Long-term Life Prediction Research Articles

Creep Phenomena, Mechanisms, and Modeling of Complex Engineering Alloys

Metal creep has been a subject of extensive study for more than 110 years because it affects the useful life of engineering components operating at high temperatures. This is even more true with ever-increasing operating temperatures of propulsion/power-generation systems and the environmental regulations to reduce greenhouse emissions. This review summarizes the recent development in creep modeling with regards to creep strain evolution, creep rate, creep ductility, creep life, and fracture mode, attempting to provide a comprehensive mechanism-based framework to address all the important creep phenomena and the long-standing issue of long-term creep life prediction with microstructural evolution and environmental effects.

Long-term properties evolution and life prediction of glass fiber reinforced thermoplastic bending bars exposed in concrete alkaline environment

Glass fiber reinforced polypropylene (GFRPP) bending bars have many advantages, such as high toughness, high durability, repeated molding and recycling, which can be used in concrete structures to replace steel stirrup for solving the problems of corrosion and service life. However, the changes in the properties of GFRPP bending bars during long-term use in alkaline concrete environments require further investigation. In the present study, GFRPP bending bars were immersed in alkaline solution at 20 °C, 40 °C, and 60 °C for as long as 180 d. The water absorption, hydrolysis, mechanical properties, and microscopic properties of the bending bars were evaluated to understand the long-term performance and mechanism of degradation. The bending bars had a higher saturated water absorption percentage and time along with a lower diffusion rate than the straight bars due to the presence of pores and micro-cracks formed during the bending process. The dissolution of the glass fibers in alkaline solution led to the partial mass loss of the GFRPP bars. Compared to the control, the tensile strength retention of the bending bars was 20.6%–56.0 %. The tensile failure mode changed from fiber bursting before immersion to shear fracture after immersion due to the decreased interfacial bonding strength and increased glass fiber brittleness. The primary degradation mechanisms were the etching of glass fibers, interface debonding, and increased void volume (∼23.7 %). The bending bars were more seriously eroded than the straight bars due to the twisting of the fibers and imperfect interfaces. The predicted degradation times of the GFRPP bending bars ranged from 1.7 years (Haikou) to 3.9 years (Harbin), corresponding to a stable tensile strength retention of 22.13 %. The results provide a basis for evaluating the durability and service life of GFRPP bending bars and promote the application of GFRPP composite stirrups in concrete structures.

Long-term life prediction of wearable CFRP lower limb exoskeleton suit by applying a multi-scale FEA and time-temperature superposition

This study explores the application of Carbon Fiber Reinforced Plastics (CFRP) in lightweight design for wearable exoskeleton suits, crucial for success in industrial settings. We aimed to predict the lifespan of the exoskeleton in terms of temperature and time rather than merely confirming its ability to withstand loads. The material’s viscoelastic behavior, establishing a master curve for long-term creep compliance, was characterized using Dynamic Mechanical Analysis (DMA). We also performed mechanical tests under various temperature conditions to measure strength in the load and fiber directions and carried out statistical analysis. From the test results, we constructed the master curves considering the probability of predicting the long-term strength variations. Subsequently, A multi-scale model assessed the exoskeleton frame’s failure, revealing no failures in the current model under given load conditions, with the highest failure index of 0.7 for matrix tensile failure. Combining the predicted long-term strength results, the lifespan prediction for matrix tensile failure under a reference temperature of 50°C was approximately five years. The findings and methodology of this study can serve as a guide for predicting long-term performance and lifespan when applying CFRP to exoskeletons.

