Long-time Service Research Articles

Recent progress on wet-oxygen corrosion resistance of SiCf/SiC composites

Being an aero-engine hot-end structural material, silicon carbide fiber (SiCf) reinforced silicon carbide (SiC) ceramic matrix composites (SiCf/SiC) display remarkable application potential. The wet-oxygen environment inside the aero-engine erodes the composites and leads to their performance degradation, which has become a key factor limiting the long-time service of SiCf/SiC. Finding an appropriate way to improve the wet-oxygen corrosion resistance of the composites is worthy of attention. This paper briefly analyzes the mechanisms of wet-oxygen corrosion and reviews the research progress in modified SiCf/SiC from three aspects: coatings, matrix, and interface. At last, the future development trend of the composites against the wet-oxygen environment is prospected.

Advancement in Soft Hydrogel Grippers: Comprehensive Insights into Materials, Fabrication Strategies, Grasping Mechanism, and Applications.

Soft hydrogel grippers have attracted considerable attention due to their flexible/elastic bodies, stimuli-responsive grasping and releasing capacity, and novel applications in specific task fields. To create soft hydrogel grippers with robust grasping of various types of objects, high load capability, fast grab response, and long-time service life, researchers delve deeper into hydrogel materials, fabrication strategies, and underlying actuation mechanisms. This article provides a systematic overview of hydrogel materials used in soft grippers, focusing on materials composition, chemical functional groups, and characteristics and the strategies for integrating these responsive hydrogel materials into soft grippers, including one-step polymerization, additive manufacturing, and structural modification are reviewed in detail. Moreover, ongoing research about actuating mechanisms (e.g., thermal/electrical/magnetic/chemical) and grasping applications of soft hydrogel grippers is summarized. Some remaining challenges and future perspectives in soft hydrogel grippers are also provided. This work highlights the recent advances of soft hydrogel grippers, which provides useful insights into the development of the new generation of functional soft hydrogel grippers.

Study on the Aging Characteristics of a ±500 kV Composite Dead-End Insulator in Longtime Service.

Composite insulators have been widely used in power grids due to their excellent electrical-external-insulation performance. Long-term operation at high voltage levels accelerates the aging of composite insulators; however, there is a scarcity of research on aged composite insulators operating at 500 kV for over ten years. In this paper, the mechanical, electrical, and microscopic properties were tested on different sheds along a 500 kV composite insulator that had been running for 18 years. Additionally, the results were compared with a new insulator and the standards for live insulator operation. The results showed that the aging of the high-voltage end of composite insulators was the most serious. The results of the physical properties test indicated that the insulator's hardness was compliant but its tensile strength and break elongation did not meet standards. Under wet conditions, the pollution flashover voltage decreases by about 50% compared to the new insulator. Combined with the microscopic test results, the shed skeleton structure could be damaged and the filler might be lost during the aging process of polydimethylsiloxane (PDMS). The hardness of the insulator would increase by the precipitation of inorganic silicon; however, inorganic silicon might destroy the hydrophobicity and other properties of insulator sheds. These results can provide theoretical references for insulator life prediction and operation protection.

Integrated optimization of components’ layout and structural topology with considering the interface stress constraint

Structural designs in the engineering field commonly require the prior embedding of several fixed-shape components to satisfy desired performance or functional requirements. In the past few decades, topology optimization has been regarded as an effective approach to deal with the optimization problems of continuous structures embedded with multiple components. However, the interfaces between the host supporting structure and embedded components are assumed perfect-bonded, which may result that the optimal design occurs interface failure and structural damage under extreme or long-time service conditions. In this study, a new topology optimization method of structures with embedded components considering the tension/compression-asymmetric interface stress constraint is proposed under the solid isotropic material with penalization (SIMP) method framework. This proposed method optimizes simultaneously the topology of the host structure and the layout of embedded components. A new interpolation model is developed to determine interface layers between the host structure and embedded components. Then, interface stress constraints are derived and imposed on each element of interface layers. For relieving the computational burden caused by enormous stress constraints, the global p-norm stress aggregation method is adopted to quantify the peak stresses. Subsequently, the interface stress constraint is introduced into the integrated optimization of multi-component layout and structural topology, the objective function is structural compliance and constraint functions are composed of volume, non-overlapping and tension/compression-asymmetric interface stress constraints. The corresponding sensitivity analyses are computed by using the adjoint method. Several two-dimensional and three-dimensional numerical examples are provided to verify the effectiveness of the proposed method.

