An experimental method for the investigation of rigid polyurethane foams in shear

Abstract

Widespread applications of rigid polyurethane and plastic foams lead to shear deformations. Therefore, methods for ensuring shear using experimental investigations are necessary, including the possibility of determining the shear modulus, strength and limit angle. Therefore, a device that allows investigating the shear properties of highly porous plastic foams was developed. The proposed device comprises a clip-on extensometer, commonly exploited in uni-axial compression/tension tests, for the determination of the shear displacement directly on the foams’ sample, on a measurement zone of certain dimensions and location. An innovative construction of the extensometer’s legs is elaborated, permitting to investigate the shear displacement field for different dimensions of the measurement zone. Precision of the device is examined by performing a penetration test on materials of different densities: (a) polyurethane foams and (b) wood. Technology for the production of isotropic polyurethane foams as a test material is described in detail. Experimental determination of shear modulus and strength of one and the same sample, in one and the same experiment is elaborated. Displacements in different zones of sample’s work beam are investigated. Experimental data are compared with the results of mathematical modelling and a good correlation is proved to exist.