FRP Structures Research Articles

Damage detection of FRP structures using the electrical resistance response of MWCNTs networks in a PDMS film substrate

Damage detection of FRP structures using the electrical resistance response of MWCNTs networks in a PDMS film substrate

DFOS monitoring system of the longest Polish footbridge made of FRP composites

The high durability, low weight, and excellent mechanical properties of fibre-reinforced polymers are the main reasons for the increasing popularity of composites as a material for pedestrian and bicycle bridges. This was also the case with the widening of an existing Carpathian bridge in the centre of Rzeszów (Poland). The new footbridge located next to the bridge consists of five simply supported spans of 4.17 + 23.55 + 23.67 + 23.67 + 23.47 m, with the total length of the superstructure 104.95 m, and is believed to be the longest Polish footbridge made of FRP composites. The footbridge spans were created in the form of sandwich panels, which were manufactured in a single infusion process by the VARTM (vacuum-assisted resin transfer moulding) method. Since the footbridge spans are made of innovative but not fully recognised / proved construction material, a decision was made to equip the structure with a reliable structural health monitoring (SHM) system. The system based on distributed fibre optic sensors (DFOS) was selected and implemented for monitoring. One of the spans was equipped with sensors in the form of SM9 / 125 single-mode fibres in an acrylic coating. The optical fibres of the DFOS system were placed inside the composite structure between the fabrics of the selected laminates, before the infusion process. Because of that, the sensors are completely integrated into the material and are not exposed to damage or the influence of the environment. The paper presents the DFOS SHM system, its implementation in the FRP structure, and the measurement results obtained during the proof load tests performed on the new structure before it was open to the public.

Characterization Specifications for FRP Pultruded Materials: From Constituents to Pultruded Profiles

Pultruded FRP composites have emerged as a promising alternative to traditional materials like concrete, steel, and timber, especially in corrosive environmental conditions. However, the unique properties of these composites necessitate careful consideration during their implementation, as they differ significantly from conventional materials. Proper testing and characterization of FRP pultruded materials is key for their efficient and safe implementation. However, the existing specifications are not unified, resulting in ambiguity among stakeholders. This paper aims to bridge this gap by thoroughly reviewing current destructive and non-destructive test methods for FRP pultruded materials, specifications, quality control, and health monitoring of FRP structures. Each subsection is further divided into subtopics, providing a comprehensive overview of the subject. By shedding light on these crucial aspects, this article aims to accelerate the adoption and utilization of these innovative materials in practical applications.

A new computational method for the assessment of the passive fire protection applied to a composite containership

The current paradigm in ship design is focused in producing ships that are more environmental friendly. Lightweight or advanced materials are the perfect candidate to make ship transportation more efficient, however the current state-of-the-art is in demand of novel techniques that aid in the design of marine composite structures when exposed to fire. This paper aims to describe a technique that couples a fire dynamic simulator with a thermo-mechanical tool specialised in the calculus of laminated FRP structures, the application can be extended to other areas of engineering as well. An application of the technique is illustrated in the analysis of one of the decks of the superstructure of a Panamax containership where a fire has ignited and the active fire protection system is disabled. A second objective addressed in this paper is the discussion of the misconception that composites, although outperforming steel in several mechanical aspects, show a substantial lower thermo-mechanical performance. The research conducted here shows that composite are advantageous from the thermal point of view, and certainly have benefits in their thermo-structural response, specially when the life of human beings is under consideration.

In-Service Delaminations in FRP Structures under Operational Loading Conditions: Are Current Fracture Testing and Analysis on Coupons Sufficient for Capturing the Essential Effects for Reliable Predictions?

Quasi-static or cyclic loading of an artificial starter crack in unidirectionally fibre-reinforced composite test coupons yields fracture mechanics data-the toughness or strain-energy release rate (labelled G)-for characterising delamination initiation and propagation. Thus far, the reproducibility of these tests is typically between 10 and 20%. However, differences in the size and possibly the shape, but also in the fibre lay-up, between test coupons and components or structures raise additional questions: Is G from a coupon test a suitable parameter for describing the behaviour of delaminations in composite structures? Can planar, two-dimensional, delamination propagation in composite plates or shells be properly predicted from essentially one-dimensional propagation in coupons? How does fibre bridging in unidirectionally reinforced test coupons relate to delamination propagation in multidirectional lay-ups of components and structures? How can multiple, localised delaminations-often created by impact in composite structures-and their interaction under service loads with constant or variable amplitudes be accounted for? Does planar delamination propagation depend on laminate thickness, thickness variation or the overall shape of the structure? How does exposure to different, variable service environments affect delamination initiation and propagation? Is the microscopic and mesoscopic morphology of FRP composite structures sufficiently understood for accurate predictive modelling and simulation of delamination behaviour? This contribution will examine selected issues and discuss the consequences for test development and analysis. The discussion indicates that current coupon testing and analysis are unlikely to provide the data for reliable long-term predictions of delamination behaviour in FRP composite structures. The attempts to make the building block design methodology for composite structures more efficient via combinations of experiments and related modelling look promising, but models require input data with low scatter and, even more importantly, insight into the physics of the microscopic damage processes yielding delamination initiation and propagation.

