Increasing Aging Time Research Articles

Advanced UV-fluorescence image analysis for early detection of PV-power degradation

Reliability and durability of photovoltaic modules are a key factor for the development of emerging PV markets worldwide. Reliability is directly dependent on the chemical and physical stability of the polymeric encapsulation materials. One method capable of detecting ageing effects of the polymeric encapsulant directly on-site is UltraViolet Fluorescence (UVF) imaging. This work deals with advanced imaging analysis of UVF images and the subsequent correlation to electrical parameters of PV modules, which were exposed to climate-specific, long-term, accelerated aging procedures. For establishing a correlation, a so called UVF area ratio was established, resulting from the typical fluorescence patterns of the encapsulant material, which arise due to stress impact (e.g., water vapor ingress, elevated temperature, irradiation) and aging/degradation processes. Results of the data analysis show a clear correlation of the UVF area ratios and the electrical parameters with increasing aging time. In particular, the relationship between power and series resistance could be confirmed by extensive long-term test series with different climate-specific aging processes. Assuming the same type of polymeric encapsulation and backsheet and a comparable climate, determining the UVF area ratio can be used to estimate the service life and electrical power dissipation of each module installed in a PV array.

Investigation on the influence of a titanium coating on the aging behavior of ATZ ceramics for implant applications

The aim of this investigation was to determine the influence of a metallic coating on the LTD behavior of an ATZ ceramic. Therefore, a 300 μm thick titanium layer was deposited by plasma spraying on a commercial ATZ ceramic containing 20 wt% alumina and 80 wt% 3Y-TZP. After aging the coated and uncoated samples in water vapor at 134 °C and 2 bar for 5 h and 30 h, respectively, the monoclinic phase content was determined using X-ray diffraction, and its impact on the mechanical properties was assessed in biaxial flexural strength tests. The results revealed an increase in strength with increasing aging time. Furthermore, the Ti-VPS-coating slows down the aging of the ceramic because it acts as a diffusion barrier for the hydroxide ions. As a result, after 30 h of aging, the monoclinic phase content of the coated samples is up to 30% lower than of the uncoated samples.

An experimental investigation on the influence of Sn addition and aging time on the mechanical and micro structural properties of AZ80-1.2RE magnesium alloy

This study investigated the effect of tin (0, 6, and 9 wt%) and aging time (0, 16, 24, and 32 hrs) on the microstructure and mechanical properties of the AZ80-1.2RE Mg alloy. The results obtained indicate that the addition of Sn improved the mechanical properties. For the AZ80-1.2RE alloy, upon Sn addition, strength of 195 MPa and percentage elongation of 7.6 are observed to be found at 6 wt% Sn, which is attributed to the precipitates of Al2RE, Mg2Sn, and Mg-Sn-RE phases. After heat treatment and aging, the properties of the casted alloys were found to be affected. As aging time increases, small precipitates are observed to be dissolved in primary Mg phase, due to which the properties are found to be decreased from the as-cast condition to aging at 16 hours. The strength of the 6wt% Sn alloy decreased due to the high stress concentration at the large precipitate site during aging from 16 hours to 24 hours and then increased due to the grain boundary strengthening effect at the 32-hour aging time.

The effect of aging temperature and aging duration on the dry sliding wear behavior of Ti6Al4V alloy

In this study, Ti6Al4V (Grade 5) alloys were first dissoluted at 850?C for 120 min and then were aged at 250, 350, 450, 550, 650, and 750?C, respectively. After each aging duration (by looking at hardness ratios aged between 9 to 54 hours), the hardness of the samples was measured. Depending on the aging temperature and time increase, hardness increased upon the formation of ?' phases. After the formation of ?' phases, the hardness started to decrease. The highest hardness value was measured in the sample aged at 450?C for 24 hours. The wear behavior of the untreated and the aged samples was investigated through a detailed pin-on-disc test. The effect of the aging temperature on the volume loss, the specific wear rate, and the coefficient of friction were examined. Metallographic analyses were performed before and after the wear tests. Both abrasive and adhesive wear formations were observed on the FESEM-EDS images of the worn surfaces. When the results were evaluated, it was observed that the highest hardness and good wear behavior were obtained for the samples aged at 450?C for 24 hours.

