Fiber Reinforced Polymer Materials Research Articles

Determination of Mechanical Properties of FRP Materials Using the DIC Method

Abstract The mechanical properties of fiber reinforced polymer (FRP) materials have been of great interest in recent years as the applications of these materials in civil engineering and other industries have expanded. However, the utilization of FRP products, especially for new materials, has been limited because of a lack of complete knowledge about their properties. The primary objective of this study is to determine the various mechanical properties of five commonly used FRP materials. The study found that carbon FRP and high-strength glass FRP would be the best suitable materials for rehabilitation of structural elements when an increase in strength and stiffness is the primary objective. However, basalt FRP and E-glass FRP would be a far better choice for rehabilitation when ductility is the primary objective. The other objective of this study was to evaluate the application of a new digital technology, known as digital image correlation (DIC) technique, for the determination of mechanical properties of FRP materials. In this study, the strain data obtained from the DIC method were validated with strain data obtained from conventional methods (strain gage). It was found that DIC is a reliable and accurate noncontact testing method that can be successfully used for determining mechanical properties of various FRP materials.

A new high-frequency eddy current technique for detection and imaging of flaws in carbon fibre-reinforced polymer materials

Using a high-frequency (50 kHz-4 MHz) alternating current field measurement (ACFM)-style inspection, non-destructive imaging of carbon fibre-reinforced polymers (CFRPs) was performed for the detection and evaluation of flaws developed during their manufacture or in-service use. This was achieved using quantum well Hall-effect (QWHE) sensors, which have proven suitability for use in different non-destructive testing and evaluation (NDT&E) applications based on their high sensitivity (they require lower strength applied fields and can detect smaller perturbations in the magnetic field), high linearity (high contrast and imaging evaluation capabilities), wide dynamic range (making them less sensitive to offset and lift-off variations), wide frequency operating range (DC to MHz) and compact size (5-70 microns depending on the application). Their advanced III-V semiconductor materials and design enable these characteristics. Their low capacitance allows them to be operated at significantly higher frequencies than coils of comparable sensitivity or size. As such, the inherent advantages of QWHE sensors have been used in conjunction with a high-frequency ACFM-style magnetic imaging inspection technique, which is referred to as quantum well eddy current field measurement (QW-ECFM) in this paper. Here, the fundamentals of this new technique are outlined, as well as the outcomes of such a technique for evaluating CFRP materials, where individual fibre bundles have been resolved in high detail with high contrast. In addition, the ability to detect fibre misalignment has been shown, suggesting technique sensitivity to 3D orientations of fibre for better material qualification and the detection of delamination down to 2 mm in diameter. Therefore, this paper aims to provide an overview of this new QW-ECFM technique and summarise its performance for the detection and evaluation of various CFRP material flaws that are commonly found during manufacture and service.

Exploitation of FRP fabric Reinforcement: Innovation beyond FRP bars

This study provides combined experimental and numerical findings for a novel use of 3D Fiber Reinforced Polymer (FRP) fabrics as reinforcements in concrete beams. Experiments demonstrate that concrete beams reinforced with the multidirectional FRP fabrics not only possess adequate strength and ductility, but also have a great potential to achieve low-impact structures. In this study, a MATLAB-based code has been developed to determine the material and geometric design details of the 3D FRP reinforced concrete beams. This code includes the complex mechanical and geometric effects, e.g. concrete cracking, FRP-concrete bond, equilibrium, compatibility and boundary conditions. This design tool has been validated against experimental results, including load–strain and load–deflection curves. The validated code provides with a valuable tool to aid in achieving optimal reinforcement designs that ensure both strength and ductility in the 3D FRP reinforced beams casted by using notably less concrete material.

