PSI - Issue 64

Wenkui Dong et al. / Procedia Structural Integrity 64 (2024) 1152–1159 Wenkui Dong and Macro liebscher et al./ Structural Integrity Procedia 00 (2019) 000 – 000

1154

3

Number of filaments Fineness of the yarn

50,000

3,450

Density [g/cm 3 ]

1.8 6.9

Filament diameter [μm] Tensile strength [MPa] Tensile modulus [GPa]

4,400

255

Resistance of single filament [μΩm]

17

Sizing level [%, by mass]

1.0

Table 2. Raw materials and mix design of the 1 L impregnation suspension

Mixture constituent Micro-cement R-X Micro-cement P-U

Density [g/cm 3 ]

Particle size [μm]

Composition [g/L]

2.9 3.1

d95<6

345.4 345.4 345.4

d95<9.5 d95<0.15

Micro-silica

1.39 ± 0.02 1.20 ± 0.03 1.20 ± 0.03

Superplasticizer (start) Superplasticizer (end)

13.0 18.1

Water

1

493.3

2.2. Production of MCF The impregnation process of the carbon fibers is automated through the utilization of a continuous pultrusion machine developed by the Institute for Construction Materials at the TU Dresden. Initially, one end of the carbon yarn was attached to a hexagonal wheel, driven by an electric motor to achieve a constant traction velocity of 360 m/h. Afterward, the yarn moved through a water bath where a metallic roller rotated counter to the yarn's direction to wet the yarn with water before impregnation. Subsequently, the moist yarn was guided into the suspension and passed through five rollers, ensuring complete impregnation. Then the freshly impregnated carbon yarn passed through a conical nozzle with an inner diameter of 4.5 mm, followed by a smaller nozzle with a 4.1 mm inner diameter, to remove the excess suspension and shape the impregnated MCF. Finally, the MCF was fixed onto the wheel at specific intervals, with an edge length of 1.2 m for the wheel before being cut to a specific size for curing in a water bath. More specific procedures can be found in Ref. by Schneider et al. (2019). 2.3. Configuration of electrode The 28-day cured MCF is then cut into short bars with a length of 12 cm. Two different electrode configurations are put forward to assess the impact on the piezoresistive performance, with one by two outer electrodes and another by inner two electrodes with a distance of 6 cm, as shown in Fig. 1. The aluminum foil tape is used as electrodes in this study. Since it is soft and bendable, at least four layers of foil tape are overlapped. The adhesive used to connect the electrodes and MCF is a conductive silver/epoxy-based paste from RS PRO Components, which is a two-part thermosetting material with a resin-to-hardener mix ratio of 1:1 by weight or volume. The specific procedures are carried out as follows: firstly, remove and clean the dust on the surface of MCF, especially the contact areas with electrodes. Secondly, the specific electrodes are fixed to the MCF with adhesive and then further fixed with an insulated rubber tape. The treatment can ensure proper Ohmic contact of electrodes to MCF and avoid electrical interference from contact resistance. Finally, the MCF is stored at room temperature for 24 h to allow the full reaction of adhesive. It is worth noting that in the first scenario, there is cross-sectional contact between the electrode and the inner filaments of the MCF. In the second scenario, the electrode wraps around the lateral area of the MCF with the largest contact area.