﻿ 线弹性断裂力学原理在木材中应用的特殊性与木材顺纹理断裂
 林业科学  2002, Vol. 38 Issue (6): 110-115 PDF
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文章信息

Shao Zhuoping, Jiang Zehui, Ren Haiqing.

THE PARTICULARITY OF APPLICATION OF PRINCIPLES OF LINEAR-ELASTIC FRACTURE MECHANICS TO WOOD AND FRACTURE PARALLEL TO GRAIN

Scientia Silvae Sinicae, 2002, 38(6): 110-115.

作者相关文章

1. 安徽农业大学 合肥 230036;
2. 中国林业科学研究院木材工业研究所 北京 100091

THE PARTICULARITY OF APPLICATION OF PRINCIPLES OF LINEAR-ELASTIC FRACTURE MECHANICS TO WOOD AND FRACTURE PARALLEL TO GRAIN
Shao Zhuoping1, Jiang Zehui2, Ren Haiqing2
1. Anhui Agricultural University Hefei 230036;
2. Research Institute of Wood Industry, CAF Beijing 100091
Abstract: The particularity about applying the principles of linear-elastic fracture mechanics (LEFM)to wood were expounded. The fracture toughness KICTL parallel to grain of wood of Chinese fir (C. lanceolata) and Masson pine (P. massoniana) were determined with different samples and methods. The results showed that LEMF based on isotropic material is suited for wood crack growth parallel to grain. The fracture toughness parallel to grain is a basic property of wood.
Key words: Wood fracture    Liner electric fracture mechanics    Fracture toughness    Test technique

1 线弹性断裂力学的原理

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Irwin (1957)利用Westergard应力函数, 从研究弹性体裂纹尖端的应力分布出发, 阐明裂尖处应力场的一般形式如下:

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 (3)

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 图 1 裂纹力学特征 Fig. 1 Crack mechanics feature
2 线弹性断裂力学在木材中应用的特殊性

 图 2 木材基本裂纹分类 Fig. 2 The six crack propgation systems of wood

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 图 3 裂纹及纤维方向示意图 Fig. 3 Crack orientation α for fiber

3 木材顺纹断裂韧性KIC的测试方法与结果

 图 4 测试断裂韧性的基本试样 Fig. 4 The basic samples of testing for fracture toughness

3.1 不同厚度下CT试样的KICTL

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 图 5 杉木(a)、马尾松(b) CT试样KICTL关于厚度B的散点图 Fig. 5 KICTL vs.thick B for CT samples of Chinese fir (a) and Masson pine (b).
 图 6 杉木WOL试样KIC关于裂纹长度a的散点图 Fig. 6 KICTL vs. length a of crack for WOL sample of Chinese fir

3.2 不同裂纹长度下WOL试样的KICTL

WOL试件是紧凑拉伸试样的改进型, 它比标准CT试样稍长, 因而可以通过由不同的裂纹长度a来测定材料的值。WOL试件尺寸为:B=20 mm, W=2.55B, H=2.48B, e=0.13 mm。为了检验裂纹长度对杉木顺纹断裂韧性是否有影响, a取不同的裂纹长度, 使a/W分别为0.3、0.4、0.5、0.6、0.7, 共11个试件。试样制作与试验程序同紧凑拉伸试件的制作要求完全一致。断裂韧性计算公式如下:

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3.3 基于能量原理的柔度法测定DCB试样的KICTL

Sih等(1965)研究了正交各向异性体单一裂纹尖端附近的应力场, 指出当裂纹与其上一对称平面平行时, 因弹性常数S16=S26=0, 而得到只含有四个独立弹性常数的能量释放率与应力强度因子的关系式:

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 图 7 杉木DCB试样的柔度标定曲线 Fig. 7 Compliance plot curve vs. a/W for DCB sample of Chinese fir
4 CT、WOL、DCB三种试样的测定结果比较分析

5 结论

 崔振源编著. 断裂韧性与测试原理和方法, 上海: 科学技术出版社, 1981, 15~ 34 国家标准局. 金属材料平面应变断裂韧度KIC试验方法(GB4161-84). 北京: 中国标准出版社, 1984 http://www.csres.com/detail/107667.html 邵卓平, 任海青, 江泽慧. 2001. 柔度法标定木材断裂韧性的研究. 林业科学, 38(2): 113-117. Barrent J D. 1976. Effect of crack-front width on fracture toughness of Doouglas-fir. Eng. Frac. Mech., 8(4): 711-717. DOI:10.1016/0013-7944(76)90044-8 Boatright S W J, Garrentt G G. 1983. The effect of microstructure and stress state on the fracture behaviour of wood. J. of Materials Sci., 18: 2181-2199. DOI:10.1007/BF00555013 Irwin G R. 1957. Analysis of stresses and strain near the end of a crack traversing a plate, J. J. Appl. Mech., 24: 361-364. Porter A W. 1964. On the mechanics of fracture in wood. Forest Products journal, 14(8): 325-316. Sih G C, Prais P C, Irwin G R. 1965. On cracks in rectilinearly anisotropic bodies using singular isoparametric elements. Int. J. of Fracture Mech., 1: 189-203. Sneddon I N, Elliott H. A. Quart, Appl Math, 1946, 4: 229 Triboulot P, Jodin P, Pluvinage G. 1984. Validity of fracture mechanics concepts applied to wood by finite element calculation. Wood Sci Techol, 18: 51-58. DOI:10.1007/BF00632130