Tapered Interference-Fit Fastener for Lower Composite Assembly Force
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Solution Overview
Problem
Existing fastener systems for composite materials in aircraft production face issues such as high installation force loads, fretting, and fatigue due to loose fits, and existing solutions like sleeved bolt systems and clearance fit fasteners with cap seals are complex and time-consuming, while interference fit solutions may not optimize installation force reduction.
Innovation Solution
The use of interference fit fasteners with a linearly tapered lead-in section and a radiused lead-in section, which reduces installation forces by promoting gradual compression, enhancing joint fatigue life and fluid tightness, and eliminating the need for sleeves and cap seals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If clearance fit fasteners are used, then assembly is easier, but joint fatigue life decreases due to fretting and movement under cyclic loading
Solution Approach 1:
The patent changes the dimensional parameter of the fastener by providing a tapered lead-in section that transitions from a larger diameter at the head to a smaller diameter at the shank. This parameter change enables the fastener to progressively compress the composite material during installation, achieving interference fit conditions that eliminate fretting and enhance fatigue life while maintaining ease of assembly through the tapered geometry
2Reliability
If oversized fasteners are driven directly into holes, then interference fit is achieved, but installation force load increases causing composite material to crack or delaminate
Solution Approach 1:
The tapered lead-in section performs a preliminary action by gradually compressing the composite material ahead of the fastener shank during installation. This progressive compression prepares the material for the interference fit condition, distributing the installation force over a longer distance and reducing peak forces that would otherwise cause cracking or delamination
3Reliability
If sleeved bolt systems are used, then interference fit is achieved, but device complexity and assembly time increase
Solution Approach 1:
The patent extracts and eliminates the sleeve component from the fastening system by incorporating the interference fit functionality directly into the fastener itself through the tapered lead-in section. This removal of the sleeve simplifies the device complexity, reduces the number of parts, and decreases assembly time while maintaining the reliability of the interference fit
4Device complexity
If clearance fit fasteners with cap seals are used, then assembly is simpler, but joint deflection increases affecting fatigue performance and assembly time increases
Solution Approach 1:
The patent merges the functions of the fastener and the seal cap into a single integrated component. The tapered lead-in section provides both the interference fit function and the sealing function, eliminating the need for separate cap seals and reducing the number of assembly steps while maintaining fatigue performance through the interference fit
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 solution decreases installation force loads, increases joint fatigue life, reduces susceptibility to electromagnetic effects, and simplifies the assembly process by reducing assembly time and manufacturing complexity.
Implementation Method 1
A linearly tapered lead-in geometry accomplishes the foregoing by promoting gradual compression of material as the bolt is pushed through the structures to be fastened
Data Source
AI summary
An assembly comprising first and second structural elements having aligned holes, a fastener that occupies at least respective portions of the holes without a surrounding sleeve, and a mating part that is coupled to the fastener. The fastener comprises: a head; a circular cylindrical shank extending from the head; a mating portion comprising external projections; and a transition portion disposed between the shank and the mating portion. The transition portion comprises a tapered lead-in section that meets the shank at a shank/lead-in intersection and a radiused lead-in section that meets the tapered lead-in section. The tapered lead-in section tapers gradually in a first axial direction toward the mating portion and has a first profile that is linear and a taper angle equal to or less than 20 degrees, while the radiused lead-in section curves abruptly in the first axial direction and has a second profile that is a circular arc having a radius.