The Mixed Mode Bending (MMB) test is a standardized material characterization technique used to determine the strain energy release rate and fracture toughness of layered composite materials under a range of combined mode I and mode II loading conditions. The compliance of any fixture’s internal components lessens the material characterization accuracy by introducing error into the displacement measurement. Correcting for system compliance often involves complex post-processing of data. To reduce error in the test and improve material characterization quality, the authors have redesigned the MMB test fixture for minimal compliance. An analytical model of the fixture was developed to isolate the components most responsible for system compliance. The components were modified, guided by a finite element optimization algorithm, to reduce deformation. The redesigned features reinforce the fixture without creating nonlinearity in the system or changing the test’s basic mechanisms that allow for variable mixed-mode ratios. The new MMB fixture will improve the accuracy of the experiment and reduce the complexity of data post-processing, leading to a safer crack-resistant design.

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