Mixed Mode Fracture Toughness Test of Bimaterial Interface in Different Humidity Conditions

The strength of an interface is subjected to temperature, humidity and different global mixed mode loading conditions. This paper describes the measurement of the interface fracture toughness as a function of relative humidity using a compact mixed mode (CMM) specimen in Instron 5567 testing system machine. In the test, The conditions of specimen are parting dry condition and moisture preconditioning (85degC /85% RH/168h and 85degC /60 %RH/168h), measuring fracture critical value of specimen with different global mixed mode loading conditions, the fracture critical value of specimen is the average failure value of 2 specimens at each loading angle of global mixed mode, the fracture critical value shows that the interface fracture toughness is decreased when relative humidity increased. Then, finite element analysis modeling for an interface crack in the CMM specimen provides the necessary stress intensity factor calculation. The results show that the mode II fracture toughness generally display a larger value than the mode I toughness in the same humidity condition. Moreover, fracture toughness is decreased when humidity increased at the same mixed mode loading. The Failure criterion based on a failure analysis diagram or effective critical stress intensity factors are proposed for interface cracks loaded under different mixed-mode and humidity fracture conditions. This method of the test for data and the finite element simulation for evaluation of interfacial fracture toughness.