摘 要

二十世纪中叶以来，冷弯成型技术得到迅猛发展，国内外对其研究也越来越深入，研究领域主要在冷弯成型的残余应力分布以及各种截面型钢的成型仿真模拟。然而，目前绝大多数的研究中，将钢板在其他工艺过程的残余应力忽略，将其初始状态定义为无应力状态直接进行仿真分析，且装甲车车身使用的高强度钢板由于屈服强度高而使成型难度变大。因此本文对高强度钢板的冷弯成型过程进行仿真模拟，比较施加与不施加初始残余应力两种情况的成型结果，来探究残余应力的影响。

本文利用Abaqus有限元软件进行了轧下率为10%，15%，20%以及25%冷轧过程和三道次以及四道次冷弯成型过程的模拟，将冷轧后的残余应力设置为钢板的初应力引进冷弯成型过程中，通过比较钢板成型结果图以及某一相同单元的等效应力与等效应变时间历程曲线，来得出施加不同轧下率时的冷轧残余应力的钢板与无残余应力钢板的成型结果的异同点，从而分析出残余应力的影响。

通过各种情况的钢板成型图以及选取单元的等效应力与等效应变时间历程曲线，可以看出钢板的成型结果和塑性应变大小及时刻大致相同，只是在等效应力图中，施加了残余应力的钢板选取单元的应力值先由200MPa左右下降，在被轧辊咬入后应力值迅速升高，之后的应力变化与不施加钢板的等效应力变化相似。因此，可以得出钢板在冷轧过程的残余应力对冷弯成型过程的影响很小，几乎不影响成型结果。

关键词：残余应力；冷弯成型；Abaqus；高强度钢

Abstract

Since the middle of the 20th century, the cold-bending forming technology has been developed rapidly, and its research has been more and more in-depth at home and abroad. The research field is mainly in the distribution of residual stress in cold-bending forming and the simulation of forming of various sections of steel. However, in most of the current research, the residual stress of steel plate in other process is ignored, and its initial state is defined as no stress state for direct simulation analysis, and the high-strength steel plate used in armored vehicle body is difficult to form due to its high yield strength. In this paper, the cold-bending forming process of high-strength steel plate is simulated, and the results of forming with and without initial residual stress are compared to explore the influence of residual stress.

In this paper, Abaqus finite element software is used to simulate the cold rolling process of 10%, 15%, 20% and 25% rolling rate and the cold-bending forming process of three and four passes. The residual stress after cold rolling is set as the initial stress of the steel plate, which is introduced into the cold-bending forming process. Comparing the forming results of the steel plate and the equivalent stress and strain time history curve of the same element, the similarities and differences of forming results of steel plate with cold rolling residual stress under different rolling rates and steel plate without residual stress are obtained, and the influence of residual stress is analyzed.

According to the forming diagram of steel plate and the time history curve of equivalent stress and equivalent strain of the selected element, it can be seen that the forming result of steel plate is approximately the same as the size and time of plastic strain, but in the equivalent stress diagram, the stress value of the selected element of steel plate with residual stress applied first drops from about 200MPa, and then rises rapidly after being bitten by the rollers and the change of stress is similar to the change of stress of steel plate without residual stress. Therefore, it can be concluded that the residual stress of steel plate in cold rolling process has little effect on the cold-bending forming process, almost no effect on the forming results.

Key Words：residual stress；cold-bending forming；Abaqus；high-stress steel

Table of Contents

Chapter 1 Introduction 1

1.1 Background 1

1.2 Cold-bending forming 1

1.2.1 Development history of cold-bending forming 1

1.2.2 Characteristics of cold-bending forming 2

1.3 Numerical simulation of cold-bending forming 2

1.4 High strength steel 3

1.5 Residual stress 4

1.6 Research status at home and abroad 4

1.7 Research significance of this topic 6

Chapter 2 Finite Element Simulation of high strength steel without initial residual stress 7

2.1 Introduction 7

2.2 The pretreatment of finite element analysis 8

2.2.1 Unit setting 8

2.2.2 Establish finite element model 9

2.2.3 Define material properties 9

2.2.4 Assembly 10

2.2.5 Analysis step setting 11

2.2.6 Set contact 12

2.2.7 Boundary conditions 12

2.2.8 Mesh division 13

2.3 Post-processing of finite element analysis 14

Chapter 3 Finite Element Simulation of high strength steel with initial residual stress 18

3.1 Cold rolling process 18

3.2 Apply residual stress 20

3.3 The forming results of angle steel with residual stress 20

3.4 Analysis of simulation results of angle steel forming with residual stress 22

3.5 Cold-bending forming results of four passes 26

Chapter 4 Conclusions and prospect 32

4.1 Major conclusions 32

4.2 Prospect 32

References 34

Acknowledgements 36

Introduction

Background

Cold-bending forming is a new technology for metal sheet forming which is material-saving, energy-saving and efficient. Using this process, not only can produce high-quality steel products, but also can shorten the product development cycle and improve production efficiency, thereby improving the market competitiveness of enterprises. In recent years, cold-formed steel products have been widely used as important structural parts in many fields such as construction, automobile manufacturing, shipbuilding, electronics industry, and machinery manufacturing.

The cold-formed steel produced by high-strength steel through the cold-bending forming process is also becoming more and more widely used on armored vehicle bodies.

Cold-bending forming

Cold-bending forming is a plastic processing method in which hot-rolled or cold-rolled steel plates are used as raw materials, and continuously pass through longitudinally arranged multi-pass rolls at normal temperature to form steel plates with a specific cross-sectional shape.

Development history of cold-bending forming