Elevated Temperature Tests Research Articles

Kinetics of the thermal degradation of lycopene in tomatoes

This research studied the kinetics of the thermal degradation of lycopene in tomatoes using elevated temperature testing. Understanding the nature and the extent of sensitive nutrient degradation in tomatoes will assist in reducing postharvest nutrient losses during storage and processing. Ripe tomatoes were sorted, washed, and blinded. Juice was obtained by filtering the blinded pulp through a muslin cloth. The samples were heated using a water bath at 70, 80, 90, and 100 °C for 20, 40, 60, and 80 minutes. The determination of lycopene was done using spectrophotometric methods at 503 nm, in hexane: ethanol: acetone (2:1:1 v/v/v) lycopene extract. The concentrations of lycopene were determined immediately after processing. The data was found to fit into first order equations. Degradation constants (k), D-value, and half-life for the thermal degradation of lycopene were determined at each processing temperature. Models were also developed for each of the chosen temperatures, which can be used to predict the degradation pattern of lycopene at other processing conditions. Z-value, Q10, and activation energy for the degradation of lycopene were also determined. Analyses showed a considerable decrease in lycopene concentration and decimal reduction time (D-value), and a significant increase in the thermal degradation rate (k) during heating from 70 to 100 °C. The finding shows that the degradation of lycopene in tomatoes followed the first order kinetics and it shows that the lycopene content decreased at 80 to 100 °C.

Stability of Strength Characteristics of Hardened by Deformation AMg6 Alloy during High-Speed Heating

The results were shown in influence of fast heating parameters on the structure and properties of cold-worked alloy AMg6 with original hot-forged structure. Based on the measured data, the change of mechanical properties of cold-worked alloy AMg6 during the process of short duration heating was evaluated. There was reviewed the role of the temperature and the time of heat on the processes of softening the samples of cold-worked alloy AMg6. The stability of mechanical characteristics of hammer-hardened alloy AMg6 under elevated test temperatures was evaluated. It is shown that the return processes in cold-deformed AMg6 alloy during heating in the temperature range studied receive the most intensive development in the first 5–10 minutes, reducing the hardening effect from cold deformation, determined by tensile strength, respectively: by 8–9% with 100 °C; 26–27% at 150 °C; 37–38% at 200 °C; 42–44% at 250 °C and 50% at 300 °C. A decrease in the yield strength during high-speed heating in the temperature range studied is much faster ,compared with the change in the tensile strength. Hour exposure at 200 °C reduces the hardening effect on the yield strength from 340 MPa to 258 MPa, while the tensile strength decreases from 430 MPa to 385 MPa.

Impact fracture energy of steel welded connections in fire and post-fire

Charpy impact tests were conducted on steel welded connections at elevated temperatures and at the ambient temperature after heating and cooling processes. The elevated temperature tests were conducted to examine the Charpy impact energies under the blue brittleness temperature (100–300 °C) of steel. V-notch specimens quarried from steel base metal, weld metal, and heat-affected zone of the welded connection were heated and subjected to Charpy impact tests. In the ambient temperature tests after the heating and cooling processes, the heated specimens were either air cooled in a furnace or quenched with water. The test results show that the Charpy impact energies do not decrease in the blue brittleness temperature, and the quenched welded connections demonstrated very low Charpy impact energies.

Studies on High Temperature Wear and Friction Behaviour of AA6061/B4C/hBN Hybrid Composites

This present work deals with the use of hexagonal boron nitride (h-BN) as a solid lubricant for AA6061/B4C composite due to its special features of self-lubricating property, thermal and chemical stability. The wear behaviour of composites at elevated temperature test, varied from 27 to 300 °C, was performed for AA6061 alloy with boron carbide (B4C) 5–15 wt% and h-BN 5–15 wt% reinforced hybrid composites under a load of 10 and 45 N at constant sliding velocity and sliding distance of 2.2 m/s and 2500 m. The prepared composites were characterized using X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis. The mechanical properties of hybrid composites were evaluated using tensile testing and hardness. The microstructural results revealed a homogenous distribution of reinforcement particles and grain refinement in the composites up to 10 wt% of h-BN. The tensile test results showed a significant improvement in the tensile strength up to 82% attained for the 15% B4C and 5% h-BN hybrid composite compared to AA6061 matrix alloy. The wear behaviour and different wear mechanisms under various testing conditions were explored. The mild-severe wear transition is noticed with increasing load and temperature for AA6061. The wear properties of a hybrid composite of C10N10 exhibited superior wear resistance due to the complete lubrication effect on the entire worn surface. The predominant wear of abrasive and adhesion occurred at room and elevated temperatures and low load conditions. Oxidative wear, plastic deformation, and delamination wear were operating with an increase in load and temperature.

