温度对重组竹短期受压蠕变性能的影响

Effect of temperature on short-term compression creep property of bamboo scrimber

通过对重组竹受压试件进行短期蠕变试验,研究温度对重组竹受压试件蠕变特性及蠕变规律的影响。针对不同应力水平下温度对重组竹短期受压蠕变的影响,研究了在同一应力水平7.5%下,重组竹在5种不同温度下的24 h顺纹受压蠕变性能;进一步比较了重组竹在应力水平为7.5%,15%,30%且温度分别为25,50,75℃情况下的24 h顺纹短期受压蠕变特点。最后,采用Burgers模型对上述不同温度变量和不同应力水平变量下重组竹短期受压蠕变曲线进行拟合分析。结果表明:在重组竹顺纹受压蠕变中,温度和材料应力水平越高,瞬时弹性变形越大,重组竹蠕变应变总量越大,重组竹抵抗蠕变性能越弱,且较高温度和较高应力水平的同时作用会对重组竹构件产生不利影响;Burgers模型的拟合决定系数基本均在0.98以上,说明Burgers模型能够较准确地描述温度对重组竹短期受压蠕变曲线特性的影响。根据试验与拟合曲线特性可知,重组竹顺纹受压蠕变中弹性变形占80%以上,说明在不同温度下重组竹顺纹受压蠕变中弹性变形占主要部分,随着温度的升高,弹性变形有所下降,黏性变形逐渐增加。

The effects of temperature at different stress levels on the short-term compressive creep of bamboo scrimber were studied.At the stress level of 7.5%,the 24-h short-term compressive creep properties along the grain direction of bamboo scrimber at six different temperatures,namely-25,0,25,50,75 and 100 ℃,were examined.The 24-h compressive creep characteristics of bamboo scrimber at stress levels of 7.5%,15%,30% at temperatures of 25,50 and 75℃ were compared.Finally,the short-term creep curves of bamboo scrimber under different temperatures and stress levels were fitted with the Burgers model.The results showed that the higher the temperature and material stress level,the greater the instantaneous elastic deformation and the total creep strain.With the increase of stress level,the instantaneous creep variable and the total creep strain of the bamboo scrimber increased,indicating that both temperature and stress level influenced the creep performance of bamboo scrimber.When the bamboo scrimber was in the low temperature environment,the initial amount of creep was small and the compressive strength of bamboo scrimber along the grain increased.With the increase of temperature,the moisture in the bamboo fiber of the bamboo scrimber would evaporate,which could weaken the strength of the bamboo scrimber,reduce its ultimate bearing capacity,and increase the total creep strain.Temperature has a great influence on the compressive creep of bamboo scrimber.When the temperature rises,the total stress of the bamboo scrimber will increase significantly.Therefore,in the structural design,when the members are in a high temperature environment,it is necessary to consider reducing the load borne by the members.The Burgers model is a series of M axwell model and Kelvin model,which can well represent the viscoelastic characteristics of the bamboo scrimber.The coefficient R2 of the Burgers model was above 0.98.In particular,the fitting correlation coefficient R2 of the Burgers model at higher temperatures were all above 0.99,which proved the accuracy of the model at higher temperatures and stress levels.According to the experimental fitting curve characteristics,it was found that the creep value of bamboo scrimber along the grain was decreased with the increase of temperature,and the elastic part and the viscous part were increased.The elastic part of the compression creep deformation accounted for more than 80%,which was much higher than that of the viscous and viscoelastic parts,indicating that the elastic deformation accounted for the main part of the compression creep at different temperatures.