Short Beam Research Articles

Composite Structural Supercapacitors: High-Performance Carbon Nanotube Supercapacitors through Ionic Liquid Localisation.

Composite structural supercapacitors (SSC) are an attractive technology for aerospace vehicles; however, maintaining strength whilst adding energy storage to composite structures has been difficult. Here, SSCs were manufactured using aerospace-grade composite materials and CNT mat electrodes. A new design methodology was explored where the supercapacitor electrolyte was localised within the composite structure, achieving good electrochemical performance within the active region, whilst maintaining excellent mechanical performance elsewhere. The morphologies of these localised SSC designs were characterised with synchrotron X-ray fluorescence microscopy and synchrotron X-ray micro-computed tomography and could be directly correlated with both electrochemical and mechanical performance. One configuration used an ionogel with an ionic liquid (IL) electrolyte, which assisted localisation and achieved 2640 mW h kg−1 at 8.37 W kg−1 with a corresponding short beam shear (SBS) strength of 71.5 MPa in the active area. A separate configuration with only IL electrolyte achieved 758 mW h kg−1 at 7.87 W kg−1 with SBS strength of 106 MPa in the active area. Both configurations provide a combined energy and strength superior to results previously reported in the literature for composite SSCs.

Effect of Thermal Exposure on Residual Properties of Wet Layup Carbon Fiber Reinforced Epoxy Composites.

Ambient cured wet layup carbon fiber reinforced epoxy composites used extensively in the rehabilitation of infrastructure and in structural components can be exposed to elevated temperature regimes for extended periods of time of hours to a few days due to thermal excursions. These may be severe enough to cause a significant temperature rise without deep charring as through fires at a small distance and even high-temperature industrial processes. In such cases, it is critical to have information related to the post-event residual mechanical properties and damage states. In this paper, composites are subjected to a range of elevated temperatures up to 260 °C over periods of time up to 72 h. Exposure to elevated temperature regimes is noted to result in a competition between the mechanisms of post-cure that can increase the levels of mechanical characteristics, and the deterioration of the resin and the bond between the fibers and resin that can reduce them. Mechanical tests indicate that tensile and short beam shear properties are not affected negatively until the highest temperatures of exposure considered in this investigation. In contrast, all elevated temperature conditions cause deterioration in resin-dominated characteristics such as shear and flexure, emphasizing the weakness of this mode in layered composites formed from unidirectional fabric architectures due to resin deterioration. Transitions in failure modes are correlated through microscopy to damage progression both at the level of fiber-matrix interface integrity and through the bulk resin, especially at the inter-layer level. The changes in glass transition temperature determined through differential scanning calorimetry can be related to thresholds that indicate changes in the mechanisms of damage.

Influence of hybridization on the mechanical and dynamic mechanical properties of aramid/S2-glass hybrid laminates

This work investigates the effect of hybridization and stacking sequence on the response of S2-glass/aramid/epoxy interply hybrid laminates, focusing on flexural, short beam, dynamic-mechanical results and, especially, quasi-static indentation (QSI) properties. Different laminates of comparable thickness were manufactured by vacuum infusion, one with only aramid fabrics ([K]4S), one with only S2-glass fabrics ([G]8S) and six interply hybrids, namely [G6K5], i.e. six S2-glass layers on top of five aramid layers (asymmetric), [G8K4] [G10K3], [K2G4]S, [G2K]S2 and [G4K2]S. QSI tests were used to determine absorbed energy, maximum energy and peak load, and the in-plane damage was analyzed. Significant differences in mechanical and dynamic-mechanical properties (pairing effect) were observed for the [K2G4]S, [G2K]2S, [G4K2]S and [G8K4] hybrids, and the adhesion factor (A) presented the closest correlation with energy absorption capacity of the laminates. The results have shown that hybridization of aramid composites with S2-glass may enhance impact absorption, and a positive hybrid effect was observed for the laminates with S2-glass fibers on the top surface, [G6K5], with peak load and absorbed energy (9.9 kN and 55 J, respectively) higher than that of the pure laminates [G]8S (5.9 kN and 41 J) and [K]4S (8.6 kN and 46 J).