Temperature Dependence of the Permeability of Sandstone Under Loading and Unloading Conditions of Confining Pressure

Rock permeability is a key parameter in evaluating the CO2 storage capacity and injectivity in geologic CO2 sequestration projects. To investigate the influences of confining pressure and testing temperature on rock permeability, seepage tests were carried out on four cylindrical sandstone specimens using a newly developed triaxial permeability measurement system. In this study, the confining pressure was loaded and unloaded stepwise between 10 and 30 MPa at different temperatures (25–90 °C). The experimental results showed that as the effective confining pressure increased in the loading process, sandstone permeability decreased nonlinearly. As the effective confining pressure decreased in the unloading process, permeability increased nonlinearly. Elevated temperature decreased the sandstone permeability, and the percentage reduction in permeability decreased with increasing temperature. Micropore space closure and thermal expansion were evidence of the permeability changes as the confining pressure and testing temperature were varied. The experimental results obtained in the seepage tests under the different confining pressures and elevated testing temperatures provide a reference for evaluating rock permeability in underground engineering.

СВОЙСТВА КОМПОЗИЦИОННЫХ МАТЕРИАЛОВ НА ОСНОВЕ СМЕСЕЙ ЭПОКСИДНЫХ ПОЛИМЕРОВ И ОЛИГОСУЛЬФОНОВ. ЧАСТЬ 4. АДГЕЗИОННЫЕ СВОЙСТВА

The influence of oligosulfons with terminal carboxyl and phenolic groups and a molecular weight from 1200 to 44500 on the adhesion properties of epoxy polymers during the shift and separation of adhesive compounds is studied. It is shown that modification leads to the formation of systems characterized by improved adhesion properties, especially at elevated test temperatures. It is established that there is an optimal range of concentrations and molecular weights of oligosulfons (approximately from 2000 to 20000), which provides the maximum effect of modification. It is assumed that the oligosulfon`s particles formed in the epoxy matrix with a small molecular weight have dimensions and volume that are insufficient to be an effective barrier to the propagation of a possible crack in the polymer. At the same time, an oligosulfon with a large molecular weight is able to include a certain part of the epoxy resin in its volume. This leads to a relative decrease in the composition of the share of the epoxy component, which largely determines the adhesion to the material to be bonded. It is shown that the magnitude of the modification effect practically does not depend on the nature of the end groups. The maximum set of properties is realized for oligosulfones with terminal carboxyl groups and a molecular weight in the range from 2500 to 4700, when the concentration of 3 – 10 mass parts on 100 mass parts epoxy oligomer. For oligosulfone with terminal carboxyl groups and a molecular weight of 4700 at a concentration of 10 mass parts manages to increase adhesive strength at a shear of 1.47 and 3.58 times and tensile strength of 1.39 and 5.08 times, respectively, at test temperatures of 293 and 423 K. The research results allow to recommend epoxy-oligosulfone mix to design of structural adhesives, operable in a wide temperature range.

Elevated Temperature Testing of Thermomechanically Treated Steel Bars

AbstractThe details of experimental testing of thermomechanically treated reinforcing bars at elevated temperatures are presented in this paper. Rebars of 10-, 12-, 16-, 20-, and 25-mm diameter wer...

