Effect Of Thermal Aging Research Articles

Effect of Thermal Aging on Viscoelastic Behavior of Thermosetting Polymers under Mechanical and Cyclic Temperature Impact.

Development of load-bearing fiber reinforced plastic (hereinafter referred to as FRP) composite structures in civil engineering, exploited under high temperatures, such as industrial chimneys and gas ducts, requires the knowledge of their long-term behavior under constant and cyclic mechanical and temperature loads. Such conditions mean that the viscoelasticity of FRP should be considered along with the thermal aging effect. This research is devoted to the effects of thermal aging on the viscoelastic behavior of polymers. Two sets of experiments were conducted: creep tensile tests and cyclic heating in a constrained state. The Kelvin-Voigt viscoelasticity model was used to determine the rheological parameters of binder from experimental creep curves. Cyclic heating was used to compare the behavior of normal and thermally aged binders and to evaluate the possibility of temperature stress accumulation. Fourier-transform infrared spectroscopy was used for polymer's structural changes investigation. Both tests showed that non-aged glassed polymer (hereinafter referred to as GP) was prone to viscoelastic behavior, while the thermally aged GP lost viscosity and worked almost perfectly elastic. It was assumed that long heat treatment had caused changes in the inner structure of the GP, reducing the number of weak bonds and increasing the number of elastic ones. Therefore, the results show that the designing of FRP structures, exploited under thermomechanical load, requires using the elastic model while taking into account the properties of FRP after long-term heat treatment.

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.

Comparison of the effect of thermal and hygrothermal sub-Tg aging on the durability and appearance of multilayered filament wound composite structure

The study conducts an experimental investigation to compare the effect of accelerated aging on a glass fiber/vinylester matrix filament wound composite. Two static aging conditions, thermal and hygrothermal, were chosen. Samples were aged at temperatures below the glass transition temperature (Tg) of vinylester for 224 days. Mechanical test – ILSS and flexure testing and physicochemical assessments – DMA, FTIR and colorimetry were conducted to gauge the aging effects on long-term durability and appearance. Results are presented as retained property values over aging durations and environments. Notably, coupons aged below 60 °C under both conditions exhibited residual curing, enhancing mechanical properties. Time-temperature coupling influenced behavior, with higher temperatures and longer durations leading to degradation. Hygrothermal aging at 80 °C prompted earlier degradation than thermal aging, highlighting moisture's impact. DMA revealed interfacial degradation for hygrothermally aged coupons, verified by fractography. Conversely, damping factor analysis indicated residual curing for thermally aged coupons. Results were confirmed through color change and FTIR, showcasing evolving chemical patterns with aging.

Thermal aging effects on Tensile and Metallurgical characteristics of Stainless steel weld joint

A girth austenitic stainless steel (say, SS) weld joints are invariably used for joining piping components in typical light water based nuclear power reactor. To avoid hot cracking during the welding of SS, some 5-8% delta ferrite is required in the filler material, which remains in the metastable phase in weld pool. Under prolonged exposure at operating temperature (300 ℃), these delta ferrite which remains in weld metal may get transformed to brittle phases that leads to reduction in its ductility and toughness. Hence, for prolonged safe operation of these piping components in power reactors, it is important to quantify the amount of degradation in toughness and ductility because of thermal aging. Therefore, present work aims at quantifying the reduction in toughness in SS weld joint by carrying out accelerated thermal ageing and thereafter carrying out micro-structural examinations, hardness and tensile tests on specimens machined from different regions of weld joint. Austenitic stainless steel (SA312 Type 304LN) pipe weld joints have been prepared using Gas Tungsten Arc Welding (GTAW) for root passes and Shielded Metal Arc Welding (SMAW) for filling passes. Full-scale pipe weld were subjected to thermally ageing for 10,000 and 20,000 hours at temperature 400 ℃. The effects of thermal aging on the structural morphology, hardness at macro and micro-scale and tensile characteristics of different zones of these joints have been quantified. Micro-structural examination reveals vermicular and lathy morphology in the ferrite and austenite phase. It has been found that, thermal aging leads to significant increase in ferrite hardness and reduction in ductility for the weld specimen from SMAW compared to that of the GTAW and no effect in heat affected zone.

