Short Beam Research Articles

Effects of seawater temperature and NaCl concentration on interlaminar shear behavior of CFRP laminates

The aim of this paper is to study the interlaminar shear behavior of CFRP in critical service conditions. The specimens were immersed in the prepared artificial seawater for 7 months to investigate the ageing time, ambient temperature and salt concentration effects. Analytical balance was used to weight the samples for analyzing the dynamic moisture absorption behavior. Short beam shear tests were carried out to evaluate the interlaminar shear properties. Scanning electron microscopy (SEM) was used to observe the ageing damage and failure morphology. The results show that moisture absorption behavior of composites follows Fickian diffusion law. Moisture absorption rate and the maximum absorption content are mainly affected by ambient temperature but not by NaCl concentration. Compared with ageing time and NaCl concentration, the shear stiffness and shear strength are more sensitive to aging environmental temperature. After exposed in 3.5%–70 °C seawater environment for 7 months, the retention rate of shear strength is only 68.8% and the failure displacement decreases by 20.5%. The shear strength increases first and then decreases with the increase of the maximum moisture absorption, which is mainly related to the release of curing shrinking stress and the damage of interface properties. The shear properties degradation after aging is mainly related to the damage of materials induced by environment (delamination, fiber/matrix interface debonding and matrix cracking).

Experimental demonstration of the short bunch extraction by bunch rotation in a high-intensity rapid cycling proton synchrotron

Short bunch proton beams are of great significance for the applications of white neutron beams and muon beams. The accelerator complex of China Spallation Neutron Source (CSNS) was designed to support the applications mainly based on neutron scattering techniques where the proton pulse length is not very sensitive. Some theoretical and experimental studies have been performed to see if one can extract a short-bunch proton beam by bunch rotation from the rapid cycling synchrotron (RCS) at CSNS. The experimental results at RCS have evidently displayed the bunch lengthening and rotation process, which demonstrates the effectiveness of this method even with a very short available time for the RF gymnastic processes and a high-intensity beam. With a beam power of 50 kW and normal longitudinal emittance at the injection, the proton beam with a bunch length of about 53% with respect to the one in the normal operation mode was obtained and transported to the spallation target. With a reduced longitudinal emittance at injection and the beam power of 30 kW, the shortest extraction bunch length obtained is about 26% of the one in the normal operation mode. Different machine settings have also been tested to show the impact of the desynchronization between the RF and magnetic fields, the influence of the non-adiabatic risetime and the adiabatic decay time of the RF voltage on the extraction bunch length. The experimental results are well consistent with the theoretical and simulated ones. It is interesting to observe that space charge has a beneficial effect on the bunch lengthening which will result in a shorter bunch at the extraction with the later bunch rotation. The controlled desynchronization method between the RF and magnetic fields in an RCS was also proven successful.

Seismic performance of beam to box-column connection by a short stub beam

In this paper, the behaviour of an innovative connection proposed to connect steel beams to box-columns is investigated experimentally and numerically. This connection eliminates the need for using continuity plate inside the box-column by introducing a new load transfer mechanism. The connection also benefits from the extended end-plate connection in its configuration, allowing for fast erection and cost-effectiveness. Two full-scale specimens were tested under reversed load cycles, and parameters including connection rigidity, ductility, and energy dissipation capacity were evaluated. In all specimens, the plastic hinge formed within the beam, and its location complied with the requirements of extended end-plate connections. The specimens could resist 6% story drift with stable hysteretic curves, revealing their qualification for use in special moment resisting frames (SMF) based on seismic provisions of AISC 341–16. Moreover, the specimens showed high ductility and energy dissipation capacity along with reasonable stiffness degradation. Finally, the unnecessity of continuity plates was investigated, which confirmed that the continuity plates were not required in the proposed connection.