Effect of Sb content on the phase structure and interface structure of Sn1.0Ag0.5Cu lead-free solder

Based on the alloy Sn1.0Ag0.5Cu, Sb powder is added at a certain mass percentage to form the solder alloy Sn1.0Ag0.5CuxSb (x = 0 wt%, 0.5 wt%, 1.5 wt%). The melting point of the solder was determined by differential scanning calorimetry, the alloy interface morphology was observed by scanning electron microscopy, and energy-dispersive X-ray spectroscopy was performed to analyze phase compositions. Thermo-Calc software was used to calculate the variation in phase content, the solidification curve, Gibbs energy, the driving force, liquid/solid phase lines, the phase diagram, and the nucleation radius of Sn1.0Ag0.5CuxSb(wt%). In addition, the calculation results were used to explain the interface growth mechanism. According to the results, the precipitation/transition temperature of each phase and the content of the newly formed phase SnSb gradually increased with the increase in Sb content. After the addition of Sb, both temperatures of the liquid-phase line and the solid-phase line slightly increased, and the calculated values showed the same trend as the measured values. Two heat absorption peaks were observed during the melting process. The Gibbs energy and nucleation radius of the Cu6Sn5 phase increased with the increase in Sb content, indicating that Sb can inhibit the growth of the Cu6Sn5 phase. The addition of Sb rendered the Sn-rich phase denser and finer and reduced the thickness of the intermetallic compound layer and the generation of cracks; these changes intensified with increasing aging time. Comprehensive analysis revealed optimal reliability of the solder for an Sb content of 0.5 wt%.

Aging Interfacial Structure and Abnormal Tensile Strength of SnAg3Cu0.5/Cu Solder Joints

In this study, the interfacial structure and abnormal long-term increase of tensile strength in the interfacial intermetallic compounds (IMCs) between SnAg3Cu0.5 solder and Cu substrates during isothermal aging were investigated. After reflow soldering, the IMC layer at the interface was thin and scallop-type. The interfacial layer became thicker with the increase in aging time. After 200 h of aging at 150 °C, the thickness of the interface gradually increased to 3.93 μm and the interface became smooth. Compared with the unaged Cu-Sn interface, the aged joint interface contained more Cu3Sn. The top of the IMC being reflown was relatively smooth, but became denser and prismatic in shape after 200 h of aging at 150 °C. The tensile strength of the joint, immediately after the reflow, reached 81.93 MPa. The tensile properties of the solder joints weakened and then strengthened as they aged. After 200 h of aging at 150 °C, the tensile strength was 83.86 MPa, which exceeded that of the unaged solder joint interface, because the fracture mode of the solder joints changed during aging.

Microstructural Influences Caused by Different Aging Strategies on the Strain-Dependent Damping of the High-Strength Aluminum Alloy AA7075

The present study focused on the influence of different aging conditions on the strain-dependent damping of the high-strength aluminum alloy AA7075. For this purpose, different artificial aging strategies were carried out after solution heat treatment with subsequent water quenching to identify correlations between microstructural evolution, hardness development, and individual material damping. The resulting material damping was measured using an experimental setup based on the principle of electromagnetic feedback. Scanning transmission electron microscopy (STEM) investigations were carried out using a scanning electron microscope (SEM) to characterize the material’s microstructure. Depending on the aging conditions, the damping investigations revealed specific characteristic behaviors in the strain-dependent range from 1 × 10−7 to 0.002. Peak aging conditions showed lower damping than the overaged conditions but resulted in the highest hardness. The hardness decreased with increasing aging time or temperature.

