Polymeric Ammunition Casing Impact Strength
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Solution Overview
Problem
Current ammunition cartridge casings made of metals face issues with weight, corrosion, and mechanical integrity, particularly at high temperatures and strain rates during firing, while polymeric materials have not been successful in meeting the necessary mechanical and thermal demands due to inadequate impact strength and ductility.
Innovation Solution
Development of polymeric ammunition cartridge casings with specific materials such as siloxane-modified Bisphenol-A polycarbonates, polycarbonates with biphenyl linkages, and polyphenylsulfones that exhibit high room temperature notched Izod impact strength and maintain impact strength at sub-ambient temperatures, ensuring the casing can absorb energy and withstand firing pressures without failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If polymeric materials are used for cartridge casings, then weight is reduced and corrosion resistance is improved, but mechanical strength and impact resistance are insufficient
Solution Approach 1:
The patent applies parameter changes by selecting polymeric materials with specific mechanical properties: notched Izod impact strength greater than 10 ft-lb/in at room temperature and a ratio of notched Izod strength at room temperature to strength at -40°C of less than 4. This ensures the polymer maintains adequate impact resistance across temperature ranges while achieving weight reduction and corrosion resistance.
Solution Approach 2:
The patent employs composite materials by combining polymeric materials with metallic components in a hybrid cartridge casing structure. The polymeric portion provides weight reduction and corrosion resistance, while the metallic base or cap contributes high strength and impact resistance, creating a composite structure that balances all requirements.
2Object-affected harmful factors
If polymeric materials are used for cartridge casings, then corrosion resistance is improved, but impact strength and ductility are inadequate at high strain rates
Solution Approach 1:
The patent addresses impact strength reliability by specifying polymers with notched Izod impact strength greater than 10 ft-lb/in at room temperature and maintaining a strength ratio less than 4 between room temperature and -40°C. This parameter control ensures adequate energy absorption capability during high-strain-rate firing events while preserving corrosion resistance.
3Strength
If casing wall thickness is increased to achieve strength profile, then mechanical strength is improved, but internal volume for propellant charge is reduced
Solution Approach 1:
The patent resolves the strength-volume contradiction by changing the material parameter from metal to polymer with specific mechanical properties. The polymer's adequate impact strength allows for optimized wall thickness that provides necessary mechanical strength while maximizing internal volume for propellant charge, unlike metals where thickness increases are required for strength.
Solution Approach 2:
The patent applies segmentation by dividing the cartridge casing into polymeric and metallic portions. The polymeric portion can be optimized for volume efficiency with thinner walls, while the metallic base or cap provides concentrated strength where mechanically demanded, achieving both strength and volume goals through functional segmentation.
4Strength
If heat treatment conditions are varied to create strength profile in metal casings, then mechanical strength distribution is improved, but this approach is not applicable to polymers
Solution Approach 1:
The patent changes the material parameter from metal to polymer, which fundamentally alters the approach to strength profiling. Instead of heat treatment, the polymer casing achieves strength distribution through material selection with specific impact strength properties and geometric design, maintaining manufacturing flexibility while achieving the required strength profile.
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
These polymeric materials demonstrate superior energy absorption and mechanical integrity, allowing the cartridge casings to survive high-strain-rate events with minimal damage, equivalent to conventional brass casings, and potentially achieving 100% casing survival rate.
Implementation Method 1
The material at the cartridge base end, which supports the primer, must first absorb the impact of a firing pin on the primer without mechanical failure
Implementation Method 2
Upon ignition and combustion of an encapsulated propellant, rapidly expanding gases create high pressure, which expels a projectile from the barrel of the fired firearm. The ammunition cartridge casing must withstand and contain the pressure developed by the explosion
Data Source
AI summary
An ammunition article is provided which comprises a casing and a cap wherein the casing is formed from a polymeric material that has a room temperature notched Izod impact value greater than about 10 ft lbs/in and then has a ratio of notched Izod impact value at room temperature to notch Izod impact value at about −40° C. of less than about 4.