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Introduction. Optical fibers are widely used for high-bandwidth transmitting communication signals over long distances. The key feature enabling this performance is signal low attenuation, that is signals experience minimal power loss propagating along the optical fiber. One of the factors influencing power loss during information transmission is the fiber bending. Bending can increase the signal transmission power loss of an optical fiber because of both macrobending and microbending. Studying the dependence of signal power losses when bending on waveguide parameters makes it possible to control the signal power losses of an optical fiber during information transmission. Aim of the Study. The study ia aimed at evaluating the effect of microbending on the field and energy of a weakly guiding optical fiber with a gradient refractive index profile in a single-mode regime. Materials and Methods. From the equations for the fields of straight and curved sections of weakly guiding fiber for an arbitrary gradient profile of the refractive index with the help of the subsequent solution of inhomogeneous Helmholtz equations by the Green’s function method, there were obtained expressions for relative energy: the ratio of the field energy of the fiber curved section to the field energy of the fiber straight section (in the first approximation for a single-mode regime). Results. The obtained expression for the relative energy depends on two parameters: the waveguide parameter and the ratio of the optical fiber radius to the radius of curvature. For the quadratic case of a power-law profile, as the closest to the actually used one, numerical calculations were used to construct the dependences of the relative energy on the parameter characterizing the bending for different values of the waveguide parameter. Discussion and Conclusion. It has been shown that in the case of microbending, the longer the wavelength or the smaller the fiber radius, the lower the losses. The results obtained can be used in calculating optical fiber profiles designed to operate in a bent state and eliminate expensive experimental modeling of light guides and in designing waveguides to solve specific applications, in particular, to increase energy efficiency, reliability and performance of the measuring instruments.

The high-sensitivity surface plasmon resonance-based optical fiber sensors for micro-pressure sensing is presented in this paper. The periodic micro-bending of two mechanical periodicities with length of 5 mm and 10 mm were used in the sensing system. The micro-pressure has been applied on the sensor for three different configurations: unclad sensor without gold (Au), unclad sensor with Au, and sensor with Au sandwiched between two layers of silicon rubber. The normalized output intensity for all configurations was calculated. The results show that the higher range of applied micro-pressure can be obtained for the configuration of optical fiber coated with Au sandwiched between two layers of silicon rubbers, with maximum sensitivity of 0.65 dB/kPs. The development model of the sensor could be a promising path for many different applications. [ABSTRACT FROM AUTHOR]

Severe mechanical and thermal loadings, as well as the corrosive environment change the near-surface microstructure of rail wheels during service. Resulting severely plastically deformed (SPD) and corrosion affected microstructures are prone to influence crack initiation along the wheel tread. To evaluate the crack initiation and fracture behaviour, the in-situ micro-bending method is first applied on rail wheel samples from field within this work. Results reveal detailed insights in material behaviour of SPD microstructures, where the conducted micro-bending investigations point out predominant plastic behaviour without cracks initiated at the artificial notch of the micro-cantilevers during bending. In contrast, micro-bending investigations in microstructural regions with increased oxygen and silicon composition show crack initiation, fracture, and low maximum stress levels (approximately one seventh of the SPD microstructure). The presented study underlines the increased risk of crack initiation in corrosion affected regions by a novel testing method in this field with high spatial resolution and acknowledge the importance of periodic reprofiling of the rail wheels in service. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cells have been used worldwide due to their high energy density and zero emissions. The metallic bipolar plate is the crucial component and has a significant effect on a cell's efficiency. However, the springback behavior of the metallic bipolar plate will greatly influence its forming accuracy in the micro-scale sheet metal forming process. Therefore, accurate calculation of the springback angle of the micro-scale metallic bipolar plate is urgent but difficult given the state of existing elastoplastic theory. In this paper, a constitutive model that simultaneously considers grain size effect and strain gradient is proposed to analyze micro-scale bending behavior and calculate springback angles. The specialized micro-scale four-point bending tool was designed to better calculate the springback angle and simplify the calculation step. A pure micro-bending experiment on a 316LN stainless steel sheet with a thickness of 0.1 mm was conducted to verify the constitutive model's accuracy. [ABSTRACT FROM AUTHOR]

