3D printing often results in defects and non-uniformities due to inter-layer adhesion inconsistencies and sharp corners, demonstrating an even greater need to have designs that help make materials flexible and repeatedly deformable.Īuxetic material designs, such as the re-entrant honeycomb with sharp corners, are particularly susceptible to stress concentrations. However, many challenges remain that need to be solved for particular composite structures, materials, and printing techniques. Many of these strategies, including composites and complex architectures, have been demonstrated as proof-of-concept through 3D additive manufacturing ( Dimas et al., 2013), which promises to revolutionize structural properties via complex material designs.
#Abaqus 6.14 set uses crack#
Most strategies to improve fracture toughness are based on microstructural design, including addition of particles that redistribute stresses in a growing crack to prevent damage ( Launey and Ritchie, 2009) or hierarchical structuring ( Shin et al., 2016). Much like the energy efficient Venus flytrap, such structures can store elastic energy and release it on demand when appropriate stimuli are present.ĭelocalization of stress is key to designing tougher materials, including nanomaterials ( Chen et al., 2008), adhesives ( Ausiello et al., 2002), and structures capable of repeated cycling deformation ( Strnadel et al., 1995 Barthelat, 2007). Mixing unit cells with different hinge angles, we designed gradient Poisson's ratio materials, as well as ones with multiple stable states where elastic energy can be stored in latching structures, offering prospects for multi-functional designs. Locally tunable deformation and much higher elastic strains than the parent material would enable the next generation of compact, foldable and expandable structures. The dynamic modeling tools developed here could be used for complex 3D designs from any 3D printable material (metals, ceramics, and polymers). Using this model, we discovered and experimentally verified a critical angle of the s-hinge enabling bistable transformations between auxetic and normal materials. We also present a simple semi-analytical model of the deformations which is able to predict the mechanical properties of the structures within <5% error of experimental measurements from a few parameters such as dimensions and material properties. We demonstrate 3D printed structures with stress delocalization that enables macroscopic 30% cyclable elastic strains, far exceeding those intrinsic to the materials that constitute them (6%). These lattices feature locally tunable Poisson ratios (auxetic), large elastic deformations without fatigue, as well as mechanical switching between multistable states. They have inspired us to develop s-hinge shaped elastic unit cell elements from which new classes of architected modular 2D and 3D lattices can be printed or assembled. Truss designs based on hinged structures exist in nature and delocalize stress rather than concentrating it in small areas. There is a pressing need for lightweight lattice designs that are dynamic, as well as resistant to fatigue. This is especially true for auxetic material designs, such as the prototypical re-entrant honeycomb with sharp corners, which are particularly susceptible to stress concentrations. In 3D lattices, however, few structures allow high elastic compression and tunable deformation.
Truss structures distribute stress well and are commonly used to design lightweight materials for applications experiencing low strains. Stress distribution has led to the design of both tough and lightweight materials. 4School of Engineering and Materials Science, Queen Mary University of London, London, United Kingdom.