Fiber Reinforced Polymer Patch Research Articles

Repair of concrete-filled FRP tube columns with damaged tubes

The effectiveness of repairing damaged Concrete-Filled Fiber Reinforced Polymer (FRP) Tube (CFFT) axial members is studied. The damage was introduced in the form of linear cuts through the full tube thickness. The effectiveness of adhesively-bonded FRP patches that may or may not include mechanical fasteners is investigated. The study varied the cut angle, the bond length of the patch, the fiber type being glass or carbon, the number and pattern of mechanical fasteners, the patch extension beyond cut tips, and compared wet layup glass-FRP (GFRP) patches to prefabricated GFRP shells cut from a similar tube. It was shown that the vertical cut reduced axial compressive strength significantly. As the bond length of the GFRP repair patch increased the axial strength recovery increased, but not fully. When the ends of the GFRP patch were overlapped, a full strength recovery was achieved. The prefabricated GFRP shell patch (cut from similar tube) provided the highest strength recovery, compared to FRP wet layup. Adding mechanical fasteners enhanced strength recovery further, to a certain point. A simple empirical design model is proposed and a design example is presented.

Evaluating the impact of different anchor configurations and patch arrangements on the performance of fiber-reinforced polymer (FRP) anchors

The use of fiber-reinforced polymer (FRP) anchors to enhance the efficiency of externally bonded (EB) FRP systems has received considerable attention in recent years. However, their widespread application has been constrained by the challenges associated with their installation due to complexity in anchor detailing. To date, there has been limited research aimed at simplifying anchor detailing while maintaining its efficiency. This paper presents an extensive experimental study involving 88 tests on concrete beams with anchored FRP material, with variations in the number of FRP strips, anchor material ratio (AMR), fan length, and rounding radius of the anchor hole. The study focuses primarily on different aspects of the anchor configuration. The first part of the study compares the performance of two anchor details, while the second part assesses the impact of different FRP patch arrangements on enhancing the performance of the anchors. The efficiency of the newly suggested end anchor detail was found to be equivalent to the previously used end anchor detail. The use of FRP patches over anchors proved very effective in certain cases but ineffective in others.

Gate‐to‐Gate Study for Collaborative Robot‐Assisted Composite Parts Manufacturing Using a Work Effort Unit Approach

AbstractThis work presents one example from a set of technologies that aim at improving the efficiency of manufacturing processes of aircraft components in one of Airbus Defence and Space plants in regards to environmental aspects. Among the proposed technologies, one relates to the automation of two key manufacturing steps of the reference technology in the composite manufacturing of omega stringers: 1) lamination of main omega stringer structure through an Automated Fiber Placement robotic process; and 2) cobotic pick‐and‐place process for Carbon Fiber Reinforced Polymer patches. To evaluate potential environmental benefits, Fraunhofer performs a gate‐to‐gate study using as main parameter the “Work effort unit,” in this case representing the average energy consumption per productive hour in a typical assembly factory. When comparing the results for the composite part manufacturing by hand lay‐up with the use of collaborative robots, the key technical parameter is the reduction in lead time. While production using robots consume additional electricity when compared to human workers, automation significantly shortens lead times (‐74%), resulting in lower energy consumption per manufactured unit. The results indicate that this new technology from Airbus Defence and Space can potentially improve the overall environmental performance of composite parts during their manufacture.

Numerical study of fatigue life of SMA/CFRP patches retrofitted to central-cracked steel plates

This study aims to evaluate the repair performance of central-notched steel plates reinforced by the self-prestressing shape memory alloy carbon fiber reinforced polymer patching system (SMA/CFRP patch) through the numerical and theoretical study of the fatigue life after experimental fatigue life results were validated with the numerical method. These methods were used to determine the effectiveness of the reinforcing technique. Different widths of SMA/CFRP patches, elastic modulus of CFRP, prestress level, initial damage degree and crack type were considered as parameters that influenced the repair effectiveness. The outcomes showed that the increase in the Young’s modulus, prestress level and width could significantly improve the fatigue life of central-notched steel plates. The effect of the prestress level was more prominent with wider width. Good agreement with the test data revealed that numerical and theoretical methods could predict the fatigue life with reasonable accuracy, and the strengthening was more effective for edge-cracked specimens than central-cracked specimens.

