Matrix‐Dependent Mechanical Performance and Fracture Morphology of Epoxy Composites Reinforced With Alumina ( Al 2 O 3 ) and Wollastonite ( CaSiO 3 ) Microparticles

This study investigates the mechanical performance and fracture morphology of RNM‐ and RIM135‐based epoxy composites reinforced with 1–10 wt.% Al 2 O 3 and wollastonite (CaSiO 3 ) microparticles. Specimens prepared by ultrasonic homogenization and vacuum degassing were characterized through tensile, three‐point bending, SEM, and EDS analyses. The optimum strength response was obtained for RNM composites at 2.5 wt.% filler. At this loading, Al 2 O 3 increased tensile and flexural strengths by 5.6% and 23.0%, respectively, while CaSiO 3 increased flexural strength by 16.1%. The maximum tensile modulus increases were 22.9% for RNM/CaSiO 3 and 40.4% for RIM135/CaSiO 3 . The highest flexural modulus improvements reached 94.0% for RNM/Al 2 O 3 and 68.4% for RIM135/CaSiO 3 , the latter occurring at 7.5 wt.%. However, high filler contents considerably reduced strength, deformation capacity, and energy absorption. In RIM135/Al 2 O 3 composites, tensile strength and tensile energy absorption decreased by up to 60.2% and 89.2%, respectively, while flexural strength and energy absorption decreased by up to 52.8% and 75.6%. SEM observations revealed uniform dispersion at low loadings but increased agglomeration, particle pull‐out, and interfacial debonding at higher contents. Overall, low‐to‐moderate filler loadings provided the best balance between stiffness and mechanical integrity.