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.
Highlights
In reactive inkjet printing (RIJ), pico-volume droplets of fluid materials are jetted onto the surface of a2015 The Authors
inverse finite-element analysis method (IFEM), provides the possibility of combining the output of the nanoindentation test with an FE model to inversely obtain the material properties, despite the complex stress state in the material induced by the indenter [15]
The evaluated material parameters using the various material constitutive models for indentation locations A and D are shown in table 3, where Ein is instantaneous modulus, τ1, τ2 and τ3 are relaxation times and g1, g2 and g3 are the corresponding relative relaxation moduli (see equation (3.3)), σs is the initial hardening yielding stress for least depth residual (see equation (3.18)), βe, β1 and β2 are the nonlinear coefficients of the nonlinear viscoelastic (NVE) and nonlinear viscoelastic–viscoplastic (NVEVP) material constitutive models (see equations (3.34) and (3.55)) and ζ and η are VP parameters, see (3.16) and (3.17)
Summary
In reactive inkjet printing (RIJ), pico-volume droplets of fluid materials are jetted onto the surface of a. Oyen [17] proposed analytical techniques to evaluate VE parameters from nanoindentation test displacement curves based on linear VE material models and hereditary integral analysis of polymer indentation data. The aims of the paper, are to introduce an IFEM which can be used to determine complex material model parameters from indentation data and to illustrate how these can be used to investigate property variation in a 3D printed (3DP) part, providing insight into the manufacturing process and enabling prediction of the mechanical performance of the printed part
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