Vibrational Microfeeding of Polymer and Metal Powders for Locally Graded Properties in Powder-Based Additive Manufacturing

Subject of this work is the contact mechanical properties and flowability of polymer and metal powders when they are dispensed on the surface of a powder bed for use in laser-based powder bed fusion in additive manufacturing. Generating local part properties in metal as well as polymer-based powder bed fusion processes is of high interest, so an approach is made to locally add additives by a vibrational microfeeding system for metal and polymer powders. To realize a controlled powder discharge, the behavior of additives, which are dropped on a surface and on a powder bed is analyzed. Influencing factors for mass flow of the powders will be excitation frequency, excitation amplitude and capillary diameter on the side of experimental setup as well as particle size distribution and physical properties on the material side.

Vibration Analysis of Piezoelectric Cantilever Beams with Bimodular Functionally-Graded Properties

Piezoelectric materials have been found to have many electromechanical applications in intelligent devices, generally in the form of the flexible cantilever element; thus, the analysis to the corresponding cantilever is of importance, especially when advanced mechanical properties of piezoelectric materials should be taken into account. In this study, the vibration problem of a piezoelectric cantilever beam with bimodular functionally-graded properties is solved via analytical and numerical methods. First, based on the equivalent modulus of elasticity, the analytical solution for vibration of the cantilever beam is easily derived. By the simplified mechanical model based on subarea in tension and compression, as well as on the layer-wise theory, the bimodular functionally-graded materials are numerically simulated; thus, the numerical solution of the problem studied is obtained. The comparison between the theoretical solution and numerical study is carried out, showing that the result is reliable. This study shows that the bimodular functionally-graded properties may change, to some extent, the dynamic response of the piezoelectric cantilever beam; however, the influence could be relatively small and unobvious.

Development of elastically graded titanium alloys for biomedical applications

Recent works have shown that the elastic mismatch observed at the bone / implant interface could be responsible for stress shielding issues causing bone resorption phenomena and potentially implant failures. In the present study, new advanced thermomechanical approaches leading to titanium alloys with graded elastic properties are proposed. The underlying philosophy and the whole methodology is detailed here, from the selection of candidates with large elastic variability to the creation of gradients, involving the identification of microstructure-properties relationships and the use of appropriate thermo-mechanical treatments. Applied on Ti-Nb-Zr alloys, these original routes enabled to get the following graded properties: elastic modulus from 85 to 65GPa over 400μm for TNZ alloy by surface deformation, and from 130 to 75GPa over 100μm for Ti-13-13 by preferential dissolution. These promising results thus validated the previously designed material-strategy-process combinations.

Imaging-based customization of lattice structures for biomedical applications

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Synovial joints can provide movement and articulation, however, with overuse, aging, and trauma, joint replacement surgeries may be needed. Commercially available joint reconstruction implants have undergone great improvement during the past decades. Nevertheless, existing solutions using available implant designs and materials have limitations that lead to potential failure, particularly with young active patients. Bone cement and stress shielding have been identified as the major reasons for premature artificial joint failures. A breakdown of the cement may happen and revision surgery may be needed because of the aseptic loosening. The stress shielding problem is caused by the significant mismatch of stiffness properties between the patient trabecular bones and metallic implant materials for joint replacement surgeries. This research introduces a novel method to develop customized lattice structures with graded properties according to the mechanical properties derived from clinical Computed Tomography (CT) scan of the bone. Various lattice design variables are being analyzed for their effects on mechanical performance and geometrical features needed for biological fixation and manufacturability. The introduced mathematical models and techniques in the proposed work facilitate generic direct digital design and manufacturing of effective customized lattice structures with graded properties for joint reconstruction applications.

Numerical Analysis on the Wrinkling Instability of a Stiff Film Adhering to an Elastic Substrate with a Graded Coating

The wrinkling instability of a stiff film adhering to a pre-strained inhomogeneous bi-layer substrate consisting of a homogeneous substrate and a graded coating is investigated in the present paper. The critical strain, wavelength and amplitude of the film/inhomogeneous substrate system are calculated numerically and analyzed comprehensively. Compared with the numerical result, a theoretical model is introduced to approximately predict the wrinkling responses of the system. The influence of various geometric and material parameters on the wrinkling behavior is mainly focused. The wrinkling responses are found to be highly related to the graded laws and the thickness of the inhomogeneous coating as well as the Poisson’s ratio. What is more, a proper choice of graded properties of a substrate can improve the wrinkling response of a film/substrate system. The present finding should be very meaningful to guide the design of various stretchable and flexible electronics.