Effect Of Heat Aging Research Articles

The Effect of Heat Aging on the Microstructure and Properties of Spray-Deposited AlZnMgCu Alloy Extruded Plates.

The heat-aging process, a practical aging technology that not only improves the comprehensive performance of Al alloys but also reflects the requirements of short processes, has an extremely practical significance. The effects of the heating rate and termination temperature on the "heat-aging" behavior of a spray-deposited AlZnMgCu alloy hot-extruded plate were investigated using hardness, electrical conductivity, room-temperature tensile strength, exfoliation corrosion experiments, and transmission electron microscopy microstructure (TEM) observation. The results show that as the termination temperature increases, the hardness of the spray-deposited AlZnMgCu alloy first increases to a peak and then rapidly decreases, while the electrical conductivity continues to increase. The increase in the heating rate improves the peak hardness corresponding to the termination temperature. The heat treatment process of heating at a speed of 20 °C/h to 200 °C after the spray deposition has similar mechanical and corrosion resistance properties to the RRA process and can effectively reduce the heating time from 40 h to 8 h, thus establishing a heat treatment process for spray-deposited AlZnMgCu alloy extruded plate with high aging efficiency.

Effect of heat aging on pull-off strength of FRP epoxy bonded concrete: An experimental study and fire modelling

In this study, the bonding strengths of three different types of externally bonded composite systems were investigated under different environmental aging conditions at high temperatures, and the finite element model for a roof fire and concrete slab fire from above evaluated if the beams were externally reinforced with fiber-reinforced polymers (FRP). An FRP system is a structural reinforcement made of a type of fiber reinforcement fixed to a concrete surface through an epoxy adhesive. The bonding strength between the FRP and concrete substrates was measured using a pull-off test machine, as described in the EN 1542 standard. This study aims to determine the deterioration and negative effects of miscellaneous high temperatures on externally bonded FRPs used for strengthening civil structures. Epoxy-bonded carbon fiber-reinforced polymers (CFRP), glass fiber-reinforced polymers (GFRP), and basalt fiber-reinforced polymers (BFRP) were exposed to various temperatures of 23°C (control conditions), 70, 85, 100, 115, 130, and 150°C. Duratek® AV21 epoxy-based lamination system was used as an adhesive between the concrete and the FRP sheet. Three bonding failure modes (adhesive, cohesive, and substrate) were investigated for each test. The results were compared for three different types of FRPs under various temperatures, which is also significant research on the heat aging of the degradation process. The test results were also evaluated using finite element (FE) software modelling for roof and slab fires exposed from above, where the beams under the slab were reinforced with FRP systems. The test pull-off test results and FE model thermal analysis results were evaluated to obtain the temperature rise in the critical section of the concrete beam/slab in existing retrofitted buildings. The FE model results showed a critical temperature rise on the beam-slab corner connection as a result of the fire above the concrete slab. The duration of the FRP systems effectively bonded to the concrete beams located under different slab thicknesses and pull-off results were evaluated at elevated temperatures.

Effect of Heat Aging on Properties and Structure of SBS Modified Bitumen Waterproof Membrane

The properties of SBS modified bitumen waterproof membrane (SMBM) will deteriorate under the action of heat. In this paper, SBS modified bitumen (SMB) and SMBM were aged at 80 °C for different times (0,10,20,30,40 days). The low temperature flexibility, softening point, viscosity and mass changes ratio of SMB and mechanical properties of SMBM before and after aging were tested, the microstructure and chemical structure of SMB were investigated by fluorescence microscope (FM) and Fourier transform infrared spectroscopy (FTIR). The results show that the low temperature flexibility, softening point and viscosity of SMB decrease significantly at the initial stage of heat aging (10 days), especially the influence of heat aging on the low temperature flexibility and viscosity of SMB is more obvious, and their properties degradation rate slowdown in the later stage of aging. The mass changes ratio of SMB first decreases and then increases with aging time. FM shows that the network crosslinking structure of SMB is destroyed gradually with the extension of aging time. The network crosslinking structure disappears after 40 days of heat aging. FTIR shows that carbonyl and sulfoxide compounds are increasing after aging, more carbonyl compounds than sulfoxide compounds are formed after aging for 10 days, and the degradation rate of SBS decreases. The maximum tension of SMBM first increases and then decreases, the elongation at maximum tension decreases with aging time.

Effect of Short-Term Aging on Asphalt Modified Using Microwave Activation Crumb Rubber.

