Effect Of Relative Orientation Research Articles

Evolution of microstructure and mechanical properties of AZ31 Mg alloy sheets processed by accumulated extrusion bonding with different relative orientation

In this study, rolled AZ31 Mg alloy sheets were subjected to accumulated extrusion bonding (AEB) process at 473 K with transvers direction (TD) parallel (0°), at 45° inclined and perpendicular (90°) to the sizing band. Deformation and dynamic recrystallization (DRX) mechanisms of AZ31 Mg alloy sheets were investigated from start to end of AEB process. Mechanical properties of as-received and AEBed sheets were then evaluated by tensile tests based on the concurrent microstructure and texture evolution. The results indicated that {10–12} tensile twinning dominated the early stage deformation, and subsequently DRX occurred and dominated the further deformation. The effects of relative orientation on microstructure and texture evolution mainly occurred in the cone die and sizing band. 0° and 90° samples exhibited an ED-tilt double peak texture, and 45° sample showed a more disperse texture components in TD. After the extruded sheets exited from extrusion die, grain growth was observed with the orientations preserved from sizing band, and the interfaces of various samples were bonded successfully with different angles to TD. Mechanical properties tests indicated that three AEBed samples exhibited similar strength and ductility with higher yield strength (145 MPa vs. 169 MPa), ultimate tensile strength (336 MPa vs. 392 MPa), and fracture elongation (24.9% vs. 28.8%) comparing to that of as-received sample along RD.

Cracks Interaction due to Sequential Indentation in Curved Brittle Coating: Effect of Relative Orientation

This study investigates the influences of pre-existing cracks to simulate defects in structures using curved bi-layer system consisting of glass coating on a polymeric support layer, to illustrate the role of defects on the evolution of failure of hard coating bi-layer system under loading. The densities of pre-existing cracks were initiated near the margins and the relative orientations were varied. The pre-existing cracks were induced by using hard spherical indenter. The failure of these samples was investigated under single-cycle axial loading tests using soft indenter of low elastic modulus. The onset of fracture was observed in situ using a video camera. Margin cracks were observed to propagate from pre-existing cracks near the margins, while the pre-existing cracks in the compression zone under the soft indenter were arrested. Experimental trends suggested that critical loads were increased with specimens having no defects (pre-existing cracks). Finite element modeling was used to evaluate the stress distribution in the brittle coating and compared with the experimental trend. It is concluded that radial cracks can initiate and propagate anywhere in the tensile region. The larger the flaws the smaller the loads required for defects pre-existing cracks to propagate radials to failure.

Oscillator strength spectrum of hydrogen in strong magnetic and electric fields with arbitrary mutual orientation

We present oscillator strength spectra of the hydrogen Balmer $\ensuremath{\alpha}$ series in crossed strong magnetic and electric fields. Field strength regimes of interest ($\ensuremath{\gamma}\ensuremath{\le}0.02\phantom{\rule{0.3em}{0ex}}\mathrm{a}.\mathrm{u}.$ and $F\ensuremath{\le}1\ifmmode\times\else\texttimes\fi{}{10}^{8}\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{m}$) are the characteristic strengths observed on the surface of white dwarf stars. Based on the pseudospectral discretization technique, two independent methods have been developed to achieve reliable oscillator strengths in crossed fields. The effect of relative orientation between the magnetic and electric fields is clarified. Compared to the parallel configuration, we have observed that for the field strength regimes of interest, the perpendicular component of electric fields only results in a weaker coupling between the states belonging to the different subspaces of magnetic quantum numbers. This observation explains why the spectrum of oscillator strengths in crossed electric and magnetic fields with arbitrary mutual orientation shows similar behavior compared to that in parallel fields. However, a careful analysis shows that the two stronger transition lines at $5546$ and $5620\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ previously attributed to the Balmer $\ensuremath{\alpha}$ series are now identified to belong to the Balmer $\ensuremath{\beta}$ series. An effective scheme has also been suggested to calculate the bound-free opacities of hydrogen atoms in crossed fields.

Oriented dynamics in van der Waals complexes

The effects of relative orientation on collision and reaction dynamics can be examined by characterizing the unimolecular decay of van der Waals complexes. Most commonly, decomposition is initiated by exciting one of the monomers within a complex, and the relative orientation is defined by the zero-point motions for the intermolecular degrees of freedom. However, if simultaneous excitation of the intermolecular degrees of freedom is achieved, a considerable range of starting configurations may be accessed. We are currently studying I 2–Rg and CN–H 2/D 2 complexes with the goal of using these systems to examine oriented dynamics. For I 2( B)–Ne we have observed excited intermolecular vibrations and the effects of these motions on the predissociation dynamics. The correlation between structure and dynamics suggested by these results can be understood using classical mechanics, but the implications of this model are at variance with accepted ideas about the topology of I 2( B)–Rg potential surfaces. Spectroscopic and theoretical studies of CN–H 2/D 2 indicate that this pre-reactive complex may be used to examine steric effects in the H 2+CN→H+HCN reaction. The complex was characterized using the A– X and B– X electronic transitions. As is often the case for weakly bound systems, the insights provided by high-level theoretical calculations were essential for interpretation of the spectra. The properties of excited intermolecular vibrations of CN–H 2 were predicted as a prelude to studies of the intra-cluster reaction dynamics.

A study of latent hardening behavior in aluminium single crystals

In order to obtain a better understanding or a complete description of plastic properties of polycrystals, especially in polycrystal modelling viewpoint, investigations on latent hardening behavior of single crystals have been performed in a great number. Recently, however, Wu et al. have pointed out that the definition of the yield stress of latent system using the conventional back extrapolation is ambiguous in terms of determining the latent hardening moduli because the initial rapid work-hardening of the transient zone is neglected. They proposed a more precise measure of the yield stress of latent system based on the decrease of the tangent modulus from the linear elastic modulus, and showed that the latent hardening, which would not plus the initial work-hardening of the transient zone, is actually lower than that obtained from the backward extrapolation. Thus, in their opinion, it is considered that the hardening behavior of latent system (such as the directionality, the effects of relative orientation and prestrain) need be newly or further studied in detail. Single crystals of aluminum have been grown with high purity to investigate this behavior.

Homologous recombination in bovine papillomavirus shuttlevecter; Effect of relative orientation of substrate sequences

Relative orientation of recombination substrates, neo gene, strongly influenced homologous recombination events in a bovine papillomavirus shuttle vector. Between direct repeats, recombination occurred at a high frequency while between inverted repeats, it was rare. Double strand break near the mutation site increased the recombination frequency between inverted repeats but not between direct repeats. Formation of long heteroduplex as a recombination intermediate may explain this apparently paradoxical phenomenon.