Improved Mixed-Mode Bending Test Apparatus through Analytical Modeling and Finite-Element Optimization for Improved Characterization

Abstract

The compliance of the mixed-mode bending (MMB) test fixtures can influence the interlaminar fracture toughness measurements for different mixed-mode ratios in an unpredictable way. The purpose of this article is to introduce the improved mixed-mode bending (IMMB) apparatus with slight modifications to the current MMB apparatus and universally recognized by current standards. The MMB apparatus is used to measure any Mode I to Mode II strain energy release rate (SERR) ratio from 0 to approximately 5. The original MMB components were investigated using a finite-element optimization algorithm and an analytical model for exploring the relationship between the component’s stiffnesses and MMB compliance. Two IMMB designs are presented. The first design addresses MMB’s compliance by modifying the dimensions of the most impactful components. The second design introduces new components in addition to dimensional changes to maximally increase MMB stiffness. The new designs enhance the MMB apparatus’s stiffness by 27% and 87%, respectively.