Pipe Coupling Groove Geometry for Fatigue-Resistant Joints
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Solution Overview
Problem
Polymeric pipe elements are prone to failure at joints due to stress concentrations caused by mechanical couplings with arcuate projections, leading to fatigue and ultimate failure under cyclic or high loads, exacerbated by manufacturing tolerances which increase geometric variability and stress at the groove corners.
Innovation Solution
A coupling design featuring segments with adjustable attachment members, semi-circular arcuate projections, and clearance relief regions of increasing radius curvature, along with relief grooves and shoulders that match the pipe elements' curvature, reducing stress concentrations and accommodating manufacturing tolerances to enhance joint performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If arcuate projections with sharp corners are used to engage circumferential grooves, then the coupling can effectively transfer forces and stresses across the joint, but stress concentrations are formed at the groove corners leading to fatigue failure
Solution Approach 1:
The invention replaces the traditional sharp-cornered arcuate projections with projections that have rounded corners and curved surfaces. The groove corners are also rounded rather than sharp. This curvature eliminates the stress concentration points that occur at sharp corners, allowing the joint to withstand cyclic loads and bending forces without initiating fatigue cracks, while still maintaining effective force transfer capability.
Solution Approach 2:
The invention modifies the local geometry at the critical groove corner regions by rounding the corners and creating curved transition surfaces. This local geometric change concentrates the contact area and distributes stresses more evenly across the projection-groove interface, preventing stress concentration while maintaining the overall force transfer function of the coupling.
2Stress or pressure
If the groove depth is minimized to reduce stress, then the engagement height between keys and groove sides is reduced, but stress concentrations at groove corners increase
Solution Approach 1:
By rounding the groove corners and creating curved transition surfaces, the invention allows for adequate engagement depth without creating stress concentration points. The curved geometry provides a gradual transition that distributes stresses evenly, enabling the groove to be deep enough for strong engagement while avoiding the stress concentrations that would occur at sharp corners.
3Ease of manufacture
If manufacturing tolerances are accommodated with geometric variability, then the coupling can be manufactured with standard tolerances, but stress concentrations are exacerbated due to variability in key/groove interface
Solution Approach 1:
The invention changes the geometric parameters of the groove and projection from sharp corners to rounded corners with specific radius of curvature. This parameter change makes the interface less sensitive to manufacturing tolerances because the curved surfaces provide a larger contact area and more forgiving geometry, reducing the impact of dimensional variations on stress distribution while maintaining manufacturability with standard tolerances.
4Force
If the key/groove interface is designed to maximize engagement height, then force transfer is improved, but stress concentrations at groove corners increase leading to fatigue failure
Solution Approach 1:
The invention uses curved surfaces and rounded corners at the groove and projection interfaces to maintain deep engagement for effective force transfer while eliminating the stress concentration points that would lead to fatigue failure. The curved geometry allows the full engagement depth to be utilized without creating high-stress zones at sharp corners.
Data Source
Figure 1~2
Figure 3
Figure 3A~3B
AI summary
Pipe elements (48, 50) have circumferential grooves (58). The grooves have a first side surface contiguous with a first floor surface. The first side surface and the first floor surface together subtend a first 90° circular arc when viewed in cross section. The grooves also have a second side surface contiguous with a second floor surface. The second side surface is in spaced relation to and in facing relation with the first side surface. The second side surface and the second floor surface together subtend a second 90° circular arc when viewed in cross section. A third floor surface is contiguous with both the first and second floor surfaces and is a flat surface. A coupling used to connect the pipe elements has arcuate projections which engage the grooves of the pipe elements. The arcuate projections have a semi-circular cross section. Relief grooves (31) are positioned adjacent to each arcuate projection.