Search

• CFRP/GFRP stacking configurations are used to hybridize face sheets. • CFRP face sheet becomes extremely brittle at low temperatures. • Hybridization is observed to improve the impact resistance at low temperatures. • Dissimilar fiber interfaces cause more delamination during low velocity impact. • Achieving pseudo-ductility of face sheet by hybridization is temperature dependent. In this study, the impact response and damage mechanisms of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) hybrid face sheet sandwich composites are investigated with the aim to provide an understanding and solution to mitigate the coupling effects of low temperature and low velocity impact damage. Hybridization of face sheet is achieved by stacking CFRP and GFRP in different thickness configurations. Samples are subjected to low-velocity impact at 23 °C and −70 °C to compare and understand the effect of cold temperature in the Arctic environment. Results show that hybridization improves the impact performance at −70 °C. CFRP layers and foam core become extremely brittle at low temperature, but GFRP layers maintain a certain extent of ductility and enhanced laminate strength at low temperature. Moreover, different damage modes (delamination, fiber breakage, core crushing, core shear, face sheet debonding, back face fiber splitting) are observed and characterized by X-ray micro-computed tomography. The additions of GFRP layers to CFRP face sheet mitigated the increased brittle fiber failure observed at low temperatures, however the impact characteristics and damage size was found to be dependent on the hybridization configuration. [ABSTRACT FROM AUTHOR]

Bending-active elastica beam is a structural configuration that is based on the elastic deformation of an initially straight beam. This deformation occurs when horizontal displacements are applied to a sliding support, causing the beam to bend into an arched shape. Previous research has focused on the stability of small-scale bending-active structures, thus not considering material strength, which is crucial in real-scale applications and structural design. This paper investigates the short-term structural behavior of bending-active elastica beams using pultruded glass fiber-polymer composite profiles, as used in real-scale structures. A series of short-term bending and service load application experiments were performed considering different bending degrees and loading scenarios. These results were used to validate finite element modeling. They demonstrated that steeper bent beams experience material failure, while shallower ones exhibit snap-through buckling. Material failure initiates on the tensile side of the beams, with cracks initiating at locations of maximum curvature. Higher bending degrees and symmetric loading result in higher maximum loads than lower bending degrees and asymmetric loading. A strain-based failure criterion, which can serve for structural design, is derived. [ABSTRACT FROM AUTHOR]

This study investigates the use of hemp/glass fiber reinforced epoxy composites for designing automotive front bumper beams, focusing on crashworthiness and pedestrian safety. The composite bumper beam model is evaluated through low- and high-velocity crash simulations and pedestrian leg form impact tests using LS-DYNA software. Optimal stacking sequences are analyzed, with high-strength glass fibers positioned on the outer layers to bear impact loads and low-density hemp fibers in the middle. The hybrid hemp (H)/glass (G) fiber composite laminate can absorb up to 90 % of the impact energy absorbed by a glass fiber composite, with a ± 45° fiber orientation, showing exceptional energy absorption capabilities. The [G(±45°) 4 , H(±45°) 4 ] S composite bumper beam offers superior impact performance, safety, and a weight reduction of 49.2 % compared to a commercial steel bumper beam. This study highlights the potential of natural fiber composites as sustainable alternatives in automotive design. [ABSTRACT FROM AUTHOR]

This study aims to investigate the influence of different thermal aggressions (resulting in the decomposition of the thermoplastic matrix) on thermal degradation and residual tensile mechanical behavior of hybrid carbon/glass fibers reinforced PolyEther Ether Ketone (PEEK) laminates. The specimens are exposed to isothermal (from melting temperature to decomposition temperature by means of a furnace) and anisothermal conditions (116 kW/m2 and 1150 ℃ kerosene flame by means of a burner bench) respectively. The mechanical tests are further conducted to evaluate the residual tensile properties at Room Temperature (RT). When the laminates are exposed to flame, the microscopic observation reveals the heterogeneous thermally induced damages, compared with the isothermal case. A significant reduction in the axial stiffness (−35 %) and axial strength (−90 %) occurs after a 900 s flame exposure, as the structural integrity of laminate is significantly affected, compared with virgin specimens. By means of a three-region modeling, the importance of different damage regions for a post-fire laminate under mechanical loading is quantified and it is possible to further predict the residual mechanical properties with different flame exposure time. [ABSTRACT FROM AUTHOR]

• The baking soda abrasive jetting method as a new surface material stripping method for glass fiber reinforced materials (GFRP) was studied. • The jetting effects of different abrasives were compared, and the advantage of low damage of baking soda abrasives was highlighted. • Chemical stripping method was used to compare cleanliness. • The surface material of GFRP stripping process was simulated using LS-DYNA. Glass fiber reinforced composites (GFRP) working in a specific environment require regular inspection and maintenance. It is necessary to remove the surface material of fiber reinforced composites to check the fracture of fibers and the damage to matrix that binds fibers in this process. In this paper, the baking soda abrasive jetting was utilized to strip the surface material of glass fiber reinforced epoxy resin (GFREP). The stripping effects of baking soda abrasive jetting technology under different jetting parameters (fiber orientation, jet angle, jet pressure) were explored, and the optimum stripping conditions were determined as parallel to the fiber, 30°, 0.4 MPa. Compared with the chemical stripping method (phenol-dichloromethane), baking soda abrasive jetting can better retain epoxy resin between glass fibers. The LS-DYNA was applied to simulate the erosion process of a single abrasive particle under the optimum stripping condition. The plastic deformation of the matrix and the slight bending deformation of the glass fiber under abrasive impact were observed. [ABSTRACT FROM AUTHOR]

• Mode I fracture process is characterized for GFRP-steel bi-material interface. • Double-cantilever beam experiments supplemented by detailed DIC measurement. • Accurate modeling of crack initiation, fiber bridging and propagation by new CZM. • Four-linear traction-separation law derived from DIC measurements and iterative FEA. Debonding is characterized as the governing failure mode in the innovative wrapped composite joints made with glass fiber composite material wrapped around steel hollow sections without welding. The prerequisite for predicting debonding failure of wrapped composite joints is to obtain fracture behavior of the composite-steel bonded interface. The mode I fracture behavior of the bonded interface was experimentally investigated using glass fiber composite-steel double cantilever beam (DCB) specimens. The crack length a and the crack tip opening displacement (CTOD) during the test were accurately measured by analyzing the digital image correlation (DIC) data while the strain energy release rate (SERR) was calculated through the extended global method (EGM). The cohesive zone modeling (CZM) was utilized in the finite element model with the proposal of a four-linear traction-separation law to simulate the mode I fracture process. An approach is introduced to determine the critical stages of the proposed four-linear cohesive law by combining accurate measurements of crack length a and CTOD, along with SERR values. The validity of the four-linear cohesive law and the introduced approach to determine the critical stages were confirmed by good agreement in both global and local behavior between the testing and the FEA results. [ABSTRACT FROM AUTHOR]

