Abstract:

Objective Alumina yarn, known for its high temperature resistance, high strength, and high modulus, is extensively utilized in the aerospace industry. However, its characteristics, such as brittleness, splitting, and fuzziness, pose challenges to weaving and fabrication of fabrics. Therefore, this investigation studies the influence of different ply numbers and twist levels on the tensile strength of the alumina yarn with an aim to provide valuable insights for the weaving and fabrication of alumina materials.

Method Two plies were twisted together, the thread linear density becomes twice that of a single ply, i.e. 150 tex. Following the same pattern, a total of five continuous alumina yarns with different thread densities of 75, 150, 225, 300 and 375 tex were produced. The yarns were divided into five groups. One group was left untwisted while the other four groups were twisted at the specified twist levels at 2, 4, 6, or 8 twists/(10 cm), respectively. They were then subjected to tensile testing using a high force tensile tester.

Results The experimental results showed that as the ply count of the aluminum oxide fiber increased, the tensile strength of the yarn exhibited a curve of decreasing trend. This can be attributed to the increasing occurrence of fiber fracture within the aluminum oxide ceramic yarn at different time intervals (Fig. 3). After twisting, the yarns of different ply counts demonstrated a trend of increasing strength with increasing twist level, followed by a decrease. However, each yarn type reached a peak strength at a different critical twist level, although the magnitudes were similar. For the single aluminum oxide yarn, the maximum strength of 32.62 cN/tex was achieved at 6 twists/(10 cm). For the double strands aluminum oxide yarn, the maximum strength of 32.73 cN/tex was achieved at 6 twists/(10 cm). For the three and four strands aluminum oxide yarn, the maximum strength of 32.34 cN/tex and 31.25 cN/tex are respectively achieved at 4 twists/(10 cm). For the five strands aluminum oxide yarn, the maximum strength of 30.31 cN/tex was also achieved at 4 twists/(10 cm) (Fig. 4). The twist factor can reflect the angle of inclination between the fiber and the yarn axis, which can measure the degree of twisting of yarns with different thread densities. The corresponding twist factor is calculated according to the formula, with the twist factor as the horizontal coordinate and the strength as the vertical coordinate to draw a sample connection diagram, the strength of alumina yarn increases with the twist factor and then decreases (Fig. 5).

Conclusion Alumina yarns showed the same pattern with increasing number of plies, 75 tex single yarn as well as 2, 3, 4 and 5 strands. With increasing number of plies, the breaking strength decreased continuously compared with single yarn, and the breaking strength decreased by 0.9%, 2.9%, 7.4% and 9.9% respectively. After twisting of alumina fibers with different number of plies, the breaking strength showed a trend of increasing and then decreasing with the increase of twist. The peak strength of alumina yarns with different number of plies was observed in twist levels from 0 to 8 twists/(10 cm), while the critical twist factor was in the range of 60-80.

Key words: alumina yarn, ply number, twist, tensile property, tenacity