Empirical Stress Intensity Factor Equations for Cracked Steel Plates Repaired with Double-Sided FRP Patches

This paper presents an approach that combines the finite element (FE) modeling and genetic programming (GP) to provide accurate empirical stress intensity factor (SIF) equations for center-cracked steel plates repaired with adhesive-bonded double-sided fiber-reinforced polymer (FRP) patches. Several past studies in recent years independently showed that the reduction on the SIF of cracked structures after the patch repair is dependent on many factors such as bonding techniques, material parameters, geometric parameters, environmental factors. In this study, the SIF of the repaired cracked steel plate was considered to be a function of seven parameters including the crack length, elastic modulus of FRP material, shear modulus of adhesive material, dimensions (width, length, and thickness) of rectangular FRP patches, and thickness of adhesive layers. Empirical SIF equations were created by the data mining process of genetic programming analyses performed on a database created from the FE results. The SIF values obtained from these equations were also compared with an analytical equation to assess whether their ability to perform well on a certain design or not. It was found that the proposed SIF equations fitted well with the FE results as the squared Pearson correlation coefficients R2 are higher than 0.9. In addition, the correlations between proposed equations and the analytical equation are approximately 0.8.

Fracture Toughness and Shear Strength of the Bonded Interface Between an Aluminium Alloy Skin and a FRP Patch

The existing techniques to determine the fracture properties such as critical energy release rate in mode I (GIc) and mode II (GIIc) of an interface between two sheets of same material were modified to determine these properties between the sheets of dissimilar materials and thickness. In addition, the interface shear strength (ISS) was also determined. Experiments were carried out on the specimens made of a pre-cracked thin aluminium alloy skin and a Fiber reinforced polymer (FRP) patch. Two kinds of surface preparation of the aluminium skin were employed; (i) emery-paper roughened surface (ERS) and (ii) Sodium Hydroxide (NaOH) treated surface (NTS). GIc of ERS specimen was found to be 36.1 J/m2, while it was found to be much higher for NTS specimens, that is, 87.3 J/m2. GIIc was found to be 282.4 J/m2 for ERS specimens and much higher as 734.5 J/m2 for NTS specimens. ISS was determined as 32.6 MPa for ERS specimen and significantly higher for NTS specimen, that is, 44.5 MPa. The micrographs obtained from a field emission-scanning electron microscope (FE-SEM) and the surface roughness test showed that the NTS was significantly rougher than the ERS, explaining the higher values of all the three kinds of NTS specimens.

Failure Analysis of Composite Repaired Pipelines with an Inclined Crack under Static Internal Pressure

The aim of the present work is to study the efficiency of the glass fiber reinforced polymer patch for repairing cracked steel pipe subjected to internal pressure. The effect of fiber orientation, [0°]8s, [90°]8s, and [0°/90°]4s, of bonded composite repair on reducing J-integral of stationary crack with different inclination angles (θ) is studied using the 3-D finite element method, FEM. Extended-FEM has been adopted to simulate the crack growth of different inclined stationary cracks in steel pipe subjected to internal pressure. It has been found that, the growing crack emanated from inclined stationary crack switched its path to be under pure mode I. The crack initiation pressure of inclined stationary crack in steel pipe with composite repair is higher than that of pipe without composite repair. The composite repair reduced the value of J-integral of stationary crack in steel pipe. This reduction is strongly affected by the crack length and θ of the stationary crack and it is fairly affected by the fiber orientation.

Debonding of Carbon Fiber–Reinforced Polymer Patches from Cracked Steel Elements under Fatigue Loading

This paper summarizes the details of a numerical and experimental research program that was conducted to study the debonding of carbon fiber–reinforced polymer (CFRP) patches from cracked steel members under fatigue loading. A preliminary numerical model was developed to investigate the influence of patch debonding on the fatigue life of cracked steel elements. Results indicated that altering the shape and increasing the size of the debonded region could change the calculated crack growth rate by up to 54 times. To validate the model, six steel edge–notched tension coupons were patched with CFRP materials and tested under fatigue loading, while full-field strain distributions were monitored using a digital image correlation (DIC)–based measurement system. Based on the experimental results the numerical model was refined to incorporate the interfacial traction-separation behavior. A parametric study was conducted using the refined numerical model. The results indicate that the size and shape of the debonded region, and therefore the fatigue crack propagation rate, are not only dependent on the fatigue detail and the crack length, but also on the maximum magnitude of the applied fatigue load and the properties of the bonded interface.

