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Nowadays cellular materials are receiving great attention for their excellent mechanical properties, being applied in energy absorbers or in structural components having optimized mass distribution. In this paper stretch-dominated lattice structures have been considered. A 3D periodic lattice structure of different cell size, TPMS (triply periodic minimal surface), made of epoxy resin by DLP technology was studied. Compression tests at different strain rate (10-3 to 103 1/s) have been performed and a constitutive model to assess the experimental findings has been calibrated.

Shape memory polymers (SMPs) represent a materials class capable of recovering their initial shape, when submitted to deformations, through an external stimulus. This paper focuses on a Shape Memory Thermoplastic Polyurethane (SMPU), characterized by a one-way shape memory effect (SME) activated by temperature. The material was characterized by Differential Scanning Calorimetry (DSC) to find transition temperature; then, it was manufactured by an injection molding machine to perform a campaign of characterization tests. Thermomechanical tests were conducted varying the prescribed strain (up to 25%, 50%, and 80%), imposed at both different strain rates ([Formula: see text], [Formula: see text], and [Formula: see text] s−1), and temperatures (50°C, 60°C, and 70°C); the results were investigated in terms of shape fixity and shape recovery ratios. An excellent memory capability was observed for all the tested conditions; otherwise, the shape recoverability is strongly influenced by all investigated parameters, especially by the strain rate, resulted to be the most effective one. In fact, the shape recovery ratio can increase as much as 20%, when the strain rate is increased from [Formula: see text] to [Formula: see text] s−1. An opposite effect was observed with the variation of prescribed strain and temperature, the increase of which reduces the ability of the material to return to its original shape.

Shape Memory Polymers (SMPs) are materials capable of changing their primary shape to a secondary shape thanks to the so called Shape Memory Effect (SME) phenomenon. The shape-shifting is achieved through the action of an external stimulus, such as heat, electricity, pH, etc. In this paper, experiments on a thermally actuated thin film of a Shape Memory Thermoplastic Polyurethane (SMPU) were performed to calibrate the parameters of a constitutive model which accounts the rubbery/glassy phase transition mechanism behind the shape memory behaviour. In particular, thermomechanical uniaxial tensile tests have been carried out in order to the Young modulus and Poisson’s ratio above/under glass transition temperature and the fixity/recovery ratio. Additionally, the hydraulic bulge test (HBT) in a thermally controlled loading/unloading cycle was used to study the behaviour of the SME at large strains under equi-biaxial stress state. The corresponding outcomes were, therefore, employed to validate the results of the initial calibration by means of a Finite Element (FE) simulation of the HBT.

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