Simulation of Locally Varying Residual Strains in 4D Printing

Abstract

ABSTRACT Shape memory polymers (SMPs) are a class of materials capable of storing deformation in a programmed shape, which can be recovered when an external trigger, such as temperature, a magnetic field, or similar is applied. In the classical shape memory cycle, programming consists of successive heating, deformation and cooling steps. In combination with 3D printing, here fused filament fabrication (FFF), these programming steps can be condensed into the filament extrusion process, so that the printed part can be regarded as a programmed shape memory polymer, hence the description as 4D printing. This effect can be observed in materials such as PLA and TPU to various extends; here, we use a TPU‐based shape memory filament that exhibits large strain recovery when subjected to 4D printing and subsequent activation. In this work, we propose an approach to predict the shape change by introducing an ansatz for the stored strain as a function of process‐dependent parameters, which impose a strain field on the part that can be recovered when the material is subject to its external trigger, temperature in this case. The parameters that are introduced with the ansatz are then fitted to a set of print parameters by measuring the curvature of the samples by using a least square fit. To combine the print settings with an FE‐simulation, the machine code (GCode) is used to directly provide the necessary parameters to an FE‐simulation, allowing the approach to predict the shape change for arbitrary geometries.