Effect of artificial aging on 3-point bending behavior of glass fiber/epoxy composites

This study looked into how artificial aging affected the mechanical behavior of composites made of glass fiber reinforced polymer (GFRP). In this context, GFRP composites were produced by vacuum infusion method and artificially aged in the aging cabinet. Three different composite specimen types were tested. These are unaged samples aged 750 h and aged 1500 h. Three-point bending tests were performed to determine the mechanical properties. The absorbed energies of the samples were determined and the maximum bending stresses were calculated. The maximum contact force and sample displacements were also determined. In addition, the damage areas of the samples were examined optically and the changes that occurred with the aging time were determined. Finally, SEM images were taken to observe the changes in the internal structure of the aging and non-aging samples. According to results, as the sample aged, a decrease was observed in the energy values absorbed by the composite samples. In addition, as the aging time increased, it was determined that there was a spread in the damage area and more visible fiber breaks occurred. The increase in the aging time caused a decrease in the stiffness of the composite specimen, worsened its mechanical properties, and increased matrix damage.

High strain rate deformation of aged TRIP Ti-10V-2Fe-3Al (wt.%) examined by in-situ synchrotron X-ray diffraction

Transformation Induced Plasticity (TRIP) is a promising avenue for tailoring the work hardening response of metastable β titanium (Ti) alloys. Here we show that aged TRIP Ti-10V-2Fe-3Al (wt.%) maintains higher elongations and flow stresses as strain rate increases, if phase stability and microstructural characteristics are tuned. Low temperature aging influences the matrix β phase stability by ω phase precipitation, which affords a promising way to impact the TRIP effect and obtain desirable mechanical properties, ranging from high damping capacity to good strength/ductility combinations. Although TRIP is active during quasi-static and dynamic testing up to 2000 s−1, increasing aging time and/or strain rate reduces the overall propensity for the TRIP effect and extent of transformation, which occurs rapidly just at the onset of yielding. TRIP with ω phase precipitation provides interesting alloying, microstructure, and property design strategies for engineering applications like lightweight protective structures, where high strains and the need for energy absorption are encountered.

Simultaneously enhancing strength-ductility synergy and strain hardenability via Si-alloying in medium-Al FeMnAlC lightweight steels

We studied the initial microstructures, mechanical responses and deformation-induced microstructures of the medium-Al Fe-21Mn-6Al-1C-xSi (x = 0, 1.5, 3 wt.%) lightweight steels both in their solution-treated and aged states. Our results reveal that nano-sized long-range ordered domains exist in the solution-treated steels, which feature L12 type ordering in the 0Si and 1.5Si steels and L′12 type ordering in the 3Si steel. Aging at 550 °C for 20 h has little effect on the microstructures of the 0Si steel, but leads to κ′-carbide precipitation in the 1.5Si steel. For the 3Si steel, aging at 550 °C for 1 h already results in the precipitation of uniformly-distributed nano-sized κ′-carbides (4.2 nm). The strength, ductility and strain hardenability of the solution-treated steels all enhance with increasing Si content. The yield strength (YS) of the aged steels with κ′-carbides enhances with increasing aging time, accompanied by the reduction of ductility. The short-time (1 h) aged 3Si steel exhibits excellent strength-ductility synergy, with YS > 900 MPa and total elongation > 50%. The increase in YS with Si addition originates from the grain boundary, solid-solution and order strengthening. For the 0Si steel, the strain hardening is governed by the evolution of high-density dislocation walls and microbands. The occurrence of both dynamic slip band refinement (DSBR) and twinning-induced plasticity effects in the 3Si steel accounts for the increase of strain hardenability with Si-alloying. The DSBR effect still exists and the progressively-formed slip bands are homogeneously distributed in the short-time aged 3Si steel, explaining its high ductility.

