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Additive manufacturing is widely used to fabricate metamaterials. The mechanical properties of these are tailored by modifying topological parameters to meet desired performance. Here, an auxetic metamaterial composed of arc-shape elements is presented. The directional dependency of the apparent stiffness was characterized through finite element analysis and tensile and compressive tests on additively manufactured samples with fused filament fabrication in thermoplastic polyurethane. Poisson's ratio was measured with computational vision. The effective Young's modulus resulted with a nonlinear relation to the wall thickness. The orientation sensibility exposed the relevance of rotational symmetry in a lattice architected metamaterial. [ABSTRACT FROM AUTHOR]

The use of curved layers in fused filament fabrication could lead to various advantages in surface finishing and mechanical properties. Here, the influence of three different structural and manufacturing parameters (volume fraction, raster arrangement, and the use of curved or planar layers) on the mechanical properties of lattice structures under three-point bending is studied. Two different raster arrangements were considered, i.e., those with rasters at planes parallel to the principal axes of the samples and those diagonally arranged, all at four different volume fractions. All different samples were additively manufactured using planar and curved layers. Samples were further dimensionally inspected to refine the computational models before their analysis via finite element simulations. The linear elastic region of the load-displacement curves was further analyzed numerically via finite element models. Predictions with finite element models resulted in good agreement with errors below 10%. Samples with diagonal rasters were 70% softer than those parallel to the principal axes. [ABSTRACT FROM AUTHOR]

The elastic response of arc structures fabricated using curved-layered fused deposition modeling was studied using finite element method (FEM). The influence of structural parameters, such as subtending angle, overlap between layers and relative density on the mechanical response of such structures was studied. The results obtained showed high influence of the overlap between layers. The FEM model predicted a range in which the stiffness of such structures can lie. This was compared with experimental results, showing good agreement. The samples were further characterized microstructurally, revealing more defects for higher values of lattice porosity, affecting the structural properties. [ABSTRACT FROM AUTHOR]

Metamaterials and lightweight structures are widely used in various engineering applications and additive manufacturing technologies have enhanced their potential. Curved elements have been increasingly used in the design of planar mechanical metamaterials or honeycombs. A honeycomb cellular structure topology with cell walls parametrized using cubic Bézier curves is proposed and analyzed here. The effective Young's modulus of the Bézier-based honeycomb is characterized semi-analytically using Castigliano's second theorem. Semi-analytical estimations of the effective Young's modulus were contrasted to those obtained with numerical finite element models and measured on additively manufactured samples. By considering the relative influence of bending, axial, and shear loads, the deformation mechanism of the honeycomb can be predicted and explained in terms of the load orientation, which depends on the definition of the Bézier curve. A large region achievable by tailoring the design parameters of the curve is presented in the so-called Ashby maps and compared to other existing topologies. The methodology presented here enables designers to propose topologies with a customized effective stiffness, expanding the design space for honeycombs in various engineering applications. • The effective Young's modulus of Bézier-based honeycombs is obtained semi-analytically using Castigliano's second theorem. • The contribution of bending, axial and shear loads in the deformation of Bézier-based honeycombs is quantified. • The role of curvature of the constituent elements on stiffness is quantified by means of energy approaches. • Analytical estimation of the effective Young's modulus agrees with finite element simulations and compressive mechanical tests. [ABSTRACT FROM AUTHOR]

The design of mechanical metamaterials often uses lattice arrangements being benefited from the increase in Additive Manufacturing technologies available. Such design freedom allows the fabrication of lattice arrangements with complex curved geometries. Here we propose a whole family of novel lattice matematerials parametrized using cubic Bézier curves. The methodology presented permits the generation of unit cells with different degrees of curvature based on the location of the Bézier control points along a spiral. The apparent stiffness of these structures was characterized using finite element analysis and compression tests on additively manufactured samples using stereolithography. The mechanical properties of spiral based cubic Bézier metamaterials were related to the location of the control points, curvature, etc. It was found that the apparent stiffness decreases proportionally to the cubic root of the distance between the control point and the predefined origin of the coordinate system. Due to symmetry conditions, the slope continuity in the curves conforming the unit cells is fulfilled and the origin of the coordinate system used coincides with the center of the unit cells. The procedure presented for the synthesis of metamaterials enables the generation of structures with customized mechanical properties by adjusting the geometry of the unit cells. Unlabelled Image • A novel method for the synthesis of spiral-based cubic Bézier metamaterials is presented. • Apparent stiffness was characterized via additively manufactured samples and computational simulations. • Apparent Young's modulus is related to the mathematical parametrization of the curves conforming the structures. • The synthesis method allows the control of the form of the stress-strain curves of the metamaterials. • Apparent stiffness decreases proportionally to the cubic root of the distance from the control point to the unit cell center. [ABSTRACT FROM AUTHOR]

The compliant version of the 3-RRR (R - revolute joint) spherical parallel mechanism known as "Agile-Eye" is presented. The kinetostatic analysis of this Compliant Spherical Parallel Mechanism (CSPM) is conducted using the Compliance Matrix Method (CMM) evaluating two different types of Rotational Compliant Joints (RCJs) and with three inputs. These independent inputs could be forces or displacements. Expressions that relate the input forces/displacements with the displacement of the moving platform are obtained from the kinetostatic analysis. These expressions are used to obtain the required inputs to perform a rotational trajectory of the moving platform; parasitic displacements are computed during this process. Analytical results are validated through Finite Element Analysis (FEA). Additionally, the CSPM geometric parameters-parasitic displacements relation is characterized. Those parameters resulting with lower parasitic displacements are determined. Finally, expressions from the kinetostatic analysis are corroborated experimentally using input displacements in a manufactured prototype with parameters selected to have reduced parasitic displacements. Results from the FEA-simulations and experimental tests demonstrated that the expressions obtained from the kinetostatic analysis can accurately describe the force–displacement relations of the proposed CSPM. • The compliant version of the spherical parallel mechanism "agile-eye" is proposed. • Compliance matrix method is formulated with inputs in terms of displacements. • The mechanism geometric parameters-parasitic displacements relation is characterized. • Experimental validation is performed in an additively manufactured prototype. [ABSTRACT FROM AUTHOR]