Thermal Aging Time Research Articles

Mechanical and thermo-oxidative resistance properties of natural rubber film reinforced by orange peel-based carbon dots

Bio-based carbon dots (CDs) have a wide range of precursor sources, abundant chemical functional groups, and good free radical scavenging ability. This makes them an excellent candidate for modifying natural rubber (NR). In this work, CDs were synthesized from orange peels using a hydrothermal process and were utilized to reinforce NR latex. The structure and properties of both the CDs (including morphology, functional groups and fluorescence emission spectra) and NR/CDs films (including crosslinking density, morphology, functional groups, and mechanical properties) were comprehensively investigated. The results indicate that the inclusion of CDs led to improvements in tensile and tear strength while maintaining undamaged elongation at break. The tube model results indicate that the Ge (the elastic modulus brought by entangled chains) is significantly higher than the Gc (the elastic modulus contributed by chemical crosslinking) in this system, suggesting that the physical entangled network play a more significant role than chemical cross-linking; and the trend of Gc+Ge with the amount of CDs aligns completely with the cross-linking density measured by swelling method. Additionally, it was observed that CDs exhibited excellent thermo-oxidative resistance properties for NR. After 24 hours of thermal aging, the aging coefficient increased from 20.7% (NR-0) to 65.8% (NR-7). Furthermore, with an increase in thermal aging time, the tensile strength and crosslinking density of NR-0 decreased at a faster rate compared with NR-5. At an aging time of 40 hours, the tensile strength of NR-0 was reduced to 0.53 MPa and almost completely failed; whereas the tensile strength of NR-5 was still maintained at 8.2 MPa. Overall, the addition of CDs dramatically improved the thermo-oxidative resistance and mechanical properties of the NR film. Simultaneously, a novel way involving the utilization of orange peel with high value is being proposed.

Evolution of carbides and Charpy toughness in a low alloy bainitic steel during step-up aging process

The low alloy bainitic steel used in reactor pressure vessels deteriorates during thermal service while the macroscopic thermodynamic parameters that cause thermal aging remains unknown. In this work, a thermal aging restructuring scheme was proposed by step-up aging the steel from 350 °C to 490 °C, with a total duration of 7500 hours. Samples from varied thickness of the steel were characterized in terms of carbides evolution and Charpy impact toughness at 20 °C. The carbide size and its fraction were statistically analyzed showing partial coarsening and dissolution during aging, while the carbide fraction was found linearly correlated with the impact energy for the first time. The critical transition temperature parameter of the aging process was found to be 470 °C for the steel. The macroscopic thermodynamic parameters, including the thermal aging time and temperature, facilitate a comprehensive understanding of the material degradation mechanism and provide a basis for long-term safety of equipment.

Investigation of microstructure and thermal behavior of CuAlTaGd alloy samples quenched in liquid nitrogen environment after increasing thermal aging times

Investigation of microstructure and thermal behavior of CuAlTaGd alloy samples quenched in liquid nitrogen environment after increasing thermal aging times

Multiscale damage evolution and fracture for thermal aging energetic material based on mesoscopic observation and molecular dynamics simulation

As a composite energetic material composed of filler and matrix, the mechanical properties of HTPB propellants change constantly due to the aging of each component and component interfaces during long-term storage. However, the study of a single component or performance parameter limits disclosure of the complex aging mechanism and mechanical property evolution. Therefore, based on accelerated thermal aging experiments, this study integrated gas detection, contact angle testing, in situ loading experiments, digital image correlation numerical analysis, and all-atom molecular dynamic simulations to explore the underlying mechanism of structural morphology and mechanical property changes during propellant aging. The results showed that the aging reaction was dominated by degradation chain breaking in the early stage and oxidative crosslinking in the later stage. Degradation chain breaking enhanced interfacial bonding between the two phases, while oxidative crosslinking deteriorated interfacial bonding. Compared with lossless specimens, short-term thermal aging weakened the strength of the matrix and enhanced bonding interfaces. During in situ loading, interfacial pore expansion and matrix damage and fracture occurred simultaneously and the matrix became the key damage source. However, with the extension of thermal aging time, the strength of the matrix increased, bonding interface weakened, and bonding interfaces became a weak point of loading. This made the high-strain area change from the matrix at the initial loading stage to the bonding interface and the damage of the bonding interface caused whole fracture of the specimen. The external loading resulted in the rearrangement of interfacial molecular chains, change of molecular spacing, and initiation and expansion of micropores between molecular chains. The tractor-separation curve conformed to the exponential cohesion model and the damage mode of the interface layer changed between adhesion and cohesion due to thermal aging.

