of filler to the composite materials will further increase the performance of composites. This revise shows that tribological and mechanical characteristics of FRP composite improves because of inclusion of comparably high elongation fibers (Glass and basalt).Now a day’s hybrid composites are used in high end applications

Development of Pseudo ductile behavior of carbon fiber reinforced composites-An Overview

Abstract Hybridization in polymer matrix composites (PMCs) is one of the novel approaches to improve the mechanical behavior. But in case of structural design most of the failure occurs without warning i.e. brittle failure. Current high-performance composites are stiff, strong and light but fail suddenly and catastrophically. These types of limitations can be overcome by introducing pseudo ductile behavior into the failure process. An overview of significant achievement in pseudo ductile behavior is presented by focusing over rate of fiber dispersion, rule of mixture, orientation of fibers, and introduction of continuous and discontinuous fibers obtained by HiPerDiF (High Performance Discontinuous Fibers) method. HiPerDiF methods offers flexibility in shape of hybrid composites along with type of fiber, fiber length, preform pattern, resin type. The most crucial arrangement of HEF (High Elongation Fiber) and LEF (Low Elongation Fiber) leads to enhance the pseudo ductile performance.

Rational design of fiber-reinforced hybrid composites: A global load sharing analysis

An analytical model based on global load sharing (GLS) theory is developed to guide design of fiber-reinforced hybrid composites with superior mechanical properties to single-fiber-type composites. The hybrid is assumed to comprise two types of fibers-low- and high-elongation-with sufficiently different failure strains. Hybridization is found to be most beneficial when small-to-moderate volume fractions of the low-elongation, high-strength/stiffness fibers are added to the high-elongation composite. In this regime, all key properties of the hybrid composite can be maintained or improved, relative to the pure high-elongation composite. Potential gains in stiffness are large (approximate to 50%), and gains in pullout stress are moderate (approximate to 10-30%), while failure strain is maintained by design. Furthermore, using discontinuous low-elongation fibers improves hybrid composite performance because such fibers fragment more gracefully over a wide range of strain. Because composite processing might be easier when both fiber types are discontinuous, the performance of hybrids using discontinuous high-elongation fibers are also investigated, and good performance can be largely maintained if the high-elongation fibers are sufficiently long. The analytical model is supported by exact GLS results, and is thus a useful design tool for developing higher-performance composites by hybridization. (C) 2015 Elsevier Ltd. All rights reserved.

Predicting The Tensile Properties Of Woven Kenaf/Polyethylene terephthalate (PET)Fiber Reinforced Polyoxymethylene (POM) Hybrid Laminate Composite

The analytical design of the hybrid composite predicts its tensile properties at different fiber orientation using classical lamination theory. The critical volume fraction of the high elongation fiberyields 0.39 which defines the composite of minimum strength. The high elongation fiber (PET) contributes more in raising the hybrid composite strengthwhile the low elongation fiber (Kenaf) increases the composite modulus more inthe longitudinal direction. Six layers hybrid composite laminates were analyzed. The stacking sequence used was symmetric angle ply (0 0 , 45 0 , 90 0 ) with an overall thickness of 12mm .The thermal expansion coefficient of the laminate increases more than that of the individual ply. The overall analytical results confirm that thehybrid composite tensile properties haveincreased significantly as compared to single fiber reinforced composite.

High-Elongation Fiber Mats by Electrospinning of Polyoxymethylene

High-Elongation Fiber Mats by Electrospinning of Polyoxymethylene

Influence of Slipping Friction on Stress Concentration in Blended Yarns

We report the effect of a variable frictional shear force distribution along a slipping broken fiber on the stress concentration (SCF) in blended yarns. Our micromechanical model leads to a system of second order differential equations, which we solve using a convenient eigenvector expansion approach. The results for an exponential variation of frictional shear on a slipping fiber, starting from zero at the broken end, are compared to those for a constant friction force. While the extent of the slip region increases by as much as 50% for the exponential variation compared to the constant friction case, the SCF changes only slightly, generally decreasing less than 6%. Decreases are smaller when a high elongation fiber is broken than when a low elongation fiber is broken. The hybrid effect in blended yarns, established in previous work, continues to be supported by these new results.

