重组竹短期抗弯蠕变特性及其微观结构研究

Study on short-term bending creep behavior and microstructure of bamboo scrimber

为探索重组竹长期载荷下的极限强度及其加工使用环境,以重组竹为对象,研究其在不同加载载荷(224,280,336和392N)、含水率(浸水、气干和绝干)及厚度(6,8和10mm),在三点弯曲条件下的96h抗弯蠕变特性。结果表明:重组竹蠕变柔量随时间的延长而逐渐增大,加载载荷越大,蠕变柔量越大,瞬时弹性蠕变柔量也越大,到达减速蠕变阶段所需时间越长;8 mm厚浸水、气干和绝干重组竹96h蠕变的总蠕变柔量分别为2.25,1.82和1.62mm,气干和浸水重组竹蠕变柔量变化较为均匀平缓,而绝干重组竹蠕变柔量变化则为阶梯式,瞬时线性增加;6,8和10mm厚气干和绝干重组竹在0.16h内的蠕变柔量分别为4.34,1.58,0.99和4.43,1.23,0.75mm,相同厚度的绝干重组竹瞬时蠕变柔量与最大蠕变柔量均小于气干材,而6mm厚气干重组竹在7.6h后呈直线加速蠕变,再经1.25h后出现断裂现象;微观形态观察发现,重组竹蠕变时产生了微裂纹,而蠕变断裂则是从胶合界面薄弱处开始并向上延伸,最终使界面上方纤维受压断裂。

In order to predict the ultimate strength of bamboo scrimber under long-term load, and to determine its processing and using environment conditions, the effects of different loads （224, 280, 336 and 392 N ）, moisture contents（ saturated, Mr-dried and oven-dried） and thickness（6, 8 and 10 mm） on creep properties of bamboo scrimber under the three-point bending mode within 96 h were studied. The results showed that the creep compliance of bamboo scrimber increased gradually with the increase of time. The higher the load, the larger the instantaneous e- lastic creep compliance was obtained, leading to the longer time to reach the deceleration creep stage. The total creep compliances of the 96 h creep for saturated, air-dried and oven-dried bamboo scrimbers of 8 mm thick were 2. 25, 1.82 and 1.62 mm, respectively. The total creep compliance was improved gradually with the increase of moisture content. The creep compliance of air-dried and saturated bamboo scrimber changed relatively uniformly, while the creep compliance change of oven-dried bamboo scrimber was ladder-like type and its instantaneous linearity increased. The creep compliances of 6, 8 and 10 mm thick mr-dried and oven-dried bamboo scrimbers in 0. 16 h were 4. 34, 1.58, 0. 99 mm and 4. 43, 1.23, 0. 75 mm, respectively. The creep compliance of bamboo scrimber decreased with the increase of thickness in the air-dried and oven-dried conditions. The transient and maximum creep compliances of bamboo scrimbers with the same thickness in oven-dried condition were lower than those of bamboo scrimbers in the air-dried condition. The air-dried bamboo scrimber of 6 mm thickness showed linear acceleration creep after 7.6 h, and then fractured in 1.25 h, indicating that the moisture content had a great influence on the creep limit and fracture of the bamboo scrimber. The cracks occurred in micro morphology of bamboo scrimber, and the creep rupture started from the weakest point of the bonding interface and then extended the fiber compression fracture along the surface.