Artificial Aging Process Research Articles

Graphene rubber composites integrated sealing rings for monitoring contact pressure and the aging process

The graphene rubber composite is a highly sensitive and large-deformation intelligent sensing material, which is used for monitoring the contact pressure and the sealing state of rubber sealing rings. First, the integration of the graphene rubber composites and the sealing rings is achieved through the preform and molding process, which is simple and convenient to operate. Second, the resistance signal of graphene rubber composites related to the contact pressure has good stability and repeatability, which can be used to quantitatively monitor the contact pressure by the developed model. Also, the resistance features of graphene rubber composites integrated sealing rings at different temperatures exhibited high sensitivity and good linearity under compression. Finally, it was found that the resistance signals can also well characterize the artificial aging process of the sealing rings at 120 °C for 72 h, which can provide important information for sealing status and life prediction of O-rings.

Mineralogical Evolution and Leaching Behaviour of a Heap of Bottom Ash as a Function of Time: Influence on Its Valorization

Waste to Energy Bottom Ash (WtE BA) in France is reused as a substitute for natural aggregates in building material for road construction. Before BA reuse, treatment operations are generally necessary such as the removal of ferrous and non-ferrous metals, ageing, and particle size separation. BA valorization depends on the leaching behavior of the main Mineral Trace Elements (MTE), which in turn depends on pH. It is well known that ageing influences the natural pH of BA, as the initial pH of fresh BA (around 12–13) can decrease to a pH of 8 in weathered BA. Ageing can be influenced by different parameters, for example the presence of ferrous metals because of their exothermic oxidation increases temperature in heap and the CO2 content of the gaseous phase in the porosity of BA. However, as the removal of ferrous metals is now increasingly efficient, BA are different according to total content and mineral content. And when WtE BA is stored in heaps, atmospheric exchange are limited, the ageing process is no longer as efficient. The main objective of this study was to measure the efficiency of the ageing process when BA is stored in heaps. The mineralogical evolution and the leaching behavior of BA were observed during 7 months. Two artificial ageing processes were carried out on the oldest sample. All the results showed that when the BA was stored in heaps, the ageing process was inefficient, with a low evolution of pH, whereas ‘artificial’ ageing processes reduced the pH. This pH decrease was accompanied by an increase in the leaching of sulfates and antimony, which is an unwanted side effect. Mineralogical characterization showed differences between all the samples, providing insight into the leaching of MTE. The presence of some mineral phases known for their affinity with certain MTE made it possible to confirm certain mobility/retention hypotheses.

Effect of Artificial Aging Temperature on Mechanical Properties and Micro Structure of Al-Mg-Si Composite

Temperature determination used in artificial aging process will affect hardness after quenching process and mechanical properties of Al-Mg-Si composite. Thus, the aim of this research is determining temperature used in aging process to obtain mechanical properties optimum. It was done by the procedures as follows: initially, solution heat treatment of Al-Mg-Si composite was set at 400°C then quenching process on water medium followed by aging treatment at various temperatures (130°C, 180°C, 230°C, 280°C and 330°C) for 1.5 hours of HT. After the process, products were analyzed by hardness test to observe the micro-structure change of the samples. The result shows that hardness value of material increased with temperature process (130-280°C) about 10%. The hardness value rises from 48.05 HV before artificial aging to 53.13 HV.

Influence of Ageing Process on Rheological Characteristic of Waste Natural Rubber Latex Modified Bitumen

Bitumen is widely used in highway pavement construction. Changes of bitumen properties occurs during the modification and ageing process. The ageing process does consequences in road deterioration; however, it is also benefits in determination of optimum properties during bitumen modification process. Thus, this study was conducted to evaluate the changes of bitumen (unmodified and modified) properties as it was exposed to artificial ageing process. In order to achieve the objective, base bitumen (PEN 60/70) was modified with waste natural rubber (NR) latex. Subsequently, the modified bitumen was subjected to a laboratory ageing process by the aided of rolling thin oven film (RTFOT) and pressure ageing vessel (PAV). Its rheological characteristic was evaluate using dynamic shear rheometer (DSR). It was found that, associating waste NR latex with bitumen improved its properties during short term and long term ageing, indicated by G*/sin δ and G*.sin δ. The performance grade (PG) also successfully improved to PG76 with the addition of 5% waste NR latex.

