PSI - Issue 75

Aijia Li et al. / Procedia Structural Integrity 75 (2025) 318–333 Aijia Li, Christian Garnier,, Marie-Laetitia Pastor, Xiaojing Gong, Clément Keller/ Structural Integrity Procedia (2025)

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Fig. 12. thermodynamic responses of the cruciform specimen in the validation test

Conclusion In this work, an optimized specimen design for two common multidirectional composites (cross-ply-[(0/90) 6 ] s and quasi-isotropic-[(0/45/90/-45) 3 ] s ) destined to tension-tension biaxial fatigue loading was proposed by considering material failure, temperature measurement, and manufacturing. The numerical simulation using the finite element method was performed in the specimen design and validation, and a feasible manufacturing approach was developed to make the specimen of good quality and at a reasonable cost. According to the results, the following conclusions can be summarized: • For the basic specimen geometry, the cruciform shape is suitable as it allows adjusting loads in two axes, and a reduced area for the gauge region can ensure a continuous stress and temperature field, compared with a hole. The stress concentration problems on the transition cannot be completely eliminated, but can be relaxed by utilizing a single circular transition and extending its radius. • Concerning the dimensions of the specimens , it would be better to improve the transition’s radius and select a middle size of the reduced area to achieve an ideal failure location and uniform stress field. • To improve the efficiency, the simulation for specimen design can begin with a simplified model for initial design, and then be progressively developed to acquire the specimen ’ s dimensions. • The proposed specimen design is suitable for two stacking sequences of multidirectional composite specimens, and has the advantage of temperature and displacement observation. In the future, more validation tests will be conducted to verify the availability of other layups.