Numerical simulation of the damage progression of pultruded GFRP beam-to-column connections under monotonic and cyclic loads

This paper presents a numerical investigation on the behaviour of GFRP beam-to-column cleated connections, using stainless steel cleats. Finite element (FE) models were developed, using ABAQUS, simulating four different connection series, which had previously been object of experimental tests. The stainless steel materials were modelled with a built-in multi-linear isotropic hardening model, while the GFRP materials were modelled, via UMAT, with a damage propagation model previously proposed by the authors. The results show that these FE models are well able to predict the monotonic behaviour observed in the experiments, indicating very reasonable predictions of the connections’ strength and failure modes. The hysteretic behaviour of two connections was also simulated with these FE models and the results compared very well with their experimental counterparts. Moreover, for both monotonic and cyclic loading, the models were able to simulate the behaviour for deformation levels well above those required by the higher ductility class of Eurocode 8. Overall, these results show the feasibility of using these FE models in the design of FRP structures, reducing the need of experimental tests, to determine the monotonic and hysteretic behaviour of the connections, which can then be used as input in the full structure design models.

Experimental investigation on mechanical properties and free vibration characteristics of epoxy‐based glass/flax laminates

AbstractIn the present study, an attempt is made to replace the synthetic glass fiber used in the FRP structures in terms of natural flax fibers without much sacrifice on static and dynamic stability of the structure. Three types of glass/flax hybrid composite laminates were prepared with different fiber volume fraction of glass and flax fibers. For better understanding purpose, a dedicated glass and dedicated flax laminates were also fabricated. All the laminates were fabricated by vacuum bag molding method with uniform laminate thickness. The mechanical properties of the fabricated laminates, such as tensile strength and flexural strength, were evaluated in accordance with ASTM standards. The impulse excitation technique was used to assess the free vibration characteristics of glass/flax laminates such as modal frequency and material damping. Based on experimentally evaluated mechanical and vibration characteristics a suitable fiber volume fraction for the preferred laminate thickness was suggested to achieve optimum static and dynamic stability.

Vibration-based monitoring of an FRP footbridge with embedded fiber-Bragg gratings: Influence of temperature vs. damage

An attractive feature of FRP structures is that Fiber-Optic Sensors (FOS) can be naturally embedded during the production process and provide important structural information immediately after construction. Thus, FOS became very useful also for Vibration-Based Monitoring (VBM) applications. In VBM, damage can be identified by detecting damage-related changes in the modal characteristics of a structure, such as natural frequencies and strain mode shapes. However, natural frequencies can exhibit a low sensitivity to certain types of damage, especially when compared to their sensitivity to temperature. Strain mode shapes though have been proved to be more sensitive to local damage and less to temperature than natural frequencies. In this work, an FRP footbridge is subjected to periodic annual VBM. The dynamic strains of the bridge are monitored with embedded Fiber-optic Bragg Gratings (FBG), a type of FOS that allows determining natural frequencies and strain mode shapes accurately from low-amplitude strain data. Vibration modes are identified from the dynamic strains and the influence of temperature and heavy loading is investigated. The identified modes are used for calibrating a finite element model. Possible damage scenarios on FRP structures are simulated and their influence on modal characteristics is investigated and compared to this of temperature.

Novel joint for pultruded FRP beams and concrete-filled FRP columns: Conceptual and experimental investigations

A novel joint, inspired by ancient mortise-and-tenon joints in timber structures, was proposed for pultruded FRP beams and concrete-filled FRP columns. FRP structures are widely known to lack appropriate joint solutions. In this regard, the proposed joint effectively provides a feasible solution for FRP frame structures. In this work, the conceptual development of this joint was first addressed. Then, the construction schemes were presented in detail, and a total of four full-scale joints were tested. To assess the structural behavior of the proposed joint, experiments including four specimens were conducted under symmetric and anti-symmetric load, i.e. the loading conditions in sway and non-sway frames. The typical failure modes were identified, including pull-out or tensile fracture of the tensile flanges and end crushing of the compressive flange. Additionally, an analytical study is carried out to develop the design method for this joint. The predicted moment capacity is found to have an excellent accuracy as compared to the experimental results. Moreover, the proposed joint can be classified as the rigid and full-strength joint based on the classifications prescribed by the European design code. It is noted that the proposed joint is completely composed of FRP composites and concrete (i.e., a steel-free joint). Thus, the joint is expected to exhibit excellent corrosion resistance, which is of particular interest for marine structures on/near oceans.

