Use Of Fiber Reinforced Plastics Research Articles

A new resistance insert spot welding method for injection-molded FRP–steel component

For weight reduction, multi-material designs comprising metal and fiber-reinforced plastic (FRP) components in vehicle body structures have been increasingly used. However, the commonly used resistance spot welding (RSW) technology for car body assembly cannot be employed to join sheet metal and FRPs, limiting the use of FRPs. To solve this problem, a novel resistance insert spot welding (RISW) technique was developed in this work for RSW of steel parts and FRP structure parts made by injection molding. Small inserts were developed by using finite element method and experiments that may be welded to different micro-alloyed and dual-phase sheet steels using the projection welding method. The usual flange width of original equipment manufacturers could be kept unchanged. Using the developed insert and welding parameters, the maximum temperature in the FRPs surrounding the inserts was limited to 255 °C, minimizing the damage to polyamide 6 (PA6) material (with 40 wt% glass fiber). A weldability range between 2.5 and 7 kA could be achieved. The joining strength of RISW between a micro-alloyed HC340 steel in 0.75 mm and 1.5 mm thickness and a 2.5 mm/3.0 mm PA6-GF40 material is 20 to 80% higher than self-piercing riveting (SPR). For high-speed loading, RISW strength increases by 39 to 56% further. Finally, RISW was successfully applied to an FRP–steel roof-frame sub-assembly that consists of 19 simultaneously integrated inserts, achieving 10% weight reduction.

Damage Assessment of Glass-Fibre-Reinforced Plastic Structures under Quasi-Static Indentation with Acoustic Emission.

The use of fibre-reinforced plastics (FRPs) in various industrial applications continues to increase thanks to their good strength-to-weight ratio and impact resistance, as well as the high strength that provides engineers with advanced options for the design of modern structures subjected to a variety of out-of-plane impacts. An assessment of the damage morphology under such conditions using non-destructive techniques could provide useful data for material design and optimisation. This study investigated the damage mechanism and energy-absorption characteristics of E-glass laminates and sandwich structures with GFRP face sheets with PVC cores under quasi-static indentation with conical, square, and hemispherical indenters. An acoustic emission (AE) technique, coupled with a k-means++ pattern-recognition algorithm, was employed to identify the dominant microscopic and macroscopic damage mechanisms. Additionally, a post-mortem damage assessment was performed with X-ray micro computed tomography and scanning electron microscopy to validate the identified clusters. It was found that the specific energy absorption after impact with the square and hemispherical indenters of the GFRP sandwich and the plain laminate differed significantly, by 19.29% and 43.33%, respectively, while a minimal difference of 3.5% was recorded for the conical indenter. Additionally, the results obtained with the clustering technique applied to the acoustic emission signals detected the main damaged modes, such as matrix cracking, fibre/matrix debonding, delamination, the debonding of face sheets/core, and core failure. The results therefore could provide a methodology for the optimisation and prediction of damage for the health monitoring of composites.

Mechanical behaviour of fabric-reinforced plastic sandwich structures: A state-of-the-art review

The use of fibre-reinforced plastics (FRPs) in sandwich structures increased for various industrial applications thanks to their strength-to-weight ratio which provides designers with advanced options for modern structures. FRP Sandwich Structures (FRPSS) are often used in aerospace, biomedical, defence, and marine products, where their high structural performance is required to sustain complex in-service loads and withstand varying environmental conditions. Progressive degradation of FRPSS under such circumstances has been a subject of interest for researchers owing to safety requirements for products with FRP. This paper reviews the state-of-the-art of the mechanical behaviour of FRPSS subjected to various loading regimes. It highlights the variation in structural performance, viscoelastic properties, damage resistance, and sequence of environmental degradation of FRPSS. Numerical methods and damage algorithms used to predict failures are also presented to provide sufficient knowledge for the design of FRPSS. This review contributes to further research on characterizing the properties of FRPSS under quasi-static and dynamic loading conditions.

