Biased Threaded Joint for Munition Cook-Off Mitigation
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Solution Overview
Problem
Current methods for joining dissimilar strength structural materials result in inefficient configurations with overly large thread engagement, leading to increased parasitic weight and volume, and fail to provide a controlled release in adverse environments, especially in insensitive munitions and shock mitigation applications.
Innovation Solution
The use of a biased equivalent strength threaded joint with unequal thread thicknesses and pitch distribution between dissimilar strength structural members, allowing for optimized non-permanent joining with minimal increase in thread engagement length and inclusion of lower strength materials for shock mitigation without compromising strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard threads with equal thread thickness are used to join dissimilar strength structural materials, then the joint can be manufactured with simple processes, but the thread engagement length becomes excessively large and parasitic weight increases
Solution Approach 1:
The patent applies asymmetry by using unequal thread thicknesses for the first and second structural members. The first thread thickness is specifically designed to be greater than the second thread thickness, creating an asymmetric thread configuration that optimizes the joint for dissimilar strength materials while reducing the required thread engagement length and parasitic weight compared to symmetric (equal thickness) threads.
Solution Approach 2:
The patent implements local quality by tailoring the thread thickness distribution to match the local strength requirements of each structural member. The region with the weaker material receives thinner threads, while the region with the stronger material receives thicker threads, creating a localized optimization that reduces overall parasitic weight while maintaining adequate shear strength at each interface.
2Ease of manufacture
If standard threads with equal thread thickness are used to join dissimilar strength structural materials, then the manufacturing process remains simple, but the thread engagement volume becomes excessively large
Solution Approach 1:
The asymmetric thread thickness configuration (first thread thickness greater than second thread thickness) reduces the required thread engagement volume by optimizing the shear area distribution. This asymmetric design allows the stronger material to contribute more to the shear resistance, enabling a shorter overall engagement length and reduced volume compared to equal-thickness threads.
Solution Approach 2:
By locally adapting thread thickness to material strength, the patent reduces the volume required for thread engagement. The weaker material region has thinner threads requiring less engagement volume, while the stronger material region has thicker threads that provide sufficient shear resistance over a shorter distance, overall reducing the total engagement volume.
3Strength
If standard threads are used for joining structural materials in adverse environments, then the joint maintains permanent strength, but the joint cannot be released when needed in cook-off or shock environments
Solution Approach 1:
The patent applies dynamics by creating a joint that transitions from a permanent strong state under normal conditions to a releasable state under adverse conditions. The unequal thread thickness configuration, combined with the use of a lower strength material for the second structural member, enables the joint to fail in a controlled manner when subjected to extreme thermal or shock loads, providing adaptability for cook-off mitigation while maintaining strength during normal operation.
Solution Approach 2:
The patent utilizes parameter changes by selecting materials with different strength properties and configuring asymmetric thread thicknesses. This creates a joint where the strength parameters are deliberately mismatched to enable controlled failure at specific thresholds. The lower strength material and thinner second threads create a predetermined failure path that activates under adverse environmental conditions, allowing the joint to transition from strong to releasable based on environmental parameters.
4Strength
If higher strength materials are used throughout the joint to ensure adequate shear strength, then the joint strength is sufficient, but the parasitic weight and volume increase
Solution Approach 1:
The patent applies local quality by using different material strengths and thread thicknesses in different regions of the joint. The first structural member uses a higher strength material with thicker threads where greater load-bearing capacity is needed, while the second structural member uses a lower strength material with thinner threads where less shear resistance is required. This localized differentiation achieves adequate overall joint strength without the parasitic weight penalty of using high-strength materials throughout the entire joint.
Solution Approach 2:
The asymmetric configuration of thread thicknesses (first thread thickness greater than second thread thickness) allows the joint to achieve sufficient shear strength through unequal contribution from each material. The stronger material with thicker threads provides the majority of the shear resistance, enabling the use of lighter, lower-strength material for the second member, thereby reducing overall parasitic weight while maintaining adequate joint strength.
Data Source
AI summary
Embodiments are directed cook-off mitigation systems. As assembled, a munition fuzewell is torqued into the aft end of a munition. The fuzewell is hollow and has an inner and an outer surface. The hollow fuzewell is configured to release during cook-off. Release is assisted by employing a biased equivalent strength threaded release ring concentric about the fuzewell. The biased equivalent strength threaded release ring has a threaded inner surface and a threaded outer surface. The biased equivalent strength threaded release ring's threaded inner surface threadingly-engages with threads on the fuzewell's outer surface. A munition case is concentric about the biased equivalent strength threaded release ring.