论文总字数：23470字

摘 要

X80钢是我国天然气、石油管道输运中使用占比极大的管线钢钢种，具有优秀的力学特性和防腐蚀性能。但由于油气管线恶劣的服役条件，局部应力集中极易导致管线产生塑性变形，进而引发管道失效。针对管线安全服役问题，需要合理分析塑性变形对X80管线钢力学性能的影响。同时，获取变形过程中损伤的分布和演化过程，最终实现塑性变形条件下管线钢强度的合理评估。

针对X80管线钢的实际应用，本文以微型试样作为实验对象，开展了不同预应变条件下X80管线钢的微型拉伸试验研究，分析了塑性变形对材料力学性能的影响。同时耦合GTN塑性损伤本构方程建立了X80管线钢的数值分析模型，揭示了不同塑性变形条件下，试样的应力、应变分布以及损伤演化情况。主要研究内容和结论如下：

（1）针对预应变量为0%，3%、6%的微型拉伸试样开展了力学性能分析，揭示了不同塑性变形情况下，材料屈服强度、抗拉强度、断后延伸率的变化规律。结果表明：随着塑性变形的增加，材料的屈服强度上升，抗拉强度变化并不显著。随着屈强比的上升，断后延伸率呈现显著下降的趋势。

（2）为了进一步讨论试样的预应变强化程度，本文结合Hollomon经验公式建立了不同应变量下X80钢的塑性变形本构方程。结果表明：Hollomon经验公式可以有效描述不同塑性变形量下材料应力、应变关系。而描述材料应变硬化程度的参数n随预应变的提升而下降。

（3）本文耦合GTN塑性损伤方程，建立了X80管线钢塑性变形数值分析模型，在合理获取GTN损伤参量的基础上，描述了塑性变形过程中的应力、应变、损伤分布情况。结果表明：拉伸开始阶段，试件的应力、应变分布均匀，随着拉伸的进一步进行，呈现显著的应力集中现象，集中区的损伤也缓慢累积，到了紧缩阶段应力应变集中在紧缩区，而紧缩区损伤急剧上升直至断裂发生。

关键词：管线钢 力学性能 塑性变形 GTN模型

Abstract

X80 steel is a kind of pipeline steel used in China's current gas and oil pipeline transportation, with great mechanical performance and corrosion resistance. The oil and gas pipelines work in a poor service conditions. As the consequence, stress concentration can easily give rise to plastic deformation of pipeline. To solve the problem of pipeline safety in service, it`s necessary to evaluate the effect of plastic deformation on the mechanical properties of X80 pipeline steel. At the same time, the damage distribution and evolution process during deformation are obtained, and the reasonable strength evaluation of pipeline steel under the condition of plastic deformation is finally realized

In view of the practical application of X80 pipeline steel, the micro-tensile test of X80 pipeline steel under different pre-strain conditions was carried out in this paper, and the influence of plastic deformation on the mechanical performance of the material was analyzed Meanwhile, finite element model of X80 pipeline steel was established coupled GTN plastic damage constitutive equation. Reveals the different plastic deformation under the condition of stress and strain distribution of the specimen and the damage evolution law. The main research contents and conclusions are as follows:

(1) Mechanical properties analysis was carried out for the micro tensile samples with the pre-strain variables of 0%, 3% and 6%. The variation rules of yield strength, tensile strength and elongation after fracture are revealed under different plastic deformation conditions. The results show that the yield strength of the material increases with the increase of plastic deformation, but the tensile strength does not change significantly. As showed yield strength ratio increasing, the break elongation shows significant downward trend.

(2) The influence of pre-strain on the material properties was discussed. In this paper, combined with the empirical formula of Hollomon, the plastic deformation constitutive equation of X80 steel under different strain variables is established. The results show that the empirical formula of Hollomon can effectively describe the stress and strain relations of materials under different plastic deformation. The parameter n, which describes the strain hardening degree of the material, decreases with the increase of the pre-strain.

(3) Coupling GTN and plastic damage equation, this paper established the X80 pipeline steel model deformation numerical analysis model. On the basis of obtaining the damage parameters of GTN reasonably, the stress, strain and damage distribution in the plastic deformation process are described. The results show that the stress and strain distribution of the specimen is uniform at the beginning of tension. With the further stretching, the stress and strain are concentrated, and the damage in the concentrated area is slowly accumulated. In the stage of contraction, the stress and strain are concentrated in the contraction zone, and the damage in the contraction zone increases sharply until the fracture occurs.

Key words：Pipeline steel; mechanical property; plastic deformation; GTN model

目 录

摘 要 I

Abstract II

第一章 绪论 1

1.1 课题背景 1

1.2 管线钢变形特性 3

1.3 管线钢应变硬化特性及本构关系模型 4

1.4 预应变条件下管线钢的力学性能变化 6

1.5 本课题的研究内容和目的 7

第二章 考虑预应变的X80管线钢力学性能研究 8

2.1 引言 8

2.2 微型拉伸力学性能试验 8

2.2.1 实验材料 8

2.2.2 试验过程 8

2.3 不同预应变量拉伸试验研究 11

2.4 本章小结 13

第三章 基于GTN模型的管线钢数值分析模型 14

3.1 引言 14

3.2 ABAQUS有限元软件介绍 14

3.3 GTN损伤模型 14

3.4 有限元分析过程 16

3.5 本章小结 19

第四章 X80管线钢塑性变形的数值模拟分析 20

4.1 引言 20

4.2 应力、应变分布规律 20

4.2.1 拉伸过程应力分析 20

4.2.2 拉伸过程应变分析 22

4.3 不同塑性变形量的等效塑性应变分析 22

4.4 塑性变形损伤演化分析 23

4.5 本章小结 24

第五章 结论与展望 25

5.1 结论 25

5.2 经济性分析 25

5.3 展望 26

参考文献 27

致谢 30

绪论

课题背景

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