Influence of thermal aging on dielectric characteristics of transformer insulating oils

Transformer oil is a liquid insulating material used in transformers as insulation and coolant. Particular characteristics insulating oil materials must be able to withstand breakdown voltages, while transformer oil as a coolant must be able to minimize heat generated, so that transformer oil is expected to protect the transformer from disturbances with these two characteristics. In order to reduce the percentage of transformer failures, it is necessary to maintain the purity of the oil. The features of aged transformer oil and pure transformer oil are investigated in this study. Pure transformer oil is heated to a particular temperature and cycled to create samples of aged transformer oil. The electric field intensity of transformer oil is measured to estimate the dielectric strength of aged transformer oil. FEM analysis is used to determine the intensity of an electric field. At aging temperatures of 130°C and 150°C, the dielectric characteristics of transformer oil for both Shell Diala and Triapar types are investigated. As a result, not only the electrical characteristics but also the effects of thermal aging on the physical and chemical properties of transformer oil are reported in this study.

Immediate and Long-Term Pull-Out Bond Strength of 3D-Printed Provisional Crowns.

Background: Over the past decade, 3D printing technology has revolutionized various fields, including dentistry. Provisional restorations play a crucial role in prosthetic rehabilitation, necessitating the evaluation of their bond strength with different provisional cement agents. Aims: This study is aimed at assessing the immediate and long-term bond strength of 3D-printed dental crowns using three provisional cement agents. Materials and Methods: Provisional crowns (N = 36) were manufactured using 3D modeling software and cemented in dentin analogues (G10 Nema resin). After the crowns' fabrication, they were randomly divided into three groups (n = 12) for cementation with Relyx Temp 3M ESPE, Provicol-VOCO, and Meron-VOCO. Tensile strength tests were conducted using a universal testing machine, with half of the specimens subjected to 2000 thermal cycles before testing. Finite element analysis was employed to assess tensile stress distribution. Results: Statistical analysis (two-way ANOVA and Tukey's test at a 95% confidence level) revealed significant effects of cement type (p = 0.006) and thermal aging (p = 0.001) on bond strength. Glass ionomer cement exhibited the highest immediate resistance, while all types of cement were adversely affected by thermal aging, resulting in decreased bond strength. Conclusion: Thermal aging significantly alters the properties of 3D printing resin and affects the bond strength of provisional cement with 3D-printed crowns. Despite the adverse effects of thermal aging, glass ionomer cement demonstrated the highest immediate resistance. Clinicians should carefully consider these findings when selecting provisional cements for 3D-printed crowns.

Effects of geometry and thermal aging on the strength of 3D-printed polymer parts

Based on advantages of additive manufacturing (AM), this technology is becoming one of the most popular and preferable manufacturing processes in different industries. Although AM was introduced for fabrication of prototypes, it has been used for production of end-use products. Consequently, the mechanical strength of AMed parts has become of significant importance. In the present study, Influence of geometry and thermal aging on the mechanical strength of AMed parts has been investigated. To this aim, polylactic acid material was used to print specimens based on fused deposition modeling process. Since geometry of AMed parts has effect on their mechanical behavior, the specimens with three different geometries are fabricated and examined. Particularly, dumbbell-shaped, smooth, and V-notched specimens were subjected to tensile load under static loading conditions. In addition, in order to evaluate Influence of thermal environment, we carried out an accelerated thermal aging within temperatures of -5°C to 35°C, which is below glass temperature of the examined material. Experimental results showed different fracture behaviors and tensile strength due to the different geometries. Moreover, based on a series of tests, the failure behavior of original and aged specimens are determined. The outcomes of this study confirmed that the geometrical appearance and environmental working conditions of AMed parts must be taken into account in the design of these components.

