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Mixed Mode I/II Damage Initiation and Evolution in 3D-Printed Soft Interfacial Layer



Inspired by biological sutures in nature, biomimetic suture specimens with different waviness and material combination were designed and fabricated via multi-material 3D printing. The damage initiation and evolution of the material in the wavy suture layer is the key to determine the strength and failure mechanisms of the biomimetic sutures. Due to the complicated geometry, the suture layer is under a mixed mode I/II loading. To explore the influences of geometry and material combination on the damage initiation and evolution of the soft suture layer under mixed mode I/II loading, based on the concept of virtual internal bonds (VIB) theory, a hyperelastic softening constitutive model was developed and numerically implemented in ABAQUS via subroutine VUMAT. Mechanical experiments were performed on the 3D printed suture specimens, and two failure modes were observed: tooth breakage mode and interface failure mode. The failure mode transition was found to be jointly determined by the geometry of the suture layer and the material properties in it. It was found that when the tooth tip angle increases and/or the strength of the material in the interfacial layer decreases, the failure mode of the suture can transit from tooth breakage mode to interfacial material failure mode. The proposed hyperelastic softening model could accurately predict the damage initiation and evolution in the interfacial layer without pre-assuming any failure criteria.

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