High-temperature stability of Cu–20Si alloy-corundum ceramic composite thermal storage materials

High-temperature stable thermal storage materials are urgently needed to meet the demand for solar thermal power generation. Herein, Cu–20Si alloy-corundum ceramic composite thermal storage materials are prepared. The thermal storage performance of the composite, and the erosion resistance of ceramic matrix to alloy are investigated during high-temperature (1000 °C) service for 1000 h. The results show that the latent heat of Cu–20Si alloy is increased by 130.76 % to 201.2 kJ/kg compared with the original. Meanwhile, the alloy forms a dense transition layer on the ceramic matrix surface by melting and spreading. Furthermore, the ceramic matrix shows superior erosion resistance to the alloy, owing to the dense structure of ceramic and no chemical reactions between the alloy and ceramic matrix. Finally, test results of long-time service confirm the stability of the composite, which can be used stably for high temperature thermal storage.

Durability improvement mechanism of polymer cement protective coating based on functionalized MXene nanosheets modified polyacrylate emulsion

Polymer cement coatings (PCCs) have a wide range of applications in the field of concrete protection. Excellent durability of the PCCs is extremely essential for protecting the concrete in long-time service life. However, one of the most popular polymer emulsion, polyacrylate based cement coatings show insufficient durability and restrict their wide application in complicated and harsh environment. In this study, the novel two-dimensional nanomaterial MXene was incorporated to PCCs for improving the durability of the PCCs, the MXene was functinalized by vinyl triethylsilane (VTEO) (V-MXene) followed by in-situ seed emulsion polymerization method to synthesize the V-MXene modified polyacrylate emulsion. The effects of V-MXene incorporation on the rheological property, mechanical properties, bonding strength, UV aging resistance, saltwater immersion resistance, thermal aging resistance of PCCs were systematically investigated and the durability improvement mechanism was revealed. When the V-MXene dosage is 0.15 wt%, the tensile strength and bonding strength of the PCCs increased by 28.76 % and 30.84 % as compared with the blank samples, respectively. The introduction of V-MXene to PCCs can remarkably improve the UV aging resistance, saltwater immersion resistance, heat resistance. The V-MXene can decrease the UV radiation energy absorbed into the PCCs, and can create a “labyrinth effect”, prolonging the penetration path of water and corrosion ions. The V-MXene can also enhance the cross-linking density of the polymer phase combined with organic and inorganic interpenetrating networks, thereby enhancing the thermal stability of PCCs. This research provides a feasible strategy for the fabrication of high performance PCCs with excellent durability.

Effects of crystallization of inter-granular glassy phase on the mechanical performance of alumina ceramics

Alumina ceramics are widely used to fabricate the insulating tubes of vacuum electronic devices. The long-term stress borne by ceramics during service may lead to failure, so it is of great significance to investigate the mechanical reliability of ceramics. Annealing is a commonly used step in the processing of an alumina ceramic, which may affect its mechanical performance. Herein, the effects of inter-granular crystalline phase induced by annealing on the service reliability of a 95% alumina ceramic are studied, and the mechanisms are analyzed by material characterizations. Moreover, the service life of annealed ceramics is predicted through theoretical calculation. The crystallization of inter-granular glassy phase results in the decreased fracture strength of the alumina ceramic, but increases its long-time service reliability. The existence of inter-granular crystalline phases is responsible for the increase of flaw tolerance and corrosion-resistance of the alumina ceramic, and therefore the alleviated static fatigue can be obtained after annealing. Furthermore, the reliability of the annealed ceramic-Kovar alloy composite joints is analyzed, in which the stresses induced by brazing may lead to cracks in the alumina ceramic. In summary, this work discusses the influence of the crystallization of inter-granular glassy phase on the mechanical performance of alumina ceramics, which is of great value for developing ceramics with excellent mechanical reliability.