Deterioration modes, mechanisms, and effects of flexible landfill facilities disposing hazardous waste

Dynamic performance and lifespan predictions are essential for understanding the whole life-cycle emissions and environmental impacts of landfills. However, there are knowledge gaps regarding the major failure modes and mechanisms in flexible hazardous waste landfills (FHWLs) and their potential effects on the service life of landfills. These issues limit the advancement of related research. In this study, focusing on flexible landfills, failure mode, mechanism, and effects analysis was conducted to identify the major failure modes, mechanisms, and impacts that may occur in landfills under extremely harsh chemical and stress conditions. The results indicate that there are approximately 33 major components and materials in landfills, corresponding to 35 potential failure modes and more than 60 underlying failure mechanisms. Notably, the failure of the drainage media in the drainage system is concerning and challenging to recover from. In contrast, the failure of the high-density polyethylene geomembrane (HDPE GMB) in the liner system (LS) is considered serious and is prone to occur, but it is also difficult to detect. Therefore, these two failure modes were identified as critical factors affecting the degradation of the performance and longevity of FHWLs. Finally, due to their high probability of occurrence and severe impacts, stress damage (physical damage) and oxidative aging were identified as the main degradation modes of HDPE GMB, the core material in FHWLs. This study provides key insights into performance prediction targets, failure modes, and failure mechanisms for further research on long-term landfill performance and life prediction. It prompts the government and stakeholders to re-examine the rationality behind the positioning of landfills, such as the assumptions of unlimited service and solid waste management endpoints. Therefore, it calls for a reassessment and optimization of the full life cycle emissions of landfills and related waste.

Alkalinity optimization and long-term life prediction for BFRP bars serving in simulated marine concrete environments

The high alkalinity of concrete matrix considerably shortens the service life of fiber-reinforced polymer (FRP) bars. Regarding the influence of metal ion and hydroxide ion concentrations, this research aims to explore the degradation behavior of basalt-fiber-reinforced polymer (BFRP) bars under different alkalinity gradients by changing the Ca(OH)2 contents in pore solution. The physical and mechanical properties of BFRP bars were evaluated. Morphology of the BFRP cross section, the chemical structure of the surface resin and ionic dissolution of fibers attacked in different pore solutions were characterized. The findings showed that reducing the alkalinity of the simulated marine concrete pore solution can effectively migrate the corrosion of BFRP bars. Notably, all experimental results indicate that there exists an optimal alkalinity value (pH = 11.07, 0.15 g/L Ca(OH)2), minimizing the degradation rate of BFRP bars under the designed alkalinity gradient at 25 °C. The service life prediction results show that lowering the alkalinity of pore solution (pH from 13.24 to 11.07) in marine concrete can prolong the service life of BFRP bars in concrete structures by up to 60 times.

Experimental study on the mechanical properties of CFRP/epoxy composite plates under seawater immersion

This study investigates the effects of seawater immersion at different temperatures on the degradation and viscoelastic behavior of carbon fiber-reinforced polymer (CFRP) composite plates. The present study investigated the effects of seawater immersion on the degradation of mechanical properties at 20 °C, 40 °C, and 60 °C of the carbon fiber reinforced polymer (CFRP) composite plates. The specimens were prepared by hand lay-up and cured under water for 7 days before immersion in artificial seawater for 6 months. Interlaminar shear strength (ILSS), tensile strength, and dynamic mechanical analysis (DMA) tests were performed periodically over a six-month exposure period, and scanning electron microscopy (SEM) was used to characterize aging damage and fracture morphology. The long-term shear behaviour of CFRP plates in seawater has been predicted using the Arrhenius theory. The results show that immersion in seawater significantly reduces ILSS, especially at higher temperatures and longer immersion times. However, the overall tensile properties of CFRP plates were not significantly affected. Dynamic mechanical analysis (DMA) revealed a decrease in the damping (tan δ), indicating a reduction of the fiber-matrix adhesion. The long-term life prediction showed that CFRP plates subjected to seawater immersion are susceptible to degradation, with a stable retention of interlaminar shear strength at 70% for the composite laminate.