Effect of porosity and crystallinity on mechanical properties of laser in-situ consolidation thermoplastic composites

In this paper, the interlaminar bond strength of laser in-situ consolidation (ISC) CF/PEEK thermoplastic composites was investigated under different process conditions. Short beam shear (SBS) tests were conducted to characterize the load-displacement response, the trend of interlaminar shear strength (ILSS), and the mechanism of porosity and crystallinity on ILSS. The experimental results show that porosity has a significant effect on ILSS. Although increasing the tool temperature results in a more stable and homogeneous crystal structure, no correlation is observed between crystallinity and ILSS. The highest measured ILSS value in the heated tool in-situ consolidation (HTISC) group is 59.59 MPa. The aforementioned represents an increase of 61.23% compared to the constant pressure in-situ consolidation (CPISC) group. The proposed method can be used to provide a reference value for acceptance criteria in engineering applications of thermoplastic composites.

Self‐compacting high performance fiber concrete for foundations: Part 2—Fiber orientation and distribution

AbstractAn investigation was executed into the applicability of self‐compacting high performance fiber concrete in foundations. The applied concrete has a concrete cube strength of about 110 MPa and contains 60 kg/m3 hooked‐end steel fibers (LF = 30 mm, DF = 0.38 mm). This publication consists of two parts: (1) Experimental assessment and verification of design rules and (2) assessment of fiber orientation and distribution. In the first part, experiments are described which were carried out to determine the pre‐ and post‐cracking strength properties, the shear resistance of short beams, the anchorage length of rebars, and the shear capacity of foundation slabs supported on piles. The test results were used for a verification and extension of design rules for fiber reinforced concrete (FRC) found in the fib Model Code 2010. The application of the FRC developed can lead to substantial savings in concrete and reinforcing steel. In the present second part, cross‐sections of two slabs and a beam of this testing series have been analyzed with regard to fiber orientation and distribution. An image analysis, executed on 111 concrete areas, indicates that a preferred fiber orientation could not be identified throughout the assessed elements. The data supports the conclusion of a good fiber distribution as well; a strong correlation was obtained for the data set of full images between measured and theoretical relation of fiber orientation and fiber density.

Ultra-Short Dual-Core Photonic Crystal Fiber Polarization Beam Splitter with Round Lattice and As2S3-Filled Center Air Hole

A circular ultra-short As2S3 filled double-core photonic crystal fiber polarization beam splitter is proposed. The finite element method is used to study the performance of the designed photonic crystal fiber polarization beam splitter. By filling high refractive index As2S3 into the central air hole, the coupling performance of the double-core PCF is improved. By optimizing geometric parameters, the splitting length of the circular beam splitter can be as short as 72.43 μm, and the extinction ratio can reach −151.42 dB. The high extinction ratio makes the circular polarization beam splitter have a good beam splitting function. The designed circular double-core photonic crystal fiber has the same cladding pore diameter, which is easier to prepare than other photonic crystal fibers with complex pore structure. Due to the advantages of high extinction ratio, extremely short beam splitting function and simple structure, the designed polarization beam splitter will be widely used in all-optical networks and optical device preparation.

Experimental Investigation of the Interlaminar Failure of Glass/Elium® Thermoplastic Composites Manufactured With Different Processing Temperatures

The aim of this study is to evaluate the effect of the processing temperature on the interfacial failure of glass/Elium® 150 composites. The vacuum assisted resin transfer molding technique (VARTM) was used to manufacture glass/Elium® 150 composites at three different process temperatures: room temperature (24℃), 50℃ and 80℃. The interlaminar shear strength, mode I and mode II interlaminar fracture toughness of the laminates were determined by performing the short beam shear (SBS), double cantilever beam (DCB) and end notched flexure (ENF) tests, respectively. It was found that the increase in processing temperature improved the interlaminar shear strength, mode I and mode II interlaminar fracture toughness by approximately 41%, 66% and 227%, respectively. A combined compressive and shear failure mode was found in SBS tests. Fiber bridging was present for all the composite specimens in DCB tests according to the travelling recording camera images. Fracture surface images obtained by scanning electron microscopy (SEM) after the ENF tests revealed that a better fiber-matrix bonding and a ductile matrix failure were obtained for higher processing temperatures.

СРАВНИТЕЛЬНЫЙ АНАЛИЗ СХЕМ ОПРЕДЕЛЕНИЯ ДИНАМИЧЕСКОЙ ПРОЧНОСТИ СЛОИСТЫХ КОМПОЗИТОВ ПРИ МЕЖСЛОЙНОМ СДВИГЕ

To determine the mechanical characteristics under conditions of intense dynamic impacts of polymer composite materials during interlayer shear, three experimental schemes were proposed and tested: dynamic three-point bending of a short beam, dynamic compression of specimens-plates with notches, and dynamic extrusion of the middle part of specimens in the form of parallelepipeds. To create shock loads and record the response of the samples, the technique of measuring rods is used. The calculation of forces and displacements is carried out according to the Kolsky formulas according to the data of tensometric measurements. Using numerical simulation, one of the fundamental assumptions and conditions for the applicability of the Kolsky method for determining the characteristics of materials in an experiment on dynamic bending of a short beam, namely, the condition of dynamic equilibrium of the sample during loading, was verified. Approbation of the schemes was carried out on samples of a layered composite material with a polymer matrix reinforced with carbon fiber. A comparative analysis of the data obtained using three different test schemes is given. It is noted that the data obtained by the extrusion method are in good agreement with the data determined during dynamic compression of notched specimens. The strength characteristic, determined by the short beam bending method, turned out to be noticeably higher. It has been found that the interlaminar shear strength values determined in the dynamic range are, on average, 25% lower than the static characteristic. Of the three schemes, the most preferable is the scheme for extrusion of the middle part of the parallelepiped specimen, since, unlike beam bending, it allows you to vary and control the loading conditions, and, unlike testing notched specimens, it is symmetrical, which eliminates the appearance of bending moments in the specimen.

Numerical analysis of crack initiation angles and propagation paths in adhesively bonded joints under mixed mode I/II loading using a novel test specimen

In the present work, first, the effect of adherent type on the fracture parameters of a novel mixed mode I/II fracture specimen called bi-material inclined notch short bend beam (BI-SBB) is investigated by using the J-integral method. Then, the crack propagation path is obtained incrementally based on the maximum tangential stress (MTS) fracture criterion. In the next step, the crack propagation path is examined once again using the hybrid XFEM-CZM approach. To do that, in the adhesive region, the elements are enriched and in the adherent and adhesive interface, cohesive surface is used. The results showed that for the mode I loading, based on both methods, the crack propagation path is along the initial crack and inside the adhesive. But under mode II and mixed mode I/II loading, the crack kinks towards the adherent-adhesive interface. However, kinking slop obtain from the hybrid approach is steeper than the path obtained from the MTS criterion. According to the hybrid approach, once the crack reaches the adherent-adhesive interface, crack growth in the XFEM domain ceases and the damage appears on the cohesive surface. Then delamination propagates at the interfaces between the adhesive and adherents as the loading increases.

Study on the Support System Mechanism of Entry Roof with Roof Cutting Pressure Releasing Gob‐Side Entry Retaining Technology

To improve the technical system of the roof cutting pressure releasing gob‐side entry retaining technology (RCPRGERT) and provide reference for the adaptive promotion and optimization of the new technology, the entry support system mechanism with RCPRGERT is studied in this paper. Firstly, the stress structure of the roof cutting short beam is analyzed by the mechanical theory analysis method. Then, taking 8304 working face of Tashan Coal Mine as an example, the stress distribution characteristics of the surrounding rock in different entry retaining stages are simulated by numerical simulation, which provides an important reference for the field support design and puts forward an idea of hierarchical support. Finally, an engineering test is carried out in the experimental working face to verify the design of the retaining entry support, which obtains a well entry retaining effect. The research results in this study provide powerful theoretical and practical references for the promotion of RCPRGERT under similar geological conditions.

ОПРЕДЕЛЕНИЕ ДИНАМИЧЕСКИХ ХАРАКТЕРИСТИК КОНСТРУКЦИОННЫХ МАТЕРИАЛОВ ПО РЕЗУЛЬТАТАМ МОДАЛЬНЫХ ИСПЫТАНИЙ

The paper studies methods for obtaining dynamic characteristics (dynamic modulus of elasticity, loss coefficient) of structural materials, such as concretes and cement mortars, based on the results of experimental modal analysis. Closed expressions for determining the loss coefficient of mechanical vibrations are presented, obtained from solving differential equations of vibrations of single-mass systems, which are caused by vibrations of extended structures in the first forms. The procedure of modal analysis of short beams made of test samples of structural materials is presented. The procedure for calculating the natural frequencies of the first forms of vibration of beams is presented. Based on the solution of the equation, a formula is presented for determining the damping coefficients and the dynamic modulus of elasticity of the beam material.

Investigation of TiO2 Nano Filler in Mechanical, Thermal Behaviour of Sisal/Jute Fiber Reinforced Interpenetrating Polymer Network (IPN) Composites

In this work, various proportionate (0%, 1%, 3% 5% & 7%) of titanium di-oxide nano-filler was utilized as particulate matter along with the sisal/jute fiber reinforcement, in the view to increase the physical properties of the composite materials. Beside, as matrix material the mixture of Epoxy (E) and Polyurethane (PE) was chosen with the proportionate of 70 and 30 wt.% respectively, in order to extract the specific qualities of both the matrices to achieve the interpenetrating polymer networks (IPNs). Moreover, to exactly find out the thermo-mechanical characteristics of the sisal/jute fiber reinforced IPN composites, tests like thermo-gravimetric analysis (TGA), tensile, flexural, Impact, short beam strength and water absorption tests were carried out as per standards. It was found that, incorporation of 5% of TiO2, increases the mechanical properties such as tensile, flexural, impact and short beam strength. Similarly, incorporation of TiO2 into IPN matrix enhances the thermal stability and water absorption resistance. All the obtained values of various filler weight % of TiO2 were compared with each other against with and without particulate incorporated IPN laminate in the purpose of using the same in construction industries.

Effect of matrix modification by addition of fillers on the interlaminar shear strength and healing efficiency of spread carbon fiber/woven carbon fiber reinforced polymers encompassing self-healing

This study examines the effect of matrix modification by addition of fillers on the interlaminar shear strength and healing efficiency of spread carbon fiber (SCF)/woven carbon fiber (WCF)/epoxy (EP) laminates encompassing self-healing. The SCF/WCF/EP laminates with fillers and microcapsules containing a healing agent mixed with a UV fluorescent dye were fabricated. The fillers used were talc and cellulose nanofiber (CNF). The short beam shear testing was carried out to evaluate the apparent interlaminar shear strength and healing efficiency of the laminates. Moreover, the damaged areas after testing were observed under UV light to investigate the relation between the microstructure and the damage behavior. Results showed that the damage behavior of the laminates modified with fillers changed, and the healing efficiency of the laminates with fillers increased compared to that without fillers.

Effect of MAPP on Interfacial Shear Strength of PP/Rice Straw Fiber Composites

Polypropylene (PP) composites filled with rice straw fiber were prepared and characterized to contribute to the realization of a low-carbon society. Generally, the mechanical properties of composites composed of cellulose fiber such as rice straw fiber and nonpolar polymer such as PP decrease due to poor interfacial adhesion. This paper reports the compatibilizer effects of maleic anhydride modified polypropylene (MAPP) on the mechanical properties of PP/rice straw fiber composites. As a result, interfacial shear strength (IFSS) between resin and fiber measured by a short beam test changes with the MAPP content, reaching a maximum value at 1 phr as a similar trend as changes in their tensile strength. Therefore, the improvement of tensile strength indicates the enhancement of interfacial adhesion between PP and rice straw fiber.

Flexural Performance of Layered Macro Fiber Reinforced Concrete Short Beams

Flexural Performance of Layered Macro Fiber Reinforced Concrete Short Beams

Enhancement of filament wound glass fiber/epoxy-based cylindrical composites by toughening with single-walled carbon nanotubes

In this study, the effect of incorporating nano-sized fillers (noncovalently functionalized with ethoxylated alcohol chemical-vapor-deposition-grown SWCNTs) within an epoxy resin on the performance of filament wound glass fiber (GF)-based cylindrical composites (GFCCs) was investigated. For this purpose, SWCNTs were dispersed with the concentration of 0.05 and 0.1 weight percent (wt.%) within an epoxy resin using mechanical stirring and calendaring (3-roll-milling) techniques. The rheological behavior of the SWCNT incorporated epoxy mixture was characterized to determine the suitability of blends for the filament winding process. It was revealed that the viscosity value of the resin was not significantly affected by the addition of SWCNTs in given concentrations. Moreover, contact angle measurements were also performed on the SWCNT/epoxy blends dropped on the GF for the evaluation of the wettability behavior of the GF in the presence of the SWCNTs in relevant concentrations. Eventually, it was observed that the wettability behavior of GF was not reasonably affected by the presence of the SWCNTs. The double cantilever beam (DCB), flexural, and short beam shear (SBS) tests were performed on the reference and SWCNT-modified GFCC specimens to evaluate the effects of the SWCNT presence on the interlaminar fracture toughness and out-of-plane properties of GFCCs. The fractured surfaces after the DCB and SBS tests were analyzed under the scanning electron microscopy to reveal the toughening mechanisms and the filler morphologies. Consequently, although SWCNT incorporation was on the outermost layer of GFCCs, it was found that the interlaminar shear strength (ILSS) values and Mode I interlaminar fracture toughness values of the curved composite samples were improved up to 22 and 216%, respectively, due to the presence of the SWCNTs.

Dynamic modeling and analysis of center rigid body Timoshenko beam model based on unconstrained mode

The transverse deformation of the beam will lead to the longitudinal shortening deformation, and this transverse-longitudinal deformation coupling will bring the dynamic stiffening effect term on the generalized rigidity of the beam model. For the rotating beam structure, the centrifugal force will cause axial tension, with coupling axial and transverse deformation of the beam and bring additional geometric stiffness, which is more obvious for the thick short beam. The central rigid body-Timoshenko beam model with a large-range-motion center was investigated. Firstly, the dynamic model with centrifugal forces was established by means of the Timoshenko beam theory and the Hamilton principle. Secondly, the unconstrained mode concept was introduced, and the unconstrained mode shape functions and natural frequencies were solved with the Frobenius method. Finally, numerical simulations were carried out to explore the difference of generalized stiffness between the unconstrained mode and the constrained mode at different constant speeds, and the effects of centrifugal forces on the model under unconstrained mode condition were discussed.

Strut-and-tie and finite element modelling of unsymmetrically-loaded deep beams

A strut-and-tie model (STM) for unsymmetrically-loaded deep beams is proposed in this paper through simplifying the unsymmetrical problem into symmetrical and anti-symmetrical problems. This analytical solution starts with derivations of principal compressive stress fields based on the theory of elasticity. Furthermore, a minimum-strain-energy criterion is adopted to define the optimal STM geometry from the stress field, including the dimensions of struts and nodal zones, and strut angles. The proposed STM is validated against 140 test results, including 14 unsymmetrically-loaded deep beams and 126 symmetric deep and short beams, and finite element models (FEMs) for the 14 unsymmetrical deep beams. The FEM is also used to simulate the load-displacement relationships of unsymmetrical deep beams that could not be modelled by STM. In addition, a worked example is presented to demonstrate in detail the procedure of analysing an unsymmetrically-loaded deep beam using the proposed solution. In summary, the STM predictions are in good agreement with experimental results and FEM predictions. Therefore, the proposed STM is capable of giving accurate and consistent predictions for both symmetrical and unsymmetrical deep and short beams.

Microfocused ultrasound with visualization: Consensus on safety and review of energy-based devices.

BackgroundMicrofocused ultrasound with visualization (MFU‐V; Ultherapy®, Merz North America) is US Food and Drug Administration‐cleared as a non‐invasive procedure that lifts the soft tissue of the neck, submentum and brow, and improves lines and wrinkles on the upper chest. Several other energy‐based devices are in use in countries outside the USA where they are marketed for indications similar to those of MFU‐V, although published studies supporting these indications are limited and none of the other devices provides visualization or verification they reach the superficial musculoaponeurotic system.MethodsDue to the evolving landscape of ultrasound technology as more devices enter the market, seven global thought leaders who are qualified experts on the use of various high‐intensity focused ultrasound (HIFU)/MFU‐V technologies convened to review data from an independent evaluation of the software, thermal characteristics, transducer acoustics and ultrasound therapy of MFU‐V and three other ultrasound‐based devices.ResultsThe independent testing demonstrated the devices have key differences in several parameters that play a role in safety and effectiveness. Specifically, MFU‐V has visualization capability but the other devices lack that feature. Other differences include the retention of patient history, consistent size and uniformity of thermal coagulation points (TCPs), precise localization of energy concentration at the focal point, and reliable thermal regulation during use. The expert panel established a consensus on the types of preventable complications associated with ultrasound‐based energy devices and techniques for preventing and treating complications.ConclusionsThe independent test results of MFU‐V/HIFU devices and the consensus panel conclusions provide strong support that real‐time visualization and the capability to detect coupling, features found only in MFU‐V, help prevent complications and enhance the safety and effectiveness of energy‐based devices. The independent evaluation also revealed that MFU‐V has several additional features that play key roles in safety and clinical effectiveness, including uniformity of TCPs, tight thermal regulation, large focal gain, and short beam length, that were not found collectively in any of the HIFU devices.

Influence of preliminary thermal aging on the residual interlayer strength and staging of damage accumulation in structural carbon plastic

Aging of composites is a pervasive problem that leads to mechanical properties degradation, reduced design life of a structure and premature accidental failure. The work is devoted to an experimental study of the preliminary temperature aging effect on the residual mechanical properties of structural CFRP. The joint use of test systems and systems for registration and analysis of acoustic emission signals was applied. The Short Beam Shear Test of CFRP specimens were carried out using the short beam method. The tests were carried out on universal electromechanical systems Instron 5882 and Instron 5965 in accordance with the recommendations of ASTM D2344. In the process of loading the samples were continuously recorded by using the acoustic emission signals system AMSY-6. A piezoelectric sensor with a frequency range of 300-800 kHz was used. The test and diagnostic systems were synchronized during the tests. In the course of the work the values of the interlayer shear strength were determined for the samples of CFRP. Typical types of the sample destruction are illustrated. When analyzing the change in the mechanical properties of the carbon fiber reinforced plastic from a temperature increase the critical values of temperatures were established in which a sharp decline in the strength and elastic characteristics of materials occurs due to an active destruction of the binder. The graphs of the energy parameter dependence and frequency characteristics of acoustic emission signals on time have been constructed and analyzed. The estimate of the processes of damage accumulation in composites is carried out. The change of the damage accumulation mechanisms was illustrated. The obtained results illustrate the effect of elevated temperatures and the duration of their impact on the mechanical behavior of structural CFRP specimens during the static tests for the interlayer shear.