Molecular dynamics study on the influence of thermal aging on the mechanical properties of epoxy resins for high voltage bushing.

Thermal aging significantly deteriorates the mechanical properties and service performance of epoxy resins used for the high-voltage bushing. Current studies on the thermal aging behavior of epoxy resins mainly focus on experimental observations. However, an in-depth understanding of the mechanism of thermal aging of epoxy resins requires the monitoring of structural evolution of epoxy resins during thermal aging at the molecular level. To thoroughly analyze the intrinsic factors affecting structural evolution and the effect of thermal aging on the mechanical properties of epoxy resin for high-voltage bushing, epoxy resin models with different crosslinking degrees were established and thermal aging treatments at various temperatures and time periods were carried out by molecular dynamics simulation. It was found that the tensile strength of the epoxy resin was enhanced with the increase of the crosslinking degree, which was related to the elevation of the proportion of C-N and O-H bonds in its structure. With the increase of thermal aging temperature, the tensile strength of the epoxy resin decreased, which was related to the formation of weak bonds. At the early stage of thermal aging and after a period of high-temperature thermal aging, the strength of epoxy resin significantly decreases. The thermal aging of the epoxy resin is accelerated under external loading. In addition, the crosslinking degree and curing agent also affect the thermal aging resistance of epoxy resins. The results of this study can provide guidance for predicting and improving the thermal aging resistance of epoxy resins. Materials Studio was used to construct molecular models and complete crosslinking reactions. DGEBA and 44DDS (or 33DDS) were mixed at a ratio of 2:1, followed by crosslinking reaction. During this process, the Nose method was used to control temperature, the Berendsen method was used to control pressure, and the polymer consistent force field (PCFF) was used to control the motion and force of atoms. Isobaric-isothermal ensemble (NPT ensemble) was used to heat up epoxy resin models to various thermal aging temperatures of 400K, 500K, 600K and 700K. The models were maintained at these temperatures for different thermal aging times of 100ps, 200ps, 300ps, 400ps, 500ps, 600ps, 700ps and 800ps. Afterwards, the models were cooled down to 300K and subjected to uniaxial tensile testing at this temperature with a strain rate of 1 × 109s-1. The structural configurations and stress-strain data during the tensile process were recorded. The flow stress of the material was derived by counting the average stress in the 20-50% strain interval.

Research on the Thermal Aging Characteristics of Crosslinked Polyethylene Cables Based on Polarization and Depolarization Current Measurement

Although XLPE cables are widely used in power transmission and distribution systems, their insulating properties are susceptible to degradation due to thermal aging. In order to clarify the influence law of the thermal aging process on the structural and dielectric properties of XLPE cables, this paper investigates the thermal aging characteristics of XLPE cables by using polarization and depolarization current measurement. Results show that when the XLPE cable is aged at 140 °C, the crystallinity of the insulation layer appears to increase and then decrease. With the increase in aging time, micron-sized microvoids appear on the surface of the XLPE. At the same time, the DC conductivity and 0.1 Hz dielectric loss factor of the insulating layer increase with the aging time. The average DC conductivity increased from 2.26 × 10−16 S/m for new cables to 4.47 × 10−16 S/m after aging for 432 h, while the dielectric loss increased from 0.11% to 0.42%. The polarization characteristics of thermal-aged cables were further analyzed using the extended Debye model. Results indicate that the time constant of the third branch of the model increased significantly with increasing aging time. A correspondence between this parameter and the thermal aging time of the cable was established. Thermal aging can damage the crystalline structure of XLPE, so that the number of interfaces between the crystalline and amorphous regions of the material increases, resulting in structural damages and a decline in the dielectric properties of the cable insulation.