Effective approaches are required to be developed to solve the poor compatibility and thermal stability problems of crumb rubber-modified asphalt (CRMA). This study focuses on a method called microwave activation. However, seldom researches pay attention to the properties of MACRMA after aging. The objective of this study was to prepare microwave-activated CRMA (MACRMA) and investigate the performance of asphalt after aging. The samples were subjected to thin-film oven test (TFOT) at different times and temperatures. The effect of heat aging on the properties of MACRMA was evaluated by three indicator tests: viscosity, dynamic shear rheology test (DSR), and repeat creep recovery test (RCRT). The test results indicated that the MACRMA after two aging conditions had noticeably lower performance values (e.g., penetration, ductility) compared to unaged samples, and thus, the need to control temperature and time for mixing and construction was verified to be important. In addition, the G*/sin δ and phase angle values were largely influenced by the TFOT aging temperature and time. The MACRMA’s ability to recover was improved after aging. Compared with the aging temperature, the aging time had a more significant effect on the deformation and recovery ability of MACRMA.

Determining the Service Life of Polychloroprene Parts: A Case Study in Aging Behavior

This paper addresses determination of the service life of an installed elastomeric part, which is an issue of great practical use every day in industry. Unfortunately, this issue is commonly misunderstood and mishandled. The perennial confusion between “shelf life” and “service life” is clarified. A comprehensive survey of published literature on polychloroprene (CR or neoprene) aging is provided. The methodology, considerations and pitfalls of similarity analysis, accelerated heat aging and prediction using activation energy are illustrated with a case study. Shear in the dynamic mode, tensile, hardness, specific gravity and volume swell were the tests used to quantify the effect of heat aging. Tensile modulus and volume swell were determined to be the tests most sensitive to changes resulting from heat aging while specific gravity was the least sensitive. Although illustrated by an example of a polychloroprene part, this methodology is equally valid for the assessment of other elastomers also.

Development of a Mode III fatigue test method and a peel test method for tire specimens

Crack growth plays an important role in the durability of tires, and it is necessary to evaluate the characteristics of crack growth and tearing energy accurately. Since a crack around the belt edge is subjected mainly to interlaminar shear deformation, a Mode III fatigue test method was developed. In addition, a peel test method was developed to assess the tearing energy. Based on the fatigue and peel test results, the effects of heat aging, temperature and belt stiffness were analyzed.

Useful lifetime prediction of rubber component

Rubber material properties and lifetime evaluation are very important in design procedure to assure the safety and reliability of the rubber components. This paper discusses the failure mechanism and material tests were carried out to predict the useful lifetime of NBR and EPDM for compression motor, which is used in refrigerator component. The heat-aging process leads not only to mechanical properties change but also to chemical structure change so called degradation. In order to investigate the heat-aging effects on the material properties, the accelerated test were carried out. The stress–strain curves were plotted from the results of the tensile test for virgin and heat-aged rubber specimens. The rubber specimens were heat-aged in an oven at the temperature ranging from 70 °C to 100 °C for a period from 1 to 180 days. Compression set results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the compression set test, several useful life prediction equations for rubber material were proposed. Significance: Useful lifetime estimation procedure employed in this study could be used approximately for the design of the rubber components at the early design stage.

Microcrystalline and kinetic parameters of glass-PEEK hybrid composites

The cowoven hybrid fiber fabric consisting of E-glass and poly(ether ether ketone) fiber was compression-molded to obtain the hybrid composites. The effect of heat aging at different temperatures (400°C and 500°C) for different time intervals (1, 2, and 5 min) on the microcrystalline properties of the composites has been investigated and it was observed that heat aging for short time enhances the structure property relationships as reflected in the changes in crystal size and volume. The microcrystalline parameters such as the nanocrystal size (<N>), lattice disorder (g), interplanar distance (dhkl), width of the crystallite size distribution, and surface-weighted crystal size (Ds) were evaluated using wide angle X-ray scattering profiles. The different asymmetric column length distribution functions namely, exponential and Reinhold distribution methods were employed to probe the microcrystalline behavior of the composites and the results were compared. The kinetics of thermal degradation (using Flynn—Wall—Ozawa) revealed that, the activation energy decreased with increase in mass loss up to 15% and remains constant thereafter.

