In-Plane Stiffness of Additively Manufactured Hierarchical Honeycomb Metamaterials with Defects

Cellular metamaterials are of interest for many current engineering applications. The incorporation of hierarchy to cellular metamaterials enhances the properties and introduces novel tailorable metamaterials. For many complex cellular metamaterials, the only realistic manufacturing process is additive manufacturing (AM). The use of AM to manufacture large structures may lead to several types of manufacturing defects, such as imperfect cell walls, irregular thickness, flawed joints, partially missing layers, and irregular elastic-plastic behavior due to toolpath. It is important to understand the effect of defects on the overall performance of the structures to determine if the manufacturing defect(s) are significant enough to abort and restart the manufacturing process or whether the material can still be used in its nonperfect state. In this study, the performance of hierarchical honeycomb metamaterials with defects has been investigated through simulations and experiments, and hierarchical honeycombs were shown to demonstrate more sensitivity to missing cell walls than regular honeycombs. On average, the axial elastic modulus decreased by 45% with 5.5% missing cell walls for regular honeycombs, 60% with 4% missing cell walls for first-order hierarchical honeycomb and 95% with 4% missing cell walls for second-order hierarchical honeycomb. The transverse elastic modulus decreased by about 45% with more than 5.5% missing cell walls for regular honeycomb, about 75% with 4% missing cell walls for first-order and more than 95% with 4% missing cell walls for second-order hierarchical honeycomb.