Hybrid Effect at Fiber Breaks in Twisted Blended Yarns

A previously developed micromechanical model is used to formulate the problem of a blended yarn, consisting of low elongation (LE) and high elongation (HE) fibers undergoing axial extension, with a fiber break in the central region of the hybrid fiber array. A hybrid parameter R, which is the ratio of the axial stiffness of the HE fibers to that of the LE fibers, is shown to have an important effect on the intact fiber stress concentration factor (SCF), and the broken fiber slip extent at the fiber break. While the SCF increases for HE fibers adjacent to broken LE fibers, it decreases for LE fibers adjacent to broken HE fibers as R takes on values away from unity (homogeneous yarn). Higher loading can therefore be sustained by the LE fibers, and a beneficial hybrid effect can be realized.

Self-monitoring, pseudo-ductile, hybrid FRP reinforcement rods for concrete applications

The feasibility of hybrid -fiber-reinforced-polymer rods that demonstrate the important safety features of self-monitoring capability and pseudo-ductility is demonstrated. The rods are intended to be the basis of improved pultruded reinforcements for concrete or other civil applications where safety is of critical importance. The lowest elongation fiber in the seven rods investigated is carbon, which by virtue of its piezoresistivity allows the monitoring of deformation and fracture throughout an entire rod with simple electronic equipment. Resistance measurements obtained during quasi-static tests clearly reveal failure of the carbon fibers. Following this easily detected event, higher loads can be safely sustained by the remaining high-elongation fibers if the carbon tows are dispersed in the cross-section rather than concentrated in one location.

Tensile Behavior of Fiber-Cement Hybrid Composites Containing Polyvinyl Alcohol Fiber Yarns

This paper presents the results of a study on fiber-cement hybrid composites containing high-performance continuous polyvinyl alcohol (PVA) fiber yarns or rovings. Two types of hybrid composites were constructed using fiber combinations of PVA and glass (either continuous glass or 38-mm chopped strand), and PVA and fibrillated polypropylene networks. The tensile stress-strain behavior of these hybrids was studied, showing that the fibers, when used in a hybrid form, could result in superior composite performance compared with their individual fiber reinforced cements. The PVA-glass hybrid composite allowed similar or more favorable composite properties to be achieved at a lower addition of the high elongation fibers when compared with polypropylene-glass hybrids. In comparison with the hybrids containing glass fibers such as polypropylene-glass and PVA-glass, the PVA-polypropylene hybrid was less efficient at small strains (up to approximately 1%) because of the high elongation of both fibers at small strains. However, the PVA-polypropylene combination was advantageous in achieving high ultimate composite strength, because the PVA and the polypropylene could simultaneously contribute to the composite strength and because of the synergistic interaction between the two reinforcing fibers.

Residual strength of centrally cracked metal/fiber composite laminates

The residual strength of metal/fiber composite laminates (MFCLs) with a central crack is studied. The laminate is a sandwich with a fiber reinforced epoxy ply (prepreg) in the middle and an aluminum alloy layer on each of the outer surfaces. Dugdale strip yielding zones in the aluminum layers at the crack tip are assumed to take into account ductile deformations of the metal layers. It is also assumed that a strip damage zone in the prepreg layer is developed at the crack tip reflecting matrix cracking and fiber breakage and pull-out. Residual strengths for the centrally cracked laminates are calculated numerically. It is found that the residual strength of CARALL (carbon fiber reinforced polymer/aluminum laminate) is always higher than that of ARALL® (using aramid fiber instead of carbon fiber) for both infinite and finite width plates in the range of initial crack lengths considered. The strengths of CARALL with high elongation (HE) fiber are also higher than those of their metal counterparts. The results for ARALL predicted from the present model agree well with the existing experimental observations. The residual strength results for cracked MFCLs suggest that CARALL, especially with HE fibers, may replace aluminium alloys in lower aircraft wings and fuselage because of its higher residual strength and lower density. However, its fatigue resistance, impact residual properties and resistance to corrosion and other environmental effects need to be studied thoroughly.

A statistical analysis of the tensile failure and hybrid effect of an intraply hybrid composite

The random critical-core probability model is adapted to model a unidirectionally arrayed hybrid sheet with alternating low elongation fibers and high elongation fibers. Utilizing this model in conjunction with the results of the stress analysis by Fukuda and Chou, both the first failure and ultimate failure of the hybrid are analysed. The concept of the hybrid effect for strains has been clarified and quantitative evaluation of the part of the hybrid effect which is not of thermal origin has been done. Numerical results are compared with available experimental data. A reasonable agreement is found between the analytical predictions and the experimental results.