Electromechanical-Mode Coupling Model and Failure Prediction of CFRP under Three-Point Bending

Carbon fiber reinforced polymer materials (CFRP) cause CFRP to bend or fail when subjected to external loads or impacts. In the case of static three-point bending, using the conductive properties of the carbon fiber inside the CFRP, the overall damage detection and failure prediction can be carried out by electromagnetic methods. The eddy current coil is used to realize real-time monitoring of damage, and the measured voltage value can be mapped to obtain the load of the sample. This paper conducts theoretical analysis and experimental verification, and obtains the relationship between CFRP stress damage and spatial conductivity change, and proposes a CFRP electromechanical coupling model under quasistatic three-point bending. Combined with the theory of electrically ineffective length, the CFRP three-point bending electromechanical coupling model was revised. Experimental results prove that the revised model can describe the load-conductivity change trend of three-dimensional braided CFRP more accurately, which provides a theoretical basis for monitoring the structural health of CFRP through electromagnetic methods.

3D Printing of Fiber-Reinforced Plastic Composites Using Fused Deposition Modeling: A Status Review.

Composite materials are a combination of two or more types of materials used to enhance the mechanical and structural properties of engineering products. When fibers are mixed in the polymeric matrix, the composite material is known as fiber-reinforced polymer (FRP). FRP materials are widely used in structural applications related to defense, automotive, aerospace, and sports-based industries. These materials are used in producing lightweight components with high tensile strength and rigidity. The fiber component in fiber-reinforced polymers provides the desired strength-to-weight ratio; however, the polymer portion costs less, and the process of making the matrix is quite straightforward. There is a high demand in industrial sectors, such as defense and military, aerospace, automotive, biomedical and sports, to manufacture these fiber-reinforced polymers using 3D printing and additive manufacturing technologies. FRP composites are used in diversified applications such as military vehicles, shelters, war fighting safety equipment, fighter aircrafts, naval ships, and submarine structures. Techniques to fabricate composite materials, degrade the weight-to-strength ratio and the tensile strength of the components, and they can play a critical role towards the service life of the components. Fused deposition modeling (FDM) is a technique for 3D printing that allows layered fabrication of parts using thermoplastic composites. Complex shape and geometry with enhanced mechanical properties can be obtained using this technique. This paper highlights the limitations in the development of FRPs and challenges associated with their mechanical properties. The future prospects of carbon fiber (CF) and polymeric matrixes are also mentioned in this study. The study also highlights different areas requiring further investigation in FDM-assisted 3D printing. The available literature on FRP composites is focused only on describing the properties of the product and the potential applications for it. It has been observed that scientific knowledge has gaps when it comes to predicting the performance of FRP composite parts fabricated under 3D printing (FDM) techniques. The mechanical properties of 3D-printed FRPs were studied so that a correlation between the 3D printing method could be established. This review paper will be helpful for researchers, scientists, manufacturers, etc., working in the area of FDM-assisted 3D printing of FRPs.

Design and material selection of optomechanical systems for the extreme environment on Mars

Mars surface composition detector (MarSCoDe) is a scientific instrument suite onboard the Mars rover of the “Tianwen-1” mission, which uses laser-induced breakdown spectroscopy and shortwave infrared spectroscopy to detect the composition of soils and rocks at the surface of Mars. The optical head unit (OHU) is the core hardware of MarSCoDe, containing a Cassegrain telescope and other optical modules for lasers generation and signals transmission. The unit lacks thermal control resources and is located outside the rover’s cabin, which will directly face the Martian surface drastic temperature changes. We introduce the optomechanical designs that realize the lightweight and high thermal stability of the OHU optical system, especially the designs and implementations of the semiopen primary mirror based on silicon carbide and the fully closed optical bench based on carbon fiber-reinforced polymer. Meanwhile, the advantages and difficulties of silicon carbide, long carbon fiber-reinforced silicon carbide composites, and carbon fiber-reinforced polymer materials used for small and compact optomechanical systems are discussed. Subsequently, the environmental adaptability of the telescope system of OHU was studied through analytical and experimental methods, which show that it can achieve the required optical performance over a temperature range of approximately 100°C.

Comparative Failure Study of Different Bonded Basalt Fiber-Reinforced Polymer (BFRP)-AL Joints in a Humid and Hot Environment.