Experimental investigation of fibre reinforced plastics (frp) structure with coconut husk under low velocity impact

Utilization of polymers, particularly Fiber Reinforced Plastics (FRP) offers a few benefits to accomplish powerful and solid constructions which is more significant for current natural circumstance. In this present investigations, the impact energy conduct of composite construction with bio filler has been researched under low velocity impact load circumstance. The coconut husk is utilized as a bio filler, while the epoxy resin is chosen as matrix material. Glass fiber has been utilized as reinforcement material. Every specimens have been made by hand layup method and combined by utilizing compression molding machine at 70 °C, with 8 bar pressure for 5 min. The specimens with four diverse direction and stacking succession are prepared. The elements of the specimens are in agreement to ASTM standard D5628. The examinations have been done on specimens by exposed it to the diverse impact energies by utilizing an impact testing machine. Different boundaries viz. energy absorption, deformation and force have been assessed from the investigations. The tested specimens were outwardly examined to contemplate the fracture behavior with respect to position of glass fiber in the cover. The experimental outcomes under low velocity impact circumstance would be correlated with standard existing literature results. The eventual outcome demonstrates that composite with filler shows superior properties than the ordinary glass/epoxy laminates under impact load circumstance.

УЛЬТРАЗВУКОВОЙ КОНТРОЛЬ РАДИУСНЫХ ЗОН КОНСТРУКЦИЙ ИЗ ПКМ (обзор)

The review of FRP structures radius zones ultrasonic non-destructive testing techniques is given in the paper. It is shown that both single-element piezoelectric transducers and phased arrays can currently be used to solve this problem. It is necessary to use special tools for positioning and creating an acoustic contact with both types of transducers. Ultrasonic testing using the described tools allows detecting defects in radius zones up to 6 mm in size.

Novel progressive failure model for quasi-orthotropic pultruded FRP structures: Formulation and calibration of parameters (Part I)

This paper presents a novel progressive failure model for the 3D simulations of pultruded FRP structures which allows the modelling of the laminates as a homogeneous material. The failure initiation model proposed requires only the strength in each direction as input, combining them to retrieve in-plane and out-of-plane failure indexes. The damage propagation model can be divided in two main stages: (i) damage progression and (ii) constant stress beyond a limit strain. The former stage uses the in-plane and out-of-plane failure indexes to determine the damage progression, using different parameters in each direction to account for the different damage responses, while the latter is characterized by a constant stress after a limit strain is reached, also different for each direction. FE models were developed with the proposed damage propagation model, requiring as input the strengths obtained from standardize experimental material coupon testing, the results of which, namely the load/stress vs. displacement/strain curves, are used to calibrate all the parameters needed to established the model. The results show that the proposed damage propagation model, using a homogenized material, is well able to predict the experimental behaviour even for very complex cases such as interlaminar shear tests. Furthermore, in a companion paper the accuracy and limitations of the model are further assessed in the simulation of transverse compact tension and web-crippling tests.

Laminate design for a tapered FRP structure with ply drop-off based on yielding of resin pockets

In this study, a design procedure is proposed for a tapered FRP laminate with ply drop-offs to suppress the damage initiation. A stress index, based on the von Mises yield criteria, is defined and applied to the resin pockets formed adjacent to cut plies. First, finite element (FE) analysis of a three-ply tapered laminate consisting of a cover layer, a dropped layer, and a base layer is conducted to relate the fiber directions with the stresses caused by a ply drop-off. Using the stress values obtained from the FE analysis, a tapered quasi-isotropic laminate with a thickness decreasing from 16 to 8 layers is appropriately designed by minimizing the overall stress indexes in ply-dropped locations. The observation of the specimen manufactured by autoclave molding reveals that the resin pockets can be effectively eliminated by the appropriate design. The tensile tests also verify the higher load capacity.