Polylactide/cellulose pulp composite paper with laminate structure via polylactide ultrafine fiber for eco-friendly straw

Paper straws with environmental friendliness have been widely used to replace plastic straws, but their poor mechanical properties and uncontrollable deformation bring an unsatisfactory experience for users. Herein, we developed a polylactic acid/cellulose fiber (PLA/CF) ultrafine-fiber paper with a sandwich‐like structure via wet papermaking and laminated hot pressing, employing PLA ultrafine fiber and CF as raw materials. The PLA/CF ultrafine fiber paper has remarkable mechanical properties due to the tangling of the fibers and the strong hydrogen bonding that occurs between the PLA and CF during hot pressing. The test results demonstrate that the tensile strength of PLA/CFs ultrafine fiber paper can reach 60.32 N/cm, and it still retains great wet strength (27 N/cm) and stiffness (117.7 mN·cm) after long-time service in various clod and hot liquids. Besides, PLA/CF ultrafine fiber paper also displays high biodegradability, with a degradation rate of 70% after being buried in soil for 120 days. We believe that PLA/CF ultra-fine fiber paper with excellent comprehensive performance can be expected to completely replace plastic straws.

In Situ Characterization of 17-4PH Stainless Steel by Small-Angle Neutron Scattering.

17-4PH martensitic steel is usually used as valve stems in nuclear power plants and it suffers from thermal aging embrittlement due to long-time service in a high-temperature and high-pressure environment. Here, we characterized the evolution of microstructures at the nano-scale in 17-4PH steel by in situ small-angle neutron scattering (SANS) with a thermo-mechanically coupled loading device. The device could set different temperatures and tensile so that an in situ SANS experiment could dynamically characterize the process of nanoscale structural changes. The results showed that with increasing thermal aging time, the ε-Cu phase precipitates and grows as the temperature is 475 °C and 590 °C, and the ε-Cu phase is spherical at 475 °C but became elongated cylinders at 590 °C. Moreover, the loading stress could aid in the growth of the ε-Cu phase at 475 °C.

Investigation of the post-treatment process for improving corrosion behaviors and adhesion strength of plasma electrolytic oxidation (PEO) coatings on pure copper

The post-treatment processes of plasma electrolytic oxidation (PEO) coatings for corrosion behaviors and adhesion strength are investigated by surface analysis and electrochemical measurements. When the PEO coating is treated with high-temperature oxidation (HTO), silane coupling agent (SCA) mixed with benzotriazole (BTA) exhibits the optimal corrosion behaviors and adhesion strength, the icorr decreases to 0.65 ± 0.35 μA/cm2, ip decreases to 4.37 ± 0.42 μA/cm2, the Epit increases to 369.6 ± 0.4 mVSCE and the bonding strength increases to 14.2 MPa. That was mainly attributed to the corrosive medium with a longer diffusion path to the interface. Moreover, only the HTO treatment at 150 °C showed superior properties for long-time service, the icorr was 2.00 ± 0.17 μA/cm2, ip was 12.30 ± 0.09 μA/cm2, the Epit was −4.7 ± 0.2 mVSCE and the bonding strength was 10.0 MPa. That was ascribed to both the outer hydroxide and the inner oxide depicted the higher compactness.

Investigation on failure of 35Cr45Ni steel at high temperature

The 35Cr45Ni steel with the high service temperature of about 1150°C was wildly used in ethylene pyrolysis device. However, the structure of 35Cr45Ni steel will change greatly after it was in service for a long time at high temperature. Therefore, in this paper, focusing on the 35Cr45Ni furnace tubes with different service time (0 and 6 years, i.e. original sample and failed sample), the microscopic morphology and elemental composition analysis were carried out to determine its failure behaviour. The results showed that the fracture morphology of the failed tube was mainly characterized by intergranular cracking, and there were carbides on the local surface of the crack, which was brittle cracking at low temperature. The precipitated phase in original 35Cr45Ni steel was mainly austenitic, M7C3 carbide and MC carbides. In a long-time service at 1000°C, the transformation of M7C3→M23C5 and MC(NbC)→Nb3Ni2Si occurred, and dispersed secondary M23C6 carbide was precipitated in the grain. Additionally, The NbC→Nb3Ni2Si transformation promoted the M7C3 to M23C5 process and the carbide precipitation as well as coarsening.

