Double cantilever indirect tension fracture testing of concrete

The Double Cantilever Beam (DCB) Mode I fracture testing has been widely used in fracture testing of especially fiber reinforced polymer composites and adhesive joints. Application of classical DCB testing to plain concrete or unreinforced ceramic specimens is not straightforward and cannot be carried out in direct separation mode as applied in such composite materials. Instead, in this study an indirect tension approach is proposed for testing concrete in Mode I fracture. Tests of notched geometrically similar DCB specimens made of normal and high strength concretes loaded eccentrically at the cantilever beam-column ends in compression have been carried out. The peak loads from these tests and their classical type II size effect analyses results are reported. The Microplane Model M7 is used to predict and verify the test results. To this end, the model is first calibrated independently of size effect test data using only the uniaxial compression tests. Next, the model M7 is used to predict the peak loads of tested specimens. Furthermore, to determine the errors involved in the size effect fracture parameters, the peak loads of virtual geometrically similar DCB specimens of appropriately chosen sizes were determined using the calibrated model. The same size effect analyses are performed on the predicted peak loads including those from the virtual specimens and the errors in the fracture parameters obtained from the classical size effect analyses of the peak loads obtained from the tests are determined.