The more common methods of characterising mechanical properties of materials are presented.
Density is a well known characteristic of materials, but for new structures like honey-comb, sandwich..., the way to calculate it is not as obvious. The ASTM C 271-94 standard test method is used to calculate the density of materials having a sandwich structure.
Young's modulus is the relationship between the elastic strain of the material and the stress which caused it. Young's modulus of linear materials is constant (elastic part), but in visco-elastic materials it varies in function of the frequency. Normally when Young's modulus is constant, it is characterise from a static model in a universal machine for tension - compression. When it varies as a function of frequency is possible to use two methods:
Non resonant method: There are tension-compression machines that allow measurement of Young's modulus when the specimen is loaded in cycles of stress traction-compression over a range of frequencies. With this method is only possible to measure the primary resonance of the system well, as the frequency range is very narrow.
Resonant method: With this method the different resonances of the system (material specimen) are measured. From these measured resonances is possible to estimate the Young's modulus at every frequency so that a material behaviour law is obtained.
Shear modulus is measured in a similar way.
Loss factor is a property which is a function of frequency and it is possible to measure it by the resonant method explained above.

All these methods are explained in more detail later on.