Composite Tube Collar Coupling for Consistent Holding Strength
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Solution Overview
Problem
The holding strength between tube fittings and collars is often inconsistent, leading to permanent failures under load, as existing solutions fail to provide a reliable and consistent interface for withstanding mechanical stresses.
Innovation Solution
A fiber-reinforced composite collar with a tapered inner surface and specific fiber orientations is used to apply a radial compressive force to the tube, enhancing the interface strength by ensuring consistent engagement with the tube's tapered outer surface, and a method involving axial loading to achieve predetermined hoop stress levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a collar is placed over the tube end to clamp the tube to the fitting, then the tube and fitting are connected, but the holding strength between the tube and fitting is inconsistent leading to permanent failures
Solution Approach 1:
The collar applies a predetermined axial load to achieve a target hoop stress level (e.g., 50% of ultimate hoop stress) in the tube, transforming the connection from relying on friction alone to a controlled stress state that ensures consistent holding strength. This parameter-based approach (controlling axial load to achieve specific hoop stress) resolves the inconsistency in holding strength.
Solution Approach 2:
The collar is made from fiber-reinforced composite material with specifically oriented fibers (e.g., 0-degree fibers for axial strength, 90-degree fibers for hoop strength) that provide consistent mechanical properties and predictable stress distribution, ensuring reliable and consistent holding strength between the tube and fitting.
2Strength
If the collar applies radial compressive force to the tube, then the interface strength is enhanced, but stress concentrations may occur leading to premature failure
Solution Approach 1:
The collar has a curved, arc-shaped cross-section that conforms to the tube's outer surface, distributing the compressive force evenly around the tube's circumference. This curved geometry eliminates stress concentrations that would occur with flat or angular contact surfaces, enhancing interface strength while avoiding premature failure.
Solution Approach 2:
The collar's fiber reinforcement is strategically oriented with fibers at different angles (e.g., 0-degree for axial compression resistance, 90-degree for hoop stress resistance) in different regions of the collar, providing locally optimized stress distribution that enhances interface strength while minimizing stress concentrations.
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 provides a consistent and strong connection between the tube and fitting, capable of withstanding loads without premature failure, with the collar's design ensuring even compressive force distribution and reduced stress concentrations.
Implementation Method 1
The collar is pressed with a predetermined axial load which positions the collar at an appropriate location over the tube and achieves a target hoop stress level in the collar
Implementation Method 2
A fiber-reinforced composite collar with a tapered inner surface and specific fiber orientations is used to apply a radial compressive force to the tube, enhancing the interface strength
Implementation Method 3
the collar's design ensuring even compressive force distribution and reduced stress concentrations
Data Source
AI summary
A method for coupling a fitting to a tubing end includes pressing a collar over the outer surface of the tubing until the strain on the collar in the hoop direction is at a predetermined level, or pressing a collar with a predetermined axial load.