Processing and evaluation of Al/B4C particulate MMC’s: Tensile strength and wear properties under different elevated temperature test condition

In the present investigation, preheated K2TiF6 flux were blended with B4C particle (an average size of 33 µm) at 0.2 ratios and were incorporated into molten Al at 750 °C through conventional stir casting. Microstructural studies of as cast 6xxx alloy and composite were done using SEM/EDS/XRD. A fairly uniform distribution of B4C particles were observed throughout the matrix with few agglomeration at certain places. Ultimate tensile strength and wear behaviour of the prepared composite were tested using computer assisted UTM and Pin-On-Disk apparatus under elevated temperature (100 °C and 200 °C) respectively. The results shows that strength of composite decreases under the influence of temperature at all testing parameters. It is believed that material had undergone severe plastic deformation before the initiation of necking and mild brittle to severe ductile transition has occurred leading to catastrophic failure at high temperature and is evident from the fractography studies. The formation of tribo-coat or layer at the Pin sample and steel disc interface restricted the direct contact with each other. Further, the addition level of test temperature and developed frictional heat encourages Al atoms to diffuse faster at the slip plane resulting in severe wear from the material surface. Small narrow abrasive lines, particle de-bonding, softened tribolayer along with few wear debris adhered to worn surface (due to micro ploughing and oxidation) were observed on the surface of composite at all conditions under 200 °C test temperatures. Presence of “O” and “Fe” peak in the EDS pattern (on worn surface) confirms the existence of oxidation layer and micro ploughing on steel disc at higher test temperature.

Properties and High-Temperature Wear Behavior of Remelted NiCrBSi Coatings

Remelted NiCrBSi coatings were examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction analysis, microhardness and wear testing. After wear tests, the surfaces of the worn samples were examined by 3D profilometry and scanning electron microscopy to investigate the effects of load and temperature on the coefficient of friction and wear resistance. In all the wear experiments, there was a momentary increase in the wear volume and a momentary decrease in the average coefficient of friction values at the elevated test temperatures. This behavior was caused by the stable oxide layer formed on the surface as a consequence of the elevated test temperature. Three dominant wear mechanisms were observed with the NiCrBSi coatings: delamination at room temperature, spalling and adhesion at 250°C, and oxidation at 450°C, whereas in the uncoated samples there was delamination at room temperature, and micro-cracking and oxidation, both at 250°C and 450°C. Remelted NiCrBSi coatings provided better wear resistance and lower coefficient of friction than uncoated STKM-13A steel, especially at higher temperatures.

Effect of wood/basalt hybridization on crystallization and mechanical properties of PLA

In this study hybrid composites based on polylactide were reinforced with wood and basalt fibres. Composites have undergone physical and mechanical tests and the water absorption after 1 and 14 days as well as the effect of biodegradation on strength properties have been determined. Additionally the effects of annealing and temperature of tests on mechanical properties were investigated. The addition of fibres considerably increased the susceptibility of the tested composites and for composites with addition of 7.5 wt% of each wood and basalt fibres increased by more than 35% at +23°C and was by 12 times higher at 80 °C . Heat treatment of composites positively influenced the results, mainly at elevated test temperatures. For pure PLA, the increase in Young’s modulus was over 22 times (from 157 MPa to 3 473 MPa). The addition of fibres resulted in a reduction of the differences between the materials before and after annealing. Impact strength was more than double for composites after heat treatment at room temperature.

Effects of Steel Slag on Durability Properties of Slurry Infiltrated Fibrous Concrete

Inthis research observed the properties of substitute of steel slag on slurry infiltrated fibrous concrete. Six series of test specimens were prepared using hook ended steel fibre with 0,2,3 and 4% volumes fractions along with 0 to 20 % steel slagsubstitute. All procedures on concrete subjected to fresh and hardened properties. For mechanical properties of concrete, compressive, splittingtingtensile and flexural tensile strength.Durability properties performed using the acidic attack test, sulfate attacktest and elevated temperature test. For workability properties to perform flowability, the passing abilitywas appraised using Slump flowand L-Boxtests. A fresh property depict the significant effect of changing steel slagsubstitute. Steel slag substitute along with 4% fibres showed that 25.73% compressive strength,20.34% splitting tensile strength,1.16% flexural strength improvement as compared to control specimen. Durability resultsuch as acid attack, sulfate attack for steel slag blend slurry infiltrated fibre concrete showed improvement over control specimen.

