扣鎖結構是自然界中廣泛適應的生物機制，見於各種生物如龜殼、犰狳胄甲、甲蟲鞘翅及海膽骨骼的舌槽接合，提供適當的強度、韌性和靈活性。其中，鐵鎧甲蟲的鞘翅中的扣鎖結構表現出卓越的抗壓和抗穿刺能力，甚至能夠承受偶爾的汽車輾壓。相比之下，菊石殼中觀察到的多階層結構，隨著複雜性的增加，顯著提高了剛性，突顯了多階層結構對機械性能的重大影響。
受這些自然結構的啟發，本研究旨在設計一種具有優異機械性能和可重複使用性的全新扣鎖結構。選擇橢圓形作為扣鎖結構的基本幾何形狀，通過調整相對位置和在表面添加固定半徑的半圓，創建了θ = 15°、20°、25° 和30° 的扣鎖葉片，形成具有層次結構的獨特扣鎖葉片設計。這些三維模型使用PolyJet積層製造技術印製，該技術允許混合2至3種材料，創建具有分級機械性能的材料，並進行反覆的單軸準靜態拉伸和壓縮測試，以評估扣鎖葉片的可重用性和機械性能。此外，還進行了有限元分析（FEA），模擬多階層扣鎖陣列在拉伸和壓縮下的應力分佈，深入分析應力分佈對機械性能的影響。
本研究選擇了四種具有不同機械性能的材料，其拉伸強度範圍為7 MPa到48 MPa，並證實θ = 15°、20° 和25° 的機械扣鎖縫合設計可進行反覆的扣鎖行為，結果呈現出較高的壓縮功而不是拉伸功。為提高扣鎖過程的穩定性和便捷性，我們在葉片之間引入了間隙。結果顯示，隨著間隙長度的增加，壓縮功和拉伸功之間的差異顯著減少，從70×10⁻³ J降至2×10⁻³ J。此外，大多數機械扣鎖縫合線仍表現出較高的壓縮功而不是拉伸功，但具有淺階層結構的θ = 20° 葉片的樣品是例外，其拉伸功（36×10⁻³ J）高於壓縮功（20×10⁻³ J），這一現象得到了基於FEA的模擬結果的證實。
這種創新的扣鎖單元不僅能通過調整參數預測機械性能，還能使韌性較低的材料表現出反覆的扣鎖行為。因此，它在航空、航天、汽車製造、建築工程、軍事和醫療等各領域中具有重要的應用潛力。通過利用來自生物啟發和先進製造技術的原理，本研究有助於開發具有量身定制機械性能的堅固、可重用的扣鎖結構，適用於各種情境的應用。

The interlocking suture structure is a prevalent biological strategy observed in various organisms, such as the turtle shells and armadillo osteoderms, the tongue-like groove joints in beetle elytra, and the skeletons of sea urchins. These structures provide an optimal combination of strength, toughness, and flexibility. Particularly notable is the interlocking suture structure in the elytra of the Diabolical Ironclad Beetle (DIB), which demonstrates remarkable resistance to crushing and piercing forces, even surviving occasional rolling by automobiles. In contrast, the hierarchical structure observed in ammonite shells, characterized by increasing complexity, significantly enhances rigidity, underscoring the profound impact of hierarchical configurations on mechanical properties.
Inspired by these natural structures, this study aims to design a novel interlocking structure that boasts exceptional mechanical properties and reusability. The basic geometric shape selected for the interlocking structure is an ellipse, with interlocking blades created with angles of θ = 15°, 20°, 25°, and 30°. These blades were formed by adjusting their relative positions and incorporating fixed-radius semicircles on their surfaces, resulting in a unique interlocking blade design with a hierarchical structure. The three-dimensional models were fabricated using PolyJet additive manufacturing technology, which facilitates the mixing of 2 to 3 materials to create materials with graded mechanical properties. These models were then subjected to repeated uniaxial quasi-static tension and compression tests to evaluate their reusability and mechanical performance. Furthermore, finite element analysis (FEA) was employed to simulate the stress distribution in the hierarchical interlock array under tension and compression, allowing for an in-depth analysis of how stress distribution influences mechanical properties.
Four materials with varying mechanical properties, exhibiting tensile strengths ranging from 7 MPa to 48 MPa, were selected for this study. It was confirmed that mechanical interlocking sutures with θ = 15°, 20°, and 25° can perform repetitive interlocking behavior and exhibit higher compressive work compared to tensile work. To enhance the stability and ease of the interlocking process, gaps were introduced between the blades. The results indicated that as the gap length increased, the difference between compressive work and tensile work decreased significantly, from 70×10⁻³ J to 2×10⁻³ J. Additionally, most mechanical interlocking sutures continued to demonstrate higher compressive work than tensile work, with the notable exception of the sample with θ = 20° blades featuring shallow hierarchical structures. This sample exhibited higher tensile work (36×10⁻³ J) compared to compressive work (20×10⁻³ J), a phenomenon corroborated by FEA-based simulation results.
This innovative interlocking unit not only facilitates the prediction of mechanical properties through parameter adjustments but also enables materials with lower toughness to exhibit repeated interlocking behavior. Consequently, it holds significant potential for applications across a variety of fields, including aerospace, aviation, automotive manufacturing, construction engineering, military, and medical industries. By leveraging the principles derived from biological inspiration and advanced manufacturing techniques, this study contributes to the development of robust, reusable interlocking structures with tailored mechanical properties suitable for diverse and demanding applications.

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