Welded Joint Backing Material for Higher Fatigue Strength
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Solution Overview
Problem
Existing welded structures, particularly large ones, face challenges in achieving improved fatigue strength due to the high cost and limited applicability of specialized steels required to prevent fatigue fracture at welded portions.
Innovation Solution
A welded structure design that incorporates a backing material made of steel with a volume per unit mass greater at room temperature than at the Ms point, which undergoes martensitic transformation during cooling, creating a compressive stress in the welded portion and thereby enhancing fatigue strength without the need for high-cost materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If specialized steel with low Ms point is used to improve fatigue strength at welded portions, then fatigue strength is improved, but material cost increases significantly
Solution Approach 1:
The invention applies different material properties to different regions: the backing material has low Ms point for generating compressive stress, while the main structural steel can be standard high-strength steel. This localized application of specialized material properties reduces overall cost while maintaining fatigue strength at the welded portion.
Solution Approach 2:
The backing material acts as an intermediary element that generates compressive residual stress to protect the welded portion from fatigue. By using a thin layer of specialized steel as the backing material rather than throughout the entire structure, the invention achieves fatigue protection at minimal material cost.
2Strength
If low Ms point steel is used throughout the welded structure, then fatigue strength is improved, but the structure becomes economically unviable for large-scale applications
Solution Approach 1:
The invention restricts the use of low Ms point steel to only the backing material region, while the main structural components use standard high-strength steel. This localized approach makes large-scale welded structures economically viable while still achieving improved fatigue strength at the critical welded portions.
3Strength
If compressive stress is introduced to prevent fatigue fracture, then fatigue strength is improved, but the complexity of achieving and maintaining the stress state increases
Solution Approach 1:
The invention utilizes the martensitic phase transition of the low Ms point steel in the backing material during cooling. This phase transition automatically generates compressive residual stress in the welded portion without requiring external stress application or complex control systems, simplifying the overall process.
Solution Approach 2:
The backing material self-generates compressive residual stress through its own martensitic transformation during cooling. This self-service mechanism eliminates the need for external stress induction processes or complex stress control systems, reducing overall system complexity.
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
The proposed welded structure achieves improved fatigue strength, making it applicable to large structures while maintaining cost-effectiveness, as the enhanced fatigue resistance is achieved using standard steel for the backing material.
Implementation Method 1
the steel constituting the backing material has a volume per unit mass greater at room temperature than at the Ms point
Data Source
AI summary
A welded structure includes a first member which is a steel plate or a cast steel, a second member which is a steel plate or a cast steel disposed adjacent to the first member with a space therebetween, a first welded portion filling the space and joining the first member to the second member, and a backing material composed of a steel and disposed in contact with the first welded portion so as to close a first opening of the space, the backing material including a transformed region having a martensitic structure in the region in contact with the first welded portion. The steel constituting the backing material has a volume per unit mass greater at room temperature than at the Ms point.