Q690D高强钢基于循环微孔扩展模型的断裂预测分析

葛建舟; 黄学伟; 赵军; 赵威; 魏晨晨

doi:10.13206/j.gjgS20061103

Q690D高强钢基于循环微孔扩展模型的断裂预测分析

doi: 10.13206/j.gjgS20061103

郑州大学力学与安全工程学院, 郑州 450001

基金项目:

国家自然科学基金项目（51608487）；国家重点研发计划（2016YFE0125600）；河南省科技攻关项目（192102310221）。

详细信息

作者简介:
葛建舟,男,1995年出生,硕士研究生。

通讯作者:
黄学伟,huangxw@zzu.edu.cn。

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出版历程
- 收稿日期: 2020-06-11
- 网络出版日期: 2021-09-16

Fracture Prediction and Analysis of Q690D High Strength Steel Based on Cyclic Void Growth Model

School of Mechanics and Engineering Science, Zhengzhou University, Zhengzhou 450001, China

摘要

摘要: 高强钢材在实际钢结构中已经开始逐步得到应用，开展钢材的超低周疲劳断裂分析是评价高强钢结构在强震作用下断裂破坏的基础。传统断裂力学方法均假定裂纹已经存在，且在初始裂纹尖端存在高应变约束，因此主要适用于研究塑性变形极其有限的脆性断裂问题，对超低周反复荷载下无宏观初始缺陷部位和发生显著塑性变形部位的延性断裂问题不太适用，基于微孔扩展机制的超低周疲劳断裂模型在钢材韧性断裂分析中开始逐步得到应用。
为研究循环微孔扩展模型（CVGM）是否适用于预测国产Q690D高强度结构钢材的断裂破坏，设计加工了17个圆棒试样和3个狗骨削弱型板状试样（DB）。应用MTS轴向伺服疲劳试验系统进行钢材圆棒试样在单调加载和超低周循环加载下的断裂破坏试验，获取了Q690D钢材的应力-应变关系、基本力学参数和试样的荷载-位移曲线，分析了加载制度对试样承载能力和变形能力的影响。
试验结果表明：1） Q690D钢材没有明显的屈服平台，存在明显的缺口强化效应和循环软化现象，由于循环加载过程中材料发生了损伤，使得循环加载后再拉伸时的断裂位移小于单调加载情况。2）通过分析试样断口形貌，发现试样裂纹均起始于试样最小截面中心处，并采用扫描电镜观察了试样断口的微观形貌，断口呈现韧窝形式的延性断裂特征，符合微孔扩展断裂力学的机理，同时通过电镜扫描结果得到了Q690D钢材的特征长度约为0.3 mm。
应用ABAQUS软件建立试样的有限元模型，基于Q690D钢材圆棒试样的试验结果，结合有限元分析，标定了Q690D高强度钢材的循环微孔扩展模型（CVGM）和退化有效塑性应变模型（DSPS）参数。单调加载时，循环微孔扩展模型和退化有效塑性应变模型退化为微孔扩展模型（VGM）和应力修正临界应变模型（SMCS）。最后，借助ABAQUS软件中的用户子程序USDFLD，采用Fortran语言对CVGM模型进行编程，在数值计算过程中，当材料单元达到破坏准则要求时，判定单元破坏，将单元的应力释放，然后按照新的状态继续进行有限元计算至试件破坏。应用钢材的CVGM，对狗骨削弱型板状试样在不同加载制度下的断裂破坏进行预测分析，得到试样的裂纹起始位置、荷载-位移曲线，断裂位移均与试验结果吻合良好，且试样极限荷载、断裂位移预测结果误差分别在2%、12%左右。
- Q690D钢材 /
- 微观断裂力学模型 /
- 断裂预测 /
- 超低周疲劳 /
- 有限元分析
Abstract: High strength steel has been gradually applied in practical steel structures. The ultra-low cycle fatigue fracture analysis of steel is the basis to evaluate the fracture failure of high strength steel structures under strong earthquake. The traditional fracture mechanics method assumes that the crack already exists, and there is a high strain constraint at the initial crack tip, so it is mainly suitable for the study of brittle fracture problems with extremely limited plastic deformation, but it is not suitable for the ductile fracture problems with no macroscopic initial defects and significant plastic deformation under ultra-low cyclic loading. The ultra-low cycle fatigue fracture model based on void growth mechanism has been gradually applied in the ductile fracture analysis of steel.
In order to study whether the cyclic void growth model (CVGM) is suitable for predicting the fracture failure of domestic Q690D high strength structural steel, 17 rod specimens and 3 dog-bone weakened plate specimens (DB) were designed and processed. The MTS axial servo fatigue test system was used to carry out the fracture test of round bar specimens under monotonic loading and ultra-low cycle loading. The stress-strain relationship, basic mechanical parameters and load-displacement curve of Q690D steel were obtained. The influence of loading system on the bearing capacity and deformation capacity of specimens was analyzed.
The experimental results show that:1) Q690D steel has no obvious yield platform, and there are obvious notch strengthening effect and cyclic softening phenomenon. Due to the damage of material during cyclic loading, the fracture displacement of cyclic loading is less than that of monotonic loading. 2) By analyzing the fracture morphology of the specimen, it is found that the cracks all start at the center of the minimum section of the specimen. The micro morphology of the specimen fracture is observed by scanning electron microscope. The fracture presents the ductile fracture characteristics of dimple, which conforms to the mechanism of void growth fracture mechanics. At the same time, the characteristic length of Q690D steel is about 0. 3 mm by scanning electron microscope.
The finite element model of Q690D high strength steel was established by using ABAQUS software. Based on the test results of Q690D rod specimen and combined with finite element analysis, the parameters of CVGM and DSPS of Q690D high strength steel were calibrated. Under monotonic loading, CVGM and DSPS degenerate into the void growth model (VGM) and the stress modified critical strain model (SMCS). Finally, with the help of user subroutine USDFLD in ABAQUS software, the CVGM model is programmed with Fortran language. In the process of numerical calculation, when the material element meets the requirements of failure criteria, the element failure is determined, the stress of the element is released, and then the finite element calculation is continued according to the new state until the specimen failure. The cyclic void growth model of steel is used to predict the fracture failure of dog-bone weakened plate specimen under different loading systems. The crack initiation position, load-displacement curve and fracture displacement of the specimen are in good agreement with the experimental results, and the prediction errors of ultimate load and fracture displacement are within 2% and 12% respectively.
- Q690D steel /
- micro fracture mechanics model /
- fracture prediction /
- ultra-low cycle fatigue /
- finite element analysis

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