Wood starts to 'cold creep' as soon as you put a load on it. The longer the load is on the greater the deflection. The folks I know who get the most consistent measurements this way put the load on, zero the gauge, and then remove the load, noting the change immediately. On advantage of the vibration testing method is that cold creep doesn't enter in directly: it probably has some bearing on damping but doesn't alter the Young's modulus measurement.
If you know some things, like the spacing of the supports, the weight, and the dimensions of the part being tested you can calculate the Young's modulus of the wood. That allows you to compare your results directly with those of other people, and effectively increases the size of your data base.
|