Compressive stress at 10 % strain
It is one of the main mechanical properties of thermal insulation products. Compressive stress at 10 % strain is determined according to the standards EN 826 / ISO 29469. This parameter can be used to establish the stresses at which to perform compressive creep tests (long-term reduction in thickness due to the pressure exerted on the materials) or to obtain reference values, from which design values can be deduced, using appropriate safety coefficients for those applications in which the insulating materials are exposed to loads of short duration, such as floors and walkable roofs. In addition to allowing transit through these elements, it is of interest that the material has a high compressive stress at 10 % deformation, since the reduction in the thickness of the material caused by transit over it will lead to a decrease in the partial thermal resistance due to the insulation, which is always the greatest in magnitude within the elements of a construction solution.
The test consists of compressing the specimens using a universal tensile-compression testing machine at a constant displacement rate of d/10 per minute, where d is the thickness of the specimen in millimetres until a 10 % deformation (reduction) of the thickness is reached, thus obtaining the force supported by the specimen at 10 % strain. A typical graph of this test can be seen in the following figure:
We can see that in most cases, as the above is a typical graph but not the only case that can occur, these materials present an elastic zone (zone in which the relationship between force and deformation is linear below the limit of proportionality; the first slope of the graph), and then present a plastic zone.