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• The static behaviour of notched PPS/GF specimens was investigated. • V-shaped notched specimens were manufactured and tested. • Different notch root radii and manufacturing processes were considered. • Different approaches for the static strength assessment were compared. In this paper the static behaviour of polyphenylenesulfide reinforced by 40% wt. short glass fibre net-shaped plain and notched specimens was investigated. The specimen geometries were obtained by injection moulding and the experimental results were compared with data obtained from machined specimens with the same material and geometries. All data were reanalysed according to several models available in the literature for orthotropic materials, to find a rapid and efficient assessment tool for predicting the strength of short glass fibre reinforced materials in the early design stages. To this end, approaches based on orthotropic linear elastic stress analysis were considered, namely the linear elastic peak stress criterion, the nominal net-stress criterion, the point stress criterion, the average stress criterion, the strain energy density criterion, the generalized stress intensity factor-based approach, the inherent flaw model, the damaged zone criterion and the Hitchen criterion. Among the models, the average stress criterion and the generalized stress intensity factor-based approach provided the most accurate predictions of the static strength, ranging from −10% to +9% and from −19% to +2%, respectively, compared to the experimental data. [ABSTRACT FROM AUTHOR]

With increasing demand for sustainable and long-lasting materials, seawater sea-sand engineered cementitious composite (SS-ECC) has emerged as a promising alternative to conventional concrete in near-ocean construction projects. Glass fiber reinforced polymer (GFRP) bar with excellent corrosion resistance is an ideal choice for these applications. This study evaluated the bond performance of GFRP bars embedded in normal-strength ECC with polyvinyl alcohol (PVA) fibers and high-strength ECC with polyethylene (PE) fibers through pull-out tests. Additionally, tests were conducted on GFRP bars in pristine ECC made with freshwater and river sand for comparison. Further investigation explored the structural properties and uncovered load transfer mechanisms. Results indicated that saline content facilitated early cement hydration of normal-strength ECC, resulting in finer pore structure (10.5% lower porosity and 12.5% lower sorptivity), slightly enhanced compressive performance (1.2% higher compressive strength and 8.3% higher elastic modulus), denser microstructure at GFRP-ECC interface (13.7% lower porous transition zone thickness, 19.2% narrower transition zone and 19.7% higher Ca/Si ratio), and superior bond performance (28.3% higher bond strength and 22.6% higher fracture energy). Conversely, saline content imposed a limited impact on the mechanical properties of high-strength ECC, primarily attributed to the ultra-fine microstructure and early strength characteristics exhibited by the silica fume (SF)-based cementitious binder. [ABSTRACT FROM AUTHOR]

The current research aims to analyze the mechanical characterization of sandwich materials through a three-point flexural test. The sandwich structures in question composed of balsa wood as a core and four different types of fiber reinforced vinyl ester composite facesheets, namely Glass, Basalt, Glass/Carbon, and Basalt/Carbon. The sandwich panels were prepared using the vacuum infused processing method. The primary objective of this investigation is to explore the feasibility of utilizing basalt fibers for the production of structural parts in shipbuilding and replacing the already existed glass fibers. The flexural test was carried out with using three-point flexural test with varying the span length from 120 mm, 180 mm, 220 mm. Additionally, an analysis of variance (ANOVA) was then carried out to compare the mean values of properties deduced from these tests. The results showed that using basalt fibers instead of glass fiber reinforced enhanced the flexural stiffness of the sandwich structure. The flexural strength and modulus are shown to depend on span length and fiber type. The flexural modulus increases with an increase in span length. Similarly, flexural strength increases in glass fiber-based structures, while a slight reduction is observed in basalt fiber-reinforced structures the larger span length. The findings of this research suggest that basalt fibers hold potential as a replacement for glass fibers in producing structural components in shipbuilding. These results offer valuable information that can aid in the design and optimization of sandwich materials in shipbuilding. [ABSTRACT FROM AUTHOR]