Effect of Thermal Aging and Chemical Disinfection on the Microhardness and Flexural Strength of Flexible Resins

This article examines the effects of thermal aging and chemical disinfection on the microhardness and flexural strength of flexible resins. The influence of the resin type on the mechanical properties was also investigated. Two flexible resins, Deflex Classic SR and Deflex Supra SF, produced by the injection method, and a thermopolymerizable acrylic resin—ProBase Hot, produced by the flasking method, were subjected to 1000 cycles of thermal aging and three chemical disinfection protocols (n = 8), with daily immersion and during a recommended time, in Corega Whitening, Corega Oxygen Bio-Active, 2.5% sodium hypochlorite, and distilled water (control). Knoop microhardness and three-point flexural strength were evaluated. Data were analyzed using Wilcoxon, Mann–Whitney and Kruskal Wallis tests (α = 0.05). The results varied between 14.5 KHN and 80.1 MPa for ProBase Hot and 7.3 KHN for Deflex Classic SR and 52.5 MPa for Deflex Supra SF. Thermal aging reduced the microhardness of the flexible resins, but not their flexural strength. The microhardness of Deflex Classic SR was influenced by chemical disinfection with Corega Bio-active (p < 0.001). The flexural strength of Deflex Supra SF was influenced by chemical disinfection with Corega Whitening (p < 0.05). It can be concluded that chemical disinfection led to changes in the flexible resins and should be used with caution to maintain the mechanical properties of the resins. Flexible resins showed reduced resistance to physical and chemical environmental influences, which can affect their longevity.

Effect of thermal ageing on the deformation behaviour of ferrite and austenite in a duplex stainless steel: Micropillar characterisation and dislocation density modelling

The deformation behaviour of the austenitic and ferritic phases in an aged duplex stainless steel is investigated experimentally and numerically. The effect of the ferritic phase’s spinoidal decomposition during thermal ageing on the mechanical behaviour of the alloy is studied through micropillar compression tests on the individual single crystal phases before and after ageing, and APT and TEM investigations of the decomposed ferrite and corresponding dislocation structures. Dislocation density-based crystal plasticity models are formulated for the austenitic and ferritic phases, and calibrated from the measured micropillars responses.A considerably higher and more homogeneously distributed initial dislocation density is observed in the austenite, resulting in a more homogeneous deformation of the austenitic micropillars than the ferritic ones. The spinoidal decomposition of the ferrite leads to a considerable increase of its initial flow stress. The strengthening effect of thermal ageing and the resulting localised deformation response of the aged ferritic micropillars are correctly described by the crystal plasticity results, which required a higher initial obstacle (dislocations + inter-phases of the newly formed α′ domains) density to dislocation motion. Moreover, a strong size effect was observed on the behaviour of the as-received and aged austenitic and as-received ferritic micropillars, but not in the aged ferritic ones. Such contrasting behaviour originates from the fact that, for the size sensitive cases, the dislocation mean free path is controlled by the mean micropillar diameter, whereas in the aged ferrite micropillars, it is by the ∼ 5 nm wide Cr-rich domains within the spinoidal decomposed ferrite.

Thermal aging effect on mechanical properties of polyamide 6 matrix composites produced by TFP and compression molding

AbstractTailored Fiber Placement is an innovative manufacturing technique that precisely positions continuous fibers in critical areas of fiber preforms for optimal structural performance. This study focuses on producing glass fiber‐reinforced polyamide composites using TFP technology and compression molding to address the durability concerns of thermoplastic matrix composites in automotive parts. The production process involved a constant temperature of 300°C, 16 bar pressure, and holding times of 270, 300, and 330 s. Short‐term thermal aging cycles were applied to simulate automotive part acclimatization. Tensile and 3‐point bending tests were conducted to evaluate mechanical properties. Statistical analysis using response surface methodology provided insights into the relationship between production parameters and mechanical properties. Differential Scanning Calorimetry characterized the composite material, and macroscopic damage analysis was performed. Results showed a potential 10% decrease in tensile strength due to short‐term thermal aging. Aging had the most significant impact on elastic modulus and tensile strength according to the Pareto chart. Flexural modulus increased, while flexural strength decreased with thermal aging. Holding time had no effect on flexural modulus but reduced flexural strength.Highlights Glass/polyamide composites were produced by compression molding with TFP technology. Short‐term thermal aging cycles were applied on the GF‐PA6 composite material. Mechanical properties were analyzed statistically according to the RSM. TFP technique can assist OEM companies in lowering desired target cost per vehicle.