Effect of Si3N4 nanoparticles on IMC as well as mechanical properties of Sn58Bi/Cu solder joints during thermal aging

This paper investigated the changes in microstructure, intermetallic compounds (IMC), and mechanical properties of Sn58Bi/Cu and Sn58Bi-0.6 Si3N4/Cu solder joints in the thermal aging process at 125 °C. With the increase of the thermal aging time, the Bi-phase was gradually coarsened, but the coarsening of the Bi-phase was suppressed after adding Si3N4 NPs. The thickness of the IMC increased continuously, and some areas even detached into the solder matrix, accompanied by gradual grain growth. For the samples with Si3N4 NPs, the IMC thickness significantly decreased, and the grain size was finer. Fractures mainly occur in the Bi-rich phase of the solder matrix following a brief period of thermal aging. However, as the aging time increases, the fracture location gradually shifts from the solder matrix to the IMC, resulting in intergranular and transgranular fractures. However, the shear strength of solder joints with added Si3N4 NPs was higher during the same aging period.

Effect of thermal aging on the low cycle fatigue behavior of Z3CN20.09M stainless steel in high-temperature pressurized water

The effect of thermal aging (0 h- 15,000 h at 400 °C) on the low cycle fatigue properties of Z3CN20.09M stainless steel was investigated. The micro-hardness of the ferrite increases with thermal aging time, while that of the austenite is almost unchanged. The fatigue life of Z3CN20.09M stainless steel in high-temperature pressurized water decreases with thermal aging time. The fatigue cracks formed everywhere, mainly including at slip bands in austenite, at the δ/γ phase boundary and in ferrite. Thermal aging promotes crack initiation and propagation in ferrite. The effect of thermal aging on the fatigue damage process is discussed.

Intermetallic compound growth behavior and mechanical performance in Sn58Bi/Cu solder joint bearing Mg particles incorporation during thermal aging

The microstructure and intermetallic compound (IMC) growth in Sn58Bi/Cu and Sn58Bi-0.4 Mg/Cu solder joints were examined in this study under varied thermal aging time (6, 12, 18, 24, and 30 h) at 120 °C. The Shear test was conducted to assess the solder joint mechanical performance. The results indicated that the precipitation of the Bi phase in Sn58Bi/Cu and Sn58Bi-0.4 Mg/Cu solder joints was not significantly inhibited by adding Mg as aging time increased. The IMC layer thickness of both solder joints increased as the aging time increased, but the Cu3Sn IMC thickness in Sn58Bi-0.4 Mg/Cu solder joint was consistently thinner than that in Sn58Bi/Cu joint. The temporal evolution of the Cu3Sn IMC layer was investigated, and it was found that the inclusion of Mg particles reduced the diffusion coefficient of Cu3Sn IMC. Furthermore, the shear test revealed that throughout the initial phases of thermal aging, fractures occurred within the solder matrix for both joints. As thermal aging time increased, fractures extended into the IMC layer, accompanied by transgranular and intergranular fractures. Simultaneously, adding Mg particles delayed brittle fracture in the solder joints, enhancing their mechanical properties.

Effect of Thermal Aging on the Microstructure and Mechanical Properties of ER308L/Z2CND18.12N2 Dissimilar Welds.

A multi-analytical approach was used to investigate the effect of thermal aging on the microstructure and mechanical properties of ER308L/Z2CND18.12N2. The results demonstrated that fractures occurred preferentially on the ER308L side. Z2CND18.12N2 exhibited superior fracture toughness compared to ER308L regardless of thermal aging time. The ultimate tensile strength significantly increased from 564.5 MPa in the unaged condition to 592.7 MPa to MPa after thermal aging and the fracture mode changed from ductile fracture into a ductile + quasi-cleavage fracture. The fusion zone (FZ) with the chemical composition gradient was about 40 μm from the Z2CND18.12N2 to ER308L. After thermal aging, spinodal decomposition and G-phase precipitation were observed for the first time in the ferrite phase of the FZ. Moreover, the hardness presented the following trend: FZ > ER308L > Z2CND18.12N2. The hardness of the ferrite phase dramatically increased from 6.13 GPa in an unaged condition to 8.46 GPa in a 10,000 h aged condition.