The applications of physics-informed neural networks (PINNs) in material parameters identification of composite laminates are currently research highlights. We present an efficient physics-constrained deep learning approach based on PINNs for solving material parameters of composite laminates. We explain the details of incorporating first-order shear deformation theory as physical information into designed loss functions. The performance of proposed approach is demonstrated through a numerical example of idealized composite laminated plates under uniform pressure conditions. The computational errors of material parameters are less than 0.1%. Moreover, the applicability of transfer learning (TL) has been illustrated for inversion of material parameters with few datasets. The ambition is to improve the identification efficiency of carbon and glass fiber reinforced plies material parameters across various loading conditions. Intensive studies are conducted to compare convergence time between with and without TL through a numerical example under thermal-force coupling conditions. The comparison shows PINNs with TL obtain average error of 0.144% and 0.077% in carbon and glass fiber reinforced plies, which is better than without TL of 0.472% and 0.284%, respectively. The proposed work emphasizes the effective application of PINNs-based approach that combines first-order deformation and data-driven solution features for inverse solving material parameters of composite laminates. [ABSTRACT FROM AUTHOR]

Adhesive bonds are subject to multiple environmental conditions that can affect their mechanical performance during service. Therefore, it is important to evaluate the influence of temperature on adhesive strength, as it can impact joint safety and should be considered during the design phase. This study presents an analysis of the effect of high temperatures on the mechanical behaviour of joints made with highly elastic adhesives, specifically a polyurethane and a silicon-modified polymer. Shear and tensile tests were conducted at temperatures of 23, 50, and 80 °C using dumbbell specimens for tensile tests and single lap specimens (SLJ) for shear tests. The tests were performed with two different substrates, aluminium (Al) and glass fibre reinforced polyester panel (GRP), and with varying adhesive thicknesses. These tests aim to assess the impact of temperature conditions on the mechanical properties of the adhesive and the behaviour of the joints. The analysis of the experimental results reveals that the adhesive degrades when exposed to high temperatures, resulting in reduced strength and stiffness, and less linear behaviour. Furthermore, this work involves the determination of a model able to reproduce the mechanical behaviour of hyperelastic adhesive at high temperatures, considering diverse constitutive modelling approaches. To achieve this, a testing protocol was conducted on basic uniaxial and planar specimens. The results indicate that the Ogden N=2 model is the most suitable for representing the non-linear behaviour of the hyperelastic adhesive at high temperatures. In contrast, the Mooney Rivlin model is more suitable to represent the material behaviour under ambient conditions. To conclude this work, the law has been satisfactorily validated by comparing the results of tests carried out on SLJ specimens with different adhesive thicknesses. [ABSTRACT FROM AUTHOR]

In this work, the glass fiber reinforced plastic (GFRP) composite pipes used as sewerage pipes in oil and gas field environments were studied. The accelerated aging experiments were carried out under the simulated environments of three typical oil field media which including circulating air, simulated produced water and standard simulated oil. Scanning electron microscopy (SEM) was adopted to observe the microscopic morphology of the aged GFRP tubes under the three conditions. The microstructural characteristics of the aged tubes and the evolution process of internal defects were also analyzed and evaluated in combination with micro-CT technology. The attenuation pattern of the hoop tensile strength of the aged pipes was measured via the separation disk method, and the service life prediction was carried out based on the Arrhenius theory with the hoop strength as the life index. The results show that the accumulation of aging time and continuous heat input will aggravate the expansion of internal pores and cause the aggregation of small-volume defects into large-volume defects. Especially in the simulated oil environment, which has the highest sensitivity to defects. The maximum porosity reaching 1.5 % and the maximum volume of individual defects exceeding 106 μm3 after aging for 4000 h at 95 °C. The thermal aging process under the three environmental conditions had similar aging characteristics, and interfacial damage of the glass fibers was observed in all of them. The variability of hydrothermal aging is related to the hydrolytic behavior of the glass fibers, which is associated with the progressive dissolution damage of the SiO 2 network in the glass fibers, as well as the breaking of silane bonds. Thus, the hydrothermal environment had the most significant effect on the hoop tensile strength decay. Ultimately, 75 % strength retention was taken as the end-of-life indicator. The predicted service life based on the Arrhenius model for the three environments of thermo-oxygen, hydrothermal and simulated oil were 23.5, 23.1 and 28.5 years at 20 °C, and 12.2, 4.9 and 10.3 years at 40 °C, respectively. [ABSTRACT FROM AUTHOR]