Modeling NBR‐ layered silicate nanocomposites: A DoE approach

AbstractThe mechanical behavior of acrylonitrile butadiene rubber (NBR) – organo modified layered silicate was modeled using Design of Experiments (DoE). Response surface methodology (RSM), a DoE tool was used to optimize the formulations for optimal performance of the nanocomposites. A Box‐Behnken design with three factors and three levels was used to model the relationship between mechanical properties and levels of ingredients. The factors studied for the design are silica content, nanoclay loading and vulcanization system. The nanocomposites were evaluated for tensile strength, modulus, elongation at break and hardness. The effect of heat aging on mechanical properties was also studied. The predicted properties of the nanocomposites are in good agreement with the experimental results, which confirmed the prognostic ability of response surface methodology. The model equations were used to generate response surfaces and contour plots to study the interaction between the variables. The contour plots were overlaid within the applied constraints to identify the required combination of variables that gives the optimum performance for the nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Fatigue life prediction of vulcanized natural rubber subjected to heat-aging

Fatigue life prediction and evaluation are the key technologies to assure the safety and reliability of automotive rubber components. In this paper, fatigue life prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Heat-aging effects on the fatigue life prediction of natural rubber were experimentally investigated. Fatigue test were performed using the 3-dimensional dumbbell specimen, which were aged different amounts. The Green-Lagrange strain at the critical location determined from the finite element method used for evaluating the fatigue damage parameter. Fatigue life prediction equation effectively represented by a single function using the Green-Lagrange strain. According to fatigue life prediction equation, fatigue life ambient temperature was longer than at 70 ∘C. Predicted fatigue lives of the rubber component were in fairly good agreements with the experimental fatigue lives within factor of two.

1010 加硫天然ゴムにおける亀裂進展速度と熱劣化の影響に関する研究(機械材料・材料加工II)

1010 加硫天然ゴムにおける亀裂進展速度と熱劣化の影響に関する研究(機械材料・材料加工II)

Heat-Aging Effect on the Material Properties and Useful Life Prediction of Rubber Materials

Rubber material properties and useful life evaluation are very important in design procedure to assure the safety and reliability of the rubber components. In this paper, the heat aging effects on the material properties and useful life prediction of rubber material for refrigerator component were experimentally investigated. The accelerated heat aging tests were carried out to predict the useful life of NBR and EPDM, which is used in refrigerator component. Compression set results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the compression set test, several useful life prediction equations for rubber material were proposed.

Fatigue Life Prediction of Heat-Aging Vulcanized Natural Rubber

Heat-aging effects on the material properties and fatigue life prediction of natural rubber were experimentally investigated. The rubber specimens were heat-aged in an oven at the temperature ranging from 50oC to 100oC for a period ranging from 1 day to 90days. Fatigue life prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Fatigue life prediction equation effectively represented by a single function using the Green-Lagrange strain. Predicted lives are in a good agreement with the experimental lives within a factor of two

A Study on Grafting of Natural Rubber and Nitrile Rubber on Thermoplastic Low Density Polyethylene Using Maleic Anhydride and Acrylic Acid

ABSTRACT LDPE/NR and LDPE/NBR blends were prepared by conventional mixing on two-roll mill. Modified blends were prepared by grafting (reactive blending). Grafting was carried out using acrylic acid and maleic anhydride. Compression-molded sheets were prepared out of the compounds and properties were evaluated. Mechanical properties like tensile strength, ultimate modulus, elongation at break, and hardness were determined. Effect of heat aging and effect of chemicals were estimated. The blends were characterized using FTIR spectrum. The electrical properties, abrasion resistance, solubility tests, and flammability tests for the compounds were also conducted. In all experiments results are found to be much higher for grafted compounds compared to ungrafted blends.

Heat-Aging Effects on the Material Properties and Fatigue Life Prediction of Vulcanized Natural Rubber

The fatigue analysis and lifetime evaluation are very important in design procedure to assure the safety and reliability of the rubber components. Heat-aging process affects not only the material properties but also the fatigue life of vulcanized natural rubber. In this paper, the heat-aging effects on the material properties and fatigue life prediction of natural rubber were experimentally investigated. The stress-strain curves were obtained from the results of tensile test. The rubber specimens were heat-aged in an oven at the temperature ranging from 50°C to 100°C for a period ranging from 1 day to 90 days. Fatigue life prediction methodology of vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue test. Fatigue life tests were performed using the 3-dimensional dumbbell specimen, which were aged in different amounts. The Green-Lagrange strain at the critical location determined from the finite element method used for evaluating the fatigue damage parameter. Fatigue life prediction equation effectively represented by a single function using the Green-Lagrange strain.

