Structural Performance Degradation Research Articles

Topologically Protected Single Edge Mode Lasing in Photonic Crystal Su–Schrieffer–Heeger Lattice with Directional Loss Control

AbstractTopological photonics is considered to be a robust and flexible platform for the design of nanophotonic devices against structural imperfections and performance degradation. Combining with parity‐time (PT) symmetry systems based on spatially distributed gain and loss, photonic crystal (PhC) lasers with micron‐size carrier reservoirs offer an ideal test bed for lasing mode competition and topological protection in nanophotonic structures. In this study, single topological edge mode (TEM) lasing is demonstrated in PhC lasers with a Su–Schrieffer–Heeger lattice comprised of coupled nanoresonators. By inducing directional loss control, a mode selection strategy is implemented, that achieves single TEM lasing with a side‐mode‐suppression ratio exceeding 30 dB. One of the TEMs exhibits remarkable robustness against local potential variation introduced by additional loss channels. This strategy integrating both topological protection and PT symmetry in nanophotonics would open up new prospects for the development of on‐chip single‐mode topological lasers unperturbed by output channels in nanophotonic integrated circuits.

Bridge performance degradation model based on the multi-variate bayesian dynamic linear method

The degradation of bridge structural performance arises from the combined influence of various factors. Performance assessment and reliable prediction of bridge performance degradation through effective utilizing of detection information updates is a challenging problem. In this paper, the concept of performance indicators is redefined, employing to delineate bridge performance degradation. A bridge performance degradation model (the error ≤8%) is formulated, considering the multiple-variable Bayesian dynamic linear method (MBDLM) and revealing the coupling mechanisms among factors influencing bridge performance degradation. On this basis, the prediction performance of the model is quantitatively evaluated by three metrics: mean squared error, predictive mean squared error and mean absolute percentage error. A methodology is presented for the assessment, prediction, and maintenance reinforcement of in-service bridge structural performance degradation. This approach holds promise for future applications in safety assessments and the decision-making process for preventive maintenance of operational bridges.

Impact of Installation Deviations on the Dynamic Characteristics of the Shaft System for 1 Gigawatt Hydro-Generator Unit

The shaft system, transferring the kinetic energy of water flow into electrical energy, is the most critical component in hydropower plants. Installation deviations of the shaft system for a giant hydro-generator unit can have significant impacts on its dynamic characteristics and overall performance. In this investigation, a three-dimensional geometry of the shaft system of an operating hydro-generator unit prototype with a rated power of 1 GW is established. Then, the calculation model of the shaft system is generated accordingly with tetrahedral and hexahedral elements. By applying different boundary conditions, the finite-element method is used to analyze the influences of installation deviations, including shaft radial misalignment and angular misalignment, on the dynamic characteristics of the shaft system. The calculation results reveal that the installation deviations change the natural frequencies, critical speeds, and mode shapes of the shaft system to a certain degree. The natural frequencies of the backward precession motion with installation deviations are reduced by 23% and 38% for the rated speed and the maximum runaway speed. Furthermore, for the forward precession motion, they increased by 30% and 48%, respectively. The critical speeds for the shaft system with radial and angular deviations are 3.2% and 3% larger than the critical speed of the shaft system without any mounting deviations. The radial and angular installation deviations below the maximum permissible values will not result in the structural performance degradation of the 1 GW hydro-generator shaft system. The conclusion drawn in this research can be used as a valuable reference for installing other rotating machinery.

Investigation on seismic performance degradation of hub large‐span roof structures considering corrosion and damage accumulation

AbstractHub transportation facilities are important lifeline projects in cities. Once they are damaged by earthquakes, their functional use will be lost, resulting in significant adverse social impacts. The roof structures of hub transportation facilities are usually made of large‐span steel structures. During service, they bear long‐term vibrations caused by multiple vibration sources such as high‐speed trains and wind loads, resulting in cumulative damage. In addition, the roof structures located in coastal areas may be exposed to a corrosive environment, which can lead to the degradation of structural performance. Currently, the relevant structural design standards do not consider the factor of structural performance variation over time. To address the above problems, this study adopts a time‐dependent constitutive model of steel considering corrosion and damage cumulative to investigate the seismic performance degradation of typical hub transportation facility roof structures. The research results show that the stiffness and seismic performance of 50‐year service hub large‐span roof structure have decreased compared to newly built structures, but the probability of serious damage is lower, indicating that the hub large‐span roof structures have good seismic performance.