Estimating the Bond Strength of FRP Bars Using a Hybrid Machine Learning Model

Although the use of fiber-reinforced plastic (FRP) rebars instead of mild steel can effectively avoid rebar corrosion, the bonding performance gets weakened. To accurately estimate the bond strength of FRP bars, this paper proposes a particle swarm optimization-based extreme learning machine model based on 222 samples. The model used six variables including the bar position (P), bar surface condition (SC), bar diameter (D), concrete compressive strength (fc), the ratio of the bar depth to the bar diameter (L/D), and the ratio of the concrete protective layer thickness to the bar diameter (C/D) as input features, and the relative importance of the input parameters was quantified using a sensitivity analysis. The results showed that the proposed model can effectively and accurately estimate the bond strength of the FRP bar with R2 = 0.945 compared with the R2 = 0.926 of the original ELM model, which shows that the model can be used as an auxiliary tool for the bond performance analysis of FRP bars. The results of the sensitivity analysis indicate that the parameter L/D is of the greatest importance to the output bond strength.

Anti-collision performance of RC columns strengthened with a composite of FRP grid and UHPC

To improve the anti-collision performance of existing reinforced concrete (RC) columns subjected to vehicle impact loading, this paper proposes a composite strengthening method involving the use of fiber-reinforced plastic (FRP) grid and reinforced ultra-high performance concrete (UHPC). An RC column strengthened with the composite of FRP grid and UHPC and an ordinary RC column were prepared to investigate their anti-collision performance under impact loading. Using the methods of numerical analysis and tests, the effects of the vehicle impact velocity, reinforcement layer thickness, and material strength on the anti-collision performance were discussed. The test results showed that the lateral displacement of the RC column significantly decreased after strengthening with the composite. This indicated that the anti-collision performance of RC columns strengthened with the composite of FRP grid and UHPC can be effectively improved. The numerical results showed that the lateral displacement of the strengthened columns was increased by 37.8 % with an increase in the impact velocity from 3.69 m/s to 4.3 m/s; however, the impact velocity had no evident effect on the impact force acting on the surface of the RC columns. In addition, the anti-collision properties of the strengthened RC columns were significantly enhanced with the increase in the FRP grid–UHPC composite thickness and material strength. The lateral displacement of the strengthened RC columns reduced by 7.5 %–13.5 %, and its peak impact force increased by 14.9 %–33.2 % with an increase in the composite thickness from 20 mm to 40 mm. Moreover, the lateral displacement of the strengthened RC columns reduced by 14.5 %–36.1 %, and its peak impact force increased by 10.9 %–46.4 % with the increase in the compressive strength of concrete from 45 MPa to 210 MPa.

Design and construction of modern FRP Japanese bows by an inverse modelling approach of the elastica theory

Modern archery bows employ composite limbs of organic materials and fibre-reinforced plastics (FRP) to increase strength and durability in a lightweight structure. However, empirical methods are often employed for the manufacturing of the bows. We propose a systematic method for the design and fabrication of FRP bows based on an inverse modelling approach of the elastica theory, which significantly simplifies the analysis of the bow’s limb deformation. The construction materials are analysed by the three-point bending test and by strain gauges. We manufacture three asymmetric FRP Japanese bows with a length of 1.6 m, a force of 5 kgf, and different unbraced curvatures by using wood and glass fibre laminates. The excellent matching between the manufactured bows and the design is confirmed by a small discrepancy in the measurements of bending stress (RMSE < 8 MPa), final force (< 5%), and deformation (RMSE < 2 mm) of the bows. The inverse model demonstrates the use of FRP in bows traditionally manufactured with organic materials, by posing constraints to preserve their long-established shape. Compared to the try-and-cut approach, our method provides the sufficient requirements and failure criteria for the construction of a bow’s limb, without involving complex numerical simulations.

Strengthening and restoration of damaged reinforced concrete structures with composite plastics

