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    邢雪峰, 李善明, 金菊婉, 林兰英, 周永东, 傅峰. 高能微波处理辐射松木材的抗弯力学性能与损伤演化特征[J]. 北京林业大学学报, 2022, 44(8): 107-116. DOI: 10.12171/j.1000-1522.20220095
    引用本文: 邢雪峰, 李善明, 金菊婉, 林兰英, 周永东, 傅峰. 高能微波处理辐射松木材的抗弯力学性能与损伤演化特征[J]. 北京林业大学学报, 2022, 44(8): 107-116. DOI: 10.12171/j.1000-1522.20220095
    Xing Xuefeng, Li Shanming, Jin Juwan, Lin Lanying, Zhou Yongdong, Fu Feng. Bending properties and damage evolution characteristics of high-intensity microwave treated radiata pine lumber[J]. Journal of Beijing Forestry University, 2022, 44(8): 107-116. DOI: 10.12171/j.1000-1522.20220095
    Citation: Xing Xuefeng, Li Shanming, Jin Juwan, Lin Lanying, Zhou Yongdong, Fu Feng. Bending properties and damage evolution characteristics of high-intensity microwave treated radiata pine lumber[J]. Journal of Beijing Forestry University, 2022, 44(8): 107-116. DOI: 10.12171/j.1000-1522.20220095

    高能微波处理辐射松木材的抗弯力学性能与损伤演化特征

    Bending properties and damage evolution characteristics of high-intensity microwave treated radiata pine lumber

    • 摘要:
        目的  探究高能微波处理对木材抗弯弹性模量、抗弯强度和弯曲塑性功的影响,并阐明处理材在静态弯曲载荷过程中的损伤演化与破坏规律。
        方法  利用高能微波设备,采用60、80、100 kW·h/m3这3组微波能量密度水平对含水率为50% ~ 70%的辐射松锯材进行处理。在声发射(AE)系统的实时监测下进行三点弯曲抗弯弹性模量、抗弯强度和弯曲塑性功的测试,并且结合试件断裂破坏截面形貌与AE参数特征分析对比处理材与未处理材在不同加载阶段的损伤演化。
        结果  未处理材抗弯弹性模量和抗弯强度平均值分别为5 520和61.7 MPa,高能微波处理材的抗弯弹性模量和抗弯强度平均变化率均小于10%。但高能微波处理均显著提高了木材的弯曲塑性功。相较于未处理材,60和100 kW·h/m3处理材的弯曲塑性功分别提高了12%和16%;而80 kW·h/m3处理材的弯曲塑性功最大,相较于未处理材的提高了22%。AE测试结果显示:随着微波能量密度的增加,处理材AE信号首次出现时间不断提前,首个损伤稳定增长阶段的持续时间、塑性变形阶段的累计振铃计数增长速率、幅度和能量活跃度逐渐增加。由此表明,在弯曲载荷作用的过程中,处理材拥有更高的损伤增长速率与应力重组效率,细胞壁产生了更多的屈曲与坍塌破坏,木材内部裂纹迅速扩展,减弱了应力集中效应,因而在一定程度上增加了木材弯曲塑性功。试件破坏形貌验证了AE测试结果,与未处理材相比,处理材的拉伸区域、中性层与压缩区域的断面形貌更加粗糙。
        结论  适当的高能微波处理可在仅小幅改变木材抗弯弹性模量、抗弯强度的前提下,显著提高木材弯曲塑性功,将为高能微波处理材的应用提供新思路。研究方法与结果能够有效地展示高能微波处理材的损伤演化特征,并将为木质材料损伤演化的相关研究提供参考。

       

      Abstract:
        Objective  The effects of high-intensity microwave treatment on the flexural modulus of elasticity, bending strength, bending plastic work were investigated, and the damage process and failure mode of treated lumber during static bending load were explored.
        Method  The radiata pine lumber with moisture contents ranging from 50% to 70% was treated by high-intensity microwave at three microwave energy density levels, i.e., 60, 80 and 100 kW·h/m3, respectively. Both the treated and untreated lumber specimens were tested for three-point bending modulus of elasticity, bending strength and bending plastic work under the real-time monitoring of the acoustic emission (AE) system, and the damage evolution characteristics of different loading stages were compared by analyzing the fracture failure section morphology and AE parameters.
        Result  The average values of modulus of elasticity and bending strength of untreated lumber specimens were 5 520 and 61.7 MPa, respectively. The treated lumber specimens presented less than 10% change in their average bending strength and modulus of elasticity compared with untreated ones. However, high-energy microwave treatment significantly increased the bending plastic work of wood. Compared with the untreated lumber specimens, the bending plastic work of wood treated at 60 and 100 kW·h/m3 increased by 12% and 16%, respectively. Lumber treated with the energy density of 80 kWh/m3 showed the highest bending plastic work value, which was 22% higher than that of the untreated lumber specimens. The parameter analysis of AE showed that, with the increase of microwave energy density, the first occurrence time of AE signal of the treated materials was gradually advanced, and the duration of the first stable damage growth stage, the cumulative ringing count growth rate, as well as amplitude and energy activity of the plastic deformation stage increased gradually. During the process of bending test, the treated lumber specimens presented a higher damage growth rate and stress recombination efficiency, which indicated that there were more buckles and collapse damage occurring in the cell wall, Therefore, the cracks in the treated lumber specimens expanded faster, which weakened the stress concentration effect and increased the bending plastic work of wood to a certain extent. The analysis on the tested specimens’ fracture morphology verified the AE test results: the cross-sectional morphology of the tensile region, neutral layer, and compression region of the treated materials were rougher than that of the untreated ones.
        Conclusion  Appropriate high-intensity microwave treatment could significantly increase the bending plastic work of wood while only slightly changing the modulus of elasticity and bending strength of wood. This suggests new potential applications of high-intensity microwave-treated lumber. The research methods and results can effectively show the damage evolution characteristics of high-intensity microwave-treated lumber, and will provide a reference to the related research on the damage evolution of wooden materials.

       

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