Effects of thermal ageing time and temperature during heat-treatment on the mechanical properties of fiber laser welded Nb-1%Zr-0.1%C alloy in continuous wave mode

The effects of thermal ageing time and temperature used during heat-treatment were studied on tensile strength, elongation, and microhardness of the laser welded Nb-1%Zr-0.1%C alloy in continuous wave mode. Post-weld heat treatment (PWHT) was carried out by varying the temperature and time in the ranges of (850–1050) °C (that is, about the recrystallisation temperature) and (0.5–4) h (as the weld samples were prepared in the form of sheets), respectively. The grain sizes of fusion zone (FZ), and FZ heat treated at 850 °C for 4 h and that at 950 °C for 2 h were found to be equal to 52.85 μm, 84.89 μm and 116.43 μm, respectively. The segregation of zirconium, carbon and oxygen increased grain boundary energy and induced brittleness to the grain boundary, resulting in loss of ductility. The micro-hardness and Young's modulus values were observed to increase in the FZ compared to that of the base metal (BM), but their decreasing trends were noticed during the heat-treatment due to the grains' softening. For the PWHT samples, the plasticity was found to decrease to about 57% of that of BM. This was attributed to the precipitation of carbides, grain growth, and dislocation pinning during the ageing process. During the heat-treatment of the welded samples, both Yield Strength (YS) and Ultimate Tensile Strength (UTS) were found to decrease to 77% and 86%, respectively, of that of the BM.

Bending behavior of 3D printed sandwich structures with different core geometries and thermal aging durations

In recent years, the Fused Deposition Modeling (FDM) method has been employed in the production of small-scale structural elements with moderate loads, such as small-unmanned aerial vehicles, sports equipment, dental implant molds, and similar applications. In these cases, the FDM technique can utilize polymers like Polyamide (PA), Polylactic Acid (PLA), and Acrylonitrile Butadiene Styrene (ABS) to manufacture structural components. Lightweight sandwich structures are utilized as structural elements in various industries due to their unique characteristics, high stiffness-to-weight ratio, and energy absorption capabilities. Although the number of studies on the mechanical properties of sandwich structures manufactured with FDM has increased in recent years, experimental data on the mechanical characteristics of sandwich structures manufactured with FDM under different thermal aging durations are still insufficient. Driven by this motivation, the energy absorption capabilities of sandwich structures with different four core geometries (i.e., circular, hexagonal, square, and triangular) were experimentally investigated under different thermal aging durations. The sandwich structures were manufactured from PLA material by the FDM method. Four different thermal aging durations, 0, 15, 30 and 45 days, were considered for environmental conditions. Quasi-static three-point bending experiments were conducted to assess the energy absorption capability of lightweight sandwich structures featuring diverse core topologies. The bending test results demonstrate that the core topology significantly affects the energy absorption abilities of sandwich structures. Moreover, fractographic analysis using scanning electron microscopy (SEM) was conducted to gain deeper insights into the impact of thermal aging on aged specimens. In addition, it was concluded that the energy absorption performances of all sandwich structures with different core structure topologies were adversely affected by increasing the thermal aging time.