Microstructure evolution and creep behavior of nitrogen-bearing austenitic Fe–Cr–Ni heat-resistant alloys with various carbon contents

In the petrochemical industry, centrifugal cast Fe–Cr–Ni heat-resistant alloy tubes are critical components that are exposed to severe conditions for long-time service. The life of the alloy tubes is primarily limited by creep damages, which can evolve into catastrophic failures. In order to improve the creep properties in a low-cost approach, the influence of N + C content on the microstructure evolution and creep behavior of the 25Cr35NiNb alloys has been studied in this work. Creep tests were carried out at 1173 K (900 °C) and 1323 K (1050 °C) with different stress levels. Microstructure investigation on precipitates revealed that the C/N ratio significantly affects the content and morphology of Cr-rich carbides and the phase transition of Nb-rich carbonitrides after thermal exposure. By adopting the threshold stress analysis, the true creep activation energy and stress exponent of all the alloys were found to be ∼270 kJ mol−1 and ∼5, respectively, which indicated that dislocation climb is the rate-controlling mechanism of creep. Furthermore, the tailored novel N-bearing alloy possessed superior comprehensive properties of creep resistance and damage tolerance compared to the 25Cr35NiNb grade alloys. Our current findings not only realize improved creep properties by the combined modification of N addition and C/N ratio, but also provide new insights into understanding the microalloying mechanisms of high-temperature materials in general.

Fatigue-resistant design in low-cycle regime by regulating the micro-structural gradient in a TWIP steel: Modelling and experiment

It remains an intricate problem how to enhance low-cycle fatigue (LCF) performance, in the premise of guaranteeing a relatively high strength (or cyclic stress) which is vital to long-time service, for engineering components. The underlying cause of this puzzle is the lack of practical theory on cracking evolution/life prediction for LCF. In this study, a two-stage constitutive LCF crack growth model was proposed for a homogeneous solid and later developed for graded structures. Based on the model, a material design strategy emphasizing the strength gradient architecture (informally, hard core and soft shell structure) is proposed and analyzed to improve the LCF properties of engineering structural materials, e.g., steels. Experimentally, sharp and gradual strength gradients were carefully introduced into a TWIP steel by a series of well-designed process combinations regarding various (heterogeneous) deformation and annealing treatments. The influences of strength/microstructure and their spatial distributions on the LCF behaviors were systematically investigated. The excellent LCF properties of the TWIP steel with a negative strength gradient are originated from the repeated strengthening and weakening of strain gradient during cyclic loading, which suppresses the fatigue crack initiation and growth. The crack initiation/propagation model developed in this study is conducive and applicable to the LCF life prediction. The theory and process of constructing microstructure gradient, and therefore mechanical property gradient, may provide new and important implications for engineering metals on anti-LCF design.

Migration and agglomeration behaviors of Ag nanocrystals in the Ag-doped diamond-like carbon film during its long-time service

Silver-doped diamond-like carbon (Ag-DLC) films are considered as promising materials for the surface modification of mechanical components and biological implants. The long-term stability of Ag-DLC films is essential for their commercial use and requires intensive investigation. In this study, DLC and 10.0 at.% Ag-DLC films were prepared using a hybrid deposition technique, and the existence and evolution of Ag atoms over time were systematically studied. The results show that Ag atoms with a lower Ehrlich–Schwoebel barrier than that of C atoms are more prone to interlaminar diffusion, refining the columnar structure of DLC films and thereby creating a compact structure. In the as-deposited Ag-DLC film, Ag atoms mainly existed as fine nanocrystals with sizes ranging from 3 to 5 nm. Ag elements diffused with time during its long-time service, and fine Ag nanocrystals agglomerated to form large nanocrystals. The calculation results by density functional theory confirmed that the proximity of Ag atoms can lower the system energy, rendering agglomeration thermodynamically stable. Molecular dynamics simulations verified the spontaneous migration and agglomeration behaviors of Ag atoms over time. This study was focused on the evolution of Ag-DLC films over time and would provide guidance for their use in long-term applications.