Effect of thermal cycling on open‐hole tensile strength of sustainable composites: An experimental investigation

AbstractSustainable composites are presently employed in applications where structural demands are minimal. Basalt fiber reinforced PLA (BFPLA) and polybutylene succinate (BFPBS) composites, incorporates bio‐based materials, offer the potential to reduce non‐renewable resource consumption and improve end‐of‐life disposal practices. Given the significance of thermal aging in semi‐structural applications and the necessity for open holes (notches) for installation and assembly, little is known about how thermal cycling (TC) affects the open‐hole strength of sustainable composites. This experimental work establishes a quantitative relationship between open‐hole strength and TC, taking into account varying abrasive waterjet pressures, and explores the impacts of thermal aging on the notch sensitivity, thermal, mechanical, and physical properties. BFPBS displayed better unnotched tensile strength and notched strength than pre‐thermal BFPLA specimens after they have been subjected to 100 TC ranging from −20 to 55°C. Thermal aging significantly influenced notch sensitivity, emphasizing its consideration in evaluating notch performance. This research provides a significant contribution to our current understanding of the effects of thermal aging on sustainable composites, enabling their informed application in a variety of industries and the results highlight their promising potential, in particular BFPBS, as strong alternative for medium load applications.Highlights Evaluated thermal aging effects on basalt fiber (BF) composites, revealing improved properties in BF/PBS composites after thermal cycles. Established quantitative link between mechanical behavior and thermal cycling using varying waterjet pressure values. Basalt fibers enhanced crystallinity and thermal stability of PLA and PBS polymers, showing promise for sustainable composites. Notch sensitivity impacted by thermal aging, underlining the importance of considering these effects in notch performance evaluation. BF/PBS composites demonstrated potential as robust alternatives for indoor products and sports equipment.

Thermal Aging Effects on the Electrical Breakdown Voltage of TiO and MWCNT Nanofluids Based on POME

Thermal Aging Effects on the Electrical Breakdown Voltage of TiO and MWCNT Nanofluids Based on POME<sub />

Effect of Thermal Aging on the Reliability of Interconnected Nano-Silver Solder Joints

Effect of Thermal Aging on the Reliability of Interconnected Nano-Silver Solder Joints

Effects of thermal aging level on the morphological structures, rheological properties and fatigue characteristics of high-viscosity asphalts

High-viscosity asphalt (HVA) provides excellent cracking and rutting resistance for ecological permeable pavement. However, HVA suffers from severe aging due to higher construction temperatures and rich porous structures, which limited its applications for urban sustainability. Currently there is still a lack of knowledge about the thermal aging effects and mechanisms of HVA. In this study, the effects of thermal aging on the morphological structures, rheological and fatigue properties of two HVAs (i.e. HVA-1 and HVA-2) at five aging levels via Simple Aging Test (SAT) are systematically investigated. HVA-1, characterized by loosen and coarse reticulated structures, undergoes significant structural changes during aging, whereas HVA-2, characterized by dense and fine reticulated structures, experiences fewer alterations. The changes in the modulus master curves of HVAs become more gradual after aging, indicating the reduced temperature sensitivity. Multiple stress creep recovery results reflect that two types of HVAs exhibit totally different dominance of oxidation or polymer degradation depending on aging level. Liner amplitude sweep (LAS) results based on damage mechanics analysis reveal that aging leads to an increase in the accumulated strain energy observed in stress-strain curves for both HVAs. As aging progresses, the proportion of elastic energy decreases due to polymer degradation, resulting in a reduction in fatigue life. Especially, the fatigue life of aged HVAs significantly decreases after SAT40. LAS results based on fracture mechanics analysis show that the crack length increases with aging due to polymer degradation and asphalt phase hardening. Aging effect on crack length was limited at initial stage but becomes more significant as crack extends. As aging deepens, the crack initial stage of HVAs tends to lengthen while the crack extension stage tends to shorten. Moreover, the crack growth process of HVAs follows a two-stage behavior of crack initiation and propagation under certain aging levels from the relationship between energy release rate and crack propagation rate. Overall, the thermal aging kinetics of various HVAs differ significantly in the structures, rheological and fatigue properties as aging deepens. HVA-2 with loosen and coarse structures exhibits greater aging resistance and lower temperature sensitivity than HVA-1 with dense and fine structures.