Aging phenomenon in low molybdenum Fe-21Cr-5Mn-1.5Ni alloy: Microstructure evolution, texture development and corrosion behavior

In the present work, the effect of long-term aging at 750°C up to 480 hours on microstructure evolution, texture development and corrosion behavior of a low molybdenum Fe–21Cr-1.5Ni–5Mn alloy has been investigated systematically. An increase in aging time results in increase in proportion of σ-phase. The σ-phase formation took place by the eutectoid decomposition reaction: δ → σ + γ 2 . The σ-phase did not show any specific orientation relationship with neighbouring δ ferrite grains. The initial solution annealed sample showed the presence of strong Brass ({110}<112>), Cube ({100}<001>), Goss ({110}<112>), and minor Cu ({112}<111>) in austenite, and strong γ-fiber (normal direction, ND//<111>) along with minor α-fiber (rolling direction, RD//<110>) in ferrite. After, long-term aging up to 480 hours, austenite showed strong Cu ({112}<111>) and minor Brass ({110}<112>) along with Cube ({100}<001>). Ferrite, on the other hand, showed γ-fiber. The lower amount of Cr/Mo and higher N in Fe-21Cr-1.5Ni-5Mn alloy was not enough to avoid the σ precipitation, however, it delayed its precipitation. The increase in σ-phase with aging time resulted in a decrease in corrosion resistance.

Reliability of laser soldering using low melting temperature eutectic Sn Bi solder and electroless Ni-electroless Pd-immersion Au-finished Cu pad

The demand for flexible wearable devices/substrates with miniaturization and improved integration in microelectronic devices has intensified the research interest in low-temperature laser soldering processes as an alternative to conventional reflow soldering processes owing to their advantages, such as local heating, non-contact heating, and short bonding time. In this study, we compared and evaluated the reliability of laser soldered and conventional reflow soldered joints using representative low melting temperature eutectic Sn Bi solder and thin electroless Ni-electroless Pd-immersion Au (ENEPIG)-finished Cu pads. Laser soldering was performed using various laser powers (130, 150, and 170 W) and times (2 and 4 s). Furthermore, an aging test was performed at 110 °C for 2000 h to evaluate the long-term reliability of the soldered joints. The mechanical properties, including the top and cross-sectional views and fracture surfaces, of the soldered joints were analyzed by conducting shear tests after aging. During laser soldering, various intermetallic compounds (IMCs) were formed at the joints depending on the applied energy. The metallization layer and Cu reacted with Sn in the solder after different aging durations, and additional IMCs were formed and grown. After aging for 2000 h, the shear strength decreased, and the interfacial IMC thickness increased. As the aging time increased, the fracture mode changed from an initial ductile fracture to brittle fracture (between the solder and IMCs and/or between IMCs and the Cu pad). The reflow soldered joints exhibited stable shear strength, resulting in ductile fracture until aging for 500 h. However, the shear strength decreased sharply after aging for 1000 and 2000 h, and Bi-segregation was observed after aging for 1000 h, resulting in inferior long-term reliability. After laser soldering at 150 and 170 W for 4 s, the strength of the samples decreased sharply after aging for 1000 and 250 h, respectively, and Bi-segregation was observed after aging for 2000 h. The shear strength of the sample laser soldered at 170 W for 2 s gradually decreased with increasing aging time and maintained a stable shear strength until aging for 2000 h. Therefore, laser soldering at 170 W for 2 s was considered as the optimal condition for long-term reliability. • Soldering properties of laser soldered Sn-58Bi/Au/Pd/Ni-finished Cu joints evaluated. • Laser soldering results were compared with conventional reflow soldered joints. • Various IMCs were formed depending on laser power and irradiation time. • Laser conditions with low applied energy displayed superior long-term reliability. • Selection of the optimal laser conditions is crucial to ensure reliable solder joints.

MoS2/CF synergistic enhancement to improve the friction and wear properties of UHMWPE composites

Ultrahigh molecular weight polyethylene (UHMWPE) is widely used in industrial machinery due to its excellent self-lubricant properties, and the development of long-lived UHMWPE matrix composite with low friction and wear is significant to solve the movement problems. In this paper, the UHMWPE/carbon fiber (CF)/MoS2 composites were prepared and the effect of aging time on the mechanical and frictional behavior of composites were investigated. Results showed that the addition of CF and MoS2 can significantly improve the frictional performance due to the synergistic effect. A low friction coefficient (0.11–0.15) and wear rates (3.8–7.6 × 10−5 mm3/Nm) were observed for UHMWPE/CF/MoS2 composite. The worn surface analysis presented that as the aging time increases, the main wear mechanism changing from abrasive wear to fatigue wear.