Hygrothermal aging behavior and mechanism of multi-filler reinforced epoxy composites for steel structure coatings

The long-term hygrothermal resistance of epoxy-based composites plays a key role as an anti-corrosion and anti-wear coating for steel structures when exposed to complex service environments. The hygrothermal aging will cause an irreversible damage to the service performances of composites. In the present paper, the multi-fillers reinforced epoxy composites (MFREC) had been successfully prepared and have been given higher expectations for steel coatings. Its hygrothermal aging behavior was experimentally investigated through the immersion in distilled water (DW) and saline water (SW) at 20, 40, and 60 °C as long as 120 days. The moisture uptake, thermal properties, mechanical properties and microstructure analysis were tested to evaluate the long-term hygrothermal evolution. The research results showed that the quasi-equilibrium moisture uptake content (3.72%) of MFREC in SW was lower than that (4.14%) in DW owing to the preferential permeation and occupation effects of small ions (Na+, Cl−). Hygrothermal exposure led to a maximum degradation of tensile strength, elongation at break and glass transition temperature of MFREC, up to 38.2%, 46.6% and 20.8% in DW, and 34.5%, 40.8% and 18.4% in SW, respectively. This was because the epoxy matrix had generated relaxation and reinforced-fillers/epoxy interfaces had been destroyed, which can be verified by hydrogen bond increasing (maximum 75.2%) from infrared test, fiber pulling out from epoxy matrix (morphology analysis), elastic modulus decreasing (maximum 37.8%) from micro-hardness measurement and pore volume increasing (maximum 53.9%) from N2 adsorption test compared to unaged samples. Based on the Arrhenius theory, the long-term life prediction of MFREC tensile strength under three typical bridge service environments was conducted to evaluate the service time as coatings. It can be found that the stable strength retentions were 63.19% and 66.03% in the simulated pure water and marine environments, respectively. Furthermore, an additional strength degradation percentage up to 11.5% can be found for MFREC exposed to steel bridge coatings in southern as long as 3 years compared to the northern environment.

Evaluation of fatigue life of semi-flexible pavement with cement asphalt emulsion pastes

Semi-flexible pavement (SFP) has been receiving more attention in pavement engineering due to its excellent rutting resistance. However, conventional SFP has a lower cracking fatigue resistance than conventional asphalt mixture due to its brittleness. To improve its fatigue resistance, cement-asphalt emulsion paste (CAEP) is employed as a more suitable grouting material to prepare SFP, and the effect of asphalt emulsion content in grout on the fatigue resistance of SFP is investigated. Since the elastic modulus of SFP with different CAEPs differs significantly, the typical tensile stress response of different SFPs in pavement structure varies greatly; thus, the fatigue resistance of SFPs is influenced considerably. To reasonably evaluate the fatigue resistance of SFPs, the fatigue life of SFPs at the typical tensile stress is studied. To this end, firstly, the fatigue models of materials were established for long-term performance evaluation and fatigue life prediction by employing indirect tensile fatigue test. Secondly, the tensile stress at the bottom of surface layer materials under realistic tire-pavement interactions was estimated by a three-dimensional (3D) finite element method (FEM). Finally, obtained tensile stresses from pavement response analysis were used in fatigue models to select an ideal SFP in terms of fatigue performance. The fatigue evaluation results indicated that conventional SFP with cement paste has much lower fatigue resistance than conventional asphalt mixture. The fatigue resistance of SFP can be greatly improved when CAEP is used as grout in SFP. When the asphalt emulsion to cement ratio by mass (AE/C) is 0.4, SFP can have better fatigue resistance than conventional asphalt mixture. Therefore, CAEP with AE/C at 0.4 is recommended as the best grout in SFP to obtain the best fatigue resistance.

Comparative Study of Durability Behaviors of Thermoplastic Polypropylene and Thermosetting Epoxy Exposed to Elevated Temperature, Water Immersion and Sustained Bending Loading.

