Shape Memory Alloy Disc Vent for Ordnance Safety
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Solution Overview
Problem
High-temperature environments can lead to 'slow cook-off' and 'fast cook-off' events in containers carrying ordnance, resulting in undesirable ignition and potential detonation, posing risks to people and equipment.
Innovation Solution
A passive safety mechanism utilizing a self-fracturing shape memory material, such as a nickel-titanium alloy, which is prestrained and notched to fracture at a predetermined temperature, allowing the container to vent and prevent over-pressurization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a container carries ordnance in high-temperature environments, then the container can store or transport ordnance, but slow cook-off events can occur leading to ignition and potential detonation
Solution Approach 1:
The patent applies preliminary action by pre-straining the shape memory alloy disc to a predetermined stress level before use. The disc is manufactured with internal residual stresses that are carefully controlled through a heat treatment process, so that when exposed to elevated temperatures during storage, the stress relief occurs at a controlled rate that prevents rapid pressurization while still venting harmful gases. This pre-conditioning of the material ensures the safety mechanism activates appropriately without requiring external intervention.
Solution Approach 2:
The patent replaces traditional mechanical pressure relief systems with a thermally-activated shape memory alloy disc. Instead of using mechanical valves or pressure sensors that require activation, the system uses the inherent thermomechanical properties of the shape memory alloy to automatically relieve pressure when temperature thresholds are reached. The disc transitions from a strained state to a relaxed state through thermal activation, providing passive safety without complex mechanical components.
2Reliability
If the container is designed with venting mechanisms, then over-pressurization can be prevented, but the structural integrity and sealing capability are compromised
Solution Approach 1:
The patent applies local quality by creating a localized stress concentration region within the shape memory alloy disc through precise notching. The disc maintains uniform strength and sealing capability in its unnotched regions, while the notched area serves as a predetermined fracture point that initiates stress relief. This localized modification allows the majority of the disc structure to maintain its integrity and sealing function while providing a controlled weakness for pressure relief activation.
Solution Approach 2:
The patent utilizes parameter changes by controlling the thermal and mechanical parameters of the shape memory alloy disc. The disc is heat-treated to specific temperatures and held for predetermined times to establish exact residual stress levels. When exposed to temperature changes during operation, the disc's mechanical properties change dynamically - maintaining strength at operating temperatures but becoming sufficiently compliant at elevated temperatures to allow controlled fracture and pressure relief.
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 mechanism effectively prevents detonation by venting the container when exposed to elevated temperatures, reducing the risk of ignition and damage from over-pressurization.
Implementation Method 1
The prestrained element can be a shape memory alloy element. The shape memory alloy element can include one or more of a nickel-titanium alloy, a titanium-nickel alloy, a copper-zinc-aluminum alloy, a copper aluminum nickel alloy, and a nickel titanium hafnium alloy. Heating of the shape memory alloy element causes a stress in the shape memory alloy that causes fracturing of the shape memory alloy when sufficient heating has been achieved.
Data Source
AI summary
A release mechanism includes a frame with an interior. The release mechanism also includes a prestrained element coupled to the interior of the frame. The prestrained element creates a seal with the frame. The prestrained element is notched in one or more regions. The prestrained element is configured to fracture when heated to a predetermined temperature allowing the interior to open. The fracture is based on the notched regions of the prestrained element such that separation initiates within the notched regions. The remaining regions of the prestrained element unfractured. The shape memory alloy element can include one or more of a nickel-titanium alloy, a titanium-nickel alloy, a copper-zinc-aluminum alloy, a copper aluminum nickel alloy, and a nickel titanium hafnium alloy. Heating of the shape memory alloy element causes a stress in the shape memory alloy that causes fracturing of the prestrained alloy when sufficient heating has been achieved.