Growing interest in carbon fiber-reinforced polyetheretherketone (CF-PEEK) for functional applications has enabled material extrusion (MEX) as a cost-effective additive manufacturing process. However, the mechanical performance of MEX fabricated CF-PEEK parts often suffers from inconsistencies arising from variations in process parameters. This study explores how two key process parameters, nozzle temperature (range of 400–440 °C) and print speed (range of 15–25 mm/s), affect the tensile behavior of CF-PEEK components. A replicated three level full-factorial design was implemented, and the results were evaluated using response surface methodology (RSM) based regression analysis to develop predictive models for ultimate tensile strength ( \(\:{\sigma\:}_{UTS}\) ) and elastic modulus (E). Analysis of Variance confirmed that both parameters significantly impact mechanical properties, with print speed emerging as the most influential factor. Slower print speeds combined with low to medium nozzle temperatures resulted in improved mechanical properties through enhanced interlayer consolidation. Multi-objective optimization confirmed 400 °C and 15 mm/s as the optimal settings, and these conditions were further validated through tension-tension fatigue tests, which established a fatigue strength corresponding to 50% of the static strength at 106 cycles. Thermal analysis through differential scanning calorimetry confirmed the semicrystalline thermal state of the optimized material condition, providing thermal state characterization for the optimized printed CF-PEEK. Fractographic examination conducted using scanning electron microscopy revealed failure features. The study offers a reliable framework for optimizing CF-PEEK MEX fabrication for engineering applications. Overall, the replicated factorial RSM framework provides a statistically supported approach for optimizing CF-PEEK MEX processing within a defined parameter window.
