No abstract

No abstract

During additive manufacturing processes, part geometry is approximated because the layer by layer deposition procedure can yield stair-step irregularities between layers. Moreover, since finite-sized filaments are deposited in the material extrusion process, air gaps are generated among the filaments. These lead to geometrical errors in additively manufacturing parts and degradation of the parts' mechanical properties, such as elastic modulus and strength, based on slicing and material deposition strategies. Geometric errors that arise during the manufacturing procedure have a particularly significant impact on fabricated lattice structures, which consist of a network of small struts, because they have large bounding surfaces that must be approximated during fabrication. In addition, since the struts in lattice structures are generally small, voids among filaments affect the structures' mechanical properties significantly even if they are small. In order to avoid property degradation it is necessary to consider these phenomena during lattice structure design. In this paper, an as-fabricated modeling approach for a material extrusion process is proposed, for use in modeling and assessing the effects of geometric degradation on additively fabricated lattice structures. The approach implements a voxel based modeling technique to consider stair steps and deposition paths at each layer. Using the proposed method, numerical models for evaluating mechanical properties are generated. Estimated mechanical properties using the as-fabricated voxel modeling approach are compared with experimental results. The effects of the stair step and deposition path phenomena on mechanical properties are quantified and demonstrate good correspondence with experiments, particularly for elastic modulus.

Many engineering applications utilize periodic lattice structures to take advantage of their favorable and tailorable mechanical properties. However, manufacturing the structures and evaluating their mechanical properties are still challenging. Additive manufacturing (AM) processes offer an alternative method to fabricate periodic lattice structures but the processes only approximate bounding part surfaces. Periodic lattice structures generally have two important geometrical characteristics, large bounding surfaces, and a large number of joints. Since geometric approximation errors on large bounding surfaces critically affect mechanical properties of the structures, designers and engineers should incorporate this degradation into mechanical property estimation procedures. In addition, the effects of joints should be analyzed in the estimation process, because joints reduce struts lengths, and as a result, they add stiffness to lattice structures. This paper presents a new homogenization approach to estimate mechanical properties of additively manufactured periodic lattice structures that is based on semirigid joint frame elements, and it takes into account effects of geometric approximation errors and joint stiffening. Effective structural parameters of a semirigid joint frame element are calculated from an as-fabricated voxel model to incorporate the geometric approximation errors. The semirigid joint frame element is integrated into a discrete homogenization process to evaluate joint stiffening effects. This paper reports results of parametric studies that investigate effects of AM process and joint properties on periodic lattice structures fabricated by material extrusion. This paper also compares estimates from the proposed approach and conventional homogenization approaches with test results. The comparison shows that the proposed method provides estimates that are more accurate.