High dielectric loss
and low breakdown strength have been two bottlenecks
restricting applications of conductor/polymer composites for high
energy storage. Herein, three kinds of layered composites, named BC,
BCB, and CBC, were fabricated through stacking up hexagonal boron
nitride (hBN)/cyanate ester (CE) (B layer) on carbon nanotube (CNT)/CE
with 0.4 wt % CNTs (C layer). The effects of ply pattern and composition
on dielectric properties, breakdown strength, and energy density of
composites were investigated and also compared with those of single-layer
0.4CNT/CE composite containing 0.4 wt % of CNTs. Results show that
three kinds of layered composites have significantly reduced dielectric
loss and improved breakdown strength and energy density. Especially,
for the CBC composite with 20 wt % hBN in B layer (C20BC), its dielectric
constant is as high as 323 (100 Hz) and retains a value larger than
270 (1–103 Hz), it is the highest value reported
so far among multilayered composites based on conductor/polymer and
insulating layers; moreover, its breakdown strength and energy density
are about 1.5 and 25 times of that of 0.4CNT/CE composite, respectively.
Note that C20BC composite has very low dielectric loss (0.049 at 100
Hz) or much less at increased frequencies (>100 Hz), only about
2.6
× 10–3 times of that at 100 Hz of 0.4CNT/CE
composite. The origin behind these attractive properties was intensively
discussed.
This paper presents a study about the buckling behavior of thin stainless-steel lining (SSL) for trenchless repair of urban water supply networks under negative pressure. The critical buckling pressure and displacement (p–δ) curves, temperature changing curves, hoop and axial strain of the lining monitoring section and the strain changes with system pressure (p–ε) of the lining under the action of different diameters, different lining wall thickness and different ventilation modes were obtained through five groups of full-scale tests. The variation principles of the post-buckling pressure and the reduction regularity of the flowing section of the lining were further investigated. By comparing different pipeline buckling models and introducing thin-shell theory, the buckling model of liner supported by existing pipe was established. The comparison between the test results and thin-shell theory indicates that one of the significances of the enhancement coefficient k value is to change the constraint condition of the aspect ratio, l/R, thus increasing the critical buckling pressure of the lining. Finally, an improved lining buckling prediction model (enhancement model) is presented. A previous test is used as a case study with the results showing that the enhanced model is able to predict critical buckling pressure and lobe-starting amount of the liner, which can provide guidance for trenchless restoration of the liner with thin-walled stainless steel.
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