The aim of this contribution is to investigate whether the order of load ratios applied to a textile structure impacts the biaxial stiffness behaviour of the structural textile itself. These investigations are performed based on biaxial tests on an architectural woven glass fibre fabric, a representative of such membranes. The first part of the paper investigates the existence and extent of load history dependency in the material response. Biaxial test results show that effects of a previous load history on the weave geometry cannot be eliminated by further load cycling in all biaxial stress ratios. Moderate to strong effects are recognized in two stress ratios, although not in both weave directions. The second part of the paper examines how these effects influence material stiffness parameters and structural calculations. Two boundary value problems are investigated: a pressure chamber test and a roof structure. Parameters obtained by fitting biaxial tests with or without history are considered. By incorporating an adaptive load-ratio dependent scheme, highly predictive numerical results are obtained, showing that while the effect of load history may appear small in the biaxial tests and pressure chamber test, it can be significant in complex structural problems like roof structures. [ABSTRACT FROM AUTHOR]

This study provides an experimental and numerical evaluation of the energy absorption performance of a 3D-printed star hourglass honeycomb structure with a novel design made from pure and reinforced PLA by chopped carbon fibers and continuous glass fiber. The study further investigates the energy absorption response of this structure after the shape recovery due to thermal stimuli under the quasi-static compressive loading. As an additive manufacturing process, Fused Deposition Modeling is used to produce the specimens with pure and reinforced PLA filament. The difference in the nonlinear response of PLA due to plasticity and damage in tension and compression loading directions, as a feature that helps the shape recovery, is considered in mechanical response analysis using the Finite Element approach. Then, in the obtained results distinguish constitutive laws in tension and compression mechanical properties are employed leading to a failure model using the appropriate algorithm consistent with the experiments. According to the obtained results which reveal good agreement regarding the experimental results, by designing appropriate auxetic configuration selecting suitable geometry parameters, and employing the proper material with diverse properties in tension and compression directions, it is possible to fabricate a lattice structure inherits the shape recovery after the compression deformation which exhibits acceptable energy absorption performance even the second shape recovery. [ABSTRACT FROM AUTHOR]

In this work, we shall implement a novel modeling approach to simulate interface debonding and bulk cracking in realistic 3D printed fiber reinforced composites. The materials are firstly manufactured with the Selective Laser Sintering of PA12 polymer powder embedding glass fibers and additive particles. An in-situ compression test on a cylindrical sample is conducted. X-ray Computed Tomography (XRCT) technique is employed to obtain experimental fracture images and to provide a complete 3D description of the morphology of each component for constructing a completely Realistic 3D microstructure mesh Model (R3M). Meanwhile, an Extended Phase Field Model (EPFM) is presented considering gradient plasticity and interfacial debonding mechanisms. Following that, numerical simulations are conducted, by using the EPFM and R3M, to investigate the fracture behavior in the fiber reinforced composite. In contrast to existing works, a qualitative comparison of fracture phenomena in experiments and simulations is conducted. Anisotropic behavior of the 3D printed fiber reinforced composite is observed both in the experiments and simulations. Our results reveal that the EPFM can well capture the experimental damage phenomena, including fiber/matrix debonding, fiber breaking and pore connecting in 3D printed fiber reinforced composites, by employing the R3M where the microstructure directly arises from the experimental XRCT. • An extended phase-field model (EPFM) with gradient plasticity and interface is proposed. • XRCT technique is employed to provide mesh models and experimental fracture results. • Numerical simulations for 3D printed fiber reinforced composites are carried out. • The proposed EPFM can well capture the experimental fracture phenomena. [ABSTRACT FROM AUTHOR]

• 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]

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]

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]

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]

In the classical composites, the hybridization of carbon and glass fibers may cause a positive hybrid effect, which relies on the increase of carbon fibers failure strain, when compared to the pure carbon-based composites. This paper focuses on the investigation of the influence of the volume ratio of carbon and glass fibers hybridization in Fiber Metal Laminates, on the static tensile strain at which the laminate fails. Analytical, numerical and experimental studies have proven that the increase of carbon fibers failure strain occurs in the Fiber Metal Laminates and can be explained by the presence of thermal stresses caused by the manufacturing process at elevated temperature. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of compression on pristine specimens and the compression after impact (CAI) response of wood-based sandwich structures. Nine different types of sandwiches, made with plywood core and different aluminum or composite (carbon or glass or flax fiber) skins, are studied. Impact energy levels were fixed at 5 J, 10 J and 15 J in order to create significant defects. Failure modes and damage scenarios are analyzed. The influence of different skins with plywood core is explained in terms of residual strength, residual stiffness, and specific properties. It is shown that this type of structure exhibits very interesting compression properties in terms of specific strength, which is superior to a reference sandwich used for aircraft flooring, and in terms of behavior, with large plateau areas that can be useful for crash issues. [ABSTRACT FROM AUTHOR]