Bridge crack segmentation and measurement based on SOLOv2 segmentation model

With the continuous increase of vehicular traffic, the safety caused by bridge crack damage is becoming increasingly prominent. Bridge crack analysis and measurement are of great significance for promoting road traffic safety. However, existing bridge crack image segmentation methods have shortcomings in processing image detail features, resulting in the inability to better measure the actual size of bridge cracks. Therefore, to further optimize the calculation method, a bridge crack image segmentation method based on improved SOLOv2 is designed to achieve more accurate bridge image segmentation. Based on the image segmentation results and combined with the skeleton data extraction method, a bridge crack calculation method is designed. From the results, the segmentation accuracy for crack images was 92.05 % and 93.57 %, respectively. The average mIoU of AM-SOLOv2 method was 0.75, significantly lower than commonly used crack image segmentation methods. In addition, the mIoU value variation amplitude of the AM-SOLOv2 method was relatively smaller. The crack length and width errors were within 0.05 mm and 0.06 mm, significantly lower than the comparison method. It indicates that this method can achieve more accurate crack image segmentation and calculation. This is beneficial for a deeper understanding of the performance degradation and crack damage evolution of bridge structures, thereby improving bridge design and construction technology.

Steel corrosion process in ultra-high performance concrete monitored by fiber bragg grating sensor

The steel corrosion in Ultra-High Performance Concrete (UHPC) would cause degradation of structural performance or even structural failure. It is an urgent need to monitor and predict the steel corrosion in UHPC, however it is still a tough task. In this paper, Fiber Bragg Grating (FBG) sensors are applied for monitoring the steel corrosion process in UHPC, by combining with steel bar, which is equidistant winding with the sensors, and connected with power supply for accelerating corrosion. The UHPC specimens embedded with steel bars are surrounded by sodium chloride (NaCl) solution, and the steels are artificially corroded with different current densities for investigation. The steel corrosion in Original C60 and Marine Concrete 60 (Marine C60) are applied for comparison. The volume expansion coefficient for monitoring the steel corrosion process, is carried out by FBG sensors, and further comprehensively monitored by three grating sensors. The results suggest that the steel corrosion process in UHPC is slowly with current density lower than 100 μA/cm2, and largely increases with current density higher than 500 μA/cm2, the volume expansion coefficient of corroded steel in UHPC is in range of 2.02–2.62 in this test, which is much different from Original C60 and Marine C60.

Co-free and low strain cathode materials for sodium-ion batteries: Machine learning-based materials discovery

Sodium-ion batteries (SIBs) are promising alternatives to lithium-ion batteries (LIBs) owing to their cost-effectiveness and similar intercalation mechanisms. Layered transition metal oxides (LTMOs) are the promising cathode candidates for SIBs owing to their high voltages and ease of synthesis. However, O3-type LTMOs undergo structural deformation and performance degradation during de-/intercalation. Owing to the limitations of single-element compounds, doping them with various elements can enhance their stability and performance. In this study, machine learning (ML) algorithms are used to predict the structural stability of O3-type materials without phase transitions to facilitate efficient material selection. ML classification models assess the phase stability of cathodes in the pristine and desodiated states. Data sampling and feature engineering enhanced the accuracy of the pristine model from 0.886 to 0.962 and desodiated model from 0.642 to 0.954. Furthermore, a novel database in the form of NaxNi0.5MayMbzO2 (0.5 ≤ x ≤ 1, y + z = 0.5; M = transition metal) was constructed using density functional theory (DFT) calculations. Out of 1,451 LTMOs candidates, we present 128 cathode candidates that satisfy the following conditions: (1) O3 phase is maintained during dis-/charging processes, (2) average voltage ≥ 3 V, (3) theoretical capacity ≥ 200 mAh/g, and (4) -5 % ≤ volume change ≤ 5 %. Among them, 125 materials showed the possibility of stable Co-free cathodes, and 13 materials exhibited -0.5 % < volume change < 0.5 %. This study suggests optimal LTMO candidates that satisfy both the high energy density and electrochemical stability and provides a reliable battery material screening platform.

