Grooved Blind Fastening Nut to Prevent Composite Delamination
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Solution Overview
Problem
Blind fastenings with splines can cause delamination in composite materials and scratching/metal crack initiation in metal structures due to rotational immobilization, especially in wet installations where the nut rotates before the screw is fully inserted.
Innovation Solution
A nut with grooving on its outer circumference, where the grooving density and radial pitch prevent rotational interference, allowing secure installation without material damage, achieved through specific ridge configurations and coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If longitudinal splines are formed on the nut outer surface to prevent rotation, then the nut is rotationally immobilized, but delamination occurs in composite materials and scratching/crack initiation occurs in metal structures
Solution Approach 1:
The invention changes the geometric parameters of the anti-rotation feature by using grooves with specific radial pitch (≤0.25 mm) and radial depth (0.6%-2% of nut outer diameter) instead of traditional splines. This parameter change allows the nut to be rotationally blocked without the material damage caused by spline penetration
Solution Approach 2:
The grooving is applied locally on the deformation zone outer circumference rather than uniformly across the entire nut surface. This localized application prevents material damage while providing sufficient rotational blocking where needed
2Reliability
If grooving with high radial pitch is used to prevent rotation, then rotational blocking is achieved, but the nut diameter exceeds the hole diameter preventing insertion
Solution Approach 1:
The invention optimizes the radial pitch parameter to be less than or equal to 0.25 mm (preferably 0.04-0.25 mm), which provides sufficient rotational blocking while keeping the maximum nut diameter in the grooving area less than or equal to the tightening zone outer diameter, ensuring proper insertion into the hole
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 nut is securely installed and rotationally blocked under operating torques without delamination or material damage, enabling reliable assembly in various structural materials, including composite and metal, even in wet conditions.
Implementation Method 1
the grooving comes into contact with the rear face and an edge forming an intersection between the hole and the rear face
Implementation Method 2
Grooving can also take the form of ridges separated by intermediate spaces... the nut is rotationally blocked under the expected operating torques
Data Source
AI summary
A nut (32) for assembling elements of a structure comprises a collar (64) capable of coming into contact with a front face of the structure; a tightening zone having an outer diameter (86) capable of being inserted into a hole of the structure; a deformation zone adjacent to the tightening zone and capable of forming a bulge against a rear face of the structure, opposite the front face; and a tapped portion (65) adjacent to the deformation zone.The nut may include grooving (82) on an outer circumference of at least one part of the deformation zone, a maximum diameter of said grooving (82) being less than or equal to the outer diameter (86) of the tightening zone.