The Research Of The Viscoelasticity Of Birch In Transverse Tension

In order to systematically study the viscoelasticity of transverse birch in a wide temperature and moisture content domain,deepen the theory of wood viscoelasticity and provide a theoretical basis for the efficient and reasonable application of birch.In this paper,the tensile creep,tensile stress relaxation and tensile dynamic viscoelasticity of birch at five moisture content levels of 0%,6%,12%,18%and 24%were studied by using Q800 DMA(dynamic mechanical analyzer),with DMA humidity accessories and coating treatment.The main results are as follows:1.The total compliance,instantaneous compliance and creep compliance of birch specimens increased with the increase of moisture content;the initial relaxation modulus and final relaxation modulus decreased with the increase of moisture content,while the stress relaxation rate increases with the increase of moisture content.2.The total compliance,instantaneous compliance and creep compliance of the specimen increased with the increase of temperature;the initial relaxation modulus and final relaxation modulus of the specimen decreased with the increase of temperature,while the stress relaxation rate increases with the increase of temperature.3.The creep and stress relaxation of some moisture content specimens have obvious changes under certain temperature conditions,and as the moisture content of the specimens increases,the changing temperature decreases.4.Under all test conditions,the creep compliance of the specimen at 30 min is always greater than the instantaneous compliance.The difference between them also increases with the increase of moisture content and temperature.5.The effect of creep caused by the change of unit moisture content is greater than the effect of change by unit temperature.Each 1%increase in moisture content has an effect equivalent to at least a 4 ? increase in temperature.6.The influence of moisture content on creep and stress relaxation is more significant at high temperature.Similarly,the influence of temperature on creep and stress relaxation is more significant at high moisture content.Moisture content and temperature play complex interactions in creep and stress relaxation.7.The storage modulus decreases with increasing moisture content and temperature.The decreasing range of storage modulus curve of five kinds of moisture content specimens increases with the increase of moisture content.8.The temperature of loss modulus peak in the range of test temperature is different for different moisture content specimens.The loss factor of the specimen increases with the increase of the moisture content of the specimen,and the loss factor curve increases with the increase of the temperature.