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金属学报  2018, Vol. 54 Issue (12): 1785-1791    DOI: 10.11900/0412.1961.2018.00122
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面外拘束效应对单边缺口拉伸试样断裂韧性的影响
李一哲, 龚宝明(), 刘秀国, 王东坡, 邓彩艳
天津大学材料科学与工程学院天津市现代连接技术重点实验室 天津 300354
Out-of-Plane Constraint Effect on the Fracture Toughness of Single Edge Notch Tension Specimens
Yizhe LI, Baoming GONG(), Xiuguo LIU, Dongpo WANG, Caiyan DENG
Tianjin Key Laboratory of Advanced Joining Technology, School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China
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摘要: 

采用API X90管线钢,对不同厚度的单边缺口拉伸(SENT)试样进行断裂韧性实验,并结合全场应变测量技术和断口分析,研究SENT试样面外拘束(试样厚度)对裂纹尖端张开位移(CTOD)的影响。结果表明,在相同的载荷水平下,随着试样厚度的增加,最大纵向应变峰值急速下降,高纵向应变区域由裂纹尖端迁移至距裂纹面一定距离的未开裂侧,裂纹尖端的塑性变形能力降低。CTOD值对厚度变化很敏感,随着试样厚度的增加而降低。当试样厚度宽度比≥4时,临界CTOD值达到下平台并保持基本不变。因此,在管线工程设计中,可将试样厚度宽度比等于4作为SENT试样断裂韧性与试样厚度无关的一个参考试样尺寸。

关键词 断裂韧性面外拘束效应单边缺口拉伸完整性评估    
Abstract

The crack-tip stress and strain fields of single edge notch tension (SENT) specimen are similar to those of the full-scale pipe containing surface cracks under longitudinal tension and/or internal pressure. It is well known that material's fracture toughness is not constant, and the specimen size has a significant influence on fracture toughness. It is thus essential to consider the transferability from fracture specimens in laboratory testing to practical structures, i.e., size effects or constraint effects. However, the specimen dimensions for SENT specimens recommended by current design procedures have not validated the out-of-plane constraint effect on the fracture toughness. In this work, the effect of specimen thickness on the crack tip opening displacement (CTOD) of SENT specimen was investigated using an API X90 grade steel. Full-field deformation measurement by digital image correlation (DIC) technique and stretching zone width (SZW) examination were performed to analyze the size effects on fracture toughness. The results show that the critical crack initiation toughness is highly sensitive to specimen thickness, and decreases significantly as specimen thickness increases until the thickness-to-width ratio (B/W) equals to 4, beyond which the effect of specimen thickness becomes relatively weak. As the specimen thickness increases, the maximum longitudinal strain and stretching zone width decrease sharply, and the location of high-strain zones changes significantly; when B/W≥3, strain is initiated from the area opposite the cracked side rather than from the crack tip, indicating a strong loss of plasticity for thicker specimens. A dimension size is recommended for the fracture toughness testing to take the out-of-plane constraint into account for SENT specimen.

Key wordsfracture toughness    out-of-plane constraint effect    single edge notch tension    integrity assessment
收稿日期: 2018-04-02      出版日期: 2018-07-05
ZTFLH:  TG407  
基金资助:国家自然科学基金项目No.51305295及国家重点研发计划项目No.2016YFC0802105
作者简介:

作者简介 李一哲,男,1992年生,博士生

引用本文:

李一哲, 龚宝明, 刘秀国, 王东坡, 邓彩艳. 面外拘束效应对单边缺口拉伸试样断裂韧性的影响[J]. 金属学报, 2018, 54(12): 1785-1791.
Yizhe LI, Baoming GONG, Xiuguo LIU, Dongpo WANG, Caiyan DENG. Out-of-Plane Constraint Effect on the Fracture Toughness of Single Edge Notch Tension Specimens. Acta Metall, 2018, 54(12): 1785-1791.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2018.00122      或      http://www.ams.org.cn/CN/Y2018/V54/I12/1785

图1  X90钢的应力-应变曲线
图2  进行断裂韧性实验的SENT试样
Specimen B / mm BN / mm W / mm a/W B/W H / mm
SENT-0.5 9 7.65 18 0.4 0.5 10W=180
SENT-1 18 15.3 18 0.4 1 10W=180
SENT-2 36 30.6 18 0.4 2 10W=180
SENT-3 54 45.9 18 0.4 3 10W=180
SENT-4 72 61.2 18 0.4 4 10W=180
SENT-6 108 91.8 18 0.4 6 10W=180
表1  X90管线钢单边缺口拉伸试样尺寸
图3  SENT试样的载荷-位移曲线
图4  不同厚度试样的裂纹扩展阻力曲线
图5  试样厚度对临界裂纹尖端张开位移(δC)的影响
图6  不同厚度SENT试样的纵向应变
图7  不同尺寸SENT试样的伸张区宽度(WSZW)
图8  不同尺寸SENT试样的钝化角(θSZW)
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