1,721,007 research outputs found
Cyclic response of 3D printed metamaterials with soft cellular architecture: The interplay between as-built defects, material and geometric non-linearity
Full text linkThe paper investigates the cyclic response of soft cellular materials undergoing repeated local instabilities. Our focus is mainly on the coupling between material non-linearities, geometric non-linearity as well as defects induced by 3D printing. Two paradigmatic lattices (triangular and hexagonal), each with its own distinct deformation mode and defect sensitivity, are examined, and the emergence of as-built material and geometric defects in the form of microporosity, strut thickness reduction, and nodal dispersion is studied via computed tomography and optical analyses. Experiments are carried out on the base material and lattice specimens for given cycling strains and cycle ratios. Numerical models are developed to understand the individual role of the main constitutive aspects of the base material, e.g. damage, creep, and visco-elasticity, as well as to assess the role of defects in each architecture. The results show that the activation of local buckling combined with the engagement of material non-linearities has multiple outcomes. It leads to local storage of inelastic strain, which in turn perturbs the lattice geometry after the second cycle and severely impacts the subsequent response, e.g. softening; it reduces the tangent modulus at zero strain; and it also decreases the maximum and minimum cyclic stresses. The detriment is further fueled by geometric deviations caused by 3D printing. Furthermore, a theoretical model is presented to obtain stress bound estimates of the stabilized response, hence offering guidelines for the design of 3D printed soft metamaterials under cycling loading. The paper concludes with a systematic discussion on the coupled role of non-linearities (material and geometry) and defects, and on the accuracy of the numerical and theoretical models herein presented
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No full textResponse of an aluminium Schwarz triply periodic minimal surface lattice structure under constant amplitude and random fatigue
Full text linkThis paper presents an investigation about fatigue behaviour of an aluminium triply periodic minimal surface lattice structures, printed with Selective Laser Melting. Aim of the paper is to experimentally characterize constant and variable amplitude fatigue strength and to assess if current methodologies for predicting random fatigue strength of solid materials can be extended also to lattice structures, in a homogenized setting. The investigation is complemented by a detailed analysis of samples fracture surface, corroborated by numerical analyses, and a comprehensive discussion on the evolution of the damage observed in the experiments
Multiaxial static strength of a 3D printed metallic lattice structure exhibiting brittle behavior
Full text linkThis paper focuses on numerical the prediction of multiaxial static strength of lattice structures. We analyze a body-centered cubic cell printed with Selective Laser Melting in AlSi10Mg aluminum alloy. Parent material is experimentally characterized, and the Gurson-Tveergard-Needleman (GTN) damage model is calibrated to predict failure in numerical simulations. The GTN model is used to predict failure of the lattice structures exhibiting brittle localized fracture, and it is validated through static tests. The results of experimental tension/compression monotonic tests on lattice samples are compared with the results of numerical simulations performed on as-built geometry reconstructed by X-ray computed tomography, showing a good correlation. Combining the damage model with computational micromechanics, multiaxial loading conditions are simulated to investigate the effective multiaxial strength of the lattice material. Yielding and failure loci are found by fitting a batch of points obtained by some multiaxial loading simulations. A formulation based on the criterion proposed by Tsai and Wu (1971) for anisotropic materials provides a good description of yielding and failure behavior under multiaxial load. Results are discussed, with a specific focus on the effect of as-built defects on multiaxial strength, by comparing the resistance domains of as-manufactured and as-designed lattices
A rare case of percutaneous exclusion of a huge aortic pseudo-aneurysm following aortic bio prosthetic endocarditis: key role of 3D echo-fluoro fusion imaging
No full textTranscatheter mitral valve replacement after transcatheter direct annuloplasty with Cardioband
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