Threaded Rivnut Installation for Brittle Composite Workpieces
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Solution Overview
Problem
The installation of conventional rivnuts in workpieces with brittle materials, such as polymer composites or ceramics, can cause localized damage like cracking or delamination due to the compressive force applied, which reduces the locking capacity and structural integrity of the final product.
Innovation Solution
A rivnut installation method involving the use of an externally threaded mandrel that softens the substrate layer with frictionally-generated heat, combined with a rivnut structural configuration featuring external threading on the hollow shaft, allowing for secure fastening without inducing damage by heating and softening the material during installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional rivnut installation method is used, then mechanical fastening is achieved, but localized damage (cracking or delamination) occurs in brittle substrate layers
Solution Approach 1:
The patent changes the physical state of the brittle substrate layer by heating it above its glass transition temperature, transforming it from a brittle state to a softened, more ductile state that can accommodate the rivnut installation without cracking or delamination
Solution Approach 2:
The substrate layer is pre-heated before rivnut installation to soften it in advance, allowing the subsequent mechanical fastening process to proceed without causing damage to the brittle material
2Strength
If compressive force is applied during rivnut installation, then mechanical anchoring is achieved, but substrate layer damage is induced
Solution Approach 1:
By changing the temperature parameter of the substrate layer to above its glass transition temperature, the material's mechanical properties are altered to become more ductile and less prone to damage under compressive loading during rivnut installation
3Adaptability or versatility
If brittle material with low ductility is used, then design flexibility is achieved, but deformation ability under load is restricted
Solution Approach 1:
The patent temporarily changes the temperature parameter of the brittle material during installation to enable deformation, then allows it to return to its original brittle state after installation, achieving both design flexibility and structural stability
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 method effectively mitigates the risk of cracking and delamination, ensuring secure mechanical anchoring and fastening of brittle materials by utilizing the heat-generated softening effect and external threading for interlocking, thereby maintaining the structural integrity of the workpiece.
Implementation Method 1
softening the substrate layer with frictionally-generated heat
Implementation Method 2
establish a threaded engagement between the externally threaded mandrel and an internally threaded bore defined by a lower wall portion of a hollow shaft of the rivet nut
Implementation Method 3
collapse the upper wall portion of the rivet nut into a radially outwardly extending bulge that bears on the back side of the workpiece
Data Source
AI summary
A rivet nut (“rivnut”) installation method and a rivnut structural configuration are disclosed that can be implemented separately in conjunction with one another to serve as an anchor in and/or a workpiece at an installation location. The rivnut installation method involves inserting a rivnut onto an externally threaded mandrel, rotating the mandrel while a free end of the mandrel is in contact with the workpiece, and driving the free end of the mandrel and the rivnut through the workpiece while continuing to rotate the mandrel. The method is particularly useful when the workpiece includes one or more substrate layers composed of a low ductility material such as a polymer composite. The rivnut structural configuration includes the incorporation of an external threading onto at least a portion of a hollow shaft of the rivnut.