Design of patch-shaped lens with thickness variations for elastic wave focusing in thin-plate structures

In mechanical engineering, focusing on elastic waves is pivotal for applications, such as energy harvesting, shock mitigation, and wave manipulation. While phononic crystals have historically been a key method for managing wave propagation, this study explores a novel technique. This method introduces gradient refractive-index (GRIN) lenses by altering the plate thickness and creating localized high-refractive-index zones. Unlike traditional methods, this localized GRIN approach aims to overcome the fabrication and structural limitations, particularly in thin structures. The patch-shaped lenses offer the potential for elastic wave focusing in thinner structures without any degradation of structural performance. Through numerical analysis, we established design principles and examined the elastic wave propagation and focusing characteristics across various thickness variation profiles. This study conducts a thorough analytical and experimental evaluation of these lenses to confirm their effectiveness, structural robustness, and suitability for optimizing wave concentration in various mechanical engineering applications. The research represents an alternative, innovative, and promising pathway in the field of wave focusing, transcending the traditional constraints of thin plate structures.

Finite element boundary element numerical simulation study on acoustic vibration coupling problems

Excessive structural resonance response in the acoustic vibration coupling environment can cause adverse consequences such as structural damage, local instability, and component failure. Accurately predicting the vibration response of instruments under external sound fields helps to avoid structural performance degradation or damage caused by vibration, and ensures the reliability and safety of the system, which is of great significance for the effective load of instrument equipment. This paper constructs a finite element boundary element equation for the acoustic vibration coupling problem, and adopts a series of optimization measures for it. In response to the low computational efficiency of finite element boundary element equations and their inability to meet the computational requirements of complex models, this paper introduces the acoustic vibration reciprocity theorem and the fast directional boundary element method to compensate for the aforementioned shortcomings. In addition, the study used the weighted residual method to construct a data exchange algorithm to ensure energy conservation during the transfer process. The research focuses on typical structures of spacecraft and conducts simulation analysis and application research on acoustic vibration coupling problems. The simulation showcases that the introduction of the reciprocity theorem markedly reduces the calculation time and memory occupied by the equation, with a required calculation time of 1.23 h and a data file size of approximately 299.56 MB generated by the calculation; The overall error of the data exchange process is below 10−4. Scanning frequency analysis is conducted on the surface and local openings of the model structure, and it is found that the displacement of the selected excitation point is in good agreement with the analytical solution. This study effectively reduces simulation time and memory requirements through the proposed strategy, ensures energy conservation data exchange algorithms, improves the reliability and safety of structural design, and has important practical value for evaluating the structural performance of key equipment such as spacecraft.

Structural effects of asymmetric magnet shape on performance of surface permanent magnet synchronous motors

This study proposes a novel surface permanent magnet synchronous motor (N-SPMSM) structure, which features asymmetric magnets attached to the rotor surface. The N-SPMSM structure exhibits reduced structural complexity and minimal electromagnetic performance degradation. The properties of N-SPMSM are analyzed by comparing its structural complexity (in terms of the shape) and manufacturing complexity and electromagnetic performance [in terms of the cogging–mutual torque ratio and back-electromotive force (EMF) values], with the corresponding values of a ring-type SPMSM (R-SPMSM) and step-skew-type SPMSM (T-SPMSM). The analysis results demonstrate that N-SPMSM has lower shape complexity than T-SPMSM and lower manufacturing complexity than both R-SPMSM and T-SPMSM. The cogging torque reduction and back-EMF performances of N-SPMSM are similar to that of R-SPMSM and T-SPMSM.