Effects of creep aging upon Al-Cu-Li alloy: Strength, toughness and microstructure

Effects of creep aging on strength and toughness and microstructure evolution of Al-Cu-Li alloy were investigated by tensile test and Kahn tear test at room temperature, combined with fractograph and transmission microstructure analysis. The specimens of pre-strain creep aging state (CA) have been studied and compared with artificial aging state (AA) and pre-strain artificial aging state (PA). It is demonstrated that pre-strain before artificial aging process can improve the strength property and the fracture toughness of Al-Cu-Li alloy. On top of that, both of them can be further improved by creep aging process: the yield strength was increased by 8.7% and the unit initiation energy of Kahn tear was increased by 11.7%. The increasing of fracture toughness has also been verified by Kahn tear fractographs that the dominating fracture type changes from the ductile intergranular fracture to the ductile transgranular fracture. Transmission electron microscopy revealed that creep aging promotes the nucleation of T1 phase, resulting in a fine and dense distribution of precipitates in the matrix, and the enrichment of subgrain boundary T1 precipitates was greatly reduced.

Effects of TiB2 particles on artificial aging response of high-Li-content TiB2/Al-Li-Cu composite

The effect of TiB2 particles on artificial aging response of cast high-Li-content TiB2/Al-Li-Cu composite at 175 °C was investigated for the first time by a combination of various techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). We discovered that the nano-sized particles, in the shapes of hexagonal or equaixed, had a strong influence on mechanical properties and microstructural evolution during artificial aging process. With the introduction of TiB2 particles, the average grain size decreased significantly. The precipitations of θ′ and T1 precipitates were promoted in the reinforced composite, however, there was no obvious difference in the size and number density of δ′ precipitates between the unreinforced alloy and reinforced composite. DSC results showed that the addition of TiB2 did not change the precipitation sequence, although both precipitation and dissolution kinetics were altered. The reinforced composite revealed a remarkable improvement in mechanical properties.

Ultrasonic wave velocity measurements for detecting decay in carbonate rocks

Ultrasonic testing is a non-destructive technique commonly employed for assessing indirectly some geomechanical parameters of natural building stones. Pulse wave propagation in rock materials depends not only on physical properties, e.g. density, elasticity, porosity and water content, but also on fabric elements and their arrangements, spatial distributions and preferred orientations. In contrast, ultrasonic velocity can reflect the state of conservation of stone by comparing data from fresh material with those obtained from tests made on decayed material. The ‘Avorio’ limestone is a valuable building and ornamental material, quarried in the Trani stone basin (Apulia, southern Italy), which is very popular in Italy and abroad where it is used in modern and historic buildings. The stone response to decay processes is not fully understood simply because this material has not yet been well studied. To better understand how durable this material is in terms of physical resistance to change with respect to salt and thermal deterioration mechanisms, selected samples of the ‘Avorio’ limestone were submitted to artificial ageing processes by thermal stresses and by stresses due to salt crystallization, performed independently. The artificial ageing processes involved thermal cycles at temperatures between 200 and 600°C, based on an experimental procedure, and a standardized salt crystallization test in sodium sulphate solution. Repeated measurements of pulse velocity, before, during and after every accelerated ageing cycle, were compared with mass loss and porosity changes, the latter by water imbibition and capillarity testing. Very statistically significant relationships between physical response and rates and patterns of the stone decay were illustrated. The experimental results showed that the ultrasonic pulse velocity decreases as deterioration of the stone increases under accelerated ageing: a strong negative correlation exists between P-wave velocity and porosity. This study confirmed that ultrasonic pulse velocity is a good indicator of damage for carbonate stones, particularly for varieties without clear anisotropies, in terms of structure and texture.

