Search Results (48)

Three-dimensionally printed cement-based composites emerge as a research hotspot in the fields of construction engineering in recent years. Current research primarily focuses on the reinforcement mechanisms of individually incorporated fibres, while a significant gap remains in the synergistic effects of hybrid fibre systems. This study investigates the effects of mono-doping (0.2 wt.% and 0.4 wt.% by the mass of the cement) and hybrid-doping (0.1 wt.% + 0.1 wt.% by the mass of the cement) with 3 mm polypropylene, basalt, and carbon fibres on the fresh-state properties and mechanical behaviours. Through quantitative characterisation of the flowability and mechanical performance of short-fibre-reinforced 3D-printed cementitious composites (SFR3DPC), coupled with comprehensive testing including digital image correlation, X-ray diffraction, and scanning electron microscopy, several key findings are obtained. The experimental results indicate that the addition of excess fibres reduces fluidity, which affects the mechanical performance and make the anisotropy of the composites more pronounced. While the single addition of 0.2 wt.% CF shows the most significant improvement in flexural and compressive strengths, the hybrid combination of 0.1 wt.% CF and 0.1 wt.% BF shows the greatest increase in interlayer bond strength by 26.7%. The complementary effect of the hybrid fibres contributes to the damage mode of the composites from brittle fracture to quasi-brittle behaviour at the physical level. These findings offer valuable insights into optimising the mechanical performance and improving defects of 3D-printed cementitious composites with short fibres. Full article

Shaping or splitting of a Gaussian beam is often desired to optimise laser–material interactions, improving throughput and quality. This can be achieved holographically using liquid crystal-on-silicon spatial light modulators (LC-SLMs). Until recently, maximum exposure has been limited to circa 120 W average power with a Gaussian profile, restricting potential applications due to the non-linear (NL) phase response of the liquid crystal above this threshold. In this study, we present experimental tests of a new SLM device, demonstrating high first-order diffraction efficiency of η = 0.98 ± 0.01 at 300 W average power and a phase range Δφ > 2π at P = 383 W, an exceptional performance. The numerically calculated device temperature response with power closely matches that measured, supporting the higher power-handling capability. Surface modification of mild steel and molybdenum up to P = 350 W exposure is demonstrated when employing a single-mode (SM) fibre laser source. Exposure on mild steel with a vortex beam (m = +6) displays numerous ringed regions with varying micro-structures and clear elemental separation created by the radial heat flow. On molybdenum, with multi-spot Gaussian exposure, both MoO₃ films and recrystallisation rings were observed, exposure-dependent. The step change in device capability will accelerate new applications for this LC-SLM in both subtractive and additive manufacturing. Full article

A novel hot-melt cyclic olefin-based adhesive was designed as a transparent, non-tacky film of amorphous thermoplastic with a unique polymer micro-structure. The aim of the present paper is to assess the mechanical properties of the 0.1 mm thick COP hot-melt adhesive film through adhesive characterizations tests. The glass transition temperature was determined using dynamic mechanical analysis (DMA). For mechanical characterization, bulk and thick adherend shear specimens were manufactured and tested at a quasi-static rate, where at least three specimens were used to calculate the average and standard deviation values. Tensile tests revealed the effects of molecular chain drawing and reorientation before the onset of strain hardening. Thick adherend shear specimens were used to retrieve shear properties. Fracture behaviour was assessed with the double cantilever beam (DCB) test and end-notched flexure (ENF) test, for characterization under modes I and II, respectively. To study the in-joint behaviour, single lap joints (SLJs) of aluminium and carbon fibre-reinforced polymer (CFRP) were manufactured and tested under different temperatures. Results showed a progressive interfacial failure following adhesive plasticization, allowing deformation prior to failure at 8 MPa. An adhesive failure mode was confirmed through scanning electron microscopy (SEM) analysis of aluminium SLJ. The adhesive exhibits tensile properties comparable to existing adhesives, while demonstrating enhanced lap shear strength and a distinctive failure mechanism. These characteristics suggest potential advantages in applications involving heat and pressure across automotive, electronics and structural bonding sectors. Full article

