A novel method to study recrystallization behavior: Continuous heating stress relaxation

The measurement of dynamic stress relaxation can reveal otherwise hidden weaknesses in rubber materials. The stress relaxation of the minimum of the restoring foce has the undesirable characteristic of being greater than the continuous stress relaxation. An increase in the amplitude of the deformation increases the decay in the minimum values of the varying retractive stress, and an increase in the prestrain makes it smaller. The normalized curve for continuous stress relaxation is found to lie somewhere between the normalized curves for the maximum and minimum of the retractive stress. The measurement of network density on specimens aged under continuous and dynamic stress relaxation indicate that the mechanism behind the degradation of the rubber network is the same in both cases. The relations between intermittent, continuous, and dynamic stress relaxation give a reasonable estimate of the dynamic stress relaxation from the other two when proper values of the coefficients are used. This relation says that results both of continuous and intermittent stress relaxation are important for predicting the life time of a dynamic seal. The relations offers an explanation of the differences between maximum and minimum values obtained during the measurement of dynamic stress relaxation and their relation to continuous stress relaxation. From these relations it can be concluded that a rubber intended for dynamic seals should contain neither reversion nor secondary crosslinking. Crosslink density should be high in order to overpower effects on crosslinking of factors in the surroundings.

A Quantitative In Situ SEM Bending Method for Stress Relaxation of Microscale Materials at Room Temperature

Continuous and intermittent stress relaxation studies on foamed polysiloxane rubber

The effect of antioxidant on the crosslinking reaction occurring during the oxidation of sulphur vulcanizates of natural rubber was investigated by using both continuous and intermittent stress relaxation measurements. Similarly, by means of continuous stress relaxation and equilibrium swelling measurements the cross-linking reaction in vacuum was followed. The presence of antioxidant or removal of air reduced considerably both continuous and intermittent relaxation and also the difference between them, which measures the crosslinking. The crosslink formation must therefore form part of the sequence of oxidative reactions.

Continuous and intermittent stress relaxation experiments were carried out on dicumyl peroxide cured cis-polybutadiene in high vacuum and in air at several temperatures. An extension of the “two-network theory” is proposed whereby the effectiveness of a cross-link at various extension ratios is experimentally defined. The effectiveness varies from unity at an extension ratio of unity to zero at very high extension ratios.

In electronic equipment, the estimated lifetime of a solder joint is being intensively investigated. For the assessment of thermal fatigue reliability, the mechanical properties of solder joints with regard to inelastic characteristics at a range of temperatures must be known. However, measuring solder's material properties is costly and time-consuming. Thus, a quick and simple technique should be established immediately. In this paper, a tensile test with a stress relaxation method is proposed in order to obtain parameters such as the creep constant and index, and also the viscoplastic parameters defined by L. Anand et al. We discuss acquiring solder parameters by the conventional method (tensile testing), and an effective method using stress relaxation, which reduces the number of necessary tests. Then, we compare our experimental results and FEM analysis results, and the effectiveness of the proposed technique is confirmed. We use a thermoelectric module as an example.

Stress relaxation in compression in air has been studied for compounds of various polymers. However, rubber seals, gaskets, and other applications are widely used where swelling agents, such as oil, are encountered. It was thought desirable to measure the stress-relaxation properties of various rubbers to determine their performance under such conditions. The results show that continuous stress relaxation is inhibited by the presence of oil and that unconfined swelling measurements predict the degree of inhibition directly. The variables of temperature and type of oil were investigated.

The method of stress relaxation has been used to study the effect of temperature on the stress decay behavior in the systems of polyethylene–xylene and polyethylene–toluene. The behavior of stress decay in the polyethylene under xylene or toluene at various temperatures was observed and the activation energies of polyethylene–xylene and polyethylene–toluene were obtained.

Viscous plastic flow in contact layers as a method of stress relaxation in dry sliding of steel against steel under electric current

Measurements of the continuous stress relaxation of thiuram vulcanizates and intermittent stress relaxation of both sulfur and C—C crosslinked vulcanizates of natural rubber were discussed. These measurements were made in the presence of either oxygen or nitrogen at various temperatures both with and without sample pretreatment. The following conclusions were drawn: 1. Determination of the rate of continuous tension loss is not suitable for measuring the oxidative degradation of vulcanizates from 1,5 polyenes according to a stress relaxation method. The reason for this is that rheological processes superimpose themselves on the chemical reactions initiated by oxygen, cause a reduction in tension, and affect both the form of the relaxation curve and also the rate of tension loss. This is particularly noticeable in the case of vulcanizates containing polysulfide bonds. 2. It was possible, using intermittent stress relaxation and by choosing suitable temperatures and frequencies, to eliminate the influence of rheological processes and thus to measure only the rate of tension loss due to oxidative degradation.

