Assessment of the Behaviour of Low-Modulus Polyurethane Foams Subjected to Severe Shear Deformation Conditions

Polymeric materials are broadly employed as buildings materials because of a number of interesting properties for specific applications. Among them, polyurethane (PU) takes advantage of outstanding mechanical properties, such as high deformability and dissipation, as well as remarkable thermal and chemical stability. As a foam, PU is arguably the most popular insulating materials, used as a supplementary layer in precast concrete panels, infill walls and roofs. Experimental assessment of the mechanical behaviour of PU foams is therefore a long-standing issue, which is demanded to validate analytical models and provide reliable parameters in FEM modelling. In particular, reliable experimental assessment to large deformations is still difficult to attain. In the present study, we carry out a preliminary mechanical characterisation of a single low-modulus PU foam by means of a testing machine prototype, which performs simple shear and shear-per-traction deformations of a square-shaped sample, according to the restraining system adopted. Simple curve-fitting of the response leads to different mechanical parameters for the same material. Shear test results are related to compressive tests and microstructural investigation of the PU foam, through Scanning Electron (SEM) microscopy. The proposed polynomial laws for the tangential and normal net forces are applicable for calibrating FEM models aimed to predict the behaviour of soft materials subjected to high deformations.