This study intended to compare and analyze the Poisson's ratio and mechanical properties of aramid knit (ARNT), 3D printed auxetic re-entrant pattern (3DP-RE), and 2 types of composite fabrics manufactured with ARNT and 3DP-RE. Specimens were manufactured by 3D printing the re-entrant pattern with a CFDM (conveyor fused deposition modeling) 3D printer and TPU (thermoplastic polyurethane) filament, combining with aramid knit in 2 ways. Then, Poisson's ratio, bending, compression, and tensile properties were tested. As a result of Poisson's ratio, 3DP-RE and its 2 types of composite fabric showed negative Poisson's ratio at all angles and deformed stable at 0° and 90° than the bias direction. The bending strength confirmed that the composite fabric showed a lower value. But, the strain at max bending strength was greater than a substrate fabric. At the compression properties, it has been confirmed that compression strength and toughness are improved when manufacturing composite fabrics. As a result of tensile properties, 3DP-RE and composite fabrics were significantly more initial modulus, elongation and toughness than ARNT and were shown to be the largest in gradient 90°. Therefore, it is confirmed that the performance is excellent when fabricated as a 3DP-RE/ARNT composite fabric, and based on the results of studies, we intend to use it as the basic data for composite fabrics of auxetic structure suitable for shoe uppers.

This study purposed to develop conductivity 3D printed (3DP) fingertips and confirm their potential for use in a pressure sensor. Index fingertips were 3D printed using thermoplastic polyurethane filament with three types of infill patterns (Zigzag (ZG), Triangles (TR), Honeycomb (HN)) and densities (20%, 50%, 80%). Hence, the 3DP index fingertip was dip-coated with 8 wt% graphene/waterborne polyurethane composite solution. The coated 3DP index fingertips were analyzed by appearance property, weight changes, compressive property, and electrical property. As results, the weight increased from 1.8 g to 2.9 g as infill density increased. By infill pattern, ZG was the largest, and the pick-up rate decreased from 18.9% for 20% infill density to 4.5% for 80% infill density. Compressive properties were confirmed. Compressive strength increased as infill density increased. In addition, the compressive strength after coating was improved more than 1000 times. Especially, TR had excellent compressive toughness as 13.9 J for 20%, 17.2 J for 50%, and 27.9 J for 80%. In the case of electrical properties, the current become excellent at 20% infill density. By infill patterns at 20% infill density, TR has 0.22 mA as the best conductivity. Therefore, we confirmed the conductivity of 3DP fingertips, and the infill pattern of TR at 20% was most suitable.

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In this research, to confirm the applicability as the actuator of the re-entrant (RE) structure strip using 3D printing with shape memory thermoplastic polyurethane material, two types of 3D printing infill conditions and five extension temperature conditions were applied. REstrip was analyzed through differential scanning calorimetry (DSC), tensile properties, Poisson’s ratio properties, and shape recovery properties according to temperature conditions. The DSC results showed that the glass transition temperature peaks of the SMTPU filament and the 3D printed REstrip were in the range of about 30–60 °C. In terms of tensile properties, the initial modulus, maximum stress, and yield stress of REstrip all decreased, while the elongation at break increased with increasing extension temperature. In terms of Poisson’s ratio, it was confirmed that as the extension temperature rises, Poisson’s ratio shows a positive value at a lower elongation, and the deformation is best at 50 °C. As a result of the shape memory property, the shape recovery ratio tended to decrease as the tensile deformation temperature increased.

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