Fiber-reinforced polymer (FRP) materials are increasingly used in automotive industrial fields to achieve lightweight. In order to study the influence of high temperature and high humidity on the bonding structure between different materials, this paper selects basalt fiber-reinforced resin composite materials (BFRP) and aluminum alloy (Al), and uses Araldite® 2012 and Araldite® 2014, two adhesives, to make single lap joints (SLJs). The aging test was carried out for 0 (unaged), 10, 20, and 30 days under the environment of 80 °C/95% relative humidity (RH) and 80 °C/pure water. In this work, simple Fickian law was used to simulate the hygroscopic change law of dumbbell specimens of two adhesives and BFRP in a pure water environment. It was discovered that Araldite® 2012 is most affected by moisture, but the time to reach the maximum water absorption in Araldite® 2014 was shorter than in Araldite® 2012. The failure strength of the joint was obtained through a quasi-static tensile experiment, and it was found that the Araldite® 2014 adhesive joint first increased and then decreased in a high temperature environment. The strength increased by 11.63% after 20 days of aging under an 80 °C/95%RH environment, and increased by 16.66% after 10 days of aging under an 80 °C/pure water environment, which indicates that post-curing reaction occurred. The strength of Araldite® 2012 joints showed a downward trend. After 30 days of aging, it reduced by 40.38% under an 80 °C/95%RH environment and 41.11% under an 80 °C/pure water environment. By observing the load-displacement curve, it was found that, as time increased, the slope of the curve decreased, indicating that the stiffness of the bonded joint decreased with time. The failure modes of the joints were analyzed by macroscopic images and microscopic SEM methods, and the results showed that the surface failure transitions from a mixed failure to a complete tear failure over time. The failure of the basalt fiber/resin interface was because the interaction between the epoxy resin in the adhesive and the epoxy resin in BFRP was greater than the force between the basalt fiber layer and the epoxy resin layer in the BFRP sheet.

Valorization of recycled FRP materials from wind turbine blades in concrete

This article examines the viability of valorizing waste glass fiber-reinforced polymer (GFRP) materials extracted from wind-turbine blades (WWTB) — (WWTB-GFRP) — into concrete. A comprehensive material characterization was carried out and the influence of WWTB-GFRP as powder, aggregate, or fiber on concrete performance was investigated. Cement replacement rates of 10–30% were attempted. Coarse aggregate replacement levels of 33–100% were considered, while fiber addition rates of 1–1.75 vol.% were investigated. Resulting concretes were characterized for their compressive strength and flexural capacity. Resulting concretes were characterized in terms of compressive strength and flexural capacity. Results show that the form at of WWTB-GFRP (as a powder, aggregate, or fiber) significantly impacts the properties of resulting concretes. Thus, while WWTB-GFRP powder leads to substantial increase in the setting time (owing to the wooden content and its associated soluble sugars) as well as to a significant drop in compressive and flexural strengths, it should be noted that mixtures with 10% cement replacement by WWTB-GFRP powder (after removal of wooden content) demonstrated comparable compressive strength as that of the reference mixture (without WWTB-GFRP) at 90 days. When WWTB-GFRP is incorporated in concrete as a fiber reinforcement, an enhancement in flexural capacity of up to 15% was achieved without noticeable drop in compressive strength. Therefore, it is feasible to valorize WWTB-GFRP in concrete to obtain mixtures with comparable long-term compressive strength while achieving higher flexural capacity and contributing to promoting the sustainable development.

PARAMETRIC STUDY ON COMPOSITE BEAMS STRENGTHENED WITH PRESTRESSED CFRP PLATES AND TENDONS

Advanced carbon fiber reinforced polymer material (CFRP) has been widely used for strengthening structures. This paper aims to improve the ultimate capacity and stiffness of the composite beam externally strengthened with pre-stressed carbon fiber reinforced polymer plate by using CFRP tendons. The models were presented by 3-D FEM (finite element model) using ANSYS program to investigate the performance of composite beam which validated with experimental results presented. Various parametric studies achieved as degree of pre-stress level of CFRP tendons, tendon profile, degree of shear connection, the most effective beam load level to add CFRP tendons. Finally, the optimum strengthening conditions for the composite beam were studied.