Parametric analysis and optimization of tubes filled with double-arrowed negative Poisson's ratio under transverse impact loadings

At present, most of the crash performance studies for negative Poisson's ratio (NPR) filled tubes are focused on the axial impact loadings. This paper focused on the transverse impact load response of filled tubes for double-arrowed negative Poisson's ratio (DANPR) structures. The effects of each structural parameter of the double-arrowed cell on the peak collision force (PCF) and specific absorption energy (SEA) of the filled tube were analyzed by numerical simulations and three-point bending experiments. Cell beam thickness, cell half-width, cell long beam angle, cell short beam angle and impact velocity were found to have significant influences on the PCF and SEA and the deformation of the filled tube. The optimal structural parameters of the DANPR filled tubes were obtained by a surrogate model and an optimization algorithm. The results shown that the maximum value of SEA and the minimum value of PCF are contradictory relationships and cannot be obtained simultaneous. However, it can be found that after optimization, the SEA can be changed to about 510 kJ/kg with the same PCF, which is an increase of about 36.45%. If its SEA is kept constant, the PCF becomes about 3.2 kN after optimization, a decrease of about 37.74%. Therefore, the practical manufacturing needs to make tradeoffs according to the weights of both, which also provides a reference for the design of DANPR filled tubes.

Low-velocity impact studies on Kevlar/Epoxy composites reinforced with carboxyl functionalized Graphene

The addition of nanoparticles as fillers improves the properties of polymer matrix composites. In this work functionalized Graphene Platelets are added to Kevlar-reinforced epoxy composites and their mechanical properties such as tensile, short beam strength and low-velocity ballistic response are evaluated. For comparison, composites prepared with 0.25, 0.5, and 0.75 wt% filler addition was compared with the condition of no filler addition. The fractured samples were examined to understand the failure mechanisms involved. The results indicated that the sample with 0.5 wt% had superior tensile, shear and energy-absorbing characteristics. A lower reinforcement weight percentage (0.25%) was unable to effectively transfer the loads while higher reinforcement percentage (0.75%) showed premature failures due to agglomeration. At the optimum reinforcement, a sufficient amount of nano-fillers passes through the matrix and the functionalization assists in good fiber–matrix adhesion through surface bonding. This leads to high interfacial properties giving high resistance to impact motion. In addition, the nanoparticles in the matrix phase help in matrix toughening giving resistance to cracking. This is evident from the micro and macroscopic fracture images which show a high fiber interaction and the least matrix failure. The lower damage area and the higher fiber pullouts also indicate the effectiveness of 0.5 wt% reinforcement.

Shear Strength Degradation Model for Performance-Based Design of Short Coupling Beams

Shear Strength Degradation Model for Performance-Based Design of Short Coupling Beams

Sensitivity analysis of shear modulus on Lateral – Torsional Buckling of PFRP Beam

An elastic constant of Pultruded Fiber Reinforced Polymer (PFRP) has a wide range of value, especially for the shear modulus which is generally ranging from 3 to 5 GPa. Lateral – torsional buckling (LTB) is a type of global buckling occurs when the beam is under bending about its major axis. The instability happens when the beam twists and move laterally. This research analyses and evaluates the sensitivity of changing the shear modulus on the critical LTB load of PFRP beam using a numerical approach by ABAQUS. It is found that the critical LTB load increases 17% for short beam and 27% for long slender beam when shear modulus increases from 3 to 5 GPa. The influence of changing of shear modulus is reduced when load position moves from top to bottom flange. It is suggested that the determination of proper shear modulus (upper and lower bound of values) is of crucial in design and in validating the compatibility between experimental work and numerical or theoretical analysis.

