基于单边缺口拉伸试验的管线钢启裂韧度确定方法对比研究

Comparative Study of the Determination Methods of the Initiation Fracture Toughness of Pipeline Steel Based on the Single-Edge Notch Tension Test

摘要

断裂韧度对管道安全运行至关重要,单边缺口拉伸(SENT)试样因裂纹尖端拘束度低、接近管道的实际工况而广受关注．本文针对SENT试样的启裂韧度确定方法展开研究,以API X65 和 API X80管线钢为试验材料,参照标准BS 8571进行断裂韧度测试,采用单试样柔度卸载法计算阻力曲线,对比评估不同方法确定的启裂韧度值．结果表明：以基于伸张区宽度(SZW)定义的启裂韧度 J_szw 为参照,标准ESIS P2-92、ASTM E1820-23和ISO 12135-2021中的偏置钝化线定义的 J_0.2BL 普遍较大,相对误差大多超过了 100%,不适合用于 SENT 管线钢试样启裂韧度的确定,而无偏置钝化线得到的结果大幅度减小,相比更合理；标准 BS 8571 定义的 J_0.2最小误差仅为5%,最大误差达到36%,可对管线钢这样的中低强度钢提供较合适的启裂韧度估计值．

Abstract

Fracture toughness is essential to the safe operation of pipelines. The single-edge notch tension(SENT) specimen has attracted considerable attention because of its low crack tip constraint which is close the actual working conditions of the pipelines. In this study,the determination method of the initiation fracture toughness of SENT specimens was investigated. API X65 and API X80 pipeline steels were used as test materials,and fracture toughness tests were conducted according to the BS 8571 standard. The resistance curve was calculated by the single-specimen unloading compliance technique,and the initiation fracture toughness values determined by different methods were compared. The results show that the initiation fracture toughness J_SZW,defined based on the stretched zone width(SZW),is used as a reference. J_0.2BL determined by the offset blunting line in the ESIS P2-92,ASTM E1820-23,and ISO 12135-2021 standards is generally large,and the relative error is more than 100%,which is unsuitable for determining the initiation fracture toughness of the pipeline steel SENT specimens,while the results determined by the blunting line without the offset are significantly reduced,which is more reasonable. J_0.2 defined in the BS 8571 standard,whose minimum error is 5% and maximum error is 36%,can provide a more suitable estimation of the initiation fracture toughness for low-strength and medium-strength steels,such as pipeline steel.

关键词

单边缺口拉伸 / 裂纹钝化 / 伸张区宽度 / 钝化线 / 启裂韧度

Key words

single-edge notch tension / crack blunting / stretched zone width / blunting line / initiation fracture toughness

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基金资助

国家自然科学基金资助项目(52075366)