Joining Properties of SPFC440/AA5052 Multi-Material Self-Piercing Riveting Joints.

With the development of new energy vehicles, the joining of lightweight alloys has received more attention. Self-piercing riveting experiments of aluminum alloy and high-strength steel sheets were performed to analyze the effects of rivet height and laying order of metal sheets on the joining quality in the work. The forming surface, cross-sectional morphology, static tensile property, fatigue property, failure mode, and mechanism were analyzed. The results show that AA5052 alloy and SPFC440 steel can be joined effectively by self-piercing riveting, and there is good contact between rivet head and sheet surfaces. When the rivet is 2.5-3.5 mm higher than the total thickness of two layers sheets, the rivet leg flares symmetrically without cracks or buckling, and the lower sheet completely encapsulates the joint button. The joints have better static tensile properties when the rivet is about 3 mm higher than the thickness of two sheets. The higher static strength is obtained when the aluminum alloy is placed at the lower position. The rivet legs fall off from the lower sheets for all the samples in the tensile tests, which is independent of the rivet height and laying order of metal sheets. The fatigue strength of the sample with the rivet height of 7 mm is the greatest, and the fatigue cracks always occur on the aluminum sheet under all experimental conditions. The findings in this work can help the practical application of self-piercing riveting for aluminum/steel sheets.

Microstructural Variation and a Physical Mechanism Model for a Ti-55511 Alloy during Double-Stage Hot Deformation with Stepped Strain Rates in the ß Region.

The microstructural variation and high-temperature flow features of a Ti-55511 alloy in the ß region are studied by utilizing double-stage compression with a stepped strain rate. The results demonstrate that the stresses in the latter stage of hot compression markedly reduce as the strain at the previous stage or the strain rate at the previous/latter stage drops. Moreover, the annihilation/interaction of substructures is promoted, and the distinct refinement of the dynamic recrystallization (DRX) in the ß grain can be found. However, the coarsening of the ß grain and the consumption of dislocation substructures are accelerated at high temperatures. Furthermore, the principal DRX nucleation mechanism of the Ti-55511 alloy during double-stage compression with a stepped strain rate in the ß region is discontinuous DRX. Additionally, by using the microstructural variation characteristics related to the forming parameters, a physical mechanism equation is modeled to forecast the forming features, the DRX fraction, and the size of the ß grain in the investigated alloy. The forecasted results are in accordance with the tested results, indicating that the established model can accurately forecast the microstructure variation and flow features of the studied alloy.

Nanoprobes for two-photon excitation time-resolved imaging of living animals: In situ analysis of tumor-targeting dynamics of nanocarriers.

Great challenges remain in the noninvasive luminescence imaging analysis of tumor-targeting dynamics of nanocarriers in living animals which is of significance for the development of anti-cancer nanomedicine. In this work, luminescent nanoparticles Eu(tta)3bpt@SMA (dav = 15 nm), which exhibited good water dispersion stability and high yields of red Eu-luminescence under near-infrared two-photon excitation, were prepared by a modified microfluidic mixing method in the absence of surfactants. Tumor-targeting agents, Arg-Gly-Asp-D-Phe-Lys (cRGD) polypeptide or transferrin (Tf), were then anchored on the nanoparticle surfaces to form the desired nanocarriers Eu@SMA-RGD or Eu@SMA-Tf. The tumor-targeting processes of the prepared nanocarriers in intact living mice were analyzed on a home-built two-photon excitation time-resolved (TPE-TR) imaging apparatus having a wide view filed. The TPE-TR strategy could effectively suppress the interference from biological autofluorescence, which allowed the targeted domains to be visualized with a high signal-to-noise ratio. It was found that the tumor-tissue trapping efficacy of Eu@SMA-RGD was much higher than that of Eu@SMA-Tf, and the desorption process from the tumor tissues of Eu@SMA-RGD was slower than that of Eu@SMA-Tf. The methods developed in this work pave a way to investigate the in vivo tumor-targeting dynamics of nanocarriers by noninvasive luminescence imaging of living animals.

Proposal of a wavelength filter with a cut corner based on Equilateral-Triangle-Resonator.

We propose an equilateral triangle resonator filter with an output waveguide and analyzed by the finite-difference time-domain technique. The filter can realize directional output with a high Q mode by means of the mode-field coupled into the output waveguide, which results a reduction in the scattering loss at the vertices. In addition, to the deformed equilateral triangle resonator filter, an optimum parameter with a cut corner of 0.23 µm, which is equal to that of the input waveguide and can be an optimal cut, is found to help increase in finesse, Q factors, extinction ratio and the output intensity on resonance of the drop port normalized with the through port .