Rock Bolt Failure Zone Machining for Predictable Ductile Breakage

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Solution Overview

Problem

Existing rock bolt technologies face challenges in ensuring predictable failure at a specific location when overloaded, as cold or hot forming notches can alter steel material properties, leading to unpredictable brittle fractures and reduced load support capabilities.

Innovation Solution

A method involving the removal of material to create a circumferential band with a reduced diameter failure zone on the rock bolt, ensuring consistent breakage within this zone under tensile load, using subtractive manufacturing processes like machining or grinding to maintain ductile fracture patterns and load-bearing performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If cold or hot forming is used to create a notch in the bar, then the bar can be induced to fail at a specific location, but the localised work hardening alters the material properties of the steel and changes the performance of the rock bolt

Engineering Contradiction:

Improvefailure location precisionVSAvoidrock bolt performance consistency

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The invention changes the manufacturing method from cold/hot forming to machining or grinding, altering the process parameters to avoid work hardening while achieving the same geometric modification (notch creation). This maintains the failure location precision while preserving the original material properties and rock bolt performance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces the mechanical forming process (cold/hot forming) with a subtractive manufacturing process (machining or grinding). This substitution eliminates the work hardening effect while achieving the desired notch geometry for controlled failure at a specific location.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If a notch is formed in the bar to induce failure at a specific location, then the severed section can be restrained by the failure arrestor element, but the support properties of the rock bolt are compromised due to altered steel properties

Engineering Contradiction:

Improvefailure control reliabilityVSAvoidrock bolt support capacity

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The invention changes the manufacturing parameter from thermal/mechanical forming to subtractive machining or grinding. This preserves the steel's inherent ability to stretch and absorb energy under load, maintaining the rock bolt's support capacity while still achieving reliable failure control at the designated location.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If material is removed by cold forming or rolling to create a notch, then the bar will fail at a predetermined location, but the dynamic energy absorption capacity of the rock bolt is reduced

Engineering Contradiction:

Improvefailure location controlVSAvoiddynamic energy absorption

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The invention replaces the cold forming/rolling mechanical system with a machining or grinding subtractive manufacturing system. This substitution creates the failure zone without inducing work hardening, thereby preserving the steel's ductility and its ability to absorb dynamic energy through stretching and deformation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS11486250B2Method of ensuring controlled failure of rock bolt bar

Publication Date: 2022.11.01 EPIROC DRILLING TOOLS AB

AI summary

Disclosed is a method of adapting a metal bar, for use as a rock bolt, to ensure that the bar will break in a predictable manner, the method including the step of removing material from the bar in a circumferential band to reduce a diameter of the bar within the band to a minor diameter thereby to provide a failure zone within which the bar will break if subjected to enough tensile load.