Influence Of Strong Anisotropy Research Articles

Morphological characteristics of Al3Sc particles and crystallographic orientation relationships of Al3Sc/Al interface in cast Al-Sc alloy

As a new type of grain refiner, rare earth element Sc has a strong grain refining effect on the microstructure of cast aluminum alloys. During the solidification of Sc-containing aluminum alloys, Al3Sc particles are formed in the molten metal and act as heterogeneous nucleation cores of Al in the nucleation process, which significantly increases the nucleation rate and refines the grains. In this paper, a focused ion beam (FIB) microscope was used to extract Al3Sc particles from an Al-Sc alloy, and the internal structure of the particles was systematically observed. At the same time, a scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) were used to study the morphological characteristics of particles and the crystallographic orientation relationships (ORs) at the interface. The study found that under the influence of strong anisotropy, the growth rate of Al3Sc crystal high-index crystal plane and low-index crystal plane is significantly different. In the process of crystal growth, the high-index crystal planes grow faster and disappear quickly, and the shape of the crystal can be ultimately determined by the slower-growing low-index crystal planes. Inside the Al3Sc particles, the (111) and (110) planes form coarse dendritic structures, the (100) planes form a large number of fine cell structures, and there are white oxide residues in the center of some particles. At the interface between Al3Sc and Al matrix, two parallel crystallographic ORs were observed, and the atomic arrangement on both sides of the interface was found to be consistent. At the same time, a special pseudomorphic solid (PS) layer was observed at the interface. On the (111) crystal plane, the atomic arrangement of the PS layer was consistent with Al3Sc at an angle of 60° with Al.

Radiative transfer in porous carbon-fiber materials for thermal protection systems

Highly porous carbon-fiber materials are used in ablative heat shields for atmospheric re-entry. These carbon fiber based materials perform well against heat convection and conduction, and have high radiation absorption. During re-entry, spacecrafts are exposed to shock layer radiation, which provides a considerable share of the heat load faced by their shields. In this work, models for reflectance and heat transfer through FiberForm, a porous carbon-fiber material, are described. The models are based on the multiphase approach and were validated by comparison with experimental data on reflectance and on effective high-temperature thermal conductivity. The morphology of FiberForm was reconstructed from X-ray tomography data and was used as an input for the models. Transmission electron microscopy and diffraction analyses of FiberForm revealed the presence of an amorphous phase and graphite nanocrystalline grains smaller than 10 nm, with no preferential crystallographic orientation. A strong influence of anisotropy in fiber orientation was observed in measured reflectance and has been included in modeling. The porosity and the extinction coefficient were obtained from X-ray tomography images. The radiative transfer modeling indicates that 90% of the incident radiation at wavelengths around 1 μm is absorbed in the 200–300 μm thick outermost surface layer.

Prediction of four, six or eight ears in drawn cups of single-crystal aluminum sheets

The new single crystal criterion developed by Cazacu, Revil and Chandola (2017) was implemented in a finite-element (FE) code and applied to forming of single-crystal cups of aluminum. Drawing simulations were conducted for circular single-crystal blanks of three different orientations: {100}〈001〉, {111} and [112] using the same set of parameters for the single-crystal yield criterion. A strong influence of anisotropy (single-crystal orientation) on the earing profile is found. While for the {100}〈001〉 orientation it is predicted that four ears develop, for the {111} and [112] crystal orientations six and eight ears are predicted, respectively. The FE simulation results are consistent with experimental observations of Tucker (1961).

Elastic Wave Propagation in Laminated Composite Plates

A stiffness method and an analytical method have been used to study the dispersion characteristics of guided waves in laminated composite plates. Both cross-ply and angle-ply plates have been considered in the analysis. The objective of the study is to analyze the effect of fiber orientation, ply layout configuration, and number of layers on the dispersion characteristics. A Rayleigh-Ritz type of approximation of the through-thickness variation of the displacements that maintain continuity of displacements and tractions at the interfaces between the layers has been used in the stiffness method. The analytical method solves the exact dispersion relation of the laminated plate by using the Muller’s method with initial guesses obtained through the stiffness method. Both methods are applicable to plates with arbitrary number of layers having distinct mechanical properties. Numerical results presented show strong influence of anisotropy on the guided waves.