关键词: 竹材, 温度, 竹节, 抗弯强度, 抗弯弹性模量

Abstract:

Objective: The aim of this study was to investigate the effects of temperature on the bending mechanical properties of Phyllostachys edulis, providing data support and a theoretical basis for its structural application in extreme environment conditions. Method: Bamboo samples aged 3–6 years from Chishui City, Guizhou Province, were used to prepare two types of specimens: with nodes and without nodes, with 66 specimens of each type. Eleven target temperatures (?60, ?40, ?20, 0, 20, 60, 100, 130, 175, 185, and 200 ℃) were set for three-point bending tests to measure the bending strength and bending elastic modulus of the bamboo. The effects of temperature on bending mechanical properties were analyzed. Correlation analysis was conducted to explore the relationships between temperature, bending strength, and bending elastic modulus. Quadratic function equations were proposed for the temperature impact coefficients of bending strength and bending elastic modulus. Microscopic structural observations were conducted to examine changes in bamboo cell walls at low and high temperatures, revealing the intrinsic mechanisms behind the changes in bending mechanical properties. Result: Temperature has a significant impact on the bending mechanical properties of Phyllostachys edulis. As the temperature increases, both the bending strength and bending elastic modulus exhibit a pronounced declining trend. At 200 ℃, the bending strength of specimens with and without nodes is reduced to 31% of the bending strength at room temperature (20 ℃), while the bending elastic modulus decreases to 44% and 41% of the corresponding room temperature values. Conversely, at ?60 ℃, the bending strength of specimens with and without nodes increases to 116% and 115% of the bending strength at room temperature, while the bending elastic modulus rises to 135% and 128% of the room temperature values, respectively. Under low-temperature conditions, Phyllostachys edulis exhibits higher strength but pronounced brittleness, whereas under high-temperature conditions, it demonstrates lower strength and increased plastic deformation. The presence of nodes had little effect on bending strength, with no significant difference observed between specimens with and without nodes under either low or high temperatures. However, nodes have a significantly adverse impact on the bending elastic modulus, particularly within the temperature range of ?40 ℃ to 130 ℃. Microscopic structural analysis revealed that under low-temperature conditions, the bamboo cell walls remain intact and tightly compacted, which contributes to enhanced mechanical performance. Under high temperatures, due to moisture evaporation and chemical composition transformation, bamboo cell walls softened and gradually thinned, resulting in a significant decline in mechanical properties. Conclusion: Our results demonstrated that the bending mechanical properties of Phyllostachys edulis under extreme environment conditions are significantly influenced by temperature variations. Low temperatures enhance the strength of Phyllostachys edulis but increase its brittleness, while high temperatures weaken its strength and promote greater plastic deformation. Our findings showed that the presence of nodes has minimal impact on bending strength but exerts a noticeable adverse effect on its elastic modulus.

Key words: bamboo, temperature, bamboo node, bending strength, bending modulus of elasticity