The long-term degradation of epoxy as the matrix and adhesive serviced in harsh environments plays a key role in engineering applications. Understanding how to improve the toughness and durability of epoxy through reasonable material replacement and design is significant to prolong the service life of engineering structures. In the present paper, thermoplastic polypropylene and thermosetting epoxy were exposed in a coupling environment of elevated temperature, water immersion and sustained bending loading. The evolutions of mechanical and thermal properties were further analyzed and compared. Long-term life prediction was conducted to evaluate the corrosive resistances of polypropylene and epoxy. It can be found that polypropylene has better hydrophobic behavior compared to epoxy. At 80 °C, the ratios of the diffusion coefficient and saturated water uptake between the two matrices were 114.4 and 2.94. At the longest immersion time of 90 days, the degradation percentages of tensile strength were 4.7% (40 °C), 7.5% (60 °C) and 8.8% (80 °C), respectively, which had the higher strength retention (>90%). The maximum strength increase in the multiples of polypropylene/epoxy and polypropylene/polyurethane was 1.95 and 1.75, respectively. The bending loading led to a maximum increase in tensile strength (~1.47%) owing to the oxygen isolation effect. The degradation mechanism was attributed to the active functional groups from the production process reacting with oxygen, resulting in the fracture of the local chain segment. By comparison, water molecules reacted with the hydroxyl groups or interrupted the intermolecular Van der Waals force/hydrogen bond of the epoxy, resulting in irreversible hydrolysis and property degradation. Through the comparison, it can be found that polypropylene and its composites have outstanding properties compared to epoxy, which can make them achieve great application prospects in engineering applications when considering a complex service environment.

Mechanical performance evolution and life prediction of prestressed CFRP plate exposed to hygrothermal and freeze-thaw environments

The long-term prestressed loss of anchorage system and mechanical property evolution play the significant role for the steel/concrete structures strengthened with prestressed CFRP plates. In the present study, a wedge-extrusion bond anchorage system was applied to provide the reliable anchorage load-bearing capacity for CFRP plate. A new prestressed tension device was put forward to realize the coupling exposure of elevated temperature (20 °C, 60 °C and −20 to 30 °C), distilled water and sustained loading (20%, 40% and 60%). The mechanical and thermal properties of CFRP plate were conducted to obtain the long-term evolution exposed to the above environments. The mechanical analysis and tensile tests of anchorage system showed the tensile failure modes under the static and cyclic loads were the CFRP burst, and there was no debonding occurring in the anchor. The higher anchorage capacity was attributed to the uniform stress distribution of CFRP plate parallel to the greatest dimension of cross section in the anchor. The new prestressed tension device can realize the maximum prestressed level (∼70%) with an allowable prestressed loss (∼300 με). Meanwhile, the prestressed loss of CFRP plate exposed at the maximum temperature (60 °C) and longest time (90 days) was found to be ∼300 με. Immersed at higher temperature and prestressed level brought about an additional degradation rate of tensile strength (5%∼10%). The minimum strength retention of CFRP plate was found at the freeze-thaw exposure for 90 days. The long-term life prediction showed the residual tensile strength retentions of CFRP plates were more than 50% for the maximum prestressed level (60%) for the service life of 30 years in civil engineering structures.

Statistical life prediction of a unidirectional carbon fiber/polypropylene laminates under creep bending load

Our developed accelerated testing methodology (ATM) based on matrix resin viscoelasticity for the long-term life prediction of carbon fiber reinforced plastics (CFRP) was applied to assess the statistical prediction of long-term creep failure time of a carbon fiber/polypropylene unidirectional (CF/PP) laminates under creep bending load. Results show that the statistical long-term creep failure times under an arbitrary constant bending load and temperature for the CF/PP laminates can be easily predicted from the statistical static strengths of the CF/PP laminates measured at several temperatures and the viscoelasticity of matrix PP.