DPIM-based global reliability analysis method for the cable-stayed bridges and the determination of global target reliability index

This study presents an approach to analyzing the dynamic global reliability of cable-stayed bridges using the direct probability integral method. The analysis considers the degradation of resistance in the concrete main beam, tower, and cables, as well as the time-varying nature of the load effect. Six types of limit state functions for failure modes are established, including bending failure of the beam, static torsional failure of the beam, wind vibration failure of the beam, transverse buckling failure of the tower, longitudinal strength failure of the tower, and strength failure of the stay cable due to fretting fatigue and corrosion. A time-dependent extreme value mapping is constructed in the time domain, then the joint probability density integral equation of time-varying extreme value mapping of multiple performance functions is established. According to the mean and variance of random variables in the evaluation reference period, the direct probability integral method with Heaviside function (DPIM-H) is employed to solve the equation, and the dynamic global reliability index of cable-stayed bridge is obtained. As an example, the Brotonne cable-stayed bridge’s global reliability is analyzed, and the reasonable value of the global target reliability index is studied considering the structural performance degradation.

Enhanced stability and electrochemical investigations of Ni/ZSM-5 catalyst layer on nickel-based anodes for ammonia-fed solid oxide fuel cells

Ammonia-fed solid oxide fuel cell (SOFC) is a promising clean energy technique with distinctive advantages of zero-carbon emission, easy storage, and high efficiency. However, the typical nickel anode for SOFC is susceptible to structural change and performance degradation under an ammonia environment, particularly at reduced operating temperatures. In addition, obtaining a deep understanding of the individual electrode processes is demanded for the rational design and optimization of NH3–SOFCs. This work enhances the cell performance and durability of ammonia-fed SOFCs by utilizing a cost-effective ammonia decomposition catalyst (Ni/Na-ZSM). The electrode processes are investigated quantitively using distributed relaxation time (DRT) and equivalent circuit model (ECM) analysis. Accelerated degradation tests are conducted for the NH3-based SOFC cells by thermal cycling at operational temperatures of 700 °C-650 °C. Compared to the conventional cell, the cell with the Ni/Na-ZSM catalyst exhibits improved cell performance and five times less decay. In situ measurements and impedance analysis combined with microstructural characterization reveal that the durability enhancement is probably ascribed to protecting the structure of the three-phase boundaries (TPBs), which maintains a stable resistance of the TPB charge transfer processes during the temperature cycling.

Performance enhancement of damaged RC structures with viscoelastic dampers: Damage assessment and optimal placement

Evaluating the performance degradation of the earthquake-damaged structure and optimizing the placement of dampers is important for retrofitting post-earthquake structures. In this study, a damage evolution model is developed to evaluate the degradation of strength, stiffness, and energy dissipation capacity for earthquake-damaged structures. The proposed damage model is validated using previous experimental results based on the nonlinear finite element analysis. Then, research on the optimal design of damper parameters and quantity is carried out. Considering the optimization range of earthquake-damaged structures, a genetic algorithm with multi-objective functions is developed to determine the optimal placement of viscoelastic dampers in damaged structures. The results demonstrate that the proposed damage model can effectively describe the performance degradation of damaged structures. The control effects of the acceleration response increase exhibited a maximum enhancement of 3.38 times after accounting for the optimization range of earthquake-damaged structures. The optimization results of the multi-objective function with the optimization range are better aligned with the objectives of designers.

Research on time dependent constitutive model and structural performance degradation prediction of silicon foam

The natural aging of silicone foam materials leads to a decline in their mechanical properties, which, in turn, affects the structural response of systems incorporating these materials. This study investigates the accelerated aging of silicone foam through stress relaxation tests, compression set tests, and uniaxial compression tests. By using the constitutive relationship as a bridge, a connection between stress relaxation and compression set is established, forming a predictive model for structural response. This model is validated against experimental results through finite element analysis. The high degree of accuracy between the predictive model and the experimental outcomes confirms its suitability for engineering applications.

