Experimental and numerical evaluation of the influence of voids on sound absorption behaviors of 3D printed continuous flax fiber reinforced PLA composites

• Published in: Composites science and technology 2024-08, Vol.255, p.110720, Article 110720
• Main Authors: Bi, Zhixiong, Li, Qian, Zhang, Zhen, Zhang, Zhongsen, Yang, Weidong, Li, Yan
• Format: Article
• Language: English
• Subjects: A. Flax fibers; B. Defects; B. Sound absorption; C. Finite element; E. 3D printing
• ISSN: 0266-3538; 1879-1050
• DOI: 10.1016/j.compscitech.2024.110720

This study aims to quantitatively analyze the effects of voids on sound absorption properties of 3D printed continuous flax fiber reinforced PLA composites (CFFRCs). Three kinds of flax yarns with different linear density were employed to prepare CFFRCs via 3D printing technology. The sound absorption performances of these composites were measured using the impedance tube based on the two-microphone transfer function method. The microstructure morphologies including cross-sections of flax yarns, voids shape and distributions of the composites were observed via ultra-depth microscope and micro-computed tomography to reconstruct the exact structures in simulation. Mercury intrusion porosimetry was applied to measure the voids dimensions of CFFRCs. The influence of voids on sound absorption mechanisms of CFFRCs were revealed based on thermoviscous acoustics theory by conducting the simulation in COMSOL software. The experimental results demonstrated that CFFRCs exhibited excellent sound absorption coefficients (close to 1) within the frequency range of 150–350 Hz and 350–550 Hz, resulting from the voids inside and between the flax yarns respectively. With the increase of linear density (diameter of the yarn), the contents of voids inside and between the flax yarns both increased. The dimensions of voids inside the flax yarns improved while those between flax yarns remained unchanged. The existence of the voids between the flax yarns resulted in a decrease in the sound absorption coefficient of CFFRCs, while more voids inside flax yarns led to the increase of the sound absorption frequency. Numerical results indicated that voids between the flax yarns contributed to a more uniform change in sound speed, reducing sound absorption performance. Whereas, voids inside the flax yarns could improve viscous friction of soundwaves due to narrow structures, enhancing sound absorption capabilities. This study is anticipated to provide a guidance for the design of integration of structure and function of 3D printed CFFRCs. [Display omitted] •Voids formation in 3D printed CFFRCs resulted from the twisted and hierarchical structures of flax yarns.•Quantitatively evaluation on effects of the voids on sound absorption performances of 3D printed CFFRCs.•Synergistic effects of the voids between and inside the flax yarns on the sound absorption mechanisms of 3D printed CFFRCs.