A novel approach to modelling the bond characteristics between CFRP fabrics and steel plate joints under quasi-static tensile loads

Carbon fiber-reinforced polymer (CFRP) materials have been effectively used as externally bonded sheets to repair damaged steel structures such as airplanes and ships. In this study, a series of double strap joints with different bonding lengths are considered and examined to experimentally and theoretically assess the effective bond length. Various models exist in the literature which are used to predict the strength of steel and CFRP joints under various loading conditions. Non-linear Lagrange stress method (NLS) which is a novel stress-based method for predicting the failure load values is presented for the first time. This approach is based on 2D and 3D linear elastic finite element analysis. Relying only on two experimental tests, the new approach proposed here can quickly and easily predict the failure load in steel/CFRP samples. In this methodology, it is assumed that the adhesive joint will fail as the normal stress along the adhesive mid-line reaches a predetermined value at a critical distance. In addition, experimental data on steel/CFRP joints gathered from the literature are compared to predictions using the NLS method. It was found that results from the theoretical predictions (NLS) were in good agreement with experimental tests conducted on double strap joints. It was also revealed that the average accuracy of the NLS method is superior to other methods such as cohesive zone model and Hart-Smith. The results revealed that under the best conditions, the NLS model is 5 times more accurate than existing models.

Axial behavior of concrete confined with flax fiber-reinforced polymers

In recent years, the use of synthetic fiber-reinforced polymer (FRP) composites has gained significant popularity in structural engineering. The confinement of concrete to improve its axial behavior has been one of the most encountered applications of such FRP materials. However, these synthetic materials are far from being friendly to the environment due to their significant carbon release during production. Besides, their high cost is still a major issue for the applications, especially in developing countries. Recently, research projects on the use of composite materials made of natural fibers have emerged in specific fields, such as the automotive and aircraft industries, due to environmental policies. The previous attempts of using natural materials for column confinement mostly rely on the use of conventional woven fabrics made of natural fibers. In this study, the FRP’s which include unidirectionally aligned flax fibers were used for the confinement of low-strength concrete. This composite material was either utilized alone or accompanied by glass or carbon FRP’s in the hybrid form. The results demonstrate that a considerable increase in strength and ultimate strain capacity is possible even for the specimens confined with only flax FRP. A higher enhancement was possible for hybrid forms.

MEASUREMENT OF SURFACE QUALITY AND OPTIMIZATION OF CUTTING PARAMETERS IN SLOT MILLING OF GFRP COMPOSITE MATERIALS WITH DIFFERENT FIBER RATIOS PRODUCED BY PULTRUSION METHOD

The final shape of fiber-reinforced polymer (FRP) materials is usually given by machining. However, machining FRP materials is complex and difficult. Appropriate cutting tools and cutting parameters should be determined to overcome these difficulties. In this work, glass fiber-reinforced polymer (GFRP) materials with 60% and 68% fiber ratio, produced by pultrusion method, were machined. End of the milling, surface roughness (Ra), delamination damage factor (Fdd), sound and vibration results were analyzed. Experiments were carried out with Taguchi L[Formula: see text] mixed design and the results were analyzed by Taguchi, ANOVA and Pareto charts. In Taguchi and Pareto analyses, the most effective parameter for surface roughness and delamination damage factor was the feed rate, and the cutting velocity for sound and vibration. Different regression models have been tried. Linear regression was found as most suitable. The significance values of the regression models are 92.04% for surface roughness, 87.12% for delamination damage factor, 98.64% for sound and 73.27% for vibration.

Strengthen strategies for reinforced concrete haunched beams using fibre reinforced polymer fabric and engineered cementitious composites