This article investigates the effects of voids, joint geometry, and test conditions on the quasi-static Mode I fracture performance of thick adhesive Double Cantilever Beam (DCB) joints such as those prevailing in wind industry and shipbuilding. The specimens were made by glass fiber reinforced epoxy adherend and SikaPower®-830 epoxy adhesive in the cm thickness range. Side-grooved shape guided the crack propagation direction and assisted stable propagation, while lower cross-head displacement rates reduced the occurrence of unstable crack propagation and prevented crack deflection. Porosities, which are inevitable due to the high viscosity of the adhesive, led to unstable propagation and promoted crack path deviations. They could also decrease the apparent fracture energy release rate (SERR) since the crack surface is reduced. In conclusion, grooved DCB joints with low void content tested at low displacement rates showed stable crack propagation without significant crack path deviation. This method enables comparison with future adhesive formulations and the refinement of full-scale blade models. [ABSTRACT FROM AUTHOR]

Structures and components need to be constantly monitored to ensure good service life and avoid failures. Structural health monitoring is a wide-ranging concept that tries to ensure the safety of components and structures. Vibration responses of small and large structures contain information about these damages. In the present study, this information is extracted and used to classify the location and severity of cracks. For this purpose, an FE model of Glass Fibre Reinforced Plastic (GFRP) free-free beam is created for beams without any crack and beams with three crack locations and three crack severities. Finite Element (FE) model is validated using modal analysis and is used to generate vibration responses from simulated hammer strikes at different locations on the beam. The vibration data consists of responses of beams that have only one crack present at a time and when two cracks are present. A 1D-CNN network is trained on the generated vibrational responses to classify damage labels assigned for each crack location and crack severity. The network was tested using datasets containing only single crack instances and only dual crack instances. The trained networks were found to be 95% and 93% accurate in determining the damage class respectively. Furthermore, datasets of these two instances combined, containing responses when single cracks and dual cracks are present, were also investigated. These networks had an accuracy of 92%. Hence, in all these instances, the 1D-CNN network classifies the healthy and damaged conditions satisfactorily. There are two advantages of using such a technique. Firstly, this approach simplifies the two-step approach: one for feature extraction and another one for damage prediction into a single step. Secondly, the use of raw vibration data for damage prediction means that real-time damage detection is possible. [ABSTRACT FROM AUTHOR]

Compared with other green natural fibers, ramie has higher mechanical properties and lower cost. In this study, ramie and glass fiber are made into composite circular tubes by two-dimensional braiding, and their torsional mechanical properties and damage mechanisms are investigated. The results show that under the unit wall thickness, compared with the pure glass fiber circular tube, the maximum torsion angle of the hybrid circular tube with ramie and glass fiber spindle ratio of 1:3 increases by 78%, the weight is reduced by 22%, the cost is reduced by 14%, the maximum torque is increased by 10% and the torsional stiffness is reduced by 18.75%. When the loading direction is the same as the implantation direction with more glass fiber content, the failure is caused by buckling. When the loading direction is the same as the implantation direction with more ramie content, the failure is caused by matrix fracture or fiber fracture. The numerical simulation results of the damage model are consistent with the experimental data and the damage morphology, which verifies the effectiveness of the finite element model. These conclusions provide a reference for the engineering application of composite circular tubes with environmental protection, lightweight and anti-torsion failure ability. [ABSTRACT FROM AUTHOR]

• Physical experimental testing of composite pressure vessels under low velocity impact. • Composites residual strength in the axial configurations. • Composite damage analysis on brooming and buckling failures. • Damage characterisation of composites pressure vessels using microscopy and Dolphicam2 NDT. Pressure vessels are being utilised in different applications that are indispensable including automobile, aerospace, underwater vehicles, oil and gas, chemical engineering among other applications. However, there is lack of knowledge on the influence of induced damage and the resulting performance of such vessels under quasi-static loading and axial compression. Specifically, the vessels studied in this study is made up of a high-density polyethylene liner and glass fibre overwraps. Therefore, this research investigated the load bearing capacities and the energy absorbed of the indented vessels in axial and hoop directions to determine the resistance of the vessels after such damaged using experiment, and damage characterisation microscopy, non-destructive testing and analysis. Quasi-static transverse and axial compression testing was performed on composite cylinders made of polyethylene liner and glass fibre overwraps. Both quasi-static and axial compression tests were performed with Universal testing Machines at crosshead speed of 500 mm/min 2.5 mm/min respectively. Microstructural damage characterisation was conducted using microscopy and Dolphicam2 ultrasonic non-destructive testing equipment. This study provides a new understanding on the performance of composite pressure vessel under damaged and undamaged conditions has established the reliability and residual strength capabilities of composites under the scenarios investigated. The results shows that the damage profile and the effect on compressive strength of the composite damaged and non-damaged cylinders was found to be relatively similar. However, when the cylinders are subjected to quasi-static compression, the polyethylene absorbs enough elastic strain energy to recover from the applied compressive load and recover without being plastically deformed. Additionally, the results demonstrate that the quasi-static compression have little or no influence on the axial strength of the cylinders. The damage characterisation on the cylinders revealed fibre break and delamination and local bucking and brooming failure at the bottom of the cylinders. This study has direct impact in composite overwrapped pressure vessels (COPVs) safety design tolerances, manufactururing strategy and operational failure conditions. [ABSTRACT FROM AUTHOR]

• The elliptic integral solution of spatial elastic is obtained for a rod under multiple loads. • A new Form-finding Method based on Spatial Elastica (FMSE) is proposed for gridshells. • Different deformation modes of Chebyshev gridshells are solved by employing FMSE. • The accuracy of FMSE predictions is confirmed by physical models built by GFRP rods. In engineering design, elastic gridshells, which are composed of a number of elastic rods, are advantageous because they are lightweight, easy to construct, and low-cost as well as have a long-span space. However, the form-finding of a gridshell is challenging owing to the large deformation and strong geometric-nonlinearity of the structure. In this paper, a new form-finding method based on spatial elastica model (FMSE) is proposed. The deformations of elastic rods, obtained via the elliptic integral solution of spatial elastica, is integrated into the overall deformation of the gridshell. A set of transcendental equations is solved using the quasi-Newton method to ensure that the deformation of the gridshell satisfies the given boundary conditions. To validate the proposed FMSE method, desktop experiments (designed using the theory of Chebyshev nets) are performed on gridshells made of glass fiber reinforced polymer rods. The predictions of the FMSE method agree well with the experimental results. Accordingly, the proposed FMSE method is expected to have potential applications in elastic gridshells, on the investigations of form-finding, load-bearing capability, non-local deformation behavior, and also stability of structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanical performance of composites post-cured under elevated and extended ambient temperature profiles are comparable. • Cure initiator form had a marginal influence on mechanical performance. • Powder form cure initiator is a promising alternative to water-based initiator to avoid porosity. • A reduction in modulus was apparent after ambient post-cure and is an important consideration for structural design. This study evaluates the effect of post-cure schedules and cure initiator form on the mechanical properties of Glass fibre reinforced polymer (GFRP) laminates manufactured using an infusible reactive thermoplastic resin. Tensile, flexural, shear and dynamic mechanical analysis tests were conducted. Fractography was also performed. Specimens fabricated using liquid cure initiator and subjected to an elevated temperature post-cure were the control specimens. Ambient cured specimens decreased by no more than 12% in the case of tensile properties (modulus of 90° specimens) and by < 14.3% in the case of flexural properties (also modulus in 90° specimens). Furthermore, the difference in mechanical properties of 0° specimens fabricated using a powder cure initiator was observed to be within ≈ 7% of respective properties of control specimens. In the context of fabricating thick laminates for large-size offshore structures, the results suggest that an extended ambient post-cure cycle in conjunction with an initiator in powder form can be employed instead of an elevated temperature post-cure schedule with initiator in liquid form. This is economically beneficial since it eliminates infrastructure required for elevated temperature curing/post-curing. The risk of porosity induced due to liquid-based initiators is also avoided. [ABSTRACT FROM AUTHOR]

