Tailored Flax-Reinforced Composites: Properties and Sustainable Applications

Tailored flax-reinforced composites (TFRC) are being investigated as a sustainable alternative to conventional glass- and carbon-fiber-reinforced composites, having a lower fiber volume than these and the structure of the laminate with two plies (two identical layers of alkali-treated flax yarns) is unidirectional, weakly twisted, oriented at ±45°, and reinforced by stitching; it is also impregnated with bio-resin and has robust reinforcement through controlled lamination. TFRC has shear-dominated behavior under both tensile and compressive loading, due to the off-axis orientation of the fibers, but the damage evolution differs significantly. Under tensile loading, the material exhibits a lower strength (55.2 MPa), whereas under compression loading, the composite achieves a higher apparent strength (99.1 MPa). The paper provides a comprehensive analysis for structural and mechanical characterization using the following: nondestructive evaluation using ultrasound to detect internal discontinuities and assess homogeneity; optical microscopy to evaluate fiber–matrix integration and porosity reduction; and Dynamic Mechanical Analysis to assess thermomechanical transitions and storage modulus stability. Finite element simulations have been used to determine elastic properties and validate the matrix-dominated shear response. The results confirm that the [±45°]4S sequences of TFRC optimize mechanical response and interfacial adhesion, promoting TFRC as an ecological solution for structural systems where progressive energy dissipation is preferred.