Heat aging effects on the material property and the fatigue life of vulcanized natural rubber, and fatigue life prediction equations

When natural rubber is used for a long period of time, it becomes aged ; it usually becomes hardened and loses its damping capability. This aging process affects not only the material property but also the (fatigue) life of natural rubber. In this paper the aging effects on the material property and the fatigue life were experimentally investigated. In addition, several fatigue life prediction equations for natural rubber were proposed. In order to investigate the aging effects on the material property, the load-stretch ratio curves were plotted from the results of the tensile test, the compression test and the simple shear test for virgin and heat-aged rubber specimens Rubber specimens were heat-aged in an oven at a temperature ranging from 50°C to 90°C for a period ranging from 2 days to 16 days. In order to investigate the aging effects on the fatigue life, fatigue tests were conducted for differently heat-aged hourglass-shaped and simple shear specimens. Moreover, finite element simulations were conducted for the specimens to calculate physical quantities occurring in the specimens such as the maximum value of the effective stress, the stram energy density, the first invariant of the Cauchy-Green deformation tensor and the maximum principal nominal strain. Then, four fatigue life prediction equations based on one of the physical quantities could be obtained by fitting the equations to the test data. Finally, the fatigue life of a rubber bush used in an automobile was predicted by using the prediction equations, and it was compared with the test data of the bush to evaluate the reliability of those equations.

Mechanical relaxations in heat‐aged polycarbonate. Part II: Statistical analysis of low‐molecular weight data

AbstractThe significance of heat‐aging effects on low‐molecular‐weight polycarbonate has been studied by performing a two‐factor Analysis of Variance (ANOVA). Although this work was primarily motivated by the large experimental scatter observed in stress relaxation results for LMW 2608 (part I), the effect of heat‐aging on the characteristics of secondary transitions (γ and β1) generated by dynamic testing was also investigated. Both types of tests were performed using a dynamic mechanical analyzer. The statistical analysis verified an earlier suggestion that both the secondary transitions were insensitive to heat‐aging. In the quasi‐static stress relaxation tests, the curve‐fitted KWW parameters (τ, Eo′ β′) were evaluated using ANOVA for increasing heat‐aging time and test temperature. Two other statistical techniques were also applied to test repeatability—the power of each aging time/test temperature combination and the number of observations needed to achieve 90% repeatability. In conclusion, both τ and β′ could describe the self‐retarding nature of volume recovery although the repeatability of β′ was substantially higher. However, the unrelaxed modulus, Eo, was found to be an unreliable indicator of whether heat‐treatment had caused changes in the intrinsic structure. Overall, the study showed that the repeatability of the stress relaxation test results is generally very poor for the confidence levels tested.

Structure-property relationship of castor oil based diol chain extended polyurethanes (PUs)

A series of 1,4-butane diol and 1,6-hexane diol based chain extended polyurethanes (PUs) have been prepared using castor oil with different diisocyanates such as methylene bis (phenyl isocyanate) (MDI), toluene-2,4-diisocyanate (TDI) and hexa methylene diisocyanate (HMDI) as crosslinkers. The prepared aliphatic diol based chain extended PU's have been characterised for physico-mechanical properties such as density, tensile strength, percentage elongation at break, tensile modulus and surface hardness; and optical properties like total transmittance and haze. The properties imparted by the chain extenders and diisocyanates on PUs have been explained on the basis of chemical structure. Effect of heat aging on mechanical properties of PUs have also studied. These changes have been interpreted quantitatively in terms of microcrystalline parameters computed using wide-angle X-ray scattering (WAXS) data.

Effect of heat aging on the properties of a nylon 6,6/poly(phenylene oxide) blend

AbstractAccelerated aging of an Initial formulation of a nylon 6,6/poly(phenylene oxide) (PA/PPO) blend resulted in a significant loss in impact strength after a relatively short aging period. Fourier transform infrared (FTIR) spectroscopy showed considerable surface oxidation in air‐aged samples. Scanning electron micrographs (SEM) of fracture surfaces showed evidence of embrittlement (glassy skin formation). This brittle skin apparently influenced crack propagation throughout the entire cross section of the test specimens. It was determined by nuclear magnetic resonance (NMR) analysis that the PPO phase of the blend contained a poly(styrene‐butadiene) copolymer, probably added as an impact modifier. The susceptibility of the polybutadiene to oxidation, especially at elevated temperature, is believed to have caused the oxidation and surface embrittlement. However, the surface oxidation also resulted in a large loss in molecular weight of the nylon phase (m‐cresol‐soluble portion) and considerable cross‐linking of the PPO phase (chloroform‐soluble portion). Samples aged in inert atmosphere showed no skin formation nor loss in impact properties, thus confirming that oxidative degradation caused the embrittlement.