A Novel Procedure for Prediction of Mixed Mode I/II in Fracture Toughness of Laminate Composites

Delamination is one of the important modes of failure in laminated composite materials. In this respect، the mixed mode I/II fracture is the most major mode of delamination incidence in laminated composite. In the present research، a relation between the fracture toughness of double cantilever beam (DCB) and asymmetric double cantilever beam (ADCB) specimens is presented. The DCB and ADCB samples are used for measuring the mode I and mixed mode I/II fracture toughness (G) of laminated composite materials، respectively. By considering the diversity of the stacking sequence of lay-ups، the test performance on all different types of lay-ups in order to measure the fracture toughness of laminated composites is a tedious، costly and time consuming task. The purpose of deriving this relation is to estimate the value of the strain energy release rate of laminated composite ADCB specimens by testing a unidirectional DCB. To develop this relationship، the geometry of DCB and ADCB specimens are considered to obtain fracture toughness of multi-directional laminate composites of ADCB samples with arbitrary ply sequence which may be used for design purposes. The procedure presented here reduces the calculation costs of the finite element modeling and its corresponding test significantly. The results obtained by this method are compared with those of experimental and numerical methods. It is shown that the fracture toughness of multi-directional lay-ups can be predicted by measuring the unidirectional ply with an error less than 10% demonstrating the accuracy of the procedure developed in the present research.