Delamination Resistance of Two Hybrid Ceramic‐Composite Laminates

Abstract

Hybrid laminar composites that are comprised of alternating layers of ceramic sheets and fiber‐reinforced ceramic‐matrix composite (CMC) layers exhibit attractive mechanical properties, including a high first cracking stress and a high strain to failure. To achieve these properties, a strong bond must exist between the ceramic and CMC layers; otherwise, delamination will occur readily between the layers. The present study focuses on the delamination resistance of such laminates at ambient and elevated temperatures. The delamination resistance of interfaces that have been subjected to mixed‐mode loading has been measured for two different hybrid composites by using edge‐notched flexure specimens. At low temperatures, delamination occurs by a process that involves multiple matrix cracking within the CMC layers normal to the fibers, followed by cracking of the matrix parallel to the fibers at or near the ceramic/CMC interface. The corresponding fracture energies are typically in the range of ∼100‐300 J/m2—comparable to the delamination resistance of the CMC itself. At elevated temperatures, delamination occurs via cavitation and rupture of the matrix within the CMC layers at or near the ceramic/CMC interface, with an attendant loss in toughness (to ∼10‐30 J/m2). The loss in toughness occurs most rapidly at temperatures that are close to the strain point of the matrix phase; this represents the life‐limiting temperature for this class of composites.