We report luminous polylactic acid (PLA) composite prepared via a solvent casting method using different amounts of phosphor strontium aluminate (SrAl2O4: Eu2+ and Dy3+) (SAO). The reason for doing this is that the changes of fluorescence and mechanical properties in the composites with different SAO contents can be directly evaluated. The SAO particles should have a variety of excellent characteristics in the PLA matrix, among which dispersibility and compatibility are particularly important; so, they can be modified by 3-aminopropyltriethoxysilane (APS) to achieve the target characteristics. The results showed that the fluorescence and mechanical properties were affected by SAO addition. The mechanical properties significantly improved with 5 wt% SAO; further, addition had no impact. And the emission band of fluorescence and phosphorescence is just at the peak of 524 nm. The composites with 15 wt% SAO have the best fluorescence properties. The fluorescence decreased with further doping. Fluorescence decay curves with various amounts of SAO particles show a similar tendency as pure SAO particles; the speed of decrease in afterglow intensity was higher for the first 30 min. In addition, the detailed morphological scanning and study by scanning electron microscope (SEM) showed that the particles had good adhesion to the matrix. In conclusion, the concentration of SAO into the PLA matrix impacts the fluorescence and mechanical properties of a SAO/PLA composite material.
Comprehensive characterization mechanical properties of aerogels and their composites are important for engineering design. In particular, some aerogel composites were reported to have varied tension and compression moduli. But conducting tension tests is difficult for the reason that low strength and brittleness will lead to unexpected failure in the non-test area. A method is presented for measuring both the tension and compression moduli of a ceramic-fiber reinforced SiO2 aerogel composite by bending via digital image correlation. First, the relationship between bending behavior and the tension/compression moduli was introduced for bimodular materials. Then a bending test was conducted to predict tension and the compression moduli of the ceramicfiber- reinforced SiO2 aerogel composite via digital image correlation. In addition, uniaxial tension and compression tests of the aerogel composites were carried out, respectively for measuring tension and compression moduli. The tension and compression moduli measured were numerically similar to results obtained from uniaxial tests with a difference of less than 14 %.
Ceramic-fiber-reinforced SiO2 aerogel (CFRSA) composite was used as core layer to prepare a stitched sandwich thermal protection structure (SSTPS). Mechanical properties of the SSTPS were experimentally investigated and compared with that of CFRSA, including flatwise tension, flatwise compression, edgewise compression and shear. Research results showed that the SSTPS can greatly improve the mechanical properties of CFRSA. To further understand the non-linear, tension-compression asymmetric and transversely isotropic properties of the SSTPS, inner configurations were investigated by X-ray computed tomography and scanning electron microscopy. Mechanical models were established to predict the overall properties of the SSTPS through performance of each component, including theoretical model and finite element analysis (FEA) model. Mixed series-parallel spring models were constructed to theoretically predict the effective elasticity modulus of the SSTPS. Representative volume element (RVE) was selected for FEA modeling of the SSTPS, which can not only predict the equivalent elastic modulus of SSTPS, but also predict the nonlinear flatwise compression behavior. In order to verify whether the mechanical properties of large area SSTPS under complex stress can be represented by the properties of uniform materials through RVE analysis, four-point bending test and FEA modeling were carried out on a large scale SSTPS specimen. Results showed that when analyzing the macro bending behavior of large area SSTPS, the method of equivalent SSTPS to uniform material were of relatively high accuracy and efficiency.
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