Welding Deformation and Residual Stress Prevention

Ninshu Ma, Hidekazu Murakawa, Yukio Ueda

• Publisher: Butterworth-Heinemann
• Year: 2012
• Print ISBN: 9780123948045
• eBook ISBN: 9780123948205
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Generally, welding produces welding deformation and residual stress in the products, which influences the quality and performance of the products. Although many engineers and researchers have made great effort how to control these incidents, they have still remained unresolved. Welding Deformation and Residual Stress Prevention provides a unique computational approach to the prediction of the effects of deformation and residual stress on materials. The goal is to provide engineers and designers with the ability to create their own computational system for predicting and possibly avoiding the problem altogether.- The basic theories including "theory of elastic-plastic analysis" and "inherent strain theory", and analysis procedures are described using a simple three-bar model- Online simulation software to perform basic analysis on welding mechanics- Examples of strategic methods and procedures are illustrated to have solved various welding-related problems encountered in the process of construction- Appendices present data bases for welding residual stresses, temperature dependent material properties, etc.

Chapter 1

Introduction to Welding Mechanics

1.1 Basic Concepts of Welding and Welding Mechanics

Fusion welding always produces thermal stress, deformation, and residual stress in products. The mechanism of production of stress and deformation and their influences upon the performance of welded structures are matters of keen concern for engineers. The theory of welding mechanics [1, 2] presents the theoretical framework for understanding these consequences. In classic welding mechanics, theories are based on an empirical formula and using simplified models. However, recently, thermal elastic-plastic analysis [3–6] by the finite element method (FEM) has become popular and has been applied to simulate the mechanical behavior of metal during welding.

In practice, general structures are fabricated by a series of production processes such as cutting, bending, joining, straightening, residual stress relieving, etc. (as shown in Table 1.1). These processes may be classified into the following three groups: utilization of thermal process, mechanical device, and chemical reaction.

Table 1.1. Manufacturing Processes for Welded Structures

Welding belongs to the first group, so-called fusion joining (welding), that is, to join components by melting a small portion of the metal.

The energy sources for melting metal are gas, arc, plasma, electron beam, laser, etc. These are selected according to the type of structure and the efficiency of the manufacturing. For example, since a heavy pressure vessel is composed of many thick plates, a highly efficient heat source such as electron beam welding, which provides a concentrated large amount of heat input, is often adopted. For large structures such as ships, bridges, etc., arc welding is widely used because its machine is cheap and can be handled easily.

Generally, fusion welding is conducted by moving a heat source along the weld line. The joining process by any type of fusion welding is almost always the same and includes the heating process, melting process, and solidification process no matter what kind of welding heat source is employed. Therefore, arc welding is selected as an example, and the basic concepts of computational welding mechanics are presented here.

Many different types of welded joints, such as butt joints, fillet joints, etc., as illustrated in Fig. 1.1, are used according to the shape characteristics of the structural components. The groove type also differs according to plate thickness to obtain sufficient penetration, as shown in Fig. 1.2 [7].

Fig. 1.1 Types of welded joints.

Fig. 1.2 Types of groove shapes.

In arc welding, the surface of the groove of the base metal is heated and molten by arc heating. Simultaneously, the electrode is also molten and fills into the groove. After cooling down, the joint is formed. Figure 1.3 is a schematic illustration of the electric power source and the welding arc....

Table of contents

• Cover Image
• Content
• Title
• Copyright
• Preface
• List of Symbols
• Chapter 1. Introduction to Welding Mechanics
• Chapter 2. Introduction to Measurement and Prediction of Residual Stresses with the Help of Inherent Strains
• Chapter 3. Mechanical Simulation of Welding
• Chapter 4. The Finite Element Method
• Chapter 5. Q&A for FEM Programs
• Chapter 6. Simulation Procedures for Welding Heat Conduction, Welding Deformation, and Residual Stresses Using the FEM Programs Provided on the Companion Website
• Chapter 7. Strategic Simulation Analyses for Manufacturing Problems Related to Welding
• APPENDIX A. Residual Stress Distributions in Typical Welded Joints
• Contents of Programs and Data on the Companion Website
• Index
• About the Authors