Bi-metal Triggering Element for Munition Thermal Safety
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Solution Overview
Problem
Existing munitions lack effective safety mechanisms to prevent accidental activation due to thermal runaway or external heating, which can lead to unsafe situations such as slow cook-off or unintended propulsive events.
Innovation Solution
A heat-activated triggering device utilizing a bi-metal element with a shape memory alloy sleeve that breaks a metal pin at a predetermined temperature, driving a firing pin into a primer to initiate detonation, while an inertial lockout and mechanical linkage ensure safe operation by preventing premature triggering and allowing controlled release of detonation products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal trigger is used to detect temperature changes, then the device can respond to thermal conditions, but it may accidentally activate due to environmental thermal runaway or external heating
Solution Approach 1:
The invention uses a bi-metallic strip that changes its physical state (bending curvature) in response to temperature changes. The strip is designed with specific metal compositions and geometric parameters so that it only activates the firing pin when the temperature reaches a predetermined threshold, preventing accidental activation from environmental thermal conditions while maintaining reliable thermal response
Solution Approach 2:
The bi-metallic strip utilizes thermal expansion and phase transition properties of different metals to create a temperature-dependent mechanical response. The differential expansion coefficients of the two metal layers cause the strip to bend and displace the firing pin only when the temperature reaches the designed activation threshold, providing selective thermal response
2Reliability
If a shape memory alloy connector is used to release pressure, then the munition can respond to thermal hazards, but the device complexity increases
Solution Approach 1:
The invention replaces complex shape memory alloy mechanisms with a simpler bi-metallic strip system that uses conventional metal properties (differential thermal expansion) to achieve temperature-responsive pressure release. This maintains the safety function while reducing material complexity and manufacturing difficulty
3Speed
If the firing pin is always ready to fire, then the munition can be quickly activated, but it cannot prevent accidental firing from thermal conditions
Solution Approach 1:
The bi-metallic strip is designed with specific geometric parameters (thickness, curvature, metal composition ratios) that ensure the firing pin remains in the safe position during normal operation and only moves to activate the primer when the temperature reaches the predetermined threshold, providing both rapid thermal response and thermal safety
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
The solution effectively prevents unintended detonation of munitions by ensuring that the firing pin is only activated at a specific temperature threshold, thereby avoiding safety hazards from thermal runaway or aerothermal heating during flight.
Implementation Method 1
a sleeve surrounding part of the pin, the sleeve being made of a second metal different from the first metal... the second metal is a shape memory alloy... the shape memory alloy is pre-compressed, expanding when a predetermined temperature threshold is exceeded
Implementation Method 2
a bi-metal triggering element including: a metal pin made of a first metal; and a sleeve surrounding part of the pin, the sleeve being made of a second metal different from the first metal... at a predetermined temperature the sleeve places a force on the metal pin, causing the metal pin to break
Data Source
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AI summary
A heat-activated triggering device, such as for a missile or munition, includes a bi-metal trigger element, with a breakable pin of a first metal surrounded by a sleeve made of a second metal that is different than the first metal. The sleeve may be made of a shape memory alloy, such as a single-crystal shape memory alloy, that is pre-compresses around part of the pin. The sleeve may be configured to put a tension force on the pin as the sleeve passes a predetermined temperature, for instance a temperature at which the shape memory feature of the sleeve is activated. The pin may have a weakened portion, such as a notched portion, at which the pin breaks. The breaking of the pin may be used to drive a firing pin into a primer, to initiate a detonation and/or combustion reaction.