Optical fibers offer various applications to cater to industrial needs, from power and data transmission to environmental sensing. Different sensing mechanisms of optical fibers depend on modifications made to the fiber itself primarily in the cladding and core sections. Different types of optical fiber sensors may require thinning of the cladding to allow propagated light to interact closer to the environmental stimuli. Chemical etching is commonly used for the de-cladding of a fiber, and there are many ways to execute this method. A conventional method of chemical etching is typically used for cladding removal. This paper reports and discusses the effectiveness of enhanced techniques for improvement towards conventional chemical etching methods with the assistance of a makeshift fiber holder. The fiber holder allows the fiber to be oriented well, allowing for smoother etching and thus conserving its mechanical structure. Thickness reduction is seen to be more consistent when the enhanced technique is employed, and the fiber takes a longer time (∼45 min) to break. This allows etching of the cladding close to the core, which is more manageable for the user if very thin cladding is required. A fiber etched without any holder tends to break earlier (∼35 min) than expected with a rather wide error margin. The lower coefficient of determination, R 2 values (95%) of the thickness reduction from conventional etching shows irregular thickness along the fibers. Optical power also fluctuates between 30â€"35 dBm for the conventional method, while the mounted fiber technique maintains stable optical power at 50 dBm during etching. Therefore, it is concluded that proper fiber horizontal fiber orientation during etching has a significant effect on the fiber strength due to the smooth cladding removal around the corecore while minimizing any permanent power loss to or the occurrence of fluctuations in the fiber. This smooth and efficient etching technique allows the production of enhanced fiber sensors with minimal structural or power defects. [ABSTRACT FROM AUTHOR]

There is an increasingly recognised requirement for high dimensional accuracy in micro-bent parts. Springback has an important influence on dimensional accuracy and it is significantly influenced by various process parameters. In order to optimise process parameters and improve dimensional accuracy, an approach to quantify the influence of these parameters is proposed in this study. Experiments were conducted on a micro W-bending process by using an I-optimal design method, breaking through the limitations of the traditional methods of design of experiment (DOE). The mathematical model was established by response surface methodology (RSM). Statistical analysis indicated that the developed model was adequate to describe the relationship between process parameters and springback. It was also revealed that the foil thickness was the most significant parameter affecting the springback. Moreover, the foil thickness and grain size not only affected the dimensional accuracy, but also had noteworthy influence on the springback behaviour in the micro W-bending process. By applying the proposed model, the optimum process parameters to minimize springback and improve the dimensional accuracy were obtained. It is evident from this study that the I-optimal design based RSM is a promising method for parameter optimisation and dimensional accuracy improvement in the micro-bending process. [ABSTRACT FROM AUTHOR]

We show the design and applicability of multi-core fiber (MCF) with the standard 125 μm cladding diameter to the telecommunication systems. It offers easier and practical use of the space-division multiplexing (SDM) technology given its excellent fiber productivity and utilization of existing standard technologies. We numerically and experimentally reveal that the simple step-index (SI) profile enables us to allocate four cores in the standard 125 μm cladding and to realize full compliance with G.657.A1 fiber. We then expand the design and concept of the standard cladding MCF and show the index profile and single-mode bandwidth offer control of XT characteristics. We elucidate the application scope of the standard cladding MCF for not only the full-band (O-L band) application to short-reach and terrestrial transmission consistent with ITU-T Recommendations G.652 and G.657, but also ultra-long haul transmission, such as submarine systems compliant with ITU-T Recommendation G.654. [ABSTRACT FROM AUTHOR]