The use of GPR to investigate the effect of steel fiber distribution on the mechanical behavior of FRC

The present work focuses on the steel fiber distribution in self-consolidating concrete short beams. The objective is to assess the feasibility of the ground penetrating radar (GPR) in evaluating the homogeneity of fibers within concrete materials, for use in testing laboratories to study the modes of placing and compaction employed for preparing specimens during quality control or material development. Self-consolidating concrete beams were cast, tested, and evaluated. A GPR survey employing a concrete scanning system with a shielded 1.2 GHz center frequency was performed on self-consolidating casted short beams just before a monotonic four-point bending test was carried out. After failure, a representative short beam was cut and the resulting slices were photographed to obtain the position and distribution of the steel fibers. Results were processed using dedicated software and an integrated analysis was accomplished. The digital and processed images correlated well with the GPR mappings in a single radar trace mode. In particular, the GPR amplitude provides information on the steel fiber density that was used as reinforcement in concrete specimens.

First operations with caesium of the negative ion source SPIDER

The negative-ion based neutral beam injector for heating and current drive of the ITER plasma (ITER HNB) is under development, at present focusing on the optimization of the full-scale plasma source in the SPIDER test stand. The production of H− or D− ions in the ion source is based on the low work function surfaces obtained by caesium evaporation. This paper describes the caesium conditioning procedure and the corresponding beam performances during the first operation of SPIDER with caesium. Technical solutions to overcome present limitations of the test stand are described. The influence of source parameters on the caesium effectiveness was investigated in short beam pulse operation; with total radio-frequency (RF) power of 400 kW and filling pressure below 0.4 Pa, and a limited number of extraction apertures, a negative ion current density of about 200 A m−2 was extracted in hydrogen, with beam energy lower than 60 keV. Beam optics and beam uniformity were assessed thanks to the acceleration of isolated ion beamlets. A possible procedure to accelerate a uniform beam was demonstrated at low RF power. The results obtained in this first investigation provided key indications on the operation of one of the largest existing sources of accelerated negative hydrogen-like ions.

Investigation of Interlaminar Shear Properties of CFRP Composites at Elevated Temperatures Using the Lempel-Ziv Complexity of Acoustic Emission Signals.

Three-point bending tests on Short Beam Shear (SBS) specimens are performed to investigate the interlaminar shear properties of plain weave fabric CFRP composites. The tests are performed in a controlled environmental chamber at two different elevated temperatures. The interlaminar shear properties of the specimens remain largely unaffected by the testing temperature. However, the SEM micrographs show different damage progressions between the specimens tested at 100 °C and 120 °C. Fibre ruptures and longer delamination between the plies, as a result of a high temperature, are observed in the specimens tested at 120 °C, which are not observed in the specimens tested at 100 °C. In addition, the acoustic emission activities during the tests are investigated by using piezoelectric sensors. The information-theoretic parameter, the Lempel-Ziv (LZ) complexity, is calculated for the recorded acoustic signals. The LZ Complexities are used for identifying the occurrence of the first delamination failure in the specimens. Additionally, the two features of the acoustic signals, LZ complexity and Weighted Peak Frequency (W.P-Freq), are used for distinguishing the different damage sources in the CFRP specimens. The results are well-supported by the time-frequency analysis of the acoustic signals using a Continuous Wavelet Transform (CWT).

Strain energy form coefficients for bending of short beams having full and thin-walled arbitrary cross section with application for FEM and Airfoils