• Custom-built 3D weaving machine was used to weave 3D spacer glass fiber fabrics. • PU foaming was directly performed in the vacancies of 3D woven I-beam composites. • Up to 43 % compressive modulus increase was obtained via in-situ PU foaming. • Energy absorption was increased in LD-PUFFIC by 173 % under three-point bending. • Post-mortem mechanical test samples were monitored by fractography. 3D weaving of I-beam structures can potentially create delamination- and joint-free structures, expanding their use in engineering applications compared to metal or traditional laminated composite beams. In addition, polymeric foams can be utilized to fill the vacancies between the web and the flanges of I beams, improving the mechanical characteristics and the structural integrity with little to no weight penalty. Moreover, interposing an adhesive layer between the I beam and the foam structure can result in a more effective bonding which intensifies the structure's robustness. In this study, high-performance I-beam composites were produced by combining polymeric foams with 3D woven glass fiber composites. Low- and high-density polyurethane foams were successfully inserted between the web and the flanges of 3D woven glass fiber composites manufactured by the vacuum infusion process using the free-rise foaming method. Samples with adhesive films were also produced to assess and compare their effectiveness with the composites made solely of polyurethane foam and I beam. The increases in energy absorption capacity and compressive and flexural properties were analyzed under compressive and flexural (three-point bending) loading. The obtained results indicate that structural integrity under bending can be substantially improved with the in-situ foaming supported by adhesive layers. [ABSTRACT FROM AUTHOR]

High performance shape-adjustable structural batteries with both excellent electrochemical performances and mechanical properties, and compatible with conventional batteries and composite processing techniques, are highly attractive for next generation electrical vehicles and electrical aircrafts. Herein, a high-performance structural lithium-ion battery composite (SLBC) is developed by encapsulating commercial-available battery core materials with hybrid fiber reinforced epoxy composite laminate shells, which can be assembled into desired irregular shapes with the conventional vacuum bagging technique. Firstly, the laminate shell layout with the combination of glass fiber woven fabric (GFWF) and carbon fiber woven fabric (CFWF) is designed and optimized. Meanwhile, a PET film is employed to wrap the battery core materials, which enables processing of the SLBC with liquid electrolyte in ambient condition. The SLBC obtained demonstrates both prominent mechanical (flexural strength of 211.7 MPa and flexural modulus of 7.7 GPa) and electrochemical properties (an initial discharge capacity of 98.5 mAh/g at 0.2C, a high energy density of 314.5 Wh kg−1, and a good cycling performance) owing to the hybrid design of CFWF and GFWF as well as a sealed environment to guarantee the battery operate well. Impressively, the in-situ mechano-electrochemical measurements are assessed under the out-of-plane compressive stress and the flexural stress conditions. These results show that the SLBC under loading can maintain stable electrochemical performance even at a high out-of-plane compressive stress of 20 MPa and a high flexural stress of 150 MPa. Furthermore, the SLBC can also maintain the excellent discharge capacity when subjected to a high impact energy, which is promising in next generation electrical vehicles. Finally, the wave-like SLBC fabricated demonstrates the effectiveness in withstanding loads and driving electric fan simultaneously, which is promising in next generation electrical vehicles.. [ABSTRACT FROM AUTHOR]

• Shear failure characterised by extensive horizontal cracks around the axis of gravity is identified as a relevant failure mode for moulded GFRP gratings. • Bending stresses as well as torsional shear stresses do not significantly increase the risk of such failure. • Shear deformation and warping torsion can have a significant influence on the load bearing behaviour of GFRP gratings. Moulded GFRP gratings provide several advantages over conventional metallic gratings and have steadily increased in popularity, even though their use within the building sector is often accompanied by costly approvals. Those are frequently required due to a lack of adequate design rules. To push the development of such rules, a comprehensive study on the load bearing behaviour of GFRP gratings is conducted and briefly presented herein. Two failure types, shear and bending failure, are identified in three-point bending tests and further studied by numerical analyses. Subroutines are developed and integrated into a commercial FE software to account for nonlinear material behaviour related to microdamage and macroscopic fracture. Thus, relevant stress and damage states at the scale of a lamina are clearly identified. Based on these investigations, a mutual interaction of bending and shear stresses on the load-bearing capacity can be excluded. Additional tests are carried out on full-size grating panels and recalculated with a structural frame analysis program. The research suggests that a warping restraint shall be assumed in the crossings between orthogonal bearing bars which significantly increases the effective torsional stiffness. It can also be shown that torsion-induced shear stresses do not contribute to the development of shear failure. [ABSTRACT FROM AUTHOR]

Hard armour plates are used in body armour for protection against high-velocity threats. The strike face often consists of a single ceramic tile that is covered by a sheet material made of a high-tenacity fibre-composite material. During impact, the ceramic will fracture but at the same time cause erosion and fragmentation of the hard core of the projectile. The composite cover is there to improve the ballistic performance by partly maintaining the integrity of the fracturing ceramic. In this study, a new production method where glass fibre yarns were filament-wound around an alumina tile in a unidirectional 0°/90° lay-up, was investigated. Ballistic testing was conducted with a 7.62 mm armour piercing projectile. The new target design gave a remarkable increase in the V 50 ballistic limit velocity by as much as 16% compared to a traditional design where a glass fibre fabric was wrapped around the tile. A higher degree of fragmentation of the projectile steel core after perforation was also observed. The high degree of fibre alignment in the filament-wound composite, as opposed to the more wavy fibres in the fabric, is believed to be the main reason for the higher ballistic performance. [ABSTRACT FROM AUTHOR]

