Interfacial fracture toughness measurement in both steady state and transient regimes using four-point bending test

The paper describes some extensions of four-point bending tests for determining the interfacial fracture toughness $$\Gamma $$, in both steady-state and transient regimes, as a function of the fracture mode mixity. Two sets of multimaterial systems were studied: (i) Aluminum alloy (ASTM 2017)/epoxy/PMMA polymer and, (ii) Aluminum alloy (ASTM 2017)/stainless steel (ASTM 301) obtained by bonding and thermal spray coating techniques respectively. The interfacial fracture toughness was investigated by means of analytical and Finite Element Analysis using ABAQUS software. The numerical trend solution of both interfacial fracture toughnesses as function of crack length, and friction coefficient has been obtained and compared to an analytical one. We will propose a method on (i) how both reversed notch position in multimaterial systems and crack delamination beyond the inner loading points (transient regime) are explored to extend the measurement of interfacial fracture toughness, (ii) how the numerical analysis is used to determine the interfacial fracture toughness through an experimental compliance measurement in transient regime, and (iii) we attempt to reveal why the interfacial toughness has strong phase angle dependence.