The aim of this work is to develop a new generalized formula and a numerical computation program for evaluating the energy form coefficient of a complex and arbitrary cross section for full and thin-walled cross section with respect to any central axis, for the bending of beams of small lengths in comparison with the transverse dimension of the section. This coefficient plays a very important role in the calculation of the deformation energy of beams subjected to bending under the effect of a shearing force for short beams. It also enters in the formulation of FEM bending model, in order to calculate the stresses and the strains due to the external forces. The application is made for complex sections used in various fields of construction and in particular for airfoils designed for aerospace construction. A method is developed to calculate this coefficient as a function of the rotation of the central axes. The calculation of the area, the moments, and the product of inertias with respect to the central axes is necessary. The formula for calculating this coefficient is presented as a definite integral of a non-analytical function determined point by point along the direction of the application of the shear force. This function is based on the calculation of the partial static moments. The calculation of the latter is based on the development of a technique by subdividing the upper part of the section into adjacent common triangles at one point for the full solid section or by segments on the boundary for the thin-walled section. To speed up the process of numerically calculating this integral with high precision and reduced time, Gauss Legendre quadrature of order 40 is used. The calculation of the distribution of the tangential stress as well as its maximum value is determined. A shear shape coefficient is therefore determined. In the second part of this work, an application is made for the static calculation by the FEM of a hyper static beam with a view to determining the influence of this coefficient on all the parameters of resistance and bending stiffness as a correction of the classical model of bending by the FEM. A study of the error made by the classical bending model on our shear effect model is presented. A coefficient of efficiency of a section is presented.

Effect of addition of graphene nanoplatelets on the mechanical properties of triaxially braided composites

Braided composites possess an advantage of good out-of-plane mechanical properties, near net-shape manufacturing, impact and damage resistance. This work aims to investigate the effect of graphene nanoplatelet (GNP) addition on glass fibre triaxial braided composites (TBC). Tensile, flexural, and short beam shear tests were conducted to investigate the mechanical performance of the pristine and hybrid TBC. A numerical model was framed to estimate the material properties of hybrid TBC which were further used as input for the finite element simulation. Results indicate a 15% increase in tensile strength, a 20% increase in flexural strength and a 10% increase in interlaminar shear strength (ILSS). The experimental results were in good agreement with the analytical results. The braided architecture along with proposed GNP combination further enhances mechanical properties and enables gradual failure of the composite which is a desirable property for load bearing structures.

Shear strength evaluation of RC D-Regions based on Single-Panel Strut-and-Tie model

In existing shear test databases of reinforced concrete D-regions (discontinuity or disturbance regions), most data points are concentrated in parameter ranges of high main reinforcement ratio, small overall dimensions, or low concrete strength. Based on regression analysis of these databases, large model errors in effective coefficients of strut compressive strength (hereafter referred to as strut coefficients) for strut-and-tie models (STMs) have been obtained. In this study, a uniformly distributed (or unbiased) large-scale shear database is generated through a mechanics-based cracking strut-and-tie model (CSTM), which has been validated against extensive test results. Then a strut coefficient with a simple form and comprehensive consideration of various design parameters is proposed through regression analysis. On the other hand, the traditional STM presents a tedious design procedure and uncertainty in structural reliability caused by the subjectivity in geometric modeling. In order to simplify the design procedure and eliminate the uncertainty, a unified shear design equation based on the strut coefficient is proposed for D-regions that the single-panel STM can well simulate. The accuracy of the unified equation is verified by an extensive shear test database consisting of simple and continuous deep beams, corbels, squat shear walls, and short coupling beams.

Interlaminar shear strength and failure analysis of composite laminates with double and triple hybrid configurations

Interlaminar shear strength (ILSS) of fiber-reinforced hybrid composites was investigated for double and triple fiber hybridizations. For this purpose, woven carbon, glass, and Kevlar fibers were used for the production of hybrid composites with different stacking sequences. Hybrid samples had a quasi-isotropic structure, and they were subjected to the short beam shear (SBS) tests according to the ASTM D2344 standard. Failure and fracture surfaces of the samples were analyzed along the loading direction with the help of microscopic photos. The degree of the hybridization effects was determined with concerning the rule of mixture in terms of ILSS and peak load, separately. Additionally, a statistical one-way ANOVA analysis for hybrid composites showing significant differences between the results was performed. The results from this study indicated that the location of fibers in the hybrid composites was a key factor regarding the ILSS and failure mechanism along the out-of-plane direction.

