Break-Away Coupling Geometry for Roadside Fatigue Resistance
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Solution Overview
Problem
Existing break-away couplings for highway and roadway appurtenances, such as lighting poles, exhibit limited fatigue strength, leading to premature failure under cyclic loads, which is a critical safety concern as they are designed to fail upon impact to mitigate vehicular damage and injury.
Innovation Solution
A fatigue-enhanced break-away coupling design featuring a central axis with a necked-down region formed by two inverted truncated cones, where the exterior surface is a curved surface of revolution with base angles θ1 and θ2 selected between 20°-40°, specifically optimized to reduce stress gradients and enhance fatigue properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional break-away couplings are designed with frangible areas or circumferential grooves to reduce bending resistance, then the coupling can fail more easily upon impact, but the fatigue strength is reduced leading to premature failure under cyclic loads
Solution Approach 1:
The patent applies parameter changes by optimizing the geometric parameters of the necked-down region, specifically the base angles θ1 and θ2 of the inverted truncated cones. By selecting specific angle ranges (20°-40°), the design achieves improved fatigue strength while maintaining the break-away function. This resolves the contradiction by finding optimal parameter values that balance fatigue resistance with impact failure capability.
2Strength
If the coupling is designed to fail at predetermined frangible areas with stress concentrators, then impact failure is facilitated, but the coupling exhibits limited fatigue strength and premature failure
Solution Approach 1:
The patent employs curvature by using inverted truncated cones with specific base angles to form the necked-down region. The curved surfaces of the cones create a smooth transition that concentrates stress for impact failure while the specific geometry (angles θ1 and θ2 between 20°-40°) is optimized to reduce stress gradients under cyclic loading, thereby improving fatigue resistance.
Solution Approach 2:
The patent optimizes geometric parameters including the base angles θ1 and θ2 of the cones, the dimensions of the necked-down region, and the overall coupling geometry. By selecting specific parameter ranges, the design achieves a balance between facilitating impact failure through stress concentration and resisting fatigue through reduced stress gradients.
3Force
If traditional break-away couplings use circumferential grooves as stress concentrators, then bending fracture is induced, but the design requires higher bending energies that may be detrimental to vehicle safety
Solution Approach 1:
The patent replaces traditional circumferential grooves with inverted truncated cones having curved surfaces. This geometric change creates stress concentration for fracture initiation while the specific cone angles (θ1 and θ2 between 20°-40°) are optimized to reduce the overall bending energy required, making the coupling more vehicle-friendly upon impact.
4Strength
If the coupling geometry is optimized for maximum tensile strength, then the structure can withstand service loads, but the resistance to lateral impact load is increased
Solution Approach 1:
The patent applies local quality by creating a necked-down region with inverted truncated cones at the critical location where impact failure should occur. The main body of the coupling maintains sufficient tensile strength to withstand service loads like wind, while the localized necked-down region with specific cone angles (θ1 and θ2) provides controlled weakness for impact failure.
Solution Approach 2:
The patent optimizes the geometric parameters of the necked-down region, including the base angles θ1 and θ2 and the dimensions of the conical portions. By carefully selecting these parameters, the design achieves adequate tensile strength for service loads while creating sufficient weakness for lateral impact failure at predetermined energies.
Data Source
AI summary
A break-away coupling is formed of metal and has a central axis and a necked-down central region formed by two inverted truncated cones each having larger and smaller bases. The cones are joined at the smaller bases by a narrowed transition region having an exterior surface formed by a curved surface of revolution having an inflection point of minimum diameter substantially midway of the coupling along the axis. The cones each define an angle θ1 and θ2, respectively, at each of the larger bases, wherein both θ1 and θ2 are selected to be within the range of 20°-40° and, preferably within the range of 30°-37°.