This research examines the production, evaluation and analysis of ultra-thick laminated Polymer Matrix Composite (PMC) beams, aiming to create high-performance PMC leaf springs for automotive uses. A novel feature of this research is the incorporation of Fiber Bragg Grating (FBG) sensors and thermocouples (TCs) to track residual strain and exothermic reactions in composite structures throughout the curing and post-curing manufacturing processes. Furthermore, the Calibration Coefficients (CCs) are determined using Strain Gauge measurement outcomes from static three-point bending tests. A significant portion of the research is dedicated to developing a well-correlated Finite Element (FE) model that accounts for Large Deflection (LD) effects through Geometrical Nonlinear Analysis (GNA) to comprehend the deformation behavior of ultra-thick composite beam (ComBeam) samples, thereby enhancing the understanding of large deformation behavior and addressing critical research gaps in composite materials. This model will facilitate the evaluation of internal strain distribution, which is validated by correlating data from FBG sensors, Strain Gauges (SGs) and FE analysis. Additionally, this research emphasizes the use of FBG sensors in Structural Health Monitoring (SHM) during fatigue tests under three-point bending, supported by load-deflection sensors: a novel method for composites at this scale. The findings of this study indicate that the fatigue performance of ComBeam samples significantly deteriorated with increasing displacement ranges, even at identical maximum levels, highlighting the potential of FBG sensors to improve SHM capabilities associated with smart maintenance.