Tailoring mechanical properties of randomly oriented tape (ROT) composites: An experimental study

Discontinuous fiber composites (DFC) have properties such as notch insensitivity, short processing times, and large shaping freedom [1-3]. However, the mechanical behavior of ROT composites is less predictable compared to continuous fiber composites due to the mesoscopic heterogeneity of the material [4]. Controlling the tape alignment is a compelling approach for tailoring the mechanical properties of the ROT composites, enabling better control and prediction of the material properties such as tensile strength and stiffness [5]. However, for a successful implementation of the alignment method in industry, a fast tape alignment method is needed. In this study, a quantitative assessment has been made between three alignment methods. The methods have been evaluated in respect of the level of alignment and the manufacturing process by means of a decision-making matrix. The level of alignment of each method has been determined using computer vision on the orientation of individual tapes. The final alignment method has been selected which uses vertical mesoscopic sieves with a high aspect ratio to rotate tapes in a preferred direction during deposition. With this alignment method, ROT have been aligned at -45˚, 0˚, and +45˚ with respect to the loading direction. With these alignment tools, CF/PEEK ROT have been deposited inside a cavity followed by a consolidation cycle at 45 bar and 385˚C. The effect of alignment was examined by comparing the mechanical response of samples with: ROT, being longitudinally aligned, and a laminate of [+45˚,-45˚]s aligned pseudo-layers. The results of tensile tests showed that by aligning tapes in the longitudinal direction, the average tensile stiffness and strength increased by 145% (from 32.5 to 79.7 GPa) and 96% (from 202 to 396 MPa) respectively compared to randomly orientated tapes. These results show the potential gain in material properties and the ease of implementation of the method.