МЕТОД РЕКОНСТРУКЦІЇ БАЛОЧНИХ МОСТІВ БЕЗ ЗУПИНКИ ЇХ ЕКСПЛУАТАЦІЇ УЛАШТУВАННЯМ НОВОЇ ЗБІРНО-МОНОЛІТНОЇ ПРОЛІТНОЇ БУДОВИ

The article contains the method of reconstruction of an emergency bridge structure by installing a new span construction without stopping its operation taking into account difficult engineering and geological conditions of construction site on the example of bridge which is situated at the state significance road M-21, near the village Pultovtsy of Vinnitsa region. Have been reviewed the technical condition of short and medium-length beam bridges, which span structures are a system of string-concrete prestressed bridge beams which are often operated in Ukraine.
 Have been described methods for increasing the capacity of bridges, which were used in Soviet times. Have been proved the systemic nature of defects and damages of prefabricated string-concrete spans and bridge structures after widening. Have been described the rational ways to strengthen such bridges. Have been proved the low efficiency of their reinforcement by standard methods due to the critical corrosive wear of the reinforcing prestressed fibers of the main beams. Have been chosen the optimal method by replacing the superstructure from the considered methods.
 Have been proposed a precast-monolithic structural scheme of the bridge with increased carrying capacity according to modern requirements.Have been developed an analytical and finite element model of the stress-strain state of reinforced precast-monolithic bridge structure, taking into account the difficult engineering and geological conditions of the construction site.
 Have been proven the needed to strengthen existing pile foundations. Have been developed a constructive scheme for strengthening the bridge supported by installing additional rows of piles.
 Have been planned to be erected the construction of a new superstructure and additional rows of piles to strengthen the foundations of bridge supports in two stages without stopping of bridge structures exploitation but only with partial blockage of traffic. Have been proposed an effective technological installing diagram for this.

A new digital beam position and phase measurement implementation based on a field programmable gate array for the high intensity heavy-ion accelerator iLinac.

A new digital beam position and phase measurement (BPM) system was designed for the ion-Linac accelerator at the high intensity heavy ion accelerator facility. The fundamental and second harmonic signals are retrieved from the BPM electrodes to simultaneously calculate their respective beam positions and phases. All data acquisition and digital signal processing algorithm routines are performed in a field programmable gate array (FPGA). The position and phase information are obtained by using the in-phase and quadrature demodulation method. A practical and straightforward method is used to generate the second harmonic reference signal for processing the second harmonic beam signal. The reconfigurable filters are integrated into the FPGA to allow the measurement of short beam pulse length. The laboratory test results show that the achieved phase resolution is better than 0.2° and 0.03° when the input signal is -60 and -45 dBm, respectively. A position resolution better than 30 μm was achieved for an input power level of approximately -60 dBm, and it can reach 7 μm with the input power higher than -45 dBm. The entire execution time of the algorithm is accomplished within 3.4 µs, which provides a sufficient reaction time for the fast beam interlock signal to the machine protection system. The performance of this newly designed prototype BPM electronics was evaluated with the online proton beam.

Carbon fiber/epoxy composite property enhancement through incorporation of carbon nanotubes at the fiber-matrix interphase – Part II: Mechanical and electrical properties of carbon nanotube coated carbon fiber composites

A new method to achieve a uniform coating of carbon nanotubes (CNTs) onto carbon fibers (CFs) has been developed which enables the scalable fabrication of CNT modified CF/epoxy composites. In this method, CNTs are coated onto CFs by immersion into a CNT/water suspension resulting in a uniform coating of CNTs. Unidirectional CF/epoxy composites with the CNT layer of 100–200 nm were fabricated by a prepregging method and mechanical/electrical properties were evaluated. The results show that the compressive, short beam shear strengths and Mode I interlaminar fracture toughness were improved by 22 %, 11 % and 48 % respectively after the incorporation of only 0.39 wt% CNTs. Electrical conductivities in 90˚ and through thickness direction were improved by two or three orders of magnitude (Log Resistivity: 1.24 and 2.31) respectively. These results indicate the importance of designing the fiber–matrix interphase to improve fiber reinforced polymer composite mechanical and electrical properties.