This study demonstrates the application of the in-situ V-notched micro-cantilever bending method in tribology by analyzing three distinct cases of near-surface microstructures occurring in common tribological contacts. The brown etching layer region of a rail wheel from service shows predominant plastic material behavior. Significant variations in material response and crack initiation are revealed in distinctive regions of a roller bearing's near-surface microstructure and a self-lubricating laser cladding. Qualitative analysis and stress-displacement graphs highlight the method's potential for gaining high-resolution insights into material behavior, contributing to our understanding of microstructural changes affecting friction, wear, and component failure in tribosystems. [ABSTRACT FROM AUTHOR]

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Abstract Micro-surgical instruments are a new application for mesoscale ceramics formed using the lost mold-rapid infiltration forming (LM-RIF) process. Instrument strength and reliability are the foremost concerns for this sensitive application. It is hypothesized that increasing grain size can improve the damage tolerance of the parts associated with the transformation toughening in the 3Y-TZP material, while retaining high strength. In this work, mesoscale bend bars (314 × 22 × 18 µm) of 3Y-TZP fabricated using the LM-RIF process were heat treated at 1400 °C for 1 h, 8 h, or 16 h, respectively, to obtain samples with different grain sizes. Strength tests were performed under three-point bending and results were evaluated using Weibull statistics. Fractographic and confocal Raman spectroscopic analyses were carried out to interpret the data. Experimental findings showed that the characteristic strength decreased with increasing grain size contrary to the damage tolerance hypothesis. An Orowan-Petch model was recalled to correlate the strength with the flaw size to grain size ratio. At fine grain sizes the strength was controlled by the flaws introduced by the LM-RIF process, whereas at large grain sizes the strength become more grain size controlled. Although larger-grained samples did have a higher propensity to transform, and thus increase toughening, exaggerated grain growth in some of the specimens tested caused an additional flaw population which led to an overall lower strength. Finally, based on the experimental observations and fracture mechanics considerations, we believe that an upper bound of ∼2.5 GPa exists for the strength of mesoscale as-fabricated 3Y-TZP ceramic parts. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

There is an increasingly recognised requirement for high dimensional accuracy in micro-bent parts. Springback has an important influence on dimensional accuracy and it is significantly influenced by various process parameters. In order to optimise process parameters and improve dimensional accuracy, an approach to quantify the influence of these parameters is proposed in this study. Experiments were conducted on a micro W-bending process by using an I-optimal design method, breaking through the limitations of the traditional methods of design of experiment (DOE). The mathematical model was established by response surface methodology (RSM). Statistical analysis indicated that the developed model was adequate to describe the relationship between process parameters and springback. It was also revealed that the foil thickness was the most significant parameter affecting the springback. Moreover, the foil thickness and grain size not only affected the dimensional accuracy, but also had noteworthy influence on the springback behaviour in the micro W-bending process. By applying the proposed model, the optimum process parameters to minimize springback and improve the dimensional accuracy were obtained. It is evident from this study that the I-optimal design-based RSM is a promising method for parameter optimisation and dimensional accuracy improvement in the micro-bending process.

In this research, micro-bending tests of electrodeposited gold with various crystal structure were conducted using micro-cantilever specimens with dimensions at 10 μm × 10 μm × 50 μm for design of gold-based movable structures in MEMS devices. The gold film fabricated by pulse-current electrodeposition with a sulfite-based gold electrolyte (PE-Su) had the finest average grain size, which was at 15.5 nm. The PE-Su gold micro-cantilever showed ductile deformation behavior and the highest yield stress, which was at 800 MPa, because of the grain boundary strengthening mechanism also known as the Hall-Petch relationship. The gold film fabricated by constant-current electrodeposition with a cyanide-based gold electrolyte (CE-Cy) had an average grain size at 17.6 nm. The CE-Cy gold micro-cantilever showed brittle fracture and the yield stress at 480 MPa. The brittle fracture was suggested to be a result of the columnar texture structure in the CE-Cy gold film. [ABSTRACT FROM AUTHOR]

