Functionalizing polymers by adding micro- or nanoparticles is a method to adjust specific material properties, such as electromagnetic characteristics or thermal conductivity. However, a high filler content can significantly influence the mechanical performance of the material. To address this issue, short- or long-fiber-reinforced plastics (FRP) are used as base material, combining the benefits of particle functionalization with the inherent strength and durability of fiber reinforcement. This approach maintains the desired properties of the material while minimizing the negative impact on mechanical performance. This study explores occurring failure mechanisms and the resulting tensile behavior of carbonyl iron-filled endless glass fiber-reinforced epoxy composite. The underlying influences are investigated through the manufacturing of a test series with varying particle content, ranging from 0 vol.% to 28 vol.%. Tensile tests are conducted according to DIN EN ISO 527. The study shares insights on the trade-off in mechanical performance opposing to increasing electromagnetic absorption properties, for instance for shielding purposes in composite enclosures.