This paper considers directions to devise methods for restoring the operational suitability of reinforced concrete structures. Mistakes of designers and non-compliance with the concreting technology of monolithic reinforced concrete structures lead to the formation of cracks and deflections of unacceptable size in reinforced concrete beams and floor slabs, as well as to insufficient strength of the elements. Such structures require not only an increase in bearing capacity but also the restoration of the operational suitability of damaged structures. A technique for restoring the serviceability of bendable reinforced concrete structures with increased deflections and excessive crack opening is proposed. To restore bendable reinforced concrete structures, surface reinforcement with pre-stressed fiber-reinforced plastics is suggested, which is ensured by the creation of a building lift in the damaged elements. Fiber-reinforced plastics have a high strain modulus, elastic nature of the diagram, and increased frost resistance; they tolerate fatigue effects well and are resistant to the effects of chemically active substances. Unlike conventional reinforcement methods, surface reinforcement techniques are characterized by high gain efficiency, corrosion resistance, low labor intensity, and short terms of work; they ensure strength increase and provide for economic feasibility. This study's results established that the use of fiber-reinforced plastics not only increases the bearing capacity of reinforced concrete structures but also helps reduce the width of the cracks formed. Thus, it is possible to avoid an increase in the cross-section of structures and reduce the time of operations, which could lead to additional costs

Application of Shape Memory Alloys in Retrofitting of Masonry and Heritage Structures Based on Their Vulnerability Revealed in the Bam 2003 Earthquake.

For decades, one of the most critical considerations of civil engineers has been the construction of structures that can sufficiently resist earthquakes. However, in many parts of the globe, ancient and contemporary buildings were constructed without regard for engineering; thus, there is a rising necessity to adapt existing structures to avoid accidents and preserve historical artefacts. There are various techniques for retrofitting a masonry structure, including foundation isolations, the use of Fibre-Reinforced Plastics (FRPs), shotcrete, etc. One innovative technique is the use of Shape Memory Alloys (SMAs), which improve structures by exhibiting high strength, good re-centring capabilities, self-repair, etc. One recent disastrous earthquake that happened in the city of Bam, Iran, (with a large proportion of masonry buildings) in 2003, with over 45,000 casualties, is analysed to discover the primary causes of the structural failure of buildings and its ancient citadel. It is followed by introducing the basic properties of SMAs and their applications in retrofitting masonry buildings. The outcomes of preceding implementations of SMAs in retrofitting of masonry buildings are then employed to present two comprehensive schemes as well as an implementation algorithm for strengthening masonry structures using SMA-based devices.

On the Application of Actively and Passively Excited Guided Elastic Waves for the Monitoring of Fiber-Reinforced Plastics

Nowadays, fiber-reinforced plastics are found in numerous industrial applications, such as aerospace, automotive engineering, railway, and naval engineering. These materials have high tensile and flexural strengths and nevertheless a low density at the same time. The use of fiber-reinforced plastics is particularly relevant in areas where large masses have to be moved and accelerated. However, testing and monitoring these structures is still a challenge caused by the different damage behavior compared to metal structures. Non-visible structural changes, such as delaminations and fiber-fractures, may cause local degradation and finally the failure of the components. In this work, active and passive ultrasonic methods based on guided elastic waves are investigated for their applicability to carbon fiber-reinforced structures. Therefore, tensile tests with cyclically increasing load are carried out on specimens with different fiber orientations until complete failure. The acoustic emissions in the specimen during the load are recorded. As a second technique, actively excited guided waves are transmitted and received during the rest periods between the measuring ramps. Different parameters are extracted from the measured data, which allow the monitoring of the specimen’s degradation. A comparison of the results of the active and passive method follows. Finally, a combination of both methods is carried out addressing issues like its informative value and its sensitivity.

Analytical prediction of thermal stresses in composite shells

The use of fibre-reinforced plastics or FRPs in various industries, such as aviation, automobiles, renewable energy, etc. has drastically increased over the past decades, owing to the significant strength to weight ratios they offer. The design phase of such components must also factor in thermal loads. Thermal expansions and contractions, when restricted, lead to the buildup of stresses in a material. The distribution of these stresses across the layers of a composite tube has been dealt with here with the help of an analytical study, taking into account any radially varying user-defined temperature profile. On account of geometry, the cases handled are axisymmetric and therefore, shear stresses aren’t considered.

Selective laser hardening of injection mould components on multi-axis machining centers

This research describes the selective laser hardening of components used in the injection moulding industry. The use of fiber-reinforced plastics is accompanied by increased wear in injection moulding tooling compared to conventional plastics. Selective hardening of locations in contact with these plastics prolongs the lifetime of these components. This paper focuses on selective laser hardening of two mould materials, stavax ESR and Sverker 21. Experiments are performed on a laser setup integrated into a multi-axis machining platform, allowing fabrication and hardening within one single clamping. Initial laser hardening tests were performed on ground samples consisting of the component base material. Microhardness measurements showed a maximum achieved hardness of 614HV for Stavax ESR and of 810HV for Sverker 21 after laser hardening. Following initial experiments, three injection moulding components, shredder blades, injection nozzles, and textured moulds are laser hardened.