Thermal stability study of gallium nitride based magnetic field sensor

We investigated the thermal stability and performance of AlGaN/AlN/GaN Hall-effect sensors under industry-relevant atmospheric conditions. The thermal stability and performance of Hall sensors are evaluated by monitoring Hall sensitivity, two-dimensional electron gas density, and Ohmic contact resistance during aging at 200 °C for up to 2800 h under atmospheric conditions. This was accomplished by characterizing AlGaN/AlN/GaN micro-Hall sensors, with and without contacts, and before and after being placed under different thermal aging times. Observed electrical performance was correlated with the micro-structural evolution of AlGaN/AlN/GaN Hall sensor heterostructures. Results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h aging at 200 °C without any significant degradation of (i) Hall sensitivity, (ii) two-dimensional electron gas, and (iii) Ohmic contacts. However, there was a small change in sheet density and mobility, which is due to a decrease in polarization, resulting from local inhomogeneous strain relief at the barrier layer. During the early stage of thermal aging, a decrease in contact resistance was also observed and attributed to (i) out-diffusion of “Ga” at the vicinity of the contact interface, and (ii) a reduction in oxygen concentration and formation of Al–Ti intermediate alloy at the GaN/Ti interface, resulting in a reduced barrier and enhanced electron transport at the contacts. However, despite these small changes, results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h thermal aging at 200 °C.

Evaluation of the Aging of Oil‐Paper Insulation Using an Improved Fractional Poynting‐Thomson Model

Assessment of the aging of oil‐paper insulation is analyzed in this article, based on an improved fractional Poynting‐Thomson model, which includes dc and hopping conductivity (P‐T model2). Based on samples of oil paper produced in laboratories with different thermal aging times, it has been found that the proposed improved model provides a better fit and a higher index of coincidence concerning the measured values than the traditional P‐T model and the model that only incorporates the effect of dc conductivity (P‐T model1). Nevertheless, comparing the proposed improved P‐T model with the traditional Cole–Cole (C‐C), Davidson–Cole (D‐C), and Havriliak–Negami (H‐N) models, the improved P‐T model2 also demonstrated a superior fit for the measured value and a higher coincidence index than another model. In addition, there was an excellent exponential relationship between the quantities εa, εb and τ of the improved model and the furfural content of the samples. Consequently, these characteristic quantities could be utilized to estimate the furfural content in the oil‐paper insulation and evaluate the insulation's condition. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

The Influence of Thermal Aging on the Surface Trap Characteristics and Surface Flashover of Epoxy Resin

Surface charge accumulation of epoxy resin is easy to cause surface flashover under DC voltage, and thermal aging is an important factor affecting surface charge and trapping characteristics. In this paper, the electron and hole trap characteristics of epoxy resin were studied by changing the polarity and amplitude of charging voltage. Then, the influence of thermal aging on the trap energy level distribution of epoxy resin is researched by conducting the thermal aging experiment, based on which the influence of the energy level distribution of electron trap on the negative DC flashover characteristics is furtherly studied. Experimental results show that the energy level of electron trap and hole trap on the surface of epoxy resin ranges from 0.70 eV to 0.96 eV, the peak energy level of hole trap is slightly higher than that of electron trap. The maximum of the density of trapped charge in the electron trap and hole trap is 1.98 × 1020eV−1·m−3 and 1.82 × 1020eV−1·m−3 respectively. The energy level of traps on the surface of epoxy resin generally shows a deepening trend after thermal aging. The peak energy level of electron trap increases from 0.84 eV to 0.98 eV after 29 d of thermal aging, which is due to the product containing strongly polar group produced by thermal aging. The results of flashover testing shows that the flashover voltage first increases and then decreases with the extension of thermal aging time. With the extension of aging time from 7 d to 29 d, the flashover voltage decreases by about 11.2%, the change of flashover voltage is related to the change of trap energy level distribution on the surface of dielectric. This paper can provide theoretical and experimental basis for the insulation design of epoxy resin applied in electric equipment.

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.

The aging property and storage life prediction of EPDM

The performance change of Ethylene propylene diene monomer (EPDM) was studied by the accelerated aging experimental method, and its lifespan was predicted. The results showed that the thermal oxidation aging of EPDM is dominated by the crosslinking reaction. With the extension of the thermal oxidation aging time, the total crosslinking density and tensile permanent deformation gradually decrease, while the tensile strength and hardness increase gradually. The life prediction formula of EPDM under the thermal-oxidative aging condition was obtained by the linearization method of the kinetic curve. When tensile permanent deformation was used as the evaluation index, the life was 30 a at the temperature of 296.15 K.