A fatigue constitutive model valid for the composite constituent will be presented in this paper. The composite behaviour will be obtained by means of the serial/parallel mixing theory that is also used as a constitutive equation manager. The constitutive formulation is coupled with a load advancing strategy in order to reduce the computational cost of the numerical simulations. Validation of the constitutive formulation is done on pultruded glass fiber reinforced polymer profiles. Special emphasis is made on the comparison between the experimental and the numerical failure mode. [ABSTRACT FROM AUTHOR]

To achieve high levels of lightweight design in automotive or aerospace industry, it is necessary to optimize certain composite material systems concerning their lightweight potential. With sandwich composites, which generally consist of a core which is coated with two face-layers, it is possible to reduce the overall part weight while increasing the specific mechanical properties under inhomogeneously distributed loads. Hereby the sandwich core ensures the load transmission while the face layers absorb the tensile and compressive loads occurring at bending stress. The aim is to increase the efficiency of said sandwiches while minimizing the weight per area by using for example (fiber-) reinforced face layers and foamed core materials. Polyphenylene sulfide (PPS) is an important high temperature, engineering thermoplastic polymer. Because of its properties it is used in the automotive, aerospace and electronics industry. As polyphenylene sulfide has a high processing temperature and requires processing know-how, there a few scientific studies on its foaming behavior. To understand the process-structure-property relationship of this material system, an experimental study on the foaming behavior of neat polyphenylene sulfide and long glass fiber reinforced polyphenylene sulfide using the high-pressure foam injection molding process is conducted. As it is also attractive from a manufacturing point of view to reduce the number of manufacturing steps and to operate with the source materials from the beginning of the process an in-line compounding and foam injection molding process is used. This allows the manufacturing of integral sandwich structures with connected, fiber reinforced face and foamed core layers in one shot via "direct thermoplastic foam injection molding". With the findings of this study researchers and manufacturers of neat and fiber reinforced PPS parts are able to identify process parameter boundaries and the influence of these parameters on the sandwich structure and mechanical properties. [ABSTRACT FROM AUTHOR]

In this work, multi-objective robust optimization of a two-dimensional tri-axial braided hollow pillar was presented. Two conflicting objectives, weight and cost, were simultaneously minimized under the constraint of mechanical safety requirements based on Probability theory. The material properties were taken into account with three design variables and two uncontrollable variables. The three design variables were the total fiber volume fraction, the relative volume fraction of carbon fiber in the total fiber volume fraction and the braid angle. The two uncontrollable variables were the fiber volume fraction of the carbon fiber tows and of the glass fiber tows. A mesoscopic analytical model of the two-dimensional tri-axial braided composites (2DTBC) was adopted to obtain the necessary mechanical parameters. Appropriate surrogate models were used to investigate the approximate relationship between the mechanical properties and the input variables, which could significantly reduce the calculation cost. The optimization problem was solved with Pareto optimal solutions through a multi-objective evolutionary solver. The results indicate that, in general, the uncertainty in the total fiber volume fraction was the main decisive factor in the robust optimization and mechanical analysis of the monolithic construction. [ABSTRACT FROM AUTHOR]

Abstract In this paper, compaction behaviors of glass fiber non-crimp fabrics (NCFs) were investigated via finite element analysis (FEM). Firstly, the compaction mechanism of NCFs was analyzed, it suggested the compaction process is mainly characterized by the decrease of macro pores and micro pores, a novel and reasonable constitutive model (porous elastic) was proposed. Then, the feasibility of modeling the compaction process for NCFs with the porous elastic material via FEM was explored. A macroscale model of NCF was established firstly, the simulation complies well to the experimental results. Then, the mesoscale models were attempted, and the effect of model parameters on simulation results were investigated, including the model size, platen location, warp cross-sectional shape. Results show that the size of mesoscale model and compaction platen position have little effect on the compaction behavior, while the cross-sectional shape of the warp yarn has a slight influence on the simulation results. Finally, compared the warp yarn cross-section changes of simulation with experimental data, it was revealed that variations in yarn cross sections in the model have a good agreement with experimental results, except that the macro-porosity differs slightly. [ABSTRACT FROM AUTHOR]