Mechanical properties of carbon/glass fiber reinforced polymer plates with sandwich structure exposed to freezing-thawing environment: Effects of water immersion, bending loading and fiber hybrid mode

In this article, two kinds of carbon/glass fiber hybrid rod with the sandwich structures were designed and developed through the pultrusion technology, including the fiber random hybrid (RH) mode with multi-layer sandwich structure and fiber core-shell hybrid (CH) mode with single-layer sandwich structure. The hybrid sandwich-structure plates were prepared from the rod and immersed in bending loading, temperature alternating and sustained water immersion as long as 360 days. The effect of fiber hybrid mode/sandwich structure on the degradation mechanism of mechanical properties was revealed through the digital image correlation and thermogravimetric analysis. Through the fiber hybrid design, the strength improvement percentages of RH plates with multi-layer sandwich structure were up to ∼50% (tensile strength), 30 ∼ 40% (flexural strength) and 18% (in-plane shear strength) compared to CH plates with single-layer sandwich structure. Higher bending loading level brought about the decrease of flexural strength and in-plane shear strength close to 18% and 19%, respectively. During the immersion, microcracks or microvoids formed and expanded in the resin tensile area under the bending loading and water diffusion, leading to the uncoordinated stress concentration for single-layer sandwich-structure CH plate. By uniformly dispersing carbon fibers into glass fibers, the uneven interface stress concentration can be effectively alleviated for multi-layer sandwich-structure RH plates. The comparison of mechanical properties with the others’ work showed the interface shear strength was more sensitive to the bending loading and immersion temperature. The long-term life prediction showed the maximum increase percentages of mechanical properties of multi-layer sandwich structure were 435.4% (tensile strength) and 149.2% (flexural strength) and 110.7–114.2% (shear strength) compared to the single-layer sandwich structure.

Combined effects of sustained bending loading, water immersion and fiber hybrid mode on the mechanical properties of carbon/glass fiber reinforced polymer composite

Fiber reinforced polymer composites have great potential to replace steel for bridge cables, underground oil extraction and ocean engineering owing to light weight, high strength and desirable corrosion and fatigue resistances. How to reduce the material cost and improve the durability through the reasonable material design is significant to promote the engineering application. In the present paper, two kinds of carbon/glass fiber hybrid plates were developed including the fiber random hybrid (RH) and core–shell hybrid (CH) modes. The exposure of sustained bending loading and water immersion as long as 360 days was conducted to investigate the effect of fiber hybrid mode and bending loading on the mechanical properties. The results showed the synergetic effects between the carbon and glass fibers can be fully developed through the random fiber hybrid mode. Furthermore, the incongruous bearing behavior and stress concentration of carbon/glass fiber/resin interface were largely relieved, which contributed to higher mechanical properties. Compared to CH plate, the maximum increase percentages of tensile and flexural strength for RH plate after 360 days were 51.3% and 39.7%, respectively. Higher bending loading level resulted in the fast formation of microcracks, which provided more storage space for the water molecule and accelerated the resin hydrolysis and interface debonding of fiber/resin. Finally, the long-term life prediction of hybrid plate in three typical bridge service environments showed the RH plate has superior corrosive resistance compared to CH plate. The retentions of tensile and flexural strength for the service time of five years were close to 30–40% and 50–60%, which provided the durability guideline based on fiber hybrid design for the engineering applications.

Water uptake and interfacial shear strength of carbon/glass fiber hybrid composite rods under hygrothermal environments: effects of hybrid modes

