Frangible Post with Hinge and Weakness Zone for Cable Release

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Solution Overview

Problem

Existing guardrail end terminal designs, such as those using breakaway posts, face challenges in reliably releasing the anchor cable during axial impacts while maintaining anchorage during downstream impacts, especially when made from ductile materials that may yield instead of break, leading to potential cable snagging issues.

Innovation Solution

A frangible post design featuring a hinge member and a zone of weakness, which separates into upper and lower portions upon axial impact, applying compressive forces to the hinge member and tensile forces to the weakness zone, allowing complete separation and reliable cable release, while maintaining anchorage during lateral impacts through a bearing plate mechanism.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a breakaway post design is used to release the cable during axial impacts, then the cable can be released to prevent snagging, but the post may not reliably fracture when made from ductile materials, causing the cable to remain caught on the post

Engineering Contradiction:

Improvecable release reliabilityVSAvoidpost strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The post is pre-modified with a central hole, side notches, and a slotted cable bracket before installation. These preliminary modifications create predetermined failure zones that guide the fracture path during axial impact, ensuring the post reliably breaks away to release the cable. The central hole and notches concentrate stress to initiate fracture at specific locations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The post has non-uniform structural properties with a central hole through the web and notches on the sides below the cable attachment point. These localized modifications create zones of weakness at specific locations, making the post more likely to fracture at these predetermined points during axial impact rather than bending uniformly throughout.

Inventive Principle:

Principle #3Local quality

2Strength

If the post is made from ductile materials such as steel or aluminum, then the material has better toughness and ductility, but the post may yield and bend over instead of fracturing, preventing reliable cable release

Engineering Contradiction:

Improvematerial toughnessVSAvoidfracture reliability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Inventive Principle:

Principle #10Preliminary action

3Ease of operation

If the central hole is sized to allow cable passage after yielding, then the cable can pass through the post, but the cable may become caught on the post instead of passing through as intended

Engineering Contradiction:

Improvecable passageVSAvoidcable release reliability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The post is divided into segments by the central hole and side notches, creating distinct zones that can separate during fracture. The slotted cable bracket is positioned above the central hole to guide cable movement. This segmentation ensures that when the post fractures, the cable can pass through the separated sections rather than being caught on a solid post structure.

Inventive Principle:

Principle #1Segmentation

4Reliability

If holes and slots are added to posts to weaken them, then the post is more likely to fail, but ductile materials may still bend at the weakening points rather than break, leaving a portion of the post to bind the portions together

Engineering Contradiction:

Improvepost failure reliabilityVSAvoidpost structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS10047488B2Frangible post for highway barrier end terminals

Publication Date: 2018.08.14 ENERGY ABSORPTION SYSTEMS INC

AI summary

A frangible post captures and holds a cable anchor to a guardrail. The post breaks when struck by a vehicle, releasing the cable. The frangible post may include hinge members, which bias the post so that weakened sections are put in tension when the post is struck, thereby ensuring that the post breaks cleanly and the cable is released when the post is struck. A method of releasing a cable anchor includes impacting the post, biasing the weakened sections so that they are in tension, breaking the post, and releasing the cable anchor. The post may be configured with a notch to engage the cable anchor, which is then released from the notch as the post is broken.