Phase-field microstructure-based effective thermal conductivity calculations in tungsten

Using a phase-field approach with the heat conduction equation, we predict the grain growth behaviors in tungsten (W) and their effects on effective thermal conductivity. Results show that the simulated grain growth kinetics is basically consistent with experimental observations. An empirical correlation is derived, describing the averaged grain area as a function of temperature and time. Further, we study the effect of grain growth, columnar crystal structure, and recrystallization on the effective thermal conductivity of W. It is found that the effective thermal conductivity increases nonlinearly with increasing grain size, and a simple correlation of converting two-dimension into three-dimension effective thermal conductivity is obtained. Interestingly, the effective thermal conductivity of the columnar crystal is relatively high along the elongated direction and higher than that of the isometric crystal. Nevertheless, the effective thermal conductivity decreases with the occurrence of the recrystallization due to the increased grain boundary density. Our results reveal that grain growth and grain structure can affect the capacity of heat transfer at high temperatures, which could be considered in the transient event of the long-time service of W materials in fusion devices.

Microstructural Evolution for Super304H Austenite Steel used in China Plants

Super304H (18Cr-9Ni-3Cu-Nb-N) austenite steel has high creep strength and has been used as the material of tubes in 600℃ class supercritical power plants in China. Many Super304H materials have run for more than 100,000 hours. Long-time service feature of these austenitic stainless steels has not been understood. An understanding of the long-term microstructural evolution under actually used conditions is a key for the improvement of these heat resistant steels. In this article, creep behavior of Super304H used in China plants was analyzed, microstructural evolution of Super304H materials after different service conditions were studied involving in optical microscope, TEM and SAXS. The results show, M23C6, Cu-rich particles, and σ phase were found to precipitate. A quantitative assessment of microstructure evolution was given during long-term creep.

Fracture resistance of naturally corroded steel after service for 128 years

The fracture resistance of steel in aged structures after long-time service can be significantly degraded by corrosion, which can lead to catastrophic failures of the structure. This paper aims to experimentally investigate the fracture characteristics of naturally corroded steel cut from a bridge girder after 128 years’ service. Mechanical tests and microstructural analyses are conducted on the specimens with various levels of corrosion and the relationship between fracture toughness reduction and corrosion level is quantitatively investigated. The fracture mechanism of the corroded steel is critically analysed and discussed. It is found from the test results that steel subjected to pitting corrosion has strong negative correlation with the local corrosion levels in front of the pre-cracks of the specimens, but is seldom related to the overall corrosion levels. The uneven corroded surfaces of specimens lead to significant differences in the J-R curves of the specimens with a similar range of average pit depth. It is also found from the fractography analyses that less ductile fracture characteristics are exhibited near the severe corrosion pits, which limits the fracture resistance of corroded steel. The findings presented in this paper can contribute to the development of optimal maintenance strategies of aged steel structures for engineers and asset managers.

Rising Again in Phoenix!