This paper describes the development of electrically insulating hybrid steel–composite cross-arm for medium-voltage overhead distribution power lines with three conductors. The main goal was to achieve substantial weight savings compared to a common steel cross-arm with three ceramic insulators widely used in the Czech Republic. The structure has been designed as a combination of two main composite components – a pultruded horizontal profile and a braided vertical conical tube. These components are connected by a steel locking component which also serves for attaching the whole cross-arm to common concrete utility poles. The hybrid cross-arm is conceived to insulate electrical current in the default configuration thanks to the properties of the glass fiber reinforced composite materials, yet additional insulating elements can be used to further increase the electrical insulation distance. The materials and components used for the construction are chosen by combining finite element simulations of mechanical and electrical behavior with experimental testing and verification of important characteristics on selected substructures. The final design of the cross-arm is then manufactured and subjected to long-term testing in real-life environmental conditions. The achieved reduction of weight exceeds 50% while maintaining the mechanical rigidity and strength of the steel solution as well as the required insulation properties. The future trend of the cross-arm development is aiming at the weight reduction and increase of manipulation capabilities resulting in lowering many additional costs. In this work the designed cross-arm has half the weight of the original one. [ABSTRACT FROM AUTHOR]

Hybrid carbon/glass fibers composites can possess pseudo-ductility of progressive failure through material design to achieve the function of load early warning. The printing design and forming thermal environment of parts have important influence on the pseudo-ductile behavior of hybrid fiber composites. In this paper, the hybrid continuous carbon/glass fibers reinforced nylon composites with progressive failure pseudo-ductility were prepared by additive manufacturing, and the effects of printing layer thickness, carbon/glass fibers layer ratio and forming thermal environment on the tensile properties and pseudo-ductility of hybrid fiber composites were investigated and characterized. The results indicate that the printing layer thickness has no significant impact on the tensile strength of hybrid fiber composites, the pseudo-ductility is obvious when the layer thickness of [G 5 C 2 G 5 ] is 0.075 mm and 0.125 mm. With the same material ratio, reducing the layers or setting the printing platform temperature (100 °C) can decrease defects generation to achieve the better pseudo-ductility. However, the pseudo-ductility immensely weakens using the annealing treatment of 120 °C for 3 h. The pseudo-ductility of the [G 5 C 2 G 5 ] 0.075 , [G 5 C 2 G 5 ] , [G 3 C 1 G 3 ] and [G 4 C 1 G 4 ] samples have been discovered successfully. [ABSTRACT FROM AUTHOR]

Continuous fiber tow reinforcements in hybrid-molded composite structures are an emerging means of replacing structural, high production volume metal components, but further study of design variable effects is critical to widespread adoption. By testing representative structures with features found on automobile components, performance was evaluated for a range of material combinations and reinforcement content. Tow reinforcements were made from continuous glass or carbon fiber reinforced PA6 prepreg tape and injection overmolded with unfilled or glass fiber filled PA6 adding a shear web and rib structures. Tow reinforcement significantly reduced warpage and in tensile loading, demonstrated potential for 340% strength increase over parts without tow. However, three-point bend performance was dominated by the overmolding material. High strain to break overmolding materials are recommended to avoid premature overmolding material cracking. [ABSTRACT FROM AUTHOR]

The aim of the work was to assess the compressive strength of Fibre Metal Laminates after impact. The main objective of the evaluation of the compression after impact assessment of FMLs was the deep analysis of damage growth range, size and mechanisms during load from various initial damage states and final post-impact strength. The glass fibre/titanium and carbon fibre/titanium Fibre Metal Laminates were tested and analysed. Laminates previously subjected to impact energies ranging from 5 to 35 J were tested. Based on the research, three load bearing states of fibre-metal laminates were identified and characterized on the basis of an analysis of force reduction characteristics. In addition, it was found that the strength reduction of FMLs in relation to impact energy does not decrease significantly. One of the most crucial grounds for the above is the protective role of the elastic–plastic metal layers against rapid local buckling of the strength-carrying composite component. [ABSTRACT FROM AUTHOR]

[Display omitted] We tested the quasi-static tension behavior of the high-strength glass fiber four-Harness stain woven composite, Kevlar fiber plain woven composite, and their laminated hybrid composite. Their representative volume element models are established based on mesoscopic cross-section photographs combined with voxel mesh. A progressive damage model for predicting the damage initiation and evolution of the 2D woven composites is proposed. The crimping effect of plain-woven composites has been considered. The 3D Hashin and the maximum stress criterion are used as the fiber yarn and matrix's damage initiation criterion, respectively. The exponential model is used as the damage evolution model of the fiber yarn. A combination of exponential and reverse tangential damage models has been proposed to describe the damage evolution of the matrix. The proposed damage model is realized using user-defined subroutine UMAT and VUMAT. Abaqus/Standard performs the uniaxial tensile simulation of the two kinds of 2D woven composites with UMAT. Abaqus/Explicit solver simulates the laminated hybrid composite with VUMAT. The simulation results highly agree with the experiment results. [ABSTRACT FROM AUTHOR]

• This paper proposes a damage-resistant Hybrid Fiber Reinforced Polymer Composites (HFRP) design method based on the interface properties. • The microscopic interface properties of composites are introduced into the investigation of interlayer interface properties. • The influence of different hybrid interlayer interfaces on the delamination damage behavior of composites is clarified. • The 3D printing technology was used to prepare specimens of the hybrid fiber-reinforced composites. In this work, the poor impact damage resistance of carbon fiber-reinforced plastic (CFRP) composites was improved by mixing carbon fibers with ductile fibers (glass fibers/Kevlar fibers). The damage behavior of five interfaces of the prepared hybrid fiber-reinforced plastic (HFRP) composites was investigated through mode-I and mode-II interlaminar fracture toughness tests and micro-droplet debonding tests. On this basis, a numerical model for predicting the impact damage of HFRP composites was established. Through a comprehensive evaluation of the impact damage resistance indexes obtained from the numerical simulations, the hybrid fiber type, hybrid ratio between different fibers, and hybrid lay-up sequence could be optimized. The specimens with optimized lay-ups were prepared by 3D printing, and the effectiveness of the numerical model was verified through low-velocity impact and compression after impact (CAI) tests. The results show that the introduction of glass fiber layers in CFRP composites can significantly improve the damage resistance of the composites. Compared with CFRP composites, when the volume fraction of the glass fibers is 25%, HFRP composites have a smaller delamination damage area (reduced by 74.08%), furthermore, the pit depth is reduced by 43.01%, the CAI is increased by 17.29%, and the strength retention rate is increased by 31.94%. [ABSTRACT FROM AUTHOR]

[Display omitted] Recently, methods for determining interlaminar shear properties have been continuously developed to achieve homogeneous stress states and avoid edge effects. In this regard, the torsion test on tube specimens represents a setup with many advantages. Therefore, fibre composites made by a winding of glass and flax fibres were produced at a new type of mandrel, resulting in tubes with a wall thickness between 370 µm (glass) and 640 µm (flax). A new method for determining the shear strain is described in the context of the torsion test. The results are in line with analogous investigations, proving the validity of the new methodology. [ABSTRACT FROM AUTHOR]