Influence of Thermal Aging on Dielectric Properties of High Voltage Cable Insulation Layer

Thermal aging is one of the main reasons for the degradation of insulation properties of high voltage cable. Dielectric properties and breakdown strength are important parameters to reflect the insulation performance of the cable insulation materials. In the work, the influence of thermal aging on dielectric and breakdown performance of the cable insulation layer was studied. Firstly, XLPE cable insulation samples were prepared and the thermal aging treatment was carried out. Secondly, the microstructure and molecular structure of XLPE samples under different thermal aging time were analyzed. The dielectric properties and breakdown characteristics of XLPE samples under different thermal aging times were characterized in macro aspect. Finally, the effects of different temperatures on the molecular microstructure of XLPE were studied. The results show that with the extension of thermal aging time, the microstructure of XLPE molecule is destroyed, the macromolecular chain is gradually cleaved, and the carbonyl absorption intensity increases. At power frequency, the breakdown strength decreases from 75.37 kV/mm to 62.18 kV/mm, the relative permittivity increases from 2.44 to 2.51, and the dielectric loss increases from 1.47 × 10−4 to 3.10 × 10−3. The free volume rate of XLPE molecules increases with the increasing temperature, and the mean square displacement gradually increases. The work has good guiding significance for the safe operation and condition assessment of high-voltage cables.

Effect of poly (acrylamide-co-acrylic acid salt) on anti-aging properties and adhesion between acrylonitrile butadiene rubber and polyester fabric

In this study, a multifunction polymeric adhesion promoter and anti-aging compound based on the triethanolamine salt of acrylamide acrylic acid copolymer (COS) was prepared and characterized using Fourier-transform infrared spectroscopy (FTIR). The impact of different COS contents on the tensile, adhesion, and thermal properties of NBR composite and NBR/PET sandwich was evaluated. The NBR composites containing COS displayed good retention of their mechanical properties with increasing thermal ageing time, while the composite without COS showed a decrease in its mechanical properties. The highest tensile strength (17.5 MPa with a retention value of 0.6%) after 7 days of thermal aging was recorded for NBR composite, which contains 5 phr (parts per hundred parts of rubber) of COS (COS 5), compared to NBR composite without COS (COS 0), which recorded 15.1 MPa with a retention value of -27.4%. In addition, the COS 5 composite displayed an improvement in peel strength of 16.4% compared to the COS 0. The results of the thermogarvemetric analysis (TGA) supported the anti-thermal ageing effect of COS, where the initial decomposition temperature (Ti) value increased by 11.7 and 9.3 °C, after addition of 5 and 10 phr of COS to NBR composite, respectively. In addition, the other thermogravemetric parameters investigated displayed a significant increase in their values, which confirms the improvement in thermal stability of NBR composite in the presence of COS. Also, the air permeability of the PET/NBR sandwich decreased by 80% after the addition of 7.5 phr of COS.

Effect of thermal oxygen aging on the crystallization and insulation properties of polyether ether ketone

AbstractAs an engineering material, polyether ether ketone (PEEK) has been widely used in many fields. It is important to study its thermal oxidative aging law for its material service optimization. The changes of chemical structure and relative properties of PEEK sheets after thermal oxygen aging at 280°C for different times were measured by universal tensile machine, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and resistance meter. The results showed that the elongation at break of the aged samples decreased with the extension of thermal aging time, while the tensile strength continuously increased within 336 h of thermal aging and then decreased gradually. Moreover, the crystallization temperature, melting enthalpy, and crystallinity of the samples decreased with the increase of thermal aging time. The crystallinity decreased to 2.3% after 2852 h aging and the initial decomposition temperature and the maximum decomposition temperature of PEEK gradually decreased from 554.3 to 523.5°C and 572.9 to 558.2°C, respectively. The increase of tan δ was more significant in the low frequency band (10−2–101) Hz. With the increase of aging time, the zeta potential of PEEK surface constantly moved to the negative direction and the volume resistivity and the dielectric strength similarly increased first and then decreased.