The Study On The Dynamic Characteristics And Influencing Factors In Larch Wood

Nondestructive evaluation techniques used to test Mechanical properties and potential quality of wood materials, have some advantages including short measuring time, simple method, no destructing lumber and requirements of continuous production, and become a hot research field in the word. Research of dynamic characteristics can be realized as a reasonable choice for nondestructivetesting technology and efficient use of wood, having very theoretical and practical value.Dynamic characteristics (dynamic modulus of elasticity, resonant frequency, bending vibration waveform, stress wave velocity) of lumber obtained from China's larch and effect factors (density, moisture content, growth characteristics) were systematically studied by using three methods of Stress wave, longitudinal vibration and transverse vibration in this paper. Vibration evaluation software was established using virtual technology. The relations between parameters of dynamic characteristics and dynamic modulus of elasticity, as well as the differences of flaw and flawless specimens were explored on the basis of three dynamic evaluation methods. Subsequently, mutual relations of resonant frequency, bending vibration waveform, stress wave velocity and effect factors were also established. The main results were as follows:1. The moisture content in the selected area, the dynamic characteristics was correlation with resonant frequency, stress wave velocity and dynamic modulus of elasticity. With the decrease of moisture content, the dynamic characteristics showed a linear increase. Bending vibration waveform of experimental lumber was close to theoretical waveform, when its moisture content was 12%.2. Dynamic modulus of elasticity of specimens without knots obtaining from three testing methods existed discrepancy in different moisture contents. The differences using longitudinal vibration were largest among three methods; however their correlation was relatively obvious.3. Along direction of Specimen width, stress wave velocity in different position increased with the increase of the size and number of knots; stress wave velocity of the same larch showed negative correlation with diameter. Furthermore it also related to degree of the twisted grain texture around the. The effects of quantity of knots on stress wave velocity were not obvious when the knots were relatively small.4. Specimens without knots specimens, the effect of growth rate of the same one on stress wave velocity was greater, and the correlation coefficient R was equal to 0.823. The correlation coefficients between growth rate and latewood percent of different specimens and stress wave velocity were respectively 0.6589 and 0.5924; especially regressioneffect was significant when it was 0.05.5. The relevance of bending and longitudinal resonance frequency specimens without knots specimens was greatly obvious; longitudinal resonance frequency and stress wave velocity had strong correlation.6. Stress wave velocity was rather sensitive to the knots and twisted grain texture. The effect of growth rate and latewood percent on stress wave modulus of elasticity was more obvious than that on vibration modulus of elasticity. Therefore, stress wave velocity can be used as a testing index of nondestructiveevaluation in-place.7. Density is not obvious on the resonance frequencies and stress wave velocity, it is some influence in the specimens without knots in the same larch.