Precipitation Stages and Reaction Kinetics of AlMgSi Alloys during the Artificial Aging Process Monitored by In-Situ Electrical Resistivity Measurement Method

The precipitation process and reaction kinetics during artificial aging, precipitate microstructure, and mechanical properties after aging of AlMgSi alloys were investigated employing in-situ electrical resistivity measurement, Transmission Electron Microscopy (TEM) observation, and tensile test methods. Three aging stages in sequence, namely formation of GP zones, transition from GP zones to β″ phase, transition from β″ to β′ phase, and coarsening of both phases, were clearly distinguished by the variation of the resistivity. It was discussed together with the mechanical properties and precipitate morphology evolution. Fast formation of GP zones and β″ phase leads to an obvious decrease of the resistivity and increase of the mechanical strength. The formation of β″ phase in the second stage, which contributes to the peak aging strength, has much higher reaction kinetics than reactions in the other two stages. All of these stages finished faster with higher reaction kinetics under higher temperatures, due to higher atom diffusion capacity. The results proved that the in-situ electrical resistivity method, as proposed in the current study, is a simple, effective, and convenient technique for real-time monitoring of the precipitation process of AlMgSi alloys. Its further application for industrial production and scientific research is also evaluated.

Different precipitation hardening behaviors of extruded Mg–6Gd–1Ca alloy during artificial aging and creep processes

How to effectively improve the precipitation hardness response of Mg alloys with relatively low RE content is an interesting and important topic. In the present study, an extra stress is added instead of just exposing the sample (extruded Mg–6Gd–1Ca alloy) in high temperature (175°C) to modify the precipitation behavior and improve the hardness of alloy. Microstructural examinations of the aged alloy by transmission electron microscopy (TEM) show that the weak age-hardening response is mainly attributed to the low number intensity and relatively large size of precipitates in grains. The results suggest that the creep process can effectively promote precipitation response compared with the aging process. TEM analyses indicate a large amount of nano-scale precipitates (espically β' phase) can be formed in grains of the crept alloy, which is mainly responsible for the obvious hardness increase of the alloy after creep. Electron backscattered diffraction (EBSD) data suggest that the dislocation increase caused by strain during creep is responsible for the precipitate increase through providing more nucleation sites.

Effect of Rice Husk ash Reinforcements on Mechanical properties of Aluminium alloy (LM6) Matrix Composites

The use of low cost material metal matrix composites is increasing rapidly in various engineering fields because of their better mechanical properties. In this study aluminium alloy (LM6) is used as matrix metal and rice husk ash (RHA) as reinforcement for developing a new metal matrix composite material. A rice husk ash 6% by weight are added and artificial aging process is done at temperature 135°C, 175°C and 225°C to develop metal matrix composites using stir casting method. The mechanical properties of composite such as hardness and wear properties were studied for the all test specimens.

Multistage artificial aging optimization for tensile properties of Duralium using Response Surface Method (RSM)

This study developing mathematical model to optimize heat treatment process to obtain the most significant parameter that affected tensile strength of duralium through multistage artificial aging. The process parameters in this study were temperature of aging, holding time of aging, and artificial aging process was conducted in double stages. The experiments were conducted according to central composite design matrix. The adequacy of developed model was analysed by analysis of variance (ANOVA). The optimum parameter of multistage artificial aging was obtained for maximum tensile strength of duralium.

Fracture load of colored and non-colored high translucent zirconia three-unit fixed dental prosthesis frameworks

Aim: The use of colored translucent zirconia may enable restorations of a more natural tooth-like appearance than previous opaque white zirconia. The shift from non-colored to colored zirconia may however entail a risk of reduced strength. The aim of the present study was to compare fracture load and fracture mode of fixed dental prostheses frameworks made of colored translucent zirconia to that of non-colored controls.Methods: A total of forty three-unit FDP frameworks were manufactured from two different high translucent zirconia materials (Zenostar, Wieland Dental, and DD cubeX2, Dental Direkt). Each group contained two subgroups, one colored and one non-colored. Coloring was performed before final sintering using two different infiltration techniques. All FDPs underwent an artificial aging process in the form of heat treatment, thermocycling and preloading whereafter the specimens were subjected to load until fracture. Fracture load and mode was registered.Results: For one of the zirconia materials, Zenostar, the non-colored frameworks showed significantly higher fracture loads (p < .0001) compared to its colored counterpart. No significant difference (p > .05) was found between colored and non-colored frameworks in the other zirconia material, DD cubeX2. All FDPs fractured through the connector. Some fractures ran through the mesial and some through the distal side of the connector but there were no significant differences in fracture mode between groups.Conclusion: Coloring before sintering of high-translucent zirconia may decrease the fracture load of FDP frameworks for certain materials and techniques. Fracture mode however, does not appear to be affected.

