An exact solution for the determination of the mode mixture in the mixed-mode bending delamination test

Mixed-mode delamination tests of composite laminates are usually carried out using the mixed-mode bending test (MMB) which was recently standardised by ASTM. The mode mixture is generally determined through the distance of the lever arm in the test rig. However, the determination of the lever arm distance for a desired mode mixture is achieved through approximate expressions or through the iterative solution of a complex equation. In the present study, an exact solution for the determination of this lever arm distance is proposed. The proposed expression is compared to the two expressions included in the ASTM standard for the determination of the mode mixture in the MMB test. It is concluded that the proposed solution determines the distance of the lever arm with better accuracy besides being formally simpler.