The 2022 CSE Annual Meeting will take place May 1–3 in Phoenix, AZ, and we have the honor of serving as this year’s Program Committee Co-Chairs. Along with our dedicated Committee members, we are working diligently to carry on CSE’s tradition of outstanding educational content and networking opportunities. We’re thrilled to announce that the theme for this year’s meeting is “Phoenix Rising: Adapting, Collaborating, and Learning in Scholarly Publishing.” As the first in-person CSE Annual Meeting since 2019, this year’s conference will offer attendees the opportunity to meet new industry colleagues on site. As we have all learned during the past few years, both professionally and personally we must be willing to adapt to changing circumstances, imagine new ways to collaborate, and consider each other as vital sources for new learning. Breakout sessions presented by expert speakers at this year’s annual meeting will be a mix of tried-and-true topics with universal interest to editorial offices, journals, authors, and reviewers, and will include lessons learned during the pandemic. We are looking forward to 2 keynotes this year. First, undoubtedly, you’ve noticed a lot of activity in the mergers and acquisitions space, with publishers buying services companies and long-time service providers buying platforms and technology startups. The Program Committee was curious about how all of these developments would affect publishers, especially society publishers. Lisa Janicke Hinchliffe, Professor and Coordinator for Information Literacy Services at the University of Illinois at Urbana-Champaign, and Roger Schonfeld, Director, Libraries, Scholarly Communication and Museums at Ithaka, have […]

Microstructure and properties evolution of Co06/Ni60A duplex coating on copper by plasma cladding

Co06/Ni60A duplex coating was fabricated on copper substrate by plasma cladding. To clarify the evolution of microstructure and wear resistance of the coating during high-temperature, the coating samples were heat-treated at 500 °C for up to 500 h in air. After heat treatment, the phases in the coating such as Cr 7 C 3 , Cr 23 C 6 and the crystal grains of the γ-Co solid solution had a tendency to grow up, and remained basically stable after 100 h. No martensite transformation (γ-Co → ε-Co) was observed. The mass fraction of Cr 23 C 6 reinforcement phase had an increasing trend, which was attributed to the conversion of Cr 7 C 3 and the precipitation of γ-Co solid solution. The diffusion degree of elements at the Co-Ni interface and Ni-Cu interface also showed a trend of stabilizing. Due to the coarsening of microstructure, the diffusion of copper and the reduction of Cr 7 C 3 , the wear resistance of the coating changed from 6.2 times to 2.9 times that of the copper substrate. The wear mechanism transformed from abrasive wear to abrasive wear + adhesive wear. Results showed that the properties of the coating have a certain decline in the initial stage, but it tended to be stable after long-time service. • Co06/Ni60A duplex coating was prepared for high temperature applications. • The microstructure evolution of the coating in high-temperature air was analyzed layer by layer. • Microstructure coarsening, copper diffusion and Cr 7 C 3 reduction reduced the wear resistance of the coating. • The gradual stabilization of the properties after long-term heat treatment indicated the usability of the coating.

Wind Effect Analysis of a High-rise Ancient Wooden Tower with a Particular Architectural Profile via Wind Tunnel Test

ABSTRACT Wooden architectural heritage is a symbol of architectural heritage worldwide and has high historical, cultural, and scientific values in Asia countries (e.g., China, Japan, Korea, and Nepal). Wooden pagoda (a kind of tower with multiple eaves in East Asia) serving as one important member of wooden architectural heritages suffers from damages that are caused in various natural disasters such as windstorm, fire, and earthquake due to its long-time service and considerable size. Wind caused damage is one of the most common damages caused by natural disasters, making the structural safety of high-rise wooden pagodas under wind action a major concern in architectural heritage protection. This study analyzes the wind effects on the Yingxian wooden pagoda in China by a wind tunnel test and computes the wind loads on the wooden pagoda. The wind characteristics of wooden the pagoda in a wind tunnel test are presented and compared with modern buildings and other types of wooden architectural heritages. Additionally, this study attempts to analyze the difference of the computed wind loads from the wind tunnel test and from the full-scale measurement. The results reveal that the wind pressure distribution at certain locations are similar to those of modern buildings or other ancient wooden architectures. However, the wind pressure distribution at some locations are distinctive due to the complexity of the architectural profile (e.g., the boundary of the pagoda is an octagon in bird view). The wind load from wind tunnel test are in good agreement with those in full-scale measurement with less than 14% error. This study extends the understanding of the wind effects and structural safety assessment on the high-rise wooden pagoda, providing useful guidelines for structural design (e.g., wind-resistant design) and for structural health monitoring (e.g., service maintenance) to monitor not just the specific wooden pagoda but also other high-rise pagodas, especially the those with top views of octagonal shapes.