Experimental Study and Numerical Simulation for the Seismic Performance of an Innovative Connection between a Flat CFST Column and an H Beam

A concrete-filled steel tube (CFST) column permits convenient and fast construction, and its use for high-rise buildings is increasing. Meanwhile, the CFST structure has great potential for use in residence buildings, owing to its smooth evaluation. A connection for a flat CFST column has also attracted increasing attention from scholars. An innovative connection between a flat CFST column and an H beam was proposed and cyclically tested in this paper. The flat CFST column, with a width that is equal to the thickness of the partition wall, was adopted to avoid the protrusion of the column into the corner of the room. The configuration of the innovative connection was introduced, and three full-scale specimens, considering different relative positions of the beam and column, were tested under cyclic load to failure. The seismic performance, including the failure mode, ductility, etc., were revealed and evaluated. It was indicated that the plastic hinge of the connection was prominently removed outward, due to the reinforced short beam and the interior-diaphragm, verifying the reliability of the innovative connection. Furthermore, an elaborated finite element model was developed, and the results of the finite element simulation were compared with the experimental simulations. This comparison confirmed the reasonability of the developed finite element model.

Shear Property and Uniform Vertical Load Capacity of Bamboo I-Beams

Bamboo oriented strand boards (BOSB) are very suitable for application in construction structures because of their excellent mechanical properties. This research investigated the shear performance of bamboo I-beams composed of BOSB to verify the structural performance of I-beams. Short beam shear tests and uniform vertical load capacity tests were performed to investigate the effects of various factors on the properties of bamboo I-beams. The results showed that shear bearing capacity and uniform vertical load capacity of bamboo I-beams exceeded the requirements for performance-rated I-Joists in APA PRI-400-2021. The shear bearing capacity, stiffness, and failure types of bamboo I-beams were determined by the web materials, flange–web joint type, and beam depth. Increasing the bamboo I-beam depth without changing the flange dimensions had no significant effect on the shear bearing capacity and stiffness of bamboo I-beams. The shear bearing capacity and stiffness of wooden orientated strand board webbed I-beams were almost half of those of bamboo I-beams with the same depth. The shear bearing capacities of specimens calculated based on the shear bearing capacity calculation formula of I-beams recommended in the Canadian standard were reasonably close to the experimental results. The uniform vertical load capacity of bamboo I-beams gradually decreased as the depth of the bamboo I-beam increased from 300 mm to 500 mm.

Interfacial and Interlaminar Shear Strength of Unidirectional Viscose Fibre-Reinforced Epoxy Composites—an Overview of the Comparability of Results Obtained by Different Test Methods

In this study, the apparent interfacial and interlaminar shear strength (IFSS and ILSS) of single fibres and unidirectional (UD) viscose fibre-reinforced epoxy composites were characterised using different test methods. Microbond and pull-out tests were used to analyse the IFSS of single fibres embedded in epoxy and the transverse tensile test was applied to measure the IFSS of UD fibre-reinforced composites. The short beam shear test, single edge notched bending test (SENB), double-notched tensile test and double-notched compression test were applied to characterise the ILSS. The composites were produced from continuous tows with fibre mass fractions of 20%, 30% and 40% and fibres of different fineness (1.7, 3.3 and 28.0 dtex). The results showed that the different test procedures led to different trends of ILSS depending on the fibre mass fraction and fibre fineness used. The transverse tensile test revealed that the IFSS decreased with increasing fibre mass fraction and fibre diameter. A different trend was found with the short beam shear test and the SENB test for the ILSS. Here, higher values were detected with increasing fibre mass content, and the influence of the fineness was less noticeable. The double-notched shear tests (tensile and compression) showed a different trend: the ILSS increased with increasing fibre mass fraction from 20% to 30%. With a further increase to 40%, the ILSS tend to decrease slightly. An influence of the fibre fineness on the ILSS could not be statistically proven. The different trends of the test methods are attributed to the constitution of the composite and the different load application caused by the test procedures.