An investigation into the depth and time dependent behavior of UV cured 3D ink jet printed objects
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An ultra-violet (UV) curable ink jet 3D printed material was characterized by an inverse finite element modeling (IFEM) technique employing a nonlinear viscoelastic–viscoplastic (NVEVP) material constitutive model; this methodology was compared directly with nanoindentation tests. The printed UV cured ink jet material properties were found to be z-depth dependent owing to the sequential layer-by-layer deposition approach. With further post-UV curing, the z-depth dependence was weakened but properties at all depths were influenced by the duration of UV exposure, indicating that none of the materials within the samples had reached full cure during the 3D printing process. Effects due to the proximity of an indentation to the 3D printed material material-sample fixing interface, and the different mounting material, in a test sample were examined by direct 3D finite element simulation and shown to be insignificant for experiments performed at a distance greater than 20 lm from the interface.
I. INTRODUCTION
Additive manufacturing (AM) or 3D printing is the technology of building three-dimensional objects layerby-layer using computer-aided designs (CAD).1 It is capable of fabricating complex three-dimensional objects, which cannot be produced using conventional manufacturing techniques. It consists of several classes of processes, including extrusion, powder bed fusion, vat photopolymerization, and importantly, material jetting (MJ), based on ink jet techniques.1–8 This latter process is significant, since it is one of the most promising routes to AM based multi-material (MFAM) production. Both extrusion and MJ methods have been used to develop MFAM, with extrusion showing interesting developments in terms of biological material scaffolds in tissue engineering9,10 amongst other applications. The fundamental difference between extrusion and MJ is the mode of delivery, where extrusion is capable of delivering relatively highly loaded or higher molecular weight materials but at lower resolution than MJ. Should MFAM be realized, it will lead to the production of new multifunctional products, including those in the electronics, bio-printing, and pharmaceutical industries. One mode of ink jet printing is reactive ink jet (RIJ). RIJ involves the deposition of one or more liquid raw materials onto the same location, after which a chemical interaction is activated, producing a new material in situ to the manufacturing process.11,12 One common method is to Contributing Editor: Paolo Colombo a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.4
use materials that are able to crosslink under the application of ultra-violet (UV) light. Commercial machines are now available where the UV source is in line with the printing head, leading to the creation of material on a layer-by-layer basis. In this regard, there are similarities to stereolithography (SLA), which also relies on UV based solidification mechanisms.13–16 This layer-by-layer synthesis approach however, whilst it has adv
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