Diamond Wire Starter Notch for Fatigue Crack Direction Control
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Solution Overview
Problem
Existing methods for initiating fatigue-cracks in aircraft structures, such as EDM, often result in cracks growing in unintended directions due to micro-cracking and thermal changes, making it difficult to achieve natural crack growth for effective nondestructive inspection evaluations.
Innovation Solution
A method using a cutting wire with a diamond impregnated wire guided by pulleys within a housing to form a starter notch in a work-piece, allowing for precise control of the notch orientation and direction, ensuring fatigue cracking occurs within a specific range relative to the notch's penetration length direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If EDM is used to produce starter notches, then very small and tight starter notches can be obtained, but fatigue-cracks grow in directions that are not along the major axis of the EDM starter notch
Solution Approach 1:
The patent changes the fundamental parameters of the starter notch formation process by switching from EDM (electrical discharge machining) to wire cutting (mechanical cutting with diamond-impregnated wire). This parameter change eliminates the micro-cracking and thermal effects inherent in EDM, thereby controlling crack growth to occur along the major axis of the starter notch as intended.
Solution Approach 2:
The patent replaces the electrical discharge machining system with a mechanical wire cutting system. The wire cutting apparatus uses a diamond-impregnated wire to mechanically cut the starter notch, avoiding the electrical arc and thermal effects that cause unwanted micro-cracking in EDM, thus ensuring reliable crack growth direction.
2Adaptability or versatility
If EDM is used to produce starter notches, then starter notches can be formed in various aircraft metals, but high temperature of the electrical arc induces change in the morphology of the metal structure
Solution Approach 1:
The patent replaces the thermal-electrical EDM process with a mechanical wire cutting process. The diamond-impregnated wire mechanically cuts through various aircraft metals (aluminum, titanium, steel) without generating the high temperatures of electrical arcs, thereby preserving the original metal structure morphology and avoiding unwanted phase changes or microstructural alterations.
Solution Approach 2:
The patent converts the potential harm of thermal effects by eliminating the electrical arc entirely. Instead of trying to manage or mitigate the thermal damage from EDM, the solution completely removes the heat source by using mechanical wire cutting, thus preventing any temperature-induced changes in metal morphology while maintaining versatility across different metal types.
3Ease of manufacture
If saw cuts are used to form starter notches, then cutting process is simple, but the notches are too large to be useful
Solution Approach 1:
The patent changes the cutting tool parameters by using a thin diamond-impregnated wire instead of a broad saw blade. This parameter change allows the formation of very narrow starter notches (comparable in size to EDM notches) while maintaining the simplicity of a cutting process, as the wire can be fed through a pre-drilled hole to create precise, small notches without the complexity of EDM equipment.
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 solution enables the formation of starter notches that promote fatigue cracking along the intended axis, reducing cracking in other directions and facilitating more accurate nondestructive inspection technologies by using a lightweight, portable wire cutting apparatus.
Implementation Method 1
A method using a cutting wire with a diamond impregnated wire guided by pulleys within a housing to form a starter notch in a work-piece
Implementation Method 2
A position of at least one of the wire guide pulleys may be adjustable to accomplish the change in cutting angle of the cutting wire
Data Source
AI summary
A method and apparatus for forming a starter notch along the length of a work-piece for subsequent fatigue testing. The starter notch is formed with a cutting wire such that it will promote fatigue-cracking in the work-piece in one defined direction and avoids cracking in directions other than the length direction of the starter notch. Improved fatigue-testing analysis may therefore be realized.