External strengthening of reinforced concrete haunched beams with and without shear reinforcement has been investigated by using carbon and basalt fiber reinforced polymer fabrics. In addition, the flexural behavior of reinforced haunched beams which are partially and entirely produced from engineered cementitious composite has been tested. The samples, which were produced from self-compacting concrete, engineered cementitious composite, and a combination of them, were prepared and tested via four-point loading tests. Reinforced haunched beams were divided into two strengthening groups. Group 1 included the shear strengthening of self-compacting concrete reinforced haunched beams (beams without stirrups) by the consideration of various strengthening configurations with both fiber-reinforced polymer fabric types. Group 2 included the flexural strengthening of reinforced haunched beams via fiber-reinforced polymer fabrics and/or engineered cementitious composite. The obtained results were depended on the ultimate load capacities, load-displacement curves, crack patterns, and failure modes of strengthened reinforced concrete haunched beams. Experimental results show that the strengthening material and strengthening configuration influence the mechanical behavior of reinforced concrete haunched beams considerably. However, the effect of strengthening configuration was higher. The highest increase in load capacity was 72.8% for shear strengthening (group 1), while the highest increase was 28.8% for the flexural strengthening group (group 2). Furthermore, the U-shaped anchorage with fiber-reinforced polymer fabrics prevented the premature failure of engineered cementitious composite layer and fiber-reinforced polymer fabrics covering the bottom face of reinforced haunched beams and increased the load capacity of reinforced haunched beams, while some losses were observed in ductility. The replacement of the concrete with engineered cementitious composite on the tension side increased the load capacity of reinforced concrete haunched beams.

Strengthen strategies for reinforced concrete haunched beams using fibre reinforced polymer fabric and engineered cementitious composites

External strengthening of reinforced concrete haunched beams with and without shear reinforcement has been investigated by using carbon and basalt fiber reinforced polymer fabrics. In addition, the flexural behavior of reinforced haunched beams which are partially and entirely produced from engineered cementitious composite has been tested. The samples, which were produced from self-compacting concrete, engineered cementitious composite, and a combination of them, were prepared and tested via four-point loading tests. Reinforced haunched beams were divided into two strengthening groups. Group 1 included the shear strengthening of self-compacting concrete reinforced haunched beams (beams without stirrups) by the consideration of various strengthening configurations with both fiber-reinforced polymer fabric types. Group 2 included the flexural strengthening of reinforced haunched beams via fiber-reinforced polymer fabrics and/or engineered cementitious composite. The obtained results were depended on the ultimate load capacities, load-displacement curves, crack patterns, and failure modes of strengthened reinforced concrete haunched beams. Experimental results show that the strengthening material and strengthening configuration influence the mechanical behavior of reinforced concrete haunched beams considerably. However, the effect of strengthening configuration was higher. The highest increase in load capacity was 72.8% for shear strengthening (group 1), while the highest increase was 28.8% for the flexural strengthening group (group 2). Furthermore, the U-shaped anchorage with fiber-reinforced polymer fabrics prevented the premature failure of engineered cementitious composite layer and fiber-reinforced polymer fabrics covering the bottom face of reinforced haunched beams and increased the load capacity of reinforced haunched beams, while some losses were observed in ductility. The replacement of the concrete with engineered cementitious composite on the tension side increased the load capacity of reinforced concrete haunched beams.

SCFs in tubular X-connections retrofitted with FRP under in-plane bending load

This paper investigates the stress concentration factors (SCFs) in tubular X-connections retrofitted with fiber reinforced polymer (FRP) under in-plane bending moment. For this aim, a finite element (FE) model was generated and validated using available 13 experimental tests. After that, 276 FE models were created to investigate the effect of the FRP (layer number, orientation, and material) and the connection geometry (β, γ, and τ) on the SCFs. In these models, the contact between the FRP sheets and the steel members (chord, weld, and braces) was modeled. Results indicated that the rise of the FRP sheet number causes a notable drop in the SCFs. Also, the increment of the elastic modulus of FRP along the fibers causes a decrement of the SCF ratios. Moreover, the SCF in an X-connection retrofitted with CFRP can be down to 37% of that of the un-retrofitted connection. Despite the notable efficacy of the FRP sheets on the drop of the SCFs in the X-connections, there is not any study or equation on the X-joints with FRP. Therefore, a precise equation was proposed for quantifying the SCFs in X-connections with FRP. Also, the proposed equation was checked according to the UK DoE acceptance standard.

