Influence Mechanism of Constituent Materials on the Interlaminar Fracture Properties of Composite Laminates

To investigate the influence mechanism of mesoscopic constituent materials on the interlaminar fracture toughness of composites, the mode I and mode II interlaminar toughness were measured for laminates composed of TZ300/7901 (fiber/matrix), TZ300/9A16, and TZ700/7901, using double-cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively. Curve analysis and data processing of the test results were conducted. The results revealed significant differences: the TZ700/7901 system exhibited higher toughness (G_Ic = 0.39 kJ/m², G_IIc = 0.97 kJ/m²) compared to TZ300/7901 (G_Ic = 0.31 kJ/m², G_IIc = 0.90 kJ/m²), while TZ300/9A16 exhibited the lowest toughness (G_Ic = 0.20 kJ/m², G_IIc = 0.66 kJ/m²). Fractography analysis via scanning electron microscopy revealed that matrix properties and fiber/matrix interface strength are the primary controlling factors, while fiber type indirectly influences toughness by modifying interfacial bonding. The relative strength between matrix and interface dictates the fracture mechanism. When the interfacial strength is significantly higher than the matrix strength, ductile fracture dominated by matrix deformation occurs. When the strengths of interface and matrix are comparable, brittle fracture occurs, with energy dissipation involving both matrix deformation and debonding. Interfacial debonding enhances interlaminar toughness by expanding the crack area, relieving stress concentration, and promoting fiber bridging.