Abstract The paper presents the influence of PU foam with an addition of glass fiber on the buckling resistance of an I-beam. Three beam types were considered: an aluminum beam (AA), a composite AA-PU beam and a composite AA-PU-CFRP beam. Each beam was made with two C-profiles connected by webs. The flanges were reinforced by flat bars. Channels were made by bending 0.08 mm thick aluminum alloy 6061-T6 sheets. Flat bars were made from aluminum alloy 6061-T6 2.0 mm in thickness. The metal sheets components were connected by Refill Friction Stir Spot Welding RFSSW and Resistant Spot Welding RSW technologies. The composite AA-PU beam additionally has the stiffening of the web by polyurethane foam with the addition of glass fiber. The PU foam filled up the I-sections in such a way that rectangular cross-sections were obtained. The composite belka AA-PU-CFRP beam was made like the composite AA-PU beam, but with CFRP plates glued to the flanges. The beams were subjected to three-point bending tests. The load-bearing capacity for a buckling resistance was analyzed. The results from experimental tests were used in numerical analysis carried out by the ADINA System program based on the Finite Element Method. [ABSTRACT FROM AUTHOR]

Abstract This study investigated the usability of hybrid sandwich structures as facade panels. The explored sandwich structure was made of mineral-glass fibre reinforced polymer (GFRP) skins and a GFRP truss core, fabricated by means of a novel manufacturing method. The compressive and shear specific strengths of the panels were assessed and compared with a few common lightweight structures to verify that the manufactured truss core had comparable values. Three-point bending tests indicated that the polyurethane foam used (required for the manufacturing process) had negligible mechanical contribution. Full-scale panels were tested under a distributed load. The tests were simulated using the three-dimensional finite element method to predict the pressure at which mineral cracks appeared in order to avoid their occurrence in the design phase. The simulation results exhibited good agreement with experimental data, and the model was validated in terms of deflection and strain responses. The occurrence of cracks and their propagation were numerically reproduced using the concrete-damage plasticity model. The link between the connector and crack positions in the mineral skin was highlighted in this study. [ABSTRACT FROM AUTHOR]

Highlights • Detailed numerical analysis of S0/A0 mode conversion phenomenon on the delamination based on spectral element method. • Analysis of wavefield (including S0/A0 mode conversion) distribution through the thickness in the delaminated region. • Implementation of the model for impact damage. • Full wavefield measurements and numerical results show good agreement. Abstract In this paper results of numerical analysis of S0/A0 elastic wave mode conversion at discontinuities in glass fibre reinforced polymer (GFRP) plates are presented. Analysis of S0/A0 mode conversion effect at Teflon inserts simulating delamination (circular Teflon inserts located at a different depth, Teflon inserts with different shapes at the same depth) and impact damage with energies 5 J, 10 J and 15 J is conducted. Numerical analysis is based on spectral element method (SEM) in the time domain. Numerical model includes a composite plate, a piezoelectric transducer and bonding layer for transducer and damage. Numerical model takes also into account the influence of material damping. Numerical results are compared with experimental results based on full wavefield measurements using scanning laser Doppler vibrometry (SLDV). It is shown that based on effects of S0/A0 mode conversion it is possible to detect the damage and determine its shape and size. [ABSTRACT FROM AUTHOR]

Abstract A hollow concrete column (HCC) is a structurally efficient construction system and uses less material. Conventionally, HCCs are reinforced with steel bars, which are prone to corrosion. This study explored the use of glass-fiber-reinforced-polymer (GFRP) composite bars as reinforcement for HCCs and evaluated the effect of the reinforcement ratio on HCC structural behavior. A total of six HCCs reinforced longitudinally with GFRP bars with different reinforcement ratios (1.78%, 1.86%, 2.67%, 2.79%, 3.72, and 4.00%) were prepared and their behavior was investigated. The different reinforcement ratios were achieved by changing the bar diameter (12.7 mm, 15.9 mm, and 19.1 mm) and number of bars (4, 6, 8, and 9 bars). The results show that increasing the diameter and number of bars enhanced the strength, ductility and confinement efficiency of HCC. For columns with equal reinforcement ratios, using more and smaller-diameter GFRP bars yielded 12% higher confinement efficiency than in the columns with fewer and larger-diameter bars. The crushing strain of the GFRP bars embedded the HCC was 52.1% of the ultimate tensile strain. Lastly, the axial-load capacity of the GFRP-reinforced HCC can be reliably predicted by considering the contribution of the concrete and up to 3000 μ ε in the longitudinal reinforcement. [ABSTRACT FROM AUTHOR]

