A non-destructive stress wave testing method for wood. Two strain gauges are disposed on a timber. The timber is struck to generate an impact compression stress wave. The impact compression stress wave is measured by the strain gauges. An oscilloscope is provided to measure the time difference of the impact compression stress wave passing through the semiconductor strain gauges. The resonance frequency of the timber is sensed by the strain gauges and displayed on an FFT spectrum analyzer. Then, the speed of sound in the timber is determined according to the distance between the strain gauges and the time difference, or according to the length and the resonance frequency thereof. The strain gauges may be semiconductor strain gauges. The modulus of elasticity of the timber is determined according to the speed of sound therein and the density thereof.
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