A combined experimental and numerical study was performed to investigate the influence of multi-axial stress states and reinforcement type on the constitutive response of fibre reinforced epoxy polymers. The constitutive behaviour of unidirectional and cross-ply layups of carbon and glass fibre reinforced epoxy resin, IM7/8552 and S2/8552 respectively, was investigated. Prismatic short block specimens at different off-axis angles were tested under quasi-static through-thickness compression. The experiments were simulated with an enhanced non-linear material model based on shear localisation planes and pressure dependency, which represents the elastic and plastic experimental behaviour better than other formulations. The results show that the overall constitutive response is highly dependent on the fibre reinforcement type and multi-axial stress state on the mesoscale. In order to obtain an accurate description of the material behaviour, measurement aspects such as determining the correct orthotropic elastic constants, especially the Poisson's ratios, are highlighted. Furthermore, particular focus is also drawn on important modelling aspects such as material non-linearity and pressure effects. [ABSTRACT FROM AUTHOR]

• Hybrid continuous carbon/glass fiber composites based on different laminated design have been 3D printed. • The prepared hybrid fiber composites have excellent balance of impact resistance and tensile resistance. • The tensile strength prediction model considering hybrid effect with good applicability is established and verified. Material extrusion has been applied to the preparation of continuous fiber reinforced resin composites successfully. However, due to the limitations of the characteristics of a single fiber material, the prepared composites usually can only obtain the reinforcement of a single properties. In this study, the effects of the content ratio and arrangement mode of carbon/glass fiber layers in the 3D printed composites on tensile and impact properties were investigated, and the influence of mixed fibers was analyzed by failure morphology. The hybrid continuous carbon/glass fiber reinforced nylon composite parts with good balanced tensile and impact properties were obtained in the experiment, compared with single carbon fiber reinforced nylon composites, the impact strength increased to 250% of the original, while the tensile strength lost only 7%. Tensile strength and impact strength of the printed hybrid composites with the same fiber content and different arrangement are different by 20% and 35%, respectively. The tensile strength of 3D printed hybrid continuous fiber composites was accurately predicted by establishing a model considering hybrid effect. [ABSTRACT FROM AUTHOR]

Fibre hybridisation is used to balance the high cost of carbon fibres and the low durability performance of glass fibres. This study investigates the residual compressive mechanical properties of filament-wound hybrid glass/carbon Fibre Reinforced Polymer (FRP) tubes after exposure to elevated temperatures. Effects of temperature exposure and fibre orientation on compressive properties have been investigated. Tubes were exposed to temperatures ranging from ambient to 350 °C. Two fibre orientation configurations, including hoop (89°) and cross-ply (20% at 15°, 40% at 40°, and 40% at 75°) were used to study the effect of fibre orientation. Compression tests were carried out to study the compressive mechanical properties of FRP tubes, while Digital Scanning Calorimetry and Thermal Gravimetry Analysis were conducted to study the thermomechanical characteristics of the specimens before and after exposure to the elevated temperatures. Finally, the level of damage and its mechanisms were investigated using Scanning Electron Microscopy. The experimental test results indicate that hybrid carbon/glass FRP (C/GFRP) tubes exhibit a performance closer to the weaker tube type, i.e. CFRP tubes rather than GFRP tubes. Moreover, when subjected to elevated temperature, tubes with cross-ply fibre orientations showed slightly better compressive performance compared to the tubes with a hoop fibre orientation. [ABSTRACT FROM AUTHOR]

This study aims to improve the web crippling performance of pultruded glass fibre-reinforced polymer (GFRP) C sections using fibre-reinforced epoxy composite (FEC). The strengthened GFRP C sections were subjected to two loading conditions: interior-two-flange (ITF) and exterior two-flange (ETF). The parameters considered were bearing lengths, FEC strengthening length and thicknesses. Two failure modes, namely web-flange junction failure and web buckling failure were observed for the pultruded GFRP C sections under ETF loading conditions as the bearing length changed. While the combination of the web-flange junction and FEC crushing failures were observed under ITF loading conditions at 20 mm and 50 mm bearing lengths. Furthermore, the average web crippling capacity of strengthened GFRP C sections improved by up to 426 % and 488 %, in comparison to control samples under ETF and ITF loading conditions, respectively. The average web crippling capacity of pultruded GFRP C sections increased up to 45 % when the bearing length increased from 20 mm to 50 mm. The finite element (FE) outcomes showed an agreement with experimental results in the context of failure patterns, load-displacement profiles and web crippling capacities. Finally, equations were proposed to estimate the web crippling capacity of pultruded GFRP C sections strengthened with FEC. [ABSTRACT FROM AUTHOR]

In this work, the static and dynamic mechanical properties of glass fiber reinforced polypropylene (GRPP) laminated self-reinforced polypropylene (SRPP) composite structure were studied, which includes the influences of the SG (SRPP/GRPP) internal and external positions (with two SG positions which are S/G/S, G/S/G) and the SG thickness ratios (with three SG ratios which are 1: 1, 1: 2, 1: 3). Results show that the tensile modulus improvement of laminates was obvious compared with SRPP. A hypothesis is constructed based on the elementary flexural beam theory. The flexural responses of S/G/S and G/S/G are highly similar to SRPP and GRPP respectively, the flexural strength and modulus of S/G/S are less than 50% of G/S/G. The flexural modulus of G/S/G- SG1: 3 is 111 % of GRPP. The impact responses of S/G/S and G/S/G are similar to GRPP and SRPP respectively, but more energy was absorbed in S/G/S. With the increase of SG ratio, less damage and deformation were shown in two structures, which their modes converge. [ABSTRACT FROM AUTHOR]

Combined with GFRP composites stress corrosion experiments, the traditional virtual crack closure technique (VCCT) is improved, and a new WDN-VCCT method is proposed to calculate the stress intensity factor (SIF) at the crack tip of GFRP composites. Its calculation formula makes up for the deficiency of the traditional VCCT method. The calculation results of the WDN-VCCT method and the calculation results of the stress extrapolation method (SEM) are compared and analyzed, and the actual accuracy of the two methods is fully evaluated. The results show that the calculation accuracy of the WDN-VCCT method is higher than that of the SEM method, the calculation efficiency is faster, and the calculation results are closer to the real value. [ABSTRACT FROM AUTHOR]

A novel experimental method for in-situ damage detection in symmetrical and balanced glass/epoxy laminates composed of unidirectional layers is introduced in this paper. A 3D finite-element micromechanical model accompanies this method to predict stiffness degradation in a cross-ply fiber-metal laminate caused by transverse cracks and metal damage. The model is developed in Abaqus. Two user-defined subroutines, UMAT and UHARD, are coded in FORTRAN and linked to the model. Using a Python script, periodic boundary conditions are applied to the model. The predictions are validated against conventional loading–unloading experimental tests. Validation shows excellent agreement between the proposed model and the experiment. [ABSTRACT FROM AUTHOR]

