Assessment of Evaluation Methods for the Mixed-Mode Bending Test

Abstract

The evaluation procedure for the mixed mode bend (MMB) delamination test is assessed with focus on analytically equivalent evaluation models, expressed in load-displacement or load-only parameters. In particular, the assessment concerns the sensitivity of the interlaminar toughness to the test rig forces as well as material and geometrical properties of the specimen. For a typical example, neglect of test rig forces causes a 10% relative error in the calculated mixed mode ratio when using methods based on load only. When all additional forces were considered, both evaluation methods produced almost identical results. However, evaluation based on load only is sensitive to variations in specimen flexural modulus and dimensions and had a larger scatter. The application of crack length corrections for calculating the Mode I component is discussed in detail. The findings of the study are summarized in recommendations for the MMB test procedure and its subsequent evaluation.