杉木正交异向蠕变行为的时温等效性

doi:10.11707/j.1001-7488.20210116

摘要/Abstract

摘要：

目的: 探究时温等效原理在杉木正交异向蠕变行为中的适用性及其特点。方法: 以含水率约0.6%的杉木木材为研究对象，采用动态热机械分析仪DMA 2980，在30~150℃范围内，基于一系列20 min蠕变试验分别获得3个应力水平和不同恒定温度水平下杉木轴向、径向和弦向的蠕变曲线。将其他温度下的蠕变曲线通过水平移动因子平移并叠合连接至参考温度(本研究中为30℃)曲线，生成一定时间范围内的蠕变主曲线。分析形成主曲线相邻分曲线叠合处的应变量以及应变量斜率是否相同，判定主曲线是否光滑。利用最小二乘拟合法，运用WLF方程和Arrhenius方程对水平移动因子与温度的关系曲线进行拟合。结果: 蠕变应变量随应力水平或温度水平增大而增加；不同方向试样的应变量之间存在明显差异：轴向试样的应变量显著低于横向(弦向和径向)试样，弦向试样的应变量约为径向试样的2倍；叠合生成主曲线时，径向和弦向试样仅使用水平移动因子即可生成光滑的蠕变主曲线，主曲线跨越的时间由10³s延长至10⁷s；轴向试样仅通过水平移动因子无法生成光滑的蠕变主曲线，经垂直移动因子修正后的各轴向蠕变曲线能够叠合出光滑的主曲线，与未经垂直移动因子修正的蠕变主曲线相比，其跨越的时间由约10⁵s降低至约104.5 s；三方向试样水平移动因子与温度关系曲线在30~150℃内满足WLF方程，标准误差小于13.41%。结论: 时温等效原理在30~150℃范围内描述木材正交异向蠕变行为是适用的；轴向试样蠕变行为时温等效的构建需通过水平移动因子和垂直移动因子的共同作用，而径向和弦向试样仅使用水平移动因子即可使得时温等效原理适用；三方向试样蠕变主曲线水平移动因子与温度的关系曲线均满足WLF方程。

关键词: 杉木, 应力水平, 正交异向, 时温等效原理, 蠕变

Abstract:

Objective: The aim of this study was to investigate the application of time-temperature superposition principle(TTSP) to orthotropic creep of Chinese fir(Cunninghamia lanceolata). Method: Dynamic mechanical analysis(DMA 2980) was used to determine a sequence of short-term(20 min) tensile creep for longitudinal(L), radial(R) and tangential(T) specimens with a moisture content of 0.6% in the temperature range of 30℃ to 150℃ and at three stress levels. All creep curves at other temperatures were shifted along the log time axis to superimpose them on a reference temperature(i.e. 30℃ in this study) curve. The extended isothermal creep strain master curve was over a wide range of time. The smooth master curve should ensure that not only the values of creep strain match, but also the slope. The horizontal shift factor was determined to be a function of temperature and fitted into the WLF equation and Arrhenius equation with the least squares method. Result: Creep strain increased with increasing stress and temperature for each specimen, irrespective of grain orientation. There were differences in creep strain among the specimens with three grain orientations. Creep strain for L specimen was significantly lower than that for R and T specimens, and T specimen was higher than R specimen almost twice. TTSP was well matched for R and T specimens only using horizontal shift factor to construct master curves, and the extended time scale of master curves was from 10³ s to 10⁷ s. An additional vertical shift factor was applied to construct smooth master curve of L specimen, the extended time scale of master curve was about reduced from 10⁵ s to 104.5 s. In addition, only the excellent fit of the horizontal shift factor to the WLF equation(standard error of estimate < 13.61%) was observed over the entire temperature range in all orthotropic directions. Conclusion: The validity of TTSP to characterize the creep behavior of dry wood was found in the range of 30℃ to 150℃. The TTSP were constructed for R and T specimens using horizontal shift factor, while horizontal shift factor and vertical shift factor were used for L specimen. The WLF equation provided a better fitting with horizontal shift factor in all orthotropic directions.

Key words: Chinese fir, stress level, orthotropic, time-temperature superposition principle, creep

中图分类号:

S781

彭辉,蒋佳荔,吕建雄,赵荣军,曹金珍. 杉木正交异向蠕变行为的时温等效性[J]. 林业科学, 2021, 57(1): 153-160.

Hui Peng,Jiali Jiang,Jianxiong Lü,Rongjun Zhao,Jinzhen Cao. Time-Temperature Superposition in Chinese Fir Orthotropic Creep Response[J]. Scientia Silvae Sinicae, 2021, 57(1): 153-160.

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参考文献 0

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应力Stress	蠕变测试应力值Stress level/MPa
应力Stress	轴向Longitudinal	径向Radial	弦向Tangential
σ₁	1.0	0.4	0.16
σ₂	1.3	0.6	0.24
σ₃	1.6	0.8	0.32

试样 Specimens	应力值 Stress level/ MPa	WLF方程WLF equation				Arrhenius方程Arrhenius equation
试样 Specimens	应力值 Stress level/ MPa	C₁	C₂	表观活化能 Activation energy/ (kJ·mol^-1)	标准误差 Standard error (%)	表观活化能 Activation energy/ (kJ·mol^-1)	标准误差 Standard error (%)
轴向 Longitudinal	1.0	1.86	96.60	33.95	6.21	33.12	29.36
	1.3	1.71	72.02	41.66	5.97	34.56	28.53
	1.6	1.50	58.35	45.18	5.56	33.69	34.89
径向 Radial	0.4	9.75	253.15	67.74	7.34	65.04	11.98
	0.6	7.69	168.35	80.30	13.41	68.23	22.31
	0.8	7.98	156.29	89.78	13.13	74.39	28.40
弦向 Tangential	0.16	4.74	87.55	95.32	8.64	61.43	35.59
	0.24	5.90	105.28	98.49	6.12	69.68	31.26
	0.32	6.42	107.74	104.84	6.50	74.93	35.86

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