Structural damage identification has been researched for a long time and continues to be an active research topic. This paper proposes the use of the natural frequencies of a novel composite structures made of glass fibre reinforced polymer (GFRP). The proposed methodology consists of an improved Artificial Neural Network (ANN) using optimization algorithms to detect the exact crack length. In the first step, the characterization of fabricated material is provided to determine Young's modulus using an experimental static bending test, tensile test and modal analysis test. Next, numerical validation is performed using commercial software ABAQUS to extract more data for different crack locations in the structure. The comparison between experimental and numerical results shows a good agreement. ANN has been improved using recent optimization techniques such as Jaya, enhanced Jaya (E-Jaya), Whale Optimization Algorithm (WOA) and Arithmetic Optimization Algorithm (AOA) to calibrate the influential parameters during training. After considering several scenarios, the results show that the accuracy of E-Jaya is better than other optimization techniques. This study on crack identification using improved ANN can be used to investigate the safety and soundness of composite structures. [ABSTRACT FROM AUTHOR]

• Increase in ultimate load up to 55 %. • Effective stiffness increased up to 51 %. • Optimum strength increase is obtained with pre-stressed implants. • Reinforcing with GFRP resulted in an up to 32 % increase in ductility. This paper brings results of the bending testing of oak-wood laminated elements for structural use. The bi-directional laminations were reinforced with six types of implants made of glass fibre reinforced polymer (GFRP), some of which were pre-stressed before embedding in epoxy resin. Previously we reported on improving the mechanical properties of oak-wood laminated elements using carbon fibre implants (CFRP). Although it proved as an efficient improvement of the mechanical properties, it also raised the question of the cost effect to the final product. Therefore, within the larger study on investigating effects of different reinforcement systems, we tested glass fibres reinforced polymer (GFRP) as an alternative. Results showed that the introduction of implants improved the effective stiffness between 4 and 51 % and the ultimate load to failure up to 55 %. Furthermore, not only that insertion of the GFRP layers significantly contributed to the strength and stiffness improvement, but the ductility of the elements increased up to 32 %. Pre-stressing of the glass fibres reinforced polymer implants in tension before their installation contributed to the strength increase to a much greater extent than the increase in the number of layers. The best reinforcement effect is obtained if two layers of pre-stressed GFRP are used. [ABSTRACT FROM AUTHOR]

Steel plate connection is popular in modern timber structures. However, the steel plate may be subjected to corrosion issue due to the presence of moisture in timbers. This paper proposes to replace steel plate with glass fiber reinforced polymer (GFRP) plate for connecting timber elements, so that the durability of the timber structure is expected to be improved. An experimental study is presented on the static and fatigue performances of the proposed GFRP-timber bolted connections. Variables including bolt diameter, number of bolt rows, number of bolt columns were selected to understand their effects on the static and fatigue behaviours of the connections. Failure modes, load–displacement curves, static bearing capacities, fatigue lives, stiffness degradations of the GFRP-timber bolted connections were reported. The residue bearing capacities of the connections were tested after the fatigue loading tests to assess the fatigue effect on the connection static behaviour. This study contributes to the understanding of the mechanical behaviour of GFRP-timber bolted connections. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of pultruded glass fibre reinforced polymer (GFRP) circular hollow section (CHS) columns under concentric and eccentric compression. The member slenderness of the selected columns was in the short, intermediate, and long range, and two different eccentricities were chosen within the column's cross section. Predominant failure modes observed in the experiment include longitudinal splitting and localized delamination buckling. The load-carrying capacities of the concentric column under different slenderness values were quantified and compared with existing design rules. Under eccentric loading, the ultimate loads of the columns decrease with increasing eccentricity and slenderness, and the load–strain behaviour displayed non–linear characteristics due to geometric non-linearity. Failure modes of all the tested columns were well predicted by the FE models, and it was found that splitting material failure was due to hoop matrix tensile rupture. [ABSTRACT FROM AUTHOR]

In this paper, a multiscale approach is presented for strength and tensile modulus prediction of carbon nanotube (CNT) reinforced glass–epoxy composite. At the micro-scale, the three-dimensional representative volume element is obtained by randomly orienting the carbon nanotube in the resin according to the weight percentage. The interphase of the nanotube and resin is modeled using a cohesive element method. The behavior of the resin is accounted with a quasi-brittle non-local damage model. At the Mesoscale, the representative volume element is estimated by using the weight percentage of glass fiber and resin generalized with nanotubes. Finite element analyses were conducted to estimate the effective mechanical properties through numerical homogenization. The effect of different percentages of carbon nanotubes on tensile behavior was investigated experimentally and numerically. The results show that adding carbon nanotubes improves the tensile modulus by about 25% and the tensile strength by about 53%. In the numerical study, the strength of the composite is predicted with good accuracy by modeling the damage of resin, glass fibers, and fracture toughness mechanisms of carbon nanotubes such as bridging and pull-out of carbon nanotubes. A good agreement was observed between the simulation results and the experimental results at different percentages of carbon nanotubes. [ABSTRACT FROM AUTHOR]

This work presents an experimental and a numerical studies on the effect of the phenomenon of porosity on the mechanical properties of Glass Fiber Reinforced Polymer (GFRP). In a first part, material elaboration, as well as its characterization using a three-point bending test to extract the basic mechanical properties of the material, is considered. In a second part, a finite element model is created to simulate the problem of air bubbles broadly. Several cases of different shapes and sizes are simulated. The results show a significant effect on the reduction of load in both tensile and bending cases as the size of the bubbles increases. Furthermore, the second part includes the application of the Artificial Neural Network-Enhanced Jaya Algorithm (ANN-E JAYA) to predict the reduction of the tensile load as a function of different crack lengths obtained from an Extended Finite Element Method (XFEM) model. Next, to verify the accuracy of provided application , a comparison is made with two other applications such as Artificial Neural Network-Jaya Algorithm (ANN-JAYA) and Artificial Neural Network-Particle Swarm Optimization (ANN-PSO). The results of the three algorithms show good convergence, with a slight increase in accuracy for ANN-E JAYA. MATLAB code and data used in this article can be found at https://github.com/Samir-Khatir/GFRP-ANN-E-JAYA.git. [ABSTRACT FROM AUTHOR]

• Precast high HPC sheet piles prestressed with GFRP bars prototypes are presented. • Three Full scale experimental tests on HPC sheet piles prestressed with GFRP bars are carried out; • The flexural behaviour is analysed, up to failure; • One more than three years aged specimen is tested for analysing the influence of the time on the global behaviour. • Effectiveness of simplified analytical sectional models. Since decades, the prestressed reinforced concrete technique, with steel strands, has been widely used in structural and infrastructural fields. The paper deals with the possibility to replace the traditional steel strands with new composite Glass Fiber Reinforced Polymer (GFRP) bars for the prestressing of precast High Performance Concrete (HPC) sheet piles. The use of prestressing combined with composite reinforcing bars could be a good solution in all those cases where the attention of the design is focus on durability, structural lightness, speed of execution, sustainability, economic savings due to the reduction of the structure maintenance. In order to evaluate the potentiality and feasibility of the proposed technique, full-scale experimental tests on sheet piles are carried out at the Laboratory of the University of Rome Tor Vergata. A suitable design and check procedure is also applied and discussed. [ABSTRACT FROM AUTHOR]