The hygrothermal aging of fiber reinforced polymer (FRP) composite rod served as bridge cables played a key role on the long-term service performances. In the present paper, two types of pultruded carbon/glass fiber reinforced epoxy hybrid composite rods, one with uniformly dispersed carbon and glass fibers, and the other with glass fiber shell and carbon fiber core, were investigated on the water uptake and interface shear strength. The aging condition was immersion in deionized water at 40 °C, 60 °C and 80 °C. Interface shear strength degradation mechanism was revealed by thermal analysis and microstructure analysis. It was found that the water absorption of two types of hybrid rods represented the two-stage behavior. For the rod of uniform fiber dispersion, more water uptake in the second stage occurred compared to that of the shell/core rod, which was attributed to the resin rich area and interface debonding of fiber/resin. Long-term hygrothermal exposure led to a remarkable degradation in the interfacial shear strength of the rods, up to 17.5% ∼ 42.1%. The resin plasticization and interface debonding were the main factors contributed to the strength degradation. Based on the Arrhenius equation, the long-term life prediction of the interfacial shear strength under two typical bridge service environments was conducted to the design guideline of hybrid rods in the bridge engineering.

Effects of rod size and fiber hybrid mode on the interface shear strength of carbon/glass fiber composite rods exposed to freezing-thawing and outdoor environments

Fiber reinforced polymer composite rod has attracted wide attentions to replace the steel rod as bearing component in bridge cable and underground oil extraction. In the present paper, three kinds of carbon/glass fiber reinforced polymer hybrid rods were developed to reveal the effects of rod size (19 and 22 mm) and fiber hybrid mode (core–shell hybrid and random hybrid) on the interface shear strength exposed to freezing-thawing and outdoor environments. Water uptake, mechanical, thermal properties and density tests were conducted to obtain the long-term evolution. The fiber random hybrid mode brought about a slight increase of water uptake compared to the fiber core–shell hybrid mode. The effects of temperature and temperature-alternating on the water uptake acceleration factors were remarkable compared to the hydraulic pressure and salty concentration. Furthermore, the increase of rod diameter prolonged the saturated water uptake time up to 81.4–136.9%. The obvious degradation of interface shear strength was attributed to the hydrolysis and plasticization of the resin owing to the water uptake and the microcracks formation. After drying, the remarkable recovery up to 20.3% of interface shear strength can be observed. Based on the long-term life prediction, the effect of temperature-alternating on the degradation of interface shear strength was more remarkable compared to the constant temperature, leading to the lowest stable strength retention of 38.7%. Furthermore, the rods with the fiber random hybrid mode and smaller diameter possessed the superior corrosive resistances, which provide the long-term design guideline in the application of bridge cable and underground oil extraction.

Long-term gear life prediction based on ordered neurons LSTM neural networks

• A new gear RUL prediction model based on ON-LSTM is proposed. • The physical explanation of ON-LSTM is firstly achieved. • The frequency center index is found to be suitable for the gear health index. • This method has better long-term prediction ability than other traditional methods. • This method can implement RUL prediction in the case of small samples. Gear failure may affect the operation of mechanical equipment, and even cause the catastrophic break of machine and even casualties. Thus, the remaining useful life (RUL) estimation of the gear has important significance. This paper proposes a gear RUL prediction model based on ordered neurons long short-term memory (ON-LSTM) networks. The proposed methodology consists of two parts: firstly, extract the health index by computing frequency-domain features of raw signals; secondly, the ON-LSTM network model is constructed for generating the target output of the RUL prediction. Unlike the traditional LSTM neural network, the developed model integrating tree structures into LSTM to use the sequential information between neurons, so it has enhanced predictive ability. In comparative experiments, the Scores of ON-LSTM, LSTM, GRU, DLSTM and DNN are 0.398, 0.129, 0.07, 0.029 and 0.102, respectively; and ON-LSTM successfully fulfils twenty-three tasks while LSTM just fulfils five tasks in long-term prediction. Moreover, ON-LSTN only requires about 400 iterations for convergence, which is much faster than other RNNs. Experimental results show that ON-LSTM network achieved the best accuracy of short-term and long-term prediction, and it has the best robustness and convergence speed. And it can be effectively applied to the RUL prediction of gears.