Microscale laser dynamic flexible forming (μLDFF) is a novel ultrahigh strain rate manufacturing technology with high efficiency and low cost. However, the μLDFF is just confined to single-layer foil at present. In this work, sheet metal laminates (Cu/Ni) were selected as the experimental material for its excellent mechanical and functional properties, and a new micro-bending method of sheet metal laminates by laser-driven soft punch was proposed in warm conditions. The micro-mold and warm platform were designed to investigate the effects of temperature and energy on formability, which were characterized by forming accuracy, surface quality, element diffusion, and so on. The experimental results show that the forming accuracy and quality increased first and then decreased with laser energy, but the hardness increased consistently. In warm conditions, the fluidity of material was improved. The forming depth and accuracy increased for the relieved springback, and the surface quality increased first and then decreased. The tensile fracture disappeared with temperature for the decreased hardness and thinning ratio, and the element diffusion occurred. Overall, this study indicates that the formability can be improved in warm conditions and provides a basis for the investigation of micro-bending of sheet metal laminates by μLDFF in warm conditions. [ABSTRACT FROM AUTHOR]

Service materials are often designed for strength, ductility, or toughness, but neglect the effects of cyclic time-variable loads ultimately leading to macroscopic mechanical failure. Fatigue originates as local plasticity that can first only be observed on the micro scale at defects serving as stress concentrators such as inclusions or grain boundaries. Thus, a recently developed technique to perform in-situ observation of micro scale bending fatigue experiments was applied. Micro-beams fabricated from copper, single grained and ultrafine grained (ufg), and an oxide dispersion strengthened (ODS) steel were subject to cyclic deformation and subsequent damage. The elastic stiffness, yield strength, dissipated energy, and maximum stress were measured as a function of cycle number and plastic strain amplitude. From these properties, cyclic stress-strain curves were developed. Initial pronounced monotonic hardening and an increasing Bauschinger effect were observed in all samples with increasing strain amplitude. Cyclic stability was maintained until plastic strain amplitudes reached a critical value. At this point, dramatic cyclic softening and microcracking occurred. The critical strain amplitude was found to be approximately 5.4×10 −3 for the copper with a refined grain structure and 1.2×10 −2 for the steel specimen. Grain rotation and noticeable changes in sub-grain structure were evident in the ufg copper after a critical strain amplitude of ε a =8.3×10 −3 . In-situ micro fatigue bending couples the cyclic evolution of bulk mechanical properties measurements with real-time electron microscopy analysis techniques of damage and failure mechanisms, which renders it a powerful method for developing novel fatigue resistant materials. [ABSTRACT FROM AUTHOR]

A novel general purpose Finite Element framework is presented to study small-scale metal plasticity. A distinct feature of the adopted distortion gradient plasticity formulation, with respect to strain gradient plasticity theories, is the constitutive inclusion of the plastic spin, as proposed by Gurtin (2004) through the prescription of a free energy dependent on Nye’s dislocation density tensor. The proposed numerical scheme is developed by following and extending the mathematical principles established by Fleck and Willis (2009). The modeling of thin metallic foils under bending reveals a significant influence of the plastic shear strain and spin due to a mechanism associated with the higher-order boundary conditions allowing dislocations to exit the body. This mechanism leads to an unexpected mechanical response in terms of bending moment versus curvature, dependent on the foil length, if either viscoplasticity or isotropic hardening are included in the model. In order to study the effect of dissipative higher-order stresses, the mechanical response under non-proportional loading is also investigated. [ABSTRACT FROM AUTHOR]