Local stress concentration occurs when faults are present in pipelines under pressure. An example of such defects is the problem of corrosion caused by the environment in the field of pipeline installation. In the first part of this paper, we attempt to model the corrosion in the hemi-ellipsoidal form in order to study the locations of stress concentration in the specimens by several experimental cases and their influence on the stress resistance. The Gurson-Tvergaard-Needleman (GTN) mesoscopic damage model is used to simulate the specimens with good accuracy. In the second part, the investigation is extended to a pipe under static pressure with and without the presence of a glass fibre reinforced polymer (GFRP) composite patch. The maximum stress and percent stress reduction in a defected pipe with a hemi-ellipsoidal defect are determined using a 3D finite element model. This part examines the impact of the geometry of the composite patches on the percentage reduction of the maximum stresses in a section of pipeline subjected to static pressure. In the third part, the stresses and the percentage reduction in the maximum stresses are predicted using an artificial neural network (ANN). An inverse problem using ANN and Jaya algorithm is proposed to predict the group level of different sizes of defects under composite patches based on the maximum stress and percentage reduction of stress that the pipe withstands. The new method relates directly to real-world pipeline construction and repair applications. It could be also used for structural safety monitoring. [ABSTRACT FROM AUTHOR]

• Increase in ultimate load up to 55 %. • Effective stiffness increased up to 51 %. • Optimum strength increase is obtained with pre-stressed implants. • Reinforcing with GFRP resulted in an up to 32 % increase in ductility. This paper brings results of the bending testing of oak-wood laminated elements for structural use. The bi-directional laminations were reinforced with six types of implants made of glass fibre reinforced polymer (GFRP), some of which were pre-stressed before embedding in epoxy resin. Previously we reported on improving the mechanical properties of oak-wood laminated elements using carbon fibre implants (CFRP). Although it proved as an efficient improvement of the mechanical properties, it also raised the question of the cost effect to the final product. Therefore, within the larger study on investigating effects of different reinforcement systems, we tested glass fibres reinforced polymer (GFRP) as an alternative. Results showed that the introduction of implants improved the effective stiffness between 4 and 51 % and the ultimate load to failure up to 55 %. Furthermore, not only that insertion of the GFRP layers significantly contributed to the strength and stiffness improvement, but the ductility of the elements increased up to 32 %. Pre-stressing of the glass fibres reinforced polymer implants in tension before their installation contributed to the strength increase to a much greater extent than the increase in the number of layers. The best reinforcement effect is obtained if two layers of pre-stressed GFRP are used. [ABSTRACT FROM AUTHOR]

This work presents an experimental and a numerical studies on the effect of the phenomenon of porosity on the mechanical properties of Glass Fiber Reinforced Polymer (GFRP). In a first part, material elaboration, as well as its characterization using a three-point bending test to extract the basic mechanical properties of the material, is considered. In a second part, a finite element model is created to simulate the problem of air bubbles broadly. Several cases of different shapes and sizes are simulated. The results show a significant effect on the reduction of load in both tensile and bending cases as the size of the bubbles increases. Furthermore, the second part includes the application of the Artificial Neural Network-Enhanced Jaya Algorithm (ANN-E JAYA) to predict the reduction of the tensile load as a function of different crack lengths obtained from an Extended Finite Element Method (XFEM) model. Next, to verify the accuracy of provided application , a comparison is made with two other applications such as Artificial Neural Network-Jaya Algorithm (ANN-JAYA) and Artificial Neural Network-Particle Swarm Optimization (ANN-PSO). The results of the three algorithms show good convergence, with a slight increase in accuracy for ANN-E JAYA. MATLAB code and data used in this article can be found at https://github.com/Samir-Khatir/GFRP-ANN-E-JAYA.git. [ABSTRACT FROM AUTHOR]

• Precast high HPC sheet piles prestressed with GFRP bars prototypes are presented. • Three Full scale experimental tests on HPC sheet piles prestressed with GFRP bars are carried out; • The flexural behaviour is analysed, up to failure; • One more than three years aged specimen is tested for analysing the influence of the time on the global behaviour. • Effectiveness of simplified analytical sectional models. Since decades, the prestressed reinforced concrete technique, with steel strands, has been widely used in structural and infrastructural fields. The paper deals with the possibility to replace the traditional steel strands with new composite Glass Fiber Reinforced Polymer (GFRP) bars for the prestressing of precast High Performance Concrete (HPC) sheet piles. The use of prestressing combined with composite reinforcing bars could be a good solution in all those cases where the attention of the design is focus on durability, structural lightness, speed of execution, sustainability, economic savings due to the reduction of the structure maintenance. In order to evaluate the potentiality and feasibility of the proposed technique, full-scale experimental tests on sheet piles are carried out at the Laboratory of the University of Rome Tor Vergata. A suitable design and check procedure is also applied and discussed. [ABSTRACT FROM AUTHOR]

The economic efficiency of pultrusion can be significantly improved by operating the process at higher pulling speeds. This experimental study analyzed the relationships between the pulling speed, morphology, and mechanical properties of pultruded glass fiber/vinyl ester resin structural composites. Four batches of 150 mm × 3.5 mm flat laminates were produced at pulling speeds of 200, 600, 1000, and 1400 mm/min. Optical and scanning electron microscopy (SEM) were used to study the morphology of the produced flat laminates. The flexural and interlaminar shear properties were determined for both 0° and 90° fiber orientations. The observed difference in the mechanical characteristics of flat laminates can be explained by the presence of bubbles, longitudinal voids, and matrix cracks and by an increase in their density and dimensions with an increase in pulling speed. This study is the first one to demonstrate the possibility of high speed pultrusion of large cross-section profiles suitable for structural application. Authors were able to achieve the pulling speed of 1000 mm/min, increasing the output by as much as 1.7 times as compared to the regular speed pultrusion, without compromising significantly the mechanical performance of produced profiles. The results of this study would be of assistance for a better understanding of high-speed pultrusion. [ABSTRACT FROM AUTHOR]

• The long-term bond durability of GFRP-RC beam structure is investigated; • The mBPE model was modified to consider the splitting of concrete cover; • The effect of working crack on structural bond performance is re recognized; • The long-term bond behavior prediction model of GFRP-RC beam was proposed. This paper investigates the long-term bond-slip behavior of GFRP (glass fiber reinforced polymer)-RC (reinforced concrete) beams. The specimens used in the bond test have been exposed to alkaline accelerated corrosion solution for eight years. In order to more accurately explore the long-term degradation law of the GFRP-RC beam, the factors of sustained load, pre-crack, and specimen form are also considered in this test. The experimental results show that the long-term degradation efficiency of specimens with pre-cracks increases significantly. The interfacial fracture energy and maximum bond strength at fracture failure are reduced by 16% and 23%, respectively. Although the overall bond performance of GFRP-RC beams will deteriorate with service time, the structure usually enters the slow degradation stage. However, the pre-cracks inhibit the arrival of this stage so that the structure will suffer more damage. In order to more intuitively evaluate the safety level of the residual bond performance of the structure in the current state, the long-term degradation prediction model of the GFRP-RC beam is established. [ABSTRACT FROM AUTHOR]

