Mixed mode fracture characterization of GFRP-concrete bonded interface using four-point asymmetric end-notched flexure test

A combined analytical and experimental study using an asymmetric end-notched flexure specimen under four-point bend loading is conducted to characterize the fracture of glass fiber reinforced polymer (GFRP)-concrete bonded interface. Both the classic composite (rigid joint) and interface deformable (flexible joint) bi-layer beam models are used to calculate the compliance and energy release rate (ERR) of the proposed four-point asymmetric end-notched flexure (4-AENF) specimen. The validity and accuracy of the models are obtained by comparison with the numerical finite element results. The results show that the flexible joint model predicts more accurately the compliance and ERR compared with those of rigid joint model in 4-AENF specimen due to the attribute of crack tip deformation. Moreover, the calculated ERR by the flexible joint model can be reduced to that of the rigid joint one when the specimen is properly sized. Then, the designed 4-AENF specimens are utilized to characterize the fracture toughness of GFRP-concrete bonded interface. To overcome the obstacle of low tensile strength and cracking behavior of concrete and prevent the premature fracture of concrete substrate before debonding of bonded interface takes place, a reduced section scheme is adopted and the steel bars are used to reinforce the concrete substrate beams. An aluminum beam with different thickness is bonded to the thin GFRP layer so as to change the stiffness of the composite GFRP/aluminum substrate, resulting in different fracture mode mixities. The fracture toughness values of GFRP-concrete bonded interface under three different mode ratios are obtained. The proposed 4-AENF specimen and data reduction procedures for interface fracture toughness evaluation can be used to effectively characterize mixed mode and mode-II dominated fracture of hybrid material bonded interface.