This paper presents a systematic simulation-based framework for comparing the structural performance and energy efficiency of robotic arm links fabricated from Aluminium 6061-T6 and Carbon Fiber Reinforced Polymer (CFRP). A two-degree-of-freedom (2-DOF) planar robotic arm is modelled using analytical beam theory for structural analysis and the Lagrangian formulation for multi-body dynamics. Mass, effective joint inertia, bending stress, tip deflection, actuator torque, and cumulative energy consumption are evaluated for both materials under identical geometric and loading conditions. MATLAB simulation of the complete dynamic model—including inertial, Coriolis, centrifugal, and gravitational torque terms—demonstrates a 90.285% per-cycle energy reduction with CFRP relative to aluminium. Constrained cross-section optimization further identifies a minimum section that, combined with CFRP material substitution, reduces link mass by 96.3% from the base. Results confirm that the primary performance advantage of CFRP is its 40.74% lower density, which propagates through all mass-dependent torque terms in the Lagrangian model to produce compound energy savings substantially exceeding the ar mass-reduction ratio.