Influence of Different CAD/CAM Crown Materials on the Fracture of Custom-Made Titanium and Zirconia Implant Abutments After Artificial Aging.

To investigate the effects of different commercially available computer-aided design/computer-assisted manufacturing (CAD/CAM) materials for fabrication of molar crowns, including polyetheretherketone (PEEK), on the fracture strength and failure mode of custom-made titanium and zirconia abutments after artificial aging. A total of 48 identical custom-made CAD/CAM abutments milled out of titanium or zirconia were divided into six test groups of eight specimens each. The groups were assigned as follows: titanium abutments restored with zirconia crowns (TiZ), with lithium disilicate crowns (TiL), or with PEEK crowns (TiP); zirconia abutments bonded to a titanium base and restored with zirconia crowns (ZrZ), with lithium disilicate crowns (ZrL), or with PEEK crowns (ZrP). The specimens were artificially aged in a chewing simulator for 1.2 million cycles of dynamic loading with simultaneous thermal cycling and then loaded to fracture in the universal testing machine. Shapiro-Wilk test was used to test for normality. One-way analysis of variance followed by post hoc analysis using Bonferroni test was used to detect statistically significant differences among groups. All specimens survived the artificial aging process simulating 5 years of clinical service. The fracture patterns and means of the fracture strength (N) varied between groups: TiZ = 4,926 N; TiL = 3,706 N; TiP = 3,878 N; ZrZ = 5,529 N; ZrL = 2,826 N; and ZrP = 3,967 N. Although the tested combinations showed different fracture patterns and loads, all tested abutment and crown materials and their different combinations could be considered to have fracture strengths suitable for clinical application.

Degradation Behavior of Nano-Glue Adhesive due to Historical Textiles Conservation Process

Fragile textiles in museums need to consolidate by natural adhesives such as animal glue due to conservation process. Sometime the animal glue becomes shrunk, cracked, and rigid after long term. The article is aimed to study using Nano animal glue adhesive in historic textiles conservation field in order to consolidate the fragile textiles. For this, an extensive experimental work was done to study the ageing behavior of Nano animal glue after artificial ageing process. Firstly, Wool fabric dyed with natural dyes such as madder and safflower dye mordanted with different mordents to similarity for the historical textiles. The wool dyed fabrics were coated with animal glue adhesive and nano animal glue adhesive. The treated wool fabrics were aged by accelerated thermal ageing for different time. A comparative study was done in order to characterize changes in properties as well as the physical and chemical degradation of treated wool fabrics before and after thermal ageing. Different type of analysis methods such SEM , FTIR, the colors are given in Commission internationale de l’eclairage (CIE L*a*b*) coordinates and mechanical properties. This article presents interesting results concerning the effect of ageing on characterization of nano glue adhesive furthermore for treated wool fabrics.

Different aging behaviors at surface layer and central region of a die-casting A380 alloy during heat treatment

Microstructural and hardness evolutions of a vacuum-assistant die-cast A380 (Al-8.67wt.%Si-3.27wt.%Cu) alloy during heat treatment were investigated. Isothermal DSC test at 200 °C revealed that the precipitation reaction in the surface layer was faster than that in the central region. This corresponded with the hardness evolution that the surface layer hardened faster. The hardness increment in the surface layer was higher than that in the central region. Further experimental evidences indicated that the differences were due to the different amounts of heterogeneous nucleation sites for precipitation in the two parts. The influence of the characteristic as-cast microstructure on the artificial aging process is analyzed and discussed in detail.