Leadfree SnAgCu Solder Materials Characterization at High Strain Rates at Low Test Temperatures and Drop and Shock Simulation Using Input-G Method

Abstract Electronics will experience high and low working temperatures during operations, handling, and storage in severe environments applications such as download drilling, aircraft, and transportation. Temperatures in the vehicle underhood applications can range from −65 °C to +200 °C. Lead-free solder materials continue to evolve under varying thermal workloads. Material characteristics may deteriorate if operating conditions are harsh or heavy. Nonetheless, lead-free solders are susceptible to high strains, which can lead to electronic device failure. A better understanding of solder alloys is needed to ensure reliable operation in harsh environments. New doped solder alloys have recently been created by adding Ni, Co, Au, P, Ga, Cu, and Sb to SnAgCu (SAC) solder alloys to improve mechanical, thermal, and other qualities. SAC-Q has recently been made using Sn–Ag–Cu and the addition of Bi (SAC+Bi). It was discovered that adding dopants to SAC alloys may enhance mechanical characteristics and reduce aging damage. There is no published data on SAC solder alloys after prolonged storage at high strain rates and low functioning temperatures. The materials characterization of SAC (SAC105 and SAC-Q) solder after extended storage at low working temperatures (−65 °C–0 °C) and high strain rates (10–75 per sec) is investigated in this article. To characterize the material constitutive behavior, the Anand viscoplastic model was utilized to derive nine Anand parameters from recorded Tensile data. The generated nine Anand parameters were used to validate the Anand model's reliability. A strong correlation was established between experimental data and Anand's predicted data. The Anand parameters were used in a finite element framework to simulate drop events for a ball-grid array package on printed circuit board assembly to calculate hysteresis loop and plastic work density. The plastic work per shock event measures the damage progression of the solder interconnects. Thermal aging effects have been studied in terms of the hysteresis loop and the evolution of PWD.

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.

Effect of Hydrothermal Aging Behavior on Surface Treated Kevlar Fiber Laminated Composites

The water sorption characteristics of Kevlar fiber–reinforced epoxy composites were studied by immersion in water at 80 degrees Celsius. The hydrothermal aging process was conducted on treated and untreated Kevlar/epoxy composites; also, the composite was evaluated by the three-point bending test. The phosphoric acid (PA) pretreated with epichlorohydrin (ECH) was used for the surface modification of Kevlar. In the case of chemically modified fiber composites, water uptake was found to be dependent on the chemical treatment done on the fiber surface. The lowest water uptake was observed for composites treated with PA with ECH. The effect of thermal aging on the flexural strength of the treated Kevlar composite was 20.42% higher than the untreated composite. Consequently, the flexural modulus was 13.9% higher than the untreated Kevlar composite. Moreover, the water diffusion coefficient of treated composite 23.19% higher with untreated composite. It was concluded that fiber/matrix degradation time at the interface region was increased in the case of treated composite

Pyrolysis mechanism of different thermal aging of PVC insulation copper cable for home decoration

Thermal aging produces irreversible aging to home decoration PVC insulation copper cables through high temperatures, and their pyrolytic behavior changes as a result. The thermogravimetric-Fourier transform infrared analysis, the model-free method and the Málek method were used to investigate the effect of thermal aging on the pyrolysis mechanism of domestic PVC insulation copper cables. It was found that pyrolysis is more easily to occur in aged cables, and 20 days of aging is the most dangerous threshold for the pyrolysis of ZR-BVR cable insulation. The pyrolysis release gases were mainly concentrated in the temperature intervals of 270-340 and 400-700°C. In addition, it should be noted that different degrees of thermal aging affect the pyrolysis behavior of cable insulation but have little effect on the pyrolysis mechanism.

