A few claims have been made as to whether compression accross the grain increases stiffness or not. Stiffness is usually described with the quantity E, the modulus of elasticity. The simplest method to calculate this is simply to take a piece of wood, load it and measure the strain it experiences. Dividing the amound of force by the amount of strain you end up with E, the measure of stiffness, for that piece of wood. The resulting value will not be the same if you change moisture content, nor will it be the same for each direction of stress. Strength properties given in tables are calcutated for a given moisture content. Usually 12 % MC. They are also calculated using standard shaped pieces of wood... usually beam like in shape. And, they are calcutated in stress directions that usually occur in building. The E that is given in these tables is not the same E for all the bending stresses the soundboard panel experiences. The soundboard is bent cross grain, along the grain, and in a host of diagonal grain directions all at once. So when quoting these tables one has to take into consideration what isnt covered. To the direct claim that stiffness (in any direction) does not increase with compression. This is simply false. It does. Wood is usually sorted into grades that are related to density, straightness of grain, grain consistancy... etc. Looking at the tables in just about any such manual one sees quickly that E, and for that matter just about all strength properties, increase as density increases. Since a compressed panel is essentialy a more dense panel then it would be without the compression, it goes without saying that it becomes stiffer. Cheers RicB
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