Influence of natural aging and pre-treatment on the precipitation and age-hardening behavior of Al-1.0Mg-0.65Si-0.24Cu alloy

Replacing steel plate with aluminum alloy as automotive structural parts is a cost-effective way to reduce body weight. The effect of 5% deformation + pre-aging treatment (170 °C, 190 °C, 210 °C for 10 min) on natural aging, subsequent artificial age-hardening of an Al-1.0Mg-0.65Si-0.24Cu alloy were studied by hardness measurement, differential scanning calorimetric (DSC), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) analysis. The formation of clusters induced by natural aging decrease the size and density of β″ phase during subsequent artificial aging, which results in a decline of peak-aging hardness. The immediate pre-treatment after quenching completely suppressed the negative effect of natural aging. In addition, it significantly increased the peak-aging hardness (higher than T6 peak-aging condition) and shortened the time (by 50%) to reach peak hardness of the alloy during subsequent artificial aging. The pre-treatment generated the β″-nuclei to be readily transform into β″ phase during artificial aging. The two types of disordered precipitates formed during the pre-treatment continued to grow with the process of subsequent artificial aging and played an important part in strengthening the alloy.

Thermal Treatment of Aviation Aluminum Alloys in Strip Processing Lines

For many years now the use of aluminum as a light weight construction material in the aviation and automotive industry is on the rise. Without the innovative aluminum materials the strategies of constructing in light-weight design cannot be implemented. Last but not least this trend is driven by official requirements directing the reduction of greenhouse gas emissions. Aluminum is used both for structural components as well as for external body parts. Aluminum products for these industries have to undergo a production process which includes homogenizing of the ingots, hot rolling and cold rolling. Subsequent to the cold rolling process, the aluminum sheets have to undergo a heat treatment process to regain formability as well as the required material strength. The material properties required by the aviation and automotive industry are achieved in the annealing furnace and downstream cooling equipment. Equal and well-aimed heating and cooling along the length and across the width provide the strips with the metallurgical properties with regard to hardness and grain size. Hence the annealing furnace and the downstream cooling equipment are the decisive process components and critical for the high quality of the end material. First the material is heated up to a temperature above 500 °C for the solution heat treatment process. The following process step foresees cooling down the material to ambient temperature. Especially 6xxx automotive-alloys as well as 2xxx and 7xxx aerospace-alloys require high cooling rates. Eventually, the material gets heated up again for a certain time to apply an artificial aging process. In floatation heat treatment furnaces the strip is guided sinusoidal and contactless by floatation nozzles through the furnace. The strip is heated up and kept at the required strip temperatures in time, so the aluminum-alloy obtains their structure. The cooling process with high cooling rates is executed as a combination of water and air cooling. A mathematical model calculates the necessary settings for the annealing and cooling process under consideration of the mechanical properties. Paper and presentation will introduce the furnace technology for aluminum strips. Especially, the heat treatment facilities for heat and chemical treatment lines will be presented. It will especially emphasize on heat treatment cycles, the materials and the applications.

The differential antioxidant capacity of watermelon flesh at different maturity stages and its inhibitory effects on seed aging may explain the significance of fruit flesh colors

Fruit can use different skin colors to attract animals for seed dispersal. Interestingly, however, many fruits such as watermelon, which has a green outer rind, also have colored flesh. The potential reasons underlying this phenomenon were investigated here. White (low maturity), pink (medium maturity), and red-fleshed (high maturity) watermelons were collected and their flesh antioxidant capacities were compared by evaluating Fe3+ reducing power and DPPH radical scavenging capacity. Results showed that the antioxidant capacity of fruit flesh at different maturity stages was highest in red flesh, lower in pink flesh, and lowest in white flesh. Moreover, extracts of these flesh samples were obtained and the germination rate and lipid peroxidation of aged seeds, which were pre-treated with these extracts during the artificial aging process, were investigated. This showed that the extracts can significantly increase germination rate, but decrease lipid peroxidation of aged watermelon seeds, with the greatest changes observed with red-flesh extracts and the smallest with white flesh. Dimethyl thiourea, a specific scavenger of free radicals and reactive oxygen species, had a similar effect on the germination rate and lipid peroxidation of aged seeds. Combining previously reported results and our findings, we propose a hypothetical model in which pigment biosynthesis results in the enhancement of antioxidant capacity to illustrate the physiological significance of flesh color on seed aging and germination.

