Polymer Cartridge Case Weight Reduction via Composite Material Design
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Solution Overview
Problem
Conventional ammunition cases made of brass are heavy, and polymer materials face challenges in achieving the necessary strength, stiffness, and ductility at low temperatures, particularly below -40°C, limiting their use as a drop-in replacement.
Innovation Solution
Development of polymer compositions that provide a balance of strength, stiffness, and ductility at high strain rates over a wide temperature range, including polycarbonate-polysiloxane copolymers, which are used to manufacture lightweight ammunition articles with a polymer cartridge case that can withstand extreme temperatures without deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If polymer materials are used to replace brass for cartridge cases, then weight is reduced, but strength and ductility at low temperatures deteriorate
Solution Approach 1:
The patent employs a composite material system consisting of a polymer matrix (polycarbonate, polyetherimide, or polysulfone) reinforced with inorganic fillers (glass beads, glass flakes, or aluminum oxide). This composite structure combines the lightweight advantage of polymers with the strength and thermal stability of inorganic materials, achieving both weight reduction and maintained mechanical properties at low temperatures.
Solution Approach 2:
The patent systematically varies the composition parameters of the polymer matrix and filler content to optimize performance. By adjusting the specific polymer type, filler concentration, and molecular weight characteristics, the material achieves appropriate balance between weight reduction and mechanical strength retention across the operational temperature range including low-temperature conditions.
2Weight of moving object
If polymer materials are used to replace brass for cartridge cases, then weight is reduced, but stiffness and performance reliability at extreme temperatures deteriorate
Solution Approach 1:
The composite structure with inorganic fillers embedded in the polymer matrix provides enhanced thermal stability and structural rigidity. The inorganic materials have higher glass transition temperatures and maintain dimensional stability at extreme temperatures, ensuring reliable cartridge case performance across the full operational temperature range while preserving the weight advantage of polymer materials.
Solution Approach 2:
The patent optimizes the glass transition temperature (Tg) of the polymer matrix through selection of specific polymer types and compositional adjustments. By controlling Tg to be above the minimum operational temperature and adjusting filler content, the material maintains appropriate stiffness and dimensional stability across extreme temperature variations, ensuring performance reliability.
Data Source
Figure 1~2A
Figure 2B~3A
Figure 3B~3C
AI summary
An ammunition article comprises a polymer cartridge case formed of a polymer composition comprising a thermoplastic polymer, preferably the polymer composition having a density of less than 1.35 determined in accordance with ASTM D792, the polymer cartridge case having a first end, an opposing second end, and a chamber disposed between the first end and the second end for receiving a propellant; a projectile attached to the first end of the polymer cartridge case; a metal base insert joined to the second end of the polymer cartridge case; and a primer carried by the metal base insert; wherein the metal base insert and the polymer cartridge case remain joined together as a single piece assembly upon loading, firing and removal from a chamber of a firearm for a polymer case temperature of -65°F (-54°C) to 165°F (74°C).