A nondestructive method and a tool for evaluating rigidity of porous sheet materials

Moulded foam (MF) is proliferating on the market of porous materials. It consists of separate factions (of different shapes and sizes) of the previously produced and often used polyurethane foam that has been crushed into crumbs and bound together by fresh polyurethane foam. In terms of rigidity, such structure forms an inhomogeneous porous material (IPM). The technology of manufacturing such materials a priori implies the inhomogeneity of rigidity both in the sheet plane and between different sheets that are cut to a prescribed thickness from a pre-formed rectangular parallelepiped of the porous material. Being able to control the rigidity of inhomogeneous porous sheet materials is an important requirement for the future high-quality produce. The testing technique used for these purposes needs to be accurate enough, nondestructive, practically feasible, and not time-consuming. In this paper, moulded foam is used as an example to consider theoretical aspects of modeling the process of IPM formation as well as practical issues related to developing and researching a nondestructive technique and a tool for measuring the rigidity of porous sheet materials, to monitoring the measurement accuracy, and to testing the created prototype of such a device.