In the paper, effect of quartz additions on the durability of a polymer composite was investigated. The tested material was based on a resin MC-DUR 1200VK with two layers of E-type glass fiber reinforcement of an area density 300 g/m2 with an emulsion binder. The quartz was added in form of powder of fraction 0.1–0.3 mm in different proportions. Durability was measured in terms of specific wear work obtained from the novel tribological tester TT-4. Its important feature was the application of friction belt instead of disc or plate, which made it possible to avoid undesirable impact of the used friction surface and wear debris on the measurement results. Apart from that, standard measurements of flexural strength, shear strength between the layers, tensile strength, proof resilience, and microhardness were performed. It was found that the examined polymer composite increased its wear resistance when it contained 1% of the quartz powder. Similarly, the best results were achieved for the composite with 1% addition of quartz for the shear strength and proof resilience. However, further increase of the addition content caused decrease of the wear resistance. On the other hand, in comparison to the composite with no quartz powder, all other properties worsened after the quartz powder was added in any proportion. Despite no clear trends in characteristics after quartz addition was present, important finding was that it was disadvantageous to increase above 1% addition of quartz powder in the composite of resin MC-DUR 1200VK reinforced with two layers of E-type glass fiber of a weight 300 g/m2 with an emulsion binder. Initial researches also demonstrated that quartz additions might have different effect on the similar composite with other sort of reinforcement. [ABSTRACT FROM AUTHOR]

In this investigation, full-scale reinforced-concrete (RC) circular-beams with glass fibre reinforcement polymer (GFRP) bars and spirals were modeled using nonlinear finite element (FE) program. All the specimens had 3000-mm length. The RC-beams were modeled in a three-dimension space, taking into account the material nonlinearity and the elastic plastic behavior of the concrete, in addition to the elastic characteristics of the GFRP materials. The results of the numerical analysis were verified by comparing them against experimental results of six similar previously tested specimens, that had 500-mm diameter. The analysis included tracing the load-deformation response of the RC circular-beams, load-strains behavior on the surface of the concrete as well as the strains in the GFRP bars. The outputs from the FE analysis showed that the program was able to foresee the experimental results with good precision. The, average, value for the experimental shear strength to the foreseen ones by the FE program, (V exp /V Model) for the six beams, is "1.00 ± 0.05″ with 2.5% COV. After ward, a parametric study was performed to expand and evaluate more parameters such as size effect (200, 300, and 400 mm), span-to-depth (a/d) ratio from 1.5 to 3.5, and spirals' reinforcement ratio between 0.32 and 1.27%. The numerical investigation confirmed the prominent effect of these parameters on the shear strength and behavior of the GFRP-RC circular-beams. [ABSTRACT FROM AUTHOR]

This work investigates the repair of corrosion damage in metallic pipes using glass fiber reinforced plastic (GFRP) patches. The main idea is to analysis of the effect of the thickness of the GFRP patch and the patch surface roughness on the effectiveness of the repair. Commonly, to perform such repair, a composite sleeve wrap is used according to international standards. The work shows that is not necessary a composite sleeve to repair low pressure leaking metallic pipes, only a bonded GFRP patch is sufficient. Burst tests were performed on API 5L gr.B steel hydrostatic specimens with a 10, 15 and 25 mm hole repaired with 100 mm X 100 mm GFRP patches with three different surface roughness. The effectiveness of the repair is strongly dependent on its thickness and surface roughness of GFRP patches. Experimental results show a relation with failure pressure GFRP patch thickness and surface roughness. Higher GFRP patch thickness, elevated failure pressures are presented. Also, high values of surface roughness produce increased failure pressures. A model based on the Linear Elastic Fracture Mechanics is used to obtain an estimate failure pressure using only one algebraic equation. [ABSTRACT FROM AUTHOR]

This study presents experimental investigation and formulation of a new anisotropic nonlinear thermo-viscoelastic constitutive model to understand the time-dependent multi-axial responses of polyamide composites subjected to various histories of mechanical loading at several isothermal temperatures: 20 °C-100 °C. The composites were tested under uniaxial tension along 0° and 90° injection molding directions and the axial and lateral responses of the specimens were recorded. Experimental results indicate that composites exhibit pronounced time-dependent responses, even at low temperatures, and mechanical loadings, even at relatively low strain levels, cause permanent deformations and hysteretic responses. A new constitutive model that accounts for continuous microstructural changes under thermo-mechanical stimuli was formulated to describe the macroscopic anisotropic responses of the composites. The model was derived based on a multi-network approach and the microstructural changes are governed by the deformations of the composites. Elevated temperatures soften the polymers, making it easier to deform the composites, and thus accelerate the microstructural changes. The model is shown capable of describing mechanical responses of polyamide composites under various loading conditions, loading histories, and temperatures. [ABSTRACT FROM AUTHOR]

In this study, the structural behavior of medium density fiber board (MDF) beams reinforced by unidirectional glass fiber reinforced thermoset polyurethane outer layers is investigated by conducting beam bending and vibration tests followed by a parametric study. First, the MDF material properties are determined by 3 point bending and cantilever beam vibration tests. Then the same tests are conducted on the composite sandwich beam specimens produced by hand layup technique and the level of increase in overall stiffness and the ultimate failure loads are determined. The experimental results obtained are found out to be in good agreement with the analytical results and the numerical results obtained using a 1D shear deformable beam model. Finally, a parametric study is conducted to determine the influence of FRP reinforcement for different span lengths and fiber volume ratios. The results obtained from this study show that reinforcing MDF beams by FRP outer layers may considerably increase the flexural stiffness for all span lengths but the ultimate failure load may not be increased for short span lengths due to core shear failure, especially when there is no constraint on maximum displacement. [ABSTRACT FROM AUTHOR]

The electromechanical impedance method (EMI) has shown its damage detection capacity under hazardous environments. Moreover, it is cost-effective, because it involves a bonded piezoelectric transducer (PZT). But the daunting task in the EMI method is the selection of robust and effective damage index, frequency ranges, and combining the information for damage quantification. In this paper, an innovative standard deviation approach is used for the selection of effective frequency ranges. The novice nature of frequency range selection is based on the difference between healthy and damaged state data. Further, a data fusion technique is introduced for damage detection and classification using analytical and experimental data in this effective frequency range. This paper presents four samples of metal and composite with different damage scenarios to demonstrate the applicability of the method. The paper investigates damage in thin aluminium (Al) plate with holes using the EMI method. Further, simulated mass damage and impact damage study to the glass fiber reinforced polymer (GFRP) composite plate. A combined C-index statistical data-driven damage matrices are calculated and further compared with the RMSD index approach. The method looks suitable for identifying the damage location and damage severity simultaneously and is more effective for the less severe damage cases. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]