A finite element model of the flexible micro-bending process based on various grain sizes of pure copper is developed. The geometrical model of grain structure is established with Voronoi tessellation, which is employed to describe the polycrystalline aggregation. A model based on dislocation density is adopted to describe the flow stress of grain interior (GI) and grain boundary (GB) quantitatively. In this paper, silicon rubber is used as the flexible punch and four annealing conditions of pure copper as the workpieces, respectively. The influence of grain structure and grain size is discussed. It is observed that as the ratio of workpiece thickness ( t ) to grain size ( d ) decreases, the forming depth increases. The inhomogeneous deformation occurs in the coarse-grained micro-parts. Furthermore, the results indicate that the surface asperity increases with grain size. The numerical simulation results agree well with the tendency of experimental results. During the micro-bending process, the phenomenon of stress concentration occurs at the grain boundary of the micro-parts. The maximum von mises stress appears at the grain boundary located at the fillet position. The maximum von mises plastic strain primarily concentrates on the junction of the grain interior and grain boundary in the fine-grained parts, while it concentrates at the surface of the grain interior in the coarse-grained parts. [ABSTRACT FROM AUTHOR]

• Laser bending of duplex stainless steel is explored which is not reported in the literature. • Effect of line energy on bending mechanism, bend angle, edge effect, and mechanical properties is investigated in detail. • The role of temperature distribution on the variation in bend angle, and mechanical and microstructural properties is explored. Laser bending is a well-established process to achieve bending with high accuracy and good controllability. This study discusses the effect of line energy on bending mechanism, bend angle, edge effect, mechanical properties, and microstructural characterization for laser bending of duplex stainless steel. Numerical simulations have been carried out for a better understanding of the bending mechanisms. Additionally, the role of temperature distribution at the bottom surface on the variation in bend angle has been analyzed. It is found that at low laser powers, the bend angle increases with line energy, but at a decreasing rate. Whereas at high laser powers, the bend angle increases with line energy; attains peak and then decreases. At constant line energy, the bend angle increases with the increase in laser power and scanning speed. The hardness of laser-scanned specimens is increased, and ductility is reduced. Besides, the ultimate strength and yield strength remain almost constant. The sigma phase formation has been observed during the microstructural analysis, which further correlates with the high hardness and low ductility. [ABSTRACT FROM AUTHOR]

Fiber Bragg grating (FBG) is a commonly used optical fiber sensing structure. FBG bent sensors in multimode fiber have been achieved. However, the structure and manufacturing process are complex. In the present study, we designed a simple structure that composed of an ordinary single-mode fiber (SMF) and a section of multimode fiber (MMF) with a FBG. It can realize the dual-parameter sensing of micro-bending and temperature simultaneously. The experimental results suggested that the structure is sensitive to micro-bending and temperature, and the sensitivities do not interfere with each other. The temperature sensitivity is 13.4 pm/ ∘ C, and the maximum bending sensitivity is 23.03 dB/m−1. • Micro-bending and temperature sensor is fabricated by femtosecond laser inscription. • The sensor structure is simple which including SMF and MMF with FBG. • Micro-bending and temperature sensitivity do not interfere with each other. • Temperature sensitivity is 13.4 pm/ ∘ C. Maximum bending sensitivity is 23 dB/m−1. • The sensor has excellent repeatability, reliability and measurement accuracy. [ABSTRACT FROM AUTHOR]

An original approach for mechanical characterization was developed using indentation assisted micro-bending. Aiming at the reliable measurement of elastic modulus of multi-scale solids, the technique relies on deflection measurements of cantilever-type beams modeled within the framework of beams on elastic foundation. The inference of elastic modulus is carried out by postulating the inverse problem and solving it via the error minimization approach. The validation performed on a set of reference materials disclosed the proposed technique's potential for accurate characterization of elastic properties and flexural strength at micro and mesoscale, motivating its extension to heterogeneous materials - cementitious composites in particular. [Display omitted] • The reliable instrumented assisted micro-bending technique has been developed. • The beam on Winkler-type foundation model was used as the mechanical representation. • Multi-variable inverse minimization has been used in the estimation of elastic properties. • Validation of the technique has been performed on reference construction materials. • The methodology was successfully applied to cementitious systems. [ABSTRACT FROM AUTHOR]