Quasi In-Situ EBSD Analysis of Twinning-Detwinning and Slip Behaviors in Textured AZ31 Magnesium Alloy Subjected to Compressive-Tensile Loading

Twinning and detwinning behavior, together with slip behavior, are studied in a textured AZ31 magnesium alloy under compressive and tensile strains along the rolling direction (RD) after each interrupted mechanical test via quasi in-situ electron backscattered diffraction technique. The results show that twinning firstly takes place under the compressive strain along the RD. With the increasing compressive strain, {1012} tensile twins firstly nucleate, then propagate, and finally thicken. While under a reversed tensile strain along the RD, detwinning occurs. No nucleation happens during detwinning. Thus, tensile twins can detwin at lower tensile strain, followed by thinning, shortening, and vanishing. Slips are also activated to accommodate the plastic deformation. In the matrix, prismatic slip can only dominate at relatively high strains. Otherwise, basal slip dominates. While in the twins, prismatic slip can activate at lower strains, which is ascribed to the texture reorientation

Resolving the mystery of electron perpendicular temperature spike in the plasma sheath

A large family of plasmas has collisional mean-free-path much longer than the non-neutral sheath width, which scales with the plasma Debye length. The plasmas, particularly the electrons, assume strong temperature anisotropy in the sheath. The temperature in the sheath flow direction ($T_{e\parallel}$) is lower and drops towards the wall as a result of the decompressional cooling by the accelerating sheath flow. The electron temperature in the transverse direction of the flow field ($T_{e\perp}$) not only is higher but also spikes up in the sheath. This abnormal behavior of $T_{e\perp}$ spike is found to be the result of a negative gradient of the parallel heat flux of transverse degrees of freedom ($q_{es}$) in the sheath. The non-zero heat flux $q_{es}$ is induced by pitch-angle scattering of electrons via either their interaction with self-excited electromagnetic waves in a nearly collisionless plasma or Coulomb collision in a collisional plasma, or both in the intermediate regime of plasma collisionality

SGC Tests for Influence of Material Composition on Compaction Characteristic of Asphalt Mixtures

Compaction characteristic of the surface layer asphalt mixture (13-type gradation mixture) was studied using Superpave gyratory compactor (SGC) simulative compaction tests. Based on analysis of densification curve of gyratory compaction, influence rules of the contents of mineral aggregates of all sizes and asphalt on compaction characteristic of asphalt mixtures were obtained. SGC Tests show that, for the mixture with a bigger content of asphalt, its density increases faster, that there is an optimal amount of fine aggregates for optimal compaction and that an appropriate amount of mineral powder will improve workability of mixtures, but overmuch mineral powder will make mixtures dry and hard. Conclusions based on SGC tests can provide basis for how to adjust material composition for improving compaction performance of asphalt mixtures, and for the designed asphalt mixture, its compaction performance can be predicted through these conclusions, which also contributes to the choice of compaction schemes

Deformation and failure analysis of pinch-torsion based thermal runaway risk evaluation method of Li-ion cells

A new pinch-torsion test is developed for safety of Li-ion batteries that shows the stable capability of making small internal short-circuit spots effectively. The further deformation and failure analysis is conducted by finite element analysis and experiments. Two different loading conditions, pure pinch and pinch-torsion, are evaluated and compared which demonstrates that the addition of the torsion component significantly increased the maximum principal strain, and thus the internal short circuit induction. In addition, the vertical load in the pinch-torsion test is significantly less than it in the pinch test to generate the failure inside the battery, thus dramatically improving the applicability of the pinch test. Finally, an analytical stick-slip model rationalizes deformation mechanisms and the conclusion is made that the additional torsion only facilitates the failure of separator at the early stage which is typically a few degrees of rotation. The systematic investigation of the Li-ion cell deformation and failure provides insight for the optimization of the future battery safety experiment design