Field performance with state-of-the-art patching repair material

Significant efforts have been made to identify the correlations between pavement design, materials and construction variables and pavement performance for new pavement construction; in response to these efforts, specifications and design standards have been developed to optimize pavement performance. On the other hand, less positive correlations have been found between pavement repair materials/methods and the performance of repairs. This issue is primarily due to the incompatibility between existing pavement and repair materials including bonding at the repair interface, as well as the complex nature of pavement behavior near distressed areas. As a result, the variability in the performance of pavement repairs has been rather large. As more pavement sections have reached or even exceeded their design lives, with more frequent distresses, it is important to identify optimum repair methods and/or materials. This paper presents the field performance of several repair strategies with Fiber Reinforced Polymer Patching Binder (FRPPB) patching material for the repairs of spalling, partial-depth punchout and longitudinal joint separations in rigid pavement, for retarding reflection cracking in asphalt overlay on jointed concrete pavement, and for repairs at the transition area between rigid and flexible pavements by the Texas Department of Transportation (TxDOT). The repairs for these distress types have been a challenge to TxDOT districts; repair specifications with acceptable properties of repair materials and methods have not been as well-developed as the specifications for new construction have, resulting in a large variability in the performance of repairs of these distresses.The performance of repairs for the distresses mentioned above with FRPPB has been excellent, with no need for repeated repairs up to this point. The results from this study indicate that if the right materials are used for repairs, along with the correct repair method, the performance of pavement repairs and rehabilitations could be substantially enhanced, minimizing traffic delays and financial resources associated with further repairs and rehabilitations.

Development of a self-stressing NiTiNb shape memory alloy (SMA)/fiber reinforced polymer (FRP) patch

The objective of this research is to develop a self-stressing patch using a combination of shape memory alloys (SMAs) and fiber reinforced polymer (FRP) composites. Prestressed carbon FRP patches are emerging as a promising alternative to traditional methods to repair cracked steel structures and civil infrastructure. However, prestressing these patches typically requires heavy and complex fixtures, which is impractical in many applications. This paper presents a new approach in which the prestressing force is applied by restraining the shape memory effect of NiTiNb SMA wires. The wires are subsequently embedded in an FRP overlay patch. This method overcomes the practical challenges associated with conventional prestressing. This paper presents the conceptual development of the self-stressing patch with the support of experimental observations. The bond between the SMA wires and the FRP is evaluated using pull-out tests. The paper concludes with an experimental study that evaluates the patch response during activation subsequent monotonic tensile loading. The results demonstrate that the self-stressing patch with NiTiNb SMA is capable of generating a significant prestressing force with minimal tool and labor requirements.

Experimental study of CFRP patches bonded on a cracked aluminum alloy panel

An experimental study was conducted to arrest a crack in 1.0-mm-thick 6061-T6 aluminum single-edge-notch tension specimen. The specimen was repaired by symmetrical bonding of carbon fiber-reinforced polymer patches made of several plies. Although J-integral was reduced drastically, the specimen failed at one of the leading edges through separation at the interface. The separation was suppressed by tapering all the four leading edges of the patches. The specimens did not fail in the patched area when loaded up to the far field stress of 272 MPa, which was higher than the yield stress, 265 MPa of the aluminum plate.

Fiber reinforced polymer patching binder for concrete pavement rehabilitation and repair

Several strategies with Fiber Reinforced Polymer Patching Binder (FRPPB) have been used for the repair of jointed concrete pavements. The primary goal of such repairs is to minimize and delay the reflective cracks through a subsequent overlay. The same material has been used successfully in various districts to repair spalls in continuously reinforced concrete pavement, to fill voids at longitudinal joints, and to repair bridge approach slabs that have significant movement. Field results from US59 indicate that FRPPB can be used effectively to retard reflected cracks in AC overlays over JCP. The responsible engineers are very pleased with the FRPPB performance, as the section has provided excellent ride quality over the last 9years and has required zero maintenance. Since most movements that cause reflected cracks are near the transverse joint, removing a slot at the transverse joint and filling it with FRPPB has proven to be a viable option for mitigation of reflected cracks. To date, the oldest spall repair has been in service for over 8years, and is still performing well. FRPPB is able to adhere and adapt to volume changes in the surrounding concrete pavement, and conforms to settled or moving concrete slabs without any crack development.

