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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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Developing conductive polymer composites (CPCs) with high stretchability and high resistance response is a challenge in the field of flexible sensing. In this study, porous CPCs with a microdome array on the surface are prepared based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs). TPU/CNT composites are designed to be strain sensors and pressure sensors capable of monitoring external strain and pressure stimuli. Due to the excellent electrical properties of carbon nanotubes, the synergistic effect of composite surface microstructure, and an internal porous structure, the sensor has greatly improved the detection range and sensitivity of traditional sensors. The sensing properties of CPC materials in terms of strain and pressure monitoring are perfectly balanced. The detection ranges of the strain sensor and pressure sensor are 0−160% and 0−55 kPa, respectively, and the highest sensitivity is gauge factor (GF) = 12.88 (90−160%) and sensitivity S = 0.08 (0−6.5 kPa), respectively. Based on the reversible change of the CNT conductive network under tensile/compression loading, the sensor has excellent stability and durability during cyclic loading. In addition, the TPU/CNT composite sensors can monitor human movements, bending of composite components, and pressure positions, showing great application prospects in electronic skin, wearable smart devices, and human−computer interaction.

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