Abstract The paper analyses the possibilities and effectiveness of using infrared thermography with optical thermal excitation by reflection approach in the case of multilayer composites reinforced fibers. The advantages and limitations of this technique have been demonstrated via composites reinforced with three types of fibers: glass, aramid, and carbon. The most common defects in such structures are: delaminations, fiber cracks, matrix cracks, and separation of fibers from the matrix. The paper describes some results of the numerical simulations of defects detection using optical IR thermography with the emphasis made on the inspection of multi-layer composite materials. The simulations were conducted in order to determine the detection of defects depending on the depth of their location under the front surface of composite material as well as their geometrical dimensions. [ABSTRACT FROM AUTHOR]

Abstract This study reports the recently found critical drawback of glass fibers as compared with carbon fibers. GFRP and CFRP composites were placed into a general water bath at 80 °C until saturation for accelerated hygrothermal ageing. After ageing, the impact properties of CFRP composites improved. For GFRP composites, however, their performance under low-velocity impact degraded significantly. After removing the moisture absorbed during ageing, the strength of CFRP laminates increased to 95.75% of its original value. In contrast, GFRP composites only retained 74.65% of the strength after hygrothermal treatment. Compared with CFRP composites, GFRP composites were much more susceptible to hygrothermal attack. Tensile tests on single glass fiber were carried out which proved that both the strength and elongation-at-break decreased significantly after hygrothermal ageing. Decrease in glass fiber strength after ageing is the major mechanism responsible for the reduced performance of GFRP composites. [ABSTRACT FROM AUTHOR]

Abstract This research investigates experimentally and analytically a novel one-way slab system reinforced with either basalt fiber-reinforced polymer (BFRP) or glass fiber-reinforced polymer (GFRP) longitudinal bars embedded in fiber-reinforced concrete (FRC) incorporating basalt macro-fibers (BMF). Twelve one-way concrete slab strips were prepared and tested to failure under four-point loading configuration. The investigated parameters included the type of fiber-reinforced polymer bars (BFRP and GFRP), the longitudinal reinforcement ratio ρ f (1.4 and 2.8 ρ bf , where ρ bf is the balanced reinforcement ratio), and the volume fraction of the fibers added (0, 0.5, 1, and 2% per volume). The test results demonstrated the promise of BMF to enhance the flexural performance of the tested slab strips in terms of ductility and load-carrying capacities. The formulations of different available codes and design guidelines were used to predict the test results. Comparison between the experimental and predicted results showed the adequacy of the models to predict the flexural performance of the tested slab strips. The findings of this study demonstrated the potential of using the BMF as alternatives to conventional fibers in flexural concrete members. [ABSTRACT FROM AUTHOR]

Abstract Heated GLARE, a Fibre Metal Laminate with an integrated heater element, has a promising potential as de- or anti-icing system in aircraft structures. To investigate the long-term durability of heated GLARE previously reported thermal cycling tests up to 12,000 cycles are extended up to 144,000 cycles and moisture conditioning is included. Similar testing up to 72,000 cycles is performed on FM906 glass-fibre epoxy laminates with an integrated heater element to study the influence of the aluminium layers in GLARE. In all test results the initial decrease in interlaminar shear values from 0 to about 10,000 thermal cycles is followed by a recovery phase and a resumed decline after roughly 60,000 cycles. The decrease in ILSS is expected to be caused by internal stress relief which is counteracted by the positive effect of physical ageing due to elevated temperature exposure. Thermal cycling of conditioned samples generally resulted in slightly larger decreases in interlaminar shear strength for both heated GLARE and heated FM906 glass-fibre epoxy laminates. [ABSTRACT FROM AUTHOR]