Aging Behavior and Precipitates Analysis of Wrought Al-Si-Mg Alloy.

Aging behavior of wrought Al-12.7Si-0.7 Mg alloy was investigated during isothermal aging at 180 °C. Two aging peaks were observed at 3 h and 8 h, respectively. To examine precipitate evolution during aging, the alloy's microstructure in different aging states was investigated by regular and high-resolution transmission electron microscopy (TEM and HRTEM). The results revealed that the variation of mechanical properties is attributed to the combining effect of Si particles, the grain boundary, and the character of precipitates. The predominant precipitates' type, size, and volume fraction vary as aging time increases.

Revisiting the thermal ageing on the metallised polypropylene film capacitor: from device to dielectric film

AbstractMetallised polypropylene film capacitors (MPPFCs) are widely used in power electronics and are generally degraded by elevated temperatures. This work aims to determine the relationships between the structural changes of MPPFC and the microstructural variations of the PP film during the thermal ageing of MPPFC at 100°C for 38 days. The capacitance of MPPFC has a slight decrease during thermal ageing. However, the breakdown voltage of the MPPFC decreases by 39.4% by the ageing. The partial discharge (PD) number of MPPFC increases linearly with ageing time. The tear‐down analysis of the MPPFC reveals that the molecular structure of the PP film has not been altered but has led to molecular chain scission and the generation of some polar fragments/groups. Meanwhile, the relative permittivity of the PP films rises as the ageing time increases. Moreover, thermal ageing causes the conversion of aluminum to alumina in the metallised electrode, which is hydrophilic for polar groups and leads to an adhesion effect between the metallised electrodes and the PP film. Contact angle measurements prove that the surface hydrophilicity of the PP sample increased after thermal ageing. Therefore, the PD/breakdown voltage in the MPPFC increases/decreases due to the uneven adhesion of the metallised PP film.

Frequency-Dependent Dielectric Spectroscopy of Insulating Nanofluids Based on GTL Oil during Accelerated Thermal Aging

Improving the dielectric properties of liquid-insulating materials is a current problem in research into the insulation system of a power transformer. Modern optimization of insulating liquids involves the potential use of unique synthetic esters enriched with nanoparticles. This study presents the results of the dielectric response of liquefied gas-based (GTL) insulating liquids during accelerated thermal aging. The dielectric relaxation spectroscopy method was used in the frequency domain to point out power losses as an imaginary part of a complex electric modulus. The relaxation spectra express the validity of applying this complex dielectric parameter. The polarization processes of the base oil alternately change position in the low-frequency band during thermal aging. Fullerene nanofluid undergoes three phases of dielectric loss changes during thermal aging. In the case of magnetic nanofluid, the effect of electric double-layer polarization disappeared after 500 h of thermal aging. It was found that with the gradual increase in the thermal aging time, there is no gradual increase in the dielectric losses investigated in the measured frequency spectrum. This study shows that the concentration of the two types of nanoparticles independently causes a different dielectric response to an applied AC electric field in the GTL base fluid.

Effect of thermo-oxidative aging on the Payne effect and hysteresis loss of carbon-black filled rubber vulcanizates

In the tire industry, the Payne effect and hysteresis loss of carbon-black (CB) filled rubber vulcanizates are the most concerning issues. CB filled rubber vulcanizates are susceptible to thermo-oxidative aging in the applications. In this paper, the effects of thermo-oxidative aging are investigated from experimental and theoretical aspects. The specimens are subjected to thermo-oxidative aging at 80, 100 and 120 °C for various periods of time ranging from 1 to 6 days and then the dynamic mechanical tests are conducted. The results show that both the storage modulus and the loss modulus increase with increasing aging time. The hysteresis loss of the material shows an increasing tendency with the increase of dynamic strain amplitude, aging time and aging temperature. The Kraus model is used to describe the Payne effect and a viscoelastic model consisting of dynamic strain amplitude and loss modulus is used to calculate the energy dissipation.

