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  • 1
    Publication Date: 2018-05-17
    Description: The creep experiments of a solid propellant samples under five different stresses are carried out at 293.15 K and 323.15 K. In order to express the creep properties of this solid propellant, the viscoelastic model i.e. three Parameters solid, three Parameters fluid, four Parameters solid, four Parameters fluid and exponential model are involved. On the basis of the principle of least squares fitting, and different stress of all the parameters for the models, the nonlinear fitting procedure can be used to analyze the creep properties. The study shows that the four Parameters solid model can best express the behavior of creep properties of the propellant samples. However, the three Parameters solid and exponential model cannot very well reflect the initial value of the creep process, while the modified four Parameters models are found to agree well with the acceleration characteristics of the creep process.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
    Publication Date: 2015-08-08
    Description: Protrusions and retrusions typically form on recrystallizing boundaries and thus the boundaries often appear rough. Characterization of the boundary roughness is necessary in order to evaluate the effects of protrusions and retrusions on boundary migration. In the current work, a variable termed area integral invariant is employed to provide quantitative information of individual protrusions/retrusions on boundaries surrounding two selected recrystallizing grains in partly recrystallized copper as well as of the overall roughness of the boundaries.
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  • 3
    Publication Date: 2015-08-08
    Description: The microstructure and softening behaviour have been investigated in an aluminum plate heavily deformed by equal channel angular extrusion and subsequently annealed at 170 ?C. It is found that at this temperature the microstructure evolves by coarsening with no apparent signs of recrystallization even after 2 h of annealing. Both coarsening and softening are rapid within first 10 minutes of annealing followed by a slower evolution with increasing annealing duration. Evidence of triple junction (TJ) motion during coarsening is obtained by inspecting the microstructure in one region using the electron backscatter diffraction technique both before and after annealing for 10 minutes. The fraction of fast-migrating TJs is found to strongly depend of the type of boundaries composing a junction. The greatest fraction of fast- migrating TJs is in the group, where all boundaries forming a junction are high angle boundaries. The fraction of fast-migrating TJs is significantly lower for jun...
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  • 4
    Publication Date: 2015-08-08
    Description: Quantitative analysis of boundary migration during recrystallization is a key task to understand the recrystallization process and to improve recrystallization models. In the last 25-30 years, quantification of boundary migration has mostly been conducted in term of average growth rates in many materials. This type of analysis has largely been based on the assumption that all or groups of recrystallizing grains grow in the same uniform manner, therefore the results represent average growth behaviors on a macro scale. Recently, significant efforts have been made to quantify the boundary migration during recrystallization on local grain scales, using different advanced experimental characterization and computer simulation techniques. This paper aims at summarizing these recent achievements with focus on the potentials of the various advanced experimental characterization techniques. Suggestions for new experimental and simulation work important for advancing the curre...
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  • 5
    Publication Date: 2015-08-08
    Description: We present simulation results based on a phase-field model that describes the migration of recrystallization boundaries into spatially varying deformation energy fields. Energy fields with 2-dimensional variations representing 2 sets of dislocation boundaries lying at equal, but opposite, angles to the moving boundary are considered. The simulations show that the shape and overall migration rate of the recrystallization front is considerably affected by spatial variations in the deformation microstructure. It is seen that, depending on characteristics of the variations in the deformation microstructure, highly asymmetrical protrusions and retrusions can develop on the migrating recrystallization front resulting in a migration velocity considerably larger than that expected from standard recrystallization models. It is also seen that, when the wavelength of the variations in a deformation microstructure along the grain boundary is larger than the wavelength of the variations in th...
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  • 6
    Publication Date: 2015-08-08
    Description: The microstructure of the oxide dispersion strengthened ferritic steel PM2000 has been investigated after compression by dynamic plastic deformation to a strain of 2.1 and after subsequent annealing at 715 ?C. Nanoscale lamellae, exhibiting a strong ?100? + ?111? duplex fibre texture, form during dynamic plastic deformation. Different boundary spacings and different stored energy densities for regions belonging to either of the two fibre texture components result in a quite heterogeneous deformation microstructure. Upon annealing, preferential recovery and preferential nucleation of recrystallization are found in the ?111?- oriented lamellae, which had a higher stored energy density in the as-deformed condition. In the course of recrystallization, the initial duplex fibre texture is replaced by a strong ?111? fibre recrystallization texture.
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  • 7
    Publication Date: 2015-04-26
    Description: The protrusions and retrusions observed on the recrystallizing boundaries affect the migration kinetics during recrystallization. Characterization of the boundary roughness is necessary in order to evaluate their effects. This roughness has a structure that can be characterized by fractal analysis, and in this study the so-called ?Minkowski sausage? method is adopted. Hereby, two cube-oriented grains in partly recrystallized microstructures are analyzed and quantitative information regarding the dimensions of protrusions/retrusions is obtained.
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  • 8
    Publication Date: 2015-08-08
    Description: The 36th Ris? Symposium focuses on the effects of deformation-induced structural variations on annealing mechanisms. Although it is widely recognized that the processes occurring during annealing of deformed metals are determined by the local environment in which they occur, much of the current understanding, analysis and modelling is based on larger scale considerations. Recent detailed investigations of deformation microstructures have led to a paradigm shift in the way these structures are characterized and analyzed. It is now clear that deformation microstructures are hierarchical, with dislocations and deformation-induced boundaries subdividing the original grains. This subdivision means that there are variations in the crystallographic orientations and in the distribution of stored energy on the scale of the subdivision, which typically is on the micrometer, sub-micrometer or nanometer scale. Structural variations in this subdivision may also be present from grai...
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  • 9
    Publication Date: 2015-08-08
    Description: Recrystallization in copper deformed by dynamic plastic deformation was investigated using electron backscatter diffraction. The recrystallized grains show a broad size distribution. The kinetics of grains of different sizes is observed to be different: In the beginning of recrystallization, the area fraction of small recrystallized grains increases rapidly. At later stages of recrystallization, the area fraction of small recrystallized grains is stable, while the area fractions of medium and large recrystallized grains increase. Correlation between the broad grain size distribution (and its evolution) and the heterogeneous deformed microstructure is discussed.
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  • 10
    Publication Date: 2015-08-08
    Description: Nucleation of recrystallization near hardness indentations has been investigated in slightly cold rolled high purity aluminium. Samples were cold rolled to 12% and 20% reductions in thickness and indentations were done with two different loads (500 g and 2000 g). The samples were annealed at 300 ?C for 1 h and nuclei were identified. It is found that the indentations are preferential nucleation sites. With EBSD maps around indentation tips, the orientation relationship between nuclei and matrix is analyzed. Finally, effects of rolling reduction and indentation load on local misorientations and stored energy distributions and thus on nucleation are discussed.
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