Investigation of Milling of Carbon Fiber Reinforced Plastic

Abstract The use of fiber-reinforced plastics has increased significantly in the past decades. Consequently, the demand for finishing and machining of such materials has also escalated. During machining, the fiber-reinforced materials exhibit machining problems dissimilar to the problems of metals. These are fiber pull-out, fiber breakage in the cutting zone, matrix smearing and delamination. The purpose of this experiment is to investigate the characteristics of the resultant force (Fe) dur-ing the milling of carbon fiber reinforced plastic as a function of input machining parameters. For the force measurements, CFR with perpendicular (0°-90°) fiber orientation was machined. The experimental design involved the central composite design method. To analyze and evaluate the measurements, we applied the response surface methodology.

FRP and ITS Applications in Asian Countries

In order to meet the need for advanced infrastructure, innovative technologies and new materials started taking its shape in the construction industry. Every technology has its limitations. With structures becoming old there is a requirement of a technique to enhance the health of the existing structure. Including India, japan and China various professionals throughout the world are using fiber reinforced plastic (FRP) for solving issues through effective and cost friendly manner. In the field of civil engineering, use of FRP is limited to certain aspects only but it could be widespread. For countries like India it will boost the infrastructural development by reducing cost and saving money because of durability. With highly moist regions in coastal plane, northeastern parts and Himalayan region have large scope of use of FRP.

Experimental and Numerical Studies on Integration Thermoplastic Composite Compatible Piezoelectric Ceramics for Actuatory Application of Cylindrical Hollow Structures

Regarding the economical use of fiber-reinforced plastics (FRP) as a construction material for structural components whose additional value caused not only in their high specific mechanical properties. Due to the layerwise structure definition of continuous fiber reinforced composites the corresponding production technologies offers a high potential for integration of additional functional elements. Past efforts to the integration of functions in fiber-reinforced composites usual provide in front of a passive use of the piezoelectric effect (eg. structural-health monitoring). Through efficient and structurally defined using of piezoceramic actuators, the planar structure topology of cylindrical hollow FRP profiles can be actively influenced. Based on experimental studies on the definition of basic concepts for the integration of thermoplastic compatible piezoceramic modules (TPM) in fiber composite tubular segments, this paper deals with the understanding and performance capabilities of such actuarical hollow frp structures. The selective excitation and manipulation of the vibration behavior of such rotationally symmetric structures serves for generation of wave effects with radial translational characteristic. The performed experimental studies on the structural behavior of active piezo integral pipe segments are abstracted and compared by means of numerical simulations using multi-physical elements.

An Investigation of Structural Behavior of Underground Buried GFRP Pipe in Cooling Water Intake for the Nuclear Power Plant

GRP pipe (Glass-fiber Reinforced Plastic Pipe) lines making use of FRP (Fiber Reinforced Plastic) are generally thinner, lighter, and stronger than the existing concrete or steel pipe lines, and it is excellent in stiffness/strength per unit weight. In this study, we present the result of field test for buried GRP pipes with large diameter(2,400mm). The vertical and horizontal ring deflections are measured for 387 days. The short-term deflection measured by the field test is compared with the result predicted by the Iowa formula. In addition, the long-term ring deflection is predicted by using the procedure suggested in ASTM D 5365(ANNEX) in the range of 40 to 60 years of service life of the pipe based on the experimental results. From the study, it was found that the long-term vertical and horizontal ring deflection up to 60 years is less than the 5% ring deflection limitation.

