Abstract Biological composites can overcome the conflict between strength and toughness to achieve unprecedented mechanical properties in engineering materials. The suture joint, as a kind of heterogeneous architecture widely existing in biological tissues, is crucial to connect dissimilar components and to attain a tradeoff of all-sided functional performances. Therefore, the suture joints have attracted many researchers to theoretically investigate their mechanical response. However, most of the previous models focus on the sutural interface between two chemically similar stiff phases with (or without) a thin adhesive layer, which are under the framework of linear elasticity and small deformation. Here, a general model based on the finite deformation framework is proposed to explore the stiffness and toughness of chemically dissimilar suture joints connecting soft and stiff phases. Uniaxial tension tests are conducted to investigate the tensile response of the suture joints, and finite element simulations are implemented to explore the underlying mechanisms, considering both material nonlinearity and cohesive properties of the interface. Two failure modes are quantitively captured by our model. The stored elastic energy in the soft phase competes with the energy dissipation due to the interface debonding, which controls the transition among different failure modes. The toughness of the suture joints depends on not only the intrinsic strengths of the constituent materials and their cohesive strength, but also the interfacial geometry. This work provides the structure-property relationships of the soft/stiff suture joints and gives a foundational guidance of mechanical design towards high-performance bioinspired composites.
Abstract The stiff/highly stretchable polymer hybrids have a broad field of applications including robotics, electronic devices, and biomedical devices. However, poor interfacial bonding between chemically dissimilar polymers makes it difficult to achieve reliable structural performance. Building a robust interface within the polymer hybrids is one of the most important concerns. Here, the structured interface with different geometrical waveform patterns, including zigzag, buzzsaw, and strip shape is investigated for their effectiveness in improving mechanical properties of the interface. The enhancement effects of different geometries of the structured interfaces on both the tensile strength and tensile toughness are characterized by uniaxial tension tests. The finite element analysis simulations of the interface are implemented to investigate the enhancement mechanism, considering both the material nonlinearity under large deformation and the geometric nonlinearity derived from the high asymmetry in the interfacial configuration. Both the interfacial geometry and the intrinsic adhesive property of materials influence the load transfer mechanism at the interface and consequently determine the failure modes. Optimal geometrical designs of the interfacial geometries are proposed to achieve the best interfacial enhancement. The present study may provide guidance for designing the interfacial geometries in the polymer hybrids.
Digital light processing (DLP) three-dimensional (3D) printing technology has advantages of fast printing speed and high printing precision. It can print objects with small and complex geometrical features and has been widely used in jewelry manufacturing and dentistry. In DLP printing, it is common to use post-treatment with UV light irradiation to improve the final mechanical properties. However, it was found that the UV post-curing process can lead to shape distortion and thus reduction of dimension accuracy. In this paper, we combined photopolymerization reaction kinetics and Euler-Bernoulli beam theory to study UV post-curing induced shape distortion of thin structures prepared by DLP 3D printing. Experiments were conducted to characterize the evolution of mechanical behavior of printed samples during the post-printing process, which was correlated to printing parameters (printing time of single-layer, height of single-layer and printing UV intensity), post-curing UV light intensity and the thickness of the strip. Moreover, post-curing induced distortion was used for the fabrication of 3D structures.
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