This paper examines the mechanical performance of fibre-reinforced composite sandwich structures (FRPSSs) for maritime applications, focusing on the impact bending and damage sequence after seawater exposure. Glass-fibre/epoxy facesheets with various PVC foam core configurations underwent low-velocity single and multiple impacts. An in situ moisture-uptake methodology monitored moisture ingress until saturation. Results showed moisture uptake reduced impact bending capacity and bending stiffness to varying degrees. While energy-absorption performance remained largely unchanged under single impacts, significant differences were noted for multiple impacts. Failure analysis confirmed the reductions in some damage modes such as facesheet fracture, indentation, and core shear failures, while core shearing, delamination, core/facesheet debonding, and fibre breakage were identified as the main failure modes. These insights enhance understanding and optimisation of FRPSSs for improved out-of-plane damage resistance in marine applications. Full article

We present the generalised design of low-complexity, small-aperture optical terminals intended for kilometre-scale, terrestrial, free-space laser links between fixed and dynamic targets. The design features single-mode fibre coupling of the free-space beam, assisted by a fast-steering, tip/tilt mirror that enables first-order turbulence suppression and fine target tracking. The total power throughput over the free-space link and the scintillation index in fibre are optimised. The optimal tip/tilt correction bandwidth and range, aperture size, and focal length for a given link are derived using analytical atmospheric turbulence modelling and numerical simulations. Full article

Basalt Fibre Reinforced Polymer (BFRP)-bonded structures are lightweight, high strength, economical, and environmentally friendly, which is very advantageous in the civil sector. The aim of this paper is to provide a comprehensive account of the hygrothermal degradation and failure mechanisms of BFRP-bonded structures by comparing the residual properties of two epoxy adhesive BFRP single-lap joints after ageing for 240 h, 480 h, and 720 h in an extreme hygrothermal environment with pure water at 80 °C. The hydrophilicity and thermal stability of the two adhesives were firstly compared by water absorption and Thermogravimetric Analysis (TGA) tests, and the hygrothermal degradation of the molecular chains and the reduction in T_g were characterised by Fourier Transform Infra-Red (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC) curves. The failure strength and load-displacement curves of the two joints were then compared, and it was found that the strength and stiffness had different trends, while the paired t-test was used to demonstrate the correlation between the failure strength and the adhesive T_g, as well as the difference in the failure mechanisms of the two joints caused by the water absorption rate. The analysis of macrosections and Scanning Electron Microscope (SEM) images summarised the process and reasons for the transition of the failure mode from fibre tearing to hybrid failure, and finally, the changes in elemental concentration and O/C values were analysed by Energy Dispersive X-ray Analysis (EDX), which proved that the degree of hydrolysis could not be used as a judgement of the degradation degree of the joint alone, and provided data support for the application of the BFRP-bonded structure in the humid and hot environment. Full article

The influence of the bonding procedure (the adhesive type, application procedure, etc.) on the static and dynamic strain transfers of bonded optical fibre sensors is studied theoretically and experimentally at room temperature. The achievable performances with four different types of adhesives (three urethane and one epoxy adhesive), and with different fibre types, are evaluated: acrylate-coated, polyimide-coated, and bare single-mode optical fibres. Static strain measurements, ranging from 20 to 200 µ strain, are performed using both fibre Bragg gratings (FBGs) and optical frequency domain reflectometry (OFDR), and are compared to reference strain-gauge measurements, and to the proposed analytical model, which is developed on the basis of stress equilibrium relations. This model is valid for bonding to all types of linear and elastic materials, as long as there is no sliding between the host material, the adhesive, and the optical fibre. The results agree between the analytical model and the experiments. Regarding the dynamic sinusoidal strain measurements, the studied dynamic range is from 10 to 100 Hz, and only the FBGs are tested. The results demonstrate that the sensitivities of strain sensors based on bonded uncoated fibres or bonded polyimide-coated fibres are comparable to those of strain gauges, and that it is possible to use bonded FBGs for precise dynamic strain measurements. Full article

This paper proposes a novel orthogonal frequency division multiplexing (OFDM) optical access scheme based on bit reconstruction. In this method, correlation is introduced into the data information of optical line terminals (OLT) through the logical coding circuits and partition mapping. Even after passing through the optical fibre channel, the strong correlation after bit reconstruction can still be used in the optical network unit (ONU) for reliable decoding. In the simulation experiments, a 60 Gbit/s bit reconstruction 64 quadrature amplitude modulation (QAM) OFDM signal was successfully transmitted over a 10/20 km single-mode fibre (SMF). The simulation results show that the proposed scheme can effectively achieve reliable transmission with gains of about 1.3 dB and 0.51 dB at a 20% soft decision-forward error correction (SD-FEC) threshold, respectively. The proposed scheme is a promising candidate for a next-generation passive optical network (NGPON) solution. Full article