A Review on Inspection and Maintenance of FRP Structures

FRP is extensively used today in all domains like concrete structures in Civil engineering, spacecraft in Aerospace Industry. It is also used in elevator and bridge cables. Although FRP has some remarkable properties, it undergoes fatigue and damage and sometimes, undetectable defects are formed. Defects like de-lamination or voids occur due to manufacturing errors, or exposure to external environmental factors can result in BVID. Thus, FRP structures have to undergo inspection to ensure its continued use and safety. The inspection and maintenance methods most commonly employed in FRP structures are NDT or Non-Destructive Testing and CM or Condition Monitoring. The integral part of both, NDT and CM is SHM. NDT is a type of inspection method wherein the sample is tested without damaging it whatsoever. NDT is commonly used for reasons such as low cost, high reliability. The techniques involving NDT are Acoustic Emission Testing, Thermography, Ultrasonic Testing, Eddy-Current testing, Radiography. This paper discusses and reviews the various types of Inspection Techniques in NDT and SHM.

On failure modes and design of multi-bolted FRP plate in structural joints

Technical recommendations for design of all FRP structures are by now available and recognized. Inside this frame, the design of all FRP bolted connections with steel bolts has a not negligible position due to its importance in application, especially when bolted connection have, or could have, a significant role in term of bearing capacity and hierarchy between structural parts. The design strength formula for bolted FRP connections – proposed in European and national normative and guidelines – define different approaches in function of the numbering of bolts, the geometrical characteristics and typology of each joint and action, that could be out or in plane. Nevertheless, the specific case of multi-bolted (MB) or high-multi-bolted (HMB) FRP plate used in structural joints has been not yet clearly faced, nor from experimental and numerical approach, nor for failure mode. Besides also the strength design approach becomes complex in presence of MB connections. By the way, this research try to investigate specifically this point starting from recent experimental based results dedicated to the structural performance of MB and HMB FRP plates used in connections, and in comparing them with expected ultimate strengths and available design formula. In comparing available formula with experimental outputs – and in verifying their reliability/compatibility – the proposed investigation shows also some thought onto the potential oversize/undersize of this kind of structural joints. The research is exclusively dedicated to the MB FRP plates produced by pultrusion process and used in joints subjected to only in plane action.

FEM based delamination damage analysis of bonded FRP composite pipe joints

Delamination damage is one of the major type of fractures encountered by laminated FRP structures, greatly effecting their structural stability. Development of finite element method (FEM) based modelling and simulation technique in order to analyze delamination growth in laminated FRP composite made single lap pipe joints, is the prime concern of the present research. Layered solid 185 elements of ANSYS 18.0 has been used for modelling the FRP composite tubes. Ansys Parametric Design Language (APDL) codes have been developed to simulate delaminations and study their effect on interlaminar stresses. Delamination damages have been considered in the ply-interfaces of the composite tubes in the close vicinity of the adhesive layer and their effect on the adhesive mid-layer stresses has been studied. Comparison of delamination damages in the outer and inner tubes on adhesive stresses revealed that damages in the inner tube are more critical as compared to the delaminated outer adherend.

FRP加固砌体结构的界面粘结性能综述

FRP加固砌体结构的界面粘结性能综述

Constitutive modeling for FRP composite materials subject to extreme loading

A physically based, finite deformation, rate and temperature dependent theory and model have been developed to simulate the deformation and failure of FRP composite materials and structures. Failure modes include: inter alia, fiber crushing and kinking as occurs during extreme compressive loading; fiber fracture as occurs in for example fragmentation; interlaminar shear as occurs at elevated temperatures and that leads to kinking; debonding and delamination including the coupling with laminate kinking; and debonding as occurs in cored FRP panels. The theory/model is capable of describing quasi-static (including creep) as occurs at elevated temperatures, and dynamic deformation and failure as occurs during shock, blast or impact. The model is implemented within LS DYNA and specific example simulations are described that illustrate the theory/model capabilities. In Part I, fragmentation is not covered in detail. Fiber fracture and fragmentation are to be covered to detail with specific examples in Part II.

КОНТРОЛЬ ДЕТАЛЕЙ И КОНСТРУКЦИЙ ИЗ ПОЛИМЕРНЫХ КОМПОЗИЦИОННЫХ МАТЕРИАЛОВ С ПРИМЕНЕНИЕМ ТЕХНОЛОГИИ УЛЬТРАЗВУКОВЫХ ФАЗИРОВАННЫХ РЕШЕТОК

КОНТРОЛЬ ДЕТАЛЕЙ И КОНСТРУКЦИЙ ИЗ ПОЛИМЕРНЫХ КОМПОЗИЦИОННЫХ МАТЕРИАЛОВ С ПРИМЕНЕНИЕМ ТЕХНОЛОГИИ УЛЬТРАЗВУКОВЫХ ФАЗИРОВАННЫХ РЕШЕТОК

3次元FRP構造の硬化分布モニタリング

3次元FRP構造の硬化分布モニタリング