Abstract Estimation of the remaining useful life (RUL) based on the elastic strain energy density using the non-contacting and full-field capabilities of Thermoelastic Stress Analysis (TSA) was applied to E-glass fiber-reinforced polymers (GFRPs) subjected to high-cycle fatigue loading conditions. A quantitative prediction was successfully attained during the material's intermediate and final fatigue life phases. The initial state of the specimen was used as the reference data for defining a damage parameter that enabled the detection of visually imperceptible subsurface cracks. [ABSTRACT FROM AUTHOR]

Abstract Pultruded glass fiber reinforced polymer (GFRP) sections face a critical issue of premature web crippling failure when loaded in the transverse direction. However, limited research on the web crippling behavior of asymmetric sections like channel section was reported in the literature. In addition, the effect of specimen length on the web crippling behavior has not been explicitly investigated. This paper presents an experimental study on the web crippling behavior of pultruded GFRP channel sections under transverse bearing load. Four channel sections with various dimensions were tested under two transverse loading conditions, i.e. interior-two-flange (ITF) and exterior-two-flange (ETF). For each section, two specimen lengths were adopted to study the effect of specimen length on the web crippling behavior. Therefore, three variables including sectional dimensions, specimen length and loading conditions were considered in the experimental program. Two failure modes, namely web-flange junction failure and web buckling failure, were observed. The load-displacement curves and web crippling capacities of all specimens were reported and compared. Finally, design equations were proposed considering the failure mechanisms. The predicted web crippling capacities generally agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

Abstract A wide experimental campaign of 40 three-point-bending tests on small-scale foamed concrete beams in the low-to-medium density range (400–800 kg/m3) is presented. The considered "extrudable foamed concrete" can keep its dimensional stability at fresh state. In order to increase the mechanical characteristics while preserving lightweight properties associated with the low densities, bi-directional grids of glass fibers are placed close to the bottom external face of the beams. Additionally, the use of short polymer fibers embedded within the cementitious matrix is investigated. Different specimen characteristics are explored, including: three curing conditions, three target dry densities, and two fiber contents. The presence of bi-directional grids increases the bending strength values for all the examined conditions: for 400 kg/m3 the increase is up to 1700%, and for higher densities is, on average, 175%. The curing condition affects the failure mode: specimens cured in water with densities higher than 600 kg/m3 exhibit a premature failure of the grid reinforcement without separation from the concrete substrate, whereas in those cured in air and cellophane typical bond failures with detachment occur. Only for densities of 800 kg/m3 the further addition of short polymer fibers produces non-negligible flexural strength increase of 31%, on average. [ABSTRACT FROM AUTHOR]

Abstract The present paper investigates the damage monitoring using the piezoresistive effect on the glass fiber-reinforced polymer (GFRP) omega stringers reinforced through-the-thickness by tufting. The experiments consisted of the electric resistance measurements from the tufted yarns during the pull-off tests on omega stringers. Acoustic emission (AE) and digital image correlation (DIC) techniques were also performed throughout the tests in order to evaluate the acoustic activity and the strain field respectively. Furthermore, non-supervised AE clustering was carried out and aided to determine the main damage events. The results presented that electric resistance measurements are in good correlation with the AE clusters, especially with those related to the delamination and tuft yarns fracture. Besides, these damage events are well distinguished from the electric resistance data. Also, DIC images exhibited that electric resistance is sensitive to local strain field as expected to piezoresistivity measurements. Therefore, tufting reinforcements have shown to be an interesting monitor of the structural health in real time, further their well-known ability to increase the mechanical out-of-plane properties of laminate composites. [ABSTRACT FROM AUTHOR]

Abstract The influence of nano-organic montmorillonites (nano-OMMTs) on mode I and mode II interlaminar fracture toughness of continuous glass fibre reinforced ammonium polyphosphate polypropylene (CGF/PP/APP) composites was experimentally studied in this paper. Nano-OMMTs modified CGF/PP/APP unidirectional prepreg composites were fabricated by hot-melt impregnation process. To investigate the effect of nano-OMMTs on the interlaminar fracture toughness of composites, double cantilever beam (DCB) test and end-notched flexure (ENF) test were conducted to obtain the mode I initiation interlaminar fracture toughness (G IC init.), mode I propagation interlaminar fracture toughness (G IC prop.), and mode II initiation interlaminar fracture toughness (G II C init.) of samples, respectively. Through comparison against to the neat CGF/PP/APP composites, with the addition of 6.5 wt% nano-OMMTs into PP matrix, the G IC init. , G IC prop. , and G II C init. of composites can be enhanced from 0.502 kJ/m2, 0.746 kJ/m2 and 0.623 kJ/m2 to 0.712 kJ/m2, 1.119 kJ/m2, and 1.195 kJ/m2, respectively. Finally, it was found that nano-OMMTs in matrix can act as "pins", which could absorb energy in the forms of nano-particles pullout and enhance the interlaminar fracture toughness values in DCB and ENF tests. [ABSTRACT FROM AUTHOR]