Micromechanical behavior of Kevlar-149/S-glass hybrid seven-fiber microcomposites: I. Tensile strength of the hybrid composite

To understand the mechanism of the ‘hybrid effect’ on the tensile properties of hybrid composites, single fiber type and hybrid microcomposites were fabricated by using Kevlar-149 as the low elongation fiber and S glass fibers as the high elongation fiber, in a DER 331/DER 732 epoxy mixture (70/30, w/w). Kevlar-149 fiber showed a significantly higher tensile strength in the microcomposite than as a single filament. For the hybrid, Kevlar-149 fibers usually broke one by one. A positive hybrid effect for the failure strain but a negative hybrid effect for the strength of the hybrid were observed. Tensile strength of the microcomposites predicted by Monte Carlo simulation agreed with the experimental results reasonably well. The tensile modulus of the hybrid followed the rule of mixture. The fiber/matrix interface properties were investigated by using single fibre pull-out from a microcomposite (SFPOM) test, which showed a significant difference between the interfacial shear strength (IFSS) of Kevlar fiber/epoxy in single-fiber type (SFT) and that in the hybrid at a constant fiber volume fraction, which shortened the ineffective length and contributed to the failure strain increase of Kevlar-149 fibers in the hybrid.

Micromechanical behavior of Kevlar-149/S-glass hybrid seven-fiber microcomposites. II: Stochastic modeling of stress-rupture of hybrid composites

To understand the stress-rupture behavior of hybrid composites, single-fiber type (SFT) and hybrid microcomposites were fabricated with Kevlar 149 as the low-elongation fiber and S-glass as the high-elongation fiber in a DER 331/DER 732 epoxy mixture (70/30, w/w). The microcomposites were stress-rupture tested at 80, 85, and 90% of their Weibull scale parameters for tensile strength. To predict the stress-rupture lifetime of a hybrid composite, a stochastic model was proposed which assumed that the failure of LE fibers in a hybrid follows a continuous-time Markov chain. Both the model and the stress-rupture tests of the hybrid and Kevlar 149 SFT microcomposites indicated that there is a negative hybrid effect for lifetime at high stress ratio while a positive hybrid effect exists at low stress ratio. The higher fraction of the total load for each LE fiber was responsible for the negative hybrid effect at high stress ratio, while smaller static and dynamic overstress was beneficial to the positive hybrid effect at low stress ratio. The mean lifetime for the hybrid and Kevlar 149 SFT microcomposites predicted using the model is reasonably close to the experimental results.

Strength of Intermingled Hybrid Composites

This paper first treats the stress concentrations in an intermingled hybrid composite. An eigenvector expansion method is used to solve the governing equations of shear-lag analyses. Two effects on the stress concentrations are examined, namely, the effect of the low elongation fiber volume fraction and the effect of the bundle sizes of the low elongation and high elongation fibers. Next, the strength characteristics of hybrid com posites with and without the scattering in the strength of the individual fibers are discussed on the basis of the stress concentrations. Finally, the occurrence of "hybrid effects" is examined.

A Dynamic Explanation of The Hybrid Effect

A theoretical analysis has been performed to evaluate the dynamic stress concentration factor in hybrid composites composed of low elongation (LE) and high elongation (HE) fibers. At a fracture of a fiber, the present model predicts two stress waves propagating along each fiber in the hybrid. The phase difference of the dynamic responses contributed by these waves at the middle section of a fiber immediately adjacent to a fiber breakage is controll ed by the fiber mass per unit length. The magnitude of the dynamic responses is determined by the fiber extensional stiffness. The study concludes that hybrid effect always exists in a beneficial manner and the case of the parent LE fiber composite provides the upper bound for the dynamic stress concen tration factor in hybrids. The validity of the approximations made in the derivations has been examined.

Blending Cottons Differing in Fiber Bundle Break Elongation

Two control cottons, differing in fiber bundle break elongation, but having other pertinent fiber properties essentially equal, were blended in different percentages, spun into warp and filling yarns, woven into a standard combed broadcloth, and then finished commercially. This report discusses the physical properties of these fabrics. Two cottons having significant differences in fiber break elongation at the fiber stage show very little difference in fabric break elongation after finishing, indicating that the influence of fiber elongation gradually becomes less evident during successive fabric finishing processes. In general, the high elongation fiber cotton produces grey fabric of superior qualities, viz., breaking and tearing strengths, elongation, and flex resistance, when compared with fabric made with low elongation fiber cotton. Furthermore, data also indicate that the values of fabric properties of the blended lots cannot be predicted from those of the controls when the fabrics are subjected to various chemical treat ments. This report corroborates other findings that no apparent advantage, from the standpoint of textile quality, exists in blending low and high elongation fibers— whether in blends of natural-natural or natural-synthetic fibers.