Performance degradation mechanism of γ-ray irradiated sol-gel silica film

γ-ray radiation effect on sol-gel silica films was investigated at different absorbed doses ranging from 10 kGy to 1000 kGy. The defect and microstructure evolutions of silica films were analyzed to understand the performance degradation behavior and mechanism of the γ-ray irradiated silica films. The cracks appear on the silica film surface and further expand at larger γ-ray absorbed dose, while surface roughness slightly decreases. During γ-ray irradiation, the thermal effect and the increased rate of diffusion-controlled process lead to the condensation of Si-OH groups and the recombination of ODCs. However, the ionization of atoms leads to generation and accumulation of E′ centers and NBOHCs. γ-ray irradiation leads to the reductions of bond lengths and bond angles of Si-O-Si groups, thus causing the densification of films. The refractive index and mechanical property firstly enhance and then reduce with the increase of absorbed dose associated with the change of silica film density. After γ-ray irradiation, the decreased contact angle and increased surface free energy indicate the reduction of anti-pollution ability of silica films. The dose-dependent surface quality, defects and mechanical properties determine the variation in laser-induced damage threshold (LIDT) of silica film. The results provide a reference to control the structural damage and performance degradation of silica films, which is very important for the research of safe operation of high-power laser facilities for inertial confinement fusion (ICF).

An approach for quantifying the calcium leaching effect on service performance of concrete cutoff wall of embankment dams

Calcium leaching is one of the essential diseases of concrete impermeable structures; therefore, an effective numerical approach to quantifying the effect of calcium leaching on concrete impermeable structures is critical for evaluating the long-term service performance of the structure. To this end, a seepage and dissolution coupling model for simulating the degradation of hydraulic concrete properties is proposed in this paper by introducing performance parameter evolutionary models based on saturated–unsaturated seepage and calcium dissolution and migration theories. The model is developed in COMSOL with a staggered solution scheme, and a detailed numerical implementation method is presented. The effectiveness of the proposed method is examined by laboratory calcium leaching tests. On this basis, the model was applied to evaluate the effect of calcium leaching on the service performance of a concrete cutoff wall (CCW) of an embankment dam in Shaanxi Province, China. The results demonstrate that the proposed method can effectively reproduce the calcium leaching process of concrete, and the variation of leaching depth based on model simulations is highly consistent with the experimental results. Calcium leaching primarily occurs at the CCW’s upstream waterfront surface, bypass seepage area and the partition of adjacent soil layers where the permeability varies greatly. Under seepage dissolution, the amount of leached calcium, average porosity, diffusion coefficient and hydraulic conductivity of the CCW increased exponentially with service duration, and solid-phase calcium leaching was the underlying cause of structural performance degradation. The length of the seepage path in the CCW decreases as the service duration increases, and the hydraulic gradient within it gradually increases. Based on the allowable hydraulic gradient of CCW, the safe service life of the CCW considering the calcium leaching effect was determined to be approximately 52a.

Degradation Mechanism of Ultra High-Performance Concrete under Coupling Erosion of Salt and Frost

Abstract With the use of ultra high-performance concrete (UHPC) in frozen areas, UHPC structures suffer from severe erosion under the interaction of salt ions and frost, resulting in significant performance degradation of UHPC structures. However, the performance degradation mechanism of different compositions and structures of UHPC under the coupling erosion of salt and frost is still unclear at present. In order to study the degraded behavior and mechanism of UHPC under the coupling erosion of salt and frost, various UHPCs were prepared and exposed to freeze–thaw (F-T) cycles and salt–freeze–thaw (S-F-T) cycles. The mass and compressive strength of the UHPCs before and after the F-T and S-F-T tests were compared to evaluate the performance degradation of UHPCs. The SPSS software correlation method, scanning electron microscope, and mercury intrusion porosimetry tests were used to analyze the mechanism of the coupling erosion of salt and frost on the UHPCs. Results indicate that UHPC with a lower water–binder ratio (WBR) and higher superplasticizer content exhibits better resistance to the coupling erosion of salt and frost. The resistance of UHPC to the coupling erosion of salt and frost will decline with the rise of WBR, and the WBR is the most significant factor affecting the coupling erosion of salt and frost for UHPC. The coupling of salt and frost decreases the compressive strength and leads to cracking of UHPC, which can be ascribed to the larger average pore size and higher cumulative pore volume caused by the salt ions. The hygroscopicity of salt ions increases the moisture in pores, and salt crystallization generates pressure in the pores, further aggravating the damage of UHPC.