Advantages of using an external Fabry–Pérot interferometer (EFPI) as a high-speed local temperature deformation sensor are demonstrated for the fibre-optic circuit combining a powerful laser beam for surface heating with a low-power probing radiation. The difference in the formation of the heating and probing radiation provides a simple basis for varying the gap between the fibre end and the surface in order to change the ratio between the heating and EFPI measuring areas. Using an example of modelling the laser heating by radiation from a standard single-mode fibre, we demonstrate the possibility of employing the EFPI to measure the temperature deformation of the surface on a quasi-isothermal area with the temperature close to the maximum at gap values of more than 100 μm. With the condition of preliminary calibration, the proposed scheme can be used to evaluate the heat treatment of the surface with the speed of the applied photodetector. The practical possibilities of the method are demonstrated on examples of heating some metal and semiconductor samples by laser pulses of microsecond duration. Full article

Long fibre-reinforced metal matrix composite materials, which are widely used in industry, have complex and diverse damage modes due to their structural characteristics. In this study, the progressive damage process and failure mode analysis of the SiC_f/TC₄ composite shafts were thoroughly investigated under single torsional loads. A bearing performance test was carried out, the damage process was monitored using acoustic emissions, and the fracture specimens were analysed using a scanning electron microscope (SME). More specifically, under reverse torque loading, the damage process was slow-varying, the interface was subjected to tensile force, and fracture occurred mostly in the form of interface cracking; further, the breaking load of the specimen was 11,812 Nm. Under forward loading, the damage process was fast-varying. The fibres were subjected to tensile forces, and the fracture form was mostly fibre fracture; the breaking load of the specimen was 10,418 Nm. Under torque loading, the first damage to the specimens appeared in the outermost layer of the composite material’s reinforced section, and the initial cracking position was at the interface, expanding from the outside to the inside. Based on the principles of macro-mechanics and micro-mechanics theory, the cross-scale models were proposed, which contain the shaft with the same dimensions as the specimen and a micro-mechanics representative volume element (RVE) model. The initial interface damage load was 6552 Nm under reverse torque loading. Under forward loading, the initial interface damage load was 9108 Nm. In comparison to the acoustic emission test results, the main goal was to calculate the progressive damage process under the same conditions as the experiment, verifying the effectiveness of the cross-scale models. Full article

Machine protection systems in high power particle accelerators are crucial. They can detect, prevent, and respond to events which would otherwise cause damage and significant downtime to accelerator infrastructure. Current systems are often resource heavy and operationally expensive, reacting after an event has begun to cause damage; this leads to facilities only covering certain operational modes and setting lower limits on machine performance. Presented here is a new type of machine protection system based upon optical fibres, which would be complementary to existing systems, elevating existing performance. These fibres are laid along an accelerator beam line in lengths of ∼100 m, providing continuous coverage over this distance. When relativistic particles pass through these fibres, they generate Cherenkov radiation in the optical spectrum. This radiation propagates in both directions along the fibre and can be detected at both ends. A calibration based technique allows the location of the Cherenkov radiation source to be pinpointed to within 0.5 m with a resolution of 1 m. This measurement mechanism, from a single device, has multiple applications within an accelerator facility. These include beam loss location monitoring, RF breakdown prediction, and quench prevention. Detailed here are the application processes and results from measurements, which provide proof of concept for this device for both beam loss monitoring and RF breakdown detection. Furthermore, highlighted are the current challenges for future innovation. Full article

