On the strengthening and slip activity of Mg-3Al-1Zn alloy with pre-induced{1012¯}twins

{1012¯}twins were introduced into the magnesium(Mg)plate AZ31 via pre-rolling along its transverse direction.The plates,both with and without the pre-induced{1012¯}twins,were subjected to uniaxial tension along different directions.Using crystal plasticity modeling,we found that the strengthening effect of the pre-induced{1012¯}twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries,rather than the orientation hardening due to the twinning reorientation(although the latter did make its contribution in some specific loading directions).Besides,the pre-existing{1012¯}twins were found,by both experiments and simulation,to promote the activity of prismatic and pyramidal<c+a>in the parent matrix of the material.Further analysis showed that the enhanced non-basal slip activity is related to the{1012¯}twin boundaries’low micro Hall-Petch slope ratios of non-basal slips to basal slip.With the critical resolved shear stress(CRSS)obtained from crystal plasticity modeling and the orientation data from EBSD,a probability-based slip transfer model was proposed.The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at{1012¯}twin boundaries than that at grain boundaries,which agrees with the experimental observation that the strain localization was primarily associated with the latter.The present findings are helpful scientifically,in deepening our understanding of how the pre-induced{1012¯}twins affect the strength and slip activity of Mg alloys,and technologically,in guiding the design of the pre-strain protocol of Mg alloys.

CUR Based Initialization Strategy for Non-Negative Matrix Factorization in Application to Hyperspectral Unmixing

Hyperspectral unmixing is a powerful tool for the remote sensing image mining. Nonnegative matrix factorization (NMF) has been adopted to deal with this issue, while the precision of unmixing is closely related with the local minimizers of NMF. We present two novel initialization strategies that is based on CUR decomposition, which is physically meaningful. In the experimental test, NMF with the new initialization method is used to unmix the urban scene which was captured by airborne visible/infrared imaging spectrometer (AVIRIS) in 1997, numerical results show that the initialization methods work well.

Facile measurement of single-crystal elastic constants from polycrystalline samples

Elastic constants are among the most fundamental properties of materials.Simulations of microstructural evolution and constitutive/micro-mechanistic modeling of materials properties require elastic constants that are predominately measured from single crystals that are labor intensive to grow.A facile technique is developed to measure elastic constants from polycrystalline samples.The technique is based upon measurements of the surface acoustic wave velocities with the help of a polydimethylsiloxane film grating that is placed on a polished surface of a polycrystalline sample to confine surface acoustic waves that are induced by a femtosecond laser and measured using pump-probe time-domain thermoreflectance.Electron backscatter diffraction is employed to measure the crystallographic orientation along which the surface acoustic wave propagates in each grain(perpendicular to the polydimethylsiloxane grating).Such measurements are performed on several grains.A robust mathematical solution was developed to compute the surface acoustic wave velocity along any crystallographic orientation of any crystal structure with given elastic constants and density.By inputting various starting values of elastic constants to compute the surface acoustic wave velocities to match experimental measurements in several distinct crystallographic orientations using an optimization algorithm,accurate elastic constant values have been obtained from seven polycrystalline metal samples to be within 6.8% of single-crystal measurements.This new technique can help change the current scenario that experimentally measured elastic constants are available for only about 1% of the estimated 160,000 distinct solid compounds,not to mention the significant need for elastic constants of various solid solution compositions that are the base of structural materials.