Three-point bending test of pantographic blocks: numerical and experimental investigation

International audienceThe equilibrium forms of pantographic blocks in a three-point bending test are investigated via both experiments and numerical simulations. In the computational part, the corresponding minimization problem is solved with a deformation energy derived by homogenization within a class of admissible solutions. To evaluate the numerical simulations, series of measurements have been carried out with a suitable experimental setup guided by the acquired theoretical knowledge. The observed experimental issues have been resolved to give a robust comparison between the numerical and experimental results. Promising agreement between theoretical predictions and experimental results is demonstrated for the planar deformation of pantographic blocks

Investigating the mechanical response of microscale pantographic structures fabricated by multiphoton lithography

International audienceThe design of micromechanical devices that can facilitate large but recoverable deformations requires a mechanical behavior that embosoms hyperelasticity. While multiphoton lithography is the epitome of microscale fabrication, the employed materials demonstrate a linear elastic response accompanied by limited ductility. In this study, we investigate how this hindrance can be circumvented through the design of microscale pantographic structures. Pantographs possess riveting hyperelastic response inherited by their structural design, providing exorbitant reversible deformations. To prove the utility of pantographs in microscale design, finite element analysis simulations are performed to unravel the behavior of the structure as a function of its geometrical parameters. In addition, to evaluate the microscale modeling, specimens are fabricated with multiphoton lithography in a push to pull up configuration to accomplish in situ SEM microindentation tensile testing due to compression. Our findings are adduced to expound how the pantographic structures can embrace hyperelastic response even at the microscale, elucidating their feasibility for structural members in micromechanical devices that require reversible large deformations

Investigating the mechanical response of microscale pantographic structures fabricated by multiphoton lithography

International audienceThe design of micromechanical devices that can facilitate large but recoverable deformations requires a mechanical behavior that embosoms hyperelasticity. While multiphoton lithography is the epitome of microscale fabrication, the employed materials demonstrate a linear elastic response accompanied by limited ductility. In this study, we investigate how this hindrance can be circumvented through the design of microscale pantographic structures. Pantographs possess riveting hyperelastic response inherited by their structural design, providing exorbitant reversible deformations. To prove the utility of pantographs in microscale design, finite element analysis simulations are performed to unravel the behavior of the structure as a function of its geometrical parameters. In addition, to evaluate the microscale modeling, specimens are fabricated with multiphoton lithography in a push to pull up configuration to accomplish in situ SEM microindentation tensile testing due to compression. Our findings are adduced to expound how the pantographic structures can embrace hyperelastic response even at the microscale, elucidating their feasibility for structural members in micromechanical devices that require reversible large deformations

An isogeometric FE-BE method and experimental investigation for the hydroelastic analysis of the horizontal circular cylindrical shell partially filled with fluid

In this study, the dynamic characteristics (i.e. natural frequencies and associ­ated mode shapes) of a partially filled horizontal cylindrical shell are investi­gated experimentally and by an isogeometric finite element-boundary element method. The proposed numerical procedure is divided into two parts. In the first part, the dynamic characteristics of the cylindrical shell under in-vacuo conditions are obtained by the isogeometric finite element method (IGAFEM) based on a linear Kirchhoff-Love shell formulation. In the second part, the fluid­structure interaction effects are calculated in terms of generalized added mass coefficients by using the isogeometric boundary element method (IGABEM), assuming that the structure vibrates in its in-vacuo principle mode shapes. By adopting the linear hydroelasticity theory, it is assumed that the fluid flow is ideal, i.e., an incompressible flow and inviscid fluid. In order to show the versa­tility of the numerical method, the results are compared with those obtained by the conducted experiments. Relevant numerical challenges in the hydroelastic vibration analysis are highlighted and it is shown that the numerical predictions and experimental results are in good agreement. <br/

Investigating infill density and pattern effects in additive manufacturing by characterizing metamaterials along the strain-gradient theory

Infill density used in additive manufacturing incorporates a structural response change in the structure. Infill pattern creates a microstructure that affects the mechanical performance as well. Whenever the length ratio of microstructure to geometry converges to one, metamaterials emerge and the strain-gradient theory is an adequate model to predict metamaterials response. All metamaterial parameters are determined by an asymptotic homogenization, and we investigate the effects of infill density and pattern on these parameters. In order to illuminate the role of infill characteristics on the strain-gradient parameters, an in-depth numerical investigation is presented for one, widely used case in three-dimensional (3D) printers, rectangular grid

Identification and validation of constitutive parameters of a Hencky-type discrete model via experiments on millimetric pantographic unit cells

International audiencePantographic metamaterial design benefits from model identification procedures starting from what can be considered as the elementary unit cell of larger pantographic structures. Results from a tensile experiment and digital image correlation are utilized to identify the constitutive parameters of a discrete Hencky-type model for a millimetric pantographic cell. In the performed calibration, two different cost functions are formulated. First, the cost function is based upon measured resultant forces on the specimen boundaries. Then, the second cost function is based upon the measured pivot displacements in addition to reaction forces. The second cost functions thus exploits the pivot kinematics, which is a key feature of the deformation of pantographic structures. The identified model is further validated by predicting the reaction forces and pivot displacements of the same specimen subjected to compression. It is shown that the identification with the cost function incorporating pivot displacements is superior. It is also noted that the calibrated parameters deviate considerably from their initial guess derived from the linear Saint Venant problem, thereby indicating microscale nonlinear affects in otherwise linear reaction force-prescribed displacement responses at the macroscale