Abstract:

Objective The purpose of this paper was to study a needling process, proposed the concept of needling prefabricated holes and the synergistic needling method of prefabrication and needling, and strengthened the connection of needled bundles through the synergistic method of pre-needling and main needling, while reducing the needled on the fabric surface. The damage of the inner fibers could improve the interlaminar peeling performance and the in-plane tensile performance of the needled fabric at the same time, which provided a new idea and method for the preparation of high-performance needled fabrics.
Method In this paper, carbon fiber non woven fabric and carbon fiber felt were used to prepare needled preforms in the form of carbon cloth/felt lamination. Under the same conditions, traditional needled fabrics and pre-needling and main needling synergistic needled fabrics were prepared using the traditional needling process and the pre-needling and main needling synergistic process. The mechanical properties of the two fabrics were characterized through a series of experiments, and the strengthening principle of the pre-needling and main needling synergistic process was revealed.
Results In the pre-needling and main needling synergistic process, pre-needling formed prefabricated holes, and the main needling was in situ needled at the pre-needling point. The synergistic effect of the two played a role in strengthening interlaminar connection and reducing in-plane fiber damage. The interlaminar peeling properties of the two were characterized by performing the interlaminar peeling experiment on the prepared needled fabrics. The interlaminar peeling property of the latter under different total needling densities were improved by 56.16%-58.46% compared with the former(Fig. 6). The 3-D profiler was used to observe the fiber bundle morphology on the interlaminar peeling surface, and the fiber bundle volume was counted. It could be seen from interlaminar peeled fabric that the pre-needling and main needling synergistic process had less shearing of the inner fibers, and less and larger needling holes were formed. The needled fabric bundles of the pre-needling and main needling synergistic needled fabric were thicker and longer and the distribution were sparse; the needled fabric bundles of the traditional needled fabric were shorter and thinner, but the distribution were denser. Compared with the traditional needled fabrics, the maximum fiber bundle volume of the interlaminar peeling observation surface of the synergistic needled fabrics increased by 349.1%-445.1%, and the total fiber bundle volume increased by 63.1%-93.2%(Fig. 9). Therefore, it could be seen that the pre/main pre-needling and main needling synergistic process increases the needled fiber bundles brought in during the main needling process and reduced the damage to the fibers in the face through the pre-needling to form the needled prefabricated holes, and improved the interlaminar of the needled fabrics peel performance. Then, tensile experiments were performed on each layer of carbon cloth of the needled fabrics to characterize the in-plane tensile property. It could be seen that the in-plane tensile strength of the pre-needling and main needling synergistic needled fabrics was 8.8%-15.7% higher than that of the traditional needled fabrics. According to the previous analysis, synergistic needled fabrics could improve the in-plane tensile property of the fabric by reducing the shear damage of the in-plane fibers.
Conclusion The new synergistic process of pre-needling and main needling significantly improved the interlaminar peeling performance of needled fabrics. For the needled preforms prepared with different total needling densities, the interlaminar peeling strength of the synergistic needling process increased by 56.16%-58.46% compared with the traditional needled fabric; the transferred in-plane fiber content increased by 63.1%-93.1%, this was because the pre needling process generated pre-fabricated holes, which was beneficial to the subsequent main needling process to bring more short fibers into the thickness direction to form needled fabric bundles. The in-plane tensile property of the synergistic needled fabricss were improved by 8.8%-15.7%. This was because the synergistic needling process adopted the idea of halving the needling density, doubling the number of times of needling, and in-situ needling, which effectively reduced the area of the damaged area of needling and improved in-plane tensile strength of needled fabrics.

Key words: needling process, preform, needled fabric, tensile property, peel property