An inverse method for determining the spatially resolved properties of viscoelastic–viscoplastic three-dimensional printed materials

Abstract

A method using experimental nanoindentation and inverse finite-element analysis (FEA) has been developed that enables the spatial variation of material constitutive properties to be accurately determined. The method was used to measure property variation in a three-dimensional printed (3DP) polymeric material. The accuracy of the method is dependent on the applicability of the constitutive model used in the inverse FEA, hence four potential material models: viscoelastic, viscoelastic–viscoplastic, nonlinear viscoelastic and nonlinear viscoelastic–viscoplastic were evaluated, with the latter enabling the best fit to experimental data. Significant changes in material properties were seen in the depth direction of the 3DP sample, which could be linked to the degree of cross-linking within the material, a feature inherent in a UV-cured layer-by-layer construction method. It is proposed that the method is a powerful tool in the analysis of manufacturing processes with potential spatial property variation that will also enable the accurate prediction of final manufactured part performance.

Damage measurements in epoxy structural adhesives using microhardness

“…The use of microhardness to characterize metals and damage in metallic materials is well established [15,18], but the use of micro-indentation in polymers has been relegated mostly to a simple, non-destructive production control test that indicates cure or chemical composition [19]. Nevertheless, there are studies that demonstrate the flexibility and usefulness of indentation techniques to determine the mechanical properties for viscoelastic materials [20,21], to measure changes in polymeric materials, such as polymorphic transitions due to loading [19], or to identify craze initiation [22]. A possible method, then, to measure the effect of damage in materials is through hardness measurements at discrete points.…”

Combined Inkjet Printing and Infrared Sintering of Silver Nanoparticles using a Swathe-by-Swathe and Layer-by-Layer Approach for 3-Dimensional Structures

“…11−13 Ink jet printing (IJP) is a drop-ondemand, noncontact material jetting process capable of direct printing circuits of complex geometries from a computer-aided design (CAD). 14 In addition to high material utilization rate and lower wastage compared to conventional methods, IJP also has the potential to simplify the manufacturing process of circuits and reduce the associated costs. 11 In recent years, the use of inks containing MNPs, such as silver, 15−18 gold, 19 copper, 20 and other conductive materials including graphene, 21 carbon nanotubes, 22 poly(3.4-ethylenedioxythiophene) polystyrenesulfonate, 23 and direct writing of liquid metals such as gallium, indium and tin have been widely explored for printing circuits.…”

“…Material jetting is considered as one of the key enablers of MFAM due to their ability to jet a wide range of materials including polymers, composites and inks containing metal nano particles (MNPs). − Ink jet printing (IJP) is a drop-on-demand, noncontact material jetting process capable of direct printing circuits of complex geometries from a computer-aided design (CAD) . In addition to high material utilization rate and lower wastage compared to conventional methods, IJP also has the potential to simplify the manufacturing process of circuits and reduce the associated costs …”

A new photocrosslinkable polycaprolactone‐based ink for three‐dimensional inkjet printing

“…The hardness and indentation modulus of the top and bottom surfaces of the printed samples as a function of postcuring time were measured using nanoindentation. It was anticipated that as the samples were produced by stacking up layers of material, with differing amounts of UV illumination for different layers, that this would lead to depth‐dependent curing level and therefore depth‐dependent properties . What was observed, however, was that the top and bottom surfaces of the sample had very similar properties prior to any postcuring treatment, suggesting that the ink with 3 Wt % PI and AC allowed homogenous curing throughout the depth of the sample (Figure , 0 minute).…”