Pipe Coupling Relief 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 that increase geometric variability and stress at the groove corners.
Innovation Solution
The coupling design incorporates clearance relief regions with increasing radius of curvature on arcuate projections and relief grooves that extend lengthwise along the segments, reducing stress concentrations and accommodating manufacturing tolerances, along with adjustable attachment members and a ring seal for secure pipe element connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If arcuate projections with groove engagement are used to connect pipe elements, then mechanical strength and joint stability are improved, but stress concentrations at groove corners increase leading to fatigue failure
Solution Approach 1:
The invention replaces sharp corner geometries with curved surfaces. Specifically, the groove corners are rounded with a radius of curvature, and the arcuate projections are designed with curved engagement surfaces. This curvature eliminates stress concentration points by distributing stresses more evenly across the joint interface, thereby improving fatigue resistance while maintaining joint strength.
Solution Approach 2:
The invention applies different geometric properties to different regions of the coupling. The groove corners are specifically modified with increased radius of curvature compared to other regions, creating localized stress relief zones. This local geometric modification targets the specific problem area (groove corners) without compromising the overall engagement strength.
2Reliability
If groove depth is minimized to reduce stress, then stress concentrations are reduced, but engagement height between keys and groove sides must be maximized for performance
Solution Approach 1:
The invention transitions from a two-dimensional groove cross-section to a three-dimensional curved engagement surface. By introducing radial curvature to the groove corners and using arcuate projections with curved surfaces, the engagement geometry extends into the radial dimension, allowing sufficient engagement height to be achieved without increasing groove depth in the axial direction.
3Manufacturing precision
If manufacturing tolerances are accommodated in coupling design, then geometric variability is reduced, but stress concentrations at key-groove interface increase
Solution Approach 1:
The invention changes the geometric parameters of the key-groove interface, specifically increasing the radius of curvature at groove corners and modifying the arcuate projection geometry. These parameter changes create a more tolerant interface that can accommodate manufacturing variations without generating excessive stress concentrations, as the curved surfaces provide a larger contact area and more gradual stress transitions.
Data Source
Figure 1~2
Figure 3
Figure 3A~3B
AI summary
Pipe elements have circumferential grooves. 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 are positioned adjacent to each arcuate projection.