Abstract The interlaminar property is essential to the application of fiber reinforced composites for the overall performance. For the purpose of enhancing the interlaminar properties, the unidirectional Glass Fibre Reinforced Plastics (GFRP) laminates were fabricated by adding carbon nanotubes (CNTs) buckypaper to the mid-plane layers under different curing pressures (1 MPa, 2 MPa, 3 MPa). In order to study the enhancement mechanism of the CNTs buckypaper, a series of experiments were designed and conducted based on double cantilever beam (DCB), end notch flexure (ENF) and interlaminar shear strength (ILSS) tests followed by scanning electron microscope (SEM) examination to study the surfaces of the specimens. It was observed that the modes I and II interlaminar fracture toughness of GFRP embedded with CNTs buckypaper were relatively higher than those without CNTs buckypaper. Considerable improvements in interlaminar shear strength of the laminates were obtained with the integration of the CNTs buckypaper between the interlayers. The micro-structure of the enhanced mixed interface of fiber-resin-CNTs responsible for interlaminar strengthening was further studied with the help of SEM. It was found that the higher curing pressure could increase the inter-diffusion of the resin and CNTs offering a stronger interfacial adhesion. The interlaminar characteristics of the specimens cured at 2 MPa pressure were found to be relatively superior with optimal interlaminar fracture toughness and interlaminar shear strength. [ABSTRACT FROM AUTHOR]

Abstract The present study presents an experimental investigation into the real-time monitoring of the drilling process of Glass Fiber Reinforced Polymer (GFRP) composite with Carbon Nanotubes (CNTs) buckypaper sensor. The spray-vacuum filtration method was employed to synthesize CNTs buckypaper sensor and then embedded into the GFRP to serve two purposes namely interlaminar enhancement and sensor monitoring the drilling process of the GFRP. Both modes I and II interlaminar fracture toughness tests were conducted to ascertain the enhancement ability of the buckypaper. Considerable improvements in both modes of fracture toughness were recorded in the specimens with CNTs buckypaper interlayer. For the CNTs buckypaper acting as a sensor, drilling experiments were carried out on the GFRP where real-time information of the drilling process particularly the drilling tool position could be predicted. This can be crucial in cases where drilling parameters like the feed rate have to be changed at a certain drilling depth in order to reduce or eliminate the exit delamination. The Scanning Electron Microscope (SEM) was finally employed to study the enhancement ability of the CNTs buckypaper and the microstructure of the drilled holes. The current work has substantiated the possibility of using CNT buckypaper both as an interlaminar enhancement and as a sensor to monitor the drilling process. [ABSTRACT FROM AUTHOR]

Highlights • This paper deals with the mechanical response of glued in rods. • It takes into account the diameter of rods, the material of rods and the direction of the grain of the timber. • It gives an overview and presents known design models and technical approvals comparing the different approaches. • Comparison between the experimental results and the main equations of the literature review. • The authors propose one equation for the case where the bars are parallel to the timbers' grain. • In addition, another one for the case where the bars are perpendicular to the timbers' grain. Abstract We address the mechanical response of glued in rods, taking into account parameters such as rod diameter, the material properties of the rods (carbon or glass fibre-reinforced polymer), and the grain orientation of the timber (rods parallel and perpendicular to the timber grain). All the experimental setups employ pull-out tests, where rods are glued in only on one side of the specimen, and these tests are assessed at the premises of the Laboratory for Composite Materials and Composite Structures at the University Claude Bernard Lyon I. In addition, we give an overview and present known design models, technical approvals and regulations, national standards, and guidance papers, comparing the different approaches among them and with the experimental results. Good agreement was shown and further useful results were observed. [ABSTRACT FROM AUTHOR]