Topic
Stress relaxation
About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.
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TL;DR: In this article, a multi-step heat treatment was used in creep age forming of 7075 aluminum alloy to decrease springback and exfoliation corrosion susceptibility without reduction in tensile properties.
67 citations
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TL;DR: In this article, the thermal expansion behavior of a SiC whisker reinforced pure aluminum composite cooled down from 580°C with lower and higher cooling rates was studied, and it was shown that the coefficient of thermal expansion was closely related to the change rate of TMS and the dislocation density of matrix of the composite.
67 citations
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TL;DR: In this paper, the authors used both a controlled stress and a controlled strain rheometer to characterize lubricating grease in shear, creep, stress relaxation, and oscillatory flow, with a main focus on determining the yield stress.
Abstract: An experimental study using both a controlled stress and a controlled strain rheometer has been undertaken to characterize lubricating grease in shear, creep, stress relaxation, and oscillatory flow, with a main focus on determining the yield stress. The yield stress was examined using a cone–plate and parallel-plate system with smooth and rough surfaces. Clear discrepancies were observed in the yield stress values obtained using different techniques where oscillatory strain sweep measurements seem to be the best choice. This technique is less sensitive to wall slip, shows good reproducibility, and is relatively easy to perform. The method also shows that the yield stress is a function of the imposed frequency and therefore of the time domain. At lower values of shear—that is, in the linear viscoelastic regime—there is no structural breakdown and the rheology of the grease can be described by the Maxwell model where the stress and the strain are almost proportional to each other. Based on this observation, a novel method to determine the yield stress is proposed: “The yield stress can be determined from the point where this linearity no longer applies.” This method is compared to those that are commonly used. The yield stress was found to depend exponentially on temperature and linearly on frequency.
67 citations
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TL;DR: In this paper, a melt-stretched isotactic polypropylene (iPP) filled with different weight fractions of β-nucleating agent was extruded via a single screw extruder with a slit die and immediately melted-stretched at the die exit.
67 citations
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15 Jan 1993-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, two high temperature chambers for X-ray diffraction were designed, allowing us to determine the stresses in both the oxide and the substrate with the sin2 ϕ technique, at high temperatures or room temperature and during heating-cooling sequences.
Abstract: In order to characterize the respective importance of the growth stresses, thermal stresses and stress relaxation developed in oxide scales, two high temperature chambers for X-ray diffraction were designed, allowing us to determine the stresses in both the oxide and the substrate with the sin2 ϕ technique, at high temperatures or room temperature and during heating-cooling sequences. It was applied to NiNiO. At room temperature after oxidation, NiO is subjected to compressive stresses whose level depends on the substrate thickness and on the oxidation time and temperature. In the substrate, compressive stresses are mainly due to internal oxidation. During oxidation at 900 °C, the oxide scale is subjected to slight tensile stresses which can be due partially to anionic diffusion, internal oxidation or the heating process. During heating-cooling sequences, the stresses in the scale decrease with increasing temperature and become negligible when the oxidation temperature is reached. The reversibility of the stress-temperature curve indicates that no stress relaxation occurs. The stresses found at room temperature are due only to thermal stresses and fit well the theoretical calculation of thermal stresses in NiO scale based on the newly determined thermal expansion coefficients of Ni and NiO. All these results show that the stresses found at room temperature are mainly generated during cooling and that the effect of the Pilling-Bedworth ratio or of factors playing a role during isothermal growth is negligible.
67 citations