The tribological behavior of niobium nitride and silver composite films at elevated testing temperatures

Niobium nitride and silver composite films with silver content ranging from 9.2 to 19.9 at.% were deposited by using a RF magnetron sputtering system and friction coefficients and wear rates of sputtered thin films were investigated at different temperatures. At the temperature below than 300 °C, the addition of silver into the niobium nitride matrix caused a decrease in friction coefficients with the increase of wear rates. Further increase in temperature changed the wear mechanism to the oxidation wear, and this aided in the reconstruction of the worn area due to the formation of tribo-film AgNbO3. At this period, friction coefficients decreased gradually with the increase of silver at the same testing temperature.

Effect of Curing Agent on the Compressive Behavior at Elevated Test Temperature of Carbon Fiber-Reinforced Epoxy Composites.

The aim of the underlying research is to understand the effect of elevated test temperatures on the mechanical properties of carbon fiber-reinforced laminates based on three different hardeners. A high-temperature stable adhesive was developed for the end tabs of the specimen. Bifunctional bisphenol A diglycidyl ether (DGEBA) epoxy cured with triethylenetetramine (TETA), isophorone diamine (IPDA), and 4,4′-diaminodiphenylsulfone (DDS) were cured and tested in a Celanese compressive test up to 250 °C. A model by Feih was applied, and sufficient accordance (R2 > 97%) with the compressive data was found. We showed that the network density and the chemical structure of the thermoset network influenced the compressive behavior.

Transport Limitations of Sodium-Ions in Type-II Clathrates

The development of material for room temperature sodium ion batteries with high cycling stability is of great significance. Clathrates are potential sodium ion conductors with the properties of cage-like frameworks. It is predicted that the open cages can easily accommodate alkali ions with negligible volume changes. In this paper, we evaluated the type II clathrate performance in sodium ion batteries. Slightly elevated testing temperature (45 oC) can improve the cell capacity and rate performance due to the improved ionic conductivity. Side reactions on the solid electrolyte interface and loss of active materials during the first sodiation process contribute to the low Coulombic efficiency of the first cycle. Electrode morphology and elemental mapping analysis for clathrate electrodes at different states corroborate the above analysis.

Bonded aerospace repairs under tensile loading: Wet chemical surface treatment and selected environmental conditions

ABSTRACTRepair of composite structures and the impact of demanding environmental conditions is a crucial issue for the aircraft industry because of the increasing use of composites in modern aircraft. Consequently, the impact of environmental conditions common for aircraft applications on repair specimens in comparison to nonrepaired specimens is studied. All specimens are produced from a woven carbon fiber‐reinforced epoxy‐based prepreg. For the repair‐specimens, an epoxy‐based film adhesive is used for the soft patch repair approach. During the repair process, the surface of the precured prepreg is prepared by a mechanical method (sanding) and an additional chemical functionalization, respectively. Moisture absorption of the repair specimens is independent of the surface preparation method and higher for the repaired than for the nonrepaired specimens. The key influencing environmental conditions for the tensile strength and the failure mode of the repair specimens are elevated temperature testing as well as hot/wet conditioning and conditioning in deionized water. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47506.

Estimation of strength degradation for engineering plastic (Under elevated temperature and humidity stress test)

A large quantity of engineering plastics are used in electric industrial products. It is necessary to estimate the life of the product made of engineering plastics because of its shorter life and lower strength than some of ceramics or metals. New test device was developed for accelerated stress test. It can make the unsaturated environment above 100 oC under atmospheric pressure using superheated water vapor. Then it becomes possible to set wide range condition of temperature and humidity. Polybutylene terephthalate (PBT) is one of the hydrolyzed engineering plastics. Test pieces of PBT were submitted to accelerated stress test under some conditions of elevated temperature and humidity. Then they were provided to three point bending test. The time required for strength degradation has a good relation with water vapor pressure at each temperature. Then it became clear that the time required for strength degradation on each water vapor pressure was accelerated with temperature using the Arrhenius type equation.