Behavior and Performance of Fiber-Reinforced Polymer-to-Steel Bond

This paper presents a detailed discussion of bond behavior and fatigue, which have a major, often overlooked, impact on the long-term performance of steel bridges strengthened with fiber-reinforced polymer (FRP) materials. The paper discusses the primary factors that affect the bonding behavior between steel and FRP materials. The mechanisms of bonding are highlighted, and the main factors that contribute to the environmental degradation of bonds are outlined. Techniques to produce high-quality, durable, and reliable bonds are presented; these techniques include surface preparation techniques, use of primers, and use of various plate end details to reduce bond stress concentrations and mitigate debonding. Various factors that affect the fatigue performance of FRP materials and structural adhesives are enumerated, and the behavior of FRP patches used to repair cracked steel members is described. This paper highlights some complexities and nuances associated with the design and installation of an FRP-based retrofit system for steel bridges and structures and some key practices that should be adopted to ensure the effective and reliable performance of the retrofit.

Finite Element Study of Cracked Steel Circular Tube Repaired by FRP Patching

As the development and application of fiber reinforced polymer (FRP) composite materials to different engineering structures are increasing gradually, composite fiber patching techniques are being considered as alternatives to traditional methods of strengthening and fatigue crack repair in steel structures, such as the boom members of draglines. In general, the dragline boom members are in the form of circular tube type structure, therefore, application of FRP patching is usually bonded on one side (the outside surface) of the tube structure. In order to examine the efficiency of the repair by single-side patching of FRP material to tube structures, finite element study of cracked steel tube structure is conducted. The objectives of the finite element study are (1) to study the reduction of stress intensity factor (SIF) of cracked steel tube member repaired with FRP patching and (2) to predict the fatigue life of welded steel tube member repaired with FRP patching. The cracked steel circular tube was modeled by using 3-D brick elements and the adhesive and FRP patching were modeled by using shell elements. The adherend stiffness ratio (Efrp tfrp / Es ts) of this study is about 0.34. Comparison of the SIF of cracked steel circular tube with and without FRP patching showed that the SIF was reduced significantly for models with FRP patching and the reduction was more than 50%. Prediction of the fatigue life of cracked circular tube member with and without FRP patching was carried out by means of the Paris equation. Due to the significant reduction of SIF for members with FRP patching, it is shown that the corresponding predicted fatigue life is increased significantly as well. In particular, the increase of fatigue life is about 22 times for model with CFRP sheet patching when the circumference half crack length grows from 25.4mm (1 inch) to 63.5mm (2.5 inch).

Fatigue Strength of Steel Girders Strengthened with Carbon Fiber Reinforced Polymer Patch

Fatigue sensitive details in aging steel girders is one of the common problems that structural engineers are facing today. The design characteristics of steel members can be enhanced significantly by epoxy bonding carbon fiber reinforced polymers (CFRP) laminates to the critically stressed tension areas. This paper presents the results of a study on the retrofitting of notched steel beams with CFRP patches for medium cycle fatigue loading (R=0.1). A total of 21 specimens made of S127×4.5 A36 steel beams were prepared and tested. Unretrofitted beams were also tested as control specimens. The steel beams were tested under four point bending with the loading rate of between 5 and 10 Hz. Different constant stress ranges between 69 and 379 MPa were considered. The length and thickness of the patch were kept the same for all the retrofitted specimens. In addition to the number of cycles to failure, changes in the stiffness and crack initiation and growth were monitored during each experiment. The results showed that the CFRP patch not only tends to extend the fatigue life of a detail more than three times, but also decreases the crack growth rate significantly.

Analysis of FRP-Strengthened RC Beam-Column Joints

Analytical models are presented in this study for the analysis of reinforced concrete joints strengthened with composite materials in the form of externally bonded reinforcement comprising unidirectional strips or flexible fabrics. The models provide equations for stresses and strains at various stages of the response (before or after yielding of the beam or column reinforcement) until the ultimate capacity is reached, defined by concrete crushing or fiber-reinforced polymer (FRP) failure due to fracture or debonding. Solutions to these equations are obtained numerically. The models provide useful information on the shear capacity of FRP-strengthened joints in terms of the quantity and configuration of the externally bonded reinforcement and may be used to design FRP patching for inadequately detailed beam-column joints. A number of case studies are examined in this article, indicating that even low quantities of FRP materials may provide significant enhancement of the shear capacity. The effectiveness of external reinforcement increases considerably if debonding is suppressed and depends heavily on the distribution of layers in the beam and column. The latter depends on the relative quantities of steel reinforcement crossing the joint panel and the level of axial load in the column. Analytical shear strength predictions were in good agreement with test results found in the literature, thus adding confidence to the validity of the proposed models.