Creep Performance Modeling of Modified 9Cr-1Mo Steels with Oxidation

In this study, the deformation-mechanism-based true-stress (DMTS) creep model is modified to include oxidation influence on the long-term creep performance of modified 9Cr-1Mo steels. An area-deduction method is introduced to evaluate oxide scale formation on the creep coupons, which is incorporated into the DMTS model formulated based on intragranular dislocation glide (IDG), intragranular dislocation climb (IDC), and grain boundary sliding (GBS) mechanisms, in modifying the true stress. Thus, the modified DMTS model can not only describe the creep curve, but also predict the long-term creep life and failure mode, which is shown to be in good agreement with the creep data generated in the authors’ laboratory as well as by the National Institute for Materials Science (NIMS) of Japan for long-term (> 104 hours) creep life prediction on Grade 91 steels. In particular, the predictability of the model is demonstrated in comparison with the Larson–Miller parameter method. In addition, the modified DMTS model provides quantitative information of mechanism partitioning, insinuating the failure mode via intragranular/intergranular deformation. Therefore, it has advantages over the empirical models in providing physical insights of creep failure, which can be useful to material design for performance optimization.

Mechanical behavior and long-term life prediction of carbon/epoxy and glass/epoxy composite laminates under artificial seawater environment

This paper presents an investigation on the long-term performance of carbon/epoxy and glass/epoxy laminates in an artificial seawater environment with 3.5% salinity. Accelerated aging tests were conducted at 60 °C for 45 days to characterize the long-term effect of seawater on the mechanical response of fiber-reinforced composite laminates. Several mechanical tests including tensile and 3-point bending tests have been carried out on the reference/dry and aged standard samples at room temperature and 60 °C to evaluate tensile strength, young’s modulus, flexural strength, secant and chord modulus of elasticity in the composite samples. The long-term behavior of carbon/epoxy and glass/epoxy samples under the service construction condition in the coast of Ireland was also predicted using Arrhenius degradation theory.

Prediction of temperature-frequency-dependent mechanical properties of composites based on thermoplastic liquid resin reinforced with carbon fibers using artificial neural networks

A considerable interest has been generated in recent years in the use of thermoplastic polymers as matrices in the manufacture of advanced composites that require high reliability during long-term operations. In this research, a new Elium® acrylic matrix developed by Arkema was studied to evaluate the accelerated test methodology based on time-temperature superposition principle of Carbon Fiber/Elium® 150 composites. The results show that the high frequencies increase the glass transition (Tg) to higher values because the free volume is favored by polymer chains movement. In addition, artificial neural network has been used to model the temperature-frequency dependence of dynamic mechanical over the wide range of temperatures and frequencies due to its complex non-linear behavior. It has been observed that low frequencies result in low damping due to the lower internal friction, while high frequencies provide greater stiffness to the chains, resulting in a high damping. The long-term life prediction using master curves confirms that this new material can be considered to acoustic or vibrational damping purposes, considering its use in temperatures above Tg.

Porcelain suspension insulator for OHTL: A comparative study of new and used insulators using 3D-CT

The 3D-CT technique, which is a non-destructive method, is used to verify the use of porcelain insulators for overhead transmission lines (OHTL). 3D-CT techniques are often used to detect defects such as cracks in automotive parts or in the medical field. The results of the 3D-CT technique applied to porcelain insulators indicate a clear difference in the size and distribution of pores between new and used porcelain insulators. The most significant difference is the degradation rate of the porcelain insulator. In the case of the used product, the largest pore size of 24 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was found in the cement part exposed to the external environment; however, no pore was found in the new product. In addition, for the used porcelain insulator, 18 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> pores were found in the pin head part, which is a part where stress is concentrated; however, few small pores were found at the same position in the new porcelain insulator. Based on the size and distribution of the pores, the areas where the deterioration was the most rapid were identified. The pore area of the cement at the bottom of the cap was five times larger than that at the top when compared to the total area of the cement. This study confirms the size and distribution of defects occurring in the insulator based on aging and provides insight into the long-term reliability and life prediction of insulators.