Variable Stand-Off Explosive Cord Assembly for Cook-Off Venting

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Solution Overview

Problem

Rocket motors and devices with energetic materials face hazards due to 'cook-off' events, where external heating can lead to uncontrolled detonation or explosion, and existing solutions are inadequate for distinguishing between slow and fast cook-off scenarios effectively.

Innovation Solution

A variable stand-off distance explosive cord assembly is introduced, featuring a thermally responsive material that adjusts the distance between the explosive cord and the casing, allowing for scoring or cutting based on the type of cook-off event, using a linear shaped charge to vent pressure safely.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a fixed stand-off distance is used for the explosive cord, then the device structure is simple, but it cannot effectively distinguish between slow and fast cook-off scenarios

Engineering Contradiction:

Improveability to distinguish between slow and fast cook-off scenariosVSAvoiddevice structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The stand-off distance is made variable through the use of a thermally responsive material that changes its physical state or dimensions in response to temperature changes. This allows the explosive cord assembly to dynamically adjust its position relative to the casing based on the thermal conditions, enabling differentiation between slow and fast cook-off scenarios without complex mechanical actuators.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent utilizes materials whose physical parameters (such as length, volume, or density) change in response to temperature variations. By incorporating such materials into the stand-off mechanism, the system automatically adjusts the stand-off distance based on the thermal environment, providing adaptability to different cook-off scenarios while maintaining relative structural simplicity.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the explosive cord is positioned close to the casing, then the venting action is more effective, but the risk of premature ignition increases

Engineering Contradiction:

Improveventing effectivenessVSAvoidrisk of premature ignition

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces traditional mechanical spacing mechanisms with a thermally responsive material that uses thermal expansion or phase change to establish the stand-off distance. This substitution allows the system to maintain an optimal distance that prevents premature ignition while ensuring effective venting when needed, based on thermal conditions rather than fixed mechanical positioning.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The thermally responsive material acts as an intermediary between the explosive cord and the casing. It provides a temperature-dependent spacing function that mediates between the need for close proximity for effective venting and the need for distance to prevent premature ignition, automatically adjusting the balance based on thermal conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If the stand-off distance is increased to prevent premature ignition, then safety improves, but the penetration depth of the explosive cord is reduced

Engineering Contradiction:

Improvesafety against premature ignitionVSAvoidpenetration depth

Core Design Contradiction:

Object-affected harmful factorsVSStrength

Solution Approach 1:

The stand-off distance is dynamically adjusted based on thermal conditions through the thermally responsive material. Under normal conditions, the material maintains a larger stand-off distance for safety. When thermal conditions indicate approaching cook-off, the material changes state to reduce the stand-off distance, thereby increasing penetration depth while maintaining safety against premature ignition.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The physical parameters of the thermally responsive material change in response to temperature, automatically adjusting the stand-off distance. This parameter change allows the system to optimize both safety and penetration depth by adapting the spacing to the current thermal environment, ensuring sufficient penetration when needed while maintaining adequate safety margins under normal conditions.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solution effectively mitigates the risk of uncontrolled detonation by varying the penetration depth of the explosive cord according to thermal exposure, allowing for controlled venting during both slow and fast cook-off events, thereby preventing explosions and ensuring safety during storage, transport, and flight.

Implementation Method 1

a thermally responsive material configured to vary the stand-off distance from a first distance to a second distance

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the explosive cord is a linear shaped charge

Methodology Applied

Scientific EffectShaped charge: Shaped Charge

Data Source

PatentUS10801822B2Variable stand-off assembly

Publication Date: 2020.10.13 GOODRICH CORP

AI summary

A variable stand-off distance explosive cord assembly for a casing is disclosed. In various embodiments, the assembly includes an explosive cord configured for positioning at a stand-off distance from the casing and a thermally responsive material configured to vary the stand-off distance from a first distance to a second distance.