Recursive partitioning and Gaussian Process Regression for the detection and localization of damages in pultruded Glass Fiber Reinforced Polymer material

Recursive partitioning and Gaussian Process Regression for the detection and localization of damages in pultruded Glass Fiber Reinforced Polymer material

SCFs in tubular X-joints retrofitted with FRP under out-of-plane bending moment

This paper presents a parametric study on the stress concentration factors (SCFs) on the chord member in tubular X-connections reinforced with fiber reinforced polymer (FRP) under out-of-plane bending moment. For this aim, a FE model was generated and validated using several available experimental tests. After that, a set of 276 FE models was created to evaluate the effect of the FRP (layer number, orientation, and material) and joint geometry (γ, τ, and β) on the SCFs. In these FE models, the contact between the FRP sheets and the steel members (chord, weld, and braces) was modeled. Results indicated that the rise of the FRP laminate number causes a notable drop of the SCFs, especially in the connections with big γ. Moreover, the increment of the elastic modulus of FRP along the fibers causes a notable decrease of the SCF. Results showed that, for certain geometrical parameters set, the SCF in an X-connection retrofitted with carbon fiber reinforced polymer (CFRP) can be down to 23% of the SCF in the associated un-retrofitted connection. Despite the notable efficacy of the FRP sheets on the drop of the SCFs in the X-connections, there is not any study or equation on the X-connections with FRP. Therefore, an equation was proposed for quantifying the SCFs in the X-connections with FRP.

InfraRed image correlation for non-destructive testing and evaluation of delaminations in glass fibre reinforced polymer materials

InfraRed Thermography (IRT) is one of the widely used Non-destructive Testing and Evaluation (NDT&E) method for characterization of fiber reinforced polymers. Among verity of testing methodologies and associated post processing schemes recently proposed pulse compression favorable thermal wave imaging methodologies gain importance due to their merits. This present paper highlights a highly depth resolved Frequency Modulated Thermal Wave Imaging (FMTWI) and its digitized version named as Digitized Frequency Modulated Thermal Wave Imaging (DFMTWI) for identification of subsurface Teflon patches introduced as defects to simulate the delaminations at various layers of GFRP test specimen of various sizes and depths.

Pongamia pinnatashell powder filled sisal/kevlar hybrid composites:Physicomechanicaland morphological characteristics

AbstractThe composite industry was attracted by natural fiber reinforced polymer materials for various valuable engineering applications due to its ecofriendly nature, less cost, and enhanced mechanical and thermal properties. This present work aimed at incorporating sisal and kevlar woven fabrics with the epoxy matrix and studying the effect ofPongamia pinnatashell powder on the sisal/kevlar hybrid composite. Six different laminates were prepared using hand layup method with filler percentage varying 2, 4, and 6 wt%. The prepared laminates cut according to the ASTM standards for performing different mechanical tests. Results reveal that the reduction of void percentage was observed at higher filler contents, while the incorporation of kevlar fabric enhances the impact strength by 279%, tensile strength by 89.77%, and tensile modulus value by 2% in comparison with pure natural fabric laminate L‐1. The flexural strength and interlaminar shear strength were higher for 2% filler composites, while the highest flexural modulus and hardness values were observed for 6% filler‐filled composites. The water absorption percentage was maximum for sisal laminate L‐1 and minimum for kevlar laminate L‐2. The fractured tensile and flexural specimens were analyzed by scanning electron microscopy.

A comparative study of mechanical and machining performance of polymer hybrid and carbon fiber epoxy composite materials

Fiber-reinforced plastics are known as advanced composite materials thanks to their high strength and lightweight features. Carbon fiber reinforced polymers (CFRPs) are one of the high-performance and high-cost fiber-reinforced polymer (FRPs) materials. They are used in several high-performance engineering applications such as motorsports, marine, aviation, energy and defense industry. The cost of carbon fiber is higher compared to many other materials, more competitive and cost-effective productions will spur the demand for composite parts exponentially. Thus, hybrid laminate composite containing carbon and glass fiber materials were manufactured as an alternative for CFRP materials. Because using glass fiber prepreg instead of carbon fiber prepreg will lead the material to become cheaper. However, machining of the FRP materials is still an important issue. For this reason, the present study is focused on the mechanical and machining performance of the polymer hybrid and carbon fiber epoxy composites.