Elasto-Plastic Mechanical Modeling of Fused Deposition 3D Printing Materials.

Fused deposition modeling (FDM) is one of the most common 3D printing technologies and is becoming a well-established production method. Short fiber-reinforced polymers represent a new class of printing materials that enhance the mechanical properties of final components, thus informing an interesting subject of analysis for this study. FDM-printed parts are characterized by a strong anisotropy, so their behavior should be analyzed accordingly. The authors proposed a modeling strategy based on a transversely isotropic behavior hypothesis, representing material behaviors associated with an elasticity matrix in relation to the elastic field and a combination of Hill's yield criterion and Voce's isotropic hardening law for the plastic field. Material properties of materials were experimentally identified through tensile tests on dog bone specimens printed with different orientations in space. The numerical model was then calibrated using the finite element software LS-DYNA and the optimization software LS-OPT. An agreement between numerical and experimental results showed the robustness of the modeling strategy proposed to describe the stress behaviors of printed materials until a maximum load is reached, while strain behaviors have yet to be correctly defined due to the difficulties associated with evaluating an equivalent deformation.

Highly-filled flowable composite in deep margin elevation: FEA study obtained from a microCT real model.

OBJECTIVES: To evaluate shear stress (SS) and normal pressure (NP) at the tooth-restoration interface of highly-filled flowable resin composite applied to deep margin elevation technique through FEM analysis generated by a microCT scan. METHODS: A reference maxillary molar with two class II cavities was prepared according to deep margin elevation protocol. A geometrical model was segmented from a micro-CT scan generating separate volumes of enamel, dentin and restorative materials. The 3D Finite Element (FE) model was subsequently built-up and an axial chewing load was simulated. Data concerning the tooth-restoration interface were analyzed in terms of SS and NP. Different materials and techniques were tested in order to evaluate the effects of the restorative material, the usage of a highly-filled flowable composite as liner and the substrate of the cervical area. RESULTS: Both SS and NP presented similar distribution, but showed significant differences between tested materials. Composites showed more homogeneous behavior in stress distribution compared to ceramic. The use of a highly-filled flowable composite as liner on the cervical margin significantly reduced SS and NP on the cavity floor and the cervical margin area. Lastly, stress distribution in the cavity floor area varied according to the cervical margin substrate: enamel showed a protective role in stress distribution. SIGNIFICANCE: Highly-filled flowable resin composites showed encouraging results when applied to deep margin elevation from an interfacial mechanical point of view. Further studies are needed to validate these data and to better define the role of cervical enamel in stress distribution.

Numerical Simulations of Laser-Induced Shock Experiments on Graphite.

The development of particle accelerators with ever increasing energies is raising the standards of the structures which could interact with the particle beams. These structures could be subjected to strong shockwaves in accidental scenarios. In order to test materials in such conditions, one of the most promising techniques is the impact with high-power lasers. In view of the setting up of future experimental campaigns within the Petawatt High-Energy Laser for Heavy Ion Experiments (PHELIX), the present work aims at the development of a numerical approach for the simulation of graphite impacted by laser beams. In particular, the focus is on the spallation damage caused by shockwave reflection: a sufficiently intense laser beam could ablate the matter until plasma conditions, hence producing a shockwave which could travel inside the material and reach a free surface. A numerical model to properly describe the spall fragmentation of graphite has been calibrated on the basis of literature-available experimental data. The numerical approach is a 'two-step' procedure: the first step is the definition of the laser-matter interaction and the second one concerns the description of the shockwave evolution into matter. The simulations satisfactorily reproduce the dynamic response of graphite impacted by two different laser sources with various intensities, despite the difficulties of characterising a phenomenon which is extremely fast and chaotic.

Numerical Simulations of Components Produced by Fused Deposition 3D Printing.

Three-dimensional printing technology using fused deposition modeling processes is becoming more and more widespread thanks to the improvements in the mechanical properties of materials with the addition of short fibers into the polymeric filaments. The final mechanical properties of the printed components depend, not only on the properties of the filament, but also on several printing parameters. The main purpose of this study was the development of a tool for designers to predict the real mechanical properties of printed components by performing finite element analyses. Two different materials (nylon reinforced with glass or carbon fibers) were investigated. The experimental identification of the elastic material model parameters was performed by testing printed fully filled dog bone specimens in two different directions. The obtained parameters were used in numerical analyses to predict the mechanical response of simple structures. Blocks of 20 mm × 20 mm × 160 mm were printed in four different percentages of a triangular infill pattern. Experimental and numerical four-point bending tests were performed, and the results were compared in terms of load versus curvature. The analysis of the results demonstrated that the purely elastic transversely isotropic material model is adequate for predicting behavior, at least before nonlinearities occur.