Myosin is the most important component of myofibrillar protein, with excellent gelling properties. To date, heating treatment remains the mainstream method for forming gel in meat products, and it has the most extensive application in the field of meat industry. However, at present, there are few reports on the effects of heating rates on myosin self-assembly and aggregation behavior during heating treatment. The present study aimed to investigate the effects of different heating rates (1, 2, 3 and 5 °C min-1 ) on the self-assembly behavior, physicochemical, structural and gelling properties of myosin. At the lowest heating rate of 1 °C min-1 , the myosin gel had a dense microstructure, the highest elastic modulus (G') and water holding capacity compared to higher heating rates (2, 3 and 5 °C min-1 ). At higher temperatures (40, 45 °C), the surface hydrophobicity, turbidity, particle size distribution and self-assembly behavior of myosin in pre-gelling solutions showed that myosin had sufficient time to denature, underwent full structure unfolding before aggregation at the heating rate of 1°C min-1 , and formed regular and homogeneous spherical aggregates. Therefore, the myosin gel also had a better three-dimensional network. The heating rates had an important effect on the quality of myosin gels, and had theoretical implications for improving the quality of meat gel products. © 2023 Society of Chemical Industry.

The recrystallization kinetics of austenite in the low-carbon steel 09KhN2MD under isothermal conditions was studied using the stress relaxation method. Before the study, the steel with initial grains of different sizes was deformed by compression on a Gleeble 3800 plastometry system. The incubation periods and the completion time of recrystallization were found.

The reaction of a Chinese bituminous coal PDS with Fe2O3 was investigated by such experimental means as thermogravimetric (TGA) coupled with Fourier transform infrared spectroscopy (FTIR) and TGA-difference thermal analysis (DTA) with focus on the effect of the heating rate. It was found that the reaction of PDS with Fe2O3 displayed three-staged reaction characteristics, and a higher heating rate facilitated more gaseous products from PDS pyrolysis to react with Fe2O3 and was more beneficial to the reaction of PDS with Fe2O3; and simultaneously, a higher heating rate made the overall activation energy for the reaction of PDS with Fe2O3 decreased from 62.79 kJ/mol at 20k/min to 56.50 kJ/mol at 35k/min, and finally, the heat needed for the reaction of PDS with Fe2O3 was less than that of PDS pyrolysis due to the exothermic reaction of Fe2O3 with H2 from PDS pyrolysis, and a higher heating rate made less heat needed for the reaction of PDS with Fe2O3. Keywords-Coal; CO2 capture; Chemical looping combustion; Fe2O3; Effect of the heating rate

These studies were made to investigate the effects of Si on the recrystallization of Al-Mn alloy.(1) Si had remarkable effects on the recrystallization temperature of Al-Mn alloy. When its sheet ingot was not preheated, Si raised the recrystallization temperature. Whereas, when it was preheated. Si lowered the temperature.(2) Heating rate also had effects on the recrystallization temperature of non-preheated Al-Mn alloy containing Si. The elevation of temperature was remarkable in slow heating, and it was maximum at the heating at 160°C.(3) Si decreased the effects of heating rate on the grain size of recrystallized Al-Mn alloy when the sheet ingot was not preheated. It gave a fine grain size even at slow heating rate. Whereas, Si increased the effects of heating rate on the grain size of the preheated alloy and a large grain size was produced by slow heating.These phenomena resulted in that Si prevented the effects of preheating on the refining of the recrystallized grains of Al-Mn alloy; and the grains obtained at the normal heating rate, which was slower than that in a salt bath, were coarser than those obtained after no preheating.

This work focuses on the effect of heating rate, i.e. conventional heating (CH) and ultrafast heating (UFH) rates on the elemental distribution between phases in a low carbon steel. Microstructural characterization was carried out using an Electron Backscatter Diffraction (EBSD) and Atom Probe Tomography (APT) technique. Nanohardness of individual microconstituents was measured. It is shown that the applied heat treatments result in the formation of multiphase microstructures consisting of a ferritic matrix with embedded martensite and retained austenite. The ferritic matrix of the CH material was fully recrystallized, whereas both recrystallized (coarser) and non-recrystallized (finer) ferritic grains were present in the matrix of the UFH material. APT analysis indirectly confirmed that recrystallized grains after both heat treatments have a lower carbon content, when the non-recrystallized grains after UFH have a higher carbon content. It correlates with the nanohardness results, i.e. non-recrystallized grains show higher hardness, while recrystallized grains have a lower hardness. The segregations of C and Mn atoms at the martensite/ferrite interface were observed after both treatments. It is hypothesized that the segregations are formed under negligible partitioning local equilibrium condition during CH, whereas the solute drag effect results in the formation of interface segregation during UFH.