Stabilization of the Tensile Strength of Aged Cellulose Paper by Cholinium-Amino Acid Ionic Liquid Treatment

In this study, a chemical stabilization method, that preserves the tensile strength of artificially aged paper pretreated with an aqueous solution of ionic liquid, is presented. Pure cotton cellulose paper samples were soaked with cholinium glycinate ionic-liquid solution either before or after the artificial aging process, which was based on thermal degradation in dry air. The tensile strength of artificially aged paper was measured by using the double-folding technique. The role of ionic liquids was investigated by mid-infrared and terahertz time-domain absorption spectroscopy. It was found that the tensile strength of pretreated samples is higher than that of other aged samples. A model for changes in the cellulose structure caused by oxidation and by the binding of ionic liquid molecules is proposed, based on the analysis of the mid-infrared absorption bands in the carbonyl/carboxyl region at 1590–1750 cm–1. Terahertz spectroscopy data indicate that the ionic liquid molecules penetrate in the larger s...

Accelerated Degradation of Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers: Performance Degradation and Steady State Liquid Water Distributions with in Operando Synchrotron X-ray Radiography

The polymer electrolyte membrane (PEM) fuel cell is a promising alternative power source for electric vehicles, forklifts, and stationary backup power due to its high power density, low operating temperature, and clean emissions. The gas diffusion layer (GDL) facilitates the transport of heat, reactant gases, water vapor, and liquid water in the PEM fuel cell. The GDL is a highly porous material composed of dense arrays of carbon fibers, resins, and polytetrafluoroethylene (PTFE). Additionally, it is typically coated with a micro porous layer (MPL), which results in the reduction of contact resistance at the catalyst layer interface and the overall improvement in water management. Effective water management must be achieved within the GDL over the entire operating lifetime in order to improve the commercial success of PEM fuel cells. Investigations into the effects of ageing on water management within the GDLs can be useful tools to guide this success. Water is required to maintain polymer electrolyte membrane hydration and ionic conductivity; however, excess water tends to accumulate in the catalyst layer, GDL, and flow channels. This accumulation limits mass transport and leads to performance losses. Therefore, effective water management in the GDLs is essential for improving cell performance, durability, and stability. Most GDL research has been focused on the impact of GDL materials and microstructure design on overall performance, rather than durability. Decreased GDL hydrophobicity has been found after only a few hundred hours of operation (1, 2). Therefore, a clear understanding of the influence of GDL degradation on the liquid water behavior is essential. As a tool to visualize this behaviour, synchrotron X-ray radiography is a powerful technique for visualizing liquid water transport behavior within an operating PEM fuel cell. High intensity X-rays generated at the BMIT-BM beamline of the Canadian Light Source were used for identifying liquid water inside the GDLs and capturing the multiphase flow behavior in an operating PEM fuel cell. Figure 1 is an example synchrotron X-ray radiograph of the fuel cell in operando, illustrating the spatial distribution of liquid water. The observed pixel brightness was correlated to the presence of liquid water, and the saturation profile across the GDL thickness was obtained. In this study, as-received fresh GDLs were immersed in a 35wt % solution of H2O2 at 90o C for 12 hours in order to perform an accelerated artificial ageing process. As-received fresh and artificially aged GDLs were then used to assemble specialized fuel cells for synchrotron imaging. Both the electrochemical performance and liquid water transport behavior were observed for a range of current densities. Additionally, the effect of changes in relative humidity on performance was compared to investigate the effect of artificial ageing. Notable differences in cell performance and liquid water transport behavior were observed at steady state operating conditions. The cell with aged GDLs showed lower cell voltage and higher quantities of liquid water than those of as-received fresh GDLs. The impacts of aging on the liquid water distributions within the GDL and on cell performance will be presented in this work. The objective of current work is to highlight the potential degrading effect on liquid water management in long term fuel cell operation.