The Effect of Food-Simulating Liquids and Thermal Aging on Surface Roughness and Color Stability of Bulk-Fill and Conventional Composites

Objectives: The aim of this study was to evaluate the effect of food-simulating liquids (FSLs) and thermal aging on the surface roughness and color stability of bulk-fill and conventional composites. Materials and Methods: A total of 320 disc-shaped samples were prepared, with 40 samples from each of 4 different bulk-fill composites (Filtek Bulk Fill, X-tra fil, Beautifil Bulk Restorative, and Estelite Bulk Fill Flow), and 4 conventional nano-filled composite resins (Filtek Z550, CeramX SphereTEC one, Admira, and Kalore). The prepared samples were randomly divided into subgroups for exposure to FSLs (ethanol, heptane, citric acid) and thermal cycling (TC) (n=10 per subgroup) for 28 days. Initial profilometric surface roughness measurements (Ra0) of all samples and AFM and SEM analyses of selected samples were followed by exposure to FSLs and TC. After completion of aging protocols, measurements and analyses were repeated to obtain the Ra1 (post-treatment surface roughness), and change in surface roughness (∆Ra1-0) was then calculated. Subsequently, initial color measurement of the samples was conducted using a spectrophotometer, followed by immersion of the samples in a coffee solution for 24 hours. Color measurements were repeated, and color change (∆E) was calculated. Two-way repeated measures ANOVA was used to compare Ra0 and Ra1 values and one-way ANOVA for comparing ∆Ra and ∆E values. Tukey and post hoc tests were employed for pairwise comparisons. The significance level was set at α=.05. Results: While the surface roughness of bulk-fill composites was affected by the protocols applied (p&amp;lt;0.05), conventional composites generally remained unaffected. Bulk-fill composites exhibited greater ΔRa and ∆E values. The highest ∆Ra and ∆E values were observed in the Beautifil Bulk Restorative group, with the greatest discoloration seen after immersion in citric acid. Conclusions: Thermal cycling and immersion in FSLs affect surface roughness and color stability of composite resins depending on the content and structure of the composites.

Aging effects on the viscoelastic behaviour of products by fused deposition modelling (FDM) made from recycled and wood-filled polymer resins

In this work, we analyse the thermal aging effects on the thermo-mechanical properties of bio-based specimens realized using fused deposition modelling technology. For the investigations, three commercial filaments made of polylactide acid (PLA) were used. The first filament was a pure virgin PLA (B-PLA); the second one was made from recycled waste production, PLA (R-PLA), and the third one was wood-filled PLA (W-PLA). Such materials were extruded under pre-optimized conditions and thermally aged in an oven at 70 °C. The as-prepared specimens were subjected to dynamic mechanical analysis (DMA) and infrared spectroscopy (IR). The experimental results are presented in terms of storage modulus (E'), loss modulus (E"), tan delta, and absorption spectra at different aging periods (0, 50, 70, 130, 175 days). For B-PLA and R-PLA, the thermal aging results in a decrease in both storage and loss moduli and in an increase in the glass transition temperature (Tg). On the contrary, for the W-PLA the storage modulus increases with the aging time, while the Tg remains constant. The IR spectra support the hypothesis of a degradation mechanism involving hydrolysis and/or hydrogen atom transfer. Based on these observations, we conclude that heat treatments always lead, through polymer degradation and structural changes, to more stable structures. The presence of wood particles slows down the aging process and makes the final products more durable.