Electroelastic moduli of piezoelectric polycrystals with bulk and film textures

The effect of crystallographic texture on the electroelastic moduli of piezoelectric polycrystals has been studied using micromechanical modeling that makes use of the uniform field concept. An orientational averaging scheme has been developed for textured piezoelectric polycrystals, which, when combined with the conventional self-consistent approach, provides an estimate of the effective electroelastic moduli in terms of texture. In the special situation where the polycrystal exhibits a fiber texture, a class of uniform fields exist under certain crystal symmetries, so that the effective electroelastic moduli can be determined exactly. This is confirmed by the coincidence of the corresponding upper and lower bounds. Numerical results are presented for both cases and compared to known theoretical predictions where possible

Nondestructive Ultrasonic Characterization of the Orientation Distribution of Short-Fiber Composites

The ease of fabrication and relatively low cost of composites containing short glass or ceramic fibers embedded in a polymer or metal matrix has made them attractive candidates for a wide range of applications. The preferential alignment, or misalignment depending on one’s view, of the short fibers results in an overall texture of the composite and strongly influences its mechanical and physical response, for example, stiffness, conductivity, strength, and so on. The orientation of the short fibers depends strongly on the processing conditions. From a process-control viewpoint, it is imperative to determine if a composite component has adequate strength, stiffness, and so on, and it is preferable to obtain this information nondestructively. In short-fiber reinforced composites, the orientation distribution of the short fibers is the most significant variable that determines these overall properties. Thus its determination is essential

Synthesis and Properties of Dipyridylcyclopentenes

A short and general route to the substituted dipyridylcyclopentenes was explored and several new compounds belonging to this new group of diarylethenes were synthesized. The study of their photochromic and thermochromic properties shows that the rate of the thermal ring opening is strongly dependent on the polarity of the solvent.

Adhesion, Stiffness and Instability in Atomically Thin MoS2 Bubbles

We measured the work of separation of single and few-layer MoS2 membranes from a SiOx substrate using a mechanical blister test, and found a value of 220 +- 35 mJ/m^2. Our measurements were also used to determine the 2D Young's modulus of a single MoS2 layer to be 160 +- 40 N/m. We then studied the delamination mechanics of pressurized MoS2 bubles, demonstrating both stable and unstable transitions between the bubbles' laminated and delaminated states as the bubbles were inflated. When they were deflated, we observed edge pinning and a snap-in transition which are not accounted for by the previously reported models. We attribute this result to adhesion hysteresis and use our results to estimate the work of adhesion of our membranes to be 42 +- 20 mJ/m^2

Electroelastic moduli of piezoelectric polycrystals with bulk and film textures

The effect of crystallographic texture on the electroelastic moduli of piezoelectric polycrystals has been studied using micromechanical modeling that makes use of the uniform field concept. An orientational averaging scheme has been developed for textured piezoelectric polycrystals, which, when combined with the conventional self-consistent approach, provides an estimate of the effective electroelastic moduli in terms of texture. In the special situation where the polycrystal exhibits a fiber texture, a class of uniform fields exist under certain crystal symmetries, so that the effective electroelastic moduli can be determined exactly. This is confirmed by the coincidence of the corresponding upper and lower bounds. Numerical results are presented for both cases and compared to known theoretical predictions where possible

Reprocessing and recycling of thermoset polymers based on bond exchange reaction

Recently, it has been reported that by properly catalytic controlled bond exchange reactions, thermoset polymers could be welded by simple heating. During the operation, polymer topology could be rearranged in complying the external deformation and release the internal stress, but the network integrity is maintained and the average functionality of polymer chains is unchanged. This novel technology also enables us to reprocess and recycle the thermoset polymers. In this study, we experimentally demonstrated that after being milled into pulverous state in microsize, the thermoset epoxy polymer with exchangeable bond could be welded and assembled again into integrity with regained mechanical properties comparable to a fresh bulk polymer. The detailed operation procedure, as well as the influence of pressure and heating time on the stretch ability of the recycled polymer sample, is demonstrated. Such an in-depth reprocessing routine could be repeated for multiple times in manufacturing complex objects and welding separated bulk polymers. Considering the efficient and robust welding effect among polymer particles, as well as the maintained merits of thermoset polymer as stress-bearing materials during the operation, this new strategy is more suitable to repair polymer structures in service and recycle the thermoset waste in most engineering applications

Labeling of Biotechnology Products

labeling of biotech products in foodSpeakers t this symposium presented issues surround the issue of labeling of biotech products and the right of the consumer to know about the ingredients of the food they eat