Determination of dynamic stiffness of resilient materials using a lightweight load plate 2-DOF method

The trend of increasing the ratio of environmentally friendly solutions in the building industry is on the rise. We increasingly encounter solutions that utilise loose-form materials or, to improve thermal insulation and acoustic properties, typically multilayer lightweight systems. However, it has been proven that predicting the impact of loose-form blown-in materials on sound insulation properties can be a matter of debate. Blown-in materials with a higher bulk density tend to connect the individual layers of lightweight walls mechanically. It is not trivial to accurately determine the stiffness of the blown-in material after application in the building structure. This is especially important when creating prediction models. This paper deals with the determination of the dynamic stiffness of soft materials using the light load plate and two degrees of freedom (2-DOF) method. Since the case of evaluating resilient materials at low loads is outside the recommended range of boundary conditions as defined by EN 29052-1, this extensive work gradually analyses the relevance of applying an alternative measurement method. It discusses the effect of compression of a soft material on its actual dynamic stiffness, the effect of the excitation form of the light load plate, and presents a preliminary measurement approach. Numerical models support individual analyses and measurements. Even though testing fibrous materials in loose form is a very challenging task, a significant change in stiffness under the influence of loading has been demonstrated.