Using Twist-off Method for Measuring CFRP/Concrete Adhesion when Exposed to Cyclic Temperature Changes, Wet-Dry and Freeze-Thaw

Materials such as fiber-reinforced plastics (FRPs) are lightweight, strong, and for the most part, non-corrodible. Hence, the use of FRPs as retrofitting materials for concrete represents a viable, durable alternative to conventional practice using reinforcing steel. This paper addresses the magnitude of the residual shear bond strengths between rigid and flexible carbon fiber reinforced plastic (CFRP) sheets and substrate concrete, after being subjected to cyclic temperature changes, wet-dry and freeze-thaw, by means of a Twist-off method. In the experimental investigation, the shear bond strength of a number of CFRP/concrete specimens was monitored. These results were then used to make comparisons between the behaviors of the two types of CFRPs. Analysis of the results indicated that while 180 freeze-thaw cycles destroy the shear bond strength of rigid and flexible CFRP completely, the same number of wetting and drying and temperature change cycles can reduce these bonds by up to about 30 and 20%, respectively. The results also showed that despite the insignificant flexible CFRP failure, the failure in the rigid CFRP material was noticeable.

An approach for the modeling of interface-body coupled nonlocal damage

Fiber Reinforced Plastic (FRP) can be used for strengthening concrete or masonry constructions.One of the main problem in the use of FRP is the possible detachment of the reinforcement from the supportmaterial. This paper deals with the modeling of the FRP-concrete or masonry damage interface, accounting forthe coupling occurring between the degradation of the cohesive material and the FRP detachment. To this end,a damage model is considered for the quasi-brittle material. In order to prevent strain localization and strongmesh sensitivity of the solution, an integral-type of nonlocal model based on the weighted spatial averaging of astrain-like quantity is developed. Regarding the interface, the damage is governed by the relative displacementoccurring at bond. A suitable interface model which accounts for the mode I, mode II and mixed mode ofdamage is developed. The coupling between the body damage and the interface damage is performedcomputing the body damage on the bond surface. Numerical examples are presented.

Use of projection moiré for measuring the instantaneous out-of-plane deflections of composite plates subject to bird strike

For the new generation aircraft families, the use of fibre-reinforced plastics is considered for the leading edge of the wings. However, this leading edge is very prone to bird strike impact. This paper presents the use of the projection moiré technique to measure the instantaneous out-of-plane deflections of composite plates subject to bird strike. Very strict constraints with regard to (i) high-speed image acquisition, (ii) vibrations of the impact chamber, and (iii) projection and observation angles, complicated substantially the development of the set-up. Moreover, the high frame rates (12,000 fps) required a very intensive illumination. In the optimized configuration, a specially designed grating with gradually changing period is projected by means of special halide hydride lamps through one of the side windows of the impact chamber onto the composite plate riveted in a steel frame. The digital high-speed camera is mounted on the roof of the impact chamber and records through a mirror the object surface with the projected fringe pattern on it. Numerical routines based on local Fourier transform were developed to process the digital images to extract the phase and the out-of-plane displacements. The phase evaluation is possible due to the carrier frequency nature of the projected moiré pattern. This carrier frequency allows separation of the unwanted additive and multiplicative fringe pattern components in the frequency domain via the application of a proper mask. The numerical calculations were calibrated for the bird strike on an aluminum plate, where the plastic deformation could be checked after the test.

The specialities of fibre-reinforced plastics in terms of product lifecycle management

Since the use of fibre-reinforced plastics and computer based data management systems increased over the last decades, the need to define and organize the material-specific data of FRP in those data management systems is demanding. Because of the differences in material characteristics of metals and reinforced plastics, most data management systems have to be adjusted. The user has to be aware of all specialties of FRP to decide about the use of those complex materials. There are differences between metals and FRP in almost every phase of the product lifecycle, like the material construction in the definition phase, like more process parameter in the realization phase, like the challenging service in the usage phase and the often-expensive disposal in the recycling phase.

224 大型軸流送風機用FRP動翼の開発(OS 高分子/高分子基複合材料(3))

Fiber reinforced plastic (FRP) features a specific gravity approximately one quarter of that of steel material, as well as superior corrosion resistance, and is therefore promising in terms of applications in high speed rotary equipment and other machinery. Although the rotor blades of large axial flow fans utilized in thermal power plants have conventionally been made of metal, the use of FRP would enable lighter weight and greater resistance to corrosion. In turn, this could allow reduction in size and longer life for moving and sliding parts, as well as lower maintenance costs. This paper presents the results of material and pilot plant tests of FRP rotor blades developed for use in axial flow fans.