A study of the mixed-mode interfacial fracture toughness of adhesive joints using a multiaxial fatigue tester

In this paper, a new technique is introduced for the control of the far field and mixed-mode crack tip of a single lap shear specimen with a crack along the interface. An investigation has been conducted to use one single lap shear specimen to obtain a series of values of interfacial fracture toughness as a function of the mixed-mode phase angle. The interfacial fracture behavior of the single lap shear specimen subjected to multiaxial concentrated line loads was investigated using a unique six-axis submicron tester coupled with a high density laser moire interferometer. The six-axis submicron tester was used to provide the displacement-controlled multiaxial concentrated line loads, whereas the moire interferometry technique was used to monitor the crack length during the test. In addition, a finite element technique was simultaneously used to determine the near crack tip displacement fields of the single lap shear specimen. The interfacial fracture toughness and phase angle were computed by using these near tip displacement variables through the analytical energy release rate and phase angle expressions derived by the authors. The results show that the facilities and methodology used in the current study can indeed be proved to possess the ability to control the far field and the mixed-mode conditions at crack tip, and to efficiently perform the mixed-mode fracture test.