Metamaterials mapped lightweight structures by principal stress lines and topology optimization: Methodology, additive manufacturing, ductile failure and tests

Abstract

In lightweight engineering, mechanical metamaterials (MMs) are suitable for additive manufacturing (AM) due to their geometry complexity. However, it is inevitable to bring about mechanical deviation and local yield for MMs infilled lightweight structures. In the current work, MMs mapped structures, named as MMs-TO-PSLs, are proposed. The design domain is divided into core-region, intermediate-region, and solid-region. Core-regions derived from topology optimization (TO) are mapped with MMs, of which the [100] orientations are aligned with the normal directions of principal stress lines (PSLs). The intermediate-regions are infilled with ribbons according to PSLs. The solid regions are allocated to stress concentrated areas. Finally, near isotropic mechanical response is achieved in core-region from anisotropic MMs, and the serious local deformation is eased. To validate such approach, the mapping strategy is carried out on a beam subjected to three-point bending. Metallic MMs-TO-PSLs and MMs infilled uniform lightweight structure are fabricated by selective laser melting (SLM). Elastoplastic simulations with ductile failure model are proposed to investigate the strengthen mechanism of MMs-TO-PSLs. Experimental and numerical results confirmed the ultimate strength of MMs-TO-PSLs can be 40% larger than conventional MMs infilled uniform structures.

Keywords

• Metamaterials
• Selective laser melting
• Mapping strategy
• Topology optimization
• Principal stress lines