Surface Confinement of Atomically Thin Pt Nanoclusters on 2D δ‐Mon for Durable pH‐Universal Hydrogen Evolution

AbstractEngineering precious metals’ sub‐nanometer cluster on 2D earth‐abundant supports provides a promising approach for the development of high‐efficient electrocatalysts in pursuit of green hydrogen. Herein, a novel solid phase deposition approach is demonstrated for the homogenous confinement of atomically thin Pt nanoclusters on 2D delta‐MoN as a viable catalyst for pH‐universal hydrogen evolution reaction. Notably, the optimized material (MoN‐5% Pt) exhibits excellent catalytic performance as evidenced by low overpotentials required, excellent mass activity exceeding 20 A mgPt−1 at 100 mV overpotential, and outstanding stability with negligible activity degradation. The enhanced performance is attributed to (1) novel nanostructure, constituting atomically thin Pt nanoclusters confined on 2D δ‐MoN substrate, thus rendering high atomic utilization and seamless surface mass transfer, and (2) influence of strong metal‐support interaction that effectively limits structural deformation and performance degradation. Theoretical simulations reveal that the strong metal‐support interaction induces substantial charge redistribution across the heterointerface, initiating an energy‐favorable multi‐active site microkinetics in which Pt atoms with an optimal hydrogen adsorption energy making way for enhanced H2 evolution, while Mo atoms situated at the heterointerface enhance water absorption/dissociation steps, enriching the catalytic surface with adsorbed hydrogen atoms.

Interfacial bonding stress transfer and failure mechanism between corrugated steel plate and reinforced concrete

The interfacial properties of corrugated steel plates and concrete are crucial for controlling the performance degradation of composite structures. To investigate the interfacial bonding performance and debonding evolution process, 13 pushout specimens are tested. The effects of concrete cover thickness, concrete strength, steel bond length, and transverse hoop height on the interfacial bonding properties are comprehensively considered. Moreover, the contributions of interfacial bonding components are investigated based on the bonding stress transfer mechanism at the interface. To study the distribution, evolution process, and damage development state of the interfacial bonding stress systematically, refined finite element models are developed. Results show that these four parameters positively affect bonding properties. The ratio of the chemical bonding force, mechanical bite force, and frictional force in the natural bond between the corrugated steel plate and concrete is 1:0.95:0.47. Additionally, the numerical results indicate that the interfacial bonding stress has a distinct non-uniform distribution. At the loading end, the bonding stress of the inclined web is generally higher than that of the flat web for the same section height. The bonding stress outside the web is greater than that inside. The outside part of the inclined web of the corrugated steel plate near the loading end is the first to exhibit interfacial damage developing towards the free end. The high stiffness at the bend of the corrugated steel plate deflects damage. Moreover, it does not fully develop in this part and is redundant.

Moisture absorption analysis of offshore wind turbine blade adhesive bonding under multi-environmental stresses

Due to long-term serving in harsh environmental conditions with high temperature, high humidity, salt fog, etc., the structural performance degradation of adhesive bonding in wind turbine blades will easily occur. Considering that material moisture absorption is closely related to structural performance, a study on moisture absorption of bonded structures under multi-environmental stresses is performed in this paper. In particular, 3 environmental stresses, the temperature, aging time, and saline concentration, are considered. A series of environmental aging tests are conducted using the variable control method. The moisture absorption properties are analyzed. The performance degradation laws of the bonded structure under the effects of multi-environmental stresses are obtained. The results are meaningful for structural performance investigation of offshore wind turbine blade adhesive bonding.