Cellular materials, in particular metal or polymer foams and beam lattices, are characterized by a complex architecture where the material is concentrated in slender struts. This study is concerned with the construction of numerically efficient sample-specific digital twin for the analysis and characterization of the mechanical behavior of such meta-materials. A method to build an explicit, light, and analysis-suitable isogeometric beam model directly from digital images is proposed. More precisely, as a main contribution, the virtual image correlation method is extended to the case of multiple interconnected beams with varying cross-sections. Special care is also given to the initialization for better efficiency and robustness. Synthetic and real examples of increasing complexity, that is, curved beams, lattices, and foams, are presented to account for the performance of the developed workflow from digital images to an isogeometric twin for mechanical modeling and simulation.
K E Y W O R D Scellular materials, digital twin, image-based models, isogeometric analysis, lattices
INTRODUCTIONCellular materials are currently gathering an important momentum in both the scientific and industrial communities. 1 They rely upon a simple idea: mimicking nature, such as bones and wood, which allows to achieve, in particular, unprecedented stiffness-to-weight ratios. 2 In practice, cellular materials are characterized by a complex micro-architecture. Most of times, the material is concentrated in small struts connected in different ways, at an intermediate scale between the constituents and the structure. Originally consisting of foams, 3,4 that is, exhibiting a random distribution of cells, the advent of additive manufacturing (AM) now pushes these materials to a new stage: it becomes possible to produce so-called lattices where well-designed unit-cells are periodically (or quasi-periodically 5 ) repeated all over a macro shape to obtain exceptional specific performances. Among others, lattices can be made highly stretchable, 6 auxetic, 7 and multi-functional, and therefore, besides being attractive for lightweight components, they appear of crucial interest for energy absorption, thermal management, design of medical implants, to name a few. [8][9][10][11] However, due to the coexistence of two very different scales, the prediction of the mechanical behavior of such materials remains an issue, especially in non-linear regimes. [12][13][14][15] Their global response is actually intimately related to the local architecture, which may not be perfectly known a priori, either because of the random aspect in foams, or because of the strut-level process-induced defects and uncertainties in lattices. [16][17][18] In view of characterizing the mechanical behavior of such materials, it thus appears of paramount importance to build a digital mechanical twin for each individual tested