Geometry‐Faithful Strain Normalization for Interface‐Controlled Strengthening in Phase‐Transforming Filamentary Composites

In deformation‐processed composites, strength is governed by refinement of a codeforming second phase into a dense filamentary architecture that constrains plasticity through interfacial barriers. When a postdeformation phase transformation alters reinforcement volume and filament geometry at fixed macroscopic dimensions, nominal true strain no longer uniquely represents the operative interfacial length scale. Here, a geometry‐faithful framework is introduced to restore a one‐to‐one mapping between deformation state and reinforcement length scale through an effective‐strain normalization that accounts for transformation‐induced filament expansion. The approach is demonstrated using a filamentary Al/Ca composite and its postdeformation converted Al/Al ₂ Ca state, combining tensile testing, quantitative filament‐thickness measurements, and barrier‐type scaling. Normalization aids direct comparison at matched filament thickness ( t ≈ 1.10–0.35 µm), enabling assessment of the geometry‐normalized apparent interfacial barrier effect separately from chemistry‐driven geometry changes. On a geometry‐consistent basis, strength in both states follows an inverse‐thickness dependence (∝1/ t ), consistent with interface‐controlled dislocation glide, while the transformed state exhibits higher strengthening efficiency at high refinement, reaching ultimate tensile strength (UTS) = 365 MPa at t ≈ 0.35 µm ( η _eff ≈ 12.7) with only a modest conductivity penalty (31.5 MS m ⁻¹ , ≈10% relative to Al). Effective‐strain normalization thus decouples deformation history from transformation‐induced geometry evolution and provides a transferable basis for ranking reinforcement efficiency in postdeformation phase‐transforming composites. The normalization is applicable when the reinforcement retains a continuous filamentary topology and transformation‐induced expansion is approximately uniform; it becomes less reliable when filament breakup, spheroidization, or reaction gradients make filament thickness no longer representative of the operative barrier spacing.