Friction Stir Welding Compressive Stress Fatigue
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Friction stir welding of large components, such as aircraft fuselage sections, faces challenges in maintaining narrow tolerances to prevent lack of penetration (LOP) defects, which reduce the fatigue limit and residual strength of welds, and existing methods like bobbin tools or machining are either impractical or costly.
Innovation Solution
Introducing internal compressive stresses into the weld edge portion of the friction stir weld using methods like laser shock peening, low plasticity burnishing, or ultrasonic peening to offset tensile stresses and prevent microcrack formation and spread, allowing for a reliable and rapid connection with minimal material usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional friction stir welding pin tool is used to weld large components, then the welding process is simple and cost-effective, but it is virtually impossible to maintain narrow tolerances to prevent LOP defects
Solution Approach 1:
The patent applies preliminary anti-action by introducing compressive residual stresses into the weld edge portion before the welding process completes. This pre-applied compressive stress counteracts the tensile stresses that would otherwise cause LOP defects and microcrack formation, allowing the use of simple pin tools while maintaining high precision penetration depths.
Solution Approach 2:
The patent changes the stress state parameter in the weld edge portion by introducing compressive residual stresses through methods such as laser shock peening, ultrasonic peening, or mechanical peening. This parameter change allows the weld edge to tolerate variations in penetration depth without forming LOP defects, effectively decoupling precision requirements from tool complexity.
2Reliability
If a bobbin friction stir welding tool is used to eliminate LOP defects, then full penetration is ensured, but the connection region must be accessible from each side and the weld is visible from each side
Solution Approach 1:
The patent inverts the conventional approach by using a single-sided pin tool instead of a two-sided bobbin tool. The innovation lies in applying compressive residual stresses to the weld edge portion after single-sided welding, which compensates for the incomplete penetration that would normally occur with pin tools. This inversion allows full penetration reliability to be achieved from one side only, eliminating accessibility and visibility constraints.
3Weight of moving object
If friction stir welding is used to connect thin-walled aluminium components, then weight is reduced compared to riveting, but LOP defects significantly reduce the fatigue limit of welds
Solution Approach 1:
The patent converts the harmful effect of tensile stresses in the weld edge portion into a benefit by introducing compressive residual stresses. These compressive stresses not only prevent LOP defects and microcrack formation but also enhance the fatigue limit of the weld. The compressive stress state acts as a protective mechanism that maintains high fatigue performance while using lightweight friction stir welding instead of riveting.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the fatigue limit and residual strength of friction stir welds to match that of the base material, enabling rapid, reliable, and cost-effective joining of large-surface components with reduced material usage and minimal risk of LOP defects.
Implementation Method 1
The shoulder heats the component surfaces adjacent to the connection region by friction, thus heating the material of the components to just below the melting point
Implementation Method 2
Introducing internal compressive stresses into the weld edge portion of the friction stir weld using methods like laser shock peening
Implementation Method 3
Introducing internal compressive stresses into the weld edge portion of the friction stir weld using methods like ultrasonic peening
Implementation Method 4
Introducing internal compressive stresses into the weld edge portion of the friction stir weld using methods like low plasticity burnishing
Data Source
AI summary
A method for the friction stir welding of two components, in particular of two shell components of a fuselage structure of an aircraft and spacecraft, said method comprising the following method steps: positioning the two components relative to one another in such a way that a connection region is formed between the two components; friction stir welding the two components by a friction stir welding tool which penetrates the connection region in order to produce a weld which permeates the connection region with the formation of an unpenetrated weld edge portion of the connection region; and introducing internal compressive stresses, at least in the weld edge portion of the connection region. Further a device for the friction stir welding of two components, in particular of two shell components of a fuselage structure of an aircraft and spacecraft is provided.