Effects of Feeding Regimes and Postmortem Aging on Meat Quality, Fatty Acid Composition, and Volatile Flavor of Longissimus Thoracis Muscle in Sunit Sheep.

The effects of different feeding regimes on antioxidant activity, meat quality, fatty acid composition, lipid oxidation, and volatile matter production in the longissimus thoracis (LT) of Sunit sheep at 0, 24, 48, 72, and 96 h postmortem were investigated. The results showed that the activity of antioxidant enzymes, tenderness, water retention, and percentage of unsaturated fatty acids were significantly higher in the pasture-fed sheep (PF) than in the concentrate-fed sheep (CF) (p &lt; 0.05). During postmortem aging, antioxidant activity, water retention, and the proportion of unsaturated fatty acids decreased in the PF and CF (p &lt; 0.05), while malondialdehyde (MDA) content, the proportion of saturated fatty acids, and the content of flavor substances resulting from fat oxidation increased. After 24 h of LT muscle aging, the pH and shear force of the meat started to increase and the color stabilized. The differences between shear force values and lipid volatile flavor substance content of sheep meat under different feeding regimes disappeared with increasing aging time. PF had better oxidative stability and fatty acid composition. Postmortem aging changed the oxidative stability of sheep meat, thus affecting meat quality and fatty acid composition and consequently meat flavor composition, while aging also eliminated to some extent the differences caused by feeding regimes.

Interplay between carbon and substitutional solute atoms during precipitation of Mn/Ni/Si-rich phases in model reactor pressure vessel steels

Trace C atoms can significantly alter the mechanical properties of steels, however, the effects of C atoms during precipitation of the Mn/Ni/Si-rich phases in reactor pressure vessel (RPV) steels remains unclear. Here, the interaction of C atoms with Mn/Ni/Si atoms during aging is investigated via the internal friction technique. Two Snoek peaks were detected: one is a superposition of the Snoek relaxation in Fe-C-Fe and the Snoek relaxation in Fe-C-Mn, and the other is the Snoek relaxation in Fe-C-Ni(Si). From the height variation of Snoek peaks with aging time, it was found that with the increasing aging time, the C atoms combine with the substitutional solute atoms at first, and then co-precipitate as MnSiC clusters at the GBs after 20 h aging at 600 °C. The variation of Snoek peak with aging time provides a reliable method to non-destructively detect the aggregation and precipitation of the M/Ni/Si-rich phases in RPV steels.

Effects of Aging Methods and Periods on Quality Characteristics of Beef.

The objective of this study was to determine effects of aging methods (wet-aged, dry-aged, and packaged dry-aged) during 60 d on quality traits and microbial characteristics of beef. Wet-aged beef was packed by vacuum packaging and stored in a 4°C refrigerator. Dry-aged beef was used without packaging. Packaged dry-aged beef was packaged in commercial bags. Dry-aged and packaged dry-aged samples were stored in a meat ager at 2°C-4°C with 85%-90% relative humidity. Meat color, crust thickness, aging loss, cooking loss, Warner-Bratzler shear force (WBSF), texture profile analysis, Torrymeter, meat pH, water activity, volatile basic nitrogen (VBN), thiobarbituric acid reactant substances (TBARS), and microbial analysis were measured or performed every 15 d until 60 d of aging time. Meat color changed significantly with increasing aging time. Differences in meat color among aging methods were observed. Aging losses of dry-aged and packaged dry-aged samples were higher than those of wet-aged samples. Wet-aged beef showed higher cooking loss, but lower WBSF than dry-aged and packaged dry-aged beef. VBN and TBARS showed an increasing tendency with increasing aging time. Differences of VBN and TBARS among aging methods were found. Regarding microbial analysis, counts of yeasts and molds were different among aging methods at the initial aging time. Packaged dry-aged and dry-aged beef showed similar values or tendency. Significant changes occurred during aging in all aging methods. Packaged dry aging and dry aging could result in similar quality traits and microbial characteristics of beef.