Electrochemical Properties and Challenges of Type II Silicon Clathrate Anode in Sodium Ion Batteries

The development of advanced anodes for low-cost room temperature sodium-ion batteries (SIBs) with high cycling stability is of great significance. Silicon clathrates are promising intercalation anodes due to their cage-like frameworks. It is predicted that the open cages can easily accommodate alkali ions with negligible volume changes. However, the complicated surface structure and chemical reactions make it challenging to understand the electrochemical performance of clathrate anodes in SIBs. In this paper, we evaluated the performance of type II clathrate anodes in SIBs. A slightly elevated testing temperature (45°C) is shown to improve the cell capacity and rate performance due to the improved ionic conductivity. However, side reactions on the solid electrolyte interface (SEI) and loss of active material during the first sodiation process contribute to the low Coulombic efficiency during the first cycle. Analysis is supported by electrode morphology, elemental mapping, and X-ray photoelectron spectroscopy (XPS) on the clathrate electrodes at different electrochemical states. Na+ ion transport behavior between clathrate cages and surface in terms of migration barriers was also computed to explain the positive effect of higher cell testing temperature, and the low Coulombic efficiency of the first cycle.

Crystal structure and high temperature tribological behavior of niobium aluminum nitride films

Niobium aluminum nitride (NbAlN) films with various aluminum content were deposited using a reactive magnetron system and the film with 22.3 at% aluminum exhibiting the highest hardness, lowest wear rate and friction coefficient at room temperature was chosen to investigate the tribological properties at elevated testing temperatures. The results showed that from room temperature to 200 °C, the absence of oxide-based tribo-phases led to the reduction in wear rate, but friction coefficient remained stable. As the testing temperature increased from 200–500 °C, there was reemergence of γ-alumina tribo-phase, this resulted in intensified interaction between the wear track and the counterpart leading to an increase in both the wear rate and friction coefficient. A further increase in testing temperature resulted in a phase transition from a porous γ-alumina to a dense α-alumina. This transition aided in the reconstruction of the worn area in the wear track and the improvement in the friction and wear resistance properties.

Intercomparative tests on viscosity measurements of phase change materials

Phase change materials (PCM) are capable of storing thermal energy within a small temperature range due to their high latent heat. When designing a thermal energy storage (TES) system with PCMs, besides the phase change enthalpy, thermal conductivity and density, viscosity based on temperature must be characterized to take into account natural convection. Taking advantage of the facilities of the different research groups working within an international network, a set of intercomparative tests were executed to determine the viscosity based on the temperature of two PCMs: octadecane and the commercial paraffin RT70 HC. Three laboratories have participated, which have used three different rheology equipments: two controlled stress rheometers, AR-G2 from TA Instruments and MCR 502 from Anton Paar and a translational rheometer, IMETER. The intercomparative tests were executed based on a starting methodology approach defined previously by some of the authors. The highest deviations were observed when temperature-controlled geometries or temperature hoods were not used at elevated test temperatures due to the temperature gradients within the sample, as consequence of the heat losses due to the room temperature. Consequently, special attention must be focused on the temperature control, since a uniform temperature throughout the sample should be guaranteed.

Coupled Hygro-Mechanical Finite Element Method on Determination of the Interlaminar Shear Modulus of Glass Fiber-Reinforced Polymer Laminates in Bridge Decks under Hygrothermal Aging Effects.

To investigate the mechanical degradation of the shear properties of glass fiber-reinforced polymer (GFRP) laminates in bridge decks under hygrothermal aging effects, short-beam shear tests were performed following the ASTM test standard (ASTM D790-10A). Based on the coupled hygro-mechanical finite element (FE) analysis method, an inverse parameter identification approach based on short-beam shear tests was developed and then employed to determine the environment-dependent interlaminar shear modulus of GFRP laminates. Subsequently, the shear strength and modulus of dry (0% Mt/M∞), moisture unsaturated (30% Mt/M∞ and 50% Mt/M∞), and moisture saturated (100% Mt/M∞) specimens at test temperatures of both 20 °C and 40 °C were compared. One cycle of the moisture absorption–desorption process was also investigated to address how the moisture-induced residual damage degrades the shear properties of GFRP laminates. The results revealed that the shear strength and modulus of moisture-saturated GFRP laminates decreased significantly, and the elevated testing temperature (40 °C) aggravated moisture-induced mechanical degradation. Moreover, an unrecoverable loss of shear properties for the GFRP laminates enduring one cycle of the moisture absorption–desorption process was evident.