By integrating fiber-reinforced composites (FRCs) with Three-dimensional (3D) printing, the flexibility of lightweight structures was promoted while eliminating the mold’s limitations. The design of the I-beam configuration was performed according to the equal-strength philosophy. Then, a multi-objective optimization analysis was conducted based on the NSGA-II algorithm. 3D printing was utilized to fabricate I-beams in three kinds of configurations and seven distinct materials. The flexural properties of the primitive (P-type), the designed (D-type), and the optimized (O-type) configurations were verified via three-point bending testing at a speed of 2 mm/min. Further, by combining different reinforcements, including continuous carbon fibers (CCFs), short carbon fibers (SCFs), and short glass fibers (SGFs) and distinct matrices, including polyamides (PAs), and polylactides (PLAs), the 3D-printed I-beams were studied experimentally. The results indicate that designed and optimized I-beams exhibit a 14.46% and 30.05% increase in the stiffness-to-mass ratio and a 7.83% and 40.59% increment in the load-to-mass ratio, respectively. The CCFs and SCFs result in an outstanding accretion in the flexural properties of 3D-printed I-beams, while the accretion is 2926% and 1070% in the stiffness-to-mass ratio and 656.7% and 344.4% in the load-to-mass ratio, respectively. For the matrix, PAs are a superior choice compared to PLAs for enhancing the positive impact of reinforcements.

Static and dynamic uniaxial tensile responses were investigated to accurately characterize and predict the mechanical properties of PEEK (polyether-ether-ketone) at strain rates ranging from 10⁻³ s⁻¹ to 200 s⁻¹ and temperatures ranging from 23 °C to 110 °C. The tensile responses showed dependences on the strain rate and temperature, and the dependences of the yield strength and elastic modulus on the temperature and strain rate were studied. A modified phenomenological Sherwood–Frost constitutive model considering a wide range of strain rates and temperatures was established to characterize the tensile mechanical response of PEEK material before yielding based on the experimental data. The results indicate that the model can accurately describe the pre-yield behavior of PEEK under different temperature and strain rate conditions, thus reducing the dependency on experimental data for subsequent researchers, thereby providing a theoretical foundation and modeling framework for the design and performance evaluation of CF/PEEK composite structures.