The work presented here investigates the risk of interstitial condensation between the existing masonry and the insulation using several materials and evaluates the water content inside the insulation (WCI) through various simulations in dynamic mode onto existing buildings located in different countries in Europe. The insulation materials considered are specifically: natural fibre materials, mineral fibre materials, and artificial materials. The scenarios were chosen considering different climate zones, according to the Köppen climate classification, and the analysed buildings were taken from the TABULA database in the years of construction from 1945 to 1969. The building typologies are single-family houses, where in each building system the insulation was placed towards the warm side with a fixed thickness of 5 cm. The simulations concerned: (a) the application scenario, (b) the type of stratigraphy chosen, and (c) the exposure of the existing building system. The outputs generated by the simulations provided the data to determine in which type of building, depending on the insulating materials, interstitial condensation is formed or not. It is shown that only for the climate zones of the cities of Oslo and Brussels, associated with their building typologies, for the insulating materials: mineral and natural, is there the formation of interstitial condensation Full article

The terahertz (THz) frequency bands are being explored as a potential means of enabling an ultra-high transmission capacity in sixth-generation (6G) radio-access networks (RAN) because higher frequencies offer broader bandwidths. When utilized in wireless communications, high-frequency electromagnetic waves impose several physical restrictions. To overcome these difficulties and to expand the service coverage, the radio-over-fibre (RoF)-based distributed antenna system (DAS), in particular, can improve the usability of future mobile networks with advantages such as seamless media conversion between wireless and optical signal, flexible multichannel aggregations, and efficiency. RoF technology’s inherent advantages are that it improves the DAS network’s usability and transmission performance by allowing it to provide both 5G and 6G THz services at the same time over a single optical fibre connection. We experimentally broadcast a single carrier-modulated 6G signal using a 256 quadrature amplitude modulation and a 5G new radio signal across a 10 km single mode fibre optic link. Additionally, the 6G signal is received through a 3 m wireless medium providing, proof of concept for fibre wireless integration. The experimental trials are assessed in terms of error vector magnitude and carrier suppression ratio. The dynamic range of the allowed RF input power for a 6G signal is 10 dB, while the dynamic range for a 5G waveform signal is 18 dB, which meets the 3GPP standardization criteria. Moreover, the bit error rate performance significantly improved as the carrier suppression ratio was increased from 0 to 20 dB. Full article

This paper presents an extensive experimental investigation to identify the influence of signal parameters on a piezoelectric harvester’s performance. A macro-fibre composite energy harvester was studied as an advanced, flexible, high-performance energy material. Gaussian white noise, and single-frequency and multi-frequency excitation were used to investigate nonlinearity and multiple-frequency interactions. Using single low and high frequencies, we identified the nonlinearity of the harvester’s vibration. Multi-frequency excitation with a series of low-to-high-frequency harmonics mimicked the practical vibration signal. Under such multi-frequency excitation, the harvester’s nonlinear behaviour was studied. Finally, the interaction effects among multiple frequencies were identified. The results show that under pure resonant excitation, high-level vibration led to high-level mechanical strain, which caused nonlinear vibration behaviour. Moreover, it was shown that the different harmonics excited the various structure bending modes, which caused the nonlinearity of multi-frequency excitation. The first four harmonics of the real-time signal were important. The experimental results emphasise the resonant nonlinearity and interactions of multi-frequency excitation effects. Full article

A long period grating Mach–Zehnder interferometer (LPGMZI) that consists of two identical long period gratings (LPGs) in a single fibre was developed to measure immunoglobulin M (IgM). The measured spectrum has fringes due to the interference between the core mode and cladding mode. This immunosensor inherits the advantages of an LPG and has the potential to compensate for unwanted signal changes due to bulk refractive index (RI) and temperature fluctuations by analysing interference fringes and their envelope. The external RI was measured from 1.3384 to 1.3670 in two different cases: (i) only the connecting section between the two LPGs is immersed or (ii) the whole LPGMZI is immersed. The fringes shift with an external RI in both scenarios, whereas the envelope stays still in case (i) or shifts at the same rate as the fringes in case (ii). The LPGMZI was also characterised at different temperatures between 25 °C and 30 °C by placing the whole LPGMZI in a water bath. The fringes and envelope shift at the same rate with temperature. The LPGMZI platform was then used to create an IgM immunosensor. The connecting section between the two LPGs was functionalised with anti-IgM and immersed into solutions with IgM concentrations from 20 μg/mL to 320 μg/mL. The fringes shift with IgM concentration and the envelope remains static. The results from this work show that LPGMZI has the potential to compensate for the temperature and bulk RI fluctuations and perform as a portable biosensor platform. Full article