In this research, polydimethylsiloxane (PDMS) and graphene
nanoplatelets
(GNPs) were used as flexible substrates and conductive layers. A facile
and template transfer method combined with a low-cost solution-spraying
process was adopted to prepare the microdome array GNPs/PDMS flexible
strain sensor. The microdome array produces different degrees of in-plane
deformation and the gradient distribution of the GNP conductive network
on the surface during stretching. This affects the contact effect
between the adjacent cells of the GNP conductive network on the film
surface in different strain ranges, thereby realizing a sensitive
resistance response. The strain sensor of the microdome array GNPs/PDMS
exhibits excellent gauge factors (GF) of 8.98 (0.26% < ε
< 20%), 18.31 (20% < ε < 43%), and 34.57 (43% <
ε < 60%), the highest of which is 8 times higher than that
of the planar GNPs/PDMS strain sensor without a microdome array. In
addition, the material exhibits remarkable stability and durability
(10 000 cycles), fast response time (125 ms), and stable relative
frequency/strain sensing performance. Finally, the strain sensors
of the microdome array GNPs/PDMS were packaged for various application
tests, showing broad application prospects in electronic skin, wearable
electronic devices, and component health monitoring.
Friction stir welding (FSW) can achieve a sound welding joint, but its residual stress and distortion cannot be avoided due to the non-uniformity of temperature distribution during welding. Stationary shoulder friction stir welding (SSFSW) was employed to butt weld 6005A-T6 aluminum alloy plates. The effects of welding speeds ranging from 200 mm/min to 600 mm/min on residual stress and distortion were investigated in detail. A thermo-mechanical model was utilized to compare the residual stress distribution between conventional FSW and SSFSW. SSFSW was beneficial to decreasing the peak temperature of stir zone (SZ) and then obtaining a narrower SZ. The peak residual stress produced by SSFSW was 50% lower than that by conventional FSW and a narrower tensile stress region was attained by SSFSW. Moreover, the stationary shoulder applied a function of synchronous rolling during the welding, which controlled the distortion effectively.
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