The
phase diagram of a binary eutectic system of poly(9,9-di-n-octyl-2,7-fluorene) (PFO) and hexamethylbenzene (HMB) has been established
via onset melting temperatures. Upon homogeneous mixing, the growth
of PFO nematic phase in binary mixtures exhibits both lyotropic and
thermotropic features. During cooling, a smectic phase of PFO developed
epitaxially on the surface of prior-developed HMB crystals, establishing
layer stacking via the packing of side chains. Upon the annealing
at 120 °C, further epitaxial organization of PFO smectic packing
on HMB crystalline substrate results in the growth of β crystalline.
Both smectic and β phases of PFO yield characteristic ultraviolet
(UV) absorption at 434 nm wavelength and photoluminescence at the
wavelength of 441 nm. While HMB crystals were sublimated prior to
the annealing treatment, α crystalline form developed instead
through the transformation of smectic packing. The UV absorption and
fluorescence of α form are relatively shorter wavelengths. As
attributing the rise of energy bandgaps to the effect of backbone
conformation, organization of less coplanar backbones within α
crystalline form is proposed as a result of the lack of epitaxial
effect. After the growth of smectic phase via the monotropic behavior
of PFO in eutectic mixture, the following routes of phase transformation
upon annealing hence unveiled the growth mechanisms of both α
and β crystalline forms of PFO.
The major concern in the aviation industry is the flight safety. Although great effort has been put into the development of material and system reliability, the failure cases of fatal accidents still occur nowadays. Due to the complexity of the aviation system and the interaction among the failure components, it is difficult to do the failure analysis of the related equipment. This study focused on surveying the failure cases in aviation, which were extracted from failure analysis journals, including Engineering Failure Analysis and Case studies in Engineering Failure Analysis, in order to obtain the failure sensitive factors or failure sensitive parts. The analytical results showed that among the failure cases the fatigue failure is the largest in number of occurrence. The most failed components are the disk, blade, landing gear, bearing, and fastener. The frequently failed materials are steel, aluminum alloy